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INTERIM REPORT

Accession No.

Report No, EGG-EA-5258

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C:ntract Program or Project Title:. Electrical Instrumentation and Control System Support

St.ebject of this Document.

Adequacy of Station Electrical Distribution System Voltages, Three MileIsland Nuclear Station Unit 1

Type of Document:Technical Evaluation Report

Author (s):

E. W. Roberts

D:le of Document:.

September 1980

R:sponsible 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 receivedft.il review and approval. Since there may be substantive changes, this document shouldnot be considered final.

EG&G Idaho, Inc.Idaho Falls, Idaho 83415

Prepared for theU.S. Nuclear Regulatory Commission

Washington, D.C.Under DOE Contract No. DE-AC07 76tD01570

, NRC FIN No. A6255 |

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- INTERIM REPORT

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TECHNICAL EVALUATION REPORTADEQUACY OF STATION ELECTRICAL DISTRIBUTION SYSTEMS VOLTAGES

THREE MILE ISLAND NUCLEAR STATION UNIT 1

Docket No. 50-289

September 1980

E. W. RobertsReliability and Statistics Branch

Engineering Analysis DivisionEG&G Idaho, Inc. *

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IAC No. 11962

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. ABSTRACT.

The Nuclear Regulatory Commission.has required all licensees to analyzethe electric power system at each nuclear station. This review is to deter-mii.e if the onsite distribution system in conjunction with the uffsite

i power sources has sufficient capacity and capability to automatically startand operate all required safety loads within the equipment voltage ratings.This Technical Evaluation Report reviews the'submittals for the Three MileIsland Nuclear Power Station, Unit 1.

The offsite power sources, in conjunction with the onsite distribution

system, has been shown'to have sufficient capacity and capability to auto- ~

matica11y start as well.as continuously operate, all required safety relatedlo' ads within the equipment rated voltage limits in the event of either ananticipated transient or an accident condition.

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' FOREWORD.

This report.is supplied as part of the selected Electrical, Instru-

mentation, .and Control Systems (EICS) issues program being conducted for3

the U.S. Nuclear Regulatory Conunission, Of fice of Nuclear Reactor Regula-

; tion, Division of Operating Reactors, by. EG&G Idaho, Inc., Reliability and '

Statistics Branch.,

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i The U.S. Nuclear Regulatory Connaission funded the work under the auth-orization entitled " Electrical, Instrumentation, and Control System Sup-port," B&R 20 19 01 03, FIN No. A6256.

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CONTENTS

1.0 INTRODUCTION ...................................................... I

2.0 DES I GN B AS IS C RITE RI A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

3.0 SYSTEM DESCRIPTION ................................................ 2*

4.0~ ANALYSIS DESCRIPTION .............................................. 2 .T-

4.1 Design / Operation Changes ..................................... 21i -

.4.2 . Analysis Conditions 4..........................................

4.3 Analysis Results 4.............................................

4.4 Analysis Verification ........................................ .6:

5.0 EVALUATION ........................................................ 6.

-6.0 CONCLUSIONS ....................................................... 8

7.0 R E FE R E N C E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9,

FIGURE ~'

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1.- TMI electric distribution ......................................... 3 .

TABLE

1. TMI-1 Class IE Equipment Voltage Ratings and'.

. Analyzed Worst-Case Terminal Voltages 5.............................1

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TECHNICAL EVALUATION REPORT,

ADEQUACY.0F STATION ELECTRICAL DISTRIBUTION SYSTEM VOLTAGES

THREE MILE ISLAND NUCLEAR STATION UNIT 1

1.0 INTRODUCTION.

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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 beingquestioned at all nuclear power stations. The NRC, in the generic letterof August 8, 1979, " Adequacy of Station Distribution Systems Voltages,"Irequired each licensee to confirm, by analysis, the adequacy of the voltageto the class 1E loads. This letter included 13 guidelines for the analysis.

