ML19341B384

Technical Evaluation Rept,Degraded Grid Protection for Class IE Power Sys,Palisades Plant.

ML19341B384
Person / Time
Site:	Palisades
Issue date:	12/31/1980
From:	Cleveland C EG&G IDAHO, INC., EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6256 EGG-EA-5321, NUDOCS 8101300847
Download: ML19341B384 (12)

Text

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FORM (G6G N6 (Rev 1173 INTERIM REPORT Accession No.

Report No. EGG-EA-5321 d:ntr:ct Program or Project

Title:

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

Technical Evaluation Report, Degraded Grid Protection for Class 1E Power Systems, Palisades Plant, Docket No. 50-255 Type of Document:

Technical Evaluation Report Author (s):

C. J. Cleveland D:ta cf Document:

December 1980

'R:sp:nsible NRC Individual and NRC Office or Division:

Paul C. Shemanski, NRC-NRR This document was prepared primarily for preliminary or internat use.it has not received 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 76f D01570 I

- NRC FIN No. A6256 lNTERIM REPORT 1

MC Resesch and Technica, Assistance Report 1!r/o / 300 5'y 7

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2326F TECHNICAL EVALUATION REPORT DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS PALISADES PLANT Docket No. 50-255 December 1980

. C. J. Cleveland Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.

l Draft 12-18-80 TAC No. 10043 l

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ABSTRACT In June 1977, the NRC sent all licensees a letter outlining three positions the staff had taken in regards to the onsite emergency power system. Consumers Power Company (CPCo) was to assess the susceptibility of the safety-related electrical equipment at the Palisades Plant to a sus-tained voltage degradation of the offsite source and interaction of the offsite and onsite emergency power system. This report contains an evalu-ation of CPCo's analyses, modifications, and Technical Specification changes to comply with these NRC positions.

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CONTENTS

1.0 INTRODUCTION

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2.0 DESIGN BASE CRITERIA ............................................. 1 3.0 EVALUATION ....................................................... 2 3.1 Existing Undervoltage Procection ............................ 2 3.2 Modifications ............................................... 2 3.3 Discussion .................................................. 3

4.0 CONCLUSION

S ...................................................... 6 5.0 R E FE R E N C E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . 7 9

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TECHNICAL EVALUATION REPORT DEGRADED CRID PROTECTION FOR CLASS 1E POWER SYSTEMS PALISADES PLANT

1.0 INTRODUCTION

On June 3, 1977, the NRC requested the Consumers Power Company (CPCo) assess the susceptibility of the safety-related electrical equipment at the Palisades Plant to a sustained voltage degradation of the offsite source and interaction of the offsite and onsite emergency power systems.I The letter contained three positions with which the current design of the plant was to be compared. After comparing the current design to the staff posi-tions, CPCo was required to either propose modifications to satisfy the positions and criteria or furnish an analysis to substantiate that the existing facility design has equivalent capabilities.

By letters dated July 28, 1978, and October 2, 1978, CPCo responded to the NRC letter proposing design modifications and changes to the plant's Technical Specifications to satisfy the criteria and staff positions.2,3 On June 6, 1979, the NRC requested additional information from CPCo to clarify some points in their proposal.4 CPCo responded by letter dated February 27, 1980, with the required information.5 The modifications consist of the installation of a second-level undervoltage protection system for the Class 1E equipment. Blocking of the load-shed feature, once the diesel generatorn are supplying the Class 1E buses, is already incorporated in the design. The NRC also required that the setpoints, surveillance requirements, test requirements, and allowable limits were to be included by CPCo in the plant Technical Specifications.

2.0 DESIGN BASE CRITERIA The design base criteria that were applied in determining the accept-ablility of the system modifications to protect the safety-related equipment from a sustained degradation of the offsite grid voltage are:

1. General Design Criterion 17 (CDC 17), " Electrical Power Systems," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.6 1

2. IEEE Standard 279-1971, "Clase IE Power Systems for Nuclear Power Generating Stations."7

3. IEEE Standard 308-1974, " Class lE Power Syhtems for Nuclear Power Generating Stations."8

4. Staff positions as detailed in a letter sent to the licensee, dated June 3, 9177.1

5. ANSI Standard C84.1-1977, " Voltage Ratings for Electri-cal Power Systems and Equipment (60 HZ)."9 3.0 EVALUATION This section provides, in Subsection 3.1, a brief description of existing undervoltage protection at the Palisades Plant; in Subsection 3.2, a description of the licensee's proposed scheme for the second-level under-voltage protection; and, in Subsection 3.3, a discussion of how the existing system meets the design base criteria.

