ML19341B079

Adequacy of Station Electric Distribution Sys Voltages, Quad Cities,Units 1 & 2.

ML19341B079
Person / Time
Site:	Quad Cities
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-5253, EGG-EA-5323-DRF, NUDOCS 8101300154
Download: ML19341B079 (9)

Text

l1 p EGnG.- .- .

FORM (GSG 396 (Rev 11791 INTERIM REPORT Accession No.

Report No. EGG-EA-5323 C:ntract Program or Project

Title:

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

Adequacy of Station Electric Distribution System Voltages, Quad Cities - Unit Nos. 1 and 2, Docket Nos. 50-254 and 50-265, TAC Nos. 12808 and 12809 Type of Document:

Informal Report Author (s):

A. C. Udy D:le of Document:

, December 1980

. Rxponsible NRC Individfal 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 5

INTERIM REPORT YlC lesearc1 anc' ecmica Assistance Report 9 o/ 3 oo/S</

t 2039F ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES QUAD CITIES - UNIT NOS. 1 AND 2 Docket Nos. 50-254 and 50-265 i

December 1980 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.

=s Draft 12-18-80 TAC Nos. 12808 and 12809

I 1

ABSTRACT The Nuclear Regulatory Co= mission 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 sources, has sufficient capacity and capability to automatically *f start and operate all required safety loads within the equipment voltage ratings. This Technical Evaluation Report reviews the submittals for the Quad Cities Station.

l The offsite power sources, in conjunction with the onsite distribution system, have been shown to have sufficient capacity and capability to auto- i matically start, as well as continuously operate, all required safety rela-ted loads within the equipment rated voltage limits in the event of either j an anticipated transient or an accident condition.

l FORE'a'O RD

-i This report is supplied as part of the selected Electrical, Instrumen-tation, and Control Systems (EICS) issues program being conducted for the U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Operating Reactors, by EG&G Idaho, Inc., Reliability and Sta-tistics Branch.

The U.S. Nuclear Regulatory Co= mission funded the work under the auth-orization entitled, " Electrical, Instrumentation, and Control System Sup-j port," B&R 20 19 01 03, FIN A6256.

t l

l kk

CONTENTS

1.0 INTRODUCTION

. . . . . . . . .. ................. 1 2.0 DESIGN BASIS CRITERIA . . . . ......... .......... 1 3.0 SYSTEM DESCRIPTION . . . . . .. ................. 2 4.0 ANALYSIS DESCRIPTION . . . . ......... .......... 4 4.1 Analysis Conditions . . .. ................. 4 4.2 Analysis Results . . . . .. ................. 5 4.3 _ Analysis Verification . ... ................ 5-5.0 EVALUATION . . . . . . . . . .. ................. 6

6.0 CONCLUSION

S . . . . . . . . . .. ................. 8

7.0 REFERENCES

. . . . . . . . . .. .................. 9 FIGURE

1. Quad Cities Station, Unit One Line Diagram ............

. 3

, IABLE

1. Class IE Equipment Voltage Ratings and Worst Case Load Terminal Voltages . ................ 5 P

I I-r l

O I

I t

5 t

1 l*

I?

ikk I

t i

l L .

ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES QUAD CITIES STATION - UNIT NOS. 1 AND 2

1.0 INTRODUCTION

4

, 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," I required each licensee to confirm, by analysis, the adequacy of the voltage supplied each class 1E load. The letter included 13 specific guidelines to be followed in determining if the voltage is adequate to start and continuously operate the class 1E loads.

Commonwealth Edison Company (CECO) responded to the NRC letter I , for

, the Quad Cities Station, with letters of November 1,1979 (which included a report on this subject, written by Sargent & Lundy) and 3

December 14, 1979 . The Final Safety Analysis Report (FSAR), test results 4

submitted on June 11, 1980 , additional analyses submitted on June 30, 1980 to answer concerns on the original analysis, and a letter of-7 September 14, 1976 , complete the,information reviewed for this report.

8 Telephone conversations in September 1980 also provided information.

Analysis on the use of the unit inter-tic was submitted on August 18, 1980.9 Based on the information supplied by CECO, this report addresses the capacity and capability of the onsite distribution system of the Quad Cities Station, in conjunction with the offsite power system, to maintain the voltage for the required class'1E 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 offsita voltage conditions in supplying power to equipment are derived from the following:

1-

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 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 IE Power Systems for Nuclear Power Generating Stations"

5. Staff positions as detailed in a letter sent to the licensee, dated August 8, 19791

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-lines Iand the above-listed documents. These positions are stated in Section 5. .

