ML20003F118

Adequacy of Station Electric Distribution Sys Voltages, Preliminary Safety Evaluation

ML20003F118
Person / Time
Site:	Salem
Issue date:	03/09/1981
From:	Weber D EG&G IDAHO, INC., EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6429 EGG-EA-5380, NUDOCS 8104200215
Download: ML20003F118 (16)

Text

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P00RORlGlNAI. March 1981 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES, SALEM NUCLEAR POWER STATION UNITS 1 AND 2, DOCKET NOS. 50-272 AND 50-311 NRC Researc1 anc Tec1nical

o. A. mese, N Assistance Report PRELIMINARY m

U.S. Department of Ener;y Idaho Operations Office

• Idaho National Engineering Laboratory E [, .

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NRC ReSearc1 anc Tec1nica Prepared for the SS Stance lep0ft U.S. Nuclear Regulatory Cocunission Under DOE Contract No. DE-AC07-76ID01570-1 $ $ g G Idaho FIN No. A6429 Yk 8104200.2/5-

0322J ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES SALEM NUCLEAR POWER STATION UNITS 1 AND 2 Docket Nos. 50-272 and 50-311 March 1981 D. A. Weber Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.

NRC Researc1 ant "ec1nica Assistance Report l

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Draft 3-09-81 TAC No. 13009 i

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INTERIM REPORT Accession No.

• Report No. ECG-EA-5380

/ Contract Program or Project

Title:

Selected Operation Reactors Issues Program (III)

Subject of this Document:

Adequacy of Station Electric Distribution System Voltages, Salem Nuclear Power Station Units 1 and 2 Type of Document:

Technical Evaluation Report

^"'" "'s. A. weber NRC lesearca and "ec'anica Date of Document:

March 1981 Responsible NRC Individual and NRC Office or Division:

Paul C. Shemanski, Division of Licensing i

This document was prepared primarily for preliminary orinternal use. It has not received i 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 Prepared for the

, U.S. Nuclear Regulatory Commission Washington, D.C.

Under DOE Contract No. DE-AC07 761D01570-1 NRC FIN No. A6429 e

INTERIM REPORT

_- .. .- . _ _ - . = _ _ _ _ _ _ . - - _ - - - - . . . _ _ . _ _ . .- ._

l ABSTRACT the Nuclear Regulatory Commission has required all licensees to analyze

, the electric power system at each nuclear station. This review is to deter-l mine if the onsite distribution system in conjunction with the offsite power sources nas 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 Salem Nuc-lear Power Station.

i The offsite power sources, in conjunction with the onsite distribution system, nave been sho.in to nave sufficient capacity and capability to continuously operate all required safety related loads, within the equip-ment rated voltage limits, in the event of eitaer an anticipated transient or an accident condition. However, a sustained degraded grid may result in spurious separation of class IE buses from the offsite source when one

! 500/13.8kV Station Power Transformer is supplying all loads of both units.

FOREWORD j

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

! Issuca Program (III)" being conducted for the U.S. Regulatory Commission, l

Office of Nuclear Reactor Regulation, Division of Operating Reactors, by EG&G Idaao, Inc., Reliability and Statistics Branch.

The U.S. Nuclear Regulatory Commission funded the work under the

authorization, B&R 20 19 01 16, FIN No. A6429.

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o XRC Research ant ecanicaL Assistance Report i

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CONTENTS 1.0 I' iT RO D U C T I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2.0 DESIGN BASIS CRITERIA ............................................. I e .

