ML20039A452

Adequacy of Station Electric Distribution Sys Voltages, Palisades Plant, Informal Rept

ML20039A452
Person / Time
Site:	Palisades, Ginna
Issue date:	11/30/1981
From:	Udy A EG&G, INC.
To:	Donohew J Office of Nuclear Reactor Regulation
References
CON-FIN-A-6429 EGG-EA-5417, NUDOCS 8112170622
Download: ML20039A452 (14)

Text

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM ggfg N'

BI[8 VOLTAGES, PALISADES PLANT, DOCKET NO. 50-255, t-

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This is an informal report intended for use as a preliminary or working document Prepared for the U.S. Nuclear Regulatory Comission Under DOE Contract No. DE-AC07-761D01570 FIN No. A6429 hEGnGwa.

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FORM EG4G 3e6 (Aev.11 F91 INTERIM REPORT Accession No.

Report No.

EGG-EA-5417 Contract Program or Project

Title:

Selected Operating Reactor Issues Program (III)

Subject of this Document:

Adequacy of Station Electric Distribution System Voltages, Palisades Plant, Docket No. 50-255, TAC No.

12780 Type of Document:

Informal Report Author (s):

A. C. Udy Date of Document:

November 1981 RIsponsible NRC Individual and NRC Office or Division:

J. N. Donohew, Division of Licensing Tnis document was prepared primarily for preliminary or internal use. it has not received full review and approva!. Since there may be substantive changes, this document should not be considered final.

EG&G loaho, 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.

A6429 INTERIM REPORT

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES PALISADES PLANT Docket No. 50-255 November 1981 A. C. Udy Reliability and Statistics Branch l

Engineering Analysis Division l

EG&G Idaho, Inc.

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TAC No. 12780

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ABSTRACT This EG&G Idaho, Inc, report reviews the capacity and the capability of the onsite distribution system at the Palisades plant, 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 Reactor Issues Program (III)" being conducted for the U.S. fluclear 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 che work under the authorization, B&R 20 19 01 06, FIN No. A6429.

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,s CONTENTS 1.0 I N TR O D UC T I O N....................................................

I 2.0 DESIGN. BASIS CRITERIA..........................................*

I 3.0 SYSTEM DESCRIPTION..............................................

3 4.0 ANALYSIS DESCRIPTION............................................

3 4.1 Design / Operation Changes..................................

3:

4.2 Analysis Conditions.......................................

3 4.3 Analysis Results..........................................

5 4.4 Analysis Veri /ication.....................................

5 5.0 EVALUATION......................................................

5

6.0 CONCLUSION

S.....................................................

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7.0 REFERENCES

. 8 FIGURE 1.

Palisades plant electrical single-line diagram..................

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I TABLE 1.

Class lE Equipment Voltage Ratings and Analyzed Worst Case Load Terminal Vol tages......................

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2.

Comparison of Analyzed' Voltages and Undervoltage Relay Setpoints....................................

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES PALISADES PLANT

1.0 INTRODUCTION

i 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 (GDC) 17 is being questioned at all nuclear po~wer stations. The NRC, in tne generic letter ofAugugt8,.1979,"AdequacyofStationElectricDistributionSystemsVolt-ages,"

required each licensee to confirm, by analysis, the adequacy of the voltage at the class IE loads. This letter included 13 specific guide-lines to be followed in determining if the load terminal voltage is ade-quate to start and continuously operate the class lE loads.

Consumers # Power Company (CPCo) responded with analyses of January 9, 1980,2 18,1980g.3 Information on required testing was sup-and March 7, 198 Subsequentconcprnswereaddressedjnletters plied on July dated August 22,1980,$ F 9, 1981,0 and March 3, 1981.

ebruary n letters of October 2; 1978,8 Additionalinformationwasobtainedj0andinthePalisadesPlantFinal February 27, 1980,9 and May 7, 1980, Safety Analysi Report (FSAR). Additional analyses were provided on July 29,1981,gI and these were' discussed by telephone in August and September 1981,12 and supported in a submittal of October 12, 1981.13 Information on annunciator and alarms for the DC power system were supplied on July 14,-1981.14 Based on the information supplied by CPCo, this report addresses the capacity and capability of the onsite distribution system of the Palisades Plant, in conjunction with the offsite power system, to maintain the vol-tage for the required class lE equipment within acceptable limits for the worst-case starting and 1 ad conditions.