3.0 SYSTEM DESCRIPTION Figure 1 of this report, is a simplified sketch of the unit one-line diagram taken from the Sargent & Lundy report 2 Figure I shows that, for Unit 1, tne class lE 4160V buses 13-1 and 14-1 are normally: supplied power from auxiliary buses 13 and 14, respectively. With loss of the unit gener-ator, tnese buses are supplied by the station auxiliary transformer (SAT)*

from the 345kV switchyard. Class IE 4160V bus 14-1 can be supplied power .

b from the other unit via 'a manual connection to class lE bus l242 1 of Unit 2. This inter-tie-can also be used in the other direction to energize i

bus 24-1 of Unit 2 from the Unit 1 SAT. The Unit 2 distribution system is:

identified as similar in the FSAR, except for different' bus and transformer numbers.

a. CECO also refers to this'as a reserve auxiliary transformer (RAT). g b.- This connecti.in between Units 1 and 2-is hereaf ter referred to as an inter-tie in this report'. -

a 2 l

J Unit Generator and 345KV Main Transformer Switchyard i /\

fs w aj Unit Auxiliary Station Auxiliary Transformer Transformer l-TTTP 11(21) 12(22) TPTm I 4160V 1 4160V I

. 11(21) 12(22)

+

i NC

] NC 1 4160V

]NO ]N0 1 l l 4160V 'T I 13(23) 14(24).

NC

[]NC To Other Unit DG A DG l-2 1(2) j

,- [] NC []N0 [] NO []NC 4160V 4160V

13-1(23-1) 14-1(24-1)

[] -[] NO .{}

480V Trans. -

'480V Trans.

. m m 18(28) s -1 1) TT - ( '}

[]NC. [] NO {} ,NO []NC' 480V 480V 18(28) .19(29)

NOTE: This diagram is for unit 1. The unit'2 class 1E distribution system

~

L is identical, with bus and equipment numbers--shown in parenthesis.

I

% Figure 1

! QUAD CITIES 1 & 2 Unit One Line Diagram j- 3 l

Each 4160V class IE bus supplies power for one 480V class 1E bus via independent transformers (4055/480V tap). These 480V buses can be connected together without technical specification restrictions.

CECO supplied the equipment operating ranges identified in Table 1.

Station 125V DC buses supply power for all class 1E switchgear, except for 480V MCC circuits which use individual control power transfermers and "

contactors.

4.0 ANALYSIS DESCRIPTION 4.1 Analysis' Conditions. CECO has determined by load-flow studies that the maximum expected offsite grid voltage is 354kV and the minimum is 333kV. The station auxiliary transformer was used for the analyses supplied.

Ceco has analyzed each offsite source to the onsite distribution system ~

under extremes of load and offsite voltage conditions to determine the terminal voltages to IE. equipment. The worst case class 1E equipment ter-minal voltages occur with the SAT supplying power and under the following conditions:

1. The maximum expected load terminal . voltages occur when the switchyard voltage-is maximum and there are no unit loads.

2. The minimum expected steady state load terminal volt-ages, when there is no sharing of offsite power. sources, occur when-the switchyard voltage is minimum and all beses are fully loaded (except'for loads shed due to a unit trip).

3. The minimum expected transient load' terminal voltages occur under the conditions of 2,' concurrent with the start of a 1750 hp condensate booster pump (4160V' loads) cr the start of the 150 hp Turbine Building Exhaust Fan on bus 29 when the Unit 1 SAT is' supplying power from Unit 2 buses 24-1 and 29 (480V loads).

4. The minimum continuous and transient load terminal voltages,.when sharing'an offsite source between units, <

occur with a shutdown'in the unit with offsite power supplied by its SAT and accident loads in the other ,

onit.

4-4

TABLE 1 i

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

(% of nominal voltage)

Maximum Minimum Rated Analyzed Rated Analyzed N'minal

'/ol tage Steady i

l Equipment (100%) state ' Transient 5

Motors 4kV Start -- --

75 --

89.9a Operate 110 109.4 90 95.5b __

460V.

Start -- --

75 --

83.6c Operate 110 112.6 90 90.Sa,e __.

Starte:rs 480V Pickup -- --

85 --

84.7 Dropout -- --

70 --

84.7.

Operate 110 107.9 85 89.8a,e __

Other Equipment d

~

a. Lord terminal voltage su ;11ed c by CECO.

b. This value includes the typical (0.5%) feeder cable voltage drop.

c. This is the lowest voltage that occurs in either unit in the CECO analysis. The inter-tie is used'for these volta as. Without use of the inter-tie, the lowest voltage is higher..

d. Self-regulated motor-generator sets presently supply power. for 120V AC essential buses - These are scheduled to be replaced with inverter sets that have their own voltage regulation.

4.2 Analysis Results. Table I shows the projected worst case class lE equipment terminal voltages for either Unit 1 or Unit 2.

4.3 Analysis Verification. The computer analysis was verified b by-measuring the switchyard voltage and the Unit 2 class IE bus and selected 5.

e k.

class 1E equipment terminal voltages while bot. units were shutdown. Since the bus loads were light, a digital voltmeter (+0.01% accuracy) was used to be sure that voltage drops could be measured. An analysis using the measured loads and switchyard voltage determined the expected bus and .

equipment voltages, and the results were compared with the measured bus and equipment voltages.

• Even though the grid voltage varied between 353.4 and 352.2kV while the measurements were made, the comparison shows that the class 1E calcu-lated bus voltages are within +0.17/-1.58% of the measured bus voltages.

