ML20043B606

Diesel Generator Voltage Response Improvement Rept

ML20043B606
Person / Time
Site:	Sequoyah
Issue date:	05/11/1990
From:	Bowman M, Demetrius Murray, Nicely G TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML20043B121	List: ML20043B120 ML20043B606
References
NUDOCS 9005310001
Download: ML20043B606 (9)

Text

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Spqwyah halcar Plant

,'Diessi Gerrat*.c Voltago R:sptns) Icprove;:nt R:ptrt g

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PREPARED BY:

D. R. Murrav Mk Datesf*IO"N srt TVA

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. #'t Electrical Engineer

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I REVIRf80 BY

M. D. Bowman fd Dates. */d*TO t

. /.. i TVA

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'i Principal Electrical Engineer-O. L. Micalv

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-Date: O \\ D -$ 0 l

i TVA i

Senior Electrical Engineer e,!

lL.,1. Sadlacik

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TVA t-Date: Fl#*Te 80M Lead Electrical Enginner APPR0' FED BY L C. Willians kC V.10

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Date: St#-9J r/4 TVA

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Chief Electrical Engineer i.-

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Pi G. Trudel Al 4 Date:

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TVA

II 80N Project Engineer

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' A Sequoyah Nucicer Plant.

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, Diesel'02m:rator Valt:g) R;;ptnse !cprove:cnt R:pgrt y-

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..s q The purpose of this report is,to document and evaluate the results of the

?c/s voltage response improvement modittoations performed on the Sequoyah

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. Nuclear Plant (80N) energency diesel generators (DG). This report sq.

fulfills TVA's commitment to quantify the amount of improvement associated with the options listed in the Voltage Response Improvement Plan.

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(Reference 2.2) which have been permanently implemented.

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2.0 MERGE,

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' w, 2.1 Letter from TVA to NRC dated 2-29-88, '8equoyah Nuclear. Plant -

Diesel Generators - Operability _and Analysis', NRC Docket Nos 50-327 and 50 324

.3

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,. c., I 2.2 Letter from TVA to-NRC dated 7-8-88,sequoyah Nuclear Plant - Diesel-Generator Voltage Response Improvement plan", NRC Docket Nos 50-327' N4W and 50-328 J

/'.

'2.3-TVA Division of Nuclear Engineering Calculation SQN-E3-015, ' Diesel Generator Voltage and Margin Analysis', Revision 1 2.4 80N Surveillance Instruction SI-26.1A, 't.oss of offsite power with Safety Injection - D/0'1A*A Test', 3-18-90 performance 4

2.5 '80N Surveillance-Instruction 81-26.1B, ' Loss of'0ffsite Power with l

Safety Injection.- D/0 1B-B Test', 3-20-90 performance J.5,,dI 2.6 ENGINEERING CHANGE NOTICE L7286B " Replacement of diesel generator i

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load sequence electro-mechnical timing relays with electronic relays' Unit 1 (B85 900309055)

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'Z 2.7 DESIGN CHANGE NOTICE N01724A~ ' Replacement of' diesel generator 1had

'c sequence electro-mechnical timing relays with electronic relays' Unit l

2,(B85 891220050) l 2.8 DESIGN CHANGE NOTICE M01367A - " Installation of ~ a voltage overshoot reductien device (V0RD), and reset exciter control current l

trer.aformer taps' Unit 1 (B25.900203506)

S 2.9 DESIGN CHANGE NOTICE M013i8A

• Installation of a voltage overshoot

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reduction device (V0RD), and reset exciter control. current 4

transformer taps" Unit 2 (B25 900203507)

I 2.10 DESIGN CHANGE NOTICE M00739B 'Resetexcitercontrolcurrent l

trknsformer taps on diesel generator 1B-B' (B85 9003,08010)

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2.11 Sequoyah Nuclear Plant 'Dissel Generator Voltage Response

'j Improvement Report

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.8equoyoh puoloar pleat

' Diesel Generat:r V:ltage Response !cptcycaent Ropstt

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' ; l.;,f.k TVA seleulation 80W R3 015 (Reference 3.3) docueented that the SON D0a

,, g will perfers their intended safety function by starting and sooelerating

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all the required loads within the required limits, with teceptable margin.

A; It es therefore eeneluded in the SON Diesel Generator Ivaluation Report

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(Re:!erence 8.1) that the Des meet the intent of Regulatory Guide 1.g.

Newever, the test data used by the analysis showed that the D0 transient' ~

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p' voltag; response did not always neet the RERRE&B&L guidelines of g,;

. Regulatory Guide 1.g, Position C.4.

8pecifica11y, the voltage did not IO always reeever to within 1 10 percent of nominal within 60 percent of the f.,[

load sequence interval (L8!). The L81 is defined as the time from W

application of a sequenced load untti application of the next sequenced

?Y lead. ha a result, TVA consitted to improve the voltage response of the

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D0:nystem in an attempt to better oosply with the numerical guidelines of W

Regulatory Guide 1 9.

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TVA has implemented the follesing DCN's to the 00 excitation system to pid gaih optimun improvement in the D0 system voltage response (Reference 2.6 thru 1.10).

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Rep 1&oe the existing pneumatic load sequence timers with more accurate-electronic timers.

