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

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

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Electrical Engineer -

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I REVIRf80 BY

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

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!. 'i Principal Electrical Engineer-O. L. Micalv '

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! Senior Electrical Engineer ,-

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l lL.,1. Sadlacik /hmL l AA d f t- Date: Fl#*Te '

TVA

, 80M Lead Electrical Enginner APPR0' FED BY L C. Willians kC V.10 =/ Date: St#-9J r/4 TVA .

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, .S ',' . Chief Electrical Engineer i .- .

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Pi G. Trudel Al 4 Date: ## 6 TVA

II 80N Project Engineer

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' A Sequoyah Nucicer Plant . .

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

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

?c/s, voltage response improvement modittoations performed on the Sequoyah I'g? . 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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' 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

.3 and 50 324

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2.2 Letter from TVA to-NRC dated 7-8-88,sequoyah Nuclear Plant - Diesel-N4 Generator Voltage Response Improvement plan", NRC Docket Nos 50-327' J

W and 50-328 -

/'. '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 i J.5, ,dI 2.6 ENGINEERING CHANGE NOTICE L7286B " Replacement of diesel generator

load sequence electro-mechnical timing relays with electronic relays' 0"! ; .

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

, 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

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

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TVA seleulation 80W R3 015 (Reference 3.3) docueented that the SON D0a

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' will perfers their intended safety function by starting and sooelerating A; all the required loads within the required limits, with teceptable margin.

It es therefore eeneluded in the SON Diesel Generator Ivaluation Report

! iI' !.',) ' ' (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' ~

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

' . Regulatory Guide 1.g, Position C.4. 8pecifica11y, the voltage did not IO f.,[

always reeever to within 1 10 percent of nominal within 60 percent of the W load sequence interval (L8!). The L81 is defined as the time from 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

/h D0:nystem in an attempt to better oosply with the numerical guidelines of i

W Regulatory Guide 1 9.

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

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g' .1) 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

? change in field power needed to maintain a constant generator terminal {

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

3)

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

system.

$W The VORD consists of silicon controlled rectifiers (SCR) that i

are connected across each phase of the exciter bridge rectifier and an

P  !

electronic voltage sensing circuit that is connected to the secondary-of the generator potential transformers (see Figure 11. The voltage

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j. sensing circuit causes the 80Rs to conduct when the terminal voltage d". of the generator exceeds an adjustable setpoint and to stop conducting

,' i when the terminal voltage decays to approximately 1 percent below the

' 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

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4 d stafEN DEsck1PTION f,b.o l

hf# - 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 hp Figure 2 autoestically starts sonording to a pre-determined sequence.

l 1  !.4% The lead sequence ceneists of the following electrical loads. The times

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. listed are the neatnal lead sequence times. ,

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Nominal Seeuanes Tina 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  ;

5 see tesidual Heat Removal pump (RNR)

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+ Essential Raw Coeling Water pump (ERCW) 10 soo Auxiliary Feedwater pump (AFW) 15 soo Compuent Cooling Water pump (CC81 20 sec

,} ? Containment Spray pump (CSP) 30 seo t,180 see l .',- 5.0 1811,,lE18991

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i  : post Hodification feats (PMT) were perfereed to determine flat-j .! l ,

ceapounding after the exciter CT tape were reest, and to determine

%,; the maximum transient voltage with and without the VORD activated in

[ .i the excitation system on all four 00's, "s. 5.2 i

, :. ru 31-26.3A and SI-26.18 performed a design accident load sequence on

%l (P, injection (SI) algnal, to document'the combined eff ,

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

1 and 2. The results of this test are documented in Tables s e  !- 6.0 ElugpY OF REAULTB

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.ta shown in Tables 1 and 2, the modifications of resetting exciter 4 l insta: ling electronio load sequenen timers, and installing the VORD j  :'eaulted

.oad riequence in the test.following average teprovement, during a design accident j

Voltaae Overshoott Voltaae Diet

,s.,{ 00 1A A 42.3 i 0.2 D0 ll B 42.2 14.3 1 i QS y- , .

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$ . 'Secueyah Nuclear plant i . ,}l: '

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

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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.

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- ( p, 1eprovemente in their voltage responses. The namieue tranatent voltage S

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

't-the maxieue transient voltage with the VORD activated was 104 percent of 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 eutage. .

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s,' 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 l S^ ' perteraanos meeting the numerical guidelines of Regulatory Guide 1.9 for the SON unit 1 D0s turing a deatyn sooident load sequence. Based on the l

% steiler pMT results for the unit,2 DG's, it is expoeted that they. will 5.G also eeet the Regulatory Guide 1.9 voluge guidelines when the load

.,V . esquence tests are performed.

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

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