ML19341B381
| ML19341B381 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 12/31/1980 |
| From: | Udy A EG&G IDAHO, INC., EG&G, INC. |
| To: | Shemanski P Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-6256 EGG-EA-5325, EGG-EA-5325-DRF, NUDOCS 8101300842 | |
| Download: ML19341B381 (14) | |
Text
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EGcG...,-
FORM EG&G 398 (Rev 1171h INTERIM REPORT Accession No.
Report No. EGG-EA-5325 e
Contract Program or Project
Title:
Electrical, Instrumentation and Control System Support Subject of this Document:
Adequacy of Station Electric Distribution System Voltages, Dresden Station -
Unit 1, Docket No. 50-10, TAC No. 12764 Type of Document:
Informal Report Author (s):
A. C. Udy Date of Document:
December 1980 R:sponsible NRC Individual and NRC Office or Division:
Paul C. Shemanski, 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 76f D01570 NRC FIN No.
A6256 INTERIM REPORT HC Researca anc ecanical
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Assistance Report 4
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2040F e
ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES DRESDEN STATION - UNIT NO. 1 Docket No. 50-10 December 1980 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
Draft 12-18-80 1
ABSTRACT The Nuclear Regulatory Commission has required all licensees to analyze the electric power system at each nuclear station. This review is to deter-mine if the onsite distribution system, in conjunction with the offsite power sourcas, 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 Unit 1.
A separate TER reviews the submittals for Units 2 and 3.
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 rela-ted loads within the.luipment rated voltage limits in the event of either an anticipated transient or an accident condition.
FOREWORD This report is supplied as part of the selected Electrical, Instrumen-tation, and Control Systems (EICS) issues program being conducted for the
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U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Operating Reactors, by EG6G Idaho, Inc., Reliability and Sta-tistics Branch.
The U.S. Nuclear Regulatory Commission funded the work under the auth-orization entitled, " Electrical, Instrumentation, and Control System Sup-port," B&R 20 19 01 03, FIN A6256.
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CONTENTS
1.0 INTRODUCTION
1 2.0 DESIGN BASIS CRITERIA..
1 3.0 SYSTEM DESCRIPTION 2
4.0 ANALYSIS DESCRIPTION 4
4.1 Design Changes.
4 4.2 Analysis Conditions 4
4.3 Analysis Results.
5 4.4 Analysis Verification 5
5.0 EVALUATION 6
6.0 CONCLUSION
S.
8
7.0 REFERENCES
8 FIGURE 1.
Dresden Station, Unit One Line Diagram, Unit 1 3
TABLE 1.
Class 1E Equipment Voltage Ratings and Worst Case Load Terminal Voltages.
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y ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES DRESDEN STATION - UNIT NO. I
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 (CDC) 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," I required each licensee to confirm, by analysis, the adequacy of the voltage supplied each class IE load. The letter included 13 specific guidelines to be followed in determining if the voltage is adequate to start and continuously operate the class IE loads.
Commonwealth Edison Company (CECO) responded to the NRC letter, fcr the Dresden Station, Unit I with a letter of February 1,'19802 (which included a report on this subject, written by Sargent & Lundy). The Final Safety Analysis Report (FSAR), additional analyses submitted on June 30, 3
4 1980, telephone calls in September 1980, and a letter of September 14, 5
1976, complete the information reviewed for this report.
Based on the information supplied by CECO, this report addresses the capacity and capability of the onsite distribution system of Unit 1 of the Dresden Station, in conjunction with the offsite power system, to maintain the voltage for the required class IE equipment within acceptable limits for the worst-case starting and steady-state load conditions.
2.0 DESIGN BASIS CRITERIA The positions applied in determining the acceptability of the offsite voltage conditions in supplying power to 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.
2.
General Design Criterion 5 (GDC 5), " Sharing of Struc-tures, Systems, and Components," of Appendix A, " General Design Criteria for Nucicar Power Plants," of 10 CFR 50.
3.
General Design Criterion 13 (CDC 13), " Instrumentation and Control," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.
4.
IEEE Standard 308-1974, " Class IE Power Systems for Nuclear Power Generating Stations."
5.
Staff positions as detailed in a letter sent to the licensee, dated August 8, 1979.1 6.
ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equipment (60 Hz)."
Six review positions have been established from the NRC analysis guide-I lines and the above-listed documents. These positions are stated in i
Section 5.
3.0 SYSTEM DESCRIPTION a
Figure 1 of this report is a simplified sketch of the Unit I unit one-line diagram taken from the Sargent & Lundy report of reference 2 and Sargent & '. undy drawing #12-E-5.
