ML20008F789

Adequacy of Station Electric Distribution Sys Voltages, Palisades Plant, Informal Rept for Apr 1981

ML20008F789
Person / Time
Site:	Palisades
Issue date:	04/30/1981
From:	Udy A EG&G IDAHO, INC., EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6429 EGG-EA-5417, NUDOCS 8105120053
Download: ML20008F789 (15)

Text

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=- INTERIM REPORT Accession No.

Report No. EGG-EA-5417 Contract Program or Project

Title:

Selected Operating Reactor Issues Program (IIT)

• Subject of this Document:

Adequacy o' Station Electric Distribution System Voltages, Palisades Plant, Docket No. 50-255 TAC No. 12780 Type of Document:

Informal Report t

Author (s): I A. C. Udy 6 J i OS6 arch and Technica!

Date of Document:

Assistance Rert April 1981 Responsible NRC Individual and NRC Office or Division:

Paul C. Shemanski, Division of Licensing This document was prepared primarily for preliminary or internal use. it has not raceived full review and approval. Since there may be substantive changes, this document should not be considered final.

EG&G Idaho, Inc.

Idaho Falls, Idaho 83415 Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.

Under DOE Contract No. DE-AC07 761D01570 NRC FIN No. A6429 INTERIM REPORT fr/05'/2.OC 53

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES PALISADES PLANT Docket No. 50-255

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April 1981 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.

Draft 4/1/81 TAC No.12780

ABSTRACT The Nuclear Regulatory Commission has required all licensees to analyze the electric power system at each nuclear station. This review is to ueter -

mine if the onsite distribution system in conjunction with the offsite power -

sources has sufficient. capacity and capability to automatically start and operate all required safety laids within the equipment voltage ratings.

This Technical Evaluation Report reviews the submittals for the Palisades

~

Pl ant. .

The offsite power source!, in conjunction with the onsite distribution system, have not been shown to have sufficient capacity and capability to automatically start as well as continuously operate, all required safety-related loads within the equipment rated voltage limits in the event of either an anticipated transient or an accident condition.

FOREWORD This report is supplied as part of the " Selected Operating Reactor Issues Program (III)" being conduct?d for the U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Licensing, by EG&G Idaho, Inc., Reliability and Statistics Branch.

l l The U.S. Nuclear Regulatory Commission funded the work under the authorization, B&R 20 19 01 06, FIN No. A6429. -

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CONTENTS 1.0 I N TR OD UC T I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2.0 D ESI GN B AS I S CRI T ERI A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3.0 SYST EM D ES C R I PT IO N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

. 4.0 ANAL YS I S D ES CRI PT IO N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1 Design / Operation Changes ..................................... 4

4.2 An a l ys i s Con d i ti o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.3 An al y s i s Re s u l ts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.4 An a l y s i s Ve ri fi c a ti o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.0 E V A L U AT I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.0 CO NC L U S I O N S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.0 R E F ER E NC E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 FIGURE

1. Pal isades pl ant el ectri cal singl e-l ine diagram . . . . . . . . . . . . . . . . . . . . 3 TABLE

1. Class lE Equipment Voltage Ratings and Analyzed Worst Ca se Load Te rminal Vol tages . . . . . . . . . . . . . . . . . . . . . . . . 5

2. Comparison of Analyzed Voltages and Un dervol tage Rel ay Se tpoi nts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 D

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES PALISADES PLANT

1.0 INTRODUCTION

An event at the Arkansas Nuclear One station on September 16,1978 is e described in NRC IE Infomation Notice No. 79-04. As a result of this event, station confomance to General Design _ Criteria (GDC) 17 is being questioned at all nuclear power stations. The NRC, in the generic letter of August 8,1979, " Adequacy of Station Electric Distribution Systems Volt-ages," I required each licensee to confim, by analysis, the adequacy of the voltage at the class 1E loads. This letter included 13 specific guide-lines to be followed in detemining if the load terminal voltage is ade-quate to start and continuously operate the class 1E loads.

Consumers Power Company (CPCo) responded with analyses of January 9, 1980,2 and March 7, 1980.3 Information on required testing was sup-plied on July 18, 1980.4 Subsequent concerns were addressed in letters dated August 22, 1980,5 February 9, 1981,0 and March 3, 1981.7 Mditional information was obtained in letters of October 2, 1978,8 and February 27, 1980,9 and in the Palisades Plant Final Safety Analysis Report (FSAR).

Based on the infomation supplied by CDCo, this report addresses the capacity and capability of the onsite distribution system of the Palisades Plant, in conjunction with the offsite power system, to maintain the vol-e tage for the required class 1E equipment within acceptable limits for the worst-case starting and load conditions.

