ML20037C827

Preliminary Adequacy of Station Electric Distribution Sys Voltages,Me Yankee Atomic Power Station

ML20037C827
Person / Time
Site:	Maine Yankee
Issue date:	01/31/1981
From:	Udy A ENERGY, DEPT. OF, IDAHO OPERATIONS OFFICE
To:	Shemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6256 EGG-EA-5324, NUDOCS 8102260584
Download: ML20037C827 (14)

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a January 1981 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES, MAINE YANKEE ATOMIC POWER STATION, DOCKET No. 50-309, TAC No. 12774 o IsoiN F

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l This is an informal report intended for use as a preliminary or working document Prepared for the U.S. Nuclear Regulatory Commission Under DOE Contract No. DE-AC07-761D01570 FIN No. A6256 b O E b idaho JAAf619 O c O b D

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INTERIM REPORT Accession No.

Report No. EGG-EA-5324 C:ntract Program or Project

Title:

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

Adequacy of Station Electric Distribution System Voltages, Maine Yankee Atomic Power Station, Docket No. 50-309, TAC No. 12774 Type of Document:

Informal Report Author (s):

NRC Researci anc Tec1nica

^- c "dv Assistance Report D:le of Document:

January 1981 R:sponsible NRC Individual and NRC Office or Division:

Paul C. Shemanski, Division of Licensing This document was prepared primarily for preliminary orinternat use. It has not received full review and approval. Since ther e 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 INTERIM REPORT L.

ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES MAINE YANKEE ATOMIC POWER STATION Docket No. 50-309 January 1981 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG6G Idaho, Inc.

TAC No. 12774

ABSTRACI The Nuclear Regulatory Commission has required all licensecs to analyze the electric power system at each nuclear station. This review is to deter-miac if the onsite distribution systeia, 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 Maine Yankee Atomic Power Station.

The offsite power sources, in conjunction with the onsite distribution system, has been shown to have sufficient capacity and capability to auto-ma*ically start, as well as continuously operate, all required safety loads within the equipment rated voltage limits in the event of either an antici-pated transient or an accident condition.

FOREWORD

~

This repart is supplied as part of the selected Electrical,'Instru-mentation, and Control Systems (EICS) issues program being conducted for the U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regula-tion, Division of Operating Reactors, by EC&G Idaho, Inc., Reliability and Statistics Branch.

The U.S. Nuclear Regulatory Com 7 1sion funded the work under the authorization entitled " Electrical, in.trumentation, and Control System Support," B&R 20 19 01 03, FIN No. A6256.

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CONTENTS

1.0 INTRODUCTION

1 2.0 DESIGN BASIS CRITERIA.

1 3.0 SYSTEM DESCRIPIION 2

4.0 -ANALYSIS DESCRIPTION 2

4.1. Analysis Conditions 2

4.2 Analysis Results 5

4.3 Analysis Verification 5

5.0 EVALUATION 6

6.0

SUMMARY

7

- 7.0 1 REFERENCES 7

APPENDIX A--TORQUE-SPEED CURVE FOR 480V SERVICE WATER PUMP.

9 FIGURE 1.

Maine Yankee Atomic Power Station, One-Line Diagram.

3 TABLE 1.

Maine Yankee Atomic Power Station Class IE Equipment Voltage Ratings and

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Worst Case Available Load Terminal Voltages.

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES MAINE YANKEE ATOMIC POWER STATION 1.0 IKfRODUCTION 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 power stations. The NRC, in the generic letter o f August 8, 1979, " Adequacy of Station Electric Distribution Systems Volt-ages,"1 required eacn 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 s oltage is adequate to start and continuously operate the class 1E loads. Maine Yankee Atomic Power Company (NYAPCo) responded to the NRC letterl and subsequent questions with let-ters of February 29, 19802 and June 30, 1980.3 Based on information supplied by MYAPCo, information found in the Final Safety Analysis Report (FSAR), and a telephone call of October 1, 4

1980,.this report addresses the capacity and capability of the onsite distribution system of the Maine Yankee Atomic Power Station, in conjunc-tion with the offsite power system, to maintain the voltage for the required class IE equipment within acceptable limits for the worst-case starting and load conditions.

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 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 Generating Stations."

4.

IEEE Standard 308-1974, " Class lE Power Systems for Nuclear Power Generating Stations."

5.

. Staff _ positions-as detailed in a-letter sent to the licensee,Jdated August 8, 1979.1 6.

