ML18046B173
| ML18046B173 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 11/30/1981 |
| From: | Cleveland C, Udy A EG&G, INC. |
| To: | Donohew J Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML18046B172 | List: |
| References | |
| CON-FIN-A-6429 EGG-EA-5321, EGG-EA-5321-R01, EGG-EA-5321-R1, NUDOCS 8112290095 | |
| Download: ML18046B173 (25) | |
Text
EGG-EA-5321, REV. 1 NOVEMBER 1981 DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS, PALISADES PLANT, DOCKET NO. 50-255, TAC NO. 10043 C. J. Cleveland A. C. Udy U.S. Department of Energy Idaho Operations Office
- Idaho National Engin'3ering Laboratory 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-AC07-76ID01570 FIN No. A6429 n
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~~ ~Gt:.G Idaho. Inc FORM EG&G*398 (Rev. 11-79)
INTERIM REPORT Accession No. - - - - - - -
Report No. EGG-EA-5321, REV. 1 Contract Program or Project Tiiie:
Selected Operating Reactor Issues Program (III)
Subject of this Document:
Degraded Grid Protection for Class lE Power Systems, Palisades Plant, Docket No. 50-255, TAC No. 10043 Type of Document:
Technical Evaluation Report Author(s}:
C. J. Cleveland/A. C. Udy Date of Document:
November 1981 Responsible NRC Individual and NRC Office or Division:
J. N. Donohew, Division of Licensing This document was prepared primarily for preliminary or internal 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*76 I 001570 NRC FIN No. A6429 .
INTERIM REPORT
0312J DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS PALISADES PLANT Docket No. 50-255 November 1981 C. J. Cleveland A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
ABSTRACT This EG&G Idaho, Inc. report reviews the susceptibility of the safety-related electrical equipment, at the Palisades Plant, to a sustained degradation of the offsite power sources. Revision one reviews analyses that were provided after the original report.
FOREWORD This report is supplied as part of the 11 Selected Operating Reactor Issues Program (III) 11 being conducted for the U.S. Nuclear Regulatory Com-mission, Office of Nuclear Reactor Regulation, Division of Licensing, by EG&G Idaho, Inc., Reliability and Statistics Branch.
The U.S. Nucle:ar Regulatory Commission funded the work under Authoriza-tion B&R 20-19-01-06.
ii
CONTENTS
1.0 INTRODUCTION
2.0 DESIGN BASE CRITERIA ............................................
3.0 EVALUATION ...................................................... 2
- 3. 1 Existing Undervoltage Protection 2 3.2 Modifications 2 3.3 Discussion 2
4.0 CONCLUSION
S ..................................................... 5
5.0 REFERENCES
...................................................... 5 i ii
TECHNICAL EVALUATION REPORT DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS, PALISADES PLANT
1.0 INTRODUCTION
On June 3, 1977, the NRC requested the Consumers Power Company {CPCo) to assess the susceptibility of the safety-related electrical equipment at the Palisades Plant to a sustained voltage degradation of the offs1te source and interaction of the offsite and onsite emergency power systems. 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 plan~ 3 1
Technical Specifications to satisfy the criteria and staff positions. '
On June 6, 1979, the NRC requested addjtional information from CPCo to clarify some points in their proposal. CPCo resgonded by letter dated February 27, 1980, with the required information.~ The modifications consist of the installation of a second-level undervoltage protection system for the Class lE equipment. Blocking of the load-shed feature, once the diesel generators are supplying the Class lE 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 (GDC 17), "Electrical Power Systems, of Appendix A, "General Design Criteria for 11 Nuclear Power Plants, of 10 CFR 50.6 11
- 2. IEEE Standard 279-1971, "Class lE Power Systems for Nuclear Power Generating Stations. 711
- 3. IEEE Standard 308-1974, "Class lE Power Systems for Nuclear Power Generating Stations. 811
- 4. Staff positions as detailed in a letter s~nt to the licensee, dated June 3; 1977.1
- 5. ANSI Standard C84. l-1977, "Voltage Ratings for Electri-cal Power Systems and Equipment {60 HZ). 9 11
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 lE 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 contro 1 room. ,
The existing logic circuitry of the undervoltage protection system does disable the load-shed feature once the diesel generators are supplying power to the Class lE buses.