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Optimise the load current oospounding of the exciter by resetting the l

enoiter current transformer (CT) taps such that the CT contribution to field current is increased to achieve flat-compounding (i.e. for a 1,? j '

given change in generator load, the exciter cts produce the exact

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change in field power needed to maintain a constant generator terminal f,

j voltage with no voltage regulator action) (see Figure 1).

b 3)

.A' Install 4 Voltage Overshoot Reduction Device (V0RD) on the excitation system.

$W The VORD consists of silicon controlled rectifiers (SCR) that are connected across each phase of the exciter bridge rectifier and an i

electronic voltage sensing circuit that is connected to the secondary-

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of the generator potential transformers (see Figure 11. The voltage

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sensing circuit causes the 80Rs to conduct when the terminal voltage j.d".

of the generator exceeds an adjustable setpoint and to stop conducting when the terminal voltage decays to approximately 1 percent below the i

adjustable setpoint. Thus, the VORD will instantaneously remove the exciter output voltage during transient over-voltage conditions to prevent the over-voltages ~from becoming excessive. The VORD is only enabled during the energency mode (i.e. blackout or a manually initiated emergency start signal).

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[.,fr Diesel Generator V01teg3 R:sponso Itproveeent Report i

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I k' l 4 d stafEN DEsck1PTION 1

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Figare a chose a staplified single line diagran of one train of the 80N Class 18 ensite peser systen and its dedicated D0.

OI3-Each load shown in Figure 2 autoestically starts sonording to a pre-determined sequence.

l hp The lead sequence ceneists of the following electrical loads.

1

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listed are the neatnal lead sequence times.,

The times

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Damarintien Nominal Seeuanes Tina w.. y L

,h 440v Motor control Center 1,oeds (440v) j Kif Centrifugal Charging pump (CCP)

At DG treaker Closure (0 soo) jc.g Safety 2njection pump (81) 2 see sL tesidual Heat Removal pump (RNR) 5 see Essential Raw Coeling Water pump (ERCW) 10 soo r w)

+

Auxiliary Feedwater pump (AFW) 15 soo Compuent Cooling Water pump (CC81 20 sec

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Containment Spray pump (CSP) 30 seo t,180 see l

5.0 1811,,lE18991

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5.1 post Hodification feats (PMT) were perfereed to determine flat-i ceapounding after the exciter CT tape were reest, and to determine j

.! l the maximum transient voltage with and without the VORD activated in the excitation system on all four 00's,

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5.2 31-26.3A and SI-26.18 performed a design accident load sequence on

, :. ru injection (SI) algnal, to document'the combined eff

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compounding, electronic load esquent.e timers, and the VORD on g-l 'i>

transient voltage.

1 and 2.

The results of this test are documented in Tables 6.0 ElugpY OF REAULTB

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.ta shown in Tables 1 and 2, the modifications of resetting exciter y;

j insta: ling electronio load sequenen timers, and installing the VORD 4

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'eaulted in the following average teprovement, during a design accident j

.oad riequence test.

j Voltaae Overshoott Voltaae Diet

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00 1A A 42.3 0.2 i

D0 ll B 42.2 14.3

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'Secueyah Nuclear plant i

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Diec 1 Generstir Volt:gs R::pinse leprsve:ent R: port l

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(;b 6.0 SumiARY OF RERULTS (Continued)

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Although a desige accident load sequence test for the unit 2 DG has not

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been perfereed, the resulta of the pMTs for these 00's show steitar.

.21 1eprovemente in their voltage responses. The namieue tranatent voltage

- ( p, without the VORD estivated was 180 percent of nominal (6900V).

S the maxieue transient voltage with the VORD activated was 104 percent of

't-nootnal (6900V). A design sooideat load sequence test ($1 26 2A and

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8124.24) will be per$ # sed on the unit 2 D0'8 during the unit 2 cycle d j.

eutage.

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laced on the results of this report, the opebined effect of resetting the one!.ter cts to achieve flat compounding, ine G ling electronio load ct:

, sequence timers, and installing a VORD has preheed acceptable voltage

' perteraanos meeting the numerical guidelines of Regulatory Guide 1.9 for l

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the SON unit 1 D0s turing a deatyn sooident load sequence. Based on the steiler pMT results for the unit,2 DG's, it is expoeted that they. will l

5.G also eeet the Regulatory Guide 1.9 voluge guidelines when the load

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esquence tests are performed.

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TAM 1 Voltap Derformance Parameters Fris Load Begwnee Tsu M IM

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'0 14.5 19.1 4.6 9.6 70.t 7.2 1

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18 19.0 15.7 17.1 9.6 44.9 4.8 i

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'tal Percent Change. msw Valu Drininal Val $e} 's 100s i

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TABLE 2: Voltap perferoame peranters from Load Segwnee fest 0019-B

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5 Dip - Witage 5Omghoot-Yoltage RecoveryTime l

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0 35.t 30.6 10.4 6.1 65 10,8 3.

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14.4 16.4 7.0 86 18.0

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14.3 10.0 9.1

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to 13.6 119 10.0 S.7 N/A 14 i

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5 Dip * (Pre fransient Voltage - Minis m Voltale) e, (21 5 Overshoot n (Maximum Voltage - 1005) -

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