ML20039A911

Adequacy of Station Electric Distribution Sys Voltages, Fort Calhoun Nuclear Station Unit 1,informal Rept

ML20039A911
Person / Time
Site:	Fort Calhoun
Issue date:	11/30/1981
From:	Weber D EG&G, INC.
To:	Donohew N Office of Nuclear Reactor Regulation
References
CON-FIN-A-6429 EGG-EA-5636, NUDOCS 8112210507
Download: ML20039A911 (17)

Text

{evenb. SS g/( feitarCN Y of EGG-EA-5636 November 1981 (QA ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM N

A f/S VOLTAGES, FORT CALHOUN NUCLEAR STATION UNIT 1, Af6/d DOCKET N0. 50-285 g ,-q ,,

N Jbi \

D. A. Weber NOV3 01981%

y ,*

CosaattS504 PRELIM! MARY U.S. Department of Energy Idaho Operations Office

• Idaho National Engineering Laboratory y;7.,.{rg'U![::.^jlA ,,K.';;'

• 3 ,

1 i, s .\ wl ! ,

\. ' .

s,dly i q ,g r. y

{ du s d@TI sud ' =cm 2 ',

6tEhcibh ;

% _ i h= M., c ,,.-J.E Wr5F4 S S ;-;_. " eM1l

-= "

, . _ . . . 'ww eurenrwmarrrrr:womarmisur'

1. N S- E P T :"3 " p

@Q ~ ^

T _1 7 d M 4 W F % % Q =_- 1 2 5 3.. ,7,..

2 \ '~ 2. ._ .~ _;+. . x *Y 0N gfm ~ *

• **f " ** ..

.d" This is an informal report intended for use as a preliminary or working document Prepared for the U.S. Nuclear Regulatory Comission g Under DOE Contract No. DE-AC07-76ID01570 E G g S ioano FIN No. A6429 YD 8112210507 811130 PDR RES

• PDR

pREGsG,.~.w FORM EG4G 308

>nm INTERIM REPORT

• Accession No.

Report No. EGG-EA-5636 s

Contract Program or Project

Title:

Selected Operating Reactor Issues Program (III)

Subject of this Document:

Adequacy of Station Electric Distribution System Voltages, Fort Calhoun Nuclear Station Unit 1 Docket No. 50-285 Type of Document:

Informal Report Author (s):

D. A. Weber D:te of Document:

November 1981 o

RIsponsible 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.

e' Under DOE Contract No. DE AC07 761D01570 NRC FIN No. A6429 lNTERIM REPORT

0388J t

ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES FORT CALHOUN NUCLEAR STATION UNIT 1 Docket No. 50-285 November 1981 o

D. A. Weber Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.

Draft 10-26-81 TAC No. 12738

i I

I I

1 o

ABSTRACT l

This report contains the EG&G Idaho, Inc. evaluation of the adequacy of 1 the station IE electrical distribution system voltages for the Fort Calhoun Nuclear Station, Unit 1.

l l

FOREWORD This report is supplied as part of the " Selected Operating Reactor Issues Program (III)" being conducted for the U.S. Nuclear Regblatory 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 author-ization, B&R 20 19 01 06, FIN No. A6429.

9

- ii

1 i I CONTENTS

1.0 INTRODUCTION

.................................................... 1

, 2.0 DESIGN BASIS CRITERIA ........................................... 1

[

3.0 SYSTEM DESCRIPTION .............................................. 2 1

~ e 4.0 ANALYSIS DESCRIPTION ............................................ 4 4.1 Design / Operation Changes .................................. 4 4.2 Analysis Conditions ....................................... 4

'- 4.3 Analysis Results .......................................... 4 i

4.4 Analysis Verification ..................................... 6 5.0 EVALUATION ...................................................... 7

6.0 CONCLUSION

S ..................................................... 9

7.0 REFERENCES

...................................................... 10 APPENDIX--REVIEW REFERENCES .......................................... 11 FIGURE

, 1. Fort Calhoun electrical single-line diagram ..................... 3 TABLES

1. Class lE Equipment Voltage Ratings and Analyzed Worst Case Load Terminal Voltages ...................... 5

2. Comparison of Analyzed Voltages and Undervoltage Relay Setpoints .................................... 5 I

l l iii i

I I

- . . =- .-. . . _ .

'I

- i ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES FORT CALHOUN NUCLEAR POWER STATION UNIT 1

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 August 8, 1979,

. " Adequacy of Station Electric Distribution Systems Voltages," I required each licensee to confirm, by analysis, the adequacy of the voltage at the class 1E loads. This letter included 13 specific guidelines to be followed in deter-mining if the load terminal voltage is adequate to start and continuously operate the class lE loads.