2.0 DESIGN BASIS CRITERIA The positions applied in determining the acceptability of the offsite voltage conditions in supplying power to the class IE equipment are derived

from the following

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1. General design Criterion 17 (GDC 17), " Electrical Power Systems,"

of Appendix A, " General Design Criteria for Nuclear Power Plants,"

of'10 CFR 50.

2.- General Design Criterion 5 (GDC 5), " Sharing of Structures, Sys-tems, and Components," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.

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3. General Design Criterion 13 (GDC 13), " Instrumentation and Con- '

trol," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.

4. IEEE Standard 308-1974, " Class 1E Power Systems for Nuclear Power Generating Stations."

5. Staff positions as detailed in a letter sent to the licensee, dated August 8,1979.I

6. ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equipment (60 Hz)."

Six review positions have been estab1'shed from the NRC analysis guide-lines land the above-listed documents. These positions are stated in Section 5.0.

i 3.0 SYSTEM DESCRIPTION l

Figure 1 is a simplified sketch of the unit electrical one-line dia-i gram.4,8 2400V Class IE Buses 1C and 10 can be supplied by either station ~

• poder transf omer (SPT) 1-2, startup transfomer (SVT) 1-2, or the reserve transformer via 4160V Bus 1F. Technical specifications require that both '-

SPT 1-2 and SVT 1-2 be operable before and during operation; however, no i specific restriction on the use of cr on the availabilii.i of the reserve transfomer is found in the technical specifications.

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345 KV T

SWITCHYARD VIA MAIN TRANSFORMER 345 KV SWITCHYARD

$ /\ A / s' STATION POWER WW STARTUP W W STARTUP WW TRANS.- -

-TRANS.

TRANS. Oq -rq 1-1 FG FG 1-3 FQ PG 1-1 r

C t

U:

'l' BUS 1A BUS 1B 'f' ' f BUS 1F l BUS 1G 4160V 4160V 4160V 4160V 0

RESERVE U TRANSFORMER mm STARTUP TRANSFORMER STATION POWER O 2

.NO TRANSFORMER o NC 1-2 m i

DG DG l-2 I l -

, o C 0 C 0 0 C 0 i

BUS 1E BUS 1D . Btc 1C 2400V 2400V 2400'!

CLASS lE CLASS IE C_

i BREAKERS SHOWN ALIGNED FOR PREFERRED OFFSITE POWER men nnqq I

l ' BUS 12 i BUS 11 480V 480V CLASS lE CLASS lE PALISADES UNIT ONE LINE DIAGRAM FIGURE 1 i

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480V Class 1E Buses 11 and 12 are supplied by independent transfomers from Buses 1C and 1D, respectively. The four 120V preferred ac buses are nomally powered by battery-supplied inverters; however, the FSAR, Section 8.3.5.2, indicates that a backup regulator, powered by the 120V instrument ac bus, is the backup source for all four of the 120V preferred ac buses.

Tne 120V instrument bus is powered by a transfomer connected to 480V Bus 11 or Bus 12.

There cre cadervoltage relays on both 2400V Buses 1C and 10.2 These --

relays separate the Class 1E buses frm offsite power should there be a degradation of offsite power, and init. ace sequencing onto diesel power.

There is a single transmission feeder from the 345kV switchyard to the three startup transfomers.6 CPCo supplied the equipment operating ranges identified in Table 1.

4.0 ANALYSIS DESCRIPTION 4.1 Design / Operation Changes. The voltages shown on Table 1 are based on the licensee changing the taps on Transfomers 11 and 12 to the i 2400Y setting. This has been accomplished in 1979.7 4.2 Analysis Conditions. CPCo has determined that the minimum expec-ted offsite grid voltage is 327.75kV (95% of 345kV). CPCo has not supplied the maximum expected offsite grid voltage.

CPCo has analyzed each offsite source to the onsite distribution sys-tem under extremes of load and offsite voltage conditions to determine the

• teminal voltages to 1E equipment. The worst case class 1E equipment ter-minal voltages occur under the following conditions: .

l 1. The minimum expected continucus load teminal voltages occur when the grid is minimum and the startup transfomers suply the maximum expected class 1E and non-class 1E loads. Startup transfomer 1-2 will be supplying all class IE loads.