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In response to the NRC generic letter, Metropolitan Edison Company2(Met-Ed) submitted a voltage analysis on October 16, 1979 . Because of2

determined voltage problems, Met-Ed proposed design and procedural changes'

in their May 15, 1980 letter. Also included was a voltage analysis basedon these changes.

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' Based on the information supplied :y Met-Ed, this report addresses thecapacity and capability of the onsi distribution system of'the Three MileIsland Nuclear Station Unit 1 (TMI-1), in conjunction with the offsitepower system, to maintain the voltage for the required class 1E equipmentwithin acceptable limits for the worst-case starting and load conditions.

2.0 DESIGN BASIS CRITERIA;

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The positions applied in determining the acceptability of the offsitevoltage conditions in supplying power to the class 1E equipment are' derivedfrom the following:

1. General Design ' Criterion 17 (CDC 17), " Electrical PowerSystems," of Appendix A, " General Design Criteria forNuclear 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 Nuclear Power Plants," of 10 CFR 50.

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3. General Design Criterion 13 (GDC 13), " Instrumentationand Control," of Appendix A, " General Design Criteriafor Nuclear Power Plants," of 10 CFR 50.

4. IEEE Standard 308-1974, " Class IE Power Systems forNuclear Power Cenerating Stations." -

5. Staff positions as detailed in a letter sent to thelicensee, dated August 8, 1979.1 '

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

Six review positions have been established from the NRC analysis guide-Ilines and the above-listed documents. These positions are stated in

Section 5.

3.0 SYSTEM DESCRIPTION

A single-line diagram of the AC class lE electrical system at TMI-1 is.

shown in Figure 1. The TMI-l class lE electrical distribution system isfed by two auxiliary transformers which are connected to different 230kV

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substation buses and provide the source of power for startup operation andshutdown requirements. Each of the unit auxiliary transformers has twoisolated secondary windings, one at 6900v and one at 4160V. Thi 4160Vwindings supply the class lE distribution systems.

4.0 ANALYSIS DESCRIPTION

4.1 Design / Operation Changes. Met-Ed submitted analyses ,3 based2

on the following proposed changes:

1. The taps on the auxiliary transformers (UAT 1A, UAT IB)will be changed from 230 kV to 224.75 kV.

2. Trip functions will be removed from 480 V bus relays.

3. Designated loads will be automatically tripped uponinitiation of an ES signal.

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4. Installation of new undervoltage relays with new set-points in place of existing electromagnetic-type relays *

for both first and second level.

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5. Institute new procedures to preclude starting either acondensate or a condensate booster pump during the ESblock loading sequence.

All of the described modifications and procedural changes will be completedprior to the next TMI-1 startup. ~

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4.2 Analysis Conditions. The following conditions were considered inthe review:

1. The maximum voltage drop between the 4160V and 480Vbuses /MCCs and connected equipment is 0.02% and 1.0%,respectively. All voltages shown in this report areequipment terminal voltages expressed as percentages ofthe respective equipment nominal voltage.

2. Automatic tripping of Bus IN and designated loads uponES actuation was assumed; manual load shedding was not.

4.3 Analysis Results. Table ) summarizes the comparison of the.

class 1E equipment voltage ratings and the Met-Ed analyzed worst case ter-minal voltages for 4160, 480 and lower voltage equipment. .

The Met-Ed analyses have determined that the worst-case steady-statelow-voltage condition occurs with the offsite grid at minimum voltage, oneauxiliary transformer supplying maximum plant loads, and both ES trains

with the largest ES load demand. Under these conditions, the analyzedminimum terminal voltages for equipment supplied by the class 1E 4160 and

480V buses is 92% for the 4160V ID and IE buses and 87% for the 480V bus1AES VCC. All other 480V bus-supplied equipment have higher voltages.

The worst-case low-voltage transient condition occurs with the above

load and grid voltage and the simultaneous manual restart of the condensate

and booster pumps. The resulting equipment terminal voltages for class 1Eequipment supplied by 4160V bus ID and 480V bus 1E are 81% and 77%, respec-tively. The transient voltages will return to steady state values withinten seconds as the pump motors come up to speed.