In response to the generic letter and questions from the staff, the Omaha i - Public Power District (OPPD) submitted information and analysis on August 31, 1979,2 March 20, 1980,3 July 2, 1981,4 and August 31, 1981.5 These submit-tals, the OPPD submittals of September 17, 1976,6 July 24, 1977,7 November 21, 4 1977,8 July 12, 1978,9 the NRC submittals of December 14, 1977,10 October 19, 1978,II October 17, 1979,12 and the Fort Calhoun Unit 1 Final Safety Analy-sis Report, complete the information reviewed for this report.

Based on the information supplied by OPPD, this report addresses the capacity and capability of the onsite distribution system of the Fort Calhoun Nuclear Power Station, in conjunction with the offsite power system, to main-tain the voltage 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 class lE equipment are derived from the following:

f 1

--. n. , , , - . _. - , . , - , , ,

1. General Design Criterion 17 (GDC 17), " Electrical Power Systems," of Appendix A. " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.  ;

l

2. General Design Criterion 5 (GDC 5), " Sharing of Structures, Systems, , j 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 lE Power Systems for Nuclear Power Generating Stations."

5. Staff positions as detailed in a letter sent to the licensee, dated August 8, 1979.I

\

j 6. ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equipment (60 Hz)."

e Six review positions have been established from the NRC analysis guide-lines Iand the above-listed documents. These positions are stated in Section 5.0.

3.0 SYSTEM DESCRIPTION Figure 1 of this report is a simplified sketch of the Fort Calhoun single-line diagram. During normal full-power plant operation, power to the station distribution system is supplied by both of the Generator Auxiliary Transformers (GATS) TlA-1 and T1A-2, and both of the Station Auxiliary Transformers (SATs)

TIA-3 and TlA-4. The loads are divided among the transform 3rs with half the auxiliaries supplied from the GATS and half from the SATs. Any two transfor-mers are capable of supplying total plant auxiliary load. Fast-acting auto-matic circuit breakers are provided to transfer full auxiliary load to either the GATS or the SATs if one of the two sources of power is lost.

2

o , * -

,345 KV 161 KV 9,

22 KV i

Q 't m Y aJss men e}

U c

(

uw m ^A

!,lA3(4160) '

lAl (4160) h il 1A4 (4160) h h IA2 (4160)

[g =

y

.em vm 1

mm vm um b mm n d L[,

i

.- O -r F @

o' 3

1B3C-4C (483)

R) 1B3C ) 1 184C (480) (480)

C l y IB3A-4A [-) IB3A ) i) IB4B g T4!$0) (480) (480) 5

" "; IB3B (480) ,) 1) IB4A (480) v.,.

'> b

." MCC 381 (480) (480) IICC 4A1 m ) I s 1 I

@ Battery 1 2 a Chargers a

2 125V DC-1 l

3 2) ,1 125 DC-2 1; 1 3 iy ij l

Inverters A C B D t v Y 9 To 120 VAC A Al C Cl B,81 D,01 '

Instrument Buses 1,lA 2,2A

T i

l The emergency diesel generators are self-contained and not dependent on normal sources of power. They are maintained in a preheited state ready for automat _ic compressed-air starting and are equipped with a closed cooling c

system.

4.0 ANALYSIS DESCRIPTION e 4.1 Design / Opera'. ion Changes. The voltages shown on Table 1 are based on the licensee's proposal to change the taps on the SATs from the 165kV tap to the 161kV tap, and to connect the primary of the battery charger D

. transformer to the 460V tap.

4.2 Analysis Conditions. OPPD has determined by load flow that the maximum expected offsite grid voltage is 169kV^ and the minimum 152kV.B OPPD has analyzed each offsite source to the onsite distribution system under extremes of load and offsite voltage conditions to determine the terminal voltages to lE equipment. The worst case class lE equipment terminal voltages occur under the following conditions: ,

1. The maximum voltage occurs when the 161kV source is at its maximum 4

value and the onsite distribution system lightly loaded.A l

l 2. The minimum steady-state value occurs when all safeguard and auxil-iary loads are running and the offsite grid is at its minimum expec-ted value.B

3. The minimum transient values occur with the sequenced starting of the safeguard loads, all auxiliary loads are running, and the off-site grid is at its minimum expected value.

-4.3 Analysis Result. Table 1 shows the projected worst case class lE equipment terminal voltages. Table 2 shows a comparison of the analyzed volt-age with the undervoltage relay setpoints.