This figure shows that the class 1E dis-tribution system is normally supplied power.from 4160V auxiliary buses 11 and 12.
TheJe auxiliary buses are supplied power from the reserve auxiliary
- transformer (RAT) TR12, or unit auxiliary transformer (UAT) TR11. After a unit trip, TR12 continues to provide offsite power to the auxiliary and the class IE distribution systems. Additionally, bus 11 (and, hence, IE buses 112,113, and 117) can be supplied power from the 34.5kV grid via trans-former TR13; however, the CECO analysis does not show any 4160V loads ener-gized from this source.
The unit generator can be isolated from the UAT to allow it to supply offsite power to the connected distribution buses as a reserve source. There are no power connections to Unit 2 or to Unit 3.
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r 34.5 KV 138 KV SWITCHYARD 138 KV SWITCHYARD VIA MAIN TRANS.
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- 1 GEN.
q q UAT mm b) b)
b)
BUS 11-BUS 12 4160V 4160V
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DG DG 480V AUXILIARIES 480V hSN' <-[]
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VIA TR 15 <--
TR 16 BUS 112 BUS 110 4160V 4160V
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CLASS lE CLASS 1E
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BUS 113 BUS 111 4160V 4160V CLASS 1E
{} CLASS 1E i
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CLASS lE 480 V CLASS lE. 480V l.
DRESDEN STATION I
UNIT ONE LINE DIAGRAM UNIT 1 i
FIGURE 1 3
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. _ -. = _ _ -.
_... ~ _....-
i Each of two 480V class lE buses is supplied power from one of two j
class IE 4160V buses via independent transformers.
Ceco supplied the equipment operating ranges identified in Table 1.
i Station 125V DC buses supply power for 4160V class IE switchgear.
I 4.0 ANALYSIS DESCRIPTION i
l 4.1 Design Changes. CECO has committed to change the tap setting of transformer 12 to +2 1/2% voltage boost.2 The discussion in this report i
and the values in Table 1 are on the basis that this tap setting has been 3
made.
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4.2 Analysis Conditions. CECO has determined by load-flow studies j
that the maximum 138kV switchyard voltage is 142kV and the minimum is 1
4 133kV.2 The 34.5kV switchyard voltage varies between 36.3kV and 34.8kV, 2
respectively (contingency plans with the historical low voltage determined the lower voltage).
CECO has analyzed each offsite source, with the exception of TR13, to the onsite distribution system under extremes of load and offsite voltage coaditions to determine the terminal voltages to the class IE equipment.
CECO has not included any 4160V bus 11 loads in their voltage analysis for-
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TR13.3 The worst case class lE equipment terminal voltages occur under the following conditions:
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- 1..
The maximum expected load voltage occurs with either.
i transformer 12 or 13 supplying power and when the switchyard voltage is maximum and there are no unit loads.
i 2.
The minimum expected continuous load voltage occurs i
with transformer 12 supplying power, the 138kV switch-yard voltage is minimum, and all buses are fully loaded (except for. loads shed due to unit-trip).
3.
The minimum expected transient load voltage occurs
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under the conditions of 2, concurrent with the start of a large load, i
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r TABLE 1 CLASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES
(% of nominal voltage)
Maximum Minimum Rated Analyzed Rated Analyzed Nominal Voltage Steady Equipment (100%)
state Transient Motors 4kV Start 75 88.8a Operate 110 109.7 90 96.lb 460V Start 75 83.8a Operate 17 0 110.1 90 91.6b Starters 480V Pickup 85 81.3 Dropout 70 81.3 Operate 110 105.5 85 88.7 Other Equipmente Load terminal voltage supplied by CECO.
a.
b.
These values include worst case (480V) or typical (4160V) feeder cable voltage drop (1.0%, 0.5%, respectively ),
2 120V vital buses are norstily supplied power by motor generator sets 3, c.
These are scheduled to be replaced by inverters. Self-regulating trans-formers provide an alternate source should the motor-generator set or inverter be out of service.4 4.3 Analysis Results. Table 1 shows the worst case voltage levels identified in the CECO analyses.
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4.4 Analysis Verification. CECO has not committed to verify the accuracy of their voltage analysis. One acceptable method would be to measure the grid voltage, the class 1E bus voltages, and the actual class IE bus load, and then compare these measured values with an analysis that uses 5
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the measured offsite source voltage and the measured bus loads. CECO must establish that the load conditions and instrument accuracies used in the test are adequate to account for impedence and transformer voltage drops in t he distribution system.
