ML20008F791

Adequacy of Station Electric Distribution Sys Voltages, Edwin I Hatch Nuclear Power Station, Informal Rept for Apr 1981

ML20008F791
Person / Time
Site:	Hatch
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-5369, NUDOCS 8105120058
Download: ML20008F791 (12)

Text

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FORM EG&Gr398 (Rev.11 F9) ,

INTERIM REPORT Accession No.

Report No. EG",-EA-5369 Contract Program or Project

Title:

Selected Operating Reector Issues Program (III)

Subject of this Document:

Adequacy of Station Electric Distribution System Voltages, Edwin I Hatch Nuclear Power Station - Unit Nos. 1 and 2, Docket Nos.5G-321 and 50-366, TAC Nos.12831 and 12832 Type of Document:

Informal Report Author (s):

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X3C 3esearCII Bnd IeChniC g }gpQ[(

. D:te of Document: .

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 received full review and approval. Since there may be substantive changes, this document si.ould f

not be considered final.

EG&G Idaho, Inc.

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

4 Under DOE Contract No. DE-AC07 76tD01570 NRC FIN No. A6429 . . _ .

INTERIM REPORT

(</ O 5/2. 00 58

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES EDWIN I. HATCH NUCLEAR POWER STATION - UNIT NOS.1 AND 2 Docket Nos. 50-321 and 50-365

- April 1981

• A. C. Udy Reliability and Statistics Branch l Engineering Analysis Division

, . EG&G Idaho, Inc.

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.I TAC Nos.12831 and 12832

l ABSTRACT The Nuclear Regulatory Connission 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 Edwin I. Hatch Nuclear Power Station.

The offsite power sources, in conjunction with the onsite distribution system, have been shown to have sufficient capacity and capability to auto-matica11y 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 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 2019 01 06, FIN A6429.

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i CONTENTS l .0 . INTRODUCTION . . . . . . . . . ................... 1 2.0 DESIGN BASIS CRI TERI A . . . . . . . . . . . . . . . . . . . . . . . 1 3.0 SYSTEM DESCRIPTION . . . . . .................., 2.

4.0 ANALYSIS DESCRIPTION . . . . ................... 2 4.1 De si gn Ch a n ge s . . . . . . . . . . . . . . . . . . . . . . . . . - 2 4.2 Analysis Conditions . . ................... 2 4.3 An alysi s Re sul ts . . . . . . . . . . . . . . . . . . . . . . . S 4.4 Analysis Verification . .................... 5 1

5.0 EVALUATION . . . . . . . . . .................... 5 6.0 CO NC L U S IO N S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 i

7.0 REFERENCES

. . . . . . . . . ................... 7 FIGURE

1. Ha tch Station Unit One Line Diagram . . . . . . . . . . . . . . . . 3

, TABLE

1. Edwin I. Hatch Nuclear Power Station

.- Class 1E Equipmert Voltage Ratings and Worst Case Load Terminal Vol tages . . . . . . . . . . . . . . . . . 4 4

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ADEQJACY OF STATION ELECTRIC DISTRIBUTION SYSTEM YOLTAGES EDWIN 1. HATCH NUCLEAR POWER STATION - UNIT NOS.1 AND 2 1.0 INTRODtETION An event at the Arkansas ibclear One station on September 16,1978 is described in NPsC IE Information 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 Augugt 8,1979, " Adequacy of Station Electric Distribution Systems Volt-a ges ," required each licensee to confirm, 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 voltage is adequate to start and coritinuously operate the class 1E loads.

Georgia Power Company (GPC) responded with an analysis on December 7, 19792 . Besides the original analysis, a letter of July 22,1977 , 3the Final Safety Analysis Report (FSAR), and additional analyses submitted on April 28,19804, complete the infomption reviewed for this report.

Telephone conversations in June 19803 clarified portions of the April 28, 1980, submittal. These c nitted on Octoger 9,1980gnversations

. MCC cor. tactor ratingsresulted in additional were supplied in mat February 1981.

Based on the infomation supplied by GPC, this report addresses the capacity and capability of the onsite distribution system of the Edwin I. Hatch Nuclear Power 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 load conditions.

The following description and evaluation of the Unit 1 design also applies to the onsite distribution system of Unit 2.

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:

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

. Design Criteria for ibclear Power Plants," of 10 CFR 50

3. IEEE Standard 279-1971, " Criteria for Protection Sys-

tems for Nuclear Power Generating Stations"

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

5. Staff positions as detailed in 9 letter sent to the licensee, dated August 8,1979.

lines {fand x review positionsdocuments.

the abova-listed have been established fromare These positions the NRC given in analysis guide- '

Section 5 of this report.

3.0 SYSTEM DESCRIPTION Figure 1 is a simplified sketch of the unit one-line diagram taken from Sheets 5-60 and 5-61 of the Reference 2 a ttachments. The distribution systems for Unit 1 and Unit 2 are identical. The Unit 1 class lE 4160V buses can be supplied offsite power from the 230kV switchyard by startup transformers 1C or 1D. These buses cannot be connected to the unit auxili-ary transfomers. l A or 18.