4 l

l

[

+

TABLE 1. CLASS lE EQUIPMENT VOLTAGE RATINGS'AND ANALYZED WORST CASE TERMINAL V0LTAGES (% of nominal voltage) j Maximum ~ Minimum Analyzed 0

Equipment Condition Rated Analyzed Rated Steady State Transient 4160V Motors 0 5 tart G 70E

-H 76.74F Operate 110 105 90 78.69 --

i- 4000V MotorsD Start -- --

70E --

79.9 F G H Operate 110 109 90 81.93 ,_

460V Motorsl Start G 70I -g 68.3J j Operate 110 109 90 78.19 --

- 460V Starters Pickup -- --

85L --

71.58N

! Dropout -- --

72M --

71.58N

! Operate 110 110 90 80.43P __

Other Equipment OperateQ 110 109 900 80.43R __

(460V Battery Chargers)

~

j i

I

( TABLE 2. COMPARIS0N OF ANALYZED VOLTAGES AND UNDERVOLTAGE RELAY SETPOINTS j . (% of nominal voltage) a e Minimum Analyzed Relay Setpoint f Location / Relays Voltage Time Voltage (Tolerance) Time 4160V bus lA3 Degraded grid 88.68S continuous 92.42 (~+0.5%) 4.8

+0.5seg b 6

T Loss of grid 85.52 <8 sec W 72 (+2.5 -0.5%) 5.9 sec j 4160V bus lA4 j Degraded grid 81.19U continuous 89.97-(+0.5%)

4.8

+0.5 secb

. Loss of grid 79.24V ~< 8 secW 72 (+2.5 -0.5%) 5.9 secc

] a. Licensec has determined by analysis the minimum bus voltages with the

! offsite grid at the minimum expected voltage and the worst case plant and

'T class 1E loads.

b. Time based on lower limit of relay setting.

, c. Oncompletelossofvoltagerglayswillactuatein4sec;at72% X l relays will operate in 8 seconds i

i 5

i 1

v-. ,

4.4 Analysis Verification. OPPD performed voltage measurement tests as part of an undervoltage study on the Fort Calhoun Station's electrical distri-bution system, including all Class lE buses down to the 120/208V level, during i December 1977. The voltage measurement tests involved electrically loading the Fort Calhoun Station's distribution buses, including all Class lE buses down to ,

the 120/208V level, to at least 30% of full load as required by the test guide-lines. Steady-state and motor-starting transient tests voltages were measured for the existing grid and Class lE buses down to the 480V level. Steady-state and motor-starting voltage measurements were not recorded at the 120/208V level because all critical safety-related electric motors at Fort Calhoun operate on 480V buses or higher.

Based on the undervoltage analysis, bus IB4B was determined to have the lowest analyzed voltage. Therefore, only transient voltage measurements on bus 1B4B were recorded. Two separate motor-starting tests were conducted with Class lE motors to provide voltage data. This test data was then com-pared to the analytically derived voltages for bus 1B4B. The first test involved starting the 300 HP containment spray pump SI-38. The second test involved the concurrent starting of two motors, containment spray pump SI-3C and ventilation air fan motor VA-7D, with combined power requirements of 425 HP. Voltage values above the 480V level were not analyzed as recording equipment measuring transient voltage changes on the distribution grid (161 KV) and bus lA4 (4.16 KV) measured no detectable voltage drops when the motors were started.

Comparison of the test and analytically derived voltage values revealed the calculated voltages to be lower than the test voltages. The calculated voltage of 429V for the motor-starting analysis of SI-3B was found to be 3.8%

lower than the measured test voltage of 446.2V. The calculated voltage of 421V for the concurrent motor-starting analysis of SI-3C and VA-70 was found to be 3.5% lower than the measured test voltage of 436.5V. Selected variable values (e.g., motor locked rotor factors) used in the calculation of the analytically derived voltages were conservative and probably accounted for the differences.

6

l j 5.0 EVALUATION Six review positions have been established from the NRC analysis guide-

• lines 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.

9 i Position 1--With the minimum expected offsite grid voltage and maximum

! load condition, each offsite source and distribution system connection combi-nation must be capable of starting and of continuously operating all_ class lE equipment within the equipment voltage ratings.

The OPPD analysis has shown that the 161kV offsite source does not have sufficient capability and capacity for starting and continuously operate all class lE loads within the equipment voltage ratings.

j The worst-case OPPD analyzed (shown in Tables 1 and 2) is with the 161kV grid degraded to 152kV (.945). OPPD recognizes that some of the IE equipment l

I may be required to start and run at voltages below their ratings. In Attachment 9,2 OPPD makes some recommendations to maintain adequate l voltages. The recommendations are unacceptable since they all require manual i actions which are not in agreement with the NRC guidelines.