5.0 EVALUATION Six review positions have been established from the NRC analysia guide-i 1
lines and the documents listed in Section 2.
Each review position is stated below, followed by the evaluation of the licensee submittals.
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 lE equipment within the rated equipment voltages.
A brief acceptable condition, when starting the largest motor on 4160V bus 11 or 12, would' prevent class IE contactor pickup, if a 480V MCC load were stopped and then restarted, until the voltage recovers.
It will not cause contactor dropout or spurious shedding of any loads.
Ceco has shown by analysis that Dresden 1 has sufficient capability and capacity for starting and continuously operating the class 1E loads within the equipment voltage ratings (Table 1),
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Position 2--kith the maximum expected offsite grid voltage and minimum load conditior., each offsite source and distribution system connection combination must be capable of continuously operating all class IE equip-ment without exceeding the rated equipment voltage.
As can be seen from Table 1, all loads are operated within allowable voltage limits, except for the potential 110.1% on the 480V buses. CECO concluded that the safety loads at Dresden Unit I would not be subjected to unacceptable overvoltage because this analysis was done for a no-load condition which does not exist when the equipment is powered; that voltage l
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drops in the supply transformers and feeder cables would reduce the 110.1%
to within an acceptable voltage range.
CECO has show?.
that by analysis that the voltage ratings of the class 1E equipment will not be exceeded.
Position 3--Loss of offsite power to either the redundant class IE distribution systems or the individual class 1E loads, due to operation of voltage protection relays, must not occur when the offsite power source is within analyzed voltage limits.
EG6G Idaho, Inc., will verify, in a separate report, that this position is satisfied (TAC No. 10020).
Position 4--Test results should verify the accuracy of the voltage analyses supplied.
CECO has not committed to verify the accuracy of the voltage analyses for Dresden, Unit 1.
Position 5--No event or condition should result in the simultaneous or consequential loss of both required circuits from the offsite power network to the'onsite distribution system (GDC 17).
CECO has analyzed the connections of the Dresden Station to the off-site power grid, and has determined that no potential exists for the simul-taneous or consequential loss of both circuits from the offsite grid.
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 1E loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.
Section 8.1.1 of IEEE Standard 308 permits the use of a single source a.
of of fsite power to be shared between units of a multi-unit station.
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1 Dresden Unit 1 is connected to offsite power independently ot' Dresden Unit 2 and Unit 3.
No common electrical connections exist; therefore, this position does not apply.
6.0 CONCLUSION
S The analyses submitted by CECO for this review were evaluated as stated in Section 5 of this report. These submittals show that, after the trans-former #12 tap settings are changed to 21/2% boosts 1.
Voltages within the operating limits of the class 1E l
equipment are supplied for all projected combinations of plant load and offsite power grid voltage conditions.
However, CECO should provide for TR13 either (a) an analysis showing acceptable voltage for 4160V loads, (b) design changes to prevent these loads from being energized from TR13, or (c) technical specifications that concur with the present analysis conditions.
2.
CECO has determined that no potential for either a simultanous or consequential loss of both offsite power sources exists.
3.
CECO has not committed to show, by test, that their analysis of the Dresden Station distribution system is an accurate representation of the actual voltages. One acceptable method is outlined in Section 4.4 of this report.
CECO should be required to perform tests to verify the' accuracy of'their analysis.
EG&G Idaho, Inc., is providing a separate review of the undervoltage relay protection at.Dresden 1.
This will evaluate the relay setpoints and time delays to determine that spurious tripping of the class 1E buses will not occur with normal offsite source voltages.
7.0 REFERENCES
1.
NRC letter, William Gammill, to All Power Reactor Licensees (Except Humboldt Bay), " Adequacy of Station Electric Distribution Systems Voltages," August 8, 1979.
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CECO letter, Robert F. Janecek to William Gammill, "Adequancy of Sta-tion Electric Distribution System Voltages", February 1, 1979.
3.
CECO letter, Robert F. Janecek, to T. A. Ippolito, U. S. NRC, " Adequacy of Station Electric Distribution System Voltages," June 30, 1980.
4.
Telecon, Hal Stolt, CECO and other Ceco personnel and Alan Udy, EG&G Idaho, Inc., September 11, 22, and 25, 1980.
5.
CECO letter, G. A. Abre11, to Karl R. Goller, U.S. NRC, "Information Concerning System voltage Conditions," September 14, 1976.
6.
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.
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