3.1 Existing Undervoltage Protection. The present design utilizes ~

three undervoltage relays on each 2400V Class IE bus. They are arranged in a three-out-of-three logic scheme with a setpoint of 70% of nominal voltage and a time delay of 0.5 second. The relays and their logic circuitry also start the diesel generator, initiate load-shedding, and trip the incoming line breaker. The undervoltage relays also activate an annunciator in the control room.

The existing logic circuitry of the undervoltage protection system does disable the load-shed feature once the diesel generators are supplying i

power to the Class lE buses.

l 3.2 Modifications. To protect the Class IE safety-related equipment from the effects of a degraded grid condition, the licensee has proposed.

! adding another set of undervoltage relays to each of the'2400V Class lE buses. Each set will be comprised of three relays, arranged in a three-out-

• of-three logic scheme, with associated auxiliary relays and timers added to the undervoltage-logic circuitry. The setpoint of the second-level protec-tion relays will nominally be 2192, +32/-8V, (91.33% of bus voltage) with a time delay of 6.5, +0.3, seconds.' When a degraded _ grid voltage persists 2.

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below the setpoint for 0.5 second, the diesel is started, and the under-voltage condition is annunciated in the control room. After another six seconds delay, incoming line breakers are tripped, load-shedding is initiated, and the diesel breaker is closed when voltage and frequency from

- the diesel gener- ator is satisfactory.

1 i Once the diesel generator is supplying its associated Class IE bus, load-shedding is blocked by interlocks and auxiliary relays.in the under-voltage protection logic circuitry. As stated above, this is already

incorporated in the existing logic circuits.

i Proposed changes to the plant's Technical Specifications, adding the i

surveillance requirements, allowable limits for the setpoint and time delay, 1 and limiting conditions for operation for the second-level undervoltage monitors, were also furnished by the licensee. A bases for limiting condi-

] tions of operation, as well as a bases for surveillance requirements per-taining to these relays, was also included in the Technical Specification changes.

3.3 Discussion. The first position of the NRC staff letter 1required that a second level of undervoltage protection for the onsite power system-be provided. The letter stipulates other criteria that the undervoltage protection must meet. Each criterion is restated below followed by a dis-

! cussion regarding the licensee's compliance with that criterion.

, 1. "The selection of voltage and time setpoints shall be l determined from an analysis of the voltage requirements

of the safety-related loads at all onsite system dis-tribution levels."

The licensee's proposed setpoint of 2192V at'the 2400V bus is 95.3% of the motor nominal voltage rating of

! 2300V. This setpoint reflected down to the 480V buses

, will be greater than the minimum allowable motor volt-

- age (90% of nominal voltage). As the motors sre the

j. most limiting equipment in the system, this setpoint is acceptable. The licensee's analysis considered other i factors, such as MCC contactor pick-op voltage and drop-out voltage.

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2. "The voltage protection shall include coincidence logic to preclude spurious - trips of the offsite power Sources.

The relay logic is arranged in a three-out-of-three logic scheme, thereby satisfying this criterion. .

. 3. "The time delay selected shall be based on the following

, conditions:

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

! The proposed time delay of 6.5 seconds does not exceed this maximum time delay. This is substan-tiated by the licensee in his proposal.

1 The proposed time delay will not be the cause of

] any thermal damage to the safety-related equipment.

i- The setroint is within voltage rsnges recommended by ANSI C8.4.1-1971 for sustained operation.

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b. "The time delay shall minimize the effect of short- .

I duration disturbances from reducing the unavail-ability of the offsite power source (s)."

The licensee's proposed time delay of 6.5 seconds is long enough to override any short inconsequen-l tial grid disturbances. Further, we have reveiwed ,

the licensee's analysis and agree with.the licen-1

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i see's finding that any voltage dips caused from the starting ~of large motors will not trip the of fsite source.

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

A review of.the licensee's voltage analysis 3' indicates that-the time delay will not cause any failures of the safety-related equipment since the

voltage setpoint is' within the allowable tolerance L

of the. equipment voltage rating.

4. "The voltage monitors shall automatically initiate the~

• disconnection of offsite power ' sources whenever the-

-voltage setpoint and time-delay limits'have been 7 q e xceeded ."

l A review of the licensee's proposal-substantiates that j .this criterion is met, f

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5. "The voltage monitors shall be designed to satisfy the requirements of IEEE Standard 279-1971."