2.0 DESIGN BASIS CRITERIA The positions applied in determining the acceptability of the offsite voltage conditions in supplying power to the class lE 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 Structures, Sys-tems, and Components," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.

3.

General Design Criterion 13 (GDC 13), " Instrumentation and Con-I trol," of Appendix A, " General Design Criteria for Nuclear Power l

Plants," of 10 CFR 50.

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345 KV UN!T

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CLASS lE BREAKERS SHOWN ALIGNED FOR PREFERRED OFFSITE POWER nom mm C

C T BUS 12 T bus 11 480V 480V CLASS lE CLASS lE PALISADES UNIT ONE LINE DIAGRAM FIGURE 1 2

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308-1974,"Cla61.EhowerSystemsforNuclearPower 4.

IEEE Standard Generating. Stations."

g, dated August 8,1979. jailed'id A, letter sent to the licensee, 5.

Staff positions as de ss s,

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ANSI C84.1-1977, "Voltige'P.htings for Electric Power Systems and Equipment (60 Hz)."

wh lines {ixreviewpositionshavebeenestablished.fromtheNRCanalysifguide-'

and the above-listed documents.

Toese positions are stated in Section 5.0.

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3.0 SYSTEM DESCRIPTION

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,q Fi gram.4'gure 1 is a simplified sketch cf the unit electricalkn2-line dia-3 Y

2400V Class lE Buses IC and 10 car, be supplied by 'either' stet onc power transformer (SPT) 1-2, startup transformer (SUT) 1-2, or the resehe (,

transformer via 4160V Bus IF. Technical specifications require that both SPT l-2 and SUT l-2 be operable before and,duririg opera ion. The reserve transformerisusedonlyduringcoldshutdownperplant,(operatingprocedure SOP-30.

480V Class lE Buses 11 and 12 are suppl'jjd by indeperdent trarisformers from Buses IC and ID, respectively. The four 120V prefer' red ac btses are normally powered by oattery-supplied inverters.

Tne FSAR,' Section)d.3.5.2, indicates that a backup regulator, powerea by the 120V instrument!ac bus, is the backup source for all four of the 120V preferred ac buses / Mechani-cal interlocks prevent more than one bus from being connected this Nay at a time. The 120V instrument bus is powered by a transformer connected to.,,'4 480V Bus 11 or Bus 12.

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b There are undervoltage relays on both 2400V Buses 1C and 'lD.E Tnese relays separate the class lE buses from offsite power should there 'be a 'l degradation of offsite power, and initiate sequencing onto diesel, power.

Thereisasingletransmissionfeederfromthe345kVswii.chyardtothe three startup transformers.6 CPCo supplied the equipment operating ranges identified in Tab!e 1.

I 4.0 ANALYSIS DESCRIPTION 4.1 Desian/ Operation Changes. The voltages shown on Table I are based on tne licensee changing the taps on Transformers 11 and 12 to the 2400V setting.

This has been accomplished in 1979.7 4.2 Analysis Conditions. CPCo has determined that the minimum expec-ted offsite grid voltage is 345kV. CPCo has not supplied the maximum j

expected offsite grid voltage.

l CPCo has analyzed each offsite source to the onsite distribution sys-l tem under extremes of load and offsite voltage conditions to determine the terminal voltages to lE equipment.

The worst case class lE equipment ter-minal voltages. occur under the following conditions:

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k TABLE 1.

CLASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES (% of nominal voltage)

.iaximum Minimum Analyzed Equipment Condition Rated Analyzed Rated Steady State Transient

-2300V Motors StaYt"s

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Operate.

\\110 106.6

'90 96.7 S'ar't.

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53.4 460V Motors Ope' rate 110 103.3 90 89.lb 55.9 440V Motors' Start a

Operate 110 108.0 90 93.4 480V Starters Pickup 85 54.8 50 54.8 Dropout Operate 125 99.0 50 86.3 Other Equipmentc a.

Rated starting voltages for motors were not supplied. CPCo supplied speed-torque curves for typical motors in lieu of this data. The curves slipplied indicate that the motors are capable of accelerating the con-nected ;ond with the minimum analyzed load terminal voltage. Also, CPCo hustptedthatthemotorswillstartassequenced,withthegridat 345kV.

