ML19341B091

Adequacy of Station Electric Distribution Sys Voltages, Dresden Station,Units 2 & 3.

ML19341B091
Person / Time
Site:	Dresden
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-6237 EGG-EA-5322, NUDOCS 8101300186
Download: ML19341B091 (11)

Text

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FORM iG4G 396

n is re INTERIM REPORT

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Accession No.

Report No. _lGG-EA-5322 C:ntract Program or Project

Title:

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

Adequacy of Station Electric Distribution System Voltages, Dresden Station -

Unit Nos. 2 and 3, Docket Nos. 50-237 and 50-249 TAC Nos. 12765 and 12807 Type of Document:

Informal Report Auth:r(s):

A. C. Udy D;t) of Document:

. December 1980 Responsible NRC Individue' O Office or Division: ,

Paul C. Shemanski, division of Licensing 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 761D01570 NRC FIN No. A6256 1

INTERIM REPORT ica <

Research and 'iechn.

Assistance Report Stot 300 /SC -

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ADEQUACY OF STATION ELECTE.1C DISTRIBUTION SYSTEM VOLTAGES DRESDEN STATION - UNIT NOS. 2 AND 3 ,

Docket Nos. 50-237 and 50-249 December 1980 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division

EG&G Idaho, Inc.

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I s-Draft 12-18-80 ,

TAC Nos. 12765 and 12807-

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I ABSTRACT The Nuclear Regulatory Commission has required all licensees to analyze the electric power system at each nuclear station. This teview is to deter- '

I mine if the onsite disttsbution system, in conjunction with the offsite power sources, has sufficient capacity and capability to automatically i start and operate all required safety loads within the equipment voltage ratings. This Technical Evaluation Report (TER) reviews the submittals for i i

i the Dresden Station Units 2 and 3. A separate TER reviews the submittals

• l for Unit 1.

With one exception, the offsite power sources, in conjunction with the onsite distribution system, have 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.

i FOREWORD ,

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

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 auth-orization entitled, " Electrical, Instrumentation, and Control System Sup-port," B&R 20 19 01 03, FIN A6256.

1 kk j.

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

CONTENTS

1.0 INTRODUCTION

. . . . . . . . . . . . . . . . . . . . . . . . . . . 1

, 2.0 DESIGN BASIS CRITERIA . . . . . . . . . . . . . . .. . . . . . . . 1 3.0 SYSTEM DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . 2 4.3 ANALYSIS DESCRIPTION . . . . .. . .... . . . .. . . . . .. . 4 i

! 4.1 Analysis Conditions . . . . . . . . . . . . .. . . . . . . . 4 I

4.7 Analysis Results . . . . .. . . . . . . . . . . . . . . . . . 6, 4.3 Analysis Verification . . . . . . . . . . . .. . .. . . . . 6 5.0 EVALUATION . . . . . . . . . . . . . . . . . . . .. . . . . . . . 6 4

6.0 CONCLUSION

S . . . . . . . . . . . . . . . . . . . .. . . . . . . . 8 "

7.0 REFERENCES

. . . . . . . . . .. . . . . . .. . . . . . . . . .. 9 FIGURE

., 1. Dresden Station, Unit One-Line Diagram, Units 2 and 3 . . . . . . . 3 TABLE

(' 1. Class 1E Equipment Voltage Ratings and

- Worst Case Load Terminal Voltages . . . . . .. . . .. ... . . . . 5 l

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES DRESDEN STATION - UNIT NOS. 2 AND 3

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 conformance to General Design Criteria (CDC) 17 is being ,

questioned at all nuclear power stations. The NRC, in the generic letter

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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 supplied each class 1E load. The letter included 13 specific guidelines to be followed in determining if the voltage is adequate to start and continuously operate the class 1E loads.