ANSI C84.1-1977,l" Voltage' Ratings for Electric Power

' Systems and Equipment (60 Hz)."

l

Six review positions have been established from the NRC analysis guide-l lines and the above-listed documents. These are stated in Section 5.

3.0 SYSTEM DESCRIPTION Section 8 of the Maine Yankee FSAR and the attachments of references 2 and 3 discuss the onsite distribution system. Figure 1 of this report, is a simplified unit one-line diagram of the Maine Yankee electric distribution system taken from Reference 2.

Figure I shows that the class IE 4160V buses 5 and 6 are supplied power from auxiliary buses 3 and 4, respectively. When the unit generator is operating, these buses are powered by transformer x24. Upon loss of the unit generator, buses 3 and 4 (and hence class IE buses 5 and 6) are auto-matica11y transferred 5 to receive power from the ll5kV grid via startup transformer x14; non-class lE, 6.9kV buses automatically transfer to startup transformer x16. The unit generator can be isolated from auxiliary trans-former x24 and the main transformers enabling them to supply offsite power to the class IE buses as a delayed second source from the 345kV grid. Bus 5 can also be powered by tertiary windings of startup transformer x16.

Plant Procedure No. 1-22-3 prevents use of this source except when all other sources of AC power have failed.

Each 4160V class IE bus supplies power for a 480V class lE bus (Nos. 7 and 8) via separate 4160V/480V transformers.

120V vital buses are supplied power from uninterruptable power supplies (UPS),3 which auctioneer power from station batteries or 480V buses 7 or 8.

MYAPCo supplied the equipment operating ranges identified in Table 1 of this report.) The FSAR shows that station 125V DC buses supply power for the 4160V class IE motor control circuits.

4.0 ANALYSIS DESCRIPTION 4.1 Analysis Conditions. MYAPCo has analyzed all but one offsite source connection to the onsite distribution system under extremes of load

- and offsite voltage conditions to determine the terminal voltages to IE equipment. However, MYAPCo did not provide analyses for bus 5 receiving power from transformer x16 as the connection is not required by GDC 17, and it is not' credited in the FSAR as being a source of offsite power. The MYAPCo voltage analyses show that:

1.

'Tne maximum load terminal voltage occurs during unit shutdown when transformer x24 carries the minimum auxiliary and class lE loads with the 345kV distri-bution system at its maximum voltage of 362kV.

2.

The minimum steady state load terminal voltage occurs when an accident occurs without loss of offsite power with transformer x14 carrying the maximum auxiliary and class lE loads with the 115kV distribution system at its minimum continuous voltage of Il6.5kV.

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t TABLE 1 MAINE YANKEE ATOMIC POWER STATION CLASS lE EQUIPMENT VOI,TAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES i

(% of nominal voltage)

Maximum Minimum Rated Analyzed Rated Analyzed

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state Transient

' Motors 4kV 7

Start-75 89.8a Operate 110 108.2

-90 95.8 t

2 460V-Start 80b 82.6c

' Operate-110 108.3 90 90.4

-- Starters 480V-Pickup:

80 79.4'

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70 79.4 f

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103.8-80 88.5 Low voltage i

instrument and; control circuitse

a.. Momentary minimum motor terminal voltage when starting a condensate pump..This assumes the condensate pumps, heater-drain pumps, and cir-e

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culating water pump have,been previously shed.

t.

... Appendix'A-shows the torque-speed curve of the. largest 480V class lE b.

load..

c.

Momentary minimum motor terminal voltage when starting 460V Service L

Water Pump.(250.hp).

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'Not-supplied by licensee.

-UPS is. powered by station batteries or rectifiers only.

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The minimum transient load terminal voltages occur with the conditions of 2 (above) with the start of a conden-sate pumpa (for the 4000V class 1E equipment) and the start of a service water pump (for the 460V class 1E equipment).

The study accounted for cable and transformer impedences. Field inspections verified the transformer tap settings. The minimum load con-sists of component cooling water pumps, lighting, and some unspecified 480V loads. MYAPCo assumed a constant 120kV at the source connections due to automatic load tapchanging2 autotransformers located there, while the Maine Yankee Atomic Power Station switchyard voltage was free to follow the load demand.

4.2 Analysis Results. Table 1 shows the worst case class 1E equip-ment terminal voltages identified in the MYAPCo analysis. The worst-case motor starting voltage transient condition will last only while starting

- the 2500 hp condensate pump. At the minimum voltages identified in Table 1, no contact srs will drop out to cause spurious tripping of loads.3 Con-tactor pice ap is prevented.until the voltage recovers.