3.2 Modifications. To protect the Class lE 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 re.lays, 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 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 generator is satisfactory.
Once the diesel generator is supplying its associated Class lE 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.
Proposed changes to the plant's Technical Specifications, adding the surveillance requirements, allowable limits for the setpoint and time delay, 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 letterl required 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.
2
- 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 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 are the most limiting equipment in the system, this setpoint is acceptable. The licensee's analysis considered other factors, such as MCC contactor pick-up voltage and drop-out voltage.
- 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 cond it i ans:
- 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.
The proposed time delay will not be the cause of any thermal damage to the safety-related equipment.
The setpoint is within voltage ranges recommended by ANSI CB.4.l-1971 for sustained operation.
- b. "The time delay shall minimize the effect of short-duration disturbances from reducing the unavail-ability of the off site power source(s)
- 11 The licensee's proposed time delay of 6.5 seconds is long enough to override any short**inconsequen-tial grid disturbances. Further, we have reviewed the licensee's analysis and agree with the licen-see's finding that any voltage dips caused from the starting of large motors will not trip the offsite source. *
- c. 11 The allowable time duration of a degraded voltage condition at all distribution system levels shall 3
not result in failure of safety systems or components. 11 A review of the licensee's voltage analysis3 indicates that the time delay will not cause any failures of the safety-related equipment since the voltage setpoint is within the allowable tolerance of the equipment voltage rating.
- 4. 11 The voltage monitors shall automatically initiate the disconnection of offsite power sources whenever the voltage setpoint and time-delay limits have been exceeded. 11 A review of the licensee's proposal substantiates that this criterion is met.
- 5. 11 The voltage monitors shall be designed to satisfy the requirements of IEEE Standard 279-1971. 11 The licensee has stated in his submittal that all cir-cuits associated with the undervoltage relays meet IEEE Standard 279-1971.
The relays are stated as being able to meet the require-ments of IEEE Standard 501-1978 also.
- 6. 11 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. 11 The licensee's proposal for technical specification changes includes all the required items. The voltage setpoint, with the maximum allowable limit included, is 2224V. The lowest bus voltage available to the under-voltage relays, as determined by CPCo, is 223lv.13 Therefore, spurious trips of the offsite source due to operation of the under-voltage relays are not expected for any combination of unit loads and normal grid volt-ages. The limiting conditions for operation, the sur-veillance requirements, the channel test frequency and the 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.
4
e e 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 auxiljary 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 ~he 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 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 buses, is tested. A simulated loss of the diesel generator and subsequent load-shedding and 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 sufficient to avoid spuri()JS 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 l. All of the staff 1s requirements and design base criteria have been met. The setpoint and time delay will protect the Class lE equipment from a sustained degraded voltage condition of the offsite power source.
The existing load-shed circuitry does comply with staff 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 staff 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.
Therefore, CPC0 1s proposed changes and Technical Specification changes are acceptable. As the second-level undervoltage protection modifications are installed, it is recommended that the proposed Technical Specification changes be approved and implemented at the earliest opportunity.
5.0 REFERENCES
- 1. NRG letter (A. Schwencer) to CPCo (D. A. Bixel), June 3, 1977.
5
- 2. CPCo letter (D. P. Hoffman) to NRC (D. L. Ziemann), July 28, 1978.
- 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.
- 5. CPCo letter (S. R. Frost) to NRC (D. L. Ziemann), February 27, 1980.
- 6. General Design Criterion 17, "Electric Power Systems, 11 of Appendix A, "General Design Criteria of Nuclear Power Plants, 11 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. 11
- 8. IEEE Standard 308-1974, "Standard Criteria for C1ass lE Power Systems for Nuclear Power Generating Stations. 11
- 9. ANSI C84. l-1977, "Voltage Ratings for Electric Power Systems and Equip-ment. 11 ( 60 HZ) *
- 10. Final Safety Analysis Report (FSAR) for the Palisades Plant.
- 11. CPCo letter (R. W. Huston) to NRC (D. M. Crutchfield), May 7, 1980.
- 12. CPCo letter (D. P. Hoffman) to NRC (D. M. Crutchfield), December 3, 1980.
