ML20080Q126

Interim Deficiency Rept Re Cracked & Broken Puffer Piston Rods in Brown Boveri 5HK 250/350,1200/2000A Circuit Breakers.Initially Reported on 830317.Insps to Be Conducted at Maint Intervals.Cracked Assemblies Will Be Replaced

ML20080Q126
Person / Time
Site:	Fermi
Issue date:	10/05/1983
From:	Duvall D BBC BROWN BOVERI, INC. (FORMERLY BROWN BOVERI CORP.
To:	Deyoung R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8310120224
Download: ML20080Q126 (4)

Text

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BBC BROWN BOVERI Brown sovari eiectric, inc.

Manufacturer of l-T-E Electricai Power Equipment October 5, 1983 i

Mr. R. C. DeYoung, Director Office of Inspection & Enforcement i U. S. Nuclear Regulatory Commission 1 Washington, D. C. 20555 l

Dear Mr. DeYoung:

On March 17, 1983 Detroit Edison Company (Fermi II) filed a 10CFR50.55(e) l report with the NRC concerning some cracked and broken puffer piston rods in the Brown Boveri Electric 5HK 250/350, 1200/2000A circuit breakers. l l

Attached is an interim report on the BBE evaluation status to date on this l condition.  !

Based on the test results and other information available at this time the BBE recommendation is to inspect for cracked or broken puffer piston push rods at grmal maintenance intervals and to replace the puffer piston assembls if this c dition is found.

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D. ALL ce President i DDD/jm Attachment cc: A. E. Boetticher W. E. Laubach E. W. Rhoads L. H. Schmidt J. R. Silverio W. Laudan, NRC I & E f f(

Switchgear Systems Division 8310120224 831005 Spring House, PA 19477 (215)628-7400 PDR ADOCK 05000341 S PDR

BBC BROWN BoVERI Brown sov;ri siectric, inc.

Manufacturer of I-T-E Electrical Power Equipment October 3, 1983 INTERIM REPORT SHK CIRCUIT BREAKERS PUFFER PISTON RODS The purpose of this interim report is to summarize the status of the evalu-ation to date and to provide a history regarding cracked / broken puffer piston rods (Part No. 193642-B) in the Brown Boveri Electric 5HK 250/350, