ML19341B374

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

ML19341B374
Person / Time
Site:	Beaver Valley
Issue date:	12/31/1980
From:	Udy A EG&G IDAHO, INC., EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6256 EGG-EA-5326, EGG-EA-5326-DRF, NUDOCS 8101300829
Download: ML19341B374 (15)

Text

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INTERIM REPORT Accession No.

Report No. EGG-EA-5326 C'intract Program or Project

Title:

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

Adequacy of Station Electric Distribution System Voltages, Beaver Valley Power Station, Unit No.1, Docke t No. 50-334, TAC No. 13110 Type of Document:

Informal Report Author (s):

A. C. Udy Dite of Document:

December 1980

. R:sponsible 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 substantiv > 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. A6256 INTERIM REPORT nica MC Research and Tech. .

Aspnnce Report

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i ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES t

f j BEAVER VALLEY POWER STATION - UNIT NO. 1 4

Docket No.'50-334  !

i December 1980 i

A. C. Udy Reliability and Stat"istics Branch *

. Engineering Analysis Division EG&G Idaho, Inc.

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i ABSTRACT i

i The Nuclear Regulatory Commission has required all licensees to analyze j 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 I

i ratings. This Technical Evaluation Report reviews the submittals for the Beaver Valley Power Station.

The offsite power sources, in conjunctio with the onsite distribution system, have been shown to have sufficient capacity and capability to auto-matically start, as well as continuously operate, all required class 1E equipment within rated voltage limits in the event of either an anticipated i transient or an accident condition.

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FOREWORD This report is supplied as part of the selected Electrical, Instrumen-tation, and Control Systems (E1CS) issues program being conducted for the

i. U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation,

Division of Operating Reactors, by EG&G Idaho, Inc., Reliability and Sta-tistics Branch.

I The U.S. Nuclear Regulatory Commission funded the work under the '

authorization entitled " Electrical, Instrumentation, and Control System Support." B&R 20 19 01 03, FIN A6256.

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CONTENTS

1.0 INTRODUCTION

.... . ....... . . . . . . . . . . . . . . . 1 2.0 DESIGN B ASIS CRITERIA . . . . . . . . . . . . . . . . . . . . . . . 1 3.0 SYSTEM DESCRIPTION . . ... . . . . . . . . . . . . . . . . . . . 2 4.0 ANALYSIS DESCRIPTION ..... . . . . . . . . . . . . . . . . . . 4 4.1 Design Changes . ..... . . . . . . . . . . . . . . . . . . 4 4.2 Analysis Conditions. ... . . . . . . . . . . . . . . . . . . 6 4.3 Analysis Results .. ... . . . . . . . . . . . . . . . . . . 6 4.4 Analysis Verification .. . . . . . . . . . . . . . . . . . . 7 5.0 EVALUATION . .. ... .... . . . . . . . . . . . . . . . . . . 7

6.0 CONCLUSION

S . ...... .... . . . . . . . . . . . . . . . . . 9

7.0 REFERENCES

. ... ...... . . . . . . . . . . . . . . .. . . 10 FIGURE

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

1. Class 1E Equipment Voltage Ratings and Worst Case Available Load Terminal Voltage . . . . . . . . . . . 5

2. Comparison of Analyzed Voltages and Undervoltage Relay Setpoints . . . . . . . . . . . . . . . . . . . 7 e

ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES BEAVER VALLEY POWER STATION - UNIT NO. I

1.0 INTRODUCTION

An event at the Arkansas Nuclear one station on September 16, 1978 is described in NRC IE Information Netice No. 79-04. As a result of this event, station confonmance 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 confirm, by analysis, the adequacy of the voltage to the class 1E loads. This letter included 13 specific guide-lines to be followed in determining if the voltage is adequate to start and continuously operate the class 1E loads.

Duquesne Light (DL) responded to the NRC letter I with letters of 2

October 15, 1979 and February _22,-1980.3 The Final Safety Analysis Report (FSAR), additional analyses submitted on June- 17, 19804 and a

, telephone call on July 11, 1980,5 provided information for this report DL documented this telephone call on July 24, 1980.6 A letter of November 11, 1976,7 was also reviewed in preparing this report.

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 1E equip-ment for the worst-case starting and load conditiona. Unit 2 is not an operating reactor, therefore this report covers only the Unit 1 distribution system.

j l 2.0 DESIGN BASIS CRITERIA i

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. Ganeral 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 Struc-tures , Systems , and Components ," of Appendix A, a

" General Design Criteria for Nuclear Power Plants," of 10 CFR 50. -

3. General Design Criterion 13 (CDC 13), " Instrumentation and Control," 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, 1979.1

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

Six review positions have been established from the NRC analysis guide-1 lines and the above-listed documents. These positions are state'd in .

