Text

Staff Exhibit S-74,consisting of NUREG/CR-3691, Assessment of Terminal Blocks in Nuclear Power Industry
	ML20118A138
Person / Time
Site:	Farley
Issue date:	05/18/1992
From:	Craft C; SANDIA NATIONAL LABORATORIES
To:	;
References
	RTR-NUREG-CR-3691 CIVP-S-074, CIVP-S-74, NUDOCS 9208030123
	Download: ML20118A138 (100)
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e in f. hl h An Assessrnent of Terminal Blocks in the Nuclear Power Industry Charles M. Craft 5

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NOTICE This report was prepered se sa screet ed wor 6 nyteored by an agency of the United States Governmeht. Nestner the Uruted

},i beates Government trot any agency thereof, or any of their em.

ployees, main any warranty, erpreened or unplad, or nasumn i

any legalIsabthey or responsibiltry for any third party's use, or the eesults of such use, of any trdormahen, apparatus product or process dischmed in this report, or represents that its use by such third party would hot ininnge pnestely owned nghts.

9 Ara 11able from CPO Seln Trostrn themon of TechrucalInformanon and Docum nt Control U.S Nuclear RegVeory Commission Washington, D C, 40555 and National Technical Information Se rice Springb Id, Virginia 22161

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t WUREC/CR-3691 SAND 84-0422 RV 1

AN ASSESSMENT OF TERMINAL BLOCKS IN THE WUCLEAR POWER INDUSTRY September 1984 Charles M. Craft 9

'Sandla National Laboratories Albuquerque, WM 87185 operated by Sandia Corporation for the U. S. Department of Energy I

Prepared for Instrumentation and Control Branch Division of Facility Operations Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Cosenteston Washington, DC 20555 Under Interagency Agreement DOE-40-550-75 NT.C Fin No. A-1327

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Abstract The primary application of terrinal blocks in the nuclear power I

industry is itetrumentation and co2 trol -(I&C) circuits. The performance of these circJits can be de6raded br low level leakago currents and low insulation resistance (IR) betwee'a conductors oe to ground. Analyses of i

these circuits show that terminal blocks, when exposed to steam environments, experience leakage currents and low surface IR levels sufficient to affect some I&C applications. Since the mechanism reducing surface IR (conductive surface rocisture films) is primarily controlled by external environmental f actors, the degradation of terminal block performance is mostly independant of terminal block design. Testing shows that potential methods cf reducing surface leakage currents will not reduce them sufficiently to prevent terminal blocks from affecting I&C circuits. Therefore, terminal blocks can cause orconeous indications or actions of the I&C circuits in which they are a component. Most of the present qualiff.ation tests of terminal blocks do not address the issue of low level leakage e.urrents, and hence do not demonstrate that l

I terminal blocks will operate properly in IEC circuU l

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q Table of Contents Eira.

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Executive Summary......................................

4 1.0 Introduction....................

4 1.1 Background................................................

4 1.2 Objectives,................................................

1.3 Terminal Blocks in tra /c sear Power Industry..............

A hk 1.3.1 Why Terminal 'J1ocir 4

5 1.3.2 Terminal Bloc -

swage...............................

1..

'isrminal Llock Applications.........................

10 12 2.0 Terminal Block Life Cyc1e.......................................

12 2.1 Terminal Block Design....

2.1.1 Te rmi n al Blo :k Ma t e. a1 s............................

12 2.1.2 Quality Assurance in Terminal Block Design..........

17 2.2 Terminal Block Manufacture.................................

17 2.2.1 Manafacturing Process...............................

17 2.2.7 Quality Assurance in Manufacture....................

17 2.3 Terminal Block Eelection. Procurement, and Installation...............................................

18 2.3.1 Role of Architect / Engineering (A/E)

Firms...........

18 2.3.2 Construction and Installation Practices.............

18 19 2.4 Inspections and Maintenance................................

2.4.1 Utility inspections and Maintenance.................

19 2.4.2 NRC Inspection Activities...........................

19 20 2.5 Summary....................................................

21 3.0 Testing of Terminal Blocks....,............

21 3.1 Standard Industry Tests...........

21 3.2 Nuclear Qualification Tests.......

3.2.1 Franklin Research Center's Iwst of Buchsnan Terminal Blocks for Pn11adelphia Electric 22 Company.............................................

3.2.2 Franklin Research Center's Test of Buchanan Terminal Blocks for Control Products Division of Amerace Corporation.....................

26 3.2.3 Vyle Laboratory's Test of Marathon Terminal Blocks for Marathon Speelal Products................

27 3.2.4 Franklin Research Center's Test of Weidmu11er Terminal Blocks for Veldmuller Terminations, 28 Inc.................................................

3 3.2.5 Vyle Laboratory's Test of Veidmullar Terminal Blocks for Washington Public Power 28 Supply System.......................................

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Table of Contents (continued)

L*Le 3.2.6 Reports on Nuclear Qualification Tests C

of Selected Phonix Terminal Blocks..................

3.2.7 Vyle Laboratory's Test of tight Marathon Terminal 29 Blocks for Commonwealth Edison Company....s..........

3.2.8 Wostinghouse Electric Corporation's Test'of 31 Terminst Block Performance in LOCA Environment......

33 4.0 Sandla Tests of Terminal Blocks in a LOCA Environment..................... Simulated 34 4.1 Terminal Blocks Tested............

4.2 Test Configuration................

34 4.3 MajorResults....................................,........

34 36 5.0 Tests of Terminal Block Perfo University...................rmance at Temple 44 5.1 Phase 1 Tests of Terminal Blocks in a Quiescent Temperature and Humidity Environment.......................

5.2 Phase II Tests of Terminal Blocks in an Active 44 Steam, Chemical Spray, and Temperature Environment........

5.3 Characterization of the Amount of Salt Deposited 50 by Fingerprints............................................

60 6.0 Theoretical Considerations Governing Film Formatio t

i Conduction on Terminal Block Surfaces.............n and 63 6.1 Qus11tative Discussion of Phenomena........................

1 6.2 63 b

Explanation of the Mode1.............................

6.3 Strengths and Weaknesses of the Mode1................

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74 7.0 Fgilure Modes of 'erminal B1ocks.........................

T 76 8.0 Examples of Possible Terminal Block Effects.....................

81 8.1 Transmitter Circuits.......................................

8.2 RTD Circuits...........................

81 8.3 Thermocouple Circults......................................

86 8.4 Solenoid Valve Circuits..........

89 8.5 Motor C1rculta...................

98 104 9.0 Pessible Methods of Reducin Curren t s................... g Te rminal Block Le akage 107 9.1 Cleaning................................................

9.2 Sea 11ng................

107 9.3 Coatings..................................................

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Table of Contents (continued) i D

10.0 Assessment Cr1teria............................................

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10.1 Terminal 81ock Design Considerations.....................

112 10.2 Testing Considerations.........._

113 10.3' System Design Considerations.............................

114 11.0 Conclusions....................................................

117 12.0 References.....................................................

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List of Figures Flr.ure f.11e 2-1 Typical Configuration for a one-Piece Terminal Block.........

13 2-2 Typic al Configuration for a sectional Terminal Block.........

14 4-1 Wiring Schematic for the S6nd'. Phase I Terminal Block Test.

35 4-2 Viring Schematic for the Sandia Phs.se II Terminal Block Test.

36 4-3 Viring Schematic for the Transmitter Circuit Tested in the Sandla Phase II Terminal Block Test...................

37 4-4 Terminal-to-Terminal Insulation Resistance for Sandla Phase T Terminal B1ocks..............................................

38 4-5 Insulation Resistance A for Sandla Phase II Terminal Blocks..

39 4-6 Insulation Resistance for One Manufacturer I, Model A Terminal Block From the Second Steam Ramp to the End of the Test..................................................

42 5-1 Experimental Test Setup for Salomon's Phase I Tests..........

45 5-2 Electrical Circuit for Salomon's Phase I Tests...............

47 5-3 Sketch of Terminal Black Showing Location of Breakdown Path..

48 5-4 Experimental Test Setup for Salomon's Phase II Tests.........

51 5-5 Electrical Circuit for Calomon's Phase II Tests..............

52 5-6 Leakage currents at 45 Vde as a Funetton of Time and Temperature for a Manufacturer I, Model A Terminal Block in the "As-Received" Cendit1on...............................

54 5-7 Leakage Currents at 125 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block in the "As-Received" Condition...............................

55 5-8 Leakage Currents at 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block After Being Washed and scated in Distilled Water.............

56 5-9 Leakage Currents at 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block After Being Washed With Distilled Water and Then Handled.....

57 5-10 Leakage Currents at 45 Vdc as a Function of Time and Temperature for a Manufseturer I, Podel A Terminal Block in the "As-Received" Condition and Subjectad to 7 Minutes of Finely Atomized Chemical Spray............................

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List of Figur$s (continued)

Eli.unt f.111 5-11 Leskage Currents at 45 Vdc as a Fune.tlon of Time and Temperature for a Manufacturer I, Model A Terminal Block Dipped in Saturated Nacl Solution and Dried..................

59 6-1 Side and Frontal Views of Simplified Geometric Model for Film Conduction on a Phenolic Substrate Material.............

67 6-2 Predicted Leakage Current Versus Applied Voltage for Selected Film Widths and Other Parcmeters as Specified in Table 6-1.................................................

73 8-1 Simplified Schematic of a Typical Transmitter Circuit in a Nuclear Power P1 ant,.......................................

82 8-2 Percert Error in a Trancmitter Circuit for Selected Values of Terminal Block Insulation Resiscance...............

84 8-3 Total Current Trace of Transmitter Circuit During LOCA Simulation...................................................

85 8-4 Indicated Pressure as a Function of Transmitter Output for a Correctly Operating Circuit and for a Circuit Vith Terminal Block Insulation Resistance Assumed to be 10 kohms.....................................................

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8-5 Simplified Block Diagram of a 3-Wire RID t acult Showing Parallel Connection Between Terminal Block Insulation Resistance and the Resistance of the RTD Sensing Element.....

88 8-6 Percent Error in the Resistance Measurement of an RTD kTD as a Function of Terminal Block Insulation Resistance...................................................

90 8-7 Simplified Schematic of a Thermocouple Circuit (Figure a) and a Temperature Profile for the Circuit That Night Ex1JL During an Accident (Figure b)................................

92 8-8 Open Circuit Voltage V2 as a Function of th. Spurious Voltage E$ for Selected Values of Terminal Block Shunt Resistances..................................................

94 8-9 Error in the Open Circuit Voltage as a Function of the for Selected Values of Terminal Spurious Voltage E$

Block Phunt Resistances......................................

95 8-10 Open Circuit Voltage V2 as a Function of tne Shunt for Selected Values of Termins1 Block Shunt Resistance R5 96 Resistances................

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List of Figures (continued)

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8-11 Error in the Open Circuit Voltage as a Function of the Bhunt Resistance R$ for Selected Values of Terminal Blork Shunt Resistances......................................

97 8-12 Simplified Circuit Schematic for one Possible Soleno Valve Circuit.......................................id 99 8-13 Typical Motor Circuit Connect.lon for a 3-Phase Mo' ar.........

105 8-14 Time-to-Trip as a Funetton of Percent of Motor Full Load Current for One Type of Directly Heated Binetal Overload Re1ay...............................................

106 9-1 Comparison of Leakage Currents for Red Clypt" Coated and Un c o a t ed Te rm i n a l B 1oc k s.....................,...............

110 9-2 Comparison of Leakage Currents for Cycloaliphatic Epery Epoxy Coated and Uncoated Terminal Blocks....................

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List of Tables Lable Par.e 1-1 Summary of Te rminal Bic:t Us a:e by Plant.....................

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3 2-1 Typict1 Radiation Damage Thresholds and Maximum Service Temperatures For Five Insulating Materials Used in Terminal Blocks Found lu U.S. Nuclear Power Plants...........

16 3-1 Comparison of Some Industry LOCA Simulations For Terminal Block Qualification.................................

23 5-1 Representative Data for Salomon's Quiescent Environment Bench Tests of Terminal Block Performance....................

49 5-2 Typical Leakage Current Data from Salomoi, for One Manufacturer 1. Model A Termiral Block Powered at 45 Vdc in a Clean Steam Environment.................................

53 5-3 Final Values of Leskage Current and the Ratio of Final to Initial values of Leakage currents for Manufacturer I, l

Model A Terminal B1ocks......................................

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5A Sample of Data for Measured Residual balt (WaC1) From One Fingerprint on a 1 cm2 Area of a Phenolic Terminal Block................

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6-1 Sample Equillia;am Film Parameters Predicted by Film s

Conducticn hadel..

72 7-1 Summary of Failure Modes for Terminal Blocks.................

77 8-1 Selected Temperatures (*C('F)) Indicated by the Type K Thermocouple Circuit Discussed as an Exampae in This Section......................................................

98 8-2 Contact Development Table for Control Switches C1 and C2.....

100' 8-3 Contact Development Table for Limit Switches 21, 22, 23 and 24.......................................................

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Mg Acknowledgments I wish to extend by gratitude to all those who contributed to the Component Asseesment program and its evaluation of terminal blocks. Mark Jacobus and Dave Furgal provided especially helpful consultation and moral support throughout the project. Mark also provided many hours of assistance in preparing the documentation.

Dr. Robert Salomon of Temple University provided independent verification of experimental results and initiated development of the theoretical considerations presented herein.

Thereafter, Mark Jacobus modified the model and put it in its current form. Gary Jotason of Portland General Electric Company supported the work with input on the circuit analyses.

He along with Dr.

Salomon at Temple, and Mark Jacobus, Mort Robertson, Frank Vyant Dave Furgal, Larry Bustard, and Tim Gilmore here at Sandia carefully sifted through the draft report making many critical and needed comments. Carol Schmidt and Della Vigil worked diligently to prepare the many iterations of the report for publication.

And finally, I especially want to thant my HRC program monitor, Ron Felt, for his patience and guidance throughout this project.

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Executive Summary Terminal blocks are used in nuclear power plant c', ass it and non-Class IE circuits inside and outside containment. Appilcations range from los voltage instrumentation and control (I&C) circuits to 480 Vac power circuits. Most terminal blocks are used in the low power I&C circuits.

The most prevalently used terminal blocks are General Electric EB series and CR-151 series, Weidmuller SAK types, Westinghouse 542247 types, States Type NT and Type ZWM, and Buchanan NQL series. All of these terainal blocks may be found in both inside and outside containment applications.

Approximately 50 percent of the utilities are planning to continue using terminct blocks in Clast 1E applications inside ccatainment. Those utilities choosing to continue use of terminal blocks operate mostly older pisnts with a large number of installed terminal bAocks. However, some of the newer plants will also use terminal blocks. Alternately, some utilities hase chosen to remove all explicit

terminal blocks in Class IE applicat!.ons inside containment, and others are removing them from selected.pplications (e.g., transmitter applications) or locations (e.g.,

below submergence level). The major trend for new plants is to use spilces inside containment.

The two major terminal blocks designs (one-piece and sectional) ara in approximately equal ussge. Of the 57 distinct models of terminal blocks tabulated in Section 1.3.3, 32 are of sectional construction and 25 are of one-piece construction. However, one-piece terminal blocks are probably more numerous in absolute terms since they are specified by a larger number of plants. To characterize terminal block types as a percentage of the total population is difficult, 61 ace data for the s

quantity of each type, as well as the total population of terminal blocks, e

are not readily available.

Since 1977, there have been a number of test progroms sponsored by both utilities and terminal block man'uf acturers that have been used to support the qualificatien of terminal blocks. These tests generally age the terminal blocts using Arrhenius techniques or the 10*C rule, expose them to a seismic and vibration test, and then conduct a Loss of Coolant Accident (LOCA) or a High Energy Line Break (HELB) simulation. Functional evaluations normally consist of insulation resistance (IR) measurements and conductor continuity checks following each of the several sequentially applied environmental stresses (i.e., thermal aging, radistica exposure, seismic stJ vibration simulation, and LOCA/HELB simulation). Although the acceptance criteria for tne functional tests were not always specifically stated, all of the industry test reports reviewed by us indicate that the terminal blo:ks performed satisf actorily during the functional IR tests subsequent to each type of expoeure.

c some of these tests, measurements of the variation in terminal block performance during these tests were not made. In other tests, magohmneter measurements were made at varirus points during the test with the block unpowered. The typical method used The term explicit refers to terminal blocks which are not an ictegral part of larger pieces of equipment such as electrical penetrations or motor operators.

l to monitor terminal block performance during the LOCA/HgLB simulation was via fuses in the circuits that provided potential to the teqminals of the terminal block.

These fuses were sized to fall at leakage currents between 1 A and 24 A depending on the test specification. Acceptance criteria during LOCA/HELB simulation were based on the terminal block's ability to carry the specified voltage and current without falling these fuses. During some of the tests, the fuses in the circuit's 'for one er more terminal blocks failsd once or twice and were replaced. Sometimes for a given terminal block, the fuse continued to fall; in those cases, the terminal block was removed from the test. The test reports do not specify the number of times that a fuse was allowed to-fall or the number of terminal blocks in the test lot that could be removed from the circuit befort the terminal blocks were deemed to have failed the te'st.

Using fuses in this manner has two drawbacks:

first, the failure of a fuse is only a single point criterion that shows only that leakage currents were at least as large as the rated value of the fuse for the time necessary to fall the fuse; and second, the siting of the fuses to "large" values provides no information about low level leakage e.orrents. As shown by the analysis of applications that may use terminal blocks, low level leakage currents on the order of all11 amperes can affect low prwer instrumentation and control circuits. These circuits are the primary terminal block applications, and, therefore, the test acceptance criteria are not, in this respect, germane to most terminal block applications.

Surface leahage currents are the primary mechanism by which terminal blocks contribute to 16C circuit degradation. During Sandia's tests of terminal blocks in a simulated LOCA environment [1), insulation resistance at 4 Vde, 45 Vde, and 125 Vdc fell to 102 to 105 ohms from initial values of 108 to 1010 ohms. At 45 Vdc leakage currents were on the order of 0.1 to 10 mA.

These values are sufficiently large to affect some 4 to 20 mA instrumentation circuits by 0.3 to 185 percent with a nominal effect of 0.5 to45percentattheirmidrange(12mA). At 4 Vdc insulation resistance ranged from 5 x 103 to 7 x 10 ohms. These values could affect RTD circuits by 0.3 to 9 percent. At 125 Vde, the irs were comparable or clightly higher (1/2 to 1 order of magnitude) than at 45 Vdc.

During the cooldown periods to 95'C and during the post-test ambient temperature period, the insulation resistance increased to 106 to 108 ohns, but not to ths pre-test levels of 108 to 1010 ohms. This behavior illustrates three points:

first, the similarity between cooldown and 9

post-test IP values indicates that the : ace conduction mechanism is probably occurring during these periods; second, IR recovery to a higher value after exposure indicates that a transient phenomenon is responsible for the low IR values during the steam exposure; and third, that some permanent degradation of the terminal block insulation resistance A conductive moisture film is the most probable explanation for occurs.

the transient phenomenon. During cooldown periods, th> residual heat of the terminal block keeps its temperature and the temperature of the film higher than the temperature of surrounding envirotment. The film's vapor pressure will exceed the partial pressure of water in the surroundius atmosphere and hence the film will vaporite, improving the terminal block's IR.

Similarly, in post-test environments the film will evsporate and the IR will increase.

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A model of film formation which predicts leakage currents that are consistent with the observed experimental results is presented. This model accounts for Joule heating of the film and the various heat loss mechanisms that exist.

Interpretation of the results of the mAdel and the Sandia test results [1) indicate that qualification testing at voltage levels above those of actual use may be nonconservative with respect to leakage currents.

All tested terminal blocks performed similarly in a stetm environment, though some eSsigns experienced irs consistently lower than other desigt.s. The formation of surf ace moisture films appears to be mostly independent of terminal block design. Three potential methods for reducing the magnitude of surface leaksge currents (cleaning, sealing, and coating) will probably not reduce leakage currents to a level acceptable for I&C applications. We erst, therefore, cenclude that leakage currents observed during LOCA testing of terminal blocks can cause erroneous indications or actions of the low power I&C circotts in whleb they are a component.

Most of the present qualification tests do not address the primary failure mode (low level leakage currents) and therefore da not demonstrate that terminal blocks will operate properly in I&C circuit.

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1.0 INTRODUCTION

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1.1 Background

Terminal blocks are used in nuclear power plant Class IE and non-Class lg circuits inside and outside containment.

Their past widespread application in critical circuits and their potential for causing common mode failure lead to questions concerning their effect on nuclaur plant safety.

Motivated by questions arising from the accident at Three Mile Island (TMI), the NRC requested that Sandia National Laboratories investigats terminal block performance in TMI conditions.

The results of this work by Stuetter [2]

affect plant safety by undergoing low voltage surface breakdown atin voltages between one hundred and five hundred volts.

Stuotter also pointed out the highly statistical nature of terminal block breakdown.

and the influence of many complex, nonreproducible parameters, inerefore, to minimite variability, Stuetter employed a controlled laboratory environment to investigate terminal block behavior.

his work was conducted at 480 Vac and used experimental configurations Most of that were not typical of actual nuclear plant installations.

basis, the work was attacked as nonrepresentative of actual industry On this practices.

The results, however, did raise sufficient concern that a sore thorough review of the terminal block issue was deemed necessary.

This document and a companion report (1) present the results of the follow-on study.

1.2 Objectives There were three rather broad objectives to the terminal block review.

These were:

(1)

Investigate the failure and degradation modes of terminal blocks in a configuretion that was typical of actual plant installations, uses, and conditions.

(2)

Assess the impact of the terminal block failure and degradation modes on nuclear power plant circuit performance.

(3)

Develop the technical bases for judging the safety significanct of terminal blocks.

i 1.3 Terminal Blocks in the Nuclear power Industry 1.3.1 Why Terminal Blocks?

Terminal blocks are used as a method for connecting electrical circuits.

They provide a convenient, low-cost method of making cable junctions.

They are easily installed and provide provide maintenance and calibrction access to the circuit by allowing circuit elements to be quickly and efficiently isolated.

They are especially convenient for maintenance in areas where anti-contamination clothing encumbers personnel.

For these und other reasons, the utilities prefer terminal blocks as a means of making circuit connections, particularly for l

low-voltage, low-power applications. The arguments against the use of terminal blocks are generally the dynamic regulatory environment and the desire tn avoid qualification problems.

1.3.2 Terminal Block Usage The use of terminal blocks As universal throughout the nuclear industry for outside containment applications.

Inside containment, terminal blocks are employed widely in older plants and in some newer plants, i. hough the current trend for rew plants is to use splices inside containment. Based on a 1981-1982 survey of 25 utilities and data in the Electric Power Research Institute (EPEI) Equipment Qualification Data Bank (EQDB) and the NRC's EQDB [3,4), approximately 50 percent of the utilities will continue to use terminal bloc'es in Class 1E applications inside containment. These utilities are pursuing two approaches to retaining terminal blocks: (1) qualify already installed blocks so as to avoid en extensive and costly replacement effort and (2) replace the terminal blocks with ones qualified by a vendor or another utility.

Some of the utilities which are replacing terminal blocks with qualified splices are continuing to use terminal blocks in outside containment applications, and some will continue to use terminal blocks in non-Class 1E applications inside containment. Some utilities are following a policy of selective terminal block replacement, with a major criteria for replacement being the location of the terminal block relative to submergence level.

Plants utilizing spitees inalde containment are not totally exempt from in-containment terminal blocks in Class 1E applications. Many pieces of equipment (e.g., Limitorque valve operators and somt electrical penetrations) contain terminal blocks as integral components. These are "irplicit" terminal blocks as opposed to the

" explicit" terminal blocks which the uti!.ities are removing.

It is difficult, if not impossible, to say that terminal blocks will or will not be used in plants still to be built and/or licensed. The decision between terminal blocks or splices depends somewhat on the preference of the utility and their Architect / Engineer (A/E). Other factors in the decision are the availability of qualified terminal blocks, and the stage of construction. These other reasons tend to be argued in either direction depending on the inclination of the utility and the A/E.

Table 1-1 summarizes the available data on terminal blocks being used in 73 of the 17 operating plants and 17 of the 68 planned or under construction plants.[5] No information was obtained from the other plants. The primary sources of data used to compile these tables were the EPRI EQDB. the NRC's EQDB [3,4) and the survey of 25 utilities. The two data bases derive their major input frot the utilities' I&E Bulletin 79-01B submissions and subsequent updates and contain essentially duplicate information. The EPRI data base, however, has been regularly updated and expanded, whereas the NRC's data base has remained relatively static since 1981. One of the limitations to both data bases is that the inputs are generally limited to the utilities' Clast 1E equipment; this limitation is in keeping with the intended cbjective of the data base, but does not permit a complete characterization of component usage within _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ -

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l a plant. Further, the location cf egulpwent is-only provided as inside or outside coptainment,- Wo detailed lor.ations are given, As a-result any generic tests of terminal blocks must use generalized, very l

conservative environments. Little informatioc is available in the date i

bases to tie down specific applications of the terminal blocks. To overcome these werknesses, the survey of 25 utilities was made.

j Corporate headquarters or site personnel were contacteo depending on the i

organization of the utility. The gus11ty of the information was limited in most cases to the persoral knowledge of the people contacted. No physical inspection of fact 11ttes was conducted.

E TABLE 1 Summary of Terminal Block Usage by Plant Plant Manu f s e t t.rt e Model Loistion

-Beaver Valley 1 Buchanan 0511. 0211 iC i

Marathon 1500 series Penn Union Series 1000 IC Big Rock Point Genera) Electric EB-15. CA-15NT IC Westinghouse 5a2247, 805432 IC Weidmu11er DK-4 SAKR Braldvood 1 & 2 Marathon 1600 NUC IC Penn Union Wo Model Number given Browns Ferry General Electric EB-25 1, 2, 3 Brunswick 1 & 2 Curtis Type L IC General Electric EB-5, EB-25 IC/DC CR-151D3 DC-

'We i daulle r SAK Types IC Byron 1 & 2 Mc sthon 1600 NUC IC Fenn Union No Model Number giveh Calvert Cliffs Buchanan B112 IC 1& 2 Marathon 1600 series

-IC Weidmuller SAKS IC Westinghouse 542247_

IC Comanche Peak Weidmuller ELKoN, SAK10 IC/bc 1& 2 Cooper Buchanan 0514 IC General Electric EB-5, EB-25 IC CR-151A6, --

TABLE 1-1 (cont)

Summary of Terminal Block Usage by Plant Plsnt Manufacturer Model Locativn Crycial River 3 Kulka 5TB, 7IB Stetes NT OC

,s.,

Davis Besse 1 Stanwick Type G IC D.C. Cook 1 & 2 No Termlual Blocks in IE circuits inside contalmeent Dresden 1, 2 Allen Bradley Ne model given IC

&3 (to be replaced)

Buchanan NQB series IC treplacements)

Duane Arnold General Electric EB-5, EB-25 (to IC/DC be replaced)

Buchanan NQB series IC (replacements)

Edwin I. Hatch Buchanan 515.212.222 IC 1&2 States IVM i

Feral 2 Weidmuller S AK Types DC k

e Fitzpatrick General Electric EB-5 EB-25 IC Marathon No Model No, given Square D Class 9080 IC Fort Calhoun 1 States M25014, M25016 IC M25018, M25112 (Type NT)

Crand Gulf 1 & 2 Buchanan 0222, 0524 Cicch Jones 8-141 General Electric 18-5 EB-25, CR2960SY139C CR-151D101 Kulka STB, 7TB, leIB, 27TB, 600J-J.

