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TECHNICAL EVALUATION OF THE ADEQUACY OF-

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:>TATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGESfFOR'THE HADDAM NECK NUCLEAR POWER PLANT|

James C. Selan!

SELECTED ISSUES PROGRAM

(Docket No. 50-211)

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February 1, 19821

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n'@ ; o ** sDe opinions and conclusions stated are those of the author and may or may not be those

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his work was supported by the United States Nuclear Regulatory Commission under]'y^W':MM. {ny%F- 3

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a Memorandum of Understanding with the Uruted States Department of Energy.-

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0204050166 820323PDR ADOCK 05000213PDR-- FL _ _ _ _ .

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DISCLAIMER

This document was prepared as an account of work sponsored by an agency of the United States Government. Neitherthe United States Government nor any agency thereof, nor any of their employees, makes any warrsnty. expressedor implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any

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information apparatus, product, or process disclosed. c' represents that its use would not infringe privately ownedrights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufac-

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turer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the UnitedStates Government or any agency thereof.The <iews and opinions of authors expressed herein do not necessarily state

or reflect those of the United States Government or any agency thereof._

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Avsilable from: Sstional Technical Information Service - U.S. Department of Commerce

5:35 Port Royal Road SpnngGeld. V A 22161 - 55.00 per copy - (Micronche 53.50s

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ABSTRACT.

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This report documents the technical evaluation of the adequacyi

)of the station electric distribution system voltages for the Haddam Neck.

The evaluation is to determine if the onsite distri- '

Nuclear Power Plant.bution system', in conjunction with the offsite power sources, has sufficient

and operate all Class lE loads within thecapacity to automatically startequipment voltage ratings under certain. conditions established by the Nuclear-

Regulatory Commission.the electric distribution system has theThe analysis shows that

capacity and capability to supply adequate voltage to the Class lE equipment,provided that the grid is maintained at or above the administrative minimumlimits.

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FOREWORD

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This report, is supplied as part of the Selected Electrical,Instrumentation, and Control Systems Issues (SEICSI) Program being con-ducted for the U. S. Nuclear Regulatory Commission, Office of Nuclear

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Reactor Regulation, Division of Operating Reactors, by Lawrence Livermore1National Laboratory.

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The U. S. Nuclear Regulatory Commission funded the work under theauthorization entitled " Electrical, Instrumentation and Control System Support,"&&R 20 19 04 031, FIN A-0250.

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TABLE OF CONTF.NTS.

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1. INTRODUCTION . . . . . . . . . . . . . .. .

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22. DESIGN BASIS CRITERIA . . . . . . . . . . . . .

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23. . SYSTEM DESCRIPTION . . . . . . . . .: .,. . .

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4. . . . . . . . . . . . . . .4. ANALYSIS .

44.1 Analysis Conditions . . . . . . . . . .

44.2 Analysis Results. . . . . . . . . . .

44.2.1 Overvoltage . . . . . . . . . . . .

44.2.2 Undervoltage. . . . . . . . . . . .

64.3 Analysis Verification . . . . . . . . .

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6. . . . . . . . . . . . . . .5. EVALUATION

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76. CONCLUSIONS . . . . . . . . . . . . . . .

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REFERENCES

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ILLUSTRATIONS

FIGURE 1 Haddam Neck Nuclear "ower Plant3Electrical One-Line Diagram. . . . . . . . . .

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{! . TABLE 1 Haddam Neck Nuclear Power Plant

Class lE Equipment Voltage Ratings and Analyzed5Worst Case Terminal Voltages. . . . . . . . . .

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TECHNICAL EVALUATION OF THEADEQUACT OF STATION ELECTRICDISTRIBUT20N SYSTEM VOLTACES*

FOR THE HADDAM NECK NUCLEAR P0t.*ER PLANT

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(Docket No. 50-213).

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James C. Selan. .. 1 - . _.s.

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Lawrence Livermore National Laboratory, Nevada. .;

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~ 1. INTRODUCTION~

The Nuclear' Regulatory Commission (NRC) by a letter dated.