- 13. CPCo letter (B. D. Johnson) to NRC (D. M. Crutchfield), July 29, 1981.
6
e *.
ENCLOSURE-2 SAFETY EVALUATION PALISADES NUCLEAR PLANT DOCKET NO. 50-255 ADEQUACY OF-STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES INTRODUCTION AND
SUMMARY
Consumers Power Company (CPCo) was*requested by NRC letter dated August 9, 1979 to review the electric power system at Palisades Nuclear Plant. The review was to consist of:
a) Determining analytically the capacity and capability of the offsite power system and onsite distribution system to automatically start as well as operate all required loads within their required voltage ratings in the event of 1) an anticipated transient, or
- 2) an accident (such as LOCA) without manual shedding of any electric loads.
b) Determining if there are any events or conditions which could result in the simultaneous or, consequential loss of both required circuits from the offsfte network to the onsite electric distr-ibutiori system and thus violating the requirements of GDC 17 ..
The August 8, 1979 letter included staff.
guidelines for performing the required voltage analysis and the licensee wa~ further required to perform a test in order to verify th~ validity of the analytical results.
CPCo responded by letters dated January 9, 1980, March 7, 1980, July 18, 1980, August 22, 1980, February 9, 1981, and March 3, 1981. A
T * * .* e. ... ,
detailed review and technical- evaluation of the submittals was performed by EG&G under contract to the NRC, with general supervision by NRC staff.
This work is reported by EG&G in Technical Evaluation Report (TER),
"Adequacy of Station Electric Distribution System Voltages, Palisades Nu cl ear Pl ant," .dated November 1981 (attached). We have reviewed this report and concur in the conclusions that the offsite power system and the onsite distribution system are capable of providing acceptable voltages for worst case station electric load and grid voltages.
EVALUATION CRITERIA The criteria used by EG&G in this technical evaluation of the analysis includes GDC 5 ("Sharing of Structures, Systems, and Components"),
GDC 13 ("Instrumentation and Control"), GDC 17 ("Electric Power Systems")
.of Appendix A to 10 CFR 50; IEEE Standard 308-1974 ("Class lE Power Systems for Nuclear Power Generating Stations"), ANSI C84.l-1977
("Voltage Ratings for Electric Power Systems and Equipmei!'lt - 60 Hz"),
and the staff positions and guidelines in NRC letter to CPCo dated August 8, 1979.
ANALYSIS AND TEST FEATURES Various analyses were performed using the offsite power system (GRID) and ~nit generator as the source of power to the onsite distribution.
system un~e~- normal grid swings and generator voltage extremes. It has been established that the emergency 2400 volt load$ will operate within allowable limits for the worst *cases analyzed.
- e. 3
) During a unit trip, when safety injection loads are automatically transferred to the startup transfonner and block loaded on to the 2400 volt _bus, a brief period exists when voltages at the 480 volt bus could degrade momentarily to prevent contactor pickup until the voltage recovers. Vo 1tage would recover in 1ess than 8 seconds and a11 *equipment would reach rated speed in less than 10 seconds. No contactor drop out or spurious shedding of load 480 volt loads will occur. This momentary inability to start 480 volt loads is not significant due to the very short time of concern. CPCo has provided analysis to show that these transients are of such short duration that sufficient time is available to allow successful starting of all required equipment within the time limits assumed in the FSAR. Additionally the 480 volt battery chargers require 432 volts to provide full output, the input voltage to the battery chargers would be reduced to 414 volts at the minimum voltage analyzed. The output of the chargers would be reduced under this situation. If th~ output should fall below the 125 volt float voltage, annunciation would be actuated in the control room and applicable LCO's will be applied.
The voltage analysis was verified by taking measurements on the 2400 volt and 480 volt emergency buses during two tests. The first test consisted of starting the emergency loads with the buses supplied from offsite power and the second test simulated an SIAS and sequenced all emergency motors on the diesel generators. The comparison showed the calculated voltages to be within -+l .07%
. of the measured voltages..
This close correlation verifies the accuracy of the analysis submitted.
- ~.
CONCLUSIONS We have reviewed the EG&G Technical Evaluation. Report and concur in the findings that:
- 1. Voltages within the operating limits of the Class lE equipment are supplied for projected combinations of plant load and offsite power grid extremes.