601J-J, 60?]-J, 603J-3, 604J-J Haddam Neck Ceaeral Electric EB-25 IC Marathon 6012 Westinghouse 805432 IC Wo.dmuller SAK Types IC/DC Indian Point 2 Westinghouse 542247 IC l

l

_7-

amEEEER

~

1 1

<\\

TABLE 1-1 (cont)

Sumasry of Terminal Block Usage by Plant Plant Esfjv;cturer Haggi Loestion

{

Indian Point 3 Westinghouse 542247 IC Joseph M. Farley States 1&2 ZWM IC Eewaunee General Electric EB-5, EB-25 IC Lacrosse Duchanan 218 IC LaSalle 1 & 2 Buchanan NC3 series IC Limerick 1 & 2 No Terminal Blocks in IE Circuits Inside Coutainment i

McGuire 1 & 2 States IVM Weidmuller OC AKZ-4 QC Maine Yankee

]

General Electric CR-151B i

Square D IC Class 9080+CBI IC (1828-C19) (to be replaced)

Waldun11er SAK Types IC t roplacemor.ts )

Millstone 1 General Electric EB-25 IC Millstone 2 Weidmuller SAK-4 IC/DC Monticello Allen Bradley 1492-CD3 OC Ceneral Electric CR-151D3 OC Nine Mile Point 1 General Electric EB-5, EB-25 IC North inna 1 & 2 Connectron NSS3 IC Ceneral Electric EB 5, EB-25 Marathon OC 2L., 1500 series DC Thermoele-tric Type 32-25 OC Nuclear one 1 & 2 Ceneral Elcetric EB-5. EB-25 Oconee 1, 2, 3 States K25004, BR5CJ8, OC M25012 (Type NT)

SLS-8 Oyster Creek 1 General Electric EB series (to be replaced)

Weidmuller SAK4 (replacement)

OC/(ICf)

T ABL7.1-1 (cont)

Summary cf Terminal Block Usage by Plant

[hg

}{a,nuf acturer

Modej, Wat lott Pallpades Weidmuller DK-4, SAKR Westinghouse 805432 IC

~~I Marathon Pro Type~~

\\

IC EM-215/6000, Prc Type IC EM-47150/6000 1.3.3 Yerminal Block Applications instrumentation and control'clecuits. Terminal blocks are used pradosleen telected plants also orploy terminal blocks explicitly in 480 Vac power circuits, but this practic is limited to 10 percent or less of the plants.

~~e low voltage (4 Vdc or less)The instrumentation circuits are typically RTD circults and low current (1 mA or less),~~

~~or l~~

l

~~, l.~~

transmit;er-circuits * (4-20 TA at 24-50 Yde). Control circuits are typica'.1:r solenoid valve circuits, motor-operator control circuits, or stated indication circuits and are normally 120 Yac or 125 Vdc and 1 A to 2 A or loss.-

l The physical location of terstnal blocks varies depending on the need to junct ion cables. Two of the most typical locations are_at_ containment psnetre.tions and near equipment. 'At these points, field wiring must be term 8.nated and connected to the penetration or to the instrument or control device pigtail.

Electrically, the terminal blocks are typically adjacent to the instrument or control device and are separated only by the resistance of the intervening cable. As will be seen, this means that terminal block faults can be viewed as impedances in parallel with the input of the instrument or control device and their effects can be analyzed as such.

