ML19351D897

Adequacy of Station Electrical Distribution Sys Voltages, Technical Evaluation Rept,Revision 1

ML19351D897
Person / Time
Site:	Three Mile Island
Issue date:	10/31/1980
From:	Roberts E EG&G IDAHO, INC., EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
EGG-EA-5258, NUDOCS 8011200346
Download: ML19351D897 (13)

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INTERIM REPORT Accession No.

Report No. EGG-EA-5258. Rev. 1 C::ntract Program or Project T:tle:

Electrical, Instrumentation and Control System Support Subject of this Document:

Adequacy of Station Electrical Distribution System Voltages, Three Mile Island Nuclear Station Unit 1

. Type of Document:

Technical Evaluation Report Author (s):

E. W. Roberts Dite of Document:

October 1980 RIsponsible NRC Individual and NRC Office or Division:

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

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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. A6256 INTERIM REPORT

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TECHNICAL EVALUATION REPORT ADEQU1CY OF STATION ELECTRICAL DISTRIBUTION SYSTEMS VOLTAGES TIIREE MILE ISLAND NUCLEAR STATION UNIT 1 Docket No. 50-289 October 1900 E. W. Roberts Reliability and Statistics Branch Engineering Analysis Division EG6G Idaho, Inc.

TAC No. 11962 Revision 1, 10-20-80 1

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4 ABSTRACT The Nuclear Regulatory Commission has required all licensees to analyze the electric power system at each nuclear station. This review is to deter-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 loads within the equipment voltage ratings.

This Technical Evaluation Report reviews the submittals for the Three Mile Island Nuclear Power Station, Unit 1.

The offsite power sources, in conjunction with the onsite distribution system, has been shown to have suf ficient capacity and capability to auto-matically 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.

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FOREWORD This report is supplied as part of the selected Electrical, Instru-mentation, and Control Systems (EICS) issues program being conducted for the U.S. Nuclear Regulatory Commission, Of fice of Nu lear Reactor Regula-tion, Division'of Operating Reactors, by EG&G Idaho, Inc., Reliability and Statistics Branch.

The U.S. Nuclear Regulatory Commission funded the work under the auth-orization entitled " Electrical, Instrumentation, and Control System Sup-port," B&R 20 19 01 03, FIN No. A6256. .

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'C0F4ENTS

1.0 INTRODUCTION

...................................................... 1 2.0 DESIGN BASIS CRITERIA ............................................. 1 3.0 SYSTEM DESCRIPTION ................................................ 2 4.0 ANALY S I S D ES C R I P T I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4.) Design / Operation Changes ..................................... 2 4.2 Analysis Conditions .......................................... 2 4.3 Analysis Results ............................................. 2 4.4 Analysis Verification ........................................ 5 5.0 EVALUATION ........................................................ 5

6.0 CONCLUSION

S ....................................................... 6 7.0 R E FE R E N C E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 FIGURE

1. TML electric distribution ......................................... 3 TABLE ~

1. Class IE Equipment Voltage Ratings'and Analysed Worst-Case Terminal Voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

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, TECHNICAL. EVALUATION REPORT ADEQUACY OF STATION ELECTRICAL DISTRIBUTION SYSTEM VOLTAGES THREE MILE ISLAND NUCLEAR STATION UNIT 1

1.0 INTRODUCTION

An event at the Arkansas Nuclear One Station on September 16, 1978 is described in NRC IE Information Notice No. 79-04. As a result of this event, statior conformance 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 Distribution Systems Voltages,"1 required each licensee to confirm, by analysis, the adequacy of the voltage to the class IE loads. This letter included 13 guidelines for the analysis.

In response to the NRC generic letter, Metropolitan Edison Company (Met-Ed) submitted a voltage analysis on October 16, 19792 . Because of determined voitage problems, Met-Ed proposed design and procedural changes in their May 15, 1980 letter. Also included was a voltage analysis based on these changes.

Based on the information supplied by Met-Ed, this report addresses the capacity and capability of the onsite distribution' system of the Three Mile Island Nuclear Station Unit 1 (TML-1), in conjunction with the offsite power system, to maintain the voltage for the required class IE 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:

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' (CDC 5), " Sharing of struc-tures, Systems, and C uponents," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50,

3. General Design Criterion 13 (GDC 13), " Instrumentation and Control," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.

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

5. Staff positions as detailed in a letter sent to the licensee, dated August 8, 1979.1

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

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Six review positions have been established from the NRC analysis guide- .

lineal and the above-listed documents. These positions are stated in Section~5.

3.0 SYSTEM DESCRIPTION A single-line diagram of the AC class IE electrical system at TMI-l is shown in Figure 1. The THI-l class lE electrical distribution system is fed by two auxiliary transformers which are connected to different 230kV substation buses and provide the source of power for startup operation and shutdown requirements . Each of the unit auxiliary transformers has two isolated secondary windings, oae at 6900v and one at 4160V. The 4160V windings supply the class IE distribution systems.

