ML20050A050

Degraded Grid Protection for Class IE Power Sys,Kewaunee Nuclear Power Plant, Informal Rept

ML20050A050
Person / Time
Site:	Kewaunee
Issue date:	02/28/1982
From:	Udy A EG&G, INC.
To:	Prevatte R Office of Nuclear Reactor Regulation
References
CON-FIN-A-6429 EGG-EA-5701, NUDOCS 8203300003
Download: ML20050A050 (10)

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' Rf.-MACSYM;hr,'#" @, .l-&u, 2sj,. n'Q-MM:A> ~ %QD'Q,.,7 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-AC07-761001570 FIN No. A6429 0 EGnG ,a,n.

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9 E G c G ... x FORM EGAG JW8 (Rev 1141)

INTERIM REPORT Accession No.

Report No. EGG-EA-5701 1 Contract Program or Project

Title:

Selected Operating Reactor Issues Program (III)

Subject of this Documents Degraded Grid Protection for Class lE Power Systems, Kewaunee Nuclear Power Plant Type of Document:

Technical Evaluation Report Author (s):

A. C. Udy Date of Document:

l February 1982 Responsible NRCIDOE Individual and NRCIDOE Office or Division:

R. L. Prevatte, Division of Systems Integration, NRC This document was prepared primarily for preliminary orinteinat use. it has not received full review and approval. Since there may be substantive phanges, this document should I not be considered final.

EG&G Idaho, Inc.

Idaho Falls, Idaho 83415 Prepared for the c 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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DEGRADED GRID PROTECTION FOR CLASS 1E POWER SYSTEMS KEWAUNEE NUCLEAR POWER PLANT February 1982 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.

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e TAC No. 10030 Docket No. 50-305 a

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CONTENTS

1.0 INTRODUCTION

.................................................... I 2.0 DESIGN BASE CRITERIA ............................................ 1 3.0 E V AL U AT I O N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

, 3.1 Existing Undervoltage Protection .......................... 2 3.2 Modifications ............................................. 2 3.3 Discussion ................................................ 2 i

4.0 CONCLUSION

S ..................................................... 5

5.0 REFERENCES

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4. Staff positions as datedJune3,1977.jetailedinalettersenttothelicensee,

5. ANSIStandardC84.1-1977,"VoltgeRatingsforElectricalPower Systems and Equipment (60 Hz)."

3.0 EVALUATION This section provides, in Subsection 3.1, a brief description of the '

existing undervoltage protection at Kewaunee; in Subsection 3.2, a descrip-tion of the licensee's proposed modifications for the second-level under-voltage protection; and in Subsection 3.3, a discussion of how the proposed modifications meet the design base criteria.

3.1 Existing Undervoltage Protection. Each Class lE bus (1-5 and 1-6) at Kewaunee has four loss of voltage relays. Initially these were set at 68% (of 4160V), and af ter September 15, 1976 were changed to trip at 80%.

Each bus then had two channels of relays consisting of one instantaneous relay and one time delay relay in series. Additionally, the output of the reserve auxiliary transformer, the tertiary auxiliary transformer and the main auxiliary transformer were mnnitored by two voltage relays. Only the bus relays, at 80%, automatically start the diesel-generators.

3.2 Modifications. The modification proposed by the licensee for second-level undervoltage protection will consist of two undervoltage relays (set at 95% of 4160V, +2%) either of which alarms a common annunci-ator after 6 +0.5 seconds witE the bus voltage below the setpoint. Should both relays trip, they initiate a cormion timer with a time delay (before automatic bus stripping and diesel-generator loading) of less than or equal to 5 minutes. Should the bus voltage recover within this time delay, the system will reset itself. Additionally, the loss of voltage relays are to be set at 87.5 +2% (of 4160V) with less than or equal to 2-1/2 seconds time delay.

Changes to the unit technical specifications 7added a requirement to test and calibrate the new relays. When one of the undervoltage-six second time delay relays is out of service, it is required to be placed in the tripped condition.

3.3 Discussion. The first position of the NRC staff letter I required that a second level of undervoltage protection system for the onsite power system be provided. The letter stipulates other criteria that the undervoltage protection system must meet. Each criterion is restated below followed by a discussion regarding the licensee's compliance with that criterion.

1. "The selection of voltage and time setpoints shall be determined from an analysis of the voltage requirements of the safety-related loads at all onsite distribution system levels."