Commonwealth Edison Company (CECO) responded to the NRC letter I , for the Dresden Station, with letters of November 1, 19792 (which included a report on this subject, written by Sargent & Lundy) and December 14, 19793 ,

Based on the information supplied by CECO, this report addresses the capacity and capability of the onsite distribution system of Units 2 and 3 of the Dresden Station, in conjunction with the offsite power system, to maintain the voltage for the required class 1E equipment within acceptable limits for the worst-case starting and steady-state load conditions. The-Final Safety Analysis Report (FSAR), additional information submitted on 4

June 30, 1980 , June 26, 19805 , and June 11, 19806 , telephone calls in September 198b , and a letter of September 14, 19768 , complete the information reviewed for this report. An analysis for use of the unit inter-tie between 4160V class 1E buses, provided on August 18, 1980,9 was also reviewed for this report.

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 Struc-

• tures, Systems, and Components," of Appendix A, " General *l 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 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-lines land the above-listed documents. These positions are stated in Section 5.

3.0 SYSTEM DESCRIPTION ,

The enclosures of references 2 and 4 discuss the onsite distribution system. Figure 1, page 3 of this report, is a simplified sketch of the class IE electric distribution system taken from the Sargent & Lundy report of reference 2.

The Unit 2 class IE 4160V buses 23-1 and 24-1 are normally supplied power from auxiliary buses 23 and 24, respectively. These buses are sup-plied power during emergency conditions by a 138/4.16kV station auxiliary

. transformer (SAT)a (Unit 3 uses a 345/4.16kV SAT). Bus 24-1 can be energized from the other unit 3by a manual connection to bus 34-1 of Unit 3.D The unit technical specifications credit this as the second

a. Ceco also refers to this as a reserve auxiliary' transformer (RAT)

b. This connection between Units-2 and 3 is referred to as an intur-tie in

, this report.

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g 138 KV SWITCHYARD (345 KV SWITCHYARD) ,

345 KV A

' SWITCHYARD

' VIA MAIN TRANSFORMER T22 (T32) w w mm nom T21 (T31) ^"^'Nmpn UNIT AUX.

TRANS. mm TRANS. -

b] BUS 21 BUS 22 (31) (32) 4160V 4160V b b BUS 23 U b BUS 24

, (33) (34) 4160V 4160V DG U DG b TO OTHER UNIT TO OTHER g O2/3 2(3) BUS 34-1 (24-1)

UNIT BUS r1 r7 r1 33-1 LJ LJ BUS 23-1 LJ . BUS 24-1 (33-1) (34-1)

CLAS5 lE 4160V CLASS 1E 4160V T28 T29 (T38) p q (T39) b b b BUS 28 (38) BUS 29 (39)

CLASS 1E 480V CLASS 1E 480V h0TE: UNIT 3 NOMENCLATURE SHOWN IN PARENTHESIS.

DRESDEN STATION UNIT ONE LINE DIAGRAM UNITS 2, 3 FIGURE 1 3

source of power required by GDC 17. This inter-tie can also be used to power bus 34-1 from bus 24-1 serving as the second source of offsite power for Unit 3. The Unit 2 distribution system is identified in the FSAR as being typical of Unit 3, except for bus and transformer numbers.

• Each 4160V class IE bus supplies power for one 480V class lE bus via independent 4160/480V transformers. 120V vital buses are normally supplied power by motor-flywheel-generator sets4 . These will soon be replaced by battery powered invercers.

CECO supplied the equipment operating ranges identified in Table 1.

Station 125V DC buses supply power for portions of the control circuits of the class IE switchgear.

4.0 ANALYSIS DESCRIPTION 4.1 Analysis Conditions. CECO has used load-flow studies with con-tingencies in determining that the maximum and the minimum expected switch-yard voltages are 142 and 132kV for Unit 2, respectively; 362 and 344kV for -

Unit 3, respectively. The reserve auxiliary transformer was used for the analysis described. CECO determined that:

1. The maximum expected load terminal voltages occur when the switchyard voltage is maximum and there are no unit loads.

2. The minimum expected continuous load terminal voltages, when not sharing an offsite power source, occur when the switchyard voltage is at a minimum and, except those loads automatically shed due to a unit trip, the auxiliary bus loads and the class lE loads are maximum.

3. The minimum expected transient load terminal voltages occur under the conditions of 2, concurrent with the start of a large load.