' The relays are stated as being able to meet the require-ments of IEEE Standard 301-1978 also.

The licensee has stated in his submittal that all cir-cuits associated with the undervoltage relays meet IEEE Standard 279-1971.

6. "The Technical Specifications shall include limiting conditions for operations, surveillance requirements, trip setpoints with minimum and maximum limits, and allowable values for the second-level voltage protection monitors."

The licensee's proposal for Technical Specification changes does include all the required items. The set-point of 2192, +32/-8V, does not infringe into the expected operating envelope and will not compromise the life of the equipment. Spurious trips are thereby not foreseen. The limiting conditions for operation, the surveillance requirements, channel test frequency, and calibration frequency are supported by bases in the Technical Specifications and do meet the criteria of the staff's positions.12 The second NRC staff position requires that the system design auto-matically prevent load-shedding of the emergency buses once the onsite sources are supplying power to all sequenced loads. The load-shedding must also be reinstated if the onsite breakers are tripped.

J. The licensee states in his submittal that this feature is already incorporated in the circuit design. A review of the logic circuitry sub-stantiates that the load-shed is blocked by interlocks and auxiliary relays and that load-shedding is reinstated upon a trip of the onsite source.

The third NRC staff position requires'that certain test requirements be added to the Technical Specifications. These tests were to. demonstrate the full-functional operability and independence of the onsite power sources and are to be performed at least once per 18 months during shutdown. The

, tests are to simulate loss of offsite power in conjunction with a simulated .

safety injection actuation signal and to simulate interruption and subse-quent reconnection of onsite power-sources. These tests verify the proper operation of the load-shed system, the load-shed bypass when the emergency 5

diesel generators are supplying power to their respective buses, and that there is no adverse interaction between the onsite and offsite power sources. .

The testing procedures proposed by the licensee do comply with the <

full intent of this position. Load-shedding on offsite power trips is tested. Load-sequencing, once the diesel generator is supplying the safety l buses, is tested. A simulated loss of the diesel generator and subsequent load-shedding andd load-sequencing once the diesel generator is back on-line is tested. The time durations of the tests will verify that the time delay of the undervoltage relays is suf ficient to avoid spurious trips and that the load-shed bypass circuit is functioning properly.

4.0 CONCLUSION

S Based on the information provided by CPCo, it has been determined that the proposed changes do comply with NRC staff position 1. All of the staff's requirements and design base criterie have been met. The setpoint and thne delay will protect the Class 1E equipment from a sustained degraded voltage condition of the offsite power source.

The existing load-shed circuitry does comply with staf f position 2 and will prevent adverse interaction of the offsite and onsite emergency power systems.

The proposed changes to the Technical Specifications do adequately test the system modifications and do comply with staf f position 3. The surveillance requirements, limiting conditions for operation, minimum and maximum limits for the trip point, and allowable values meet the intent of staff position 1.

It is therefore concluded that CPCo's proposed changes and Technical '

Specification changes are acceptable. The second-level undervoltage pro- ,

tection modifications are being installed during the present refueling cutage. It is, therefore, recommended that the proposed Technical Specifi-cation changes be approved and implemented at the earliest opportunity.

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5.0 REFERENCES

l. NRC letter (A. Schwencer) to CPCo (D. A. Bixel), June 3, 1977.

- 2. CPCo letter (D. P. Hof fman) to NRC (D. L. Ziemann), July 28, 1978.

j 3. CPCo letter (D. P. Hoffman) to NRC (D. L. Ziemann), October 2, 1978.

4. NRC letter (D. L. Ziemann) to CPCo (D. A. Bixel), June 6, 1979.

I' 5. CPCo letter (S. R. Frost) to NRC (D. L. Ziemann), February 27, 1980.

6. General Oesign Criterion 17, " Electric Power Systems," of Appendix A,

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

" Domestic Licensing of Production and Utilization Facilities."

7. IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations."

8. IEEE Standard 308-1974, " Standard Criteria for Class IE Power Systems for Nuclear Power Generating Stations."

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9. ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equip-ment." (60 HZ).

10. Final Safety Analysis Report (FSAR) for the Palisades Plant.

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11. CPCo letter (R. W. Huston) to NRC (D. M. Crutchfield), May 7. 1980.

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12. CPCo letter (D. P. Hoffman) to NRC (D. M. Crutchfield), December 3, 1980.

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