ML20010E833

Adequacy of Station Electric Distribution Sys Voltages, Dresden Station,Units 2 & 3.

ML20010E833
Person / Time
Site:	Dresden
Issue date:	08/31/1981
From:	Udy A EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
EGG-EA-522, EGG-EA-5322, NUDOCS 8109080320
Download: ML20010E833 (13)

Text

50- R.3 7 EGG-EA-5322 AUGUST 1981 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES, DRESDEN STATION - UNIT NOS. 2 AND 3,

b. DOCKET NOS. 50-237 AND 50-249, TAC NOS. 12765

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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 Commission Under DOE Contract No. DE-AC07-76ID01E70 FIN No. A6429 U E G n G ,s.n.

8109080320 810831 PDR RES 9109080320 PDR

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FORMfG4G306 N. It F9)

INTERIM REPORT Accession No. ._._

Report No. EGG-EA-5322 Contract Program or Project

Title:

- Selected Operating Reactor Issues Program (III)

Subject of this Document:

Adequacy of Station Electric Distribution System Voltages, Dresden Station -

Unit Nos. 2 and 3, Docket Nos. 50-237 and 50-249, TAC Nos. 12765 and 12807 Type of Document:

Informal Report Authot(s):

! A. C. Udy Date of Document: NRC lesearca anc ~~ecanical I

August 1981 N Assistance Report

! Responsible NRC Individual and NRC Office or Division:

Paul C. Shemanski, Division of Licensing j This document was prepared primarily for preliminary orinternal use. it has not received l full review and approval. Since there may be substantive changes, this document should

! not be considered final.

EG&G Idaho, Inc.

Idaho Falls, Idaho 83415 i -

, Prepared for the U.S. Nuclear Regulatory Commission i 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.

DRESDEN STATION - UNIT N05. 2 AND 3 Docket Nos. 50-237 and 50-249 August 1981 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division

EG&G Idaho, Inc.

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YlC lesearc.i anc' Tec;inical Assistance Report l

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TAC Nos. 12765 and 12807

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ABSTRACT The Nuclear Regulatory Commission has required all licensees to analyze f#

the' electric power system at each nuclear station. This review is to deter-b- .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 (TER) reviews the submittals for the Dresden Station Units 2 and 3. A separate TER reviews the submittals l_ for Unit 1.

l The offsite power sources, in conjunction with the onsite distribution system, have been shown to have sufficient capacity and capability to auto-matically 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.

I FOREWORD This report is supplied as part of the " Selected Operating Reactor

. Issues Program (111) 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 20 19 01 06, FIN A6429.

l l

gc Research andTechn Assistance RB90I l 11

r-k CONTENTS

'l.0 I N TR O D UC T I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2.0 DESIGN 8 ASIS CRITERIA ........................................... I 3.0 SYSTEM DESCRIPTION .............................................. 2 4.0 ANALYSIS DESCRIPTION ............................................ 2 4.1 Analysis Conditions ....................................... 2

• 5 o L 4.2 Ar.alysis Results ..........................................

4.3 Analysis Verification ..................'................... 5 5.0 EVALUATION ...................................................... S

6.0 CONCLUSION

S .....................................................- 7

7.0 REFERENCES

...................................................... 7 ilGURE

1. Dresden Station, Unit One Line Diagram, Units 2 and 3 ........... 3 1

TABLE

1. Class lE Equipment Voltage Ratings and Worst Case Load Terminal' Voltages ............................... 4 1

l l NRC Researci ant Tec1nical

(- Assistance Report iii

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' ADEQUACY OF STATION 9.ECTRIC DISTRIBUTION SYSTEM VOLTAGES DRESDEN SIATION - UNIT N05. 2 AND 3 1.0 INTROD_UCTION l

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-eveat, station conformance 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-ages," required each licensee to confirm, by analysis, the adequacy of the voltage supplied each class 1E load. The letter included 13 specific guidelines to be followed in determining if the voltage is adequate to start aqd continuously operate the class lE loads.