1 0 1

4 OPPD also analyzed the minimal lE motor terminal voltage requirements

under LOCA conditions. Their analysis show that if the 161kV grid is greater i than 158kV (98%) then all the lE motors will start and operate. The lower 1

1 limit of the degraded voltage (2nd level) relay settings are based on this

) analysis. Table 1, which is derived from the licensee's August 31,_1979 4

l submittal 2 and the tables in the submittal of July 2, 1981 shows that j some of the 460V motor starters may not pick up when required under transient

! (starting) conditions.Al In addition some of the safety-related equipment 0 may be required to operate continuously below their minimum rating.A2

I

Therefore this position is not met, even if the grid is held at 161kV i under maximum loading conditions, j '..i 7

OPPD has also indicated that the onsite distribution system may be sup-plied from the 345kV grid 4and have indicated that the minimum acceptable l

voltage will be 336kV. They have not provided lE bus and equipment terminal voltages (transient and steady state) for a degraded 345kV grid suppling plant LOCA loads (161kV grid unavailable).

p Position 2--With the maximum expected offsite grid voltage and minimum load condition, each offsite source and distribution system connection com-

! bination must be capable of continuously operating the required class lE equipment without exceeding the equipment voltage ratings.

OPP.D has shown, by analysis, that the voltage ratings of the class lE equipment will not be exceeded.

Position 3--Loss of offsite power to either of the redundant class lE l

L distribution systems due to operation of voltage protection relays, must not occur when the offsite power source is within expected voltage limits.

j As shown in Table 2, voltage relays can cause loss of class lE distribu- ,

tion systems when the offsite grid voltage is within expected voltage limits.

Position 4--The NRC letter, requires that test results verify the

! accuracy of the voltage analyses supplied.

OPPD provided test results in their submittal of August 31, 1981.5 The testing performed by OPPD does not meet the intent of the NRC guidelines as testing only considered the starting of motors associated with one 480V_ bus.

Not included were: (1) starting tests on other lE 480V buses, (2) starting tests on the IE 4160V buses and their effect on 4160V and 4000V motors, and the lE 480V buses and loads, (3) starting tests of a large non-lE load showing the effect on the lE buses and loads (a condition that could occur when the 161Vk line is supplying all plant loads), and (4) final (steady-state) values  ;

for the lE distribution system and loads following the above motor starts.

Therefore this position is not satisfied since the testing does'not verify the "

analysis for all buses under analysis conditions.A5 l

l 8

l 4

Position 5--No event or condition should result in the. simultaneous or consequential loss of both required circuits from the offsite pawer network to

. the onsite distribution system (GDC 17).

j 5 .

OPPD has analyzad the onsite connections to the offsite power grid, and ig determined that no potential exists for simultaneous 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 lE loads with an accident in'one

] unit and an orderly shutdown and cooldown in the remaining units.

l This applies to multi-unit plants. It does not apply to the Fort Calhoun

! single-unit station.

i

]

6.0 CONCLUSION

S i

I g

~The voltage analyses submitted by 0 PPD for Fort Calhoun were evaluated in Section 5.0 of this report. Considering the changes described in Section 4.1, it was found that:

t j 1. Voltages within the operating limits of the class lE equipment are

not supplied for all projected ccmbinations of plant load and offsite power grid conditions.A4 j

j 2. The test used to verify the analysis is incomplete.

3. OPPD has not provided onsite distribution system analysis when it is j supplied by the 345kV grid.A3

,' e

4. There is no potential for either a simultaneous or consequential loss of both offsite power sources.

ls J

9 i

i 4

-.,---, . , - - - - , . - - . . - - -,e.,,. - - - . . , - . - , .,,,,7., ,

~

! 1 l-

5. Loss of offsite power to class lE buses, due to spurious operation

of voltage protection relays, can occur with-the offsite grid voltage within its expected limits. <.

7.0 REFERENCES

a l

l 1 . NRC letter, William Gammill, to All Power Reactor Licensees (Except Hum-boldt Bay), " Adequacy of Station Electric Distribution Systems Voltage,"

-August 8, 1979.