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TABLE 1 CLASS lE EQUIPENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES (% of nominal voltage) ~

Maximum Minimum Analyzed Equic'nent Condition Rated Analyzed Rated Steady State . Transient 2300V Motors Start -- --

a --

73.4

. Operate 110 106.6 90 91.1 --

460V Motors Start -- --

a --

51 . 4

. Operate 110 103.3 90 82.7 --

440V Motors Start -- --

a --

53.8 Operate 110 108.0 90 86.5 --

480V Starters Pickup -- --

85 80.9 53.4 Dropout -- --

50 --

53.4 Operate 125 99.0 50 80.9 --

Other Equipmentb

a. Rated starting voltages for motors were not supplied. CPCo supplied speed-torque curves for typical motors in lieu of this data. The curves supplied showed a single curve for an unspecified voltage. It is impossible to detemine this value from the CPCo-supplied infomation. However, CPCo indicates that the motors will start with the grid at 345kV. CPCo has not made such a statement with the grid at 327.75kV (95% of nominal).

b. Other equipment includes battpry chargers, rated to full output voltage at an input voltage down to 432V/ The output voltage decreases below this input voltage. Should the output voltage be reduced below the battery voltage, the battery will supply the de loads; however, how long this con-i dition will go uncorrected is not a part of the unit technical specifica-

! ti en s. Tne four 120V ac preferred instrument buses can be powered by the 120V ac instrument bus. CPCo did not supply any infomation for these instruments or expected voltage levels.

2. The minimum expected transient load terminal voltages occur when the offsite grid is minimum and an accident trips the unit gener-ator and initiates the simultaneous start of all the safety injection loads at an initial assumed power factor of 0.2.

3. CPCo identified the condition: that lead to a maximum continuous bus voltage as "nomal grid and generator voltage extremes."O l

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CPCo has not provided an appropriate analysis for use of the reserve transfomer, statirg that it has "no normal operating conditions or automatic loading schemes."7 4.3 Analysis Result. Table 1 shows the projected worst case class 1E equipment teminal voltages.

i 4.4 Analysis Verification. CPCo providad testing to verify the accuracy of their analysis.4 All metering was within 21/2% accuracy. ~

The test consisted of measuring loads and voltages and calculating corres-ponding voltages for the same grid and load conditions. The deviation between the measured and the test calculation voltages was within +1.07%_,

for all buses. ,

5.0 EVALUATION Six review positions have been established from the NRC analysis guide-lines land the documents listed in Section 2.0 of this report. Each review position is stated below followed by an evaluation of the licensee submi ttal s. The evaluations are based on completion of changes described in Section 4.1.

Position 1--With the minimum expected offsite grid voltage and maximum load condition, each offsite source and distribution system connection combination must be capable of starting and of continuously operating all class 1E equipment within the equipment voltage ratings.

CPCo has not supplied evidence to show the capability of the class lE motors to start under accident conditions concurrent with the offsite grid at 95% of nominal.

CPCo has shown (Table 1) that the 460V and 440V motors and the 480V battery chargers do not have sufficient voltage to operate continuously when the offsite grid is at 95% and the unit loads are maximum. Moreover, Table 1 shows that the 480V starters will not start additional loads, which may be required by the accident condition, at these expected steady-state 6

vol tages. Additionally, CPCo has not shown that the instruments needed in an accident situation will have adequate voltage for correct readout when the voltages are at this level.

CPCo has shown, by analysis, that the Palisades Plant does not have sufficient capability and capacity for starting and continuously operating the class 1E loads within the equipment voltage ratings (Table 1). -

- Position 2--With the maximum expected offsite grid voltage and minimum load condition, each offsite source and distribution system connection combination must be capable of continuously operating the requin!d class lE equipment without exceeding the equipment voltage ratings.

CPCo has shown, by analysis, that the voltage ratings of the class IE ,

equipment will not be exceeded.

Position 3--Loss of offsite power to either of the redundant class lE dis tribution systems due to operation of voltage protection relays, must not occur when the offsite power source is within expected voltage limits.

As shown in Table 2, the degraded grid voltage relay setpoints are higier than the minimum expected continuous operating voltage for the 2400V buses. Additionally, the time delay for the degraded grid undervoltage relays may not be sufficient to prevent the loss of the offsite source l during the start of tne safety injection loads. CPCo has not identified the duration of this transient condition when the offsite grid is 95% of noainal. Further, since no voltage or time tolerances have been provided by CPCo for either the degraded grid or the loss of grid relaying, all of

_ the setpoints could be challenged. From the infonnation supplied by CPCo, it appears that there is r. potential of spurious separation of the class lE

. buses from the offsite source with ef '.aer set of relays when nonnally expec-ted vol tages are present.

I Position 4--The NRC letter requires that test results verify the accuracy of the voltage analyses supplied.

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TABLE 2 COMPARISON OF ANALYZED VOLTAGES AND UNDERVOLTAGE RELAY SETPOINTS

(% of nominal voltage)

Minimum Analyzed" Relay Setpoint' Location / Relays Voltage Time Voltage (Tolerance) Time 2400V bus Degraded grid 87.3 continuous 91 6.5 s '

1 Loss of grid 70.3 4.5 sc 70 0.5 s

a. Licensee has detemined by analysis the minimum bus voltages with the-offsite grid at the minimum expected .oltage and the worst case plant and class lE loads.

b. Tolerance not identified by CPCo.

c. Based on a grid voltage of 100%. CPCo has not identified the duration of the voltage recovery for the worst case transient condition (grid at 95%

and the simultaneous start of all the safety injection loads).