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b.

CPCo has determined that operation at this voltage is not detrimental to either the life of the equipment or the capability to operate the t-connected load. This is because the motor rated horsepower exceeds the load requirements and the torque available at this voltage is in excess of the load requirements. Thermal ratings of these worst case loads are stated as not exceeded.13 c.

Other equipment includes battery chargers, rated to full output voltage at an input voltage down to 432V. The output voltage decreases below this input voltage.

Should the output voltage be reduced below the battery voltage, the battery will supply the dc loads; however, how long this con-dition will go uncorrected is not a part of the unit technical specifica-tions.

120Vac vital instrumentation is powered by inverters or a back-up regulated transformer.

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1.

The minimum expected continuous load terminal voltages occur when the grid is minimum and the startup tr'ansformers supply the maxi-mum expected class lE and non-class IE loads. Startup transfor-mer 1-2 will be supplying alliclass lE loads.

2.

The minimum expecte.d trans'ient'_ load terminal voltages occur when the offsite grid is minimum and an accident trips the unit gener-ator and initiates the simultaneous start of all of the safety injection loads at an initial assumed power factor of 0.2.

3.

CPCoidentifiedtheconditionsthatleadtcamaximumcontingous bus voltage as " normal grid and generator voltage extremes."

4.3 -Analysis Results.

Table 1 shows the projected worst case 1

class lE equipment terminal voltages.

The table shows that some 460V motors can be operated continuously at less than rated input voltage. CPCo indicates that this is pos the load on the motor is less than the motor horsepower rating.gible since 82 Since themotorhasreservepower,someofthiscanb'eusedtocompegateforthe less than rated input voltage, without loss of equipment life.

During a simultaneous start of all of the safety injection loads following a unit trip, contactor pickup for the 480 V motor control center loads is prevented by low bus voltage.

However, this condition is temporary, and the loads will start as the voltage recovers above voltage needed for starter pickup.

It will not cause contactor dropout or spurioJs shedding of any-loads.

Continuous output of the battery chargers has not been assured by CPCo for when the input voltage is less tnan the minimum battery charger rating.

4.4 Analysis Verification. CPCo provided testing to verify the accuracy of their analy315.4 All metering was within 2 1/2% accuracy.7 The test consisted of measuring loads and voltages and calculating corres-ponding voltages for the same grid and load conditions. The deviation between the measured and the test calculation voltages was within +1.07%

for all buses.

5.0 EVALUATION lines {ix review positions have been established from the NRC analysis guide-and the documents listed in Section 2.0 of this report. Each

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review position is stated below followed by an evaluation of the licensee submittals. The evaluations are based on completion of changes described in Section 4.1.

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

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V CPCo has shown, by analysis,'that except for the battery chargers, the J

Palisades station has sufficient capability and. capacity for starting an'd continuously operating all class-lE-equipment within allowable equipment ratings.

batteryvoltageislessthanthefloatvoltage.gnunciationwhenthe The DC power systems at Palisades provide

' This happens when the battery charger output is less than 125 V, such as might happen if.the.

input voltage to a battery charger is degraded. The CPCo analysis shows that it is possible to have a degraded-input voltage to the battery chargers; the effect on the output-is not known. When the annunciator sounds a limiting condition of operation, per technical specifica-tion 3.7.lh and.3.7.2f and h, would be impased.

Since the limiting-condition is imposed when the battery' charger output is affected by a

' degraded input voltage, and the battery charger is not damaged under this 7

input voltage the. possibility of operating in this condition is acceptable.

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 the required class lE equipment without exceeding the equipment voltage ratings.

CPCo has shown, by analysis, that the voltage ratings of the class lE equipment will not be exceeded Position 3--Loss of offsite power to either of the redundant class lE distribution systems:due to operation of voltage protection relays, must not occur when the offsite power source is within expected voltage limits.

As shown.in Table 2, voltage relays will not cause the loss of~ class' 1E distribution systems when the offsite grid voltage is within expected limits.

Position 4--The NRC letterl requires that test results verify the accuracy of the voltage analyses supplied.

CPCo has supplied the required information which shows the analysis 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 the simultaneous or consequential loss of both required circuits from the offsite power network to the onsite distribution system (GDC 17).