2. OPPD letter, W. C. Jones,'to U.S. Nuclear Regulatory Commission, August 31, 1979.

3. OPPD letter, W. C. Jones, to U.S. Nuclear Regulatory Commission, March 20, 1980.

4. OPPD letter, W. C. Jones, to U.S. Nuclear Regulatory Commission, l July 2, 1981.

5. OPPD letter, W. C. Jones, to U.S. Nuclear Regulatory Commission, August 31, 1981.

6. OPPD letter, T. E. Short, to U.S. Nuclear Regulatory Commission, September 17, 1976.

7. OPPD letter, T. E. Short, to U.S. Nuclear Regulatory Commission, July 24, 1977.

w

8. OPPD letter, T. C. Short, to U.S. Nuclear Regulatory Commission, Noventer 21, 1977.

9. OPPD letter, T. E. Short, to U.S. Nuclear Regulatory Commission, July 12, 1978.

10. NRC Memorandum, W. R. Butler to K. R. Goller, " Safety Evaluation of Proposed Modifications for Undervoltage Monitors and Test Circuitry,. Test Program Details, and Changes to Technical Specifications," December 14, 1977.

11. NRC Memorandum, G. C. Lainas to B. K. Grimes " Safety Evaluation of Proposed Design Modifications __and Changes to Technical Specifications RE: Grid Voltage Degradation (TAC 10023), October 19, 1978.

12. NRC letter, R. W. Reid to OPPD, W. C. Jones, " Loss of Offsite Power and i Attendant Effects on Grid Voltage and Frequency", October 17, 1979.

e' 10

APPENDIX REVIEW REFERENCES Note: The following references are contained in the submittal of Aucust 31, 1979 unless otherwise noted.

4 A Attachment 5, Sheet 7 B Attachment 5, Sheet 4, Condition 2 C Attachment 9, Tables 1 and 2, Case 6 D Sheet 18, middle of page E Sheet 11, item C.l.b.6 F Submittal of July 2, 1981, Table 1 (transient conditions), Case 6--motor terminal voltage not provided--assumed 2-1/2% drop. Actual drop would probably be higher under starting transient conditions. The 79.9% value for the 4000 V motor is on a 4000 V base.

G Attachment 9, Sheet 2, top of page H Sheet 18 allows 2-1/2% maximum voltage drop. Submittal of July 2, 1981, Table 1; steady-state values are on a 4160V base. The 81.93% value for

, the 4000 V motor is on a 4000 V base.

I Attachment 9, middle of page 1 J Attachment 9, Table 1, Case 6--see note K Submittal of July 2, 1981, Table 1 (steady-state), Case 6, adjusted to 460V base.

L Sheet 11, item C.l.b.2 M Sheet 11, item C.l.b.3 N Attachment 9, Table 2, Case 6--adjusted to 460 V base O Sheet 17, item f: Value for the 460 V starter is assumed P Submittal of July 2, 1981, Table 1 (steady-state), Case 6--adjusted to 460 V base Q Sheet 13, item ii R This value (80.43%) does not consider cable voltage drop from bus to battery charger.

S Submittal of July 2, 1981, Table 2 (steady-state), Case 6 T Submittal of July 2, 1981, Table 2 (transient), Case 6 U Submittal of July 2, 1981, Table 1 (steady-state), Case 6 V Submittal of July 2, 1981, Table 1 (transient), Case 6 11

l l

W Sheet 16, item 4.e.i X Sheet 19, middle of page V Sheet 28, middle of page Z Sheet 6, 7, 8 and Table 2-1 of Attachment 1 Al The worst case is approximately 75% from attachment 1 A2 Reference submittal of July 2, 1981, Table 2 (steady-state), Case 3, Bus 1838. The lowest steady-state voltage is approximately 80% on a 460V base.

A3 OPPD's submittal of October 17, 1979 12 provides a list of events which shows that the 161kV and the 345kV grids can be lost. Therefore an analysis of the 345kV grid supplying maximum loads, when the grid is at its minimum expected value, is essential.

A4 The OPPD analysis,2 sheet 15, concludes that if the 161kV grid does not degrade below 98.1% then adequate voltage will be supplied to all lE motors. Their analysis supports this conclusion. However the IE bus voltage is so low that some of the motor starters may not pick up and some may drop out during the start of a large lE or non-lE motors from the 4160V buses. Even at 161kV with maximum loading (10.7 fjW, Case 3, Table 2, for bus lA3 and 17.9 MVA, Case 5, Table 1 for bus lA4)2 the i lowest 460V starter terminal voltage will be 75.6% for bus lA3 and 78.3%

for bus lA4. The minimum starter pick-up voltage is 85%. OPPD's test ~

results showed the actual starting voltage was 3.5% higher than calculated. Adding the error to the calculated starter terminal values will still result in starter voltages below the minimum pick-up value, in 6ddition, the steady-state analysis supplied by OPPD4shows that some of the 460V motor starters and motors may be required to operate below their minimum ratings of 90%.

AS The test was performed in December 1977. Considering possible modifications to the plant electrical system since then, additional testing should be performed. Also, OPPD stated that steady-state measurements were taken but they did not provide them in their submit-tal.b r 12