4.3 Analysis Verification. MYAPCo measured the grid, generator and bus voltages, and the actual load of the buses and selected equipment.

This was done twice, with the transformer loading as follows:

Loading

(% of rated)

Transformer Test 1 Test 2 Buses Supplied x24 (4160V) 63.4 65.6 3, 4, 5(IE), 6(IE)*

x26 (6900V) 95.2 96.0 1, 2 x507 (480V) 68.0 68.9 7(IE) x608 (480V) 58.0 58.8 8(1E)

• Buses 3 and 5 are located adjacent to each other, and

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I the study considered them at identical potential, with l

separate load groups. Buses 4 and 6 are the same.

' Analy'ses were done.using the measured. generator source voltage and' the j

measured. loads, and the'results compared with the measured bus voltages.

1 This ~ pump was studied as the largest load on the same transformer that a.

.suppliesspower to-the class 1E buses.- Although larger motors are in service at the Maine. Yankee Atomic Power Station, they use 6.9kV from separate transformers.3 5'

Two' comparisons were made which show the analysis to be within +1.30/

-2.42% of the actual neasured bus voltages for the class IE buses. For all buses, the deviation was within +1.30/-3.56%.

A negative figure indicates that tne actus1 measured voltage is higher than the predicted voltage.

5.0 EVALUATION Six review positions have been established from the NRC analysis guide-l lines and documents listed in Section 2.0.

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 combination must be capable of starting and of continuously operating all class' IE equipment within the rated eqaipment voltages.

MYAPCo has shown by analysis that the Maine Yankee Atomic Power Station has sufficient capability and capacity for starting and continuously oper-ating the class IE loads within the equipment voltage ratings (see Table 1).

However,-MYAPCo has not analyzed for when the tertiary winding of the trans-former x16. supplies power to class 1E bus 5.

Position-2--With the maximum expected offsite grid voltage and minimum load condition,.each offsite source and distribution system connection 4

combination must be capable of continuously operating all class IE equip-ment without exceeding the. rated equipment voltage.

MYAPCo has-shown.by analysis that the voltage ratings of the class 1E

-equipment will.not be exceeded.. MYAPCo states that even if a switchyard voltage of 124kV (4kV higher than the maximum expected voltage) was present, that no load would have its voltage limit exceeded.3 Position 3--Loss of'offsite power to either the redundant class IE distrioution systems or the individual class 1E loads,' due to operation of voltage protection relays, must not occur when the offsite power source ic

. 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. 10032).

Position '4--The -NRC letterl requires that test. results verify the I

accuracy of the voltage. analysis supplied.L 1MYAPCo has supplied,the. required'information,4 which shows the 2

' esiculations to be an. accurate representation of the class IE buses and' loads. The test was performed using the unit: auxiliary transformers; how-ever, since the case studies using the. unit auxiliary and the startup.trans-Eformers are_in'close correlation, the test results are considered valid.

~

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).

6 1

_ _. _ = --

MYAPCo has analyzed the Maine Yankee connections to the offsite pow.tr grid and has determined that no potential exists for the simultaneous or consequential loss of both circuits from the offsite grid.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 0

and operating voltage for all required class IE loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.

J i

This applies to multi-unit stations. It does not apply to the single-unit Maine Yankee station.

6.0

SUMMARY

The analyses submitted by MYAPCo for this review were evaluated as stated in Section 5.0 of this report.

It was found that:

1.

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

i However, the NRC should require the MYAPCo to incorpor-ate limiting-conditions of operation in the unit Tech-nical Specifications that restrict use of the bus 5 feeder from the tertiary windings of transformer x16 as prescribed in Plant Procedure No. 1-22-3.

4 2.

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

3.

MYAPCo has determined that no potential exists for eitner a simultanous or a consequential loss of both

-offsite power sources.

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

7.0 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.

'MYAPCo' letter, Robert H. Groce to Office of Nuclear Reactor Regulation, U. S.. NRC, " Adequacy of Station Electric Distribution System Voltages,"

' February 29, 1980.

.3.

~NYAPCo letter, Robert H. Groce to U.S. NRC, " Request for Additional Information on Adequacy of Station-Electric Distribution System Volt--

ages," June' 30,:1980.

7

4.

Telecon, A. C. Udy, EG&G Idaho, Inc., P. Johnson, Yankee Atomic Elec-tric Company, October 1, 1980.

5.

Yankee Atomic Electric Company report No. 1204 " Auxiliary Power System Voltage Study for Maine Yankee Atomic Power Station," dated February 28, 1980, attachment to Reference 2.

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