Section 5.

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 1E 4160V buses IAE and IDF are supplied power from auxiliary buses 1A '

and ID, 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 IA and IB to the 138 kV switchyard. The unit generator cannot be isolated from the unit generator, therefore, the main transformer cannot supply offsite power to the class 1E buses from the 345kV switchyard.

Each 4160V class 1E bus supplies power to two 480V class 1E buses via j separate 4160V/480V transformers. 120V vital buses are normally supplied '

, power from uninterruptable power supplies (UPS), however, when a UPS is undergoing maintenance, separate 480V/120V transformers supply power to the i

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120V vital buses. Other 120V buses that supply instruments and control systems as required by GDC 13 are powered by 480/240/120V transformers.

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There are two class IE undervoltage relays on each 4160V class IE -

bus.2,6 The relays separate the class 1E bus from offsit.e power should there be degradation of offsite power. There are also class IE 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 class IE 4160V and 480V switchgear is 125V DC. 480V MCCs use AC control power.7 l

DL supplied the equipment operating ranges identified in Table 1. I 4.0 ANALYSIS DESCRIPTION 4.1 Design Changes. DL submitted analyses ,4 based on the following, proposed changes:

1. DL will install automatically controlled 6.3 MVAR capacitor banks on 4160V normal buses 1A and ID.3 l (These buses supply the class IE buses.) The capaci-tors will be automatically placed on their respective bus when the bus voltage is less than 101% (of 4160V),

and will be automatically removed from their bus when the bus voltage rises above 108%. Manual operation will also be possible. Until these capacitors are installed and operational, DL has administrative pro-cedures to change the taps on the system station service transformers to ensure that no undervoltage condition will occur following a reactor trip and automatic transfer to the system station service transformers.3

2. The taps on the 480/240/120V transformers will be changed to give a 2-1/2% voltare boost.4

3. The transformers that supply bat.kup power to the vital buses are being replaced with relf-regulating trans- .

formers which will maintain the bus voltage within the required limits.4 The discussion in the text and the values in Table 1 of this report reflect that these modifications have been completed.

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l TABLE 1 CLASS 1E EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES

(% of nominal voltage)

Maximum Minimum

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Nominal Voltage Steady Equipment (100%) state Transient Motors 4160V Start -- --

80a --

84.0 Operate 110 b 90 99.6 --

460V Start -- -

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78.5 Operate 110 b 90 91.8 --

CC Starters 480V Pickup - -

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75.2 Dropout -- --

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75.2 continuous 110 b 80 90.0 --

Other 240c, 120V 110 b 90 91.8 d Equipmente Instruments and Controls

a. DL states 6 that they, "do not have documentation that all motors will start at 80% voltage, but by experience, we believe they will." 80% is conservative for the ratings of similar equipment in other nuclear stations.

b. This data not supplied by DL; however, DL has stated 2 that the maxi-mum credible voltages at the emergency buses do not exceed 110% for a no-load condition.

c. 208V is used in heat tracing systems and is not subject to the limits imposed on other equipment.

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d. This information not supplied by DL.

e, The 120V vital buses are normally supplied power by inverters. Should an inverter by out of service, self-regulating transformers are used to maintain the vital bus voltage within +2% for a +10% change on the input voltage.6 5

4.2 Analysis Conditions. DL has determined by load-flow studies that the maximum 138kV switchyard voltage is 143.4kV and the minimum is 134.9kV.

DL has analyzed each offsite source to the onsite distributien system -

under extremes of load and off site voltage conditions to determita the terminal voltages to the class lE equipment. The worst case clr.ss IE equip-ment terminal voltages occur under the following conditions:

1. The maximum expected load terminal voltages occur when the grid is maximum, each system auxiliary transformer is supplying power for its class IE buses, and no unit loads exist.

2. The minimum expected continuous load terminal voltages occur when the grid is minimum and each system auxiliary transformer is supplying the maximum connected auxiliary and class IE loads.

3. The minimum expected transient load terminal voltages occur under the same conditions as 2, concurrent uith the start of a 6000 hp reactor coolant pump.

4.3 Analysis Results. Table 1 shows the projected worst case class IE equipment terminal voltage.

In a no load condition and with a maximum offsite system voltage, the maximum terminal voltage has been determined not to exceed 110% of the equipment rated voltages.2,4 I

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! A review of Table I shows that, with the exception of the transient condition on the 460V motors and 480V cont actors, all the class IE loads t

are within the equipment rated voltages. This worst case transient condi-3 l tion will last less than 22 seconds before normal operating voltages (i.e., greater than 90%) are restored.4 Contactor pickup for the 480V MCC loads is prevented until the voltage recovers. It will not cause con- ,

1 tactor dropout or spurious shedding of any loads.