~~1 i~~

~~4 e~~

l

~~Due to the susceotibility of transmitter circuits to leakaga current, most utilities are now employing splices in these circuits or are planning to change to spilces within the near future.~~
l.
2.0 TgP.MINAL BLOCK LIFg CYrLE
~
2.1 Terminal Block Design Terminal blocks are considered to be "off-the-shelf" items with designs that have not changed for many years. The two basic types of designs are one-piece and sectional. The primary distinguishing feature of the one-piece terminal block is that the insulating material which forms all of the barriers and the support for all electrical terminals is a n.ngle piece of molded insulating material. The number of terminals is fixed by the molding. Mounting plates or channels do not comprise part of the one-piece terminal block design, and the block is typically mounted directly to the enclosure structure.
The primary feature of the sectional terminal block is that each section is an individual unit of insulating material and conductor.
gach of these sections may or may not have one inter-terminal barrier as part of each rection's molding.
If the barrier is separate, it will be held in place by all nment tabs. The sections are mounted on a channel or 6
base plate to form a multi-terminal terminal block assembly.
The l
sections are either individually attached to the mounting plate, or they are gang-mounted using a antins dovetail-like arrangement between the sectlans and mounting channel. Special end-pieces keep t he sections fram sliding off of the ch:nnel.
Figures 2-1 and 2-2 111ustrate typical one-piece and sectional 1
terminal block configurations, re.spectively. The sectional corstruction has a gap between sections from the top sutface of the terminal block to the mounting rail. This gap does not exist in the one-piece terminal blockr.
The width of the gap depends on how tightly the end pieces e
compress t'ne sections together. Given the proper conditions. this gap has the potential to retain a moisture film that could be a conducting path to greund.
Of the terminal block models reported in Table 1-1, 25 models were identified as one-piece and 32 as sectional. However, in terms of quantity installed..there are probably more one-piece than sectional terminal blocks in use simply because the majority of plants specify one-piece terminal blocks.
All terminal blocks have squared corners, erevices, and other convoluted surfaces which may retain deposits of contesinants and would be difficult to clean.
Further, these designs make use of conformal coatings ineffective becauss a complete coating is difficult to achieve with the many concealed areas.
2.1.1 Terminal Block Materials for the terminal blocks listed in Table 1-1, five insulating materials were identified.
phenolic with either a glass or cellulose filler is the primary material used for the insulation (39 of 57 models used this material) and alkyd, melamine, diallyl phthalate, and cylon -
.. ~... _
= _.
I.
i l
i I
f I
l
'i i
l A
+
1 a
n e
7 o
n b
L e,
4 ax i
SECTION A-A A
i i
t Figure 2-1: Typical Configuration for a One-Ploce Terstinal Block-j.
I e
A l
g_
er'
-u If j
w I
~
f
[M o
SECTION A-A 4
A I,
Figure 2-2: Typical Configuration for a Sectional Tenninal Block e
I
l (five or fewer models each) make up the remainder. These materials are normally chosen because of cost considerations, moldability, and their relatively good electrical insulation properties. Table 2-1 summarites some of the relevant properties for generic formulations of these materials. Product literature for models which stilize phenolic insulation indleates a maximum service temperature of 150'C (302'F),(9.10,11.12,13) This value is in agreement with Table 2-1.
l Qualification tests of terminal blocks for nuclear service j
(14,15,16,17,18,19,20,21] typically age samples between 120'C (248'F) and j
165'C (329'F) and subsequently expose them to accident profiles that j
reach sustained temperatures of 170'C (338*F). The specimens tested i
survive these thermal environments showing only minor degradation. Thus,
)
from a thermal standpoint, the selectica of a phenolic or other polymeric material rated at a 150*C (302*F) service temperature is reasonable for i
nucleer application.
Radiation sensitivity is influenced by insulator fill material.
Vestinghouse Research Laboratories, in reference to Westinghouse terminal blocks, evaluated the radiation properties of phenolics as follows (22):
"Cellulese-filled phenolics...are less radiation resist =ut, in general, than unfilled or mineral-filled phenolics. Information on paper, paper-laminate, and linen-filled phenollen indicates that they all begin to defrade at approximately 5 x 105 rads. The most radiation sensitive properties, elongation and impact strength, are reduced by 25% at doses from 3 to 8 x 106 rads. The icellulose-filled phenolics) will probably exhibit similar behavior. Electrical properties are not affected by doses < 2 x 107 rads."
e One manufacturer experienced a fallare of their cellulose filled melamine terminal blocks during radiation and steam testing which is possibly attributable to radiation effects. They experienced cracking of the terminal block insulation material. The postulated mechanism was that radiation degraded the surface resin material and perhaps opened the structure sufficiently to allow moisture to be absorbed 8nto the filler.
Subsequently, when the high temperature accident transient was applied, this moisture vaporized, pressurizing *he interior of the insulation in a time frame short enough to prevent preasure equilibration. Hence, the material cracked to relieve the stress.
The selection of a f!11 material typically affects the radiation tolerance of a material by plus or minus one to two orders of magnitude (6) with organic fillers such as cellulose decreasing radiation tolerance and mineral or glast fillers increasing tolerance. The radiation doses quoted in Table 2-1 are for degradation of mechanical properties such as flexural or tensile _ strength.
It has been knoen for some time that the electrical properties of many polymeric materials, such as volume resistivity, dielectric strength, and arc resistance, appear to be unchanged by radiation levels which cause extensive physical damage to the material.(23) Thus, with proper selection of fill material (e.g., -
- =-
2
i Table 2-1 Typica7 Radiation Damage Thresholds and Maximum Service Temperatures for Five Insulating Materials Used in Terminal Blocks Found in U.S. Nuclear Power Plants Insulating Radiation Damage Service Temperat1re Material Threshold (Rads (C))
~~C (*F) 161 (71 Phenolics glass filled 1010 160-190 (320-374) 8 10.go9 120-220 (248-428) cellulose filled Alkyd glass filled 109 149-191 (300-376) cellulose filled 108 191 (376)~~
Melamine (Resin) 108 glass filled 109 204 (399) cellulose filled 107 99-150 (210-302)
Diallyl Phthalate glass filled 108 204 (399) cellulose filled 107 160 (320) 5 10 _1o6 130 (266)
Nylon 61 (8) glass), the radiation levels quoted in Table 2-1 indicate that there will be minimal effect on the insulating materials normally used for terminal blocks by nuclear plant radiation doses (estimated doses:
5 x 107 rad operating life and estimated 1.5 x 108 rad accident).
The metallic terminals are typically stable to temperature and radiation levels which exceed the aging and accident environments postulated for nuclear power plants. Thus, we would not expect degraded performance of the conducting material based on pure radiation and/or temperature effects. There is, however, potential for material inLeracLlon problems such as corrosion or galvanic action to occur. The selection of metal coatings and base conductor material should be such that these effects are minimized in both the normal operating environment (e.g., 80-110*F and 10-1001 RH) and the postulated accident environments which include steam and chemicals. One specific example would be to avoid the use of cadmium as plating material because in a steam-chemical spray environment it may be a reactant in a galvanic reaction. -
2.1.2 Quality Assurance in Terminal Block Design The manufacturer's quality assurance manuals reviewed by us (24,?5,26] do indicate that design reviews are conducted by the their engineering organizations. The manuals are vague concerning what specifically is reviewed, but they do explicitly cover such items as drawing control, change control, compliance with appilcable standards and regulations, and analysis of tolerances and dimensions.
It is not clear whether or not consideration is given to appropriate material selection, material comFatibility, or terminal block designs to reduce leakage I
currents or contamination. Apparently, some of these considerations are
~
l addresaed as evidenced by a t rend towards the use of glass-filled i
phenolics, the elimination of cadmium-plated conducting parts in terminal l
blocks for nuclear applications, and new designs to increase conductor separation.
2.2 Terminsi Block Manufaccure 2.2.1 Manufacturing Process There are several processes applicable to the manufacture of terminal blocks. These include injection, transfer, and compression molding. As long as the Quality Assurance / Quality Control (QA/QC) programs assure that specified raw materials are used, that molds conform to specification, and that processes and assembly operations function correctly, there should be little reason to suspect the manufacture of terminal blocks as contributory to the failure and degradation modes.
One potential area may be the use of sold release and the retention of a residue on the insulation surface which could affect performance. Based on our limited experience in procuring terminal blocks from niae manufacturers, we found no observable variations or defects and all were in confermance with catalog specifications. For a simple item such as terminal blocks, one would expect this type of reproducibility and quality.
2.2.2 Quality Assurance in Manufacture The quality assurance manuals [24,25,26) vary in the thoroughness with which they describe the QA programs appilcable to the manufacturing process. Some are sufficiently detailed to octlined the inspection programs which include inspection of the first production unit, last ten production units, and ten production units per case. The manuals also vary is the thoroughness of their stated raw material segregation, Letcecbility, and receiving inspection requirements. Those vendors claiming compilance with 10 CFR 50, Appendix B appear to have scod material centrol, lot traceability, verification that production units match design, and production line quality control.
In general, the QA applied by the vendors to the manufacturing process appears to adequately meets the requirements for nuclear application.. _ - _ _ _ _ _ _ _ _ _ _ _ _ _ ______
2.3 Terminal Block Selection, Procurement, and Installation 2.3.1 Role of-Architect / Engineering (A/E) Firms The issue of terminal block selection, procurement, and installation tras discussed with three (Bechtel, Burns and Roe, and Sargent and Lundy)
I of approximately twelve A/E firms participating in nuclear plant design.
Though not a large sarple in terms of total number of A/E' firms
)
participating in nuclear plant construction, these firms represent allshtly more than 50 percent of the 140 planned and operating plants in the U.S.
Generally, the A/Es function in a key advisory role in deciding whether or not to use terminal blocks and what terminal blocks to use.
As the funding agency and the licensee, the utility retains final responsibility over the decision, but the policy and practices of the A/Es bear on the final choice. The A/E firms call out in the design specificatio when terminal blocks will be used and what makes or models are acceptable. Typically, an A/E might specify a particular make and model with purchasing to be done on an "or equivalent" basis.
It is act clear, however, who makes the determination of what constitutes "or equivalent" or what criteria are used to make the determiascion. No other detailed controls over procurement or selection of terminal blocks are in place. On site, the A/Es do not provide any specific quality 4
assurance function for terminal blocks except as might be provided in site quality assurance plans.
2.3.2 construction and Installation Practices Construction procedures are not normally written by the A/E unless they are also *be constructor. The A/Es do, however, review and comment e
on the constructi'a procedures and thus play an important role in determining how a cemponent will be installed. The installation procedures we have reviewed give minimum clearances for terminal blocks, how cables are to be terminated, how wires are to be labelled, etc.
Terminal block orientation within the enclosure was not mentioned nor was the entry direction for bringing wiring into the bor. There is an effort to keep like voltages and applications on the swme terminal block.
For example, a single solenoid valve's power, actuation signal and indication signal might typically be on the same terminal block, but a pressure transmitter circuit or an RTD circuit would not also be on that block.
There is also an effort to segregate appilcations by electrical box. For example, several transmitter circuits may all be on different terminal blocks but within the same enclosure, while terminal blocks in RTD circuits would be in a different enclosure.
The construction procedures are important in determining the installation quality assurance program since they document the basis for inspection and control. Typteal quality control checks might include assuring that qualified terminal blocks are used in Class IE applications and that installation procedures are followed with respect to spacing, circuit continuity, and wiring technique. As evidenced by the utility and A/E surveys, no written procedural check for cleanliness is made except to insure that large foreign objects do not remain in the elcetrical enclosures..
4 Termins1 blocks are typically installed in a National Electrical Manufacturers Association (NEMA) Class 4 enclosure.* However, selected plante use enclosures f abricated to a company specification which may or may not meet NEMA-4 specifications. Other plants have different NEMA class boxes in use. All new construction that we are aware of employs NEMA-4 enclosures.
The conduit entries are normally made with conduit terminations that j
have neoprene or other organic material as seals. These entries may j
penetrate the box from the top, side, or bottom, but typically are top or side entries. There is no provision made to trap and drain condensate in the conduit to prevent it from flowing down the interstitial space between the cable and conduit and entering the box. The sealing of the conduit entry and exit points is utility depeadent.
Some utilities have sealed them with materials like Room Temperature Vulcanizing (RTV) sealant or Red Glypt"; however, most utilities have not sealed the conduit entries.
All but one of the utilities contacted indicated that a 1/4" to 1/2" ditmeter weep hole is drilled in the bottom of the electrical enclosures. The primary reason for this hole is to permit condensation which accumulates under normal operating environments to drain from the box. The utilities also indiccic.d that the weep hole will allow rapid pressure equilibration during a LOCA steam pressurization of the external atmosphere. To our knowledge, flow retarcars are not installed in there holes.
2.4 Inspections and Maintenance 2.4.1 Utility Inspections and Maintenance Most utilities surveyed indicated that no special maintenance or QA s
activities occur with respect to terminal blocks subsequent to installation. When circuit maintenance is performed, a visual inspection is made.
If Class 1E circuits are involved, a check is made to assure pecper reconnection of the circuits'. No specific check for cleanliness is made. However, one utility that we are aware of, has modified its installation procedures for terminal blocks so that when new terminal boxes are installed or'old terminal boxes are modified, the terminal blocks tnerein are cleaned with deionized water and allowed to air dry.
2.4.2 NRC Inspection Activities The following comments are based on discussions with Region II and Region IV personnel and a review of NRC Inspection and Enforcement (IEE) inspection procedures.[28] During construction. NRC inspectors review the terminal block qualification documentation and verify whether or
NEMA-4 enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against wind blown dust and rain, spisshing water, and hose-directed water.(27) The lid gtsket is normally neoprene and it is incumbent upon the installer to use conduit terminators that maintain the integrity of the box.
~
not the blocks are installed in accordance with the w&y they were qualified. For example, if the quellfication was for non-harsh environment areas, then the blocks must be installed in non-harsh environment areas. They check the enclosures to assure compilance with the manner in which the blocks were protected during quellfication.
With respect to the terminal blocks themselves, there are no stringent inspection procedures. They do examine the installation to assure that the blocks are correctly installed in accordance with construction procedures, that the terminals and cable terminations are tight, that the blocks are not cracked or broken, that the elottrical enclosures are dry and nothing is stored in them, and that no stress is imparted to the blocks by the cable. They also check cleanliness, but the Gegree of cleanliness is a personal judgment decision. NRC/ILE Inspection procedure 51063C (28) simply says that after installation...
cable trays, junction boxes, etc. !should be) reasonably free of debris." No speelfic.tanderas for cleanliness exists other than the general housekeeping st*ristb, ANSI N45.2.3 and IEEE 336-1977.(29,30)
These standards address caeanliness only generally and do not reference any specific type of equipment or standard to be applied. IEtt 336 simply refers to ANSI N45.2.3, stating that housekeeping should be ir accordence with ANSI N45.2.3.
ANSI N45.2.3 sets up tones with different degrees of cleanliness and access requirements for each. For operational plants, no espilent standard addressing cleanliness exists. Only to the extent that ANSI N45.2.3 carries over does a standard exist for operational plant cleanliness.
The NRC inspectors espect a different degree of cleanliness depending on the type of equipment in the en:losure.
For ex ample, a
enclosures with relays require a higher degree of cleanliness than enclosures with sirple termine1 blocks.
Surface dust is almost always present.
a inspectora do not regularly tnspect terminal blocks in operational plants.
However, this does not mean that terminni blocks are never inspected, but rather that they are not an explicit point on an inspection agenda.
2.5 summary The above sections highlight that terminal blocks are considwred an "off-the-shelf" component with relatively few requirements that must be met.
Their designs have been relatively static for a long period of time.
Their simple, passive nature coupled with the industry's f amillselty and traditional use of terminal blocks, has led to a relatively methoalcal approach in their selection, installation.
{
faspection, and maintenance. QA activities designed specifically to assure adeguate and appropriate attention to terminal blocks in these phases of their life cycle have not been diligently pursued, perhaps due to a lack of consideration about the relative importance of terminal blocks. - _ - _ - _ _ _ _ - - -
\\
3.0 TESTING OF TLEMINAL BLOCKS 3.1 Standard Industry Tests All terminal biccks that we are aware of comply with the provisions of UL Standard 10!? 131) or NKKA Standard ICS-4-1977.132] These I
strndards specify I nimum terminal spacing and insulation dimensions, properties to be considered in material selection, standard temperature rise at rated current, criteria for wire pull out, mar.?'ng standards, connection types, and dielectric-voltage withstand test criteria. The standards and teste to assure compilance are designed to provide a high grade, industrial application product, which they do.
In addition, some vendor catalogs quote that their insulating material fall in one of four flammability categories defined by UL Standard 94.133) Other tests for tracking indez (34,35] or arc resistance (361 are generally not quoted by the terminal block vendors, though orlginal m. ' Jacttrers of the l
Insulating materials may have dtta testleble, soference 7 tabulates t
electrical properties for many generic polymer materials such as the l
phenolics, r41 amines and alkyds used for terminal block insulations.
l 3.2 Nuclear Qualification Tests Since 1977. t here have been a number of test programs eponsored by both utt11ttes and terminal block manuf acturers that have been used to l
support qualification of terminal blocks.[14,15,16,17,18,19,20,71) These tests generally consisted of thermally aging terminal blocks using Arrhenius techniques or the 10'C rule, exposing the terminal block to normal vibration and seismic tasts, and then conducting a LOCA/HELB simulation.
Functional tests normally consisted of insulatlon resistance i
l (IR) measurements and conductor continuity (necks subsequent to each of 8
i l
the sequentially applied environmental stresses (i.e., thermal aging, radiation exposure, setemic tests, LOCA/HELB simulation.)
All industry test reports reviewed by us indicated that the terminal blockt passed the functional IR tests subsequent to each type of esposure. Measurements,of the variations in terminst block performance i
during these tests with the blocks powered were generally not conducted, though many of the tests removed power from the blocks and made megohmmeter measurements during the LOCA slaulation. The typical method used to monitor terminal block performance during the LOCA/HELB simulation was via fuses in the circuit providing potential to the terminal block.
These fuses were sized to fall at leakage currents l
between 1 A to 24 A dependtrt on the test speelfication. Acceptance criteria were based on the terminal block's ability to carry the r
i specified voltage and current. During most of the tests, the fuses in the circuits to one or more terminal blocks f ailed once or feelce and were replaced. Sometimes with a given terminal block, the fuse continued to 1
I f all; in that case, the terminal block was removed from the test. An important reint which is not speelfled in any of the reports was how of ten a fuse was allowed to f all or how many terminal blocks were allowed to be removed from the tiet before the test lot was dete:alnvd to have failed. Only the Washington pubile power Supply System test of z-
Weidmuller blocks in a post-LOCA soak environment [18) and the phontz tes'. of their own blocks (19] made definitive measurements of leakage currents during the tests in ad11 tion to the fusing techniques.
Using fuses to monitor during-test performance has two drawbackst first, the failure of a fuse is only a single point criterion that shows that leakage currents were at least as large as the rated value of the fuse for the time necessary to fall the fuse; and second, the sizing of the f uses to "large" values provides no information about low level leakage currents. As shown by analyses in Section 8, low level leakage currents can eff ect low power, instrumentation ar.d control circuits.
These elrcuits are the primary terminal b1'.:. appilcations, and, therefore, the acceptance criterla were not, in this respect, germane to the majority of terminal block appitcations.
Table 3-1 provides a brief comparison and summary of some industry terminal block goalification reports, and the following sect'.is give a more detalleJ synopsis of each.
3.2.1 Franklin Research Center's Test of Buchanan Terminal Blocks for Philadelphia Electric Company [14)
This test series consisted of two phases. A and B.
Each is discussed in turn.
In phase A, sit Buchanan terminal blocks were evaluated (2 each 2B104 ar.d 4 errh 2B108). These blocks are similar except for number of terminala (A en4 8).
The insulating material for these terminal blocks la a filled phenolic. No further detatis on the material such as fill material or phenolic formulation were available.
Two terminal blocks were subjected to 100 Mrads Co-60 gamma radiation and then thermally aged at 136*C (277'F; for 160 hours0.00185 days 0.0444 hours 2.645503e-4 weeks 6.088e-5 months , two terminal blocks were subjected to 50 Mrads Co-60 trradiation and not thermally age, and two were neither treadiated nor thermally agedi All terminal blocks were then subjected to a 14-day steam /deminerallred water spray (S/D) environment to simulate a LOCA esposure.
During the S/D exposure, the blocks were installed in either steel compartments or vented aluminum boxes of philadelphia Electric design; the terminal blocks were energized with 150 Vac and 12.5 A.
If more than 1 A of leakage current was required to maintain the spectfled potential, the specimen was removed from the circult.
During the LOCA test, four specimens h.d to be doenergized for a 0.9-hour period when suspected flooding of the test chamber occurred; the two other specimens had to be deenergized for a 16-hour period when insulation resistance was low and leakage currents hight and one of these latter two terminal blocks had to be deenergized permanently 4.9 days into the S/D esposure, apparently due to the blockage of the drain hole which permitted 11guld to partlally submerge th1 terminal block.
IR was measured befo e and after each sequential tert and at selected times during S/D exposuse. The circuits had to be deenergized to make the IR mencurements.
No failure
.iteria were promulgated for IR readings.
Initial IR measured 108 ohms or greater at 500 Vdc for all specimens and there was insignificant change af ter gamma ar.d thermal exposures.
Early in the S/D exposure, the IR for all semples dropped to less than.
Table 3-1 Compattoon of Some Inde4 f t,0CA Steelat tone f or Tereinal plock Quelificetten negotemeter measereeenta t **W 5 Utt36ty/
T9 po.
Acceptance lehes) (500 voc anlese notedi Sreelet e2 aan Test Latt 10 T*ssed ceaterle Power Der i M t.oC 4 Post-1.DCA mares rey,ee oef.
FMesseelphia swehanan Ablaity to carry ISO vac
<5sici 102 t o 1912 on,egoen r,e,,ed is o 34 i
Esectrac/
28804 2
specifsed current at 12.5 A at 50 Vdc fram test at 4.9 Phace a rwC*
29109 4
orecifted etItage.
days.
Ot her e removed at earloos tames.
Philadelphia pochenen Ability to car ry 150 vac
<Se10%
< $ s 188 ene to removed free 7d le Electrac/
28809 3
arecifted corrent at 12.5 a at 50 Vdc at SO V4e to from t**t after Phase e rac*
marathon spectfled weltage.
<5:305 5.3 heers.
Itse 2
at 30 yde Generic /
Duchanen Paint ain potent ial 220 Wee
<5st04 Post-test Dettag t. ora, lestege 74 13 rat
~~PJel06 1~~
~~of 120 y and estrent 25 A at 10 V t o bipet te t corrente mere~~
~~200 en pys!!2 8~~
of 25 A.
2:1012 to < S en for all esup106S 1
et 500 V terminal blocks WQall2S I
together.
puo Series 1
I Cenersc/
marathon t.eatage corrents 112 vae, mene
<S:10%
stew 23 A feee og 33 d Is 3
orte i.0. -
ices t t,an 2 2 A.
or
>>A for a n 32.,
~~32. vee opn i - e.~~
g (Meeteellte) 1500 NUC 6
19 4, or 24 A.
264 vac, bosee memoord free teet.
142 WUC Monttsted by (see, J3 A plew IS A fase on
$28 vec, 264 vac erecimene.
33 A peplaced (see and centnamed.
Generic /
teeldeeller 5
meintain 600 Yac 600 vac mone 2.4al87 to voltage reduced to 29 hr 17 FMc*
SAR T3peu and 29 A with !*enage 20 A
.5s10" 150 V wh+n ersey i
corrent less then I A.
at $"O Vde Introduced to Monitored bF fase.
maintain 1*abege corrent less t hem 1 A.
areC e rrenesin semearch center e
L
Table 3-1 feenttweed)
Comparison of scee Fedest r y LOCA Simulatloce f or Tere
~~mal Bloct Qualificatten Utility /~~
TB Mo.
Acceptance toheel (500 voc entese not ed!
tength megebeeeter peamer*ee=to Test Lab ID Tested Crsterle Power Der t ag 1.rica
,oet-Lnch wetes Special cf LOCA trpaeore _
f.
wress/wyle wetomuller 1 A Lestege current 600 vec none 1.231C5 to poseered testage 32 d 18 thorcol SAs typee monit ored by f use 2n A S.9s1010 teme* Tse as and discrete time current during test.
tested by eeni t or ing o f
?*st was cely a post-wendealler, leakage estrents.
test TAXA seat.
230*p met. 3) e*d 29 pelg. 2004 relat e s, host dt t y.
No steee.
Generief Phocia kyse ssa series 30 wone spectried 420 vac (Marcol teramic watte wene seperted 2 esperheated stese 24 hr 19 20 A pte settee esposed 44 vde periode, no teatege Ceramic 24 Vdc corrent messeremente ssa series LOCA of DC circuite, pelaman*
4 40 mA to a Series
~~700 e4 current Polye9ter ebeeeeed in 420 vac (3 Typest case cc -. wealth parathos~~
, k Edtoon/wyte settem 6000 2
less than 30 A.
!$ A Leenage cartent 175 vae men *