4. The minimum continuous and transient load terminal voltages while sharing an offsite power source occurs with the unit SAT supplying the shutdown loads in the ,

unit with offsite power and the accident loads in the unit being supplied by the inter-tie.

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TABLE 1 CLASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WCRST CASE TERMINAL VOLTAGES

(% of nominal voltage)

Maximum Minimum Analyzed Equipment Condition Rated Analyzed Rated Steady State Transient UNIT 2 s

4000V Motors Start -- --

75 --

88.5a Operate 110 109.7 90 94.lb __

460V Motors Start -- --

75 --

81.8a,e Operate 110 108.3 90 90.lb ,c __ i 460V Motorsd Start -- --

75 --

81.9a  !

Operate 110 e 90 88.la __

480V Starters Pickup -- --

85 --

81.5 t Dropout -- --

70 --

81.5 F Operate 110 103.8 85 88.0d --

UNIT 3 4000V Motors Start -- --

75 --

90.4a Operate 110 109.0 90 95.9b __

460V Motors Start -- --

75 --

85.2a  :

Operate 110 112.3 90 92.0b __

460V Motorsd Start -- --

75 --

81.7a Operate 110 e 90 87.9a __

480V Starters Pickup -- --

85 --

84.7 Dropout -- --

70 --

84.7 Operate 110 107.6 85 91.2 --

Other Equipment  ;

Units 2 and 3f i

a. Load terminal voltage supplied by CECO.

b. These values incluae the worst case (480V) or typical (4160V) feeder i cable voltage drop (3.2%, 0.5%, respectively2 ),

c. Lowest voltage on Unit 2 480V buses when either Unit 2 SAT or Unit 3 SAT supplying power to Unit 2.

d. When SAT 2 is supplying the Unit 2 shutdown loads and the Unit 3 LOCA loads.

e. This information not supplied by CECO; however, the voltage is not expected to be higher than when the inter-tie is not in use.

f. 120V vital buses are normally supplied power by motor-flywheel generator

. sets 4.. These will soon be replaced.by battery-powered inverters.

5 g w m, yv+-- +y ~ - + . T'- - ey

4.2 Analysis Results. Table 1 shows the worst case voltage levels identified it. the CECO analyses.

4.3 Analysis Verification. The computer analysis has not been veri-fied at the Dresden station. Ceco states 4 that the same computer program was verified for the. Zion station 3and Quad Cities Unit 2 6by measuring the grid and bus voltages and the actual load of the buses and selected equipment while these units were shutdown. An analysis was done using the '

measured offsite source voltage, and the results compared with the measured bus voltages.

The comparison for each of the three units shows that the class IE bus calculated voltages are within close correlation to the measured bus volt-ages. This verifies the adequacy of the submitted analyses for those units.

Since the station-dependent data used (transformer taps and impedences) were field verified as correct,4 the verification of the accuracy of the other units can be extended as verifying the analysis for Dresden Units 2 and 3. .

t 5.0 EVALUATION Six review positions have been established from the NRC analysis guide-lines 1and the documents listed in Section 2. 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 l class 1E equipment within the rated equipment voltages.

l Table 1 shows that when using the inter-tie, the steady state 460V I

l motors are subjected to an undervoltage condition in both Unit 2 (supplying the power) and Unit 3. With Unit 3 feeding the Unit 2 class 1E load, ade-l quate voltage levels are maintained.9 1

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i A brief acceptable condition, when starting a large non-class 1E load I when all class 1E loads are operating, would prevent class 1E contactor pickup if a 480V MCC load were stopped and then restarted, until the voltage t recovers. It will not cause contactor dropout or spurious shedding of any loads.

CECO has shown that the minimum expected continuous and transient class 1E voltages are within the rated capability of the class 1E equipment j except for the 480V loads when 'he inter-tie is used. CECO should provide design changes so that this second source of offsite power can be used on demand without unacceptable equipment voltages.

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

, As Table 1 shows, the Unit 3 480V loads were analyzed to have a poten-tial 112.3% for a no-load conditions. CECO concluded that these loads I

would not be subjected to unacceptable overvoltages because the analysis was done for a no-load condition and, when a load is added, voltage drops in the supply transformers and feeder cables reduces the voltage to "very clcse to 110%."3 Ceco has shown that, with the grid voltage at the maximum expected

, value, the voltage ratings of the class 1E equipment, when connected, are not exceeded.