CPCo does not meet the General Design Criteria (GDC) 17 requirements for two independent circuits from a minimum of two offsite power sources.

This is being considered by the NRC separately, under the Systematic Evalu-ation Program, Topic VII-3, Safe Shutdwon.

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

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' TABLE 2.

COMPARISON'0F ANALYZED VOLTAGES AND UNDERV0LTAGE RELAY SETP0INTS'

(% of nominal. voltage) a 9

Minimum Analyzed Relay Setpoint Location / Relays Voltage Time

. Voltage (Tolerance)

Time 2400V' bus Degraded grid 93.0

' continuous

.91.9(+0.9) 6.5 s b

Loss of grid-

' 74.4 -

4.0s 77.5(+3.3)=

c b

Loss of grid 74.4' 4.Os 64 Instante-neous Ta.: Licensee has determined by analysis the minimum bus voltages with the offsite grid at the minimum expected voltage and the worst case plant and-class lE-loads.

b.

Time until s voltage recovers to above the nominal degraded grid relay setpoint c.

This is an. inverse time delay rela For a trip at 70% of nominal voltage,14secondswillhaveelapsed.{I and operating voltage for all required class lE loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.

This applies to multi-unit plants.

It does not apply tc the Palisades Plant,'a single-unit station.

6.0 CONCLUSION

S Tne voltage analyses' submitted by CPCo for the Palisades plant were evaluated in Section 5.0 of this report. The change described in Section 4.1 has been completed, and it was found that:

1.

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

2.

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

9 3.

The NRC is considering the simultaneous or consequential loss of both offsite power sources separately in the Systematic Evalua-tion Program, Topic VII-3.

4.

Loss of offsite power to class 1E buses, due to spurious opera-tion of voltage protection 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

Humboldt Bay); " Adequacy of Station Electric Distribution-Systems Voltage," August 8, 1979.

2'..

CPCo letter, David P. Hoffman, to Director, Nuclear. Reactor Regula -

tion, NRC, " Adequacy of Station. Electric Distribution Systems Volt-ages,"' January 9,"1980.

3.

CPCo. letter,-Roger W. Huston, to Director of Nuclear Reactor Regula-

' tion, NRC, " Response to Adequacy of Station Electric Distribution

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Systems Voltages," March 7, 1980.

4.-

CPCo letter, Steven R. Frost, to Director, Nuclear Reactor Regulation,

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NRC,= " Response to Verification of Analytical Models for Adequacy of Station. Power," July 18, 1980.

5.

CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula-tion, NRC, " Response to Adequacy of Station Power," August 22, 1980.

6.

CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula-tion, NRC, " Response to Station Electric Distribution System Volt-ages," February 9,-1981.

7.-

CPCo letter, Steven R. Frost, to Director, Nuclear Reactor Regulation, NRC, " Response to Adequacy of Station Electric Distribution System Voltages," March 3, 1981.

18.

CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula-tion, NRC,'" Response to Emergency Supply Generic Issues," October 2, 1978.

9.

CPCo letter, Steven R. Frost, tn Director, Nuclear Reactor Regulation, NRC, " Response to Additional Information for Degraded Grid Voltage,"

February 27, 1980.

10. CPCo letter, R. W. Huston to Director, Nuclear Reactor Regulation, NRC, " Additional Information on Degraded Grid Voltage," May 7,1980.

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11. CPCo letter, B. D. Johnson to Director of fluclear Reactor Regulation, NRC, " Adequacy of Station Electric Ditribution System Voltages i

Additional Information," July 29, 1981.

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12. Telecons, R. Prevatte, NRC, B. Johnson, D. May, C. Toner, CPCo, A. Udy EG&G Idaho,.Inc., August 17, 1981, August 24, 1981 and September 15, 1981.

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13. CPCo letter, T. C. Bordine to Director, Nuclear Reactor Regulation, NRC, " Response to Additional NRC Questions Regarding Adequacy of Station Power," October 12, 1981.

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14. CPCo letter, R. A. Vincent to Director, Nuclear Reactor Regulation, NRC, "SEP Topic VIII-3.B, DC Power System Bus Voltage Monitoring and Annunciation," July 14, 1981.

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