<l.as19 ee go,, periods of 3A.9 hr 20 6
i n
(Munteetilel series 1600 2
Monitored by f use.
to 2.2m POI 2 superheat In accident j
f at 550 Vac esposere. Ore blott eeceeded IO A lentage
~~off ocele cur r ent--shee t ed t o lew.~~
M*seure-ground.
ment wit h Digittal mustim*ter read 3.5 chee Ceneric/
Cuttle ST pone specified 400 vae erl#I to 2nl8IO westenghouse Canch Jones o
g,e,9e c,gg,ng,
~~21 br 21 Sei SalN 2.3s10I not monttered Weseanghouet during test with 342-247 blocte powered.~~
~~Marathon 1500~~
~~/eC e Frannt;n Research Center e~~
-.. ~.
"Md 5 x 104 ohms at 10 Vde, but then recovered to less than 5 x 105 chas at 50 Vdc for the remainder of the S/D exposure. Af ter the s/D asposure, the IR varied f rom 120 ohms to 1012 ohms at 500 Vdc.
Leakage currents were not monitored during the S/D esposure.
Post-LOCA simuistion observations by Franklin Research Center wares a) Af ter gamma radiation (50 Mrad or 100 Mrad air equivalent dose depending on semple)
Dark deposits on metal parts of tbs b) After thermal aging (136'C (277'F) for 160 h)
Green deposits on TB mounting screws oily residue inside bor Thick, gray, crusty deposits on terminals c) After steam /delonized water exposure (14 days)
Conduit seals marginal Bos gaskets marginal (EPR rubber)
Marker strips deteriorated Cable insulation spilt, swollen, stuck together Rust colot sediment White and tan deposits on all metals parts of the tbs Debris from test satarisis clogging drain holes Phase B of the FRC/ philadelphia Electric test exposed three Buchanan 2B108 and two Marathon 1608 terminal blocks to 26 Head (air) ganma irradiation and a 7-day steam / demineralized (C/D) exposure. No thermal aging was conducted. As in Phase A, the blocks were installed in either a steel compartment or vented aluminum boxes of Philadelphia Electric design.
Insulation resistance was measured before and after each environc2nt and during S/D esposure. Again, the circuits were doenergized to make 9 ohns the IR measurements.
Initial IR at 500 Vdc was greater than 10 and no significant change was noted afte gamma radiatien. During the S/D exposure, the IR for all specimens measured less than 5 x 105 ohns 4
at 50 Vdc. The Phere A test reported IR values as less than 5 x 10 ohms; the factor of ten discrepancy was not explained.* After the S/D exposure, the IR of one Marathon and one Buchanan terminal block measured less than 5 105 ohms at 50 Vdc. The irs of two Buchanan ters.inal blocks were not measured after S/D (no reason stated). One Maratho.1 terminal block was deenergized 5.1 hours1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months into the test. After the test, 4 ohms at 50 Vdc. The the IR of this block measured less than 5:10 Different megohmmeters were used in each test. They presumably had different lower limit values and hence the irs of the tbs could have been the same. All that is positively known is that in both Phase A and Phase B the irs went below the range of the meter.
l l
l I
l report postulates that the reason for the low IR which caused the block's removal from the test was the 7eesence of conductive moisture and/or deposits on the molding ridges between the energized terminals and the box.
The acceptance criteria for the phase B test as stated in the test plan was "when the... insulation is degraded to the extent that the specimen is no longer capable of carrying the specified current at the specified voltage."
not givar..
A more precise definition of acceptarce criterla was 3.2.E Franklin Research Center's Test of Buchanan Terminal Blocks for Control products Division of Amerece Corporation (15)
Twelve one-piece, WQB series terminal blocks and three assemblies of selected WQO sectional terminal blocks were exposed to thermal aging (165'C (329'F), 39.6 days fcr WQB samples and 121*C (250*F) for HQO samples), gamma irradiation (200 Mrad at 0.56 Mrad /hr, Co-60),
for 8.3 days vibration aging (10 pairs of acceleration and frequency between 0.03 and 0.74 t's and 3 and 60 Hz with 15-minute dwell at each acceleration-frequency pair), and seismic fragility tests (five 20-second dwells at greater than operating basis earthquake (CEE) acceleration of 5.5 lerels with a peak greater than safe shutdown earthquake (SSE)t's between 2.5 and 13 Hz and one 30-acceleration of 8 g's between 2.5 and 13 Hz).IcVel with a peak Four of the WQB r rles samples and one of the NQO assemblies were then submitted to a /-day steam and chemical spray exposure.
The terminal blocks were protected v' y NEKA-4 enclosures.
samples were energized with 120 Vac and 25 A except during the petiod The when IR measurements were made.
IR measurements after ths thermal aging were greater than 1.4 x 1012 ohms, and after the gamma irradiation they were greater than 5.1 x 1011 ohms.
the seismic and vibration tests.
Similar results were obtained after During the steam / chemical spray exposure, the one-piece terminst blocks experienced variations in IR from 3 x 105 ohms at 10 Vdc to 2 x 1012 i
ohms at 500 Vdc. The sectional terminal blocks experienced IR variations from less than 5 x 104 at 10 Vdc to 1.9 4 109 ohms ohms at 500 Vdc. Though leakage currents were not measured for each terminal block individually, nor were they recorded throughout the test, the test report makes the following statement which we assume is based on periodic meter readings:
"The leakage / charging currents which eneegized the specimens at 120 V were less than 200 mA during the dwells at 174*C (346*F).
The leakage / charging currents decreased to less than 5 mA for the remaining portions of the steam / chemical spray exposure."
The specimens withstood a 5-minute 2200 V high potential withstand test after the steam / chemical spray exposure Acceptance criterls were not specifically mentioned, though reference wa made to the maintenance of 120 Vac and 25 A.
3.2.3 Wyle Laboratory's Test of Marathon Terminal Blocks for Marathon Special Products (16)
Three sets of terminal blocks, each consisting of two Series 1600 RUC terminal blocks, two Series 1$00 NUC terminal blocks, and two Series 142 WUC terminal blocks were tested. The blocks were protected in NEMA-4 enclosures. The test sequence was radiation exposure (200 lirads at 0.58 Mred/hr), thermal aging (120*C (248'F) for 18.5 days), vibration aging (0.1 g peak acceleration between 5 to 200 Hz), seismic simulation (5 OBE and 2 SSE) and LOCA simulation.
The planned accident str11stion consisted of two 174*C (345'F),
50 psig steam plateaus each of 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months duration, followed by a 42 hour4.861111e-4 days 0.0117 hours 6.944444e-5 weeks 1.5981e-5 months plateau at 163'C (325'F), 83 psig, and a 28-day, 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months plateau at 144'c (291*F), 45 psig. The two initial steam plateaus had initial rknips to 196'c (384*F), which lasted momentarily and then retreated to 174*C (245'F) in approximately 2 minutes.
It should be noted that the 174'C (345'F), 50 psis condition is 26 C' (47 F') superheated, while the other two temperature-pressure periods are saturated.
Chemical spray was applied throughout the 30-day exposure.
Arrhenius techniques were used tc compress a one year accident profile to a 30-day simulation.
Each set of terminal blocks was powered at dif f erent voltage levels. One cet was powered at 132 Vac, 33 At one set at 264 Vac, 33 A; and one set et 528 Vac, 33 A.
The accept 6nce criteria specified that 106 ohms was to be the minimum allowable IR for the functional tests and that during the accident exposure the 132 Vac specimens should not exceed 12 A leakage current the 264 Vac specimens should not exceed 13 A leakage current, and the 328 Vac specimens should not exceed 24 A leakage current.
Functional IR measurements were made initially and subsequent to each e
10guentialexposure. The pre-test baseline measurements ranged from se to 1010 ohms; subse variedbetween2.4x10guenttotheradiationexposJre,theIts 10 ohms; subse 11'and1.2x10guenttothethermal and 3 x 10 2 ohms.
Similar aging IR values varied betwnnn 10 values were obtained after the vibration and seismic tests. During the-first LOCA ramp, the 1e.akage current for the 528 Vac terminal blocks exceeded 25 A and failed the f.se used to monitor tne leakage currents.
Also, the 18 A fuse in one of the 264 Vac circuits failed but did not fall a second time after it was replacec. During the second steam ramp, the 25 A fuse in the 528 Vac circuit failed sgain and the 528 Vac specimens were removed from the test. Leakage currents were monitored daily by using a clamp-on current probe for the specimens that remained in the test, though these readings are not reported other than to ray that they were below the acceptance criterla.
Also during the accittent exposure, a power failure occurred whleh doenergized all terminal blocks. When power was respplied approximately 15 minutes later, it was turned on abruptly and all leakage current fuses failed. This same phenomenon was observed in the Sandia tasts (1) where rapid changes in applied voltages caused severe drops in terminal block 1R.
The post-accident IR functional tests yleided value.: between less than 5 x 10$
10 ohms for the other ohms for the 528 Vac specimens to 1.2 x 10 7
8 ohm specimens. There were, however, a large number of 10 -10 readings thich indicated that, in genersi, the Its did not recover to the pre-accident levelt. _
3.2.4 Franklin Research Center's Test of Weidmuller Terminal Blocks for Veldmuller Terminations Inc. (17) rive terminal block assemblies each containing five TAR series terminal blocks were tested. The terminal blocks were molded of a glass-filled pbcaolic material.
The terminal blocks were thermally aged (140*C for 7 days), exposed'to 200 Head (air equivalent) Co-60 gamma dose at less than 1 Mrad /hr, vibrationally aged (3 to 60 Hz), and subjected to a multifrequency seismic vibration (1 to 40 Hz) which included five 30 cecoco dws11s at OBE levels and one 30-second dwell at sst levels.
The specimens were then divided into two groups and mounted in NEMA-4 enclosures.
Each test group was then separately subjected to a 29-hour steamichealcal si sy exposure to simulate a LOCA environment. The profile for one w/oup reached a maximum temperatu e of 246*C (475'F) and 70 psig (89 C' (161 F') cuperheat) and then retreated to 185'C (365'F) after 6 minutes and to 174*C (345'F) after 14 minutes into each of the peaks.
The 174*C (345'F) periods lasted for approximately 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months and were at saturation pressure. After the second 174'c (345*F) period, two additional temperature plateaus completed the profile:
164*C (328'F) for 9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months and 156'c (312*F) for 17 hours1.967593e-4 days 0.00472 hours 2.810847e-5 weeks 6.4685e-6 months . Again, both of these plateaus were at saturation conditions. The peak temperature reached by the second group was 232*C (450*F) at 68 psig. The remainder of the profile followed the first group's profile. The terminal blocks were energized during the steam exposure with 600 Vac and 20 A.
The acceptance criterion was to maintain a leakage current less than 1 A at the 600 Vac energizing level. Monitoring of leakage currents was secomplished by a 1 A fuse. For both test groups, it was observed that the 600 Vac PC oatial had to be reduced to approximately 150 Vac at the times when fe,sh, room temperature solution was sprayed into the test ehtsber. With '
potential at 150 Vac or less the leakage currents remained less than 1 A.
The leakage paths appeared to heal themselves after the recirculated spray reached temperatures of approximately 93*C (200'F).
Ik mecouroments at 500 Vdc before the LOCA simulation varied between 1 x 108 and 1.5 x 1010 ohms; after the LOCA simulation thty varied between 4 x 107 and 3.5 x 108 ohms.
Two of these terminal block assemblics were subjected to further seismic qualification tests in a subsequent test program.
i l
3.2.5 Wyle Laboratory's Test of Weidmuller Terminal Blocks for i
Washington pubile Power Supply System [18]
This test program tested the same five terminal block assemblies subjected to the LOCA pieviation discussed in paragraph 3.2.4 These assemblies had been stored by W41dmu11er at normal office temperatures and humidities in the intervening two years.
The test was a post-LOCA soak of the terminal blocks with intermittent periods of demineralized water spray.
The terminal block assemblies were protected with the atme NEMA-4 enclosures used
'.e the Franklin test.
New cabling was installed to puwer the terminal b.ocks. The test environment did not introduce steam; rather, the chambet was filled with demineralized watar to within one foot of the specimens and submersion heaters were used to bring the test chamber and specimens to 110*C (230*F).
pressure was maintained at 20 psig which means that the system was approximately 17 C' (29 F') below boiling temperatura.
The relative humidity in the chamber was 100 I
~28-
percent. Spray was on one out of every three hours. The terminal blocks were energirei with 600 Vac and 20 A.
The acceptance criterion was 1 A leakage curtwnt, monitored 'oy a fuse.
In addition, leakage currents were monitored throughout the test by a digital voltmeter and computer setup which sampled each of ten channels (two per terminal block assembly) continuously throughout the test. The sampling rate was not reported, but approximately once every eight minutes a printout of the maximum, sinimum and average leakage currents that occurred in the preceding eight minutes was made. The leakage currents for four of the five terminal block assemblies remained less than 0.2 mA throughout the test and for most of the time were less than 0.1 mA.
One terminal block assembly i
failed the 1 A fuse but post-test inspection of the assembly indicated l
that the failure occurred at the test chamber penetration and not the terminal block, pre-test IR values sere approximately 4 x 109 to 5 x 109 ohms at 500 Vdc and post-test IR values were 1 x 105 to 1 107
)
ohms.
Forty-eight hours after the test, the IR values had recovered to 5 x 108 to 5 x 109 ohms. This recovery is similar to the recovery experlenced in the Sandia tests.[1]
3.2.6 Reports on Nuclear Qualification Tests of Selected phonix Terminal Blocks (19) l These reports summarits qualification tests conducted on terminal blocks of European origin. One ceramic type block, one thermosetting insulation type block, and two types of thermoplastic insulation type blocks were tested. A total of twenty-nine blocks were tested in the LOCA/HELB simulation.
precise identification of the blocks is given in the reports but detailed specificat ion of the materials was not provided.
The test sequence was as follows:
e a.
pre-test dimensional checks, insulation resistance (at 500 ide),
voltage strength (3 kV ras (50 Hz) for 1 minute), and contact (i.e., conductor) resistan'ce zessurements.
b.
Thermal aging, at 140*C (284*F) for 30 days.
(Thermal aging parameters based on 10*C rule and assumed ambient operating temperature of 50*C (122'F)).
c.
Damp heat of $$*C (131*F) and 80 percent relative humidity for 48 hours5.555556e-4 days 0.0133 hours 7.936508e-5 weeks 1.8264e-5 months .
d.
camna irradiation with co-60 to 50 Mrad (alr) Total Integrated Dose (TID) 9t a maximum dose rate of 0.442 Mrad /hr (ale),
e.
Vibration test. Terminals energized with current loads of 20 mA.
4 f.
Seismic test. Terminals energized with current loads of 20 mA.
g.
Second gamma irradiation with Co-60 to 150 Mrad (200 Mrad cumulative TID) at a maximum dose rate of 0.43 Mrad /hr (alr).
h.
HELB test. Tte test profile selected for PELB simulation reflects both LOCA and HELB and lasted 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months . -
l i
Two inillat high temperature steam phases consisted of a 2-minute ramp to 256'C (493*F), 2 minutes at 256'C (493*F) followed' by a 2-minute ramp to 185'c (365'F), 8 minutes at 185'c
)
(365'F) fcilowed by a 2 minute ramp to 174*C (345'F) and 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months , 46 minutes at 174*C (345'F).- The two high temperature steam phases were separated by a 2-hour ramp to 50'C (122'F).
j i
Subsequent to the second high tempereture steam phase, ramps to a 9-hour 164'C.(327'F) plateau and an 38-hour 156*C (313'F)-
plateau completed the test. Chemical spray was initlated at the beginning of each of the 174*C (345*F) plateaus and continued until the peginning of the ramp to 50'C (122*F) ending the flrst hlsh temperature phase and to the end of the 30-hour test.for the second high temperature phase.- The terminal blocks were energiaed with one of four scl. emes:-(1) 420.Vac and 20 11 (2) 420 Vac no current)-(3) 48 Vde, unspecifled current; and (4) 2 24 Vde, unspecified current. It was not clest from the reports whether or not leakafe currents wert monitored thecughout the HELB simulation.
1.
Second thermal aging (post-LOCA aging) at 135*C (275'F) for 100 hours0.00116 days 0.0278 hours 1.653439e-4 weeks 3.805e-5 months .
(parameters based on 10*C rule and assumed amblent temperature of 70'c (1$8'F)).
b
~~j. Voltage strength test at 3 kV ras (50 Ha).~~
The main results of the tests are as follows:
i The mean insulation resistance of all samples in the pre-test a.
s condition was 1013 ohms.
9 l
b.
No pre-test breakdowns at 3 kV were experienced.
Contact resletance was on the order of 0.1 to 0.3 mohms.
c.
d.
The first thermal aging and damp heat environments did not affect the physical characteristics of the materlui.
Insulation teststance measurements at the conclusion of each environmental exposare was about a factor of ten greater than the pre-test mens stoments.
I Wo* adverse effects occurred during vibration and seismic e.
te9 ting, During these tests, the terminal blocks were loaded with a 20 mA current. Circuit continuity was maintained throughout the test, i
l f.
No adverse effa:ts were notes 3ther than slight matertal discoloratton af ter olther_ gamma irradiation.
Insulation resistance decreased by an order of magnitude g.
L to 1012 ches subsequent to the HELB environment. Of-the 29 o
terminal block assemblies tested in the HELB simulation, only one experienced an irreversible short circult. This block was made from thermoplastic type insulation and energlaed with ii p
420 Vac, but no current. A second thermoplastic insulation terminal block assembly energized to 420 Vac and 20 A experienced a leakage current of greater than 5 A at the beginning of the second chemical spray period.
After i
replacement of circuit fuses, this assembly successfully completed the test.
Five of the thermoplastic insulation t10cks and one of the thermosetting insulatten blocks were badly deformed by the HELB test environment.
Four of them were so badly deformed that they fell off of their mounting rail due to their own weight.
i l
h.
Three kV ras (50 Hz) voltage strength tests were conducted after l
the post-HELB thermal aging. All ceramic terminal blocks passed l
the voltage withstand tests. The six plastic insulation block
(
assemblies that were badly deformed by the HELB simulation Wire not subjected to this test. One of the eight thermosetting insulation blocks tested f ailed the terminal-to-terulsal test.
Of the seven thermoplastic insulation blocks tested, three failed the terminal-to-terminal tests and one failed the terminal-to-ground test.
No definition of failure or acceptance criteria was provided in tho test report. The conclusion drawn from these tests was that only ceramic e
terminal blocks should be used for in-containment applications.
3.2.7 Wyle Laboratory's Test of Eight Marathon Terminni Blocks for Commonwesith Edison Company 120)
This report documents testing performed on Series 6000 and 1600 Marathon fixed barrier terminal blocks.
Two assemblies of ters.inal l
blocks were tested, each consisting of three Series 6000 terminsi blocks and one Series 1600 terminal block. They were housed in so slectrical enclosure manufactured to Commonwealth Ediend specifications and l
connected in the usual alternating t4rminal, serpentine type wiring scheme used in other industry qualification tests of terminal blocks.
Okonite 10 AWG Hypalon insulated cable was used to make the connections.
l The test sequence was as follows:
a)
Baseline Functional Tests l
b)
Irraoistion to 206 Mrad gamma (Co-60) c) Functional Test d) Thermal Aging - one assembly at 120*C (248'F) for 466 hours0.00539 days 0.129 hours 7.705026e-4 weeks 1.77313e-4 months (20-year equivalent Ilfe) and one assembly at 120*C (248'F) for 932 hours0.0108 days 0.259 hours 0.00154 weeks 3.54626e-4 months (40-year equivalent life) e) Functional Test f) Seismic Test g)
Functional Test
'+hh
$Mi=
h) Accident Exposure Eleulation
1) Functional Test The acceptance criterla for the baseline functional test were to possess an insulation resistance of at least 109 ohms and a resistance through the terminal block / cable conducting path of less than 10 char.
For all of the post-test functionals, the acceptance criteria were to maintain IR greater than 100 chas and resistance through tt. LO:fucting path less than 10 ohms. During the LOCA 6lmuistion, the original acceptance criterion was to maintain leakage currents less than 2 A, but this criterion was changed by Commonwealth Edison to 10 A.
In the report, the figure showing the schematic of the electrical circu!L shows anseters set up to measure leakage current along with fuses to limit leakage current. However, no leakage currents are reported in the test documentation.
The accident exposure was originally planned for 34 hours3.935185e-4 days 0.00944 hours 5.621693e-5 weeks 1.2937e-5 months which was based on an Arrhenius calculation to compress a one year accident exposure. The original profile called for two 10 second ramps from initial conditions of 57'C (135*F) and 0 psis to 196*C (384*F) and 50 psis, then retreating after 100 seconds to 174*C (345'F) and 50 psig for a hours.
During the 3 hour3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months exposure for margin and during the first 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months r the accident exposure portion of the profile, chemical spray 2
was to be sprayed at 0.5 gal / min /ft.
After thi first 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months of the accident exposure portion of the profile, the following conditions werw to prevall:
163*C (325'F), 45 psig (28 C* (50 F') superheat) for 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months , 163'c (325'F), 25 ttig (47 C' (85F') superheat) for 18 hours2.083333e-4 days 0.005 hours 2.97619e-5 weeks 6.849e-6 months , and finally 163*C (325'F), 20 psig (54 C' (9) F') superheat) for 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months .
e Due to the inability of the test f acill'.y to maintain superheat conditions for such high spray rates, the spray rate was modified to 0.04 gal / min /ft? for the 3 hour3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months margin peak and the first 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months of the accident exposure. To make up for this deficierey from planned spray rates, at the end of the 163*C (325'F), 45 psis period, a 3 hour3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months period was added at 127 'C (260*F), 45 pais (8 C* (15 F') subcooled) with spray 2
at 0.5 gal / min /ft.
The spray was terminated at the end of this per)od (the 9 hour1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months point of the accident exposure).
From the 9 hour1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months point the remainder of the planned proflie was run except an extra 2.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months was added at the end to account for the 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months at 127'c (260'F).
The data in the report indicates that the first transient (for margin) had one thermocouple (TC) reading a maximum of 163*C (325*F) 24 seconds tfter introduction of the steam, while the second and third thermocouples had reached 141*C (285'F) an6 93*C (200*F) respectively at this time.
By 52 seconds, the first TC was reading 141'c (285'F) and the second TC began tracking it.
At the 3 minute point, the readings of these TCs diverged from a common value of 121*C (250*F). The third thermocouple was reading 82'C (180'F) at the 3 minute point. All data ceases at the 3.9 minute point and no further data are presented untti the secoed ramp begins. -
~_
s Notice of Anomaly 14 in the Wyle test report esplains that during the first transient (for margio), the chamber rupture dise burst at 20 psig.
At Wyle's suggestion additional time was to be added to each temperature plateau of the main espesure rather than repeattug the initial transient. Looking at the temperature proftles achieved, apparently 30 minutes was added to the 174*C (345*F) plateau. The profile octJally achieved during the main exposure was 182*C (360'r) to 210*C (410*F) (depending or thermocouple), 50 psig at approrisately 40 seconds elapsed time, 177'c (350'r), 50 psig from approximately 2 minutes to 3.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months elapsed time, 163'c (325'F), 45 psig fron 3.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months to 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months elapsed time, 127'c (260'P), 45 psig f rua 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months to 9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months elspeed time, 163'c (325'F), 25 psig from 9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months to ?5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months elapsed time and finally 163*C (325'F), 21 psig from 25 Snurs to 36.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months elapsed time.
At approximately 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months and 50 minutes into the test (during the 174*C (345'r), 50 pois. 0.04 gal /mit/ft2 period), Notice of Aromaly 17 reports that a 6000 Series terminal block exceeded 10 amperes leakage current.
Inspection showed that it was shorted to ground and so it was removed from the test circuit and the test continued. During the remainder of the test the leakage currents of the other terminal blocks remained below 10 Emperes.
In the post-LOCA functional tests, the circult-to-circuit insulation resistance of the terminal block removed from the test was 3.6 ohms. The post-teet inspection notes that the area where the failurn occurred could be seen. The post-LOCA irs of the other tseminal block were between 106 and 1012 ohms.
3.2.8 Westinghouse Electric Corporation's Test of Termins' Block performance in LOCA Environment [21) e This report documents testing performed on Curtis BT, Cloch Jones 541. Westinghouse 542247 and Marathon 1500 Series terminal blocks.
No thermal or vibrational aging was conducted and no seismic simulations or l
radiation exposures were reported. 'fhe test was an exposure to an unspecified LOCA steam prcfile of approximately 5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months , 30 mihutes duration. Chemical spray was sprayed for one hour at 0.32 gal / min.
It is unclear from the report whether the terminal blocks were mounted in a NEMA-4 enclosure. During the test the blocks were energized with 600 Vse.
l No acceptance cr!teria are stated in the report.
IR measurements were taken before, at vacious times during, and after the steam exposure.
I Before and af ter the exposure t' e IR values were 1010 to 1012 nhms.
n During the test IR values vnried from 8 x 103 to 2.6 x 105 ohms. The conc 1wding statement says that " Although the insulation resistance decreased more than six orders of magnitode, the torminal blocks...were l
able to function at 600 Vac throughout LOCA."
l l
l 4.0
'lAWDI* TESTS OF TERMINAL BLOCKS IN A SIMULATED LOCA ENV!kONMENI 4.1 Terminal Blocks Tested Earlier work at Sandia f 2) consisted of testing terminal blocks under TMI Londitions. This test raised questions regarding terminal block performance but was not conclusive in that there were several areas where test conditions deviated from actually installation conditions. Therefore, to quantify the performance of realistically installed and protected termiual blocks in a LOCA environment and to investigate terminal block f ailure and degradatica modes, we tested 24 terminal blocks ($ models from I
4 manufacturees*) in a simulated LOCA environment.ll)