3.0 SYSTEM DESCRIPTION ................................................ 2 j 4.0 ANALYSIS DESCRIPTION .............................................. 4 4.1 Analysis Conditions .......................................... 4 4.2 Analysis Results ............................................. 4 4.3 Analysis Verification ........................................ 7 5.0 EVALUATION ........................................................ 7

6.0 CONCLUSION

S ....................................................... 9 7.0 R E FE R E N C E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 FIGURE

1. Salem Nuclear Power Station Units 1 and 2 electrical single-line diagram showing circuit breaker alignment for normal operations ............................................. 3 TABLES

1. Class 1E Equipment Voltage Ratings and Analyzed Worst Case Load Terminal Voltages ........................ 5

2. Comparison of Analyzed Voltages with tne Unde rvol tage Re lay Se t point s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 i

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES SALEM NUCLEAR POWER STATION UNITS 1 AND 2

1.0 INTRODUCTION

j 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 of August 8, 1979, " Adequacy of Station Electric Distribution Systems Volt-ages," ' requireo eac'- licensee to confirm, by analysis, the adequacy of the voltage at the class 1E loads. This letter included 13 specific guide-lines to be followed in determining if the load terminal voltage is adequate to start and continuously operate the class 1E loads.

Public Service Electric and Gas Company (PSE&G) responded to the NRC letter on March 2, 1980.3 . This submittal, submittals of October 10, 1979,2 September 24, 1980,4 the NRC submittal of January 19, 1981,6 and the final Safety Analysis Report (FSAR) complete the information reviewed for this report.

Based on the information supplied by PSE&G, this report addresses the capacity and capability of the onsite distribution system of the Salem Nuclear Power Station, in conjunction with the offsite power system, to maintain tne voltage for the re. quired class 1E equipment within acceptable limits for the worst-case starting and load conditions.

2.0 DESIGN BASIS CRITERIA TPe positions applied in determining the acceptability of the offsite voltage conditions in supplying power to the class 1E equipment are derived from the following:

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1. General Design Criterion 17 (GDC 17), " Electrical Power Systems," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.

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2. General Design Criterion 5 (CDC 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.

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 l licensee, dated August 8, 1979.1

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

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Six review positions have been established from the NRC analysis guide-l I lines and the above-listed documents. These positions are stated in Section 5.0.

3.0 SYSTEM DESCRIPTION Figure 1 of this report is a simplified sketch of the Units 1 and 2 single-line diagram showing the circuit breaker positions (opened or closed) for norm'al full power operation.

The class IE distribution system consists of three independent IE buses for each unit supplied from the 500/13kV Station Power Transformers (SPTs) I and 2 via the 13/4kV SPTs 11 and 12 for Unit 1, and 21 and 22 for Unit 2. During normal full power operation, two of the three 1E buses of 3

one unit are supplied from one 500/13kV SPT and the third IE bus from the other 500/13kV SPT. The four non-1E buses of each unit are supplied from their respective unit Auxiliary Power Transformers (APTs). Should a unit trip, the non-lE buses will automatically transfer from the APT source to j the SPT source.

O If one of the '500/13kV SPIs is out of service, the 13kV ring bus could be closed and the remaining SPT could supply all IE buses of both units.

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Salem Noeleat- Power St.ition Units 1 .ind ! .?lectrical .< i n a l - l i a.-

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Control power for each of the IE buses is supplied by a normal feed f rom one battery, and au emergency feed is available from a second battery i source through an auto-transfer switch. Each of the IE instrument buses are supplied through static inverters from AC/DC supplies and have an alter-nate emergency supply through an auto-transfer switch.

'd 4.0 ANALYSIS DESCRIPTION 4.1 Analysis Conditions. PS&G has determined by load flow studies that the maximum expected offsi;e grid voltage is 530kV (106%) and the minimum 489kV (97.8%).

PSE6C has analyzed each offsite source to both units, including one 500/13kV SPr supplying all loads of ooth units, to determine the IE equip-meat terminal voltages. The worst case class IE equipment terminal volt-ages occur under the following conditions:

1. Tne maximum voltage occurs when the 500kV grid is at ,

its maximum expected value with minimum station loads.  !

2. The ninimum voltage occurs when the 500kV grid is at its minimum expected value, one 500/13kV transformer "

supplying both units, a simultaneous trip of Unit 1 and a LOCA in Unit 2. ,

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3. The minimum transient voltage occurs with the start of a 6,000 hp reactor coolant pump (RCP) under conditions described in 2 above.