CPCo has supplied the required infomation which shows the analysis to be an accurate rep esentation of the worst case voltage conditions for the class 1E buses and ' cads.

Position 5--No event or condition should r' ult in the simultaneous or consequential loss of both required cirtuits from the offsite power network to the onsite distribution system (GDC 17).

CPCo does not meet the General Design Criteria (GDC) 17 requirements for two independent circuits from a minimum of two offsite power sources.

The switchyard that supplies the Palisades Plant is located 0.5 mile away from the unit. All three startup transformers (and, hence, the reserve transfomer) are supplied power by a single' overhead transmission from the switchyard. The feeder has a single disconnect device (#24R2) and no individual circuit breakers or isolation switches (per Palisades Drawing WD 1421).

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CPCo justifies the departure from the GDC 17 requirements based on a low probability of losing both diesel generators and the offsite source simultaneously. CPCo identifies this probability as 2.9 x 10-6 (per year) . This figure is arrived at by multiplying the probability (0.0029/ year) of losing the single circuit to the switchyard by the prob-ability (10-3) of both diesels failing to start (units not identified,

- but WASH-1400 identifies this as per attempt). CPCo does not identify the

[

number of attempted diesel starts per year. The probability of losing the

- single cin:uit to the switchyard (0.0029/ year) is based on an outage of five minutes or more.7 GDC 17 does not condition outage rates only for durations of five minutes or longer.

The CPCo analysis did not take into account the probability of the failure of the switchyard bus, of component failure leading to the failure of the bus, of startup transformer failure (there is no evident means to disconnect a faulty transfonner from the feeder circuit), of the disconnect switch failure, or of component failure that contributes to failure of the switch.

Position 6--As required by GDC 5, each offsite source shared between units in a multi-unit station must be capable of supplying adequate starting and operating voltage for all required class lE loads with an accident in one unit and an onierly shutdown and cooldown in the remaining units.

This applies to multi-unit plants. It does not apply to the Palisades Plant, a single-unit station.

6.0 CONCLUSION

S.

' The voltage analyses submitted by CPCo for the Palisades plant were evaluated in Section 5.0 of this report. The change described in Section 4.1 has been completed, and it was found that:

1. Voltages within the operating limits of the class lE equipment are not supplied for all projected combinations of plant load and offsite power grid conditions.

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2. The test used to verify the analysis ~ shows the analyses to be an accurate representation of the worst case conditions analyzed.-

3. CPCo has potential for ei ther a simultaneous or consequential loss of both offsite power sources. They have not provided adequate justification to be exempted from this GDC 17 req'airement-

4. Loss of offsite power to class lE buses, due to spurious opera-tion of voltage protection relays, can occur with the offsite .

grid voltage within its expected limits.

I recomend that the NRC require CPCo to impose operative restrictions on the reserve transformer to prevent it from being overloaded to the point tnat inadequate voltages would be supplied to the class lE loads.

7.0 REFEREEES

1. NRC letter, William Gamill, to All Power Reactor Licensees (Except Humboldt Bay), "Mequacy of Station Electric Distribution Systems Voltage," August 8,1979.

2. CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula-tion, NRC, "Mequacy of Station Electric Distribution Systems Vol t-ages," January 9,1980.

3. CPCo letter, Roger W. Huston, to Director of Nuclear _ Reactor Regula-tion, NRC, " Response to Mequacy of Station Electric Distribution Systems Voltages," March 7,1980.

4. CPCo letter, Steven R. Frost, tc Director, Nuclear Reactor Regulation, NRC, " Response to Verification of Analytical Models for Mequacy of Station Power," July 18, 1980.

5. CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula-tion, NRC, " Response to Mequacy of Station Power," August 22, 1980. l

6. CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula- -

tion, NRC, " Response to Station Electric Distribution System Volt-ages," February 9,1981.

7. CPCo letter, Steven R. Frost, to Director, Nuclear Reactor Regulation, NRC, " Response to Mequacy ef Station Electric Distribution System Voltages," March 3,1981.

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8. CPCo letter, David P. Ibffman, to Director, Nuclear Reactor Regula-tion, NRC, " Response to Emergency Supply Generic Issues," October 2, 1978.

9. CPCo letter, Steven R. Frost, to Director, Nuclear Reactor Regulation, NRC, " Response to Mditional Infomation for Degraded Grid Voltage,"

February 27, 1980.

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