Btsed on our reviews of the qualification documents, we determined that neithat the accelerated aging process nor the seismic testing significantly affected terminal block perfccmonce. Thus, we tested terminal blocks in the "as received" condition. To simula'e normal handling during installation, no special care was taken during test preparation to prevent the deposit of finger-prints or other normal conteminants on the terminal block surf aces; howeser, we did not simulate depoLits of construction dirt or other sediments which tend to accumulate over time. As such, the terminal blocks were probably in the best initial condition that might possibly exist for terminal blocks installed in the field. The terminal blocks were protected by HEMA-4 electrical enclosures with 1/4" dis. meter weep holes in the bottom.
Cables entered the boxes from the sida through nuclear grade, liquid-tight condult. To almulate cables entering a conduit from a cable tray system, the conduit we.s terminated inside the test chamber and was unsealed at both ends.
S 4.2 Test Configuration The test was divided into two phases, phase I exposed 12 terminal
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blocks (three each of four designs) to an 11-day steam-only environment.
3 Phase II exposed 12 terminal blocks (six each of one design and three each g
of two other designs) to approximately one day of simultaneous steam and b
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chemical spray followed by five days of a steam-only environment.
Both temperature profiles closely followed the PWR temperature profile recommended by IEEE-323-1974, Appendit A.[37] Saturated steam conditions were maintained throughout both test phases.
In Phase I, the terminal blocks were connected in an alternating terminal serpentine, siellar to the wiring scheme used in industry qualification tests (Figure 4-1).
In Phase II, the terminal blocks were connected in a configuration more representative of actual plant connections with one terminal powered and the two adjacent terminals and base plate monitored for leakage currents (F16ure 4-2).
One terminal block in the Phase II test was connected to a
p. essure transmitter in a circui' :onfiguration representative of a plant transmitter circult. This transmit'.or circuit was included to validate the results obtained from the other circuits and to confirm the analysis of the effects of terminal block degradation on low power circuits.
~~Figure 4-3 shows the transmitter circuit wiring.~~
~~1able 1 in Reference 1 identifies the manufacturers I thsough IV and the Models A through E.~~
That comenclature is continued in this report, and is extended in Table 5-1 to Manufacturer V Model F. _ _ - - _ _ _ _ _ - _ _ _ -
The, terminal blocks wers powered at voltages typical of in-plant spplicationst 4 Vdc typical of RTD circuits (Phase I test only). 45 Vdc typical of instrumentation circuits, and 12% Vdc typical of control circuits. Tl.e terminal-to terminal leakar.o currents were rionitored in both Phase I and Phase 11 tests, and the terminal-to-ground (base plate) leakage currents were monitored in the Phase II tests. The data were acquired at discrete time steps by data loggers. The time interval between successive measurements varied depending on the esperimental l
activity being conducted.
For exer-ple, during stesa ra.mps or other 2
transients, nionitneing was accomplished as rapidly as possible (about every 6 seconds); during *.ong periods of steady st.=te conditions, the monitoring interval was lengthered to 30 minutes.
Besed on these data, insulatit,n resistances were calculatsd for each leakage path on each terminal block.
Four channels of leakage current data were monitored continuously by strip chart recorders throughout the test.
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These values are sufficiently large to aff9et 4 to 20 mA instrumentation circ 2its by 0.3 to 185 percent with a nomitial effect of 0.5 to 45 percent at the mid-range of instrument output. At 4 Vde, insulation resistance was raried from 5 x 103 to 7 x 104 ohms, values which are sufficiently low to affect RTD measuremetits by 0.3 to 9 percent. At 125 Vde, the IR values were comparable to the 45 Vdc values and were at times slightly (approxisately 1/2 to 1 order cf magnitude) higher.
Reference 2 reports stif,htly lower but comparable results for TMI-2 conditions; leakage currents between 0.08 and 0.3 mA are reported therein for terminal blocks protected by an electrical enclosure..
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Insulation Resistance A for Sandla Phase II Terminal Blocks l
Insulation resistance A is the IR calculated for the A path (see Figure 4-2).
Terminal Blocks 1-6 powered at 125 Vde, 1 A and Terminal Blocks 7-12 powered at 45 Vde, 20 mA.._
We expertenced one open failure where the leakage currents increased i
over a 90-minute period to values which contributed to the separation of the 12 AVG wire supplying power to the terminal block.
The separation occurred close to the terminal block-wire junction and was primarily caused by test induced tensile stresses.[1]
During the pertoas of cooldown to 95*C (203*F) and the post-test ambient tenperature period, the insulation resistance values increased to 106 to 3 98 ohns but not to the pre-test values of 108 (e tolo chms.
TMs behavior illustrates three points:
first, the similarity between addown and post-test Ik values indicates that the same conduction mechanism is probably occurring during these periods; secend, 1R recovery to higher values after esposure indicatss that a transient phenomenon is responsible for the low IR values during the steam exposure; and third, that some permanent degradation of the terminal block insulation resistance occurs.
i A conductive moisture flim is the most probable explanation for the transient phenomenon.
During cooldown periods, the residual heat of the terminal block will keep its temperature higher than the surrounding atmospheric temperature.
Since the surface flim will be close to the terminal block temperature, its vapor pressure will exceed the surrounding atmosphere's pressure, causing the film to vaportte.
In the post-test case, the same pheno.aenon occurs untti the terminal blocks cool to ambient temperature. Then the normal relative humidity regime
)
takes over.
The permanent degradation of the terminal block IR may have been caused by either carbonizatirn of the termins) block surface or other organic materials in the vicinity or by residues of potentially j
semicon' acting mediums such as cadmium sulfide.
Post-test chemient j
analysis of three phase II terminal blocks showed tt.e presence of both i
cadmium sulfide deposits and carbonaceous residues in e graphite-like structure.
i There was a noticeable dependence of IR on temperature.
The irs at temperatures less than 110*C (23t*F) tended to be 1/2 to 1-1/2 orders of magnitude greater than irs at temperatures greater than 110*C (230'F).
All of the terminal blocks tested exhibited similar tempert.ture related performance trends, though there were block-related differences in absolute performance.
This result le in agreement wit!. the findings of Reference 2 and the theory of electrolytte conduction 138) which (ndicates increased conductivity with increased temperature.
Since saturated steam conditions wer...intained throus;hout the test, the temperature dependence could also have been interpreted 3s a pressure dependence.
pressure per se, though, is not the governing factor in film conduction, but it le important in determining the conditions necessary for film formation.
Exclusive of contamin elon effects, if a system is superheated and at equilibelum, filns will not form and the performance of the terminal olock will be relatively good.
Similarly, if the terminal block temperature is above the dew point in an air environment, the same condition will exist.
Alterr.a t ely, if the terminal block temperature is below the dew point in an air environment, or if films have formed due to a coo. terminal block being surrounded with steam and the system remains ation, flims will form and remain on the surface of the terminal at er bloc.
During the chemical spray periods of the Sandla phase II tests, no effect of the chemical spray was observed. This finding was somewhat surprisirs since we expected the chemical spray to enter the conduit, penetrate down through the condult-cable interstitial space, and drip onto the terminal blocks. We hypothectaed that the introduction of Na*
and OH-lons to the surface flim would enhance the conductivity of the film. The lact of any observed change in leakage currents initially indicated to us that the NgKA-4 enclosures with unsealed conduit entrances provided adegante protection against the intrusion of chemical sproy. To cherk this result, at the conclusion of the phase II environstatal esposure we conducted a submergence esperiment to observe the performahce of blockF positively knoVn to be spray Contaminated.
In this test three blocks were submerged in a chemical spray and steem condensate solutten and three blocks were left unsubmerged.
irs in a steam environment af ter the submergence were compared.
They indicated that there was only slight difference between submerged and unsubmerged blocks, with the unsubmerged blocks being siishtly better. This data coupled with the observation that the Sandia phase I test results were compatible with the Sandle Phase II-results shows that even if spray had penetrated the enclosures little difference in leakage currents may have been observed. Apperently, the additional conducting ions from the spray may not significantly alter the conductivity of the film.
It also precludes a definite conclustor, about the effectiveness of the NgMA-4 enclosure in preventing chemical spray f rom penetrating to the terminal blocks. However, we believe the htMA-4 enclosures as they were installed in the Sandia tests are reasonably effective in preventing such penetrations. This result correlates well with the results reported in Reference 18.
r Figure 4-6 shows the insulation resistance measured during Phase I e
of the Sandla tests for one Manufacturer I, Model A terminal block. The data begin with the second transient and continues to the end of the test. One of the first things to note is that IR does not remain constant. There are periods when the IR improves dramatically (e.g.,
just after temperature reduces from 160*C (320*F) to 150*C (302*F) there is an increase in IR from 10 kohms to 63 kohms) and then deteriorates just es dramatically (e.g., following the spike to 63 kohms the IR drops back to the 10 kohm region).
The introduction of steam is one parameter which causes the IR to drop and as already discussed, changes in temperature caused observable changes in IR.
Another important factor la voltage gradients. Whenever power is applied or the voltage increased suddenly to an otherwise qu!escent terminal block the irs were always observed to decrease by large amounts, of ten to values below the range settings on the recording instruments.
Two illustrations of this effect are apparent in Figure 4-6:
the first is at hour 121 where power was reapplied after 25 hours2.893519e-4 days 0.00694 hours 4.133598e-5 weeks 9.5125e-6 months without power and the second is at hour 238 where a transition from 4 Vde to 45 Vdc occurred. In both cases an immediate decrease in IR is apparent, and then over a period of hours, an increase in IR is observed.
In the first instance the IR increased eventually tc. the 65 kohm region.
In the second case the recovery was back to the 60 kohv region at whleh point the test was terminated.
In both cases a period of some 10-20 hours was required to make the recovery.
Also note that at the same environmental temperature, the mean IR level at 4 Vdc is less than at 45 Vdc by about a factor of three..
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The model in section 6 predicts a pearly constant value of steady state IR as long as the number of conducting ions in the film remains conettet. The transient application of potential increason the current through the leakage paths more than would be espected if tne It was a e
constant value. At the higher current values, more Joule heating exists and the film temperature increases. More convective and conductive heat transfer occurs, but during the transient period the primary energy lass mechanism is vaporitation (and hence thinning) of the film. As the flim thins, the la slowly increases towards an equilibrium value. Joule heating decreases to a point where it is in balance with convective and conductive heat losses. At this point, not vaporttation of the film 1
ceases and a new equilibrium film thickness is established. The approach to egu.11brium is a slow process, as evidenced by the rather long time constants observed for recovery of the irs to higher values after application of an increading voltage gradient, i
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5.0 TESTS OF TERMINA1. BLOCK PERP0pAANCE AT TEMPLE LTNIVERSITT To provide independent tests of terminal block performance. Temple University was contracted to perform laboratory bench testa of terminal blocks. The tests were designed and directed by Dr. Robert Salomon of the Temple University Chemistry Department. The tests at Temple were ccaducted in two phases, phase I tested terminal blocks in 100 percent telative humidity and at the TMI accident temperature of 86*C (187'F).
phase II tested terminal blocks at somewhat lower temperatures, and used steam as a heat source.
Phase II also introduced chemical spray into some of the test environments during selected periods of the test.
5.1 p..aae *, Tests of Terminal Blocks in a Quiescent Temperature and Hun!Jity Environment the phase I experiments tested three* models of terminal blocks in l
100 percent relative humidity and 86'c (187'F) with little chanca for temperature gradients. The sasic premise here was that if temperature i
gradients were eliminated, then leakage currents would be small since no l
special preference for initiating moisture condensation would exist.
Test voltages werc 480 Vac, 400 Vac, 300 Vac, 200 Vac, and 100 Vac.
The experimental setup used is illustrated in Figure 5-1.
A battery jar was used as the envircnmental chamber. The terminal blocks were suspended from a polycarbor. ate lid above a water or hcl solution via the electrical leads. The leads were connected to adjacent terminals of the terminal block and if a metal base piste was part of the terminal block design, it was connected to one of these terminals.
Thus, the leakage paths were f rom one terminal to an adjacent terminal or from one terminal to sn s
adjacent terminal and the base plate. The solution in the battery jar was four inches deep and was either delonized water or a 10 percent by volume solution of HC1. The solution was stirred vigorously throughout the test by a high speed magnetic stirring device. The motion of the solution also stirred the atmosphere in the battery jar above the solution.
l Heat was supplied to the system via heating wire wrapped around the outside.of the battery jar from the bottom, to a level just i
below the level of stationary solution la the jar. The exterior of the battery jar was insulated with fiberglass insulation to reduce any l
thermal gradients within the jar.
In addition, for some of the experiments run in phase I, an infrared lamp was used to prevent i
condensation of moisture on the terminal block. The ! sap was positioned such that its rays penetrated the polycarbonate lid and impinged on the I
terminal block. Without this light, visible droplets of moisture would condensa on the yolycarbonate lid; however, at no time, either with or without the infrared i mp, was moisture observed on the terminal blocks.
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Two of the three models tested were also tested in the Sandia tests.[1]
Thet< were Manufacturer I, Model A, and Manufacturer II, Model C.
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Figure 5-2 shows the electrical circuit used in Salomon's phase I tests.
Initially a princeton Applied Research lock-in ampilfter was used to measure the leakage current, but this instrument fa!!ed and the resistor-diode-electrometer" circuit shown in Figure 5-2 replaced it.
The system was calibrated against known resistances, and to protect against giant current surges, the Variae supplying power to the primary side of the transformer was underfused. The guard ring was tightly pressed against the polycarbonate lid and completely encircled one electrode feeding through the lid.
less than the guarded electrode.
It was always at a potential slightly Any possible leakage currents along the surface of the polycarbonate lid were thus returned to the power supply without affecting the measurements of terminal block leakage current.
Initially the blocks were tested in the "as-received" condition and no spet';4 care was taken to clean them. These blocks therefore were contaminated with fingerprints.
The leakage currents were measured as a function of time and temperature as the system moved toward the final system temperature of 86'C (187'F).
The experiments lasted froe one to three hours.
Generally leakage currents with the detonized water solution in the jar were in the micro-ampere region or lower if the infrared lamp was turned on.
The leakage currents with the hcl solution in the jar were sometimes slightly higher, but not significantly so since hcl has a high vapor pressure at 86*C (187'F).
After testing the blochs in the "as-received" condition, they were soaked briefly (a few minutes) in 1%. 10% (0.26% and 2.6% by weight) and saturated Nacl solutions, oven dried at 90*C (194*F) j and then reinstalled in the expsrlmental setup.
The experimental procedure was then repeated.
The leakage currents generally increase monotontvally with the WaCl concentration of the soaking solution.
For those blocks tsaked in the saturated salt solution, the leakage currents reached the milliampere region before the final system temperature of 86'c (187'F) was reached.
In some case, the heavily contaminated blocks experienced a decrease in the leakage current as applied voltage increased.
We attribute this phenomenon to Joule heating of the conducting film which caused drying and precipitation of salt and therefore reduced conductivity.
There also may be some formation of drybands which would reduced path continuity.
One actuni breakdown was experienced at approximately 400 Yac for a terminal block soaked in saturated WaCl solution.
The breakdown path is illustrated in Figsre 5-3 and was evidenced by severe blistering of the phenolle material.
A summary of some of Salomon'a phese I results is given in Table 5-1.
The electrometer was a Keithley Model 610C. _
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5.2 phase II Tests of Terminal Blocks in an Active Steam Chemical Spray, and Temperature Environment Ie phase II, seven different models of terminal blocks from four manufacturers were tested. The test arrangement was similar to the one used in phase I except for the modifications in the lid for steam and chemical spray entrance ports and the use of a commercial temperature controlling baih apparatus in sd of a battery jar as the environmental chamber. No infrared lamp was vd in the phase II t?sts. Figure 5-4 illustrates the experimental arrangement for phase II tests. The steam was produced from a commercial vaporiter modified with an asbestos wrapped tube leading to the bath controller lid.
Delonized water was used in the vaporizer together with a small amount of sodium sulfate as a nonvolatile cot.ductor. Delonized water was used to avoid the potential for volstflu impurities being introduced into the terminal block environment. The steam made in this manner was condensed, and the conductivity of the condensate measured.
It measured 3 s 10-4 ohm'lem~1 Steam was delivered to the system at low pressure and at a rate equal to approximately 20 ml of condensate per minute.
Temperature in the chamber was tontrolled by an auxiliary beater in the l
bath which supplemented the energy introduced via the steam. The l
temperature of the system never excewdad GC*C (194*F) in any of the experimen t s.
l The composition of ?.he chemical spray was that specified by IEEE
??3-1974 Appendix A.[37] It est introduced into the system by forcing a stream through a small glass nozzle at ap preatmately 20 psis. This strean was intersected with a jet of nitrogen at the skme 20 puls. The l
result was a finely atomized spray in the chamber. The point of a
j inte.section for the chemical spray stream and the nitrogen jet was spproximately 9 cm from the terminal block, and thus the chemical spray stream did not directly impinge on the terminal block. A polycarbonate lid sealed the hath contro11er' opening. The terminal block was suspended from this lid by the electrical leads just as the phase I terminal blocks l
were installed in the battery jar. The electrical wires used glass enclosed leads to penetrate the polycarbonate lid. One of these leads was electrically guarded to prevent leakage entreats along ths interior surfaces of the chamber from entering into the measurements. The leads.
were connected to adjacent terminals oa the terminal blocks.
For those l
terminal blocks which had a base plate as an integral part of t'e design, l
this piste was connected to one of these terminals. Thus, either terminal-to-terminal or terminal-to-terminal and base plate leakage currents were measured. Figure 5-5 shows a schematic of the electrical connections.
Twenty-four experimental runs were made using various combinations of terminal block model, spray, and no-spray. When spray was introduced, it was always after the steam had been on for at least 30 minutes. Table 5-2 summarizes the data obtained from one run with one Model'I, l
Manufacturer A terminal block.
Figures 5-6 through 5-11 give the results of all runs made with thc. model of terminal block. These plots show i
three pieces of information: leakage currents as a function of time, leakage currents as a function of temperature and temperature as a function of time. l
r f
Ng
~~t SPRAY N~~
2 R ES ER YOf f:\\
j S TE A M LIN E S PF4 AY
/
\\
GUARD RING i
VAPORIZER t
7t x
I l
POLYCARBONATE 4#
BLOCK if OOOOO OOOOO SPRAY
/
ATOMlZATION 7
~
TERMIN AL BLOCR W ATER LEVEL f
/
AUXILfARY
.7
,/
HEATEA BATH CIRCULATOR t
Figure 5-4:
Experimental Setup for Salomon's Phase II Tests The environsact included clean steam and controlled additions of atoetred chemical spear at selected times.
GUARD RING 1
=
POLYC AHBON ATE PL ATE-
= En\\\\n]
[%\\\\\\R]
[\\\\\\%%\\q su-su TERMIN AL BLOCK\\
B ASE PL ATE-0 0
6 0
0 (FLO ATIN G) y o
o o
o o
~
POWER
~.__-
SUPPLY ELECTROMETER O
G--
Figure 5-5:
Electrical Circuit for Salomon's Phase II Tests I '
l i
-I Table 5-2 Typical Leakage Current Data From Salomon for One Manufacturer I, Model A Terminal Block Powered at 45 Vdc in an Clean Steam Environment i
Measurement Time Temperature Leakage Current No.
(min)
(*C)
(mA) i 1
0 22 0
2 1
70 0
3 2
75 0.1 x 10-3 4
3 77 0.4 x 10-3 5
4 77.5 1.2 x 10-3 6
8 80 3.7 x 10-3 7
10 81 5.6 x 10-3 8
15 83 8.0 x 10-3 9
22 85 11.0 x 10-3 10 25 86 12.4 x 10-3 t
11 30 86 15.0 x 10-3 12 55 86 21.4 x 10-3 13 60 86 29.0 x 10-3 Salomon's data, not all of which are presented herein, show several things. First, the data show a great deal of variability in the magnitude of the leakage currents. Variations between 10-7 a to 10-3 A were e
noted, with the latter value being rare. Although, the example in Figure 3-10 does not clearly show the effect, when containment spray was present the currents were frequently. enhanced and often reached the milliampere region. One was as high as 6 mA.
The greatest variety of tests were run on the Manufacturer I, Model A terminal block. Table 5-3 tabulates the leakage currents observed at the end of the test for these blocas. The environmeat_f.emperature for these observations war betweer 80*C (176*F) and 90*C (194*F).
Except for the block dipped in saturated MaCl rolution and dried, the final leakage currents are the highest values observed during the test. For similar block conditions, these endpoint leakage current values compare r6asonably well with data reported for the Phase I quiescent tests by Lalomon. The "as-received" condition in the Phase I test had values vtrying from 0.024 mA at 100 Vac to 0.095 mA at 400 Vac, while the Phase II value was 0.029 mA at 45 Vdc. During.the Phase I tests, the termin ' bicek which had been dipped-in saturated WaCl solution and dried experienced leakage currents _of 9'mA at 10 Yac to 200 mA and breakdown at 400 Vac. For this same block condition, a maximum of only 0.33 mA was observed in the Phase II test. This difference may possibly be attributed to the polarization of the electrolytic solution 161) that occurs in conductive solutions when a de potential is applied.
1 m'
e TEMPER ATURE ('C!
10 30 50 70 90 110 130 l'
I I
I i
l l
1 i
T-" !
36 180 O CURRENT vs. TIME A CURRENT vs. TEMPER ATURE 170
~
V TEMPER ATURE vs. TIME 32 160 150 O
A T, 2 8 140 x
130
$ 24 120 U
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A 1100 i
1 y 20 100$
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A 50 8
O A
~
40 O
A 30 41 O
A 20 O
A 10 OO '
-a A dl--
O 20 40 60 80 100 120 140 o
TIME (minutes) q -
Figure 5-6:
Leakage currents et 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block in the "As-Received" Condition Environmental temperature as a funetton of time is 12 also shawn. _ _ _ _ _ - _ _ _ _ - _ -
m i
TEMPERATURE (*C)
'" 4 90 110 130 19 190' I
I I
I I
i i
i i
i 1
l l
180 18 0 CURRENT vs. TIME 17 170
~
A CURRENT vs. TEMPER ATURE V TEMPER ATUPE vs. TIME g,
15 150
? 14 140
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379 30 2
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to OO OCDOd.OQ[
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I I
i i
0 20 40 60 80 100 120 140 TIME (minutes) 4 Figure 5-7: Leakage Currents at 125 Vdc as a Function of Time and Temperature for a Manufacturar I, Model A Terminal Block in the "As-Received" Condition Environmental temperature as a function of time is also shown.
l
w TEMPER ATURE ('C) 10 30 50 70 90 110 130 190 I
I I
I I
i I
i 6
I I
I i
45 O CUR 8 TENT vs. TIME 130 A CURRENT vs. TEMPER ATURE V TEMPER ATURE vs. TIME 170 40 160 150 o
a
-7 35 140 130
$30 O
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O a
10 g 40 0
30 57-20 i
00 g
o a
10 I
I I
I I
I I
i 0
0 0
20 40 00 80 100 120 140 TIME (minutes)
Figure 5-8:
Leakage currents at 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal i
Bloct. Af ter Being Washed and Soaked in Distilled Water Environmental temperature as a function of time is also shown.
)
TEMPEQATURE ('C)
~~
10-30-s0 70 30 110 130 200 J
l I
I I
i i
i 1
i I
I i
190 0 CURRENT vs, TIME 45 A CURRENT vs. TEMPER ATURE.
140 V TEMPERATURE vs. TIME 170 40 160 0
-150 C
b35 0A 140 OA 130 r
120?
E. 3 0 O A
[
O A
110g s
a
+
100y g25 z
E 90 E g
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A 3
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O 6
7 7
4 70 y
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y L-j j '5 4 7
SO V
V 50 v7 O
A 10 V
40 V
O A
-V O
A 30 7
O A
5-7 g
20 O
A to ON
-M 'O I
O O
20 40 60 80 100 120 140 TIME (minutes)
Figure 5-9: Leakage Currents at 45 Vdc 6s a Function of Time and Temperature for a Manufacturer I Model A Terminal Block After Being Washed Vith Distilled Water and-Then Handled Environmental temperature as a function of time is also shown. t
'rEMPER ATURE ('C) 10 30 10 50 70 30 110 130 g
g g
y g
g 200 I
O CURRENT vs. TIME 1
t A CURRENY vs. TEMPERATURE 190 cr-V YEMPErlA7URE vs. TIME 9
180 170 8
160 150
[
7 o
140 130 E
6 g
iRO e
a O
A 110.O m
W 5
W I
100$
l r
' 90 $
o 4
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80:g w
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60
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40 O
O A 30 l
l 1 "-
,op aA p,
g 20 i
go OTO.d-oMO[ dhA[O I
I I
I i
l
[
q 0
20 40 00 80 100 120 140 I
TIME (minutes)
Figure 5-10:
Leakage Currents at 45 Vdc as a Function of Time and and Temnerature for a Manufacturer I, Model A Terminal Block in the "As-Received" Condition and Subjected to 7 Minuter of Finely Atomized Chemical Spray Environmental temperature as a function of time is also
~~shown, o~~
1 (
TEMPER ATURE ('C) 10 30 50 70 90 110 130 50 200 0 CUf: MENT vs. TIME 190 A CURRENT vs. TEMPER ATURE 45 V TEMPER ATURE vs. TIME 180 170 00 O
A6 A 40 OO O
OCA A AA 160 00 MO A
~~50 O~~
A
? 35 140 o
O A
O A
130 w
O A
E 30 O
A 120 E
~
t e
0 110 L I
m y
$ 25 100g W
904 v
D V V U 2C V
1 80 v
2 We v
W
-1 70 H 4
y x
V
$ 15 Y
60 v
Of A
50 g#
10 40 l
30' O
A 57 20
'l 1'
n g
I 3
I I
I I
I I
I I
I I
I
-00 O
O 20 40 60 80 100 120 140 TIME (minut 3s) t Figure 5-11: Leakage currents at 45 Vdc as a Funetton of Time and Temperature for a Manufacturer I. Model A Terminsi l
Block Dipped in Saturated Nacl Solution and Dried l
Environmental temperature as a function of time is i
also shown.
i l
l
-s,-
1
~
table 5-3 Finul Valt es of Leakage Current and the Ratio of Final to Initial Va*6ues of Leakage curr:*nt for Manufacturer I, Model A 7etvanal Elocks