4.0 ANALYSIS DESCRIPTION 4.1 Design / Operation Changes. Met-Ed submitted analyses 2,3 based on the following proposed changes:

1. The taps on the auxiliary transformers (UAT 1A, UAT IB) will be changed from 230 kV to 224.75 kV.

2. Trip functions will be removed from 480 V bus relays. -

3. Designated loads will be automatically tripped upon ,

initiation of an ES signal.

4. Installation of new undervoltage relays with new set-points in place of existing electromagnetic-type relays for both first and second 1cvel.

5. Institute new procedures to preclude starting either a condensate or a condensate booster pump durinh the ES block loading sequence.

All of the described modifications and procedural changes will be completed prior to the next TMI-l startup.

4.2 Analysis Conditions. The following conditions were considered in the review:

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1. The maximum voltage drop between the 4160V and 4800v buses /MCCs and connected equipment is 0.02% and 1.0%,

respectively. All voltages shown in this report are equipment terminal voltages expressed as percentages of the respective equipment nominal voltage. ~

2. Automatic tripping of Bus IN and designated loads upon .

ES actuation was assumed; manual load shedding was not.

4.3 Analysis Results. Table 1 summarizes the comparison of the class IE equipment voltage ratings and the Met-Ed analyzed worst case ter-minal voltages for 4160', 480 and lower voltage equipment.

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CLASS lE EQUIPMENT VOLTACE RATINGS AND

• ANALYZED WORST CASE TERMINAL VOLTACES

{% of nominal voltage)

Maximum Minimum Analyzed Equipment Condition Rated Analyzed Rated Steady State Transient 4000V Motors Start -~ --

80.1 --

81 Operate 110 110 90 92 --

460V Motorsb Start -- --

75 --

77 Operate 110 111 86 87 --

430V Starters Operate 110 106 82 84 --

Pickup -- --

75 --

75 Dropout -- --

55 --

75 Below 480V 110 c 90 c c

a. Revision 1, 10-20-80. ,

b. All 460V motors have a service factor of 1.15. Because of this, Met-Ed has demonstrated, utilizing IEEE Standard 141-1976 and NEMA Standard MGI-12.42, that no thermal damage to the motor will occur if the motor is continuously operated 14% below the nominal voltag. with the ambient temperature below 4000 and motor loading at or below the nameplate rating.

c. No terminal voltages analyzed. All lower voltage class IE loads are supplied from +15% regulated trans formers.4,5,6 The Met-Ed analyses have determined that the worst-case steady-state low-voltage condition occurs with the offsite grid at minimum voltage, one auxiliary transformer supplying maximum plant loads, and both ES trains with the largest ES load demand. Under these conditions, the analyzed minimum terminal voltages for equipment supplied by the class IE 4160 and

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480V buses is 92% for the 4160V ID and IE buses and 87% for the 480V bus IAES VCC. All other 480V bus-supplied equipment have higher voltages.

The worst-case low-voltage transient condition occurs with the above load and grid voltage and the simultaneous manual restart of the condensate -

and booster pumps. The resulting equipment terminal voltages for class IE

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equipment supplied by 4160V bus ID and 480V bus IE are 81% and 77%, respec-tiveF The transient voltages will return to steady state values within .

ten - conds as the pump motors come up to speed.

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1 The Met-Ed analyses have determined that maximum voltages of 111% and 110% will occur on the respective 48t and 4160V buses with a maximum grid voltage and a minimum load on the plant buses.

4.4 Analysis Verification. Med-Ed had previously determined by measurements the actual worst case voltage drops between buses /MCCs and loads for 4160 and 480V bus loads. Therefore, Met-Ed's verification test was only conducted to verify the analyzed bus voltages.

The Met-Ed verification method required the measurement of the grid voltage and IE bus /MCC loads, phase angles, and voltages. Using the measured grid voltage and bus /MCC loading, all 1E bus /MCC voltages were calculated using the analysis methods. The measured and calculated bus /MCC voltages were then compared.

Met-Ed provided the test data and results of their test verification with their May 5, 1980, submittal. The 4160V buses were loaded over 30%.

However, during the. tests only four 480V IE buses were loaded to 30% of their analyzed loading with all IE 480V buses /MCCs loaded less than 1%.

The results of their voltage comparison indicate thae the analysis voltages are within 4% of the measured voltages for all IE buses /MCCs.

. 5.0 EVALUATION Six review positions have been established from the 13 NRC analysis guidelineal and the references listed in Section 2.0. Each review posi-tion is stated below, followed by the evaluation of the licensee submittals.

The following evaluations are based on completion of changes in Section 4.1 and utilized the analysis submitted by Met-Ed on May 15, 1980:

Position 1--With the minimum expected offsite grid voltage and maximum load condition, each offsite source, in conjunction with the onsite distri-bution system, must be capable of starting and of continuously operating all class 1E equipment within the equipment voltage rating.