Table 2 compares the undervoltage relay setpoints and time delays with bus voltages derived from Table 1.

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l TABLE 2 COMPARISON OF ANALYZED VOLTAGES AND i

UNDERVOLTAGE RELAY SETPOINTS

(% of nominal voltage)

. Minimum Analyzed Relay Setpoint Location Action Voltage" Time Voltage (Tolerance) Time i

i 4160V bus Degraded 99.6 continuous 90 (+3) 90 see Loss 84.0 22 sec 75 1 sec 480V bus Degraded 89.4 continuous 90 (+3) 90 see Loss 75.2 22 sec 75 41 sec i

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a. DL submitted voltages.

4.4 Analysis Verification. The computer analysis is to be verified 4 i

by measuring the grid and bus voltages, and the actual 1 cad of the buses and selected equipment while the unit is being restarted from the current shutdown.5 An analysis to determine bus voltages will then be completed 4

using the measured of fsite source voltage. The accuracy of the DL analysis l

will be verified by comparing the results with the measured bus voltages.

l DL must establish that the load conditions and instrument accuracies are adequate to account for impedence and transformer voltage drops in the distribution system.

5.0 EVALUATION Six review positions have been established from the NRC analysis guide-I lines and the documents listed in Section 2.0. Each review position is stated below, followed by the evaluation of the licensee submittals.

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

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DL has shown that, with the modifications of Section 4.1 completed, the Beaver Valley Power Station, Unit 1, has sufficient capacity and capa-bility for starting and continuously operating the class IE equipment. ,

While the class IE 460V motors and 480V contactors can have transient volt-ages below the motor starting rating and the contactor pickup rating, this -

should not be a problem, as the class IE motors are running when this transient voltage occurs and the contactor dropout voltage rating is not exceeded. It does not affect the ability t< start the class IE loads nor will spurious tripping of these loads occur.4 Position 2--With the maximum expected offsite grid voltage and minimum load conditicn, each offsite source and distribution system connection coabination must be capable of continuously operating all class IE equip-ment without exceeding the rated equipment voltage.

DL has stated thct, with the grid voltage at the maximum expected value and no unit loads, the voltage ratings of the class 1E equipment are ~

not exceeded.

Position 3--Loss of offsite power to either the redundant class IE 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.

The voltage protection relays will not separate the class IE buses f rom the off site power source during the analyzed starting transients.

However, as can be seen in Table 2, the setpoint (including +3% tolerance) of the 480V degraded grid undervoltage relays (93%) is above the minimum expected continuous voltage (89.4%). This presents a potential for unnecessary tripping of the class lE distribution system from the offsite power source.

Position 4--Test results should verify the accuracy of the voltage -

analyses supplied.

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-. ._. - _ - . _ _ _ _ . _ . = _ . - - - . _ . . . -- - - .- _ - -

l DL has not yet shown the calculations to be an accurate representation of actual conditions of the class IE buses and loads; however, they have an

. acceptable test method and have scheduled the testing4and the comparison of test results to an analysis of identical conditions.

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

i LL has analyzed the Beaver Valley, Unit I 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 gri(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 starting and operating voltage for all required class IE loads with an accident in {

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one unit and an orderly shutdown and cooldown in the remaining units.

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

6.0

SUMMARY

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 IE equipment are supplied for all projected combinations of plant load and offsite power grid conditions.

Two of the three proposed changes (Section 4.1) have been made. DL has provided suitable analysis for the use of capacitors on the 4160V auxiliary buses, but has not installed these capacitor banks. DL is investi-gating the use of capacitor banks on the class IE 480V buses instead.5 This would be acceptable provided DL shows, by analysis, that the revised capacitor instal-lation provides voltage to the class IE buses that is equal to or better than the originally proposed capaci-tor installation.

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2. The proposed test will verify the analysis accuracy.

3. DL has determined that no potential for either a simul-tanous or consequential loss of both of fsite power sources exists.

4. The class IE 480V bus undervoltage relay setpointe are above the analyzed minimum bus voltage. Unnecessary separation of offsite power to the class IE distribution system could result. This does not appear to comply with the requirements of GDC 17. DL should be required to make the changes necessary to keep the class IE buses powered by the offsite power source as long as acceptable voltage is available with that source.

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. DL letter, C. N. Dunn to Director of Nuclear Reactor Regulation, U. S.

NRC, " Response to Requests for Information on Station Service Bus Voltages", October 15, 1979.

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

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

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

NRC, " Adequacy of Station Electric Distribucion System Voltages,"

June 17, 1980.

5. Telecon, Ray Burski, DL, Tom Mayers, DL and Alan Udy, EG6G Idaho, Inc., July 11, 1980 at 4 p.m. EDT.

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

U.S. NRC, " Station Service Busses Undervoltage Relays," July 24, 1980.

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

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