~~45 Vde-----~~

~~125 Vde- ---~~

~~I e~~
f
/
~~f I'l a~~
LmAl i
LeAJ l
As Reesived 0.029 290 0.0175 175 nished & Soaked in 0.0037 60 Distilled Water Washed & Souked in 0.0038 76 Dietilled Watec, Handled As Shipped. With 0.00$$
183 Chemical Spray Dipped in Saturated 0.33 330 WsC1 Solution and Dried
~~If = Final value of leakage curectt t~~
It = Initial value of leakage current Also included in Table 5-3 L e the ratios of f8nal leakage current I, to beginnthg leakage current, I.
f the relative change observed during the test.Ttese ratios give an idea of 1
change occurred between 35'C (95*F)
For the most part, this and 80*C (176*F) and for some terminel blocks it occurred over a much narrower range--nominally $5*C i
(131*F) to 70*C (158*F).
The temperature behavice is readily spparent in observed in these tests veesus those observed in the Sa Elsetrolytic conductivity is known to follow an Arrhenius j
relaticnship.[38}
However, the overall behavior results from the l
influence of the many other ractors, especially changes in concentration which affect the conductivity of the film solution.
l 5.3 Characterization of the Amount of Salt Deposited by Fingerprints In order for a Loisture film to be conductive, it must contain dissociated ions.
the surface of a tetminal block.There are potentially many sources for these ions on These iceluded surface dust contkuination, residue from manufacture and salt frou fingerprints.
Of
these, the most ilkely source is the esit doposited from the fingerprints of those who handle the terminal block during its life. On this promise, a brief experimental detercisation of the salt deposited by fingerprints was undertaken.
All mearurements were made with six Westinghouse #542247 te rniv al blocks.
This terminal block is made from a cellulose-filles phencile insulation material. The experiment consisted of cleansing the surface to be tested, then masking off a square area 1 cm on a side and touching this area with the tip of the inder finger. The pressure of the contact was not measured, but ras assus ed to be typical of an average man picking up a terminal block.
Three subjects, A, B, and C participat:J in the test. bef.ch helped average both the amount of salt deposited and the conteet pressure between the fingertip and the terminal block.
To measure the amount of salt deposited, the area was flooded with between 0.3 cc and 0.5 cc of deionized water.
Tbis drop was held on the contact eres by surface tension. After 30 seconds of contact, the water was removed with a syringe and a portion was ceded to a siero conductivity cell. This cell was calibrateu against solutions of accurately known NiC1 concentra 1ons. By measuring the sample's conductiv!ty, the concentration of salt was datermined, and knowing the sample volume the moles of salt were calculated. A test of the rinse solution's ability to remove the salt was made by making a second rinse and esavuring the residual salt in the second solution.
It was fcund that the primary rinse removed virtually all the available salt.
Two sets of measurements were made, the first bsing w!th dry fingers, the second with wet fingers. A sample of the results is included 1. Table 5-4.
TL5 3reatest contamination occurred for wet fingers (5 x 10-6 moi,, y,cife,2), while the dry fingers left contaminations approximately two orders of magnitude less (5 x 10-8 2
moles NaC1/em ).
~
A measure of the Nacl contamination on a 1 cm2 area of several blocis in the "as-received" condition was made. These measurements varied widelv, but were within the ranse of the dry finger contamination level. The results from these measucements give an order of magnitude feel for the amount of ions available en " clean" terminal blocks for dissolution in a moisture film. We use the term " clean" to imply the contamination level that may be present after installation end assuming loose dust and other contaminants have been removed. We see in the next section that 10-7 moles of salt is sufficient to provide approximately i
l 1.C mA of leakage current depending on the applied voltsge.
l' l
l l
\\
l t
I I l Inzw
3 Table 5-4 Sample of Dat a for Measured Residual Salt (Nacl) From one Fingerprint on a 1 cm2 Area of a Phenolle Terwinkl 1;1ock Moles of Nacl Subieet Wet (W) or Dry (D)
(10-?)
A L
1.1 B
D 1.04 A
D 0.8
)
A D
2.0
't A
D 1.0 A
D 3.5 A
D 0.56 i
C D
0.30 D
0.22 j
C D
0.25 C
D 0.32 C
D 0.26 A
W
?$
j A
V 40 A
W 34 A
W 52 A
W 33 A
W 28 A
W 53 o
A W
20 A
W 50 A
W 63
6.0 THEORETICAL CONSIDEEATIONS COVERNING F11.M FORMATION AND CONDUCTION ON TERMINAI. 3 LOCK SVRFACES The model presented in this section is based on the work of Dr.
Robert Salomon of Temple University and Mark Jacobus of Sandia. The objective of this work was to provide a basic understanding of the mechanisms of film formation and to predict, if possible, the conditions where dryband formation and tracking breakdown will occur. Thace were two motivationt. to develop these theoretical considerations. /lest, the data from the Sandia tests '.wdicated that film formation was the most probable explanation for the transient phenomena and it was therefore desirable to explain the mechanisms which governed this behavior.
Second, the formations cf drybas.ds due to Joule heating of the moistute film has been proposed by others 139] as a possible mechanism leading to tracking breakdown and it was desirable to estimato the potential for this mechanism to be operable at the voltage and current levels of g
instrumentation and control 'pplications.
The model assumes thet ta terminal bloc 6 is initially contaminated with salt from fingerprin*a and there is 100 percent relative humidity in the environment surro"ading it.
The basic premise is that at steady state the vapor pr.ssure of the film will equal +.he partial pressure of the water vape. to the atmosphere. At 100 percent relative humidity, this partial presst re is equal to the saturation pressure of teater at the ambient temperature. The model employs a basic relationship for the vapor pressure of a liquid at two different temperatures which is derivable from the well known Clausius Clapeyron equation. An addit snal factor is incorporated into this basic equatioa to account for the vapor pressure lowering resulting from the presence of a solute (dissolved impurity) in the film. The derivation makes some reasonable assumptions such as the applicability of the ideal gas equation of state, a large molar volume of vapor compared to the molar volume of liquid, and a temperature independent heat of vaporization. The model also uaes data from the International Critical Tables IAO) to predict the conductivity of sodium chloride in water as a function of temperature.
6.1 Qualitative Diicussion of phenomena Moisture will initially condense on a terminal bloch surrounded by a steam environment because it will be at a temperature below the saturation temperature of the steam. In the absence of any contamination or imposed voltage between the terminals, the film on the block will reach a temperature squilibrium with she surrounding environment. As Icng as the surrounding environment is at 100 percent relstive humidity, j
the film will remain on the surface and not evaporate.
If the surface of the terminal block is contaminated with salt
'e.g.,
from fingerprints), then the fi'
's vapor pressure will be lowered relative to the vapor pressure of pure water at the same temperature.
Thus, the film vaper pressure will be below that of the surrounding water vapor's partial pressure, and water will condense into the film. The addition of water dilutes the film, resulting in less film vapor pressure lowering. The condentation process raiser the tilm temperature because -
I i
f the latent heat of vaporization is deposited in the film, while heat transfer back to the surroundings tends to return the film temperature te the ambient temparature.
The process of condensing vapor, dilutlng the film solution, and transferring heat away from the film continues until l
an infinite dilution is reached. At this point, there is no longer any film vapor pressure lowering.
1 when an electric potential is apn11ed, a current flows in the film electrolyte. This current is an additional source of energy to th9 film, heating it through Joule heating. The film temperature rises accordingly, and the vapor pressure equilibrium point it reached before j
'nfinits dilution is achieved. Thus, the additional aJergy from Joule beating the balancing factor which compensates #or the vapor pressure l
lowering due to the salt. Disregarding the physical dissusions for the moment, the equilibrium point is a result of tL.: interactios o* three parameters: the amount of salt present, the applied voltage, and the
[
external envlronment's temperature. The onount of salt governs the l
solution concentration and hence the amount of vapor pressure lowering i
that occurs.
It is also the primary contributor to the film conductivity since it is the source of ions in the solution. The applied voltage determines the amount of current which will flow for a specific solution conductivity and hence is a f actor in determining the amount of Joule l
heating that acurs. The external environment's ;emperature affects the heat transfer from the film surface slightly by enacting the associated convective heat transfer properties. With some geometric assumptions concerning conductive film dimensions and the heat transfer areas, and by specifying the three parameters just discussed, the equilibrium salt concentration, film temperature, and film thickness can be esiculated.
g Also, as an integral part of the calculation, a leakage current can be l
de te rmi ned,
t l
l The flim thickness as especially interesting since it provides insight to the onset of dryband formation. As stated at the beginnins of this section, dryband formation is believed to be the initial step in l
tracking breakdown.nf a moist surfacer which lords to the permanent degradation of surface resistance even aftar the film is deled.(39, 41]
i l
l l
6.2 Explanation of the Model i
l A very appropriate and useful model of the phenomena is a steady-state model which calculates the conditions that exist in the film for a given set of pararsters. We begin by considering the vapor pressure cf the film given tq:
l i
1
1 l
0 0
?\\
OH 1-1 1-Eq. 6-1 P '= P exp g 7, T
R j_(
g j n
where Py = vapor pressure of flim at temperature T (atmospheres)
P, = vapor prest :are of pure water at temperature T. (atmospheres) 7, = ambient temperature of externa environment (Kelvin)
T = film temperature (Kelvin) 6H = heat of vaporization of water (calories / mole) ideal gas constant (1.987 calories /(mole Kelvin))
R =
n2 = moles of salt dissolved in film n1 = moles of water in film s
Except for the (1 - 2ny/ng) factor, this equation is derivable from the Clausius Clapeyron equation w?ich describes the relationship be". ween saturation (vapor) pressures and temperatures. The (1 - 2ng/nt) factor modifies the expression to account for the vapor pressure lowering which results from the salt dissolved in the filt. It is based on the knowledge that the vapor pressfre of solutions is lowered to a factor of 1 - 1 of the initial value ediere I is the mole fraction of solute. The
""" arises from the diss3ciation of the Nacl into Wa+ and C1' ions.
Hence, for every mole of salt, two moles of ions are generated in the dissolution process. To apply Equation 6-1 to the film model wo first express n2, the mole of salt, as:
e n2 = C+V where C is the concentration of salt.in the solution in moles /cc of solution and V is the volume of the flim in cc.
P is the saturation o
pressure of pure water at temperature T. and hence, for 100 percent relative humidity, it is the partial pressure of water varor in the atmosphere at temperature T.*
Thus, the etndition of equilibrium between the pactial pressure of water vapor in the atmosphere and the flim vapor pressure can be expressed as:
Py/Po = 1 "Ste that in the test set up used at Sandia the entire pressure in the amber was due to steam and hence the water vapor partial pressure w,
the entire measured pressure. The test set up of Salomon closely achieved 100 percent relative humidity.
I ____- _ _ _ _ _ _ _ _ _ _ _ _ _ _ -
Applying this condition to the flim and substituting for n2' Equation 6-1 can be rearranged to express salt concentration, C, in terms of tem'pe r a t ure :
.1 \\. -
C=
1 - exp M
I Eq. 6-2 2Kd R
(T T, j,
It this equation, the leading coefficient, nt/2V, has been espressed as p/2tfd ehere p is the density of water and Ed is the molecular weight cf water. Making this change in coefficient assumes that the volume of the solution does not change when the salt is dissolved in tLe water.
Equation 6-2 prcVides us with a relitionship between the salt i
concentration in the film, the temperature or the film, and the external temperature.
In order to apply Equm* Inn
'.,-2, it is necessary to know two of these three pare. meters. Befcre the colubil!ty limit of salt is reached, the obvious pararseters to determine from other means are the twc temperatures.
T is normally specified as an environmental condition either in a test or an accident sptsification.
T, the film tem 9erature, can be determined by balancies the energy sources and sinks for the film. To achieve this balancing, consider a simplified get, metric model of a film on a phenolic Jurface pictured in Figure 6-1.
j A phenolic substrate material of width, w, sno length, 1, and g
depth, d, is covered on one surf 6ce with a flim of thickness h.
The film is at temperature T and the surrounding environment is at temperature
[ s T.
To simplify the calculations the back boundary of the phenolic l
block is assumed to be at temperature T.,
an assumption that is not i
entirely correct, but which seems to work fairly well for the order of magnitud3 calculations being conducted. gey 11 the convective heat j
lost from the film to the surrounding environa.si; gcd is the j
(
conductive heat lost from the film to the phenolic block. The power, P, 1
I laput to the flim arises from the leakage current I.
Thus:
4 i
2 p i KI = E /Z l
where E is the potential across the film and Z 12 the resistance of the film.
At steady state the temperata23 of the flim will be determined by the balancing of heat loss and hen ! nput. Thus:
2 E /Z - qcy - gcd = 0 Eq. 6-3 l
{
I g
FILM PHENOLIC l^
1
l
\\',!,\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
o
+
m 4 FILM SURFACE _
4ed INSULAYED
.{.
7, T
SOUNDAR ES i
T *-
4 g
+=
-s-
=_
7
+
,=
+
u
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\W
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'
hd
+-
b d.
~~l SIDE VIEW FP.ONT VIEW Figure 6-1: Side and Frontal Vf vs of Simpilfled Geometric Model for Film Conduction on a Phenolle S;bstrate Material~~
l 4
4 Each of these terms are evaluated in turn below.
F.8.rst, consider the power input tere, E /Z.
E is the applied 2
potential, in volts, across the phenolic block.
In the case of a terminal block, it is the potential between the poles. 2 is tue resistance of the film in ohms.
In the model, the film is considered to be a Nacl salt rolution.
lo obtain the relationship between T and film temperatura, data from the International Critical Tables 140] was used. T'ais data is retorted as equivalent conductivity values in em3 [(ohmeca) mole).
/
By definition, equivalent conductivity A, is the conductivity, s divided by the concentration. That is:
A = s/C It is known that A follows an Arrhenius relationship of the form:
}
A = u* exp - EA ET J where u is the temperature independent part of the son mobility and Eg is the activation energy for conduction, Using the International Tritical Table Data 140) to evaluate u and E, we find that u = 17800 3
A J
cm /[(ohmacm) mole) and EA = 3100 calories / mole. R is the ideal gas constant and T is the solution temperature.
Combining the two above equations yields the film conductivity, s:
L
.s s =.uCe exp A
RT,
and since s = 1/2, the power input to the film is:
r P = E uCoexp - EA Eq. 6-4 L
ET,
Equation 6-4 is the desired expression for the first term in Equation 6-3, the power input to the flim as a result of Joule heating.
1 Noting the value of E, it is clear that though s varies with T, large changes g
in T are required to change s significantly. This t'act, combined with the knowledge that T will be close to T,, is used in the computer implementation of this model to obtain the initial guess of the power input to the film.
I i
! i l
l
-...A_.sn A
a-The second term in Egaation 6-3 is the convective heat loss, gey, given by:
gey = h'A(T-T,)
Eq. 6-5 where gey is the heat lost per unit time in watts, b' is the average convective heat transfer coefficient, in watta/(ce?* Kelvin), A is the 2
heat transfer surface area in cm, and T - T, is the difference between the f ilm and ambient temperatures in Kelvin. From the dimensions in Figure 6-1, we see that:
A = dW Evaluating h', however, is not nearly us straightforward as evaluating A.
First, the espression for b' depends on the orientation of the heat transfer area. Since terminal blocts are typically mounted on walls, the heat transfer crea is assumed to be vertical and hence:
b' = Nu e.h_
w where Nu is the average Nusselt number, k is the thermal conductivity of the gaseous medium surrounding the heat transfer area in watts /(ca* Kelvin),
i end w is the vertical dimension of the heat transfer area in cm.
The average Nusselt number for a vertical flat plate is:
a 174 0.670 (Ra)
Nu = 0.63 +
9 ;6 #/9
/
1+
0.497 4 Pr j
where Ra is the Rayleigh number and Pr is the Prandt1 number. The Prandt1 number is the diuensionless retto of the molecular momentum to the thermal diffusivity of the medium surrounding the heat transfer area, and is a measure of how rapidly momentum is dissipated compared to the rate of' diffusion of heat through a fluid. The Raylaigh number is the product of the Crashof number ated the Prandt1 number. The Crashof number is used in natural convection and may be interpreted sa the ratio of the buoyancy forces to the viscous forces. Thus,the Rayleigh number is a measure of relative convective forces on a body compared to the rate of host diffusion. Tbe Rayleigh numbor is given by the relation:
g8 T.- T, w Va -
-u as m.
.m.
m.
m..
l l
l where g is the acceleration of gravity in :m/see?, 8 is 2/(T + T )
i Kelvin-1, v is the kinematic viscosity in em2 in 2
/sec, and a is the thermal diffusivity in em /sec.
that the expression for h' is:
Combining these equations, we find 387-T w
/4 0.670 I
b' =._k 0.68 +
-)
va Eq. 6-6 g,If 0.497
/16
/9 Pr
\\
l Equation 6-6 coupled with Equation 6-5 gives the convective heat los s.
The third tern in Equation 6-3 is the conductive beat transfer per unit time.
9ed, in watts.
9ed is given by:
T-T gcd
~~d where k is the thermal conductivity of the phenolic in watts /(cm* Kelvin)~~
A is the cross sectional area through which the heat is the conduction distance.
. is conducting, and d the temperature of the opposite side of the phenolic.Here T is the film temperature, an above, for simplicity we assume that As mentioned temperature of the surrounding ambient envircnment.this T, is the same as the further refinement is not warranted.tends to overestimate qcd; however, for Using Equations 6-7, all of the terms in Equation 6-3 are defined in terms of know6-4, 6-5, 6-6, and assumed values and the film temperature, T.
n er potential E, and tsing appropriate values for the constants. T can be Assuming an applied easily four.d.
algorithm in 6.he computer implementation of this model.The solution for T the salt in the film.now possible to return to Equation 6-2 and solve for the concentration o Knowing T.
It is T and T, in Et:uction 6-2.This process is a straightforward substitution for Then, having determined the salt concentration and knowing the width and length of the film, tbs film thickness, h, can be found as follows:
I C = n2/V I
= n2/1wh t
j or rearranging I
h = n2/twc !
l n2 is the numbr' of moles of salt initially assumed to be on the surf ace, C was Just calculated from Equatlo.s 'o-2, and 1 and w are the assumed dimensions of the conductive film.
Though not explicitly given above, the leakage current in the film can be easily obtained from the computation of power since volt. age and resistance Lee both available.
It should be emphasized that the output obtained from the model is at steady state.
The transient process of vaporitation resulting in the thinning of the film is not modeled; we look at the flim after this transient process has occurred.
Table 6-1 gives a sample output from the computer simulation implementing the above model for an assumed ambient temperature of 450 K (177'C (351*F)), en initial salt contamination level of 10-7 moles (approximately one fingerprint), an electrical conduction length of 2 cm, a film width of 0.75 cm, and a thermal conduction length through the block of 1.25 cm.
Figure 6-2 shows the predicted leakage currents as a function of voltages for this set of conditions but with varying flim widths.
The change in film widths increases the peak leakage currents predleted as well as the voltage at which it occurs.
In all cases, the peak leakage current occurs at the point where the solution is saturated.
Thereafter, higher voltages cause addillonal heating and hence additlocal vaporitation of the film. Since the film is saturated, precipitation of the salt occurs, reducing the number of ions available for conduction and
)
At each voltage the balance between
)
hence lowering the leakage current.
Joule heating and convecti've and conductive heat losses determines the equilibrium value of leakage current.
The wider film widths increase ti.e film volume and the heat loss mechanisms, and hence the amount of heat input necessary to achieve equilibrium is increased both when saturation is approached and subsequently when salt precipit ates.
A potentially important implication of these-results is that gustification testing which incorporates incrassed voltage for margin may actutlly be donconservative; after a threshold is reached, the mods 1 predicts that the leakage currents will dec ase with increasing vultage.
Some experimental support for this type of behavior was cbserved in the Phase I results of the Sandia tests.111._
- m
~
Table 6-1 Sample Equilibrium Film Parameters Predicted by Film Conduction Model*
Applied Leakage Salt Film Film Potentla!
Current Concentration Temperature Thickness (Vde)
_ ira )
_(moles /ce)
(K)
(cm) 5 0.064 0.000044 450.074 1.51E-03 15 0.19 0.00034 450.578 1.94E-04 25 0.32 0.00088 451.496 7.59E-05 33 0.46 0.0016 452.78) 4.15E-05 45 0.60 0.0025 454.442 2.66E-05 3
55 0.74 0.0035 456.461 1.88E-05
}
65 0.89 0.0047 458.854 1.42E-05 r-75 1.1 0.0059 461.636 1.12E-05 85 1.0 0.00658*
462.932 8.89E-06 95 0.93 0.0065 462.932 7.12E-06 105 0.84 0.0065 462.932 5.83E-06 i
115 0.77 0.0065 462.932 4.86E-06 125 0.71 0.0065 462.932 4.11E-06 135 0.66 0.0065 462.932 3.52E-06 145 0.61 0.0065 462.932 3.06E-06 Parameters assumed are an initial salt contamination of 1.0E-07 mo ambient environment temperature of 450 K, electrical conduction length of 2 cm, electrical conduction width of 0.75 cm, and a thermal conduction length of 1.25 cm.
450 K is 2.99E-04 watts /(cm* Kelvin).The thermal conductivity of steam at
~~Solubility limit of Nacl is -0.0065 moles /ce.~~
If the salt concentration calculated by the above method exceeds C,, the solubilscy limit of salt (~0.0065 moles /cc), a different computation procedure is used*.
First the salt concantration is set equal to the solubility limit; ther. using Equation 6-2, a f!La temperature is calculated.
reached, the film temperature becomes a constant. Note that once the solubility lim Such a condition is entirely reasonable since for a satursted solution the maximum vapor pressure lowering has occurred, and thus the film has reached its maximum temperature.
Note that the solubility limit of salt is only weakly dependent upon tempersiure, and hence the model does not incorporate this-minor effect..
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O.0 0 20 40 60 80 100 120 140 APPLIED VOLTAGE (V) 1 Figure 6-2:
Predicted Leakkge Current Yersus Applied Voltage for selected Fila Widths and Other Farameters as Specified in Table 6-1 e
\\
losses become constant and any additional Joule hea eat vaporization of water and begins precipitating salt.
er the model, a reduction in the number of salt ions avai The film thickness In conduction occurs due to precipitation of the salt.
r the rate of Joule heating (leakage current)
This effect reduces convective and conductive heat loss to the environmen6..until it equals the rate of the film dimensions are fixed.model the saturation limit may be artificial However, in this the 3?wer potential, the salt remains in solution with diff rIn tne real ca e
diment ions.
and a localized voltege gradient may be large enough to e ent film In this case surf ace breakdown, rather than film leakase curr ng.
experienced.
by extrapolating the film conduction model to higher volta ents, may be
, but that the film thickness reaches the 10-6
, we see to go-7 300 volts.
probably means dry bands have formed somewhere in cm range at about Thus we night reasonably expect drybands to become an import mechanism at or above 300 volts.
ant surface by Salomon at 400 Vac. data, is supported by it since the only confirm as observed 6.3 Strengths and Weaknesses of the Model explanation for the observed phenomena based on fir r
e only assumes idesi gas behavior and temperature independence of two 7t parameters:
With reasonable assumptions for the dimensions of t of salt.
conduction path, the model predicts leakage current values within Lt range observed by both Sandia and Salomon.
leakage currents (as illustratad by Figure 6-2)The dimensional dependence of i
fluctuations in the size of the conducting path.the observed saturated steam or a 100 percent relative humidity environmentThe model works fo it will work with minor modifications as long as the perce t In fact, the presence of a solute in the moisture film. humidity exceed n relative aused by various parameters and phenomena involved.fromework that al
(
e temperature, and film conduction is not strongly depend ment's temperature.
the conducting geometry.Of more importance is the amount of salt (ions) present and s
i The primary weakness of the model is its inability to simultaneo predict both high and low temperature data using fixed film dimensions usly This effect may be a result of a change in mechanism or a change in fil dimensions at lower temperatures which is not accounted for in thm model.
whereas this may not always be the case.Further, the model assumes tha e
Salomon's data are about an 1 l I.
order of magnitude below the values-predicted by the model;
however, almost all of his data ends with a strong upward trend in leakage current. Since his_ experiments proceeded only to a specified_ temperature and_were of relatively short duration, bl.a data may represent only transient behavior. The true steady-state values predicted in the model were perhaps never athieved in his experiments. As already noted, dimensional sonritivity exists and it is, therefore,-incumbent upon the analyst to choose reasonable dimensions. The fixed dimensions do not.
allow for parallel conducting paths that would change leakage currents and effective its for a given set of conditions.- Finally, the uniform-film thickness assumed by the model does not recognize that the film -
undoubtedly undergoes localized heating and cooling which leads to localized thinning and reforming of the film.
e
l 7.0 FAILURE MODES OF TERMINAL BLOCKS
'I Table 7-1 provides a summary of terminal block f ailure modes.
The three broad categories of failure modes presented therein are gross electrical breakdown, leaksge currents, and open circuits.
Cross electrical breakdown is one end of the spectrum of leakage currents and is defined as that leakage current which makes the circuit inoperable.
It may be either permanent as in the case whers carbonited tracks fora on the insulator surface or it may be temporary as in the case where voltage is applied rapidly in the presence of a moisture film and the IR momentarily decreases to virtually zero.
Leakage currents imply any level of leakage which does not render the circuit totally inoperable, but doce affect the operation in some manner.
Leakage currents are the usual precursor to gross electrical breakdown.
The dividing line between leakage currents and gross electrical breakdown is not precise and is application depe dent.
Fcr example, milliampere leakage currants in an instrumentation circuit may make that circuit inoperable, but mil 11 ampere leakaae currents in a power circuit are probably acceptable.
An open circuit is the final terminal block failure mode.
It is rimply the breaking of the desired electrical conduction path.
Cross electrical l
breakdown precipitated by leakage currents is one possible mechanism which could lead to an opes circuit.
A momentary surge of current, or a sustained high level of leakage current in conjunction with stress, corrosion, or other f actors may cause the cable or the terwinal block or their interface to separate.
As reported in Reference 1, we observed one such f ailure in the Sendia tests of terminal blocks.
Another example of an open circuit failure mode is the embrittlement of the metal forming the "U" clip in a sliding link terminal block and subsequent torquing of i
the screw in the sliding link.
studied.[42,431 This failure mode has previously been Table 7-1 shows the three basic failure modes and then correlates some relevant mechanisms by which these modes may occur.
The term "causes" refers to those conditions which enable the mechanism to proceed.
"Causes" may be independent of one another, but more likely they will work synergistically.
" Contributing factors" are those items which aid and abet, or in some way affect a "cause" or "causes", but are probably act sufficient by themselves to cause the failure mechanism to proceed.
" Effects and/or symptoms" summarize the consequences that the failure mode has on the circuit or the terminal block.
Normally, these effects would be observable or at least detectable by the operator.
t l
l
^
r Table 7-1 i
semmary of railure Modes for Terminal Blocks Potential Contributing Effect/
Failure Mode Mechanism Causes Factors
_ Symptom Comments t
4
' Cross Electrical Low Voltage Surface Environmental Conditions voltage Exposure Lrse of Circult-Temporary Breakdown preakdown*
High Temperature Time Operability te.g., low Humidity / Moisture contaminants insulation Type
.i rentstance path terminal-to-volatile / Soluble Surface contaminant Temporary terminal or' Contamination Deposition Rate terminal-to-base plate Radiation Aging Normal Accelerated High Laakage Currents and Surface Tracking Permanent i
Hon-Volatile Surface Corrosion contamination Products t
l w
Conductive Residue
'I' High Temperature Loss of Circuit-Permanent Conducting Path Thermal and/c r Pryolytic Decomposition Operability i
of Insulation Exposure to Burning Environment 4
Structural rallure Excessive Cracting of Permanent Temperature Insulation Encessive Thermal Shock vibration High voltage breakdown not included due to lack of HV circuite in nuclear applications 3
e
Table 7-1 (continued) j Summary of yallure Modes for Terminal Riocks Potential Failure Mode Mechanism Contributing Effect/
causes Factors symptom Commente Grose Electrical Conducting Structural rallure Improper breakdown Path icontinued)
Maintenance (continued)
(continued)
Improper Instelletton Aging Bulk Insulation Padiation Dreakdown Moisture Absorption Cracking Moisture Splitting of Absorption insulation and formation of conducting pathe I
Leakage Currents Surface conduction Surface Contamination Installation Low Frequency Some leskage
~~g Practices Line Moise will alvsys e~~
occur. The Environmental Maintenance Circuit question is conditions (e.g.,
Practices Crosstalk a matter of High Temperature degree.
Hueldity/ Moisture, Voltage Level
' Excessive Leakage of I
Contaminants) l Power Draie a few milli-l amperes may Aging Bissed be detri-Readings on tal to an Instrument instrumen-Outputs tation circuit, but Radiation Access for Cross have no beta-emitting Breakdown effect on isotopes a power circuit.
l l
l 9
W
'W 4
a
,i.
e Table 7-1 (continued)
Summary of Failure Modes for Terminal Blocks Potentia!
Contributing Effect/
Failure Mode Mechanism causes Factors Symptom Commente Leakage Currents surface Conduction Structural Failure Excessive Cracking of (continued)
(continued)
Temperature Insulation Excessive Thermal Shock vibration Improper Paintenance Improper Installation Open Circuit Separation of Loose Terminal Screws Loss of Circuit Conductor Operability e
Contact Corrosion Chemical Reagents Y
Moisture /
Humidity Structural Failure Vibration Cracking of Conductor thermal shock Impr' ope r Maintenance Improper Installation l
Differential Espansion e
.~
Table 7-1 (continued)
Summary of rallure Modes for Terminal Blocks Potential Contributing Effect/
Pallure Mooe Mechanism causes rectors symptom Comments Open circ uit Separation of Illgh Leakage currents (cont imsed) conductor icontinued) railure to Reconnect careless Main-Terminals tenance Procedures Lack of Quality Assurance 1
E oo e
s
.a n-- - - - '
. I
' l e
i 8.0 EKAMPLES OF POSS19LE TERMINAL BLOCK EFFECTS 8.1 Transmitter circuits
- A pressure transmitter typically operates with 4-20 mA of current in the instrument-loop.- At aero pressure, or the low end'of=the calibrated
- span, 4 mA is allowed to flow in the circuit, at full pressure 20 mA is allowed to flow. The key word here is " allowed." A transmitter essentially functions as a variable resistor in the circuit, limiting the-amount of current flowing in its branch of the circuit to a value
- proportional to the input pressure; it is.not a current source. This characterization is extremely simplified, but it captures the essence of circuit behavior and permits terminal block effects to be analyzed.
Figure 8-1 shows how a transmitter might typically be connected in an actual plant application.
The transmitter will operate correctly as long as the voltage remains in a specified range. For example, a typical transmitter will operate to specification as long as the voltage across the transmitter terminals remains betwaen 15 and 50 Vdc. The loop resistance external to the transmitter (f ror, the current-to-voltage amplifiers, the cable, and the-other external resistances) also may vary over a specified range depending on the <oltage supplied to the transmitter. For a typical transmitter, if the power supply voltage is 45 Vde, the external loop resistance me.y vary between 250 and 1,500 chas. Note from Figure 8-1 that the potential across the transmitter, OV, is essentially the T
potential across the terminal block and therefore would be the driving potential for any terminal block leakage current. OV7 can be expressed in terms of the normally constant power supply voltage.-V,,
and the voltage drop, OV,, across the external locp resistance, Rei 6VT*Vs - OV, ll 6Vy = Vs - E,1L Eq. 8-1 where-In is the total loop current. The leakage current ITB, across s
the term
~~block is:~~
OVT TB " RTB is the insulation resistance of the terminal block. The where ETB total loop current, which will be observed in the control-room as the transmitter signal, will be the sum of the transmitter output current, 1, and the terminal block leakage current:
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OUTSIDE CONTAINMENT l INSIDE CONTAINMENT i
i l
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,l; TB k
i TERMINAL BLOCK a
<L l
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l LINE READOUT I TO V I
SIGNALS ISOLATION AMPLIFIERS AT 250D EACH Re Figure 8-1: Simplifted Schematic of a Typical Trsusmitter Circu1*, in a Nuclear Power Plant i
Z
-. _ _ _ ~ _ _ _
It=178 + IT E9* 8-7 under normal conditions, ITE will be aero or negligibly small compared to I.
However, under accideal conditions, IT8 can become a T
alaable fractton of I, and therefore, becomes a slaable portion of-the T
total loop current serted by control room instrumentation. The error, e, in the signal will simply be the ratio of the terminal block leakage current to the transmitter signal current.
That ist I
~I I
L T
TB Eq. 8-3 e=-
=
T T
Using the above equations, we can express e in terms of V,, 's., RIBa and 1 :
7 V, - R,IT r
e-Eq. 8-4 T(TB e) i Figure 8-2 shows a plot for the signal error as a function.of transmitter output for conunon values of V,, R,, and several assumed i
I values of.Ryg.
Note that the error is expressed as a percent of output f
current (or reading) rather than a percent of calibrated span. This was done intentionally to illustrate the error that would actually be observed especially at the low end of the transmitter calibration.
I The errors can be quite significant when the terminal block leakage current approaches the. values of_the transmitter signal or equivalently, when the terminal block IR approaches-the values of transmitter input impedance. At 45 Vde, the transmitter input impedance will vary from approalmately 2 to 10 kohns as its output varies from 20 to 4 mA.
~~Hence, j~~
l the terminal blocks may be viewed as a resistor in parallel with the l
l transmitter and, as such, acts as a current divider. -Figure 8-3 shows j
l thv current trace of total-circuit current as a function of time for the
]
terminal block connected in the transmitter circuit during the Sandia d
test.(1] For'the period of time covered by the plot, the transmitter was operating at -A mA base signal level. ' Clearly, the total circuit l
l current observed is in agreement with the above analysis. During the 4
l cooldown period when the film vaporises, the transmitter current returns j
to its base current level.
To illustrate the impact of.these errors, suppose that the transmitter in question was a narrow range reactor coolant system (RCS) pressure monitor calibrated from 1700 to 2500 psi. Thus, each milliampere of signal corresponds to a 50 psi increment in pressure. The sensed pressure will be based on the total loop current, I. Assuming t "
L 200 VdLUE OF R TB 5kohms 160

