ML20062A497

Adequacy of Station Electric Distribution Sys Voltages, Beaver Valley Power Station,Unit 1, Informal Interim Rept

ML20062A497
Person / Time
Site:	Beaver Valley
Issue date:	05/31/1982
From:	Udy A EG&G, INC.
To:	Prevatte R Office of Nuclear Reactor Regulation
References
CON-FIN-A-6429 EGG-EA-5840, NUDOCS 8208040018
Download: ML20062A497 (13)

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May 1982 __

ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES, BEAVER VALLEY POWER STATION, UNIT NO. 1 AF48.

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INTERIM REPORT Accession No.

, Report No. EGG-EA-5840 Contract Program or Project

Title:

Selected Operating Reactors Issues Program (III)

• - Subject of this Document:

Adequacy of Station Electric Distribution System Voltages, Beaver Valley Power Station, Unit No. 1 Type of Document:

Informal Report Author (s):

A. C. Udy Date of Document:

May 1982 Responsible NRC Individual and NRC Office or Division:

R. L. Prevatte, Division of Systems Integration This document was prepared primarily for preliminary or internal use. it has not received 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-AC07-761001570 NRC FIN No. A6429 INTERIM REPORT

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I ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES.

I BEAVER VALLEY POWER STATION, UNIT N0.1

, May 1982 i

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

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Docket No. 50-334 TAC No. 13110 i

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f f' ABSTRACT l' This EG&G Idaho, Inc. report reviews the capacity and the capability of the onsite distribution system at the Beaver Valley Power Station, in conjunction with the offsite power sources, to automatically start and  ;

continuously operate all required safety loads.

FOREWORD This report is supplied as part of the Selected Operating Reactors issues Program being conducted for the U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Licensing, by EG&G Idaho, Inc., Reliability and Statistics Branch.

The U.S. Nuclear Regulatory Commission funded the work under the authorization B&R 20 19 10 11, FIN A6429.

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CONTENTS

1.0 INTRODUCTION

...........................................t........ 1 2.0 DE S IGN BA SI S CRI TE RI A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3.0 SY ST E M D E SC R I P T I ON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

, 4.0 ANALYSIS DESCRIPTION ............................................ 2 4.1 Design Changes ............................................ 2 s

4.2 A n a ly s i s Co n d i t io n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.3 A n a l y s i s R e su l t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.4 A naly si s Ve ri f ic at io n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.0 EVALUATION ...................................................... 6 6.0 C O NC L U S I O N S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

7.0 REFERENCES

...................................................... 8 FIGURE

1. Beaver Valley Station Unit One Line Diagram ..................... 3 TABLES

1. Class lE Equipment Voltage Ratings and Worst Case Avai lable Load Termi nal Volt age . . . . . . . . . . . . . . . . . . . . . . 4

?. Comparison of Analyzed Voltages and U nde rv o l t ag e R e l ay S et p oi nt s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 D

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o ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES BEAVER VALLEY POWER STATION, UNIT NO.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, station snformance to General Design Criteria (GDC) 17 is being questioned at all nuclear power stations. The NRC, in the generic letter of August 1979, " Adequacy of Station Electric Distribution Systems 3 ,

Voltages,"y, required each licensee to confirm, by analysis, the adequacy of the voltage to the Class lE loads. This letter included 13 specific guidelines to be followed in determining if the voltage is adequate to start and continuously operate the Class lE loads.

Duquesne Lig NRC letterI with letters of October 15,1979,gtand (DL) responded February to th22, 1980.3 The Final Safety A 17, 1980,galysi and a s Report (FSAR), additional analysgs submitted on June telephone call on July 11, 1980, provided informat DL docunented this telephone call on July 24,1980.fonforthisreport.

A letter of November 11, 1976,7 also provided info report. Letters of December 15,1981,gationfortheprepagationofthis and March 11, 1982, provide further information and analyses regarding the installation of automatic load tap changers on the stati A tel conversation on April 7,1982,g service transformers.and a letter of May 3,1982,gh provided additional clarification and information.

Based on the information supplied by DL, this report addresses the capacity and capability of the onsite distribution system of the Beaver Valley Power Station, in conjunction with the offsite power system, to maintain the voltage within acceptable limits for required Class lE equipment for the worst-case starting and load conditions. Unit 2 is not an operating reactor, therefore this report covers only the Unit 1 distribution system.

2.0 DESIGN BASIS CRITERIA The positions applied in determining the acceptability of the offsite voltage conditions in supplying power to 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, Systems, and Components," of Appendix A,

" General Design Criteria for Nuclear Power Plants," of l 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.

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

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

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

t Six rgview positions have been established from the NRC analysis guidelines and the above-listed documents. Th'ese positions are stated in Section 5. j i

3.0 SYSTEM DESCRIPTION Figure 1 of this report is a unit one-line diagram of the power sources and the Class 1E distribution system taken from Figure 8.1-1 of the FSAR. Class lE 4160V buses lAE and 1DF are supplied power from auxiliary buses lA and 10, respectively. When the unit generator is operating, these buses are powered by independent unit transformers. On a unit generator trip, these buses are automatically and independently connected via separate system auxiliary transformers lA and 18 to the 138kV switchyard.