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TABLE 1

TMI-1 CLASS 1E EQUIPMENT VOLTAGE RATINGS ANDANALYZED WORST-CASE TERMINAL VOLTAGES

(1 of equipment nominal voltage).

Maximum * Minimum"*

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Allowed Analyzed Allowed Analyzed

Nominal SteadyEquipment Voltage State Transient

Motors 4000 (100%)bStart NA NA 80.1% 92% 81%

Operate 110% 110% 90% 92% NA

460 (100%)cStart NA NA 75% 87% 77%Operate 110% 111% 86% 87% NA

Starters 480 (100%)Operate 110% 106% 82% 84% NA,

Pickup NA NA 75% 84% 75%

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Dropout NA NA 55% 84% 75%

Below 480V 110% d 90% d d.

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Grid stability analysis has determined minimum and maximum grid voltagesa.of 225 and 242kV, respectively,

b. NA - not applicable.

c. All 460V motors have a service factor of 1.15. Because of this, Met-Edhas demonstrated, utilizing IEEE Standard 141-1976 and NEMA Standard MG1-12.42, that no thermal damage to the motor will occur if the motor iscontinuously operated 14% below the nominal voltage with the ambient temp-erature below 40cc and motor loading at or below the nameplate rating.

d. No terminal voltages analyzed. All lower voltage class 1E loads aresupplied from +15% regulated transformers.4,5,6

The Met-Ed analyses have determined that maximum voltages of 111% and

110% will occur on the respective 480 and 4160V buses with a maximum grid,

voltage and a minimum load on the plant buses..

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4.4 Analysis Verification. Med-Ed had previously determined bymeasurements the actual worst case voltage drops between buses /MCCs andloads for 4160 and 480V bus loads. Therefore, Met-Ed's verification testwas only conducted to verify the analyzed bus voltages.

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The Met'-Ed verification method required the measurement of the grid.

voltage and IE bus /MCC loads, phase angles, and voltages. Using themeasured grid voltage and bus /MCC loading, all IE bus /MCC voltages werecalculated using the analysis methods. The measured and calculated bus /MCCvoltages were then compared.

Met-Ed provided the test data and results of their test verificationwith their May 5, 1980, submittal. The 4160V buses were loaded over 30%.However, during the tests only four 480V IE buses were loaded to 30% oftheir analyzed loading with all IE 480V buses /MCCs loaded less than 1%.

The results of their voltage comparison indicate that the analysis voltagesare within 4% of the measured voltages for all 1E buses /MCCs. .

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5.0 EVALUATION

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Six review positions have been established from the 13 NRCianalysis1

guidelines and the references listed in Section 2.0. . Each review posi-tion is stated below, followed by the evaluation of the licensee submittals.The following evaluations are based on completion of changes in Section 4.1and utilized the analysis submitted by Met-Ed on May 15, 1980:

Position 1--Wi.th the minimum expected offsite grid voltage and maximumload condition,_ each of fsite source, in conjunction with the onsite distri-bution system, must be capable of starting and of continuously operatingall class 1E equipment within the equipment voltage rating.

As shown in Teble 1 and discussed in Section 4.2, the analyzed equip-ment terminal voltages for all class 1E equipment will be above their

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minimum voltage rating with the minimum offsite grid voltage and under allsteady state and transient loading conditions.

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Position '2--With the ' maximum expected offsite grid voltage and minimumload conditions, each offsite source and-distribution system connection

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combination must be capable of continuously operating all class 1E equip-

| ment without exceeding the rated equipment voltage.*

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The licensee's analysis indicates that, with the grid maximum and the,

plant load minimum, the voltage at the class 1E 480V buses /MCCs will be'

less than 1% above the maximum allowable value for 460V motors. Since the" analysis was made with the plant in shutdown condition and no motors con--{ nected to the 1E buses, the voltages will be within the motor rating when

accident conditions require the connection of class 1E motors to the buses.The voltage for the buses and other class IE equipment will also be withintheir ratings. Therefore, the' requirements as expressed in the above posi-tion are satisfied.