Position 3--Loss of offsite power to either the redundant class 1E distribution systems or the individual class 1E loads, due to operation of voltage protection relays, must not occur when the offsite power source is within analyzed voltage limits.

EG&G Idaho, Inc., will verify, in a separate report, that the require-ments of this position are satisfied (TAC Nos. 10019 and 10021).

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

CECO has not committed to verify the accuracy of the voltage analysis for Dresden Units 2 and 3.

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

CECO has anclyzed the connections of the Dresden Station to the off-site power grid, and has determined that no potential exists for the simul-taneous or consequential loss of both required circuits to the offsite i power source.2 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 i

and operating voltage for all required class .1E loads with an accident in +

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

The unit transformers are independently connected to the offsite power a

grid, but the station has the capability to interconnect certain class 1E buses between Units 2 and 3 (but not Dresden Unit 1). Ceco has shown that

! the use of the inter-tie between Dresden Units 2 and 3 will not supply adequate operating voltages to the 480V class 1E buses 29 and 39 when the Unit 3 busca 34-1 and 39 are supplied power from Unit 2 bus 24-1.

6.0 CONCLUSION

S e

The analyses submitted by CECO for this review were evaluated as stated in Section,5.0 of this report. It was found.that:

a.- Section 8.1.1 of IEEE Standard 308 permits the'use of a single source of offsite power to be' shared between units of a multi-unit station.

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1. Voltages within the operating limits of the class 1E equipment are supplied, with one exception, for all projected combinations of plant loads and offsite power grid conditions, including an accident in one unit and the safe shutdown of the other unit. The exception is when the Unit 2 SAT supplies Unit 3 class 1E bus 34-1 loads in addition to the Unit 2 auxiliary and class 1E loads.

Since CECO has not demonstrated that adequate voltages can be maintained for this condition, Ceco should pro-vide either Technical Specifications to prevent the use - '

of the inter-tie when inadequate voltages would result or circuit modifications to ensure that this second source supplies adequate voltage to the connected class 1E equipment.

2. CECO had determined that no potential for either a '

simultaneous or consequential loss of both offsite power sources exists.

3. CECO has not performed a test that shows their analysis of the Dresden station distribution system is an accur-ate representation of the actual voltages present.

. These tests would be acceptable if they follow the method outlined in Section 4.3 of this report.

EG&G Idaho, Inc., is performing a separate review of the undervoltage relay protection at the Dresden station. This will evaluate the relay setpoints and time delays to determine that spurious tripping of the class 1E equipment will not occur with normal offsite source voltages.

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7. 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. CECO letter, Robert F. Janecek to William Gammill, "Adequancy of Sta-

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tion Electric Distribution System Voltages", November.1, 1979.

3. CECO letter, Robert F. Janecek to William Gammill, " Adequacy of Sta-tion Electric Distribution System Voltages", December 14, 1979.

4. CECO letter, Robert F. Janecek to T. A. Ippolito, U. S. NRC, " Adequacy

, of Station Electric Distribution System Voltages," June 30, 1980.

5. Ceco letter, Robert F. Janecek, to Darrell G. Eisenhut, U.S. NRC, "Second Level of Undervoltage Protection for 4kV Onsite Emergency Power Systems," June 26, 1980.

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6.

CECO letter, Robert F. Janecek, to William Gammill, U.S. NRC, " Adequacy of Station Electric Distribution System Voltages," June 11, 1980. .

7. Telecon, Hal Stolt, CECO and other CECO personnel and Alan Udy, EC&G Idaho, Inc., September 11 and 22, 1980. ,

8. CECO letter, G. A. Abre11, to Karl R. Coller, U.S. NRC, "Information Concerning System Voltage Conditions," September 14, 1976.

9. CECO let ter, Robert F. Janecek, to Darrell G. Eisenhut, U.S. NRC,

" Additional Response concerning Adequacy of Station Electric Distribu-tioa System Voltages," August 18, 1980.

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