4.2 Analysis Result. Table I shows the projected worst case class 1E equipment terminal voltages under conditions of 1, 2, and 3 above.

PSE6G letter of provided an analysis of a single transformer supplying both units under minimum offsite grid conditions of 0.978 pu resulted in a 13.8kV grid voltage of 0.865 pu and a 4160V bus voltage of 0.8824 pu. The 4160V class IE bus undervoltage relays are set to drop out at 0.91 pu. The values in Table I were calculated from this

', letter and the information in Appendix 3 of PSE&G's submittal of March 3, 1980. Table 2 shows a comparison of the analyzed voltage with the undervoltage relay setpoints.

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4 IABLE 1 i

CLASS lE EQUIPMENT VOLTAGE RATINGS AND i ANALYZED WORST CASE TERMINAL VOLTAGES

! (% of nominal voltags) i i Maximum Minimum i .

g Analyr.ed Equipment Condition Rated Analyzed Rated Steady State # Transient E 4000V Motors Start -- -

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460V Motors Start - -

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a. PSE&G indicates that these values will improve after approximately three i minutes due to the action of the automatic load tap changer (LTC) on the i station power transforers 11, 12, 21, and 22. They did not take credit

! forthe LTC in their analysis. The automatic LTC changes 5/8% every

! 30 seconds resulting in an approximate 3.75% improvement in voltage over a

, three-minute period.

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b. Transient due to the start of a 4000V Reactor Coolant Pump.

c. Transient due to the start of the largest 230V motor.

I d. The minimum and maximum analyzed voltages are within the voltage ratings l of tne battery charger, imrerters, and other IE equipment, giving credit for

operation of the automatic. load top chargers on the Starter Power Transformers.

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TABLE 2 COMPARISON OF ANAL.YZED VOLfAGES WITH Tile UNDERVOLTAGE RELAY SETPOINTS

(% of nominal voltage)

Minimum Analyzed Relay Setpoints#

Location / Relays Voltage Time Voltage _ Time w

4160V Vital Buses Degraded Grid Transfer relays b 88.24C 3 min 91 10.5 see Bl oc kou t relays d 88.24 3 min 91 13 see Loss at Voltage relays e 83.13f 25 sec 70 inst,

a. Based on information in Reference 6.

b. Relays will transfer the ous (or buses) to the alternate power source when the undervoltage condition presets for at least 10.5 seconds.6

c. this value occurs when one Station Power Transformer (SPT 1 or 2) is supplying ooth units with a LOCA in one unit and a shutdown in the other.

The voltage will improve at a rate of 5/8% every 30 seconds over a three-minute period due to the action of the automatic load top chargers on SPts 11, 12, 21, and 22. PSE&G has not taken credit for operation of the LTCs.3

d. Relays will operate when an undervoltage condition exists on at least two of the three vital buses for 13 seconds and will act to desconnect the offsite power source from the emergency buses.6

c. Relays will operate at 70% of rated bus voltage and will (1) isolate buses f rom tne of f site source, (2) start the emergency diesel generators (DGs), (3) start load shedding, and (4) permit closure of the DG breaker.6

f. The value is due to the start of a 6000 hp RCP motor. The second level undervoltageschemewillbeadministrativelybypassedduringthestartof the motor.

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1 4.3 Analysis Verification. PSE&G's submittal of March 3, 1980, included test procedures and data to verify their analysis. Actual load data, obtained over a 24-hour period, was used as a basis to calculate a voltage profile. This profile was then compared with the actual measure-4 ments. The results showed an error of 1% or less at the 4kV and 460V levels

, and a maximum error of 1.7% at the 230V level u

! fransformer and bus loadings were sufficiently high to obtain reason-ably accurate data. The results of the test verify the analysis.

5.0 EVALUAfl0N Six review positions have been established from the NRC analysis guide-l lines and the documents listed in Section 2.0 of this. report. Each ,

1 review position is stated below followed by an evaluation of the licensee submittals and are based on PSE&G's analysis of two transformers supplying both units. The use of one transformer to supply both units.is evaluated in Position 6.