August 8, 1979 (Ref. 1], expanded its generic review of the adequacy ofthe station electric distribution systems for all opercting nuclear power

facilities. This review is to determine 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 loadswithin the equipment voltage ratings. In addition, the NRC requested eachlicensee to follow suggested guidelines and to meet certain requirementsia the review. These requirements are detailed in Section 5 of this -

re po rt.

By letters dated November 15, 1979 [Ref. 2], March 6, 1980 (Ref. 3],August 21, 1980 (Ref. 4], November 4, 1980 (Ref. 5], October 23, 1981(Ref. 6], and December 10, 1981 (Ref. 7]. Connecticut Yankee Atocic PowerCo' pany (CYAPCO), the ficaniee~, ~sulimitted their analysis and conclusionmregarding the adequacy of the electrical distribution system's voltages atHaddam Neck Nuclear Power Plant.

The purpose of this report is to evaluate the licensee's submittalwith respect to the NRC criteria and present the reviewer's conclusion on theadequacy of the station electric distribution systems to maintain the voltagewithin the desig'n limits of the ' required Class lE equipment for the worst cases' tarting and load conditions.

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2. DESIGN BASIS CRITERIA.

The design basis criteria that were applied in determining theadequacy of station electric distribution system voltages to start and

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operate all required safety loads within their required voltage ratings,

are as follows:

(1) General Design Criterion 17 (GDC 17), " Electric Power - .

Systems," of Appendix A, " General Design Criteria for-Nuclear Power Plants," in the Code of Federal Regulations,Title 10, Part 50 (10 CFR 50) (Ref.,8]. ,

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(2) General Design Cr1terion 13 (GDC 13), " Instrumentation andControl," of Appendix A. " General Design Criteria forNuclear Power Plants," in the Code of Federal Regulations,Title 10, Part 50 (10 CFR 50) (Ref. 8].

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(3) ANSI C84.1-1977, " Voltage Ratings for Electric Power Systemsand Equipment" [Ref. 9].

(4) IEEE Std 308-1974, " Class lE Power Systems for Nuclear PowerGenerating Stations" [Ref. 10]. ..

(5) " Guidelines for voltage Drop Calculations," Enclosure 2, toNRC letter dated August 8, 1979 [Ref. 1].,

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3. SYSTEM DESCRIPTION

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A one-line diagram of the plant's electrical distribution systemis shown in Figure 1. The electrical distribution system is designed sothat during plant startup conditions, the total station service demand issupplied by the 115 kV system through service station transformers 389 and399. Af ter the plant has attained operating conditions, 4160-volt buses1-13 and 1-1A are transferred to service station transformer 309. Shouldthe supply through service station transformer 309 fail, buses 1-1A and1-1B are automatically transferred to the 115 kV supply (transformers

- 389 and 399).

With the loss of a normal 115 kV supply to buses 1-2 or 1-3, theloads will automatically be transferred to the remaining bus section byclosing tie breaker 2T3 (normally open). Upon restoration of the 115 kVsupply, an automatic retransfer will return the lead groups to their normalsupply and open tie-breaker 2T3.

Tie-breakers between 480-volt bus sections permit manual transferto adjacent buses, but interlocks prevent concurrent closure with the supplybreakers to prevent circulating currents. Tie-breaker ST6 is permanentlyremoved from its cubicle to prevent paralleling of the redundant load groups.

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11. KV115 KV. 1206

345 KV 1772.

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FIGURE 1

HADD AM NECK NUCLEAR POWER PLANTELECTRICAL ONE-LINE DIAGRAM

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4. ANALYSIS.