5.0 EVALUATION Six review posicions have been established from the NRC analysis guide-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 di stribution system connection combination must be capable of starting and of continuously operating all class 1E equipment within the rated equipment voltages.

As shown in Table 1, a brief acceptable condition, when the buses are fully loaded, would prevent class 1E 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.

No technical specification restrictions have been identified on the connection between class 1E 480V buses 18 and 19 (28 and 29). CECO has not provided an analysis for use of this connection. Since the worst case 480V voltage without the connection is 90.5%, Ceco should put appropriate restrictions on the use of this connection.

CECO has shown by analysis that the Quad Cities station has sufficient capability and capacity for starting and continuously operating the class 1E .

loads within equipment voltage ratings (Table 1).

6

1 Position 2--With thc maximum expected offsite grid voltage and minimum load condition, each offsite source and distribution system connection combination must be capable of continuously operating all class 1E equip-4 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 112.6% on the 480V buses. CECO concluded that the cafety loads at the Quad Cities Station would not be subjected to unaccepteble overvoltages because the analysis was done for a no-load condition and, when a load is added, voltage drops in the supply transformers and feeder cables reduces the voltage to "very close to 110%."3 CECO has shown by analysis that the voltage ratings of the class 1E equipment can be slightly exceeded with no loads connected to power. How-ever, when loads are connected, feeder drops and transformer impedences

~ lower the available terminal voltage so-that overvoltages are not supplied to the class IE equipment.

• Position 3--Loss of offsite power to either the redundant class 1E

distribution systems or the in'jividual 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 the require-ments of this position are satisfied (TAC Nos. 10046 and 10047).

i e

Position 4--Test results should verify the accuracy of the voltage l analyses supplied.

i CECO has shown a close correlation between measured and calculated 1

-voltages that verifies the adequacy of the analysis submitted for Unit 2.

i Since both units' electric distribution systems are similar and unit depen-dent variables were field verified5,. this test for Unit 2 is considered -

l as verification of the 'Jait 1 analysis.

\-

7

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 Quad Cities Station to the -

offsite power grid, and has determined that no potential exists for the

~

simultaneous or consequential loss of both circuits from the offsite grid.2 Position 6--As required by GDC 5, each offsite source ashared 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.

CECO has shown that, by using the inter-tie between the two Quad Cities units, adequate starting and operating voltages are supplied to the class 1E equipment for an accident in one unit and an orderly shutdown and cooldown in the remaining unit (Table 1).

6.0 CONCLUSION

S The voltage analyses submitted by CECO for the Quad Cities station were evaluated in Section 5.0 of this report. It was found that:

1. Voltages within the operating limits of the class 1E 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.

However, CECO should establish appropriate technical specification restrictions on consecting two class 1E 480V buses 18 and 19 or 28 and 7/ together.

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

l l

[

j a. Section 8.1.1 of IEEE Standard 308 permits the use of a single source of i of fsite power to be shared between units of a multi-unit station.

l

! 8 1

I i

f

i

3. CECO has 'atermtaed that no potential for either a simultanoas or consequential loss of both of fsite power Sources atists.

j j

EG&G Idaho, Inc., is performing a separate review cf the undervoltage relay protection at the Quad Cities station. This will evaluate the relay

, setpoints and time delays to determine that spurious tripping of the class IE buses will not occur with normal offsite source voltages.

7.0 REFERENCES

l 1. NRC letter, William Gammill, to All Power Reactor Licensees (Except i Humboldt Bay), " Adequacy of Station Electric Distribution Systems Voltages," August 8, 1979.

2. Ceco letter, Robert F. Janecek, to William Cammill, "Adequancy of Station Electric Distribution System Voltages", November 1, 1979.

3. Ceco letter, Robert F. Janecek, to William Gammill, "Adegnacy of Sta-tion Electric Distribution System Voltages", December 14, x;79..

~

4. CECO letter, Robert F. Janecek, to William Gammill, U.S. NRC, " Adequacy 2

of Station Electric Distribution System Voltages," June 11, 1989.

5. CECO letter, Robert F. Janecek, to T. A. Ippolito, U. S. NRC, " Adequacy

{ of Station Electric Distribution System Voltages," June 30, 1980.

6. CECO letter, Robert F. Janecek, to Darrell G. Eisenhut, U.S. NRC, f

"Second Level of Undervoltage Protection for 4kV Onsite Emergency' Power Systems," June 26, 1980.

7. CECO letter, G. A. Abrell, to Karl R. Goller, U.S. NRC, "Information Concerning System Voltage Conditions," September 14, 1976.

8. Telecon, A. C. Udy, EG&G Idaho, Inc., to H. Stolt, CECO, September 11, I

1980.

9. Ceco letter, Robert F. Janecek, to U.S. NRC, Darrell G. Eis', hut, l

" Additional Response concerning Adequacy 'of Station Elect 'istribu-tion System Voltages," August 18, 1980.

I k

l i

9 1

-- , - , , - . , , . . - , - , ... . ,. , ,. . . . . - . -