ML19206A688

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Reactor Bldg Spray Pump Motors Were Modified by Westinghouse to Meet B&W Specs.Motors Returned to Site & Installed. Forwards Westinghouse Info on Problem & Repairs
ML19206A688
Person / Time
Site: Crane 
Issue date: 04/21/1975
From: Arnold R
METROPOLITAN EDISON CO.
To: Knuth D
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
GQL 956, GQL-0956, NUDOCS 7904200350
Download: ML19206A688 (8)
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{{#Wiki_filter:/ t, s n .G., -n l /M =' i jgJ 9 9~- 8 -- -..wm METROPOLITAN EDISCN COMPANY ~ 'OST CFC5 30x 542 P E AtlNG. PSN*.SYLV ANI A 19603 rELENONE 0'S - ?:?-25:* April 21,19~'5 s r; r~~ -~ Mr. D. F. Knuth, Director Office of Inspection and Enforce =ent Nuclear Regulatory Cc= mission Washington, D. C. 20555

Dear Mr. Knuth:

Subject:

Three Mile Island Nuclear Station, Unit No. 2 Docket No. 50-320 Reactor Buildinz Serav Pu=o Motor Modifications

Reference:

Metropolitan Edison Co=pany Letter, February 4, 1974, J. G. Miller to D. R. Knuth In the referenced letter, page 2 last paragraph, we infor=ed your office that the Unit 2 spray pu=p otors had been returned to Westinghouse. We now vish to advise NRC that the subject motors were modified by the =anufacturer, and with these =odifications their acceleration time does =eet specification. For a review of the proble and its solution, we enclose the vendor's attach =ent, pages 1 through 6. Pages 1 and 2 offer a Westinghouse explanation of how the reduced starting voltage proble was discovered and how the proble altered the equivalent circuit for the motors which was used for =otor design parameters. Page 3 of the attach =ent is a diagra indicating generally how the ctors were repaired with increased sized end rings and the use of a different alloy for the end rings. To de=onstrate that the repaired =otor =et the 3&W specification requirements of accelerating the load to full speed in less than 6 seconds at reduced voltage, Westinghouse perfor=ed dynanc=eter tests. A =easured speed torque curve for the motor was obtained by taking readings of torque frc= the d/naco=eter and readings for the speed were taken fro: a tache =eter. Once the experimental speed torque curve was developed frc= the torque and speed test data. Westinghouse used points of the curve as an input to a computer program which uses the data from the pu=p load speed torque curve and utilizes a technique s1=ilar to the following relationship to determine the =otor accel-eration time:

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Page 2 To: Mr. D. F. Knuth, Director Nuclear Regulatory Cc==ission WE O N t = 308T time of ar.celeration, sec. where t = total =; r and load inertia being accelerated,cil WK' = referred the =otor shaft rated speed, lb-ft ". 6N change of, t, rp= = net accelt: ion torque, lb-ft. T = T= TT. - Tf T = Motor torque ib-ft T= = Load torque Ib-ft T1 = Frictional torque Tf = Pages 4, 5. and 6 of the attach =ent are the test report for the Reactor Building spray pu=p =otor which indicate that nineteen (19) test points were used to develop a =easured speed torque curve for the =ctors. Page 6 of the attach =ent is a copy of a computer printout which shows the speed torque test points and the points fro = the =easured curve which were used as input to the acceleration calculation. Notice that sc=e of the test points were taken in the reverse direction of rotation in order to verify that the speed torque curve at points near zero speed did not have irregularities. The values of torque for the speeds of -480.0, -210.0, 50.0 and 200.0 were nearly identical, thus confir=ing that the curve at points approaching zero RPM have no irregu-larities or " dips". The calculated acceleration ti=e for the repaired motors is now 3.37 sec. at reduced voltage which exceeds the specified 6 sec. limit. The subject =otors have been returned to the Site and installed, and we consider the =atter satisfactorily closed. Very truly yours, h fl d hp R. C. old Vice resident RCA/ESK:k Attachment t'u{I ' S ?.

Page 1 .TTACEMEN! / 1. THE CONCERN The calculation nethod for induction =otors is based on a solution of an equivalent ci:tuit. This circuit has re=ained essentially unchanged since the 1920's, and is used by the industry. In order to calculate the =otor output vc. lues frc= the equivalent circuit, it is accessary to define the proper values of resistance, reactance and other para =eters for that specific speed. About 1957 the calculation was changed fro: a hand calculation (about ten hours per point) to a co=puter calculatien, where =any points could be obtained in =inutes. There was no change in the =ethod. Fro = tt:e to tt e the ec=puter calculation =ethod was correlated with results from tested =otors. This was to enable ene engineer to have confidence in his guarantees of Ef ficiency Power Factor, Locked Current and correlation of other ite=s such as Full Out Torque and Locked Torque. We had a proble= with a pump motor that was used on a pipeline. The =otors would not accelerate under a low voltage condition (approximately 70%). In order to verify the suspected low voltage accelerating difficulty a special test procedure was set up to get more accuracy in the critical area below the pull cut torque. This area had not previously been of specific concern, since motors applied to purps had a=ple torque =argin to accelerate at 90% rated voltage. No field troubles due to failure to accelerate on low voltage had been reported. In the review of test motor records only a few tests were found that had sufficiently detailed tests (points in the critical area) to be used for correlation. Therefore a test progrs= was initiated tc acquire sufficient test data fro: motors of various sizes and speeds. This was for the purpose of correlation. A co=puter correlation program was started. This progra= takes each speed-torque point and analy:es it, using as input the observed test values and also the motor para =eters (winding data, motor geometry, =aterial properties, etc.). Such an analysis leads to determination of the causes of deviations between calculated and tested perfor=ance. As tests began to ec=e-in, and enough tests were available and corre-laced to begin correction of the =athematical =odel of the =otor equiva-lent circuit; basic odification involving new theoretical considerations were introduced, such as the more realistic change in rotor end ring reactance and resistance as the frequency varies during acceleration. Also revision of the end winding and rotor end ring =utual reactances. Also = ore individualized evaluation of stray load torque losses than before. Previous calculation =ethods and technical literature had not accurately treated these areas. < ; (3 A 6. h' L-

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