- 2. The test used to verify the analysis shows the analysis to be an accurate representation of the worst case conditions analyzed .
. 3. Upon review and approval of the degraded grid protection modifications currently being evaluated by EG&G, there will be acceptable assurance that spurious tripping of offsite power to the Class lE equipment will no~ occur with the offsite grid voltage withiri its expected limits.
- 4. We note that Palisades does not meet the requirements of GDC 17.
This issues is not within the scope of this review and therefore will be.evaluated separately under Systematic Evaluation Program, Topic V.II-3.
. *e ..
.. - ..*. EGG-EA-5417 NOVEMBER 1981.
ADEQUACY OF STATION ELECTRIC DlSTRIBUTION*SYSTEM VOLTAGES, PALISADES PLANT, DOCKET N0 *. 50-255, TAC NO. 12780 * **r . . - ' :. ..
- ........ **. . i*
A. C. Udy *-
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U.S. Department of* Energy Idaho Operations Office
- Idaho National Engineering Laboratory
- - **- *~***-"""'._ /~-~--
This is an lnf.ormal .report Intended for use as a preliminary or working. document Prepared. for the* . *:' :~* ..:-t:{ .: _-* * ,. _
U.S. Nuclear Regulatory Commission Under DOE Contract No. DE-AC07-76ID01570 - ,'
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FIN No. A6429 *. . *: *' :~~ ~** ~* *
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J1~ EGC..G 10.hO. Inc.
FORM EG&G-3911 (Rev. 11-79)
INTERIM REPORT Accession No. - - - - - - -
Report No. EGG-EA-5417 Contract Program or Project
Title:
. Selected Operating Reactor Issues Program (I II)
Subject of this Document:
Adequacy of Station Electric Distribution System Voltages, Palisades Plant, Docket No. 50-255, TAC No. 12780 Type of Document:
Informal Report Author(s):
A. C. Udy Date of Document:
November 1981 Responsible NRC Individual and NRC Office or Division:
J. N. Donohew, Division of Licensing This document was prepared primarily for preliminary or internal 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*76 ID01570 NRC FIN No. A6429
- INTERIM REPORT
- e .
0358J ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES PALISADES PLANT Docket No. 50-255 November 1981 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
. . e* . ---.- .
- ~.
ABSTRACT
- This EG&G Idaho, Inc. report reviews the capacity and the capability of the onsite distribution system at the Palisades plant, in conjunction with the offsite power sources, to automatically start and continuously operate all required safety loads.
FOREWORD This report is supplied as part of the "Selected Operating Reactor Is~ues Program (III)" 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 No. A6429.
ii
CONTENTS
1.0 INTRODUCTION
...................................... '" ............ . 1 2.0 DESIGN BASIS-CRITERIA ........................................... 1 3.0 SYSTEM DESCRIPTION .*.....**..**........*....**..*.*...***.....*. 3 4.0 ANALYSIS DESCRIPTION ****************.********** ~................ 3
- 4. 1 Design/Operation Changes ********************************** 3 4.2 4.3 Analysis Conditions
- Analysis Results 3
5 4.4 Analysis Verification ************************************* 5 5.0 EVALUATION ***************.*********************** ~.............. 5
6.0 CONCLUSION
S .................................. ................. .
~ 7
7.0 REFERENCES
...................................................... 8 FIGURE
- l. Palisades plant electrical single-line diagram ******.************ 2 TABLE
- l. Class lE Equipment Voltage Ratings and Analyzed Worst Case Load Terminal Voltages 4
- 2. Comparison of Analyzed Voltages and Undervo l tage Re 1ay Setpoi nts * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
- 7 ii i
ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES PALISADES PLANT
1.0 INTRODUCTION
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 *Augult 8, 1979, 11 Adequacy of Station Electric Distribution- Systems Volt-ages, 11 required each licensee to confirm, by analysis, the adequacy of the voltage at the class 1E loads. This letter included 13 specific guide-1ines to be followed in determining if the load terminal voltage is ade-quate to start and continuously operate the class lE loads.