Commonwealth Edison Company (CECO) responded to the NRC letter I , for '

.the Dresden Station, with letters of November 1, 19792 (which included a report on this subject,-written by Sargent. & Lundy) and December 14, 19793 ,

Based on the information supplied by CECO, this report addresses the capacity and capability of the onsite distribution system of Units 2 and 3 of the Dresden Station, in conjunction with the offsite power system, to maintain the voltage for the required class lE equipment within acceptable limits fnr the worst-case starting and steady-state load conditions. The Final Safety Analysis Report June 30,1980,Jne26,1980{FSAR),additionalinformationsubmittedon 4

, and June ll, 1980 6, te in September 1980 9 , and a letter of September 14,1976gephonecalls

, complete the information reviewed for this report. An analysis for use of the unit inter-tie between 4160V class lE buses, provided on August 18, 1980,9 as supplemented on March 18, 198110 and information on the use of unit 480V bus ties submitted on June 22, 1981,11 were also reviewed for this report.

2.0 DESIGN BASIS CRITERIA The positions applied in determining the ac'ceptability 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 Plants," of 10 CFR 50.

NRC Researc1 anc "ecanical Assistance Report 1

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

75. _ Staff' positions'as' detailed in 9 letter sent to the.

licensee,-dated August 8,--1979.'

16. ANSI C84.1-1977, " Voltage Ratings for Electric. Power Systems and Equipment (60 Hz)."

' lines {ixreviewpositionshavebeenestablishedfromtheNRCanalysisguide-and the above-listed documents. These positions are stated in Section 5. .,-

3.0 SYSTEM DESCRIPTION The. enclosures of references 2 and 4 discuss the onsite distribution system.. Figure 1, page 3_of this report, is a simplified sketch of the class lE-' electric distribution system taken from the Sargent & Lundy.recort of reference 2.

-The Unit 2 class lE'4160V buses 23-1 and 24-1 are normally supplied' power from auxiliary buses 23 and 24, respectively. These buses are sup-pliedpowerduringemergencyconditionsbya 133/4.16kV station auxiliary transformer (SAT) (Unit 3'usgs'a345/4.16kVSAT). Bus 24-1 can be energized from the other unit by a manual connection to bus 34-1 of Unit 3.D The unit technical specifications credit this as the second source of power required by GDC 17. This inter-tie can also be used to power bus 34-1 from bus 24-1 serving as the second source of offsite power for Unit 3. The Unit 2 distribution system is identified in the FSAR as being typical of Unit 3, except for' bus and transformer numbers.

Each 4160V class 1E bus supplies power for one 480V class lE bus via independent 4160/480V transformers. lj0Vvitalbusesarenormallysupplied power by motor-flywheel-generator sets . These will soon be replaced by battery-powered inverters.

CECO supplied the equipment operating ranges identified in Table 1.

Station 125V DC buses supply power for portions of the control circuits of.

the class IE switchgear.

4.0 ' ANALYSIS DESCRIPTION 4.1 Analysis Conditions. : CECO has used load-flow studies with con-

'tingencies.in determining that the maximum and the minimum expected switch-

• yard voltages ar 2142 and 132kV for Unit-2, respectively; 362 and 344kV for

.6 CECO also refers to this as a reserve auxiliary transformer (RAT)

'b' . . This connection between Units 2 and 3 is referred to as an' inter-tie in this. report.

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1. 2 N 138 KV SWITCHYARD (345 KV SWITCHYARD)

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(T38) p q (T39)

. O O O O BUS 28 (38) l BUS 29 (39)

CLASS lE 480V CLASS lE 480V NOTE: UNIT 3 N0MENCLATURE SHOWN

'IN PARENTHESIS.

DRESDEN STATION UNIT ONE LINE DIAGRAM UNITS 2, 3 FIGURE 1 3

TABLE 1 CLASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES

(% of nominal voltage)

Maximum Minimum Analyzeo Equipment Condition Rated Anal"ged Rated Steady State Transient .