The unit generator cannot be isolated from the unit transformers; therefore, the main transformer cannot supply offsite power to the Class lE buses from the 345kV switchyard.

Each 4160V Class lE bus supplies power to two 480V Class lE buses via separate 4160V/480V transformers. 120V vital buses are nonnally supplied power from uninterruptable power supplies (UPS), however, when a UPS is undergoing maintenance, separate 480V/120V transformers supply power to the 120V vital buses. Other 120V buses that supply instruments and control systems as required by GDC 13 are powered by 480/240/120V transformers.

T bus.2,gere Thearerelays two Class lE undervoltage separate the Class lErelays on each bus from 4160V offsite Class power lE should there be degradation of offsite power. There are also Class lE undervoltage relays on 480V buses IN and IP that operate the same as the 4160V relays. Loss of voltage relays are on these same buses.

The FSAR indicates that control power for the Clasy 1E 4160V and 480V switchgear is 125V DC. 480V MCCs use AC control power.  ;

DL supplied the equipment operating ranges identified in Table 1. ,

4.0 ANALYSIS DESCRIPTION 4.1 Design Changes. DL submitted analyses3 ,4 based on the 8 following proposed changes:

1. DL will install new station service tra have automatic tap changing capability.gsformers The tap that changers can also be manually set from the control room.

2

345 KV SWITCHYARD 138 KV W W MAIN SWITCHYARD TRANSFORMER l

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lA 1C ID 18 s GGD %D %D %D r3 (*n rn On r3 rn On r3 MAIN GEN.

BUS 1A BUS IB BUS 1C BUS 10 4160V 4160V 4160V 4160V DG DG __

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CLASS 1E BUS lAE BUS 1DF 4160V 4160V

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CLASS lE {} CLASS lE {} CLASS lE BUS IN BUS IN1 Bus 1p BUS 1P1 480V 480V 480V 480V UNIT ONE LINE DIAGRAM BEAVER VALLEY STATION FIGURE 1 l

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s TABLE 1. CLASS lE EQUIPMENT V0LTAGE RATINGS AND ANALYZED WORST CASE BUS VOLTAGES (% of nominal voltage) i i

Maximum Minimum Analyzed (

Voltage Steady Equipment (100%) Rat ed Analyzed Rat ed - state Transient 4160V Motors Start 4160V -- --

80 --

82.5 Operate 110 106.1 90 103.5a __

460V Motors Start 460V -- --

80 --

80.7 Operate 110 1 08.1 90 98.4 a __

460V MCC Starters Pickup 460V -- --

80 --

80.7 Dropout -- --

55 --

80.7 Continuous 110 108.1 80 98.4 --

Other 120V Equipment b Instruments and Controls

a. Bus voltage has adequate margin to allow for feeder cable voltage drop.

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b. The 120V vital buses are normally supplied power by inverters. Should an inverter by out of service, self-regulating transformers are used to i

maintain6 the vhal bus voltage within 12% for a 1J0% change on the input voltage i

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2. The taps on the 480/240fl20V transformers will be changed to give a 2-1/2% voltage boost.

3. The transformers that supply backup power to the vital buses are being replaced with self-regulating transfomers wh h will maintain the bus voltage within the required limits The discussion in the text and the values in Table 1 of this report reflect that these modifications have been completed.

J DL has determin 4.2 Analysis Conditions.

the maxigum 138kV switchyard voltage andis 143.4kVgd that by load-flow studies th the minimtsn is i 133.7k V. DL has shown that the automatic load tap changers of the station service transformers can maintain the output of each transfomer at 4360V + 52v, through all expected variations of the grid voltage.

DL has analyzed each offsite source to the onsite distribution system under extremes of load and offsite voltage conditions to determine the bus voltages available to the Class 1E equipment. The worst case Class lE equipment terminal voltages occur under the following conditions:

1. The maximum analyzed load teminal voltages occur when the grid is maximum, each system auxiliary transformer is supplying power for its Class lE buses, and no unit loads exist.

2. The minimum analyzed continuous load terminal voltages occur when the grid is minimum and each system auxiliary transformer is supplying the maximum connected auxiliary and Class lE loads.

3. The minimum analyzed transient load terminal voltages occur under the same conditions as 2, concurrent with the start of a 6000 hp reactor coolant pump. The voltage is fully recovered within the 30 second deadtime of the automatic load tap changers.

4.3 Analysis Results. Table I shows the projected worst case Class lE equipment terminal voltage.

A review of Table 1 shows that all the Class lE loads are operated at voltages within the equipment ratings.

a 4.4 Analysis Verification. The computer analysis was verified9 by measuringthegridandbusvoltages,andtheactualloadofthebusegand selected equipment while the unit was being restarted from shutdown. An analysis to determine bus voltages was completed using the measured offsite source voltage. The accuracy of the DL analysis is verified by comparing the results with the measured bus voltages.