~~10 kohms~~

-- 60 kohms I
~
- 500 kohms -
120
% ERROR IN
~
.I CONTROL ROOM stGNAL s
'N 80 i
cs 1
y s %
~%
40
.,'~~
~....................g-..."**i........4..u.*g........,,,,,,,,1...+x-"

~~~~~~~'~~

++
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O 4
6 8
10 12 14 16 18 20 l
l l
l TRANSMITTER OUTPUT CURRENT (mA)
. Figure 8-2:
Percent Error in a Transmitter Circuit for Selected Values of Terminst Block Insulation Resistence (R,
1000 O and V, = 45 Yde) 1
l l
I I
I I
I I
I I
I I
I 13.7 l
11.7' 17 5 *C 161
~~C 95*C 14 9'C 9.8 TRAH 2.7 m A LE AK AGE CURRENT RC T~~
~
I*O
~
CURRENT (mA)
W

:
h 5.9 w
(
3.9 TRANSMITTER B ASE COOLDOWN
~
19 SIGNAL LEVEL PERIOD O.0 ----- C POWER ON I
l l
l 1
I I
I I
I i
1 I
O 30 60 90 120 150180 210 240 270 300330 RELATIVE TIME (minutes)
Figure 8-3: Total Current Trace of Transmitter Circuit During LOCA Simulation e
2 everything else in the circuit works perfectly Figure 8-4 shows the readouts that would be observed in the control room for V, = 45 Vde, R, = 1000 ohms, and RTA = 10,000 ohms.
is 1886 psi at the minimum transmitter current level of 4 mA. Note that the minlaum r One of the uses for a narrow range pressure monitor is to provide an actuation signal for high pressure injection (HPI).
A typical set point would be 1750 psi whleh is less than the minimum reading of 1886 psi caused by the suasning of the 4 mA base current signs 1' of the trantaitter and the terminal block lestage current.
In fact, any setpoint less than 1886 psi would not be achieved. The result is that one or more of the instrumentation loops required for actuation of HPI by low RCS pressure would not reach their set points, and hence HP1 may not be automatically j
l accomplished; in this situation another means of actuation would have to i
be implemented.
This type of error would also affect the pressure readings observed 'sy the o.oerator.
Not only would the readings themselves be in error, but the operator would also be faced with a discrepancy in readings between narrdw and wide range gauges.
B.2 RTD Circuits RTD circuits are low voltage, low current circuits.
They are nut, bowever, inuune to the effects of terminal blocks.
An RTD circuit typically eperates at 4 Vdc or less with currents in the range of 1 mA or less.
The resistance tu a typical RTD might vary from 200 ohms to 500 ohms over the full temperature range of the RTD.
Figure B-5 shows in a block to connect the RTD to the remainder of the circuit.very simp The IR of the terminal block is a parallel cennection with the RTD resistance.
~~Hence, a~~
the bridge or constant current circuit used to sense the esistance of the RTD is actually sensing the effective resistance, Regg, of this parallel combination.
R gg is:
e TB RTD off " Rg + (D and the fractional error e is:
i i
1 RTD erf R
~
TB RTD kg + bTD l
l 2500 I
I i
RESPONSE CURVE WITH 10 KD TERMINAL 4
BLOCKIR d
~~o N 2300 o+~~
~~RESPONSE~~
INDICATED A
CURVE FOR PRESSURE CORRECTLY 7
~
$[4 (psi)
OPERATING CIRCUIT 1900, -
[
ASSUMPTIONS:
0+
R, = 1 KG toes V =45 Vdc f
s Ryg=10 Kn 17so I
I I
1700
~ 16 20 4
8 12 TRANSMITTER OUTPUT (mA)
Figure 8-4:
Indicated Pressure as a Function of Transmitter Output for a Correctly Operating Circuit and for a Circuit With Terminal-Block Insulation Resistance Assumed to be 10 kohns T
~~-4a g -, e... A sat i '~~
- ^ ^
ME a.ama eve a s a t N se. h, C a.,
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-0 0
l R
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$R TB
_h RTD l
POWER SUPPLY
+
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l Figure 8-5: Simplified Block Diagram of a 3-Wire RTD Circuit Showing Parallel Connection Between Terminal Block Insulation Resistance and the Resistance of the RTD Sensing Element 9
.i
W-'
' sie*4
,g For a typical 200-ohn RTD which varies in resistance from 200 to 480 ohms-over its temperature range, a terminal block resistance cf 10,000-ohms introduces an error in measured resistance of 2.0% at-the low ond of the enlibration and an error of 4.6% at the high end. Figure 8-6 shows the two. bounding curves of percent arror in measured resistence for a commonly used 200-ohm RTD as a function of terminal block insulation resistance. For an RCS temperature monitor calibrated from 93*C (200*F) to 399'C (750*F) the 2.0% and 4.6% resistance errors translate to a 4*C (7'F) error at the low end and a 24*C (43*F) error at the high end.
Since the parallel connection will make the measured resistance less than the actual RTD resistance, the indicated temperature will always be lower than the actual temperature.
To illustrate the effect that these errors may have, consider the i
hypothetical example where the RTD is sessuring a temperature of 327'C l
(621*F) and the pressure is 1800 psia. If the RTD is calibrated as j
assumed above, it should have a resistance of 414 chas at that temperature. A terminal block insulation resistance of 10,000 ohms in
{
parallel with the RID would give an effective resistance for the pair of l
398 ohns or a temperature readout of 309*C (589'F). Thus the dispisyed temperature would be 18'C (32*F) less than what setually existed. Since the saturation temperature at 1800 psia is 327*C (621*F). the coolant at the RTD could be vaporizing, where as the perceived condition would be 18 C* (32 F*) subcooled. Thus, even relatively large terminal block 1Rs (e.g.,10,000 ohms compared to 414 ohms for the RTD) can have a significant impact on the perceived conditions. The temperature and pressure in this example are only illustrative; any set of conditions close to the saturation point could have been chosen with similar 4
results.
Also, it is important to recognise that an evaluation of accident sequences is necessary to determine the relevance of such misperceptions in coolant condition to accident management.
8.3 Thermocouple Circuits Another important temperature measuring device that may empicy terminal blocks in the circuit is a thernocouple (TC). One common TC circuit design closely approximates a null calance circuit; that is, the sensing device balances the potential across its input terminals so that no current flows through its branch of the circuit. Thus, if the TC circuit is properly designed and installed and is operating correctly the potential across the sensing circuit is the open circuit potential generated-as a result of the temperature difference between the measurement and the reference junctions of the TC.
The presence of moisture flims on terminal blocks may cause shunt resistances to form between the TC elements or between a TC element and groun6. As Moffat 144) points out, the introduction of shunt paths into a TC circuit can cause significant effects on the output of the TC circuit, that is, on the potential across the input y
of tha sensing circuit. In order to analyze the effect of these possible shunt resistances and any associated spurious cmfs, it is necessary to locate the thermoelectric sources of emf within the circuit relative to the potential shunt resistances and spurious omfs.
Reed (45j has developed a p
-8 b
10 a
9
-- 'I TYPICAL 200R RTD 6
- j
-- - - R RTD-480R l
t RRTD=2OOR 7
1 i
t i
i PERCENT 6-1 ERROR IN g
MEASURED HTD 5 g
RESISTANCE
\\
4 g
\\
s l
3 1
f 2
\\
N, ' ' ~ ~
j
~ _,
~ ~
O I
i O
50000 100000 TERMINAL BLOCK INSULATION RESI";TANCE (G)
Figure 8-6:
Percent Error in the Resistence Measurement of an RTD as a Function of Terminal Block Insulation Resistance o
~~_____T^~~
~
^
m-~+
~
functional model of a TC circuit which clearly highlights the location of.
enfs in-the circuit and permits one to electrically locate the relevant circuit elements for analysis. The key ingredient in Reed's model is the terporature profile for the entire TC circuit.
For illustrative purposes consider a typical.in-containment thermocouple application such as core-exit therm 6 couples. The measurement junction of these TCs will be near the core flow exit point in the reactor vessel. From there, the TCs are typically routed down i
through the core and exit the reactor vessel from the bottom; shortly af ter the vessel exit point they may physically junction via a terminal block or ottor similar connecting device to TC ortension wire which runs Ibrough containment to a heated reference junction. At this point, the I
circuit converts to a coemon conductor type such as copper, and proceeds via a containment penetration to the sensing circuit (device) located in the control roon. Newer TC circuit designs locate the reference junction outside the containment.
Figure 8-7 illustrates one possible core-exit thermocouple circuit arrangement and shows a hypothetical, but reasonable, temperature profil for the circuit that might exist during a LOCA. The reference junction for this example is inside containment.
Section I represents the l
thermocouple from the measurement junction to its junction with extension wire just outside the reactor vessel. Section 2 reprosents the run of extension wire from the vessel etterior to the referance junetton.
Section 3 represents the circuit from the reference junction through the measurement circuit in the control room. Using the method ot Reed [45) and assuming homogeneous wires in each section of the circuli, Itered possible omf ources are shown in Figure 8-7.
Et is the not etaf resulting from the temperature difference between the measueeuw L #nd reference junctions. For this example the temperatures of the mescurement and reference junctions are assumed to be 550'F and 150*F, respectively. Thus El for a Type K thermocouple is 9.036 mV.
E2 is a possible est resulting from temperature gradlects that may exist within containment along Section 2 of the circuit; for this example Section 2 of the circuit is assumsd to be isothermal since an accident is in progress and the containment temperature and the reference junction temperature will most likliy be the same. Thus, E2 is zero and is not considered further in this e: ample. E4 and Es are spurious emfs which may be introduced by the terminal blocks in the
~~hunt paths.~~
These enfs may be of galvanic or other origin as discussed in Reference 1.
R1 is the lumped resistance of the TC wire in Section 1 of the circuit and R2 18 the lumped resistaace of the TC extension wire in Section 2 cf the circuit. For this example these values are assumed to be 598 ohms and 117 chas, respectively and were chosen as follows:
Rt = (100 feet of 0.01 inch diameter Type K TC wire)*(5.98 ohm / double foot) = 538 ohms; R2 = (200 feet of 20 AVG Type K TC extenelon wire)*(0.586 ohms / double foot) = 117 ohms.(46, 47, 48] 24 and R5 are the ohmic resistances of l
the shur.ts caused by the terminal blocks.
4 SECTION 1 i.
SECTION 2 J-SECTION 3
_A g-
9,
,Ti' t
-w -
1
\\
En
\\
~
8 b
p,t 8
i Idl l
I NULL
,/ '" %,
l'!
fl S
I I BALANCED l
SENSING I
Tu R!*8
{
l CIRCUlf AND d
Rs}
I INDICATINO
'l I 'l CIRCulT.
1d,,8 j
y gt o.,
I
<; p TCNWY I
J (a)
THERMOCOUPLE CIRCUlf WITH TWO SHUNT PAT tef s
f00
~~6501 3-~~
~~F m~~
\\
r..,
> 16 0 E
T g
cNW7 2
N 70 RELATIVE CIRCUIT POSITION t
(b)
HYPOTHEllCAL TEMPERATURE PROFILE Figure 6-7:
Simplified Schematic of a Thermocouple Circuit (Figure a)
During an Accident (Figure b)and a Temperature Profile for the t
F$gure a shows the circuit with shunt paths located at cable junction points just esturior to the reacter vessel and at the thermocouple reference junction.
shows a potential temperature profile for an accident Figure b situation.
As a result of the accident T T
ref *nd er.mt are shown equal, and therefore, E2 becomes zero.
~92-
The parameter of interest in Figure 8 7 is 7, the potential across 2
the sensing circuit input.
For a properly operating, null balanced. TC t.ircuit V2 equals E.
However, the pcesence of shunt resistancos and 1
spurious emf s changes V, anc' hence changes the indicated temperature 2
in the control room, The error in the voltage across the sensing
~~circuit, e, is E) -V2 e=~~
E 1
By any one of several methods V2 car. be expressed in terms of the other circuit elements, E, E, E, R, R, R, and R.
The i
4 5
1 2
4 S
result is:
R,R E. + R E E, + (RR7 + R)R, + R R E 3
g3 2
5 Eq. 8-7 2
RR2+RR4+ RR$+RR24+ 4 3 RR Examining Equation 8-7, we see that V2 varies linearly with any one of the potentials (E, E, or E ) while the other potentials are held 1
4 constant.
Figures 8-8 and 8-9, respectively, show the opan circuit voltage, V, and the voltage error, e, as a function of the spurious 2
potential E.
In these figures, E4 is assumed to be tero and the 5
shunt resistances, R 3
4 4 and v$, are 10, 10, and 105 ohms as noted.
An interesting point illustrated by these figures is that large s*J 3t resistances (e.g., 105 ches or more) tend to mitirita the effect oi large o
spurious emfs in the shunt paths.
For example, if both R, and R5 are 1N ohms, then the error in the desired 9.036 mV value of V2 for this
=iample varies from +9.7% to -6.5% (using Equation 8-6) as the spurious emf E5 varies from -0.1 Y to +0.1 V.
The.eason for this mitigating effect is that the large spurious tmfs generate significant currents to the shunt paths (compared to the virtually zero current in the properly operating TC circuit) which in turn cause most of the spurious emf to be dropped across the large shunt resistances.
Hence, V2 is cot affected as dramatically as might te expected since 0.1 Y is 11 times the desired 9.035 mV.
Of course, changing the relative values of R and R5 also affects the 4
error in Yp.
To compare to the above numbers, if R4 is 104 ohms and R$ is 105 ohms, then V2 varies from 413.8% to -1.2% as E5 varies from -0.1 V to +0.1 V.
And as expected, as the shunt resistances fall, the effect of the spurious emfs increases. In the limit when R 5 is zero, V2 will equal E5 The effect of varying R5 on V2 and e is illustrated in Figures P 10 and 8-11, respectively.
In these figures the three curves represent different values of E3 (-0.01 V, 0.0 V, and 40.01 V); R4 is assumed to be 104 c hins. These figures show R$ varying only up to 11000 ohms, 1,ut th. trend is clear. As R5 increases we see that V2 approaches k /(R; + R )*E, and if R4 is large compared to R, then V 4
4 1
1 2
approaches E.
As expected, for R$ equal to zero V2 is exactly the 1 ;
L m
.. ~ ~....
f 1
0.05 i
i i
i i
O.04 O.03 0.02 0.01
[
/
\\
4 AND Rs = 104 4
s" N N R O.00
-0.01
-0.02 8
R AND R = 10 D 4
3
-0.03 i
-0.04
-0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 E s Figure-8-8: Open Circuit Voltage Y2 as a Function of the Spurlost Voltage E5 f Resistances,or Selected Values of Terminal Block Shunt
)
1 6
8 R4 AND Rs=10 O 5
4 1
I t3
~
~
l trO tc 2
4 h
R4 AND Rs.= 10 0 1
4 z
N j
o0
---\\
l P
AND R = 10sg O _I R4 3
4 I
IL l
-2 i
-3 l
l
-4 I
I
I I
I
' 0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 Es Figure S-9:
Error in the Open Circuit Yoltage as a ranction of the for Selected Values of Terminal Spurious voltage E5 Bltack Shunt Resistences 1
n
.~._.
0.010 0.009
/
O.008
- E, = + o.o 1 l
0.007 E = 0.0 0 5
0.006 g
/
O.005
\\
Es =-0.01 O.004 0.003 0.002 0.001 a
0.000
-0.001 a
f
-0.002
-0.003
-0.004 I
-0.005
-0.006
-0.007 -
-0.008
-0.009
-0.010 O
2000 4000 6000 8000 10000 R 3 Figure 8-10: Open Circuit Voltage V2 as a Function of the Shunt for Selected Values of Terminal Block Resista-ce R$
Shunt Resistances
a I
2.2 2.0 1.8 1.6 m
o14 E s= -0. 01 g
l
@ 1.2
.J l
4 1.0
.1 z
l O
l h,,
i~ 0.8 i
o
$ 0.6 LL 0.4 I
~-
f l
0.2 E,=o.co O~O j
[
Es = 0.01 I
I I
I I
i t
I t
- 0. 2 0 2000 4000 6000 8000 10000 R g Figure 8-11: Erroc in the Open Circuit Voltage as a Function of the
)'
for Selected Yalues of Terminal Shunt Reelstence R5 Block Shunt Resistentes
N-
.1:
value of the spurious voltage, E. Clearly, negative spurious omfs 5
relative to the sign conv6SLlon shown.in Figure 8-7 are more detrimental 3
to circuit performance than positive spurious amfs.
It is also cleaF that the value of the shunt resistance is a more dominant factor in-r determining circuit performance than the value of the spurious enfs.
Since R, R. E, and Es can vary perhaps continuously over 4
4 fairly large ranges, a definitive prediction of V 2 is impossible.
Finally, to illustrate precisely what these effects on V2 mean in terms of indicated temperature, a few V2 values predicted by the above extmple for selected vslues of R$ and E5 wers transisted tuto temperatures. This conversion assumed (ist the sensing device adds the reference junction compensating voltage to the value of V2 before converting the indication to temperature. These temperatures are sunmarized in Table 8-1.
The assumed values of the other parameters (keyed to Figure 8-7) are noted in the table.
Table 8-1 Selected Temperatures ('C('F)) Indicated by the Type K Thermocouple Circuit Discussed as an Example in This Section*
(Correct temperature indication in all cases should be 288'c (550*F))

~~R5(~~

hms)--------------------
5 1920 5000 10000 s
-0.1 off scale low off scale low 104 (220)
-0.01 90 (194) 221 (429) 247 (476) 0 190 (374) 251 (403) 253 (487)
+0.01 289 (555) 279 (53$)
278 (532)
+0.1 1184 (2164) 536 (996) 415 (779)
Values of the other circuit parametets used to derive the results-in this table (see Figure 8-7):
El = 9.036 mV E4 = 0.0 V R1 = 598 chas Ry = 117 ohms 4
R4 = 10 ohms 8.4 Solenoid Valve C1 *:ults Terminal blocks are commonly installed in 120 Vac and 125 Vdc control circuits for solenoid valves.
Figure 8-12 is a simpilfied schematic showing one possible solen 'd valve circuit. Before addressing the effects of terminal blocks, it is important to understand the normal I
10 A l
+
C1 i
C2 o
Z1::
Rygg 5
12O Vac i
~.
OR
~
f
'-~~~'
125 Vdc R s2.
Z2
Z3
~~1Z4 T~~
i
?
R SOLENOM
' - - +
o TB3 VALVE 3
l
's STATUS L2 I
L1 S
i
'N INDICATING LAMPS l
STATUS PANEL LIGHT J
1 Figure 8-12: Strap 11 fled Circuit Schematic for One Possible Solenoid valve Circuit g
operation of this circuit.
To begin, assume that the valve is normally open and that whet. energix'd, it closes. The desired position fot operation is open.
The contacts C1 and C2 are control switches in the control room.
These switches can be any one of a number of t'. pes, but a common t*pe might be three position momentary contact er
.ches.
That is, there is a neutral position which is the rest position t'or the suitch, and there are
(
open and cle e positions which must be held by an operator in order for I
the switch to make contact in that porition. Thus, when aa operator moves the lever to open and releases it, the switches return to the neutral position. Assume thai Loth C1 and C7 are operated by the same lever.
21, 22. 13 and La are two position limit switches located on the valve itself.
L1 and Li are indicator lamps in the control room and indicate ' Sat the valve is not closed and not open, respectively.*
S is a status panel light which lights when the valve is in the vormally desired Po s i'. l o n.
Tables 8-2 and 8-3 are the contact development tables for this circuit.
An "x" means that contact is made in that switch position.
Table 8-2 Contact Development Table For control Switches C1 and C2
---Switch and Valve Position---
Open Neutral Close C1 e
x x
C2 x
xu contact made
- = contact not made r
~~The terms "not open" and "not clos 3" i.ie used rather than " closed" and "open" because that is the irve mear'~~
-f the lamp. The "not open" lamp lights when the valve leaves th> ed.n position and is thus lit both while the valve is closing and mien it is closed.
Similarly the "not closed" Itsp lihhts when the valve leaves the closed position and is thus lit both while the valve is opening and when it is open.
If both lamps are lit simultaneously, then "not open" and "not closed" are both true which means tttt the valve is changing state.
If only one lamp is lit, then it means that the valve is either open (anot closed")
or closed ("not open").
-100-
Tabla 8-3 Contact Development Table for Limit Switchet 21, 22, 23, and 24

~~..--Valve position---------~~

Qpen JAirrtedIate Qlqsa e
n x
22 x
23 z
24 z
z z = contact made
= contact not made If the valve is open, we see from Tables 8-2 and 8-3 that C1, C2, Z1, and Z4 are open. Only 22 and 23 are closed which means L1 and S are lit and the indicatled is that the valve is open (see footnote on "not open" and "nt. closed").
If the operator now wants to close the valve, he moves the lever for C1 and C2 to the "close" position.
Both C1 and C2 make contact and, because 22. is still open, power is applied to the valve via C2.
The valve begins to close; 23 trips open extinguishing S and 24 trips closed lighting L2.
Both L1 and L2 are now lit, and hence we know i
the valve is changing position.
If the operator releases the lever before the valve 's fully clossd it will return to the full open (nonenergized) position Jince Z1 is not yet closed and C2 is open when in the neutral position. When the valve resches the fully closed position, 21 and 22 change state.
Il closes so that when the operator releases the switch lever, power to the valve will be applied through C1 and 21; 22 opens turning L1 oil. The sequence h,appens in reverse wher, opening a closed valve. The operator moves the switch lever tr pen, thus opening C1; C2 was already open.
power to the valve is lost med it begins to open. As it does, 21 and 22 thange state. 21 onens to ensure that power will not be reapp".!ed when C1 la relcased to ti.e neutral position.
22 closes, lighting Lt.
When the valve reaches fu11; open. Z3 and 24 change state. Z3 cloces, lightleg S, and I'-
> pans turning L2 off.
The dots in Figure 3-12 indicate circuit nodes which are pnysical junctions to fleid wirias near the valve. These may very likely be adjacent terminals on a terminal block. 1stee nossible terminal block leakage paths have been indicated on Figure 8-12 by dotted resistors.
Each may have a detrimental effect on the operation of the solenold circuit.
First, cos ' der RTB1, a leakage path between the always powered node of 22, 13 and Z4, and the solenoid valve. This leakage path bypasses the v4?ye control switches C1, C2, and 21.
The effect of this leakat
,urrent could be the inadvertent energizing of the valve when a stean environment quickly envelopes the terminal block.
If RTB1 is small enough, a leakage current sufficient to power the valve may
-101-I n
~
x--
b'!
occur.
If the valve to question is a 17.4 watt, de service valve, then the steady state resistance of the valve is:
=
er 900 0 E
In actuality, becau n of the fintte valvo of RTBl* th' 'AtIf8 power supply potential will not be dropped across the solenoid valve, i
The alntmum voltage to actuste the valve is approximately 90 Vdc (49) and hence the current necessary for thir condition is:
0.1 A I, =
gg
=
If at least 90 volts must drop across the solenoid valve, then a assimum of 35 volts can drop across RTBl. Lising the 0.1 A current requirement to operate the valve, we see that Y
~~350 0 Rg~~
Thus, a transient terminal block insulation resistance of 350 ohms would cause the valve to close when it was intended to be open. Industry '
qualification teste espertence leakage currents suf fit lantly large to indicate that such low 1R values are possible.
Further, low values of IR would be most likely to occur.under transient conditions (see Figures 4-6 and 8-3).
The question here is whether or not such low values of ik would prevall for a parlod sufficiently long to complete the cloetog of the valve.
Sandla test results indicate that the answer is pro ably yes, because solenoid actuation is fairly rapid and the low values of terminal block IR prevailed for seconds to minutes after their onset.
Next consider the leakage path designated by RTB2 This path is a leakage path by limit switch I2 and the not result could be a falso lighting of Indicating lamp Lt.
Analogous paths, not shown in Figure 8-12, would erroneously light la:npa L2 or S.
The current and voltage re9uired to light L1 will undoubtedly vary from design to design, but two casts might be considered as w amples.
In the first case, the lamp is in
~~(erles connection as shown in Figura 8-12.~~
A typteal 125 Vdc lamp for much an appiteation might require a annimum of 110 Vde to operate.(50) i The lamp its*1f might typteally have a resistance of 2000 chas and hence the current necessary would be:
= 0.055 A I
,,p
=
00 t
-102-
m i
b Thus, the terminal block insulation resistance would have to bei TB7
0 5 A*
e F
Again, this value of IR is not unreasonable for transtant conditions though sustained values at this low level are unlikely.
The second lamp configuration would replace the actual lamps with a relay which would turn separately powered lamps on or cff. Thus L1, L2, i.nd 8 would be the pick-up coils for these relays.
Such relays might typically have a pick-up voltage of 15 percent of the rated voltsgo and a coil resistance of 13000 ches. The required current therefore woald bat
'""I'
~~0.0072 A 1relay~~
13000 Q The voltage drop seross the terminal b'.ock could be at most 257. of 125 Vdc or 31 Vdc and henco:
= 4300 0 ITB7
~~O O2A Thus, a much larger terminal block 1R would permit false operation e~~
of the Indicating or status luops if they were switched on and off by a less than 4300 ohms would cause the lamps to relay. Any value of RTB7 i
falsely illuminate for the assumed type of relay, The final fault shown in Figure 8-12 la RTB3 This path leaks by the valce itself and would cause a probism only if the leakage current became large enough to aske the circuit fuse fail. For the worst case with a 17.4 watt de valve energized and all three lamps illuminated, the current in the circuit would be:
I Y~ = 0.377 A
-- + 3
~~2000 Q 1~~
=
sax 175 V If the circuit were fused at 10 A, then 9.673 A would have to leak around the valve to cause the fuse to fall. With the valve remaining energited at 125 V, fuse fat),ure would occur at a terminal block 1R of:
~~13 0 TB3~~
~~7 A~~
-103-
M This value is essentially a dead short; however, if the circuit were fused at 1 A, fuse f ailure would occur at a terminal bluck IR of 186 ohms.
These low IR values are not impossible to 4chieve, but for any sustained period seem improbable.
Momentary high Isakage currents may cause the fuse to open. At these high leakage current levels, one must also be ccncerned with the power being dissipated by the terminal block and the effect such power dissipation may have on permanently degrading the block's surface.
In summary, the above discussion indicates that terminal blocks may interfere with the proper operation of a solenoid valve circuit when the terminal block's insulation resistance decreases to about the 4 kohm i
level. At this value of terminal block IR, indicating Itmps may falsely Ilght depending on how they are wired into the circuit.
At a few hundred ohms of insulation resistance, the valve may falsely energize and at a i
few ohms of insulation resistance the leakage current may be large enough to fall circuit fuses.
Being slightly conservative, we may conclude that at IR values above 5 kohms, terminal blocks probably do not affect the operation of solenoid valve circuits.
8.5 Motor Circuits consider the casa where a terminal block is used to connect a motor to a motor control center (MCC). A typical connection might look like Figure 8-13.
The terminal block leakage path is indicated as a fault resistance, Ryg, between lines.
In this case the leakage currest does not affect the motor directly, but rather would affect the thermal overload protection devices and the circuit breakers. The amount of y
leakage current that would be significant would depend on the settings of these devices.
Figure B-14 shows time-to-trip as a function of percent of Motor Full Load Current 1511 for one type of directly heated bimetallic overload relay. There.are many manufacturers of such devices, both bimetallic type and magnetic type, and tne selection of time-to-trip characteristic curves are extremely varied. Thus, the following discussion is only representative of the type of concerns that may be a problem; each application must be antlyzed individually, probably the most sensitive case is for sus 11 1/2 hp or 1/3 hp motors which draw ~1 A at full power.
From Figure 8-14 we see that 200 percent of motor full load current requires approximately 40 seconds to trip the overload protection relay; at 500 forcsat the time to trip is down tC Peconds. These overload Currents Correspond to ~2 A and
~5 A currents for the small 480 Vac motors, or leakage currents of
~1 A and ~4 A.
These values of leakage currents have been observed in industry qualification tests of terminal blocks.
Sandia and industry test data suggest that it is possible to have these leakages for periods of time sufficiently long to trip the overload protection devices, and hence, the line-to-line faults caused by terminal blocks may cause them to trip. Acceptable levels of leakage curront are those which do not exceed the excess current capacity of the overload protection for the time necessary to trip the device and do not dissipate damaging amounts of power on the terninal block surf ace.
Small, low current motors aro l
i I
-104-r v
l 4s0vea WCC
)
)
,) CIRCulf BME AKER ggggy 1HERM AL OVERLO AD PROTECTlDN DEVICES Ra f
TERWIN AL SLOCK m.. w,. +
MOTOR Figure t-13: Typical Motor Circuit Connection for a 3-phase Motor the most susceptible motor appilcations because with larger sites, the full load current is higher and larger leakage currents are required to trip the protection devices.
However, industry qualification tests have reported failures of 25 A fuses used to monitor leakage currents and therefore even circuits for larger motcrs may be affected.
e The limiting condition for a terminal block to open a circuit breaker is the set point of the circuit breaker. This value is typically l
well above the motor f ull-load current and hence the terminal bicek Unless leakage currents would have to be very large to trip a breaker.
the terminal block was nearly shorted, such would not be the case.
However, if the motor is off and then switched on, the transient application of voltage to the terminal block will cause much higher than average leakage currents. The high transient leakage current coupled with the motor starting current may reach values large enough to trip the breaker.
In summary, terminal blocks in motor circuits may be a problem, not to the motor itself, but rather to the circuit that supplies power to the The most sensitive devices in the circuits are the thermal motor.
overload protection devices and the fast sensitive situations are where they protect small horsepower motors. Also, the tripping of circuit breakers may be a problem on motor start-up. The effect of a tripped overload protection device or a tripped breaker would depend on the function of the motor, the ability of the operator to recognize tnat a protection device or breaker had tripped, and his ability to prevent the problem from recurring.
I I
-105-
summmenswwww. sets i
200 i
i 1
l l
1
.A 1000 e
w o
f100 E
O H
i g
s H
10 I
l l
l I
l l
i i
100 200 300 400 600 600 700 800 PERCENT HOTOR FULL LO AD CURRENT l
Figure 8-14:
Time-to. Trip as a function of Percent of Motor Full Load Current for One Type of Directly Heated Bimetal Overload Relay [51)
-106-I
l l
POSSIBLE METHODS OF REDUCING TERMINAL BLOCK LEAKAGE CURRENTS 9.0 Three possible methods were considered candidates for reducing cleaning, sealing, and surface leakage currents in moisture films:
coating. Each is discussed in turn.
9.1 Cleaning cleaning c' terminal blocks was a possible remedy for terminal block Specifically, performance suggested by Stuetter in his earlier work.(2)he stated that "a ve subsequently washed with alcohol) and sealed with RTV... regenerated Stuetzer reported leakage completely and functioned like a new block."
{
currents of approximately 0.7 mA for this cleaned block and the new These results are entirely consistent with the blocks that he tested.
Reference 1 also reports results reported in the later Sandla tests.[1]
that one new terminal block was cleared prior to testing by soakingNo segeentially in cienn baths ot freon, detonized water and freon.
improvement in the performance of this terminal block compared to the This result was somewhat surprising new, uncleaned blocks was noted.
since we espected the cleaning to remove salts and other sources of ions Stuetr.er's data supports this finding since his for flim conduction.
clesned block performed essentially the same as his new blocks.
The fact that cleaning is not as effective as originally hoped for should not actually be surprising. Terminal blocks are extremely convoluted surfaces with covered cavities and many small crevices that In the sectional designs the interface between are not casily accessed.
adjacent sections is not accessible without disassembly of the terminal For these reasons a thorough cleaning of a terminal block block unit.
is difficult to achieve.
In a unit, even in a laboratory environment, fleid environment it may be practically impossible to schleve and
/
The observed performance of a cleaned, new L
nelntain cleanliness.
terminal block in Landia tests indicates that cleaning does not reduce leskage currents to levels that will not affect instrumentation end Note that this statement does not imply that routine control circuits.
cleaning should not be performed as a part of preventive maintenance.
9.2 Sealing An Terminal blocks are typically installed in NEMA-4 enclosures.
obylous question la whether these enciesures can be sealed to prevent the As the eteam environment from surrounding the terminal blocks.
enclosures now exist with weep holes and conventional condult/ cable entries, the practical answer is probably no.
The biggest problem would be the conduit entries. To effectively seal the interstitial space intrusion would require between the cables and the conduit against>stens a penetration into the NEMA-4 boxes similar to a containment Using a stitcone compound such as RTV may stop condensed penetration.
moisture, but achieving a reliable vapor seal in all possible conduits would be unlikely.
-107-
Gives that the electrical enclosure could be sealed successfully, another set of questions arises.
First is the question of structural integrity of the box.
Rapid dzternal pressurization may collapse the box around the terminal blocks.
In tests of new WEKA-4 enclosures without wvep holes or conduit entries, external pressurication with nitrogen gas to 20-35 paid deformed the boxes sufficiently so that they leaked and equilibrated pressure.
These pressure levels are below the design basis containment pressures specified in IgEE 323-1974, Appendix A.[37)
{
Another question is the phenomenon of cable " piping
~~observed during~~
(
Sandia and industry qualification tests.
In these tests, a compression I
fitting around a cable forms a pressure barrier between the test chamber and the environment.
In cable " piping", differectial pressure drives moisture along the cable between the insulation and the conductor from the high pressure end to the low pressure end.
If the terminal blocks are hermetically sealed in the MEMA boxes, this differential pressure condition could be set up in reverse during an accident situation.
Moisture would then be driven along the cables directly onto the terminal blocks.
Such a condition would be extremely undesirable.
It would be difficult, if not impossible to practically achieve total enclosure sealing.
Even if it could be achieved, another set of questionable effects such as NEMA enclosure strength and cable " piping" would arise.
Thus, sealing the enclosures does not appear to be a viable solution.
9.3 Coatings Conformal coatings for terminal blocks were investigated as a means of sealing the exposed conductors.
Several classes of costles materials were looked at including polyamides, silicones, polyurethanes, epoxies, I
and proprietary materials.
The coatings were judged according to their moisture permention, dielectric strength, heat resistance, strippability, end applicability. Based on these criteria, two materials were chosen as I
likely candidates for coating terminal blocks.
These were Red Clypt" insulating varnish which has been available for some time, and a new class of epoxy, cycloaliphatic epoxy, which has recently become I
commercially available.
The advantage of both of these materials is that they are one part systems and easily applied.
Red Clypt" dries by esposure to air and its maximum operating temperature is quoted in the manufacturer's catalog as 10?*C (710*F).
To test its ability to function at higher temperatures, copper substrates were coated with Red Glypt" and then baked for 10 to 180 minutes et 160*C (320*F).
The higher temperatures did not affect the resistivity of the material, however, it bens.me quite hard and some creep was observed.