UNIT 2 4000V Motors Start -- --

75 --

88.5a Operate 110 109.7 90 94.lD --

460V Motors Start -- --

75 -- 81.8a,c Operate 110 108.3 90 90.l b,c __

460V Motorsd Start -- --

75 --

81.9a Operate 110 e 90 90.4a,f __

480V Starters Pickup -- --

85 --

81.5 Oropout -- --

70 --

81.5 Operate 110 103.8 85 88.0d --

UNIT 3 4000V Motors Start -- --

75 --

90.4a Operate 110 109.0 90 95.9b __

460V Motors Start -- --

75 --

85.2a Operate 110 112.3 90 92.0b __

460V Motorsd Start -- --

75 --

81.7a Operate 110 e 90 90.3a __

480V Starters Pickup -- --

85 --

84.7 Oropout -- --

70 --

84.7 Operate 110 107.6 85 91.2 --

Other Equipment Units 2 and 39

a. Load terminal voltage supplied by CECO.

b. These values include the worst case (480V) or typical (4160V) feeder cable '

voltage drop (3.2%, 0.5%, respectively2 ),

c. Lowest voltage on Unit 2 480V buses wnen either Unit 2 SAT or Unit 3 SAT -

supplying power to Unit 2.

d. When SAT 2 is supplying the Unit 2 shutdown loads and the Unit 3 LOCA loaos,

e. This information not supplied by CECO; however, the voltage is not expected to De higher than when the inter-tie is not in use,

f. The load terminal voltage, when in addition to this worst case analysis, the 480V bus tie is ised, is 86.5.Il 9 120V vital buses are normally supplied power by motor-flywheel-generator 4

sets . These will soon be replaced by battery-powered inverters.

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• s . Unit 3, respectively.

' The reserve-auxiliary transformer was_used for the analysis. described. CECO determined that: "

1.. The maximum expected. load' terminal voltages occur whe'n i

the switchyard vo?tage is maximum and-there are.no unit l loads.

l (2. -The mi'nimum expected continuous' load terminal voltages, 6

• when not sharing an.offsite power source,'. occur when the switchyard voltage is.at a mir:imum and, except 4 *-

those loads automatically shed due to a unit trip, the

! . auxiliary bus loads and the class 'E loads are maximum..

! 3 .- The minimum expected transient load terminal _ voltages occur under the condition; of 2, concurrent with the start of a large load.

l 4. The minimum continuous and transient load terminal voltages while sharing an offsite power source occurs

with the unit SAT supplying the shutdown loads in the unit with offsite power and the accident leads in.the

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unit being supplied by the inter-tie'.

4.2 Analysis Results. Table 1 shows the worst case voltage-levels l identified in the CECO analyses.

The use of the 480V bus tie simultaneously with the unit intertie under the worst case conditions identified in Section 4.1 produce 480V load ,

termi.nal voltages down to 86.5% of the equipment rated voltages. Tnis will be discussed in- a separate EG&G Idaho, Inc. report (TAC Nos.10019 'and l 10021).

! 4.3- Analysis Verification. Thecomguteranalysishasnotbeenveri-fied at t 4 Dresden station. CECO states that the same computer program was verified for the Zion station 3 and Quad Cities Unit 26 by measuring the grid and bus voltages and the actual load of the ouses and selected equipment while these units were shutdown. An analysis was done using the measured offsite source voltage, and_the results compared with the. measured bus voltages.

The-comparison for eacn of the three units shows that the class lE bus i_ calculated voltages are within close correlation to the measured bus volt-i ages. This verifies the adequacy of the submitted analyses for_those. units.

, Since the station-dependent data-used (transformer taps and impedences) were field verified as correct,4 the verification of the accuracy of the other units can be extended as verifying the analysis for-Dresden Units 2 and 3.

l L 5.0 EVALUATION' l

Six I review positions have been established from the NRC analysis guide-lines and the documents listed in Section 2. Each review position is l

stated below, followed by the evaluation of the licensee submittals.

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5

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

A brief condition exists, when starting a large non-class lE load when all class 1E loads are operating, that would prevent class lE contactor pickup if a 480V MCC load were stopped and then restarted cnncurrent with a large non-class lE load, until the voltage recovers. It will not cause

• contactor dropout or spurious shedding of any loads. ,

CECO has shown that the minimum expected continuous and transient

• class lE load terminal voltages are within the rated capability of the class lE equipment.