Comparison of the measured and the analyzed voltages shows that the difference between the two voltage values is less than 0.66% for any Class lE bus, including the steady state condition and the start of a reactor coolant pump.

5.0 EVALUATION Six rgview positions have been established from the NRC analysis guidelines and the documents listed in Section 2.0. Each review 6 position is stated below, followed by the evaluation of the licensee submitt al s.

Position 1--With the minimum expected offsite grid voltage and maximum i' 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 rated equipment voltages.

DL has shown that, with the modifications of Section 4.1 completed, Unit 1 of the Beaver Valley Power Station has sufficient capacity and capability for starting and continuously operating the Class lE equipment.

Position 2--With the maximum expected offsite grid voltage and reinimum load condition, each offsite source and distribution system connection

combination must be capable of continuously operating all Class lE equipment without exceeding the rated equipment voltage.

DL has shown that, with the grid voltage at the maximum expected value and no unit loads, the voltage ratings of the Class lE equipment are not exc eeoed .

Position 3--Loss of off site power to either the redundant Class lE distribution systems or the individual Class lE loads, due to operation of voltage protection relays, must not occur when the offsite power source is within analyzed voltage limits.

As shown in Table 2, the voltage protection relays will not separate the Class lE buses from the offsite power source during the analyzed starting transients or during maximum steady state load conditions.

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

DL has shown the calculations to be an accurate representation of actual conditions of the Class lE buses and loads.

• Position 5--No event 'or condition should result in the simultaneous or consequential loss of both required circuits from the offsite power network t to the onsite distribution system (GDC 17).

OL has analyzed the Beaver Valley, Unit 1 connections to the offsite power grid and determined that no potential exists for either a simultaneous or consequential loss of both circuits to the offsite grid.4 6

TABLE 2. COMPARISON OF ANALYZED VOLTAGES AND UNDERVOLTAGE RELAY SETPOINTS

(% of nominal voltage)

I Minimum Analyzed Relay Setpoint Location a Action Voltage Time Voltage (Tolerance) Time 4160V bus Degraded 103.5 continuous 90 (+3) 90 sec Loss 82.5 22 sec 75 1 sec I 480V bus Degraded 94.3 continuous 90 (+3) 90 sec Loss 77.3 22 sec 75 41 sec

a. DL submitted voltages.

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 orderly shutdown and cooldown in the renaining units.

The Beaver Valley Power Station is presently a single unit station, therefore, this position does not apply.

6.0 CONCLUSION

S The voltage analyses submitted by DL for Unit 1 of the Beaver Valley Power Station were evaluated in Section 5.0 of this report. It was found that, upon the completion of the changes described in Section 4.1:

1. Voltages within the operating limits of the Class lE equipnent are supplied for all projected combinations of plant load and offsite power grid conditions.

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

3. DL has determined that no potential for either a simultanous or a consequential loss of both offsite a power sources exists.

4 Loss of offsite power to the Class 1E buses, due to spurious operation of the voltage protectio 1 relays, will not occur with the offsite grid voltage within its expected limits.

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7.0 REFERENCES

1. NRC letter, William Gammill, to All Power Reactor Licensees (Except l Humboldt Bay), " Adequacy of Station Electric Distribution Systems Voltages," August 8, 1979.

2. DL letter, C. N. Dunn to Director of Nuclear Reactor Regulation, NRC, l " Response to Requests for Information on Station Service Bus Voltages", October 15, 1979. t.

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3. DL letter, C. N. Dunn to Director of Nuclear Reactor Regulation, NRC,

" Station Service Bus Voltage Study", February 22, 1980. ,

4. DL letter, C. N. Dunn to Director of Nuclear Reactor Regulation, NRC,

" Adequacy of Station Electric Distribution System Voltages," June 17, 1980.

5, Telecon, Ray Burski, DL, Tom Mayers, DL and Alan Udy, EG&G Idaho, Inc., July 11, 1980, at 4 p.m. EDT.

6. DL letter, C. N. Dunn, to Director of Nuclear Reactor Regulation, NRC,

" Station Service Busses Undervoltage Relays," July 24, 1980.

7. DL letter, C. N. Dunn, to R. W. Reid, U.S. NRC, " Operation Under j Degraded Voltage," November 11, 1976.

8. DL letter, J. J. Carey to Director of Nuclear Reactor Regulation, NRC,

. " Emergency Bus Transient Voltage Regulation", December 15, 1981.

9. DL letter, J. J. Carey to Director of Nuclear Reactor Regulation, NRC,

" Emergency Bus Transient Voltage Regulation", March 11, 1982.

10. Telecon, T. A. Mayers, DL and A. C. Udy, EG&G Idaho, Inc., April 7, 1982.

l 11. DL letter, J. J. Carey to Director of Nuclear Reactor Regulation, NRC, l

" Emergency Bus Transient Voltage Regulation," May 3,1982.

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