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 equipment voltage ratings.

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, PSE&G's analysis, as re flected in Table 1, snows that terminal i

voltages will go below the continuous ratings of IE motors and the pickup and operating ratings of the motor starters during the worst-case stea<ly-state minimum-voltage conditions. However, since the transformer LTCs will raise this voltage to acceptable levels in approximately three minutes, the motors have a 1.15 service factor, and this low-voltage condition requires several unusual conditions for the expected minimums to occur, the minimum voltages are acceptable.

For the above reasons, it is believed that the Salem Nuclear Power j g Station aas sufficient capability and capacity for starting and 7

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continuously operating all the class IE loads within their equipment vo l t age- ratings (see position 6).

Position 2--Witn 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 IE

• equipment without exceeding the equipment voltage ratings.

PSE&G has shown, by analysis, that the voltage ratings of the class IE equipment will not be exceeded for the conditions analyzed.

Position 3--Loas of offeite power to either of the radandant class IE d i s t r ii>u t i on systems due to operation of voltage protection relays, most not occur when the offsite power source is within expected voltage limits.

NRC, DSS has indicated, in a separate report, that the requirements of this position are satisfied when both SPTs 1 and 2 are supplying both Units 1 and 2 based on PSE&C's analysis of March 3, 1980. However, as noted in Taule 2, this position is not met when one SPf (1 or 2) is supplying noth units.

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

PSE6C has shown that the calculations accurately represent the IE buses and loads.

Positio M --No eveat or condition should result in the simultaneous or consequential loss of both required circuits frem the offsite power r.etwork to the onsite distribution system (GDC 17).

PSE&G has analyzed the onsite connections to the offsite power grid, and determined that no potential exists for simultaneous or consequential loas of ooth circuits t.om the offsite grid.

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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 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.

Salem Nuclear Power Station is the site of two nuclear units. The six d IE ouses of both units are normally shared between two offsite 500/13.3kV station power transformers (SPTs). The FSAR, Section 8.3.1, indicates that, if one of the SPTs is out of service, the 13kV ring bus can be closed and the remaining SPT can supply both units. PSE6G's analysis for this coadition5indicates that one SPT is capable of supplying the loads of ooth units. Therefore, this position is satisfied (see position 1).

6.0 CONCLUSION

S The voltage analysis submitted by PSG&E for the Salem Nuclear Gener-ating Station were evaluated in Section 5.0 of this report. it was found taat:

1. Voltages within the operating limits of the class IE equipment are supplied for all projected combinations of plant load and normal offsite power grid conditions; including an accident in one unit and the safe shutdown of the other unit with power to both units supplied from one offsite transformer.

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

3. PSE&G has determined tnat no potential for either a simultanous or consequential loss of both offsite power sources exists.

4. Loss of offsite power to class IE buses, due to spurious operation of voltage protection relays, will not occur with the offsite grid voltage within its expected limits and both 500/13.8kV transformers supplying both Units 1 and 2. However, spurious operation may occur with one 300/13.8kV transformer supplying both units under mini-mum grid conditions.

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7.0 REFERENCES

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1. NRC letter, William Gammill, to All Power Reactor Licensees (Except Ilumooldt Bay), ' Adequacy of Station Electric Distribution Systems q- Voltage ," August 8, 1979.

i i i 2. PSE&G letter,.F. P. Librizzi, to Director of Nuclear Regulation, y October- 10, 1979.

3. PSE&G Letter, F. P. Librizzi, to Director of Nuclear Regulation, j March 3, 1980.

j 4. PSE&G letter, F. P. Librizzi,.to Director of Nuclear Regulation, September 24, 1980

5. NRC letter, S. A. Varga, to PSE&G, F. W. Schneider, " Degraded Grid

, Voltage Protection for the Safety Related A-C Power System,"

January 19, 1980.

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