1 In order to test the importance of film uniformity on resistance, other samples were coated by brushing Red Clypt" on to them with no attempt being made to achieve a uniform coating.
At 500 V applied potential, one sample experienced periodic breakdowns and another semple experienced corens discharge.
No breukdowns were observed on samples coated uniformly.
These breakdowns illustrate the importance of uniform coating since the material is too viscous to flow and provide a pinhole free film.
l
-108-1
The cycloatlphatic eposy is cured by esposure to ultraviolet light rather than by using an amine curing agent as is required for common oposy materials. This makes field application reasonably easy.
It also has reasonably good electrical properties measured at 150*C (302'F) and maintains these properties up to -180'C (356*F) which envelopes the IEEE 323 design basis temperatures.
To test the effectiveness of these two materials, four termir.Al blocks were coated with them, two with Red Clypt" and two with the opory.
To achieve a good coating, the metallic conducting parts of the terminal blocks were removed from the insulating material and otherwise conesaled surfaces were coated.
Such a procedure probably would n9t be possible in a fleid application. Wires were attached in a serpentine configuration identical to the electrical connections reported for the phase 1 Sandia tast.(1) Continulty though the desired conducting paths was verified and surface coatings were applied so that no electriisi continuity existed between the adjacent terminals and cable terminations.
These four terminal blocks were installed in a NEKA-4 enclosure along with two uncoated terminal blocks which acted as test controls. All terminal blocks were of the same make and model.
These terminal blocks were exposed to a saturated steam LOCA simulation profile which approximately followed the temperature profile recommended by 1 EEE-3 23-19 7 4, Appendix A.(37]
Figures 9-1 and 9-2 show the leakage currents of the Red Clypt" and epony coated terminal blocks respectively, as a function of time.
The control block leakage current traces are also included for comparison.
Basically the coated blocks performed like the unccated blocks. These results point to the fact that complete coatings were not achieved, and that leakage paths existed.
Post-test examination and diagnostic tests showed that the primary connection point between the metallic conductors and the phenolic insulation was the screw which attached the conductors to the phenolic.
In fact, the mating threads of the phenolle insulation were carbonized into a powder which appeared to enhance the connection between the metallic conductcrs and the insulation surface. The threeded mating surface of the screws, though originally ccated, were not coat.d at the end of the test.
Reinserting them into the phenolic probably removed the coating from the screw surface. The results of this test indicate that coatings applied under laboratory conditions do not achieve a significant improvement in terminal block perf ormance.
A field application would most likely be less perfect; hence we must conclude that conformal coatings, short of a complete potting, do not provide the desired improvement in terminal block performance.
A coating which was not investigated or tested is a spray of a silicone-based fluid.
Silicones are extremely hydrophobic and may inhibit film formation for some period of time.
Such a coating would not be permanent and would require routine recoating to maintain its protective quality. Further, the inrush of steam may strip the silicone from the surface and render it ineffective.
It may also have detrimental effects such as enhanced agglomeration and retention of dust and dirt.
-109-
10 1 i
i a
CONTROL (S) 100 i
Q
- 10_g RED GLYPT" COATED
<5 f
$10-2 w
Ca 10-3 o
i w
10-4 nED CLYPT" M
COATED
<w.J 10 -5 _
(
g % cNrnot 10-6 _.
C f
f INTRODUCTION UV I
OF STEAM 10-7
-0.05 0.00 0.05 0.10 0.15 0.20 RELATIVE TIME (hrs)
Figure 9-1: Cooperison of Leakago Currents for Red Glypt" Coated and Uncoated Te:1mina'. Biceks
a_s -
1 amumo m m -
1 10 l
~
O CONTROI.
1O EPOXY CO ATED Q10-1 E
l v
$ 10-2 u.I C
E D 10-3 I
o b
I EPOXY 7
10-4 COATED
$ 10-5 m
CONTRO!,
10-6 INTRODUCTION OF STEAM
{
/
-0.05 0.00 0.05 0.10 0.15 0.20 10-7 RELATIVE TIME (hrs)
Comperison of Leskege Currents for Cycloaliphatic Figure 9-2:
Epoxy Coated and Unconted Terminal Blocks i - - - -__
l7 I
~~10.0 ASSESSMENT~~
CRITEPIA The question asked at the outset of this effort was what are the failure and degradation modes of terminal blocks and what are thele effect on system performance. The answer, of course, is not simple or straightforward.
It depends on many compics and interacting factors.
This report and the report of the Sandla tests of terminal blocks (1) provide en insight into the performance of terminal blocks.
This report also illustrates some simple analyses which can be performed to define the effect of terminal blocks in various appilcations.
It is not the intent of this study to judge the safety significance of terminal blocks, but rather to provide the necessary technical bases to make a safety judgment.
The following paragraphs summarize the conclusions about terminal blocks which we believe are supported by the data obtained and the anslyses made.
Engineering judgments and recommendations are clearly noted as such.
10.1 Terminal Block Design Considerations The two basic designs of terminal blocks (sectional and one piece) do not appear to be radically different in their performance in a LOCA environment.
Although some sectional blocks did perform comparably to the one-piece blocks, other sectional blocks performed noticeably worse (one or two orders of magnitude) during the LOCA simulation.11) The materials from which terminal blocks are commonly made (phenolic and ceramle) do not appear to dramatically affect their performance during a LOCA environment.
This result arises because the primary mechanism for degrading terminal block performance (flim formation) is somewhat independent of the underlying insulation material of the terminal block, liowever, some dif f erence in film formation and continuity may result from differences in the surface wettability characteristics of the insulating material.
Thoagh we did n0t include radiation in any of the Sandia tests, evidence from industry indicates that it is good engineering practice to choose a fill material for the phenolic, such as glass or mineral, which is as radiation resistant as possibic.
Cellulose, a commonly used filler material, has a lower radiation resistance than glass or mineral fillers and may contribute to failure modes such as cracking or crazing or water absorption. These phenomena were not examined in the Sandia tests.
Terminal blocks are, by their very nature, convoluted surfaces with inaccessible cavities and interfaces.
For example, a hole may exist below the conducting plate to accommodate the screw which attaches the lug terminating the wire to the terminal block; or, in sectional designs the interface between adjacent sections is not accessible without disassembly of the terminal block unit.
Pcr these reasons, a thorough cleaning of the terminal olock surface, especially in at installed plant situation, may be difficult if not impossible to achieve.
Sandia's test of a " clean," one-piece terminal block further indicates that for our cleaning method (soaking in freon and deionized water), little improvement in performance over that of new, but uncleaned blocks can be expected.
-112-
Thus, for common term.nal block designs with highly convoluted surfaces, and inaccessible cavities and interfaces, cleaning may not be an effective method of reducing low level leakage currents that exist during exposura to a steam environment.
proper cleaning cannot make the situation worse, but it is douotful that it will reduce leakage currents to a level acceptable for most instrumentation and control applications.
The large, positive impact on terminal block perfornance that was originally believed te accrue f rom cleat.ing was not observed in the sandia tests.
During the Sandia tests, relatively intse emfs (0.01 mV to 0.5 V at
~0.1 sa) were observed to be generated within unpowered test units.* A possible explanation for theso emfs is oxidation-reduction reactions between dissimilar metals at f.he interfaces of the terminal block terminals, the ring-lugs, and the cable conductors. The addition of high temperature, conducting moierpre films provides the electrolyte necessary for these reactions to occur.
Cadmium sulfide was found as a residue on the terminal blocks at the conclusion of the Sandia tests, suggesting the possibility of salvanic reactions.** Emis may have significance to low power circuits such as thermocouples and points to a design / installation need for using metals with like cuidation patentinis and system components which will not form potentially detrimental compounds under accident conditions.
10.2 Testing Considerations The primary objective in testing components for nuclear power appilcations is to determine their performance in adverse accident environments. Using data obtained from these tests. analysis can determine the effect of component performance on t'*
.ystems. Thus, e<d (1) demonstrate qualifiestion testing of components has two objet that the equipment will perform its function in an accident situation; and (?) provide data that characterizes the component's performance in an accident situation. Thouf,h easily stated, achieving these objectives is less than trivial.
As a minimum, sufficient knowledge about the equipment's required functions must be known.o that relevant data can be collected and relevant acceptance criteria formulated. Also, knowing the g
function of the equipment allows one to put the failu.a modes into perspective. Test methods must be adequate to detect failure modes if they exist and to scnitor the performance of the equipment.
1he test unit consisted of the electrical cable, crimp type ring-lugs and the terminal block.
The cadmium source was the plating on a 1/4-20 nut used to attach the enclosure mounting plate to the NEKA-4 enclosure studs. The sulfur was hypotherized to be from the sodium thiosulfate added to the chemical spray solution or from the cable jacket materiel. The occurrence of Cds pott,ts to a system consideration tu assembling the terminal block-NEKA-4 enclosure unit:
even an innocuous nut or bolt somewhere in the unit may affect the performance of the unit in an l
accident environment.
-113-i
l The primary appilcation of terminal blocks in the nuclear power industry is in instrumentation and control circuits. Therefore, generic testing should be geared to this application.
For these applications leakage currents on the order of a fraction to a few mil 11 amperes can become significant to the operation of a circuit.
T!.us, test apparatus should be designed to obtain such data; the common practice of measuring leakage current with a 1 A or larger valued fuse provides no information about leakste currents less than i A.
Industry test reports indicate s
numerous failures of these fuses.
It is necessary to obtain low level leakage current data if analyses of the effects of terminal blocks are to be made.
If on-off power cycling is anticipated in the operation of a h
circuit (e.g., a motor circuit), then the ability to measure transler.c.
high levt1 leakuge currents and their duration should be part of the test.
Because film formation followed by Joule heating of the film may lead to film vaporization, higher potentials may actually lead to higher film resistances.
Thus, the te ting of terminal blocks at increased potentials for margin may actually be less conservative in termo of measuring terminal block performance than testing at actual use potentials.
Test environments must be such that they include the presture-temperature conditions expected to be present in the predominant accident sequences. This consideration is important since pressure in concert with temperature govern the conditions necessary to form and sustain a moisture film.
Tests which maintain superheat throughout the test are inappropriate unless superheat is expected throughout all possible accidents.
Thus, the practice of using Arrhenius techniques to compress accident exposures by elevating temperatures into superheated regimes does not test terminal blocks in saturated steam and condensing stean environments.
The seturated environments are commonly accepted as a predominant long-term accident environment.
Further, the use of Arrhenius techniques to accelerate. aging and accident simulations is based on the time-temperature superposition phenomenon of polymer chemical degradation; it has nothing to do with the primary failure mode of terminal bloc.ks--film formation and conduction through these flims.
In general, test methods and procedures must be germane to the application, and they must provide data for analyses of the effects of component performance on system performance.
To accomplish this goal, an understanding of the fallare and d?ce?.dation modes is required.
10.3 System Design Conriderati;ns Terminal blocks will affect the operation of instrumentatlori and control circuits.
proper utilization of terminal blocks is therefore a celtleal question in nuclent plant applications.
For high impedance circuits such as transmitters and thermocouples, terminal blocks can signifiesntly change the sensed output of the circuit.
A graphic illustration of the effect was presented in Figure 5.3.
RTD circuits are also important since they are the primary temperature monitoring device for the primary coolant system and the containment building.
Valve
-114-
circuits are not as susceptible as RTDs or high impedance circuits.
especially from an operability point of view, but the existence of power on a terminal block close to a valve may falsely provide power to valve indication lights.
The results would be erroneous valve position indications to an operator in the control room.
Motor circuits are relatively inmune to the effects of degraded terminal block operation, except to the extent that leakage currents may cause thermal overload protection devices or circuit breakars to trip.
L'afortunately, these effects will occur at the time when operators are under pressure to i
respond to a plant transiest and are inundated with alarms. They will most likely be performing activities of a higher priority tnan determining that circuit breakers have tripped or thermal overload protective devices have actuated. Thus, terminal blocks may affect motor circuit operation, though not directly.
The question of terminal block failure is one of relative magnitude of the effect. Clearly, if terminal blocks are to be used, then analyses specific to tl=
.pplication are required to insure that the circuit operation is not detrimentally affected.
Tha current method of terminal block installation appears to be as good as can be practically achieved. The NEKA-4 ehrlosures with a veep hole in the bottom protects the blocks from direct impingement of chemical spray and permits condensation to drain from the enclosure.
Based on the results of Sandia chemical spray and submergence data, the presence of spray external to the electrichl enclosuro does not significantly offect terminal block perfornance.
A logical measure to prevent condensed moisture and spray from penetrating the interstitial space between the cable and conduit and then uripping onto the terminal block would be to bring the cables into the enclosure from the side or bottom.
Top entry of cablen into the enclosure would not prevent moisture from dripping onto the terminal blocks.
Hermetically sealing the terminai block enclosures is probably an impractical solution. The chances of echieving good seals aroPnd all the cables where they enter the NEMA-4 enclosure or where the esbles entor conduit is remote.
Further, the NEKA-4 enclosures do not have good i
ability to withstand external pressurization for long parlods.
Depending on the pressurization rate, the maximum differential pressure that can be tolerated is 20 to 35 paid.
Hermetically *$211ag the enclosures also
[
creates a condition where, due to differential pressure, moisturo can be driven along the cables between the conductor and insulation ihto the
[
terminal block encic'dre. Since the cable insulation continues right up l
to the terminal block, the moisture could be driven onto the terminal i
block.
This " piping" phenomenon is commonly observed in both Sandia and industry tests of cables and terminal blocks where unspilced cables penetrate test chtsber boundarias. Therefore, hermetic sealing of terminal block enclosures is not advised, nor is it easily achieved.
-115-
. _. -. _ _ _ _. ~._.
-- : ver, Coatings were initially believed to be a feasible solution to i
terminal block leakage problems.
However, as with hermetic sealing, achievlog 6 good conformal coating, especially for already installed terminal blocks, wl'1 be almost impossible.
The test run at sandla to test two possible c stings showed no observable difference or delay between leakage currente observed on coated terminal blocks and unconted blocks. Thus, we do not believe that coatings are a viable means of limiting terminal block leaksge currents.
In conclusion leakage currents observed during 1.0CA testing of terminal blocks can cause erroneous indications and/or actions in low
-i power instrumentation and control circuits.- possible solutions such as cleaning, sealing, or costing do not appear to have the desired corrective effect, and hence two possible courses of action are apparent:
(1) analyte for the effects of terminal blockt in circuits and account for.these effects circuit designi or (2) remove terminal blocks from instrumentation and control applications.
If the first option is i
chosen. then quellfication activities should monitor leakage currents at levels appropriate to the application.
i I
E
-116-
~~11.0 CONCLUSION~~
S 1.
The primary application of terminal blocks la 'he nuclear power industry is instrumentation and control circuits.
2.
Terminal blocks receive minimal quality assurance attention in selection, installation, inspection and maintenance activities.
3.
Most Industry qualification tests do not continuously monitor for low level leakage currents durinf. LOCA simulation tests of terminal blocks. Without quantitative knowledge of these leakage currents, adequate analyses of their effects on instrumentation and control circuits cannot be performed.
j 1
4.
Surface moisture films are tlie most probable explanation for degradation in terminal block performance during esposure to a steam environment.
Because the existence of moisture flic.s is highly dependent upon environmental conditions, test environments must realistles11y reflect the predominantly expected accident environments. For example, superheated test conditions may not accurately represent the terminal blocks' performance.
5.
The 'Jse of voltage levels above actral use conditions in quellfication tests of terminst blocks may be nonconservative with respect to the measurement of low level leakage currents which are the primary Jegradation mode of termir.a1 blocks.
6.
Terminal block leakage currents in a steam environment may degrade performance of instrumentation and control circuits to j
an extent sufficient to cause erroneous indications and/or actions.
7 Cleaning wlli probably not reduce leakage curronts to a level acceptable for most instrumentation and control appilcations.
The large, positive impact on terminal block performance that was originally belicued to accrue from cleaning was not observed Further, terminal block leakage currents were not significantly reduced by the appilcation of either of two costings tested.
-117-i
4 l
~~12.0 REFERENCES~~
i 1.
C. Craft " Screening Tests of Terminal Block Performance in A blmulated LOCA Environment," NUREC/CR-3418, SAND 83 1617 Sandla National Laboratories August 1984.
2.
O. Stuetter " Electrical Insulators in a Reactor Accident Envi ronment," NUREC/CR-1682, S AND80- 195 7 Sandla National Laboratories January 1981.
3.
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Prepared by NUS Corporation, Clearwater, FL.
4 U. S. Nuclear Regulatory Comrission, " Equipment Qualification Data Dank,"
Prepared and operated for USNRC by Frank.lin Ra;earch Center.
August 1981.
(Vla Personal Communication with alli Booth USNRC/NRR/EQB August 20, 1981).
5.
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2.,
February, 1984.
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l 7.
The International Plastics Selector Book A 1978.
Estruding and Molding Grades, Cordura Pubilcations, Inc., 1200 Prospect Street, LaJolla, CA 92037.
4 8.
Personal Communication, Mr, Harold Heywood, Allen Br6dley Co., 6100 Industrial Court, Milwaukee, WI, September 22, 1981.
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" Terminal Block Technology," Catalog of Products, Circa 1901, Weldmuller Terminations Inc., 821 Southlake Blvd., Ulchmond, VA
~~23235, 10.~~
" Buchanan Terminal Blocks and Accessories," Catalog of Products.
Circa 1981, Amersee Corp., control Products Ulvision, 2330 Veuxhall R4., Union, NJ 07083.
11.
"2WM Terminal Block Materials," Product Data Sheet, Circa 1981, i
States Company. Multi-amp Corporation, 4271 L onze tky, Dallas, TK
~~75237, 12.~~
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b w
-118-
.. - - - - - -. - ~... - - -. - -.- ~ -...
. ~ -
D' i
14.
Franklin Research Center "Quellfication Tests of Tersinal block; and Splice Insulating Assemblies in a Simulated Lose of Coolant Accider.t Environment, Phase A and Phare B " FRC Reports F-C5022-1 and F-C5022 2, October 1978 and November 1978.
Prepared for Philadelphia Electric Company.
15.
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Wyle Laboratories Qualification Test Program for Terminal Blocks," Wyle Report 45603-1 Huntsville, AL, February 1982.
Prepared for Marathon Special Products.
17 Franklin Institute Research Laboratory, "Qualificallon Test Program f or Terminal Blocka," FRC Reports F-C4959, October 1978. F-C5205-3, October 1979, and F-A5385, October 1980.
Prepared for Weidmuller Terminations, Inc.
18.
Wyle Laboratories, " Loss of Coolant Accident Testing of Five Waldnuller Terminal Blocks for Washintton Public Power Supply System," Wyle Report $8687, Norco, CA, Jur.e 29, 1982.
Prepered far VoPSS and Weidmuller Terminations, Inc.
19.
Phonix Klemmen Documentation to support Qualification of Phonix Terminal Blocks, consirting of the following test reports:
a)
Bundesanstalt fur Materialprufung, Berlin, Test Reports 3.42/444 and 3.43/444-1 b)
Institute National des Radloelements. Fleurus, Belgium, Test Report Q. N. 21 and Q. h.
24 c)
Societe pour la Perfectionnement des '.interials et Equipments Aerospertiaux, Velity-Villacoubicy, France, Test Reports 1424633 and LV14711/1 J) Wyle Labor 6 tories, ScienLific Services and 3ystems Group Norco Facilsiy, California, Test Report 58610
~~/ O.~~
Wyle Lsbsratorie9, "Neelear Environmental Test Program on Four 0-2 Cedney Tonduit Sealing Bushing Assembiles, Two 0-2 Cedney condu!t Sat. ling Bushing /NAMCO Limit Switch Assenblies, and Two Marathon Fixed Barrier Terminal Block Assemblies," Wyle Report 45611-1, Huntsville, Alabara, February 24, 1982.
Prepared for Connonwealth Edison Co.
21.
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(
PEW-TR-83.
September 13, 1977, 22.
Westinghouse Electric Corporation, Letter from J. P. Boyd to F.
'J.
Chandler of TVA, dated Mtrch 9, 1978,
~~Subject:~~
" Data for Westinghouse Terminal Blocks."
-119-i l
23.
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Depart-hant of Cornerce, Washington, DC, 2/5/62.
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25.
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26.
Control Pro (pets Divistou, Attrace CorperCtion, Quality Assurance Manual, Appro*?vd C /li/82.
Control Products D171slen, 1065 Floral Avenue, Union, NJ 0T483, 27.
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28.
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29.
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31.
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32.
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33.
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-120-L
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36.
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39.
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6.,
~~December, l~~
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40.
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41.
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42.
Southwestern Laboratories, " Failure Analysis and Embrittlement Tests on Brass U clips," Report #2-591t-70 November 7, 1971.
Report to Multi-Amp Corporation by Southwestern Laboratories.
43.
L.
L. Bonton, et al.,"LOCA-Simulation Thermal-Shock Test of Sliding Link Terminal Blocks," NUREG/CR-1957, S ANDB1-0151. Sandia National Laboratories, May 1981.
44.
R. Hoffet, " Notes Concerning Temperature Measurement," Department of Mechanical Engineering Stanford University.
Prepared for ISA 29th International Instrument Symposium, May 7 5,1983.
45.
R. Reed, " Validation Diagnostics for Defective Thermocouple Circuits," TempelatureJt s Mea suremer.t and Control, Vol. 5. Part 7, 1902.
Published by Am(rican Institute of Physics.
46.
Omega Engineering, " Temperature Measurement Handbook," Omega Eng't ?ering, One Omega Drive, Don 4047, Stamford, CT 06407.
-121-
- - - ^
-- - - ~ ~ ~ ~ ^-"~ ~ ' ' ~ ^ " ' ~ ' ^ -\\
i 47.
relentific Engineerths and Manufacturing Company. "Sempac Metal Sheathed. Mineral Oxide Insulating Haterials," 11305 Varowen Street, l
North Hollywood, CA 91605.
48.
A. Williams and N. Wilde, "An Asbessment of Pressurized Water Reactor (PVR) Core Exit Thermocouples Durirg Accident and PJsf-Accident Situations," EGG ED-6*J61, Idaho National Engines ' int 1.aboratory, Idaho Falls ID, October 1983.
l 49.
Automatic Switch Co., "ASCO 3 and 4 Way solenoid Valves For Pilot Control of Diaphragm and Cylinder Operated Valves Used in Nuclear Power Plants," Catalog No. NP-1.
1978.
Automatic Switch Co., $0-56 Hanover Road, Florham Park, NJ 07932.
l 50.
General Electric Catalog, Control Switches and Accessories, 7165 Indicat ing 1. asps, Apell 11, 191.'.
I 51.
Could inc., Industrial Controla Division, "Could Industrial Control Controlfas 1982." Could Electronic and Electrical Products Catalog, j
861 Baltimore Blvd., Westminster, MD 21157.
j l
1 h
a 1
t I
f
-727 -
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DISTRIBUTION:
E Division of Techn! cal Information Atcmic Energy of Canada. Ltd.
j Chalk kiver Nuclear Laboratoriet
~
and Document Control NRC Distributton Contractor Chaik River. Ontario K0J IJO U.S. Nuclear Re6ulatory Commission CANADA j
15700 Crabbs Branch Way Attnt C. F. Lynch Rockville. KD 20850 Atomic Energy of Canada. Ltd.
!s 375 copies for RV 1600 Dorchester Boulevard ' Jest U.S. Nuclear Regulatory Commission Montreal Quebec H3H IP9
, i Electrical Engineer!ns and CANADA E
Instrument Control Branch Atin S. Nish
\\l Room 126 Bhabha Atomic Research Centre 5650 Nicholson Lane Rockvills, MD 20852 Health Physics Diviolon Attnt R. reit (10)
_BARC Bombay-85 INDIA Ansaldo Implanti Attn S. K. Mehta Centro Sperimentale del Boschetto
)
Corso F.M. Perrone. 118 British Nuclear Fuels Ltd.
16161 Genova Sprintfleids Works 17ALY Attnt C. Bottolo Salwick. Preston Lancs Ansaldo 7mplant!
ENGLAND Via Cabrlels D'Annunzio, 113 Attn W. G. Cunliff. Blds 334 j
1612A Cennva Brown Bovern Reaktor GMBH
-)
ITALY Attn S. Grifont Postfach $143 D-6800 Mannhelm 1 VEST CERMANY ASEA-ATOM Attnt R. Schemmel Department KRD
^
Box 53 Bundesanstalt fur Materialprufung S-721 04 Unter den Elchen 87 Vasteras D-1000 Berlin A5 SWEDEN Attnt A. KjellberS WEST CERMANY Attnt K. Wundrich ASEA-ATOM CEA/CEN-FAR Department TQD Departement de Surete Nucleatre Box 53 Service d' Analyse Fonctionnelle S-721 04 BP N' 6 Vasteras SWEDEN 92260 Fontenay-aux-Roses Attnt T. Granberg FRANCE Attnt M. Le Meur ASEA KABEL AB J. Henry P.O. Box 42 108 S-126 12 CERN Laboratorie 1 Stockholm CH-1211 Geneva 23 SWEDEN Attnt B. Dellby SWITZERLAND Attn H. Schonbacher
-123-
==
Canada Wire and Cable Lirsited Electricito da France Power & Control Products Divisicn Direction das Etudes et Recherches 22 Comercial Road Les Renardieres Toronto, Ontarlo JP N' 1 CANADA H40 124 77250 MORET SUR LORING Attn Z. S. Panirl FRANCE Attn Ph. Rousrarle Comissariat a l'Energie Atomique V. Detion ORIS/ LABRA J. Ribot BP N' 21 91190 Clf-Sur-Yvette EURATOM FRANCE Comission of European Comunilles Atta C. Caussens C.E.C. J.R.C.
J. Chenlon 21020 Ispra (Varase)
F. Carlin ITALY Atto:
C. hancin!
Commissarlat a l'Energie Atomique CEN Cedarche DPE/STRE FRAMATOME BP N' 1 Tour Flat - Cedex 16 13115 Saint Paul Let Durance 92084 l'arls La Defense FRANCE FRANCE Attn:
J. Campan Attn:
C. Chauvin E. Raimondo Conductores Monterrey. S. A.
P.O. Box 2039 Furukawa Electric Co., Ltd.
Monterrey, N. L.
Hiratsuka Wire Works HERICO 1-9 Higashi Yawata - 5 Chome Attn:
P. C. Murga Hiratsuka, Kanagawa Pref JAPAN 254 Electrictie de France Attn:
E. Oda Service 5tudes et Projets Thermiques et Nucleaires (S.E.P.T.E.N.)
Cese11schaft fur Reaktorsicherheit Tour EDF CDF (CRS) mbH Ceder N* 8 Clockengasse 2 92080 Paris - La Defense D-5000 Koln 1 FRANCE WELT CERMANY Attn:
M. Herouard Attn:
Library M. Hermant Health & Safety Executive Electricite de france Thames House North Direction des Etudes et Recherches Milbenk
~~1. Avenue du Ceneral de Gaulle London SW1P AQJ 92141 CLAMART CEDEX ENGLAND FRANCE Attn:~~
W. V. Ascroft-Hutton Attn:
J. Roubault L. Deschamps ITT Cannon Electric Canada Four Cannon Court Whitby, Ontarlo LIN SV8 CANADA Attn:
B. D. Va11111ee
-124-
_m Q 9 4 T' KraftweJk Union AG Imatran Voima Ly Department R361 Electrotechn. Department Hammerbecherstrasse 12 + 14 P.O. Boa 138 D-8524 Erlangen 8F-00101 Helsinki 10 VEST CERMANY r!NLAND Attna
1. Terry Attna B. Regne11 K. Koskinen Kraftwerk Union AC section R541 Institute of Radiatios Protection Postfach 1240 Dephetsent of Reactor Safety D-8757 Karlstein P.O. Box 268 WEST CERMANY 00101 Helsinki 10 Attn V. Siegler FINLAND Attn:
L. Reiman Kraftwerk Union AG Hanenerbacherstrasse 12 4 14 Instituto de Veterro110 y Diseno Postfach 3220 Ingar - Santa re D-8570 Erlanger, Avellaneda 3657 VEST CERMANY C.C. 348 Attn V F.orell 3000 Santa Fe REPUBLICA ARCENTINA Motor Columbus Attn:
N. Labath Parkstrasse 27 CH-5401 Japan Atomic Energy Research Institute l
Beden Takasaki Radiation Chemistry SWITZERLAND Research Establishment Attna H. Fuchs Watanuki-mach!
Takasaki, Cunma-ken National Nuclear Corporation JAPAN Cambridst Road Attn W. Tamura Whetstone K. Yoshida Leicester LE8 3LH T. Seguchi ENGLAND Attn A. D. Hayward i
Japan Atomic Energy Research Institute J. V. Tindale Tokai-Mura Naka-Gr.n NOK AC Baden Ibaraki-Ken Beznau Nuclear Power Plant 319-11 CH-5312 Doettingen JAPAN SVITIERLAND Attut Y. Koizumi Attn O. Tatti Japan Atomic Energy Research Institute Norsk Kabelfabrik Osaka Laboratory for 3000 Drammen Radiation Chemistry NDRWAY 25-1 Mil-Minami machi.
Attna C. T. Jacobsen i
Neyagaws-shi Osaka $72 Nuclear Power Engineering Test-Center JAPAN 6-2 Toranomon. 3-Chome Atta Y. Nakase Minato-ku No. 2 Akiyana Building Tokyo 105 JAPAN Attn:
S. Maeda 125-lL
Ontarlo Hydro Alabama Power Co.
700 University Avenue P.O. Box 2641 Toronto, Ontario M5C II6 Flintridge Blds B301 CANADA Birmingham, AL 35291 Attnt R. Wong Atta M. Lalor B. Kukre',1 Amerate Corporation Oy Stromberg Ab 2330 Vsushall Road Helsink! Works Union, NJ 07083 Box 118 Attn:
M. Marstelowlcz FI-00101 Helsinki 10 FINLAND Carolina Power & Light Co.
Attnt P. Paloniemi P.O. Bos 1551 Raleigh, NC 27602 Rappini Attn T. ?.11eman ENEA-PEC J. L. Harness Vla Arcoveggio 56/23 Bologna Combustion Engineering ITALY 1000 Prospect Hill Road Attn Ing. Ruggero Windsor, CT 06095 Attn J. Clatman Rheinisch-Westfa11scher Technischer Uberwachunge-Verein e.V.
Detroit Edison Postfach 10 32 61 2000 Second Avenue D-4300 Essen 1 Detroit, MI 48226 WEST CERMANY Attnt R. J. Seguin Attnt R. Sartori Duke Power Company Sydkraft P.O. Box 33189 routhern Sweden Power Supply Charlotte, NC 28242 21701 Malmo Attn:
B. Coley UVEDEN Attn:
O. Crondalen EDS Nuclear, Inc.
350 Lennou Lane UKAEA Walnut Creek, CA 94598 Materials Development Division Attnt C. Sellers Building 47 AZEE Harwell EC&G Idaho, Inc.
OION 0111 ORA P.O. Box 1625 ENGLAND Idaho falls. ID 83415 Attn D. C. Phillips Attnt A. Williams United Kingdom Atomic Energy Authority Farwell & Hendricks, Inc.
Safety & Reliabi'ity Directorate P.0. Box 209 Wigshaw Lane Milford OH 45150 Culchoth j
Atta:
J. R. Hendricks Warrington WA3 4NE ENGLAND Marathon Special Products l
Atta:
M. A. H. C. Alderson P.O. Box 468 i
Bowling Creen, OH 43402 i
Waseda University Atto H. Black Department of Electrltal Engineering 4-1 Ohkubo-3, Shinjuku-ku Tokyo JAPAN Attn:
E. Yahagi
-176-
Phonis Terslaal Blocks, Inc.
Yankee Atomic Electrle C3.
1900 creenwood street 1671 Worcester Road Narrisbur5, PA 17104 Framinghna, MA 01701 l
Atta D. B. Springer Attas D. Hansen Portland General Electric 1870 R. E. When 121 SW salmon street 7165 J. R. Gover Portland, OR-97204 71$$
~~0. M. Stietter Attna~~
~~0. L. Johnson (2) 6400 A. W. snyder-6410 J. W. Hickman Rochester Ces and Electric Corp.~~
6417 D. D. Carlson 6470 J. V. Walker 89 East Avenue Rochester. NY 14149 6430 W. R. Ortla Atto G. S. Lint 6440 D. A. Dahlgren 6447 W. A. Von Blesemann Stone and Webster Engineering Corp.
6445 J. H. Lineberger 644$
L. D. Bustard 245 Summer Street Boston, KA 07107 6445 C. M. Craft (25)
Attat H. V. Redgate 6445 D. 7, Purgal 6445 M. J. Jacobus i
(446 L. L. Bonton Temple University 6446 P. V. Those Department of Chemistry i
Philadelphia, PA 19177 6447 D. L Berry Attnt R. E. Salomon 6450 J. A. Seuscher 3141 C. M. Ostrander ($)
3151 W. L. Carner The States Company 8424 M. A. Found 4271 Bronze Way Dallas. Texas 75737 Attnt W. C. Wright TRW Cinch Connectors 1500 Norse Avenue Elk Grove Village. IL 60007 Atta R. M. Pontone YEPC0/0JRP-5 P.O. Box 26666 Richmond, VA 23761 Attnt C. Smith Washington Pubile Power supply System 3000 George Washington Wey Nall Drop 981T Richland, WA 99352 Attat C. 2eamer 9
Weldmuller Terminations, Inc.
371 Southlake Boulevard Richmond, VA 73735 Attat J. N. Tyler i
Westingh9 usa Hanford Co.
P.O. Sox 1970 Richland, WA +9352 Atto:
P. Cat.not.
-127-4 y
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i NUREG/CR-3691 mas.**. sm NY Bl8L10 GRAPHIC DATA SHEET SAND 84-0422 c: isweve. o.,-i.s vi.it i.i i... ix..
i AN ASSr.SSMENT Or TERMINAL BLOCKS IN TifE NUCLEAR POWER INDUSTRY l
.o July 1984
...$ -e.
ic Charlec M. Craft i
i
.oe.
September 1984 j
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........ 6 o.. 4. i..... i.. &... s... a. m..,,, t.
Sandia National Laboratories Division 6445 P.O. Box 5800 A-1327 Albuquerque, New Mexico 87185
...i........*,
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Division of Facility Operations Office of Nuc1 car Regulatory Research U.S. Nuclear Regulatory Commission
.... c o c a. i.. o......
Washington, DC 20555 o
...........oisi i,
i..c i a.
The primary appilcation of terminal blocks in the nuclear power Industry is instrumentation and control (16C) circuits.
The performance of t.hese circuits can be degraded by low level leakage currents and low insulatloa-resistance (IR) between conductors or to ground.
Analyses of these circulta show that terminal
~~blocks, when esposed to steam environments.~~
experience Irakage currents and low surface IR levels suf ficient to a'fect some I&C appilcations.is Since the mechanism reducing surf ace IR (conductive surf ace moisture filmA) primarily controlled by external environmenta? ' f actors. the degradstion of terminal block performance is mostly independent of terminal block ds.!gn.
Testing shows that potential methods of reducing surf acw leakaga :urrents will not reduce them sufficiently to prevent terminal blocks from affecting I&C circuits.
Therefore.
terminal blocks can cause erroneous indications or actions of the I&C circuits in which they are a component. Most of the present qualification tests of terminal blocks do not address the issue of low level leakage corrents, and hence do not demonstrate that terminal blocks will opers'.e properly in I&C circuits.
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ML20118A138

Text

1.0 INTRODUCTION

1.1 Background

RESPONSE

350 0 Rg

0.0072 A 1relay

10.0 ASSESSMENT

11.0 CONCLUSION

12.0 REFERENCES

Subject:

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