The two class lE 600V buses 1C and 1D are each normally connected by 4160/600V transfomers to class lE 4160V buses lE and 1G, respectively. An identical 4160/600Y transfomer, connected to class lE 4160V bus IF can be connected to either 600Y bus 1C or 10 by disconnect links. The FSAR indi-cates that procedures prevent both 600V buses being connected to the same transformer or being operated in parallel. Class lE buses 1C and ID supply essential power to the 120/208V AC instrument power system by two separate transfomers. While the instrument power system supplies both essential and non-essential loads, Section 8.3.1.1.4a of the FSAR indicates that failure of a nonessential load will not affect the ability of the system to supply the essential (class lE) loads. .

GPC supplied the equipment operating ranges identified in Table 1 of this report.4 -

4.0 ANALYSIS DESCRIPTION a.1 Design Ghanges. GPC has changed the tap settings to 0.925 (i nstead of 1.00)3 on all of the Hatch Station transfomers that supply voltages of less than 600Y.

4.2 Analysis Conditions. GPC has determined by load-flow and grid contingency studies that the maximum expected offsite grid voltage is 239.2kV (104%) and the minimum is 225.4kV (98%).

GPC has analyzed each offsite source to the onsite distribution system under extremes of Ioad and offsite voltage conditions to detemine the teminal voltages to the class 1E equipment. The worst case class 1E equipment teminal voltages occur under the following conditions:

1. Start-up transfomer 10 supplying power to the Unit 1 class lE buses is the worst-case condition 5 (trans-fomer 2D for Unit 2).

2. With one unit operating and one unit shut down, GPC ,

detemined the maximum expected bus and load voltages using the maximum expected grid voltage.

2

Unit Gen 230 KV SWITCHYARD (UNIT 1)

1. 1 ~ 500 KV SWITCHYARD (UNIT 2)

VIA MAIN TRANSFORMER 230 KV

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BUS IB 00 BUS 1C 00 BUS 1D 4160V 4160V 4160V .4160V t

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DG DG DG 1A 1B 1C TO BUS 2F Ex] O O Ex] - g gx3 l BUS 1E BUS 1F BUS 1G 4160V 4160V 4160V

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CLASS lE CLASS lE y CLASS 1E X

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, X X t BUS 1C BUS 1D 600V 600V CLASS lE CLASS 1E

1. UNIT 2 IDENTICAL EXCEPT FOR SHARED D-G SET 1B

2. BREAKERS SHOWN ALIGNED HATCH STATION FOR PREFERRED OFFSITE UNIT ONE LINE DIAGRAM SOURCE TO CLASS lE BUSES FIGURE 1 m

TABLE 1 CLASS 1E E0VIPENT YOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL YOLTAGES

(% of nominal voltage) 5 s

Maximum Minimum Analyzed Equipment __ Condition Rated Analyzed Rated Steady State Transient ,

a 4000V Motors Start -- --

75/70 -- 75.5 Operate 110 107.8 90 91.4 --

a 550V Ntors Start -- --

75/70 -- 75.1 Operate 11 0 110.0 90 92.0 --

600V MCC Pickup -- -- 74.8 -- 68.9 contactors Dropout -- -- .54.8 -- 68.9 (115V coil) Operate 108.7 100.8 N/A 85.4 --

208V Motors Start -- --

75/70a -- 71 .2 -

Operate 11 0 108.8 90 90.4 --

208V MCC Pickup -- -- 74.8 -- 72.6 contactors Dropout -- -- 54.8 -- 72.6 (115V coil) Operate 108.7 108.8 N/A 91 .4 --

Low voltage ins truments ~

and cont 501 cin:uits

a. 30-second stall rating.

GPC states 4 , 'The buses may supply instruments and control circuits b.

as required by GDC 13. We do not know of any connected equipment which is not capable of withstanding the analyzed voltages. However, not all manufacturers' responses are yet available. If any equipment is dis-covered which does not meet the functional requirements in the expected conditions, it will be the sub',:ct of a report to the NRC."

3. With one unit in normal shutdown and one unit in a LOCA condition and all buses in service, GPC detemined the minimum expected continuous bus and load-voltages using the minimum expected grid voltages. ,

4. With an automatic and simultaneous ' start of the class 1E -

ioads and a condensate pump, GPC detemined the minimum l expected transient bus and load voltages with the mini-mum expected grid voltage.

4

I To make the analyses more conservative, the measured bus loadings were I increased by 5% for some of the maximum load analyses. Separate analyses were supplied for both units. -

l These conditions are the worst of those supplied by the GPC submittals.

The voltage levels supplied for analyses using transfomer 1C assumed that buses lA and 18 are not transferred from onsite power (transfomer 1B) to transfomer 1C on a unit trip.

4.3 Analysis Results. Table 1 shows the projected worst case class lE equipment teminal voltages. It shows that, in all steady-state cases, the class lE loads have voltages that are within the equipment rated limits.

The worst case transient vo'ltage condition wil onds before nomal operating voltages are restored.{ 1ast At these less than 12 sec minimum voltages, no contactors will drop out to cause spurious tripping of loads.