As shown in Table 1 and discussed in Section 4.2, the analyzed equip-ment terminal voltages for all class 1E equipment will be above their minimum voltage rating with the minimum offsite grid voltage and under all steady state and transient loading conditions.

Position 2--With the maximum expected offsite grid voltage and minimum load conditions, each off site source and distribution system connection combination must be capable of continuously operating all class IE equip-ment without exceeding the rated equipment voltage.

The licensee's analysis indicates that, with the grid maximum and the plant load minimum, the voltage at the class 1E 480V buses /MCCs will be

. less than 1% above the maximum allowable value for 460V motors. Since the analysis was made with the plant in shutdm n condition and no motors con-nected to the IE buses, the voltages will be within the motor rating when accident conditions require the connection of class 1E motors to the buses.

The voltage for the buses and other class 1E equipment will also be within their ratings. There fore , the requirements as expressed in the above posi-tion are satisfied.

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Position 3--Loss of offsite power to either the redundant class 1E ,

distribution systems er the . individual class IE buses, due to operation of voltage protection relays, must not occur when the offsite grid voltage is within expected voltage limits. -

Subsequent to the renoval of the trip function for the 480V bus relays (Section 4.1), the degraded grid protective relays are'the only ones which could cause a loss of offsite power to safety loads when the offsite grid voltage is within normal operating range. The potential for spurious loss of offsite power will be reviewed in the ongoing EG6G Idaho, Inc., evalu-ation of the TMI-1 (3 graded grid protec- tion (TAC No. 10055).

Position 4--Test results should verify the accuracy of the voltage analyses supplied.

4 The testing by Met-Ed to verify the submitted voltage analysis is not satisfactory. The loading of the MCCs was too low to accurately determine the voltage drop (impedance) from the supplying bus. The 480V MCCs an both trains had less than 1% of full analysis load and no voltage drop was measured.

Position 5--No event or condition should result in simultaneous or consequential loss of both required circuits from the of fsite power network -

to the onsite distribution system.

Met-Ed has determined that there are no events or conditions which could result in simultaneous or consequential loss of both required offsite circuits and, therefore, TMI-1 presents no violation of GDC 17 in this regard.3 Position 6--As required by GDC 5, each offsite source shared between units in a multi-unit station must be capable of supplying adequate otarting and operating voltage for all required class IE loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.

Three Mile Island is the location of two nuclear power generating stations, TMI-1 and TMI-2. Each unit is independently connected to offsite power sources and have no common electrical power interconnections between units. Therefore, Position 6 is not applicabic to t4I-1.

6.0 CONCLUSION

S I have reviewed the Med-Ed submittals and find that, upon completion of the changes included in Section 4.1, there will be reasonable assurance that:

1. Each offsite source, in conjunction with the onsite distribution systems, has the capacity and capability ,

to start and operate all class lE loads without exceco-ing the equipment voltage rating with the of fsite power sources within expected limits. (This is contingent on each THI-1 class 1E 460V motor being operated within its load rating and with an ambient temperature below 400C.)

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2. Met-Ed has determined that no potential exists for a simultaneous or consequential loss of both of f site electrical sources.

3. The test verification provided by Met-Ed does not ade-quately verify the submitted analyses.

2 The general' method used by Met-Ed to verify the analysis is acceptable if each IE bus and MCC is loaded during

. the testing to at least 30% of its analysis loading.

If this is not possible, Met-Ed should demonstrate that each bus or MCC is loaded sufficiently and the instru-mentation is accurate eno' ugh to ensure the correct

readings.

EG&G Idaho, Inc., is performing a separate review of the undervoltage relay protection at THI-1. This will evaluate the relay setpoints and time delays to determine that spurious tripping of the safety related loads will not occur with normal offsite source voltages.

7.0 REFERENCES

. 1. NRC letter, William Gammill, to all power reactor licensees (except Humboldt Bay), " Adequacy of Station Electric Distribution Systems Voltages , August 8, 1979.

2. Met-Ed letter, J. G. Herbein, to NRC, W. P. Gammill, dated October 16, 1979.

3. Met-Ed letter with technical report entitled, "TMI-l Electri: Distri-bution System Voltages," Revision 1, to NRC, R. W. Reid, dated May 15, 1980.

4. Final Safety Analysis Report (FSAR) for TMI-1, Section 8.2, "Electri-cal System Design."

5. Telecon, D. D. Iann, NRC, C. Cleveland, EG&G Idaho, Inc., J. Torcivia, GPUSC, and D. Mitchell, Met-Ed, June 5, 1980.

6. Het-Ed letter, J. G. Herbein, to NRC, Office of Inspection and Enforce-ment, dated June 27, 1980.

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