Consumers Power Company (CPCo) responded with analyses of January 9, 1980,2 and March 7, 198~.3 Information on required testing was sup-plied on July 18, 1980~ .Subsequent concerns were addressed in letters dated August 22, 1980,;, February 9, 1981, 6 and March 3, 1981.I Additional information was obtained jn letters of October 2, 1978,8 February 27, 1980,9 and May 7, 1980, 10 and in the Palisades . Plant Final Safety Analysis Report (FSAR). Additional analyses were provided on July 29, 1981, ll and these were discussed by telephone in August and September 1981, 12 and supported in a submittal of October 12, 1981.13 Information on.annunciator and alarms for the DC power system were supplied on July 14, 1981.14 aased on the information supplied by CPCo, this report addresses the capacity.and capability of the onsite distribution system of the Palisaces Plant, in conjunction with the offsite power system, to maintain the vol-tage for the required class lE 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 the c1ass lE equipment are aerived from the following:
- 1. Seneral Design Criterion 17 (GDC 17), 11 Electrical Power Systems, 11 of Appendix A, 11 General Design Criteria ror Nuclear Power Plants,"
of 10 CFR SO.
2 * . General Design Criterion 5 (GDC 5), "Sharing of Structures, Sys-
.terns, and Components," of Appendix A, "General Design Criteria for Nuclear Power Plants, 11 of 10 CFR 50.
- 3. General Design Criterion 13 (GDC 13), "Instrumentation and Con-trol," of App~naix A*. "General Design ~riteria for Nuclear Power Plants," of 10 CFR 50.
1
- c ' l
......... - - * - * - - * - - - - ___ ..,_ - ~-- **-
--~-**.- *-*-*-** . -* -- -- *--*- ...
- 4. IEEE Standard 308-1974, "tlass lE Power Systems for Nuclear Power Generating Stations."
- 5. Staff positions as delailed in a letter sent to the licensee, dated August 8, 1979.
- 6. ANSI C84.l-1977, "Voltage Ratings for Electric Power Systems and Equipment (60 Hz)."
'ix review positions have been established from the NRC analysis guide-1ines and the above-listed documents. These positions are stated in Section 5.0.
3.0 SYSTEM DESCRIPTION Fi~ure l is a simplified sketch of the unit electrical one-line dia-gram.4~ 2400V Class lE Buses lC and lD can be supplied by either station power transformer (SPT) 1-2, startup transformer (SLIT) 1-2, or the reserve transformer via 4160V Bus lF. Technical specifications require that both SPT 1-2 and SLIT l-2 be operable before and during operation. The re~erve transformer is used only during cold shutdown per plant operating procedure SOP-30. .
480V Cl ass lE Buses 11 and 12 are supplied by independent transformers from Buses lC and lD, respectively. The four 120V preferred ac buses are normally powered by battery-supplied inverters. Tne FSAR, Section 8.3.5.2, indicates that a backup regulator, powered by the 120V instrument ac bus, is the backup source for all four of the 120V preferted ac buses. Mechani-cal interlocks prevent more tnan one bus from being connected this way at a time. The 120V instrument bus is powered by a transformer connected to 480V aus 11 or aus 12.
There are undervoltage relays on both 2400V Buses lC and lD.2 These relays separate the Class lE buses from offsite power should there be a Jegradation of offsite power, and initiate sequencing onto diesel power.
There is a single transmission feeder from the 345kV switchyard to the three startup tr~nsformers.6 CPCo supplied the equipment operating ranges identified in Table l.
4 .0 ANALYSIS DESCRIPTION 4.1 Design/Operation Changes. The voltages shown on Table l are based on the licensee changing the taps on Transformers 11 and 12 to the 2400V setting. This has been accomplished in 1979.7 .
4.2 Analysis Conditions. CPCo has determined that the minimum expec-ted offstte grid voltage is 345kV. CPCo has not supplied the maximum
- expected offsite grid voltage.
CPCo has analyzed each offsite source to the onsite distribution sys-tem under extremes of load and offsite voltage conditions to determine the terminal voltages to lE equipment. The worst case class lE equipment ter-minal voltages occur under the following condition~:
3
' \ . .. *
- --*e** e.
- 1. The minimum expected continuous load terminal voltages occur when the grid is minimum and the startup transformers supply the maxi-mum expected class lE and non-class lE loads. Startup transfor-mer 1-2 will be supply~ng all class lE loads *.