Only the 20BV motors are not capable of accelerating at the analyzed volt-age level; however, they will start as the voltage recovers above 75%.

Their operation is at a voltage above the 70% stall voltage (i.e., opera-tion at 70% and full load is acceptable for 30 seconds).

As stated in footnote b of Table 1 of this report, GPC has detemined that the 120V AC instruments and control circuits are capable of with-standing the analyzed voltages.

GPC has not supplied a. minimum continuous duty rating for their AC

. powered contactors. As shown in Table 1, this rating needs to be at least i 85% . The contactors are shown to have an analyzed voltage of 0.1% higher than the contactor rating for maximum coninuous duty. The rating is lower

< than NEMA standards call for. The analyzed voltage is not significantly higher than the rating to cause concern.

4.4 Analysis Verification. The load flow analysis was verified 4by measuring the grid, generator and bus voltages, and the actual load of the buses and selected equipment while thit 1 was operating and thit 2 was in a nomal shutdown. The analysis model was developed from this measured loading. The model was then used for the GPC analysis. An analysis was done using the measured generator and offsite source voltages, and the results compared with the measured bus voltages. The voltages analyzed for the measured load are within +0.58% of the duplicate measured bus voltages.

While GPC did not directly verify the analysis for buses at voltages less than 4160V, they did include the load measurements and system imped-ences in developing the model of the distribution system. In lumping the Icwer voltage bus loads on the 4160V bus base, the analysis verification does account for the low voltage buses.

5.0 EVAlllATION i 4 Six review positions have been established from the HRC analysis guide-

.' linesl and the documents listed in Section 2 of this report. Each review position is stated below, followed by the evaluation of the licensee submi ttal s.

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Posit, ion 1--With the minimum expected offsite grid voltage and maximum load condition, each offsite source and distribution system connection combination must be -apable of starting and of continuously operating all class 1E equipment thin the rated equipment voltages.

GPC has shown, by analysis, that except for the AC powered contactors, '

the Hatch Station has sufficient capability and capacity for starting and continuously o' +ating all class 1E equipment within the equipment voltage ratings. -

GPC should detennine the ability of the AC contactors to opera'e continuously, without damage, down to 85% (of 600Y).

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 all class 1E equip-ment without exceeding the rated equipment voltage.

GPC has shown, by analysis, that the voltage ratings of the class 1E equipment 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 No.10025). ,

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

analyses supplied.

GPC has has supplied the required infomation 2 which shows the anal-ysis to be an accurate representation of the worst case voltage conditions for the class 1E buses and loads.

Position 5--No event or condition should result in simultaneous or cor: sequential loss of both required cin uits to the offsite power network (GDC 17 ) .

GPC has analyzed the connections of the Hatch Station to the offsite 2

power grid and has detennined that no potential exosts for either a simultaneous or a consequential loss of both circuits from the offsite grid.

a 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 1E loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.

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

l l

Each unit is independently connected to offsite power and no common electrical connection exists between units; therefore, this position does not apply to the Hatch Station.

6.0 COPELUSIONS i

The analyses submitted by GPC for the Edwin I. Hatch Nuclear Power Station were evaluated in Section 5.0 of this report. It was found that:

1. With one exception, voltages within the operating '

limits of the class 1E equipment are supplied for all projected i:ombinations of plant load and normal offsite power crid conditions; including an accident in one unit a?;d the safe shutdown of the other unit.

GPC should be required to document, by suitable qualification tests, that their AC contactors can operate continuously down to 85% (of 600Y).

2. The test used to verify the analysis shows that the analysis is an accurate representation of the worst  :

case conditions analyzed.

3. GPC h&s datermined that no potential for either a simultanots or consequential loss of both offsite power sources exists.

I EG&G Idaho, Inc., is perfoming a separate review of the ur.dervoltage relay protection at the Edwin I. Hatch Station. This will eyr.luate the l relay setpoints and time delays to determine that spurious tripping of the class 1E buses will not occur with nomal offsite source voltages.

7. 0 REFEREPCES

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

2. GPC letter, R. J. Kelly, to U.S. Nuclear Regulatory Commission, "Mequacy of Station Electric Distribution System Voltages," dated December 7,1979.

3. GPC letter, Chas. F. Whitmer, to U.S. Nuclear Regulatory Commission,

" Emergency Power Systems," dated July 22, 1977.

4. GPC letter, W. A. Widner, to U.S. Nuclear Regulatory Commission, i

"Mequacy of Station Electric Distribution System Voltages," dated j April 28, 1980.

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5. Telecons, D. Verelli, NRC, R. Baker, GPC, A. Udy, EG&G Idaho, Inc.,

j June 11,1980, June 13,1980, June 23,1980, and June 25, 1980.

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6. GPC letter, W. A. Widner, to U.S. kclear Regulatory Comnission,

" Response to Request for Additional Information--System Voltage

- Study," dated October 9,1980.

7. Telecons, R. Baker, GPC, A. Udy, EG8G Idaho, Inc., December 17 and 23, 1980, January 7 and 26,1981, and February 13, 1981. ,'

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