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 IE eouip-ment without exceeding the rated aquipment voltage.

As Table 1 shows, the Unit 3 480V loads were analyzec, to have a poten-tial 112.3% for a no-load conditions. CECO concluded that these loads would not be subjected to unacceptable overvoltages because the analysis was done for a no-toad condition and, when a load is added, voltage drops in the supply t ansformers and feeder cables reduces the voltage to "very close to 110%."

CECO has shown thai, with tne grid voltage at the maximum expected value, the voltage ratings of the class lE equipment, when connected, are not exceeded.

Position 3--Loss of offsite power to either the redundant class lE distribution systems or the individual class lE 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 (TAL Nos. 10019 and 10021).

Position 4--Test rer,ults should verify the accuracy of the voltage analyses supplied.

CECO has tested, in similar nuclear units, the accuracy of the voltage analysis metheds, and field verified for Dresden Unit nos. 2 and 3, the s'.ation dependent data. Thus, CECO has verified the accuracy of thair -

m .:.oge analysis for Dresden Unit nos. 2 and 3.

~

Position 5--No event or condition should result in the simultaneous or consequential loss of botn required circuits from the offsite power network to the onsite distribution system (GDC 17).

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

6

CECO has analyzed the connections of the Dresden Station to the off-site power grid, and has determined that no potential exists for the simui-taneous or co powersource.gsequentiallossofbothrequiredcircuitstotheoffsite Position 6--As required by GDC 5, each offsite source a shared between units in a multi-unit station must be capable of supplying adequate starting 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.

The unit transformers are independently connected to the offsite power

• grid, but the station has the capability to interconnect certain class lE buses between Units 2 and 3 (but not Dresden Unit 1). CECO has shown that the use of the inter-tie between Dre: den Units 2 and 3 will supply adequate operating voltages to the class lE buses when the buses are connected together.

6.0 CONCLUSION

S The analyses submitted by CECO 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 lE equipment are supplied for all projected combi %tions of plant loads and offsite power grid conditions, including an accident in one unit and the safe shutdown of the other unit.

7. CECO had determined that no potential for either a simultaneous or consequential loss of both offsite power sources exists.

3. The t%t used to verify the analysis shows the analysis to ' an accurate representation of the worst case concitions analyzed.

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

7. 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. CECO letter, Robert F. Janecek to William Gammill, "Adequancy of Sta-tion Electric Distribution System Voltages", November 1, 1979.

3. CECO letter, Robert F. Janecek to William Gammill, " Adequacy of Sta-tion Electric Distribution System Voltages", December 14, 1979.

7

4. CECO letter, Robert F. Janecek to T. A. Ippolito, U. S. NRC, " Adequacy of Station Electric Distribution System Voltages," June 30, 1980.

5. CECO letter, Robert F. Janecek, to Darrell G. Eisenhut, U.S. NRC, "Second Level of Undervoltage Protection for 4kV Onsite Emergency Power Systems," June 26, 1980.

6. CECO letter, Rcbert F. Janecek, to William Gammill, NRC, " Adequacy of Station Electric Distribution System Voltages," June 11, 1980. *

7. Telecon, Hal Stolt, CECO and other CECO personnel and Alan Udy, -

EG&G Idaho, Inc., September 11 and 22, 1980. ,

8. CECO letter, G. A. Abrell, to Karl R. Goller, NRC, "Information Con-cerning System Voltage Conditions," September 14, 1976.

9. CECO letter, Robert F. Janecek, to Darrell G. Eisenhut, NRC, "Addi-tional Response concerning Adequacy of Station Electric Distribution System Voltages," August 18, 1980.

10. CECO letter, Rnbert F. Janecek to T. A. Ippolito, NRC, " Adequacy of Station Electr ical Distribution System Voltages," March 18, 1981.

11. CECO letter, T. J. Rausch to T. A. Ippolito, NRC, " Response to Request for Additional Information Concerning Adequacy of Station Electric Dist,ibution System Voltages," June 22, 1981.

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