- 2. The minimum expected transient load terminal voltages occur when the offsite grid is minimum and an accident trips the unit gener-ator and initiates the simultaneous start of all of the safety
- injection loads at an initial ass~med power factor of 0.2.
- 3. CPCo identified the conditions that lead to a maximum continuous bus voltage as "normal grid and generator voltage e~tremes."8 4.3 Analysis Results. Table 1 shows the projected worst case class lE equipment terminal voltages.
The table shows that some 460V motors can be operated continuously at less than rated input voltage. CPCo indicates that this is possible since the load on the motor is less than the motor horsepower rating. 12 Since the m-otor has reserve power, some of this can be used to compe~3ate for the less than rated input voltage, without loss of equipment life. .
t: ~:>
During a simultaneous start of all of the safety injection loads ""'\. ~~~c\
following a unit. trip, contactor pickup for the 480 V motor control center ' ,
loads is prevented by low bus voltage. However, this condition is ~~
temporary, and the loads will start as the voltage recovers above voltage *ill'~
needed for starter pickup. It will not cause contactor dropout or spurirus ~vi\;.~_:..
shedding of any loads. ;*
Continuous output of the battery chargers has not been assurea by CPCo for when the input voltage is less tnan tne minimum battery charger rating.
4.4 Analysis Verification. CPCo provided testing to verify the accuracy of their analysis.4 All metering was within *2 1/2% accuracy.7 7he test consisted of ~easuring ioads and voltages ana calculating corres-ponding voltages for the same grid and load conditions. The deviation between the measured and the *test calculation voltages was within +l.07%
for all buses.
5.O* EVALUATION Six re~iew positions have been established from the NRC analysis guide-lines 1 and the documents listed in Section 2.0 of this report. Each review position is stated below followed by an evaluation of the licensee submittals. The evaluations are based on completion of changes described in Section 4. 1.
Position 1--With the minimum expected offsite grid voltage and maximum load cond1tion, each offsite source and distribution system connection combination must be capable of starting and of continuously operating all class lE equipment within the equipment voltage ratings.
5
-- ----~ .-! - .. ------ ****-.
_. . f .\ "
TABLE 2. COMPARISON OF ANALYZED VOLTAGES AND UNDERVOLTAGE RELAY SETPOINTS
(% of nominal voltage)
Minimum Analyzeda Rel~y Setpoint 9 .
b Location/Relays Voltage Time Voltage (Tolerance) Time 2400V bus Degraded grid 93.0 cpntinuous 91.9(+0.9) 6.S*s Loss of grid 74.4 4.0sb 77.5(+3.3) c
- Loss of grid 74.4 4.0sb 64 Instante-neous
- a. Li~ensee has determined by analysis the minimum bus voltages with the offsite grid at the minimum expected voltage and the worst case plant and class lE loads.
- b. Time until ~~s voltage recovers to above the nominal degraded grfd relay setpoint. *
- c. This is an inverse time delay relay For a trip at 70% of *nominal voltage, 14 seconds will have elapsed. 11 and operating voltage for all required class JE loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.
This applies to multi-unit piants. It does not apply to the Palisaaes Piant, a single-unit station.
6.0 CONCLUSION
S The voltage analyses submitted by CPCo for the Palisades plant were evaluated in Section 5.0 of this report. The change described in Section 4.1 has been completed, and it was found that:
- 1. Voltages within the operating limits of the cl~ss lE equipment are supplied for all projected combinations of plant load and offsite power grid conditions. *
- 2. The test used to verify the analysis shows the analyses to be_ an accurate representation of the worst case conditions analyzed.
- 3. The NRC is considering the simultaneoos or consequential loss of both offsite power sources separately in the Systematic Evalua-
~ tion Program, Topic VII-3.
- 4. Loss of offsite power to class lE buses, due to spurioos opera-tion. of voltage protection relays, will not occur with the offsite grid voltage within its expected limits.
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~-*' ,
.'l .. *
- 14. CPCo letter, R. A. Vincent to Director, Nuclear Reactor Regulation, NRC, "SEP Topic VIII-3.B, DC Power System Bus Voltage Monitoring and Annunciation," July 14, 1981
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