4.1 ANALYSIS CONDITIONS-

CAYPCO has analyzed each offsite source to the onsite distrib'utionsystem under minimum and maximum load demand conditions and offsite voltages.to determine the voltages at.the terminals of the Class 1E equipment. c.The-;minimum offsite grid voltage used was 106 kV. .The 106 kV value is below

'the grid' administrative limit of 106.4 kV when both service station trans- *

formers 389 and 399 are in service. When only one'of the two service station ,

transformers is in service, an administrative limit of 110.8 kV is used. Themaximum expected grid voltage used in the analyses is 117 kV. However, present

. operating limits specify an upper. limit of 114.7 kV. Calculated typical voltage

drops of 10 volts for 480-vole running loads, 50 volts for 480-volt startingloads, 20 volts for 4160-volt running loads, and 100 volts for 4160-volt startingloads were used in the analyses. Both charging pumps, all service water pumps,and all CAR fans are considered in operation for normal full load case studies.When starting these individual loads, the running load of the motor is stillconsidered to be part of the normal full load, thus making the analysis moreconservative. The effect on the Class 1E equipment when starting a large non- '

Class lE load after the Class lE buses are fully loaded was also analyzed..

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4.2 ANALYSIS RESULTS

The worst case Class lE equipment terminal voltages occur under thefollowing conditions:

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4.2.1 OvervoltageMinimum station load with a maximum grid voltage of 117 kV, unit-in shutdown mode, and either 1 or 2 station service transformersin service.

4.2.2 UndervoltageF1:nt trip with LOCA, minimum grid voltage of 106 kV, two stationservice transformers in service, normal full loads', accident loads

-- starting and running.

These worst case Class lE equipment terminal voltages are shownin Table 1.

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TABLE 14

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FJWDAM NECK NUCLEAR POWER PLANCLASS lE EQUIPMENT VOLTAGE RATINGS AND

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ANALYZED WORST CASE TERME!AL VOLTACES(in : of Equipment Nominal Voltage Rating)

Maximum tiinimum

' Rated Analyzed (a) Rated Analyzed (a)-

Nominal*Voltage ;

- Racing Steady SteadyEquipment (100 %) State State Transient (b)Motors 4000

start 80 87.9Operate 110.0 110.1 90 95.8 .

440start 80 80.9Operate 110.0 112.0 90 96.1

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Starters 440Pickup 87.7 96.1Dropout 48.6 80.9Operation 110.0 112.0 90 96.1

OtherEquipment (c)

Footnotes:

(a) CTAPCO does not consider backfeeding through main transformer 319 andservice station transformer 309 a viable source connection; therefore noanalysis was submitted. Bus loading is considered to be conservativebecause while starting individual loads (i.e. charging and service water

| pumps and the CAR fans), the running load for these starting motors arei not removed from the loading condition on the buses.r -

(b) These voltages represent the lowest transient voltage reached at theterminals of the Class 1E equipment during load starting.

(c) All " vital low voltage AC" is supplied from inverters and all " semi-vitallow voltage AC" is supplied by regulating transformer with the exception ofthe service water filter motors which are not considered Class lE.

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4.3 ANALYSIS VERIFICATION. ..

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CYAPCO verified their gomputerized . voltage analyses calculations ,

by measuring the loads and voic4ges on each cf the buses and the offsite ~ '

supply voltage. Using the measured loads and offsite source voltage, bus* voltages were calculated using the cciputerized transformer voltage drop

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method. The measured voltages were then compared to the calculated, voltages r

producing error differences of -0.86 to_-2.56 percent for steady state condi-|* tions on the 4160-volt and 4,80-volt buses respectively. The plant was at

full load with bus loading from 29% to 91". A minus percentage error indicates'

," the measured values to.be higher than the calculated values. ,

5. EVALUATION

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The NRC generic letter (Ref. 1] stated several requirements thatthe plant voltage analysis must meet. These requirements and an evaluationof the licensee's submittals are as follows:

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(1) With the minimum expected grid voltage and maximum load'

condition, each offsite source and distribution systemconnection must be capable of starting and continuouslyoperating all Class lE equipment within the equipment'svoltage ratings.

The voltage analysis submitted by CYAPCO shows that the'.

offsite sources, in conjunction with the onsite distributionsystem, have the capability and capacity to automatically-

start and continue to operate all Class lE equipment withintheir design ratings at the grid voltages of 106 kV (two servicetransformers in service) and 110.6 kV (one service stationtransformer in service).

l (2) With the maximum expected offsite grid voltage and minimumload condition, each offsite source and distribution systemconnection must be capable of continuously operating the

, . required Class lE equipment without exceeding the equipment's

|voltage ratings.

