ML20150F929

Diesel Generator Voltage Response Improvement Plan

ML20150F929
Person / Time
Site:	Sequoyah
Issue date:	06/17/1988
From:	Bowman M TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML20150F920	List: ML20150F917 ML20150F929
References
PROC-880617, NUDOCS 8807190131
Download: ML20150F929 (4)

Text

• SEQUOYAH NUCLEAR PLANT DIESEL GENERATOR VOLTAGE RESPONSE IMPROVEMENT PLAN PREPARED BY: M. D. Bowman Dates _6/1 88 -

TVA / ' ' '

Electrical Engineer W. H. Nelson TVA Date:[#!/I!8h Electrical Engineer [ l' / /

Technical Specialist REVIEWED BY: J. D. Hutson TVA

! Date: 4 TF Assistant Chief Electrical Engineer M. R. Sedlacik TVA MM/ A Date /,- n- FF l

SON Lead Electrical Engineer C. Concordia # O, O M *2 [ Dates d/ dN .9 Private Consultant '

J. V. Posoisil NEI Peebles, Inc.

4 2A .s'I

// Dates d/f8 Manager of Engineering Y' r b.c e n en Y4bb b

u. vn a a s:A. .

APPROVED BY: W.

TVA S. Rauchiev (D 2<._ , 2 - Dates blN(

f) j Chief Electrical Engineer

() G J. B. Hosmer TVA

,'.-~ I R# Dates _ d//7M,9

~

/

SON Project Engineer P

4 i

I I

SEQUOYAH NUCLEAR PLANT DIESEL OENERATOR VOLTAGE RESPONSE IMPROVEMENT PLAN I. PURPOSE The purpose of this report is to document the acceptability of the voltage response improvement plan for the Sequoyah Nuclear Plant (SQN)  ;

emergency diesel generators (DG). This report fulfills TVA's commitment to evaluate various ways of improving the DG transient-voltage response.

II. BACKGROUND On February 29, 1988 TVA provided NRC with the SQN Diesel Generator Evaluation Report (DGER) in reference 2. This report documented that the SQN safety-related systems / components would perform their intended safety function when powered by the DGs with acceptable margin.

Charles Concordia, a recognized industry expert retained by TVA to review this report, mentioned several factors that could be considered to improve the transient-voltage performance of the DGs. TVA subsequently committed to review these recommendations to determine the optimum improvement.

t III. EVALUATION OF OPTIONS TVA has conducted an extensive evaluation of several DG improvement options. The options considered for evaluation included those previously mentioned by Mr. Concordia in reference 2 as well as other options that were recognized as having a high possibility of improving the DG voltage response after further review of the existing DG test data. The evaluation was performed by TVA engineers along with Mr.

Concordia and SQN's generator vendor, NEI Peebles - Electric Products, Inc. Each of the selected options was evaluated to determine the expected effect on exciter performance, system-voltage response, and DG reliability.

IV. OPTIMUM IMPROVEMENT The following options have been selected as the optimum improvement.

1. Optimize the load current compounding of the existing exciter by resetting the exciter-current transformer taps such that the current transformer contribution to field current is increased to achieve flat compounding.

2. Replace the existing pneumatic-load-sequence timers with more

a. curate electronic timers as previously planned.

3. Install a voltage overshoot-reduction device on the existing exciter. This device will consist of silicon-controlled rectifiers (SCR) placed across each phase of the exciter's bridge rectifier which are triggered by an electronic circuit when it senses en overvoltage condition beyond a preset value.

. .- VJ EXPECTED RESULTS

.0ption 1 will improve the inherent voltage regulation of the excitation system, thereby reducing the amount of required voltage regulator action. This will result in less transient voltage dip and better overall performance of the excitation system, and it is expected to reduce transient-voltage overshoot.

Option 2 will increase the accuracy and repeatability of the DG load sequence. This sill enhance the diesel generator voltage response by increasing the starting time bandwidth for those loads whose starting time intsrval is less than that predicted. This enhancement will allow more time for voltage recovery in the load sequence time intervals.

Option 3 will instantly remove the exciter field-forcing voltage during excessive transient-voltage overshoot conditions. This will significantly reduce the amount of transient-voltage overshoot.

VI. CONCLUSION Options 1, 2, and 3 have been selected as the optimum improvement with respect to DG voltage response. A qualitative evaluation of these options has shown that they will improve the voltage response. However, further testing of the DG system is necessary in order to quantify the amount of improvement related to each option.

Initially, option 1 and 2 will be performed on one DG unit followed by the performance'of the appropriate postmodification test (PMT) to j ascertain the amount of voltage response improvement. An evaluation of the results from options 1 and 2 will be performed. If further improvement is desired, option 3 will also be performed on the same unit  !

and the amount of additional improvement determined using another FMT. l Upon completion of this effort, implementation of the appropriate options will be performed on the remaining diesel generators by the end  !

of the unit 1 cycle 4 outage. '

. . . _ _ . . _ - _ , _ -m -

_ - .r, ,,- yr

ENCLOSURE 2 l

COMMID1ENT LIST

1. TVA will perform the following modificaticas to enhance the DG transient-voltage response for one SQN DG:

a. Reset the exciter-current transformer taps to achieve flat

~

compounding and,

b. Replace the existing pneumatic-load-sequence timers with more i accurate electronic timers, i

2. Upon completion of item 1 above, TVA will perform a PMT on the affected DG and evaluate the results to determine if the improvement in the DG transient-voltage response is acceptable.

3. If the evaluation from item 2 above is found to be unacceptable. TVA will install a voltage-overshoot-reduction device on the existing DG exciter '

in which item 1 above was implemented.

4. TVA will perform another PMT on the DG sffected by item 3 above, evaluate the results, and determine if the transient-voltage response improvement is acceptable.

5. TVA will implement the modifications (i.e., either item 1 or 3 above) that provide an acceptable improvement in the transient-voltage response on the three remaining SQN DGs.

6. TVA will perform the associated PMTs upon completion of item 5 above on I the three remaining DGs, evaluate the results, and determine if the transient-voltage response for these DGs is acceptable.

7. TVA will provide NRC with the evaluation and test results of the PMTs which provide acceptable improvement in ' he four SQN DG transient-voltage responses.

I