The licensee proposed setpoint of 95 +2% is in accordance with the analysis submitted on October 11, 1979.4 All Class IE motors are identified as having a service factor of 1.15. This 2

effectively allows them to operate at a lower terminal voltage than the rated limit. This allows some margin between the set-point, as reflected down to low voltage (less than 600V) loads and the load required voltage.

2. "The voltage protection shall include coincidence logic to pre-clude spurious trips of the offsite power sources."

The proposed modification incorporates a one-out-of-two logic to alarm, a two-out-of-two logic, with a common time delay relay to actuate bus shedding and diesel generator loading.

3. "The time delay selected shall be based on the following con-ditions:"

a. "The allowable time delay, including margin, shall not exceed the maximum time delay that is assumed in the FSAR accident analysis."

The proposed maximum time delay of the second-level under-voltage relay channels exceeds the maximum time delay that is assumed in the FSAR. WPSCO states that " continued opera-tion of these loads at a condition above the first level (87.5% +2%) will not unacceptably degrade the requiredtomitigateaDesignBasisAccident."9quipment This furthersubstantiatedinaWPSComeetingwiththeNRC. gas Some 480V MCC heaters are being replaced.as a result of the investigation required by the NRC to verify this statement.9 A schedule for this replacement will be agreed to between WPSCo,theOfficeofNuclearReactorggulationandthe Office of Inspection and Enforcement.

b. "The time delay shall minimize the effect of short-duration disturbances from reducing the unavailability of the offsite power source (s)." >

The licensee proposed minimum time delay of five minutes is

, sufficient to ride through the start of a reactor coolant j pump with the grid in a degraded condition. The licensee's proposed minimum time delay is long enough to override any short, inconsequential grid disturbances or motor starting

! transients in the station,

c. "The allowable time duration of a degraded voltage condition at all distribution system voltage levels shall not result in failure of safety systems or components."

l The licensee maintains that the systems and components will C not fail in the time period needed for the automatic opera-

, , tion of the second-level undervoltage channels.

l l 4. "The voltage monitors shall automatically initiate the disconnec-tion of offsite power sources whenever the voltage setpoint and i time-delay limits have been exceeded." ,

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would occur only on a bus fault or mechancial failure of the diesel. In either case, the automatic reconnection of a diesel generator to the Class lE distribution system would not occur.

4.0 CONCLUSION

Based on the information provided by WPSCo, I find that the proposed modifications and technical specification revision 29b as modified on November 30, 1981, and February 1, 1982, comply with the first NRC position.

I also find that the second position is complied with and that the revised technical specifications comply with the third position.

5.0 REFERENCES

1. NRC letter, A. Schwencer to E. W. James, WPSCo, dated June 3, 1977.

2. WPSCo letter, E. W. James to A. Schwencer, NRC, August 4, 1977.

3. WPSCo letter, E. R. Mathews to A. Schwencer, NRC, " Degraded Grid Volt-age Questions," September 11, 1979.

4. WPSCo letter, E. R. Mathews to A. Schwencer, NRC, " Adequacy of Station Electric Distribution Systems Voltages," October 11, 1979.

5. WPSCo letter, E. R. Mathews to S. A. Varga, NRC, October 14, 1980.

6. WPSCo letter, E. R. Mathews to S. A. Varga, NRC, " Degraded Grid Volt-age Protection Technical Specifications," January 28, 1981, NRC-81-10.

7. WPSCo letter, E. R. Mathews to S. A. Varga, NRC, " Degraded Grid Volt-age Protection Technical Specifications and Responses to March 13, 1981, letter from S. A. Varga to E. R. Mathews," May 1, 1981, NRC-81-64.

8. Interoffice memo, S. Maskell, NRC to R. Licciardo, NRC, " Conference on Degraded Grid Voltage Protection for the Kewaunee Nuclear Power Plant," October 22, 1981.

9. WPSCO letter, E. R. Mathews to S. A. Varga, NRC, " Degraded Grid Voltage," November 30, 1981, NRC-81-192.

10. Telecon, R. Licciardo, NRC, C. Schrock, WPSCo, A. Udy, EG&G Idaho, Inc., December 16, 1981.

i 11. WPSCo letter, E. R. Mathews to S. A. Varga, NRC, February 1, 1982, q NRC-82-19.

, 12. General Design Criterion 17, " Electric Power Systems," of Appendix A.

" General Design Criteria for Nuclear Power Plants," to 10 CFR 50,

" Domestic Licensing of Production and Utilization Facilities."

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