Position 3--Loss of offsite power to either the redundant class 1E,

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; distribution systems or the individual class 1E buses, due to operation ofvoltage protection relays, must not occur when the offsite grid voltage is -

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within expected voltage limits.

: Subsequent to the removal of the trip function for the 480V bus relays] (Section 4.1). the degraded grid protective relays are the only ones.whichi could cause a loss of offsite power to safety loads when the offsite. gridi voltage is within' normal operating range. The potential for spurious loss

of offsite power will be reviewed in the ongoing EG&G Idaho, Inc., evalu-,

f ation of the TMI-1' degraded grid protec- tion (TAC No 10055).i

4 Position 4--Tes,t results should verify the accuracy 'of the voltageanalyses supplied.

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The testing by Met-Ed to verify the: submitted voltage analysis is notsatisfactory. The loading of the MCCs was too low to accurately determine

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the voltage drop (impedance) from the supplying bus.- The 480V MCCs on both.

trains had less than 1% of full analysis load and no voltage drop was!, measured.

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Position 5--No event or condition should result in simultaneous orconsequential loss of both required circuits from the offsite power networkto the onsite distribution system.

Met-Ed has determined that there are no events or conditions which *

could result 'in simultaneous or consequential loss of both required of fsite,

circuits and, therefore, THI-1 presents no violation of GDC 17 in thisregard.

Position 6--As required by GDC 5, each offsite source shared betweenunits in a multi-unit station must be capable of supplying adequate startingand operating voltage for all required class IE loads with an accident inone unit and an orderly shutdown and cooldown in the remaining units.

Three Mile Island is the location of two nuclear power generatingstations, TMI-A and TMI-2. Each unit is independently connected to offsitepower sources and have no common electrical power interconnections between *

units. Therefore, Position 6 is not Spplicable to TMI-1..

6.0 CONCLUSIONS

I have reviewed the Med-Ed submittals and find that, upon completionof the changes included in Section 4.1, there will be reasonable assurancethat:

1. Each offsite soerce, in conjunction with the onsitedistribution systems, has the capacity and capabilityto start and operate all class 1E loads without exceed-ing the equipment voltage rating with the offsite powersources within expected limits. (This is contingent oneach THI-1 class 1E 460V mo:or being operated withinits load rating ar.d with an ambient temperature below400C.)

2. Met-Ed has determined that no potential exists for asimultaneous or consequential loss of both of fsiteelectrical sources.

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3. The test verification provided by Met-Ed does not ade-.quately verify the submitted analyses. -

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The general method used by Met-Ed co verify the analysis i

is acceptable if each IE bus and MCC is loaded duringthe testing to at-least 30% of its analysis loading.If this is not possible, Met-Ed should demonstrate thateach' bus or MCC is loaded sufficiently and the instru-mentation is accurate enough to ensure the correct, ,

readings..

EG6G. Idaho, Inc., is performing a. separate' review of the undervoltagerelay protection'at TMI-1. This will evaluate the relay setpoints and timedelays - to determine that spurious tripping of the safety related loads will '

not occur with normal of fsite source voltages.

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7.0 REFERENCESi

! 1. NRC letter, William Gammill, to all power reactor licensecs-(except' Humboldt Bay), " Adequacy of Station Electric Distribution Systems

Voltages," August 8,'1979.

2. Met-Ed letter, J. C. Herbein, to NRC, W. P. Gammill, dated October 16,,

1979.

3. Met-Ed letter with technical report entitled, "TML-1 Electric Distri-~

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bution System Voltages," Revision 1, to NRC, R. W. Reid, dated May 15,1980.

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4. ~ Final Safety Analysis Report (FSAR) for TMI-1, Section E.2, "Electri-,

| cal System Design."

5. Telecon, D..D. Iann,'NRC, C. Cleveland, EC&G Idaho, Inc., J. Torcivia,GPUSC, and D. Mitchell, Met-Ed, June 5, 1980.

6. Met-Ed letter, J. G. Herbein, to NRC, Office of Inspection and Enforce-ment,-dated June 27, 1980.

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