The analysis shows that for the conditions detailed in Section4.2.1 the voltage at the terminals of the Class lE equipmentcould exceed the design ratings by 2% at the 480-volt level.The licensee has proposed to install overvoltage monitors on<

the 4160-volt and 480-volt Class lE buses. The relays will be

Class lE, and will alarm through non-Class 1E annunciators.; The relays' setpoints are 492 volts at the 480-volt buses and

4410 volts at the 4160-volt buses.

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(3) Th'a analysis =ust show that there will be no spurious sepa-ration from the offsite power. source to the Class lE busesby the voltage protection relays when the grid is withinthe normal expected limits and that the loading conditionsestablished by the NRC are being met.*

LLNL will verify in a separate report (TAC No. 10025) that..

the requirements of this position are met.

(4) Test results are required to verify the voltage analysescalculations submitted.

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CYAPCO verified the voltage analysis by test. The errordifferences between measured values and the calculatedvalues confirm that the analysis results are acceptable.

(5) Review the planr's electrical power systems to determine ifany events or conditions could result in the simultaneousloes of both offsite circuits to the onsite distributionsystem (compliance with CDC 17).

CYAPCO reviewed the electrical power system and identifiedtwo events which could result in the simultaneous loss ofboth required circuits. These events are the failure of4160-volt tie breaker 2T3 and the failure of 115 kV breaker389T399 (Fig. 1). The failure of 2T3 will automatically

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clear 4160-volt buses 1-2 and 1-3 to isolate the fault.The failure of 389T399 will automatically. trip the two

115 kV lines (1772 and 1206).'

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6. CONCLUSIONS

Based on the information submitted by CYAPCO which is evaluated in|

Section 5 of this report, it is concluded that:\

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(1) By installing the proposed Class LE overvoltage monitors which~|

will alarm through non-Class lE annunciators, corrective action' can be taken to eliminate overvoltages at the terminals of the

Class lE equipment.

(2) A separate review of the undervoltage protection scheme will bemade to determine that spurious tripping from the offsite sources

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(3) The test verification results verify the accuracy of the voltageanalysis submitted.;

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(4) The Class 15 equipment will be operating within the voltagedesign li=its for the worst case loading conditions with thegrid voltage at 106 kV for two service station transformeroperation and at the administrative limit of 110.6 kV for ,

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(5) Additional studies should be made on the two single events whichcould result in loss of both offsite sources, that are detailed in

Section 5. Item 5.- The additional studies will be made by thesystematic evaluation program (SEP) under topic- 7.3, entitled" Systems Required-for Safe-Shutdown". ;__ _ . -.

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I recommend that NRC approve the voltage' analysis submitted which showsthat the station electric distribution system is adequate to supply acceptablevoltages for the worst case loading conditions.

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REFERENCES,

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1. NRC letter (W. Gammill) to all Power Reactor Licensees,dated August 8, 1979.

2. Northeast Utilities letter (W. G. Counsil) to NRC (D. L. Ziemann),,

dated November 15, 1979

3. CYAPCO letter (W. G. Counsil) to NRC (D. L. Ziemann),dated March 6, 1980. _

4. CYAPCO letter (S. G. Counsil) to NRC (D. M. Crutchfield),dated August 21, 1980. - -

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S' . CYAPCO letter (W. G. Counsil) to NRC (D. M. Crutchfield),dated November 4, 1980.

6. CYAPCO letter (W. G. Counsil) to NRC (D. M. Crutchfield),.

dated October 23, 1981.,

, 7. CYAPCO letter (W. G. Counsil) to NRC (D. M. Crutchfield),dated Dece=ber 10, 1981.

8. Code of Federal Regulations, Title 10, par: 50 (10CFR50),General Design Criterion 13 and 17 of Appendix A for Nuclear PowerPlants.

9. ANSI CS4.1-1977," Voltage Ratings for Electric Power Systemsand Equipment".

10. IEEE Std. 308-1974, " Class lE Power Systems for Nuclear PowerGenerating Stations".

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