ML20150D572
| ML20150D572 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah, 05000000 |
| Issue date: | 03/08/1988 |
| From: | Kusko A FAILURE ANALYSIS ASSOCIATES, INC. |
| To: | Marinos A NRC |
| Shared Package | |
| ML20150D366 | List: |
| References | |
| FOIA-88-129 NUDOCS 8803240365 | |
| Download: ML20150D572 (4) | |
Text
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m ENCLdSURE 1 l
Failure Ar*=**'dvsis
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we Mcrch 0, 1988 s.1g Mr. Angelo Marinos il.S. h'uclocr Rcqulatory Commission it'S5 Rockvillo Piko
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TV!. Soquoyah Nuclear Plant Cc : Er. ::crinos:
"hc Nuclect Regulatory Commission (NRC) retained the Kusko
":.calrf cc.'. Group ot' Failure Analysis Associates (FaAA) to assist
...: HC staff in evcluating reports submitted by TVA on tost r c:. u '. a a n c: calculations on'the emergency diesel generators SED 03) for the Scquoych Nuclear Plant.
This lettor summarizes cur review of the performance of the generators, as described in the TVA rcports.
Cur verk included the following:
Review of the TVA report entitled "Diesel Generator Voltage Analysic" dated January 21, 1938, including the results of field tosts on EDcs and predictions of the minimum voltagoc during cequentici loading.
2.
F.evi ew of the design of the static exciter and voltage cgulater for tho EDG, C.
Independent calculations of the generator voltage dips for the ccheduled sequontini loads using a more comprehensive renorater clectrical modol than that used by TVA.
4.
F.c V i o '> of the second TVA report antitled "Sequoyah Nuclear
' Mant Diesel Conorator Evaluation Report" dated February 22, 988 including the predictions of the minimum generator voltagos during sequential scheduled loading by a new nothod, 6.6-kV and 480-V motor voltagas to sustain load,
. 4EO-V sycto= voltago drops and the l' O-V contactor pick-up A
r.nd drop-out voltcges.
Reports from TVA consultant,
C.
Concordic, J.V.
?osposil and R.E.
Allen, were also reviewod.
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Meetings" in Washington (Rockville) with the NRC staff, A.
Marinosi E.
Goodwin and others, and meeting with TVA representatives.
As a result oi' our work Ve conclude the followingt 1.
3ocause of the unprodictability of the excitation system atate and ths EDO terminal voltage prior to each schedulsd Oce:uontial load step, th.3 magnitude of the 'Acrat caso test v>1 taco dips should be increased by 2 to 3 percoat. to 1
..: count for the scheduled load, voltace level, regulator drccp and ether factors.
2.
0" exnination of the TVA laboratory tests and calcula::iona
. <? 2.o pick-up voltages of tho 120-V contactors indicato3 nt :/. ore ';ny be ao voltaqo margin at the timo of the 2DG
" r'.. : - '. vo.'.:Ma d17 durin0 a lead step.
Thes3 tests and r'. ;t:.'.tions caould M roviavod by TVA.
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3.
'!i :5 the present EDG voltaQo regulatora, the worst cose voi: age.marJina for :Justalaing the 6.6-kV ' ond 430-V motors spoor adequa.:o.
The EDG voltage dips are not entirely
' 3 -J ! a':cb12 ?or cach soqu0ntial load step because the m ulater deos not stabili2e the EDO terminal voltage.
4.
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ahould lollo9 Mr. Concordia's suggcations to make
. :..T ;;r'oraanco improvement c, including invoatigating
' IM V ).!': r; ) n W.atorc lad replacing the.a with colid-
, 2nr: :37Tacnaa r0gulalora at tho blne of tho next
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31.3 u d.11 insun ;tubilinctien of the 2DG
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l TRUE COPY OF THE SIGNED ORIGINAL Failure Analysis-Associates March 8, 1988
\\
Mr. Angelo Marinos U.S. Nuclear Regulatory Ccnynission 11555 Rockville Pike Rockville, MD 20850 Re:
TVA Sequoyah Nuclear Plant
Dear Mr. Marinos:
The Nuclear Regulatory Commission (NRC) retained the Kusko Electrical Group of l
Failure Analysis Associates (FaAA) to assist the NRC staff ia evaluating i
reports submitted by TVA on test results and calculations on the emergency diesel generators (EDGs) for the Sequoyah Nuclear Plant.
This letter sunmarizes cur review of the performance of the generators, as described in the TVA reports.
Our work included the following:
1.
Review of the TVA report entitled "Diesel Generator Voltage Analysis" dated January 21, 1988, including the results of field tests on EDGs and predictions of the minimum voltages during sequential loading.
2.
Review of the design of the static exciter and voltage regulatory for the EDG.
3.
Independent calculations of the generator voltage dips for the scheduled secuential loads using a more comprehensive generator electrical model than that used by TVA.
4 Review of the second TVA report entitled "Sequoyah Nuclear Plant Diesel Generator Evaluation Report" dated February 22, 1988 including the predictions of the minimum generator voltages during sequential scheduled loading by a new method, 6.6-kV and 480 V motor voltages to sustain load, 480-V system voltage drops and the 120-V contractor pick-up and drop-out voltages.
Reports from TVA consultants, C. Cordorcia, J.V. Posposil and R.E. Allen, were also reviewed.
1 5.
Meetings in Washington (Rockville) with the NRC staff, A. Marinos, E.
Goodwin and others, and meeting with TVA representatives.
As a result of our work, we conclude the following:
1.
Because of the unpredictability of the excitation system state and the EDG terminal voltage prior to each scheduled sequential load step, the magnitude of the worst case test voltage dips should be increased by 2 to 3 percent to account for the scheduled load, voltage level, regulator, droop and other factors.
2.
Our examination of the TVA laboratory tests and calculations for the pick-up voltages of the 120-V contractors indicates that there may be no voltage margin at the time of the EDG terminal voltage dip during a load step. These tests and calculations should be reviewed by TVA.
3.
With the present EDG voltage regulators, the worst case voltage margins for sustaining the 6.6-kV and 480-V motors appear adequate.
The EDG voltage. dips are not entirely predictable for each sequential load step because the regu'lator does not s.tabilize the EDG terminal voltage.
4.
TVA should follow Mr. Concordia's suggestions to make further performance improvements, including investigating the EDG voltage regulators and replacing them with solid-state, fast-response regulators at the time of the next refuelling.
This will insure stabile _acion of the EDG excitation system and terminal voltage prior to each sequential loan step and insure predictable terminal voltage dips.
Sincerely,
/s/ Alexander Kusko Alexander Kusko
/s/
Syed P. Peeran KUSK0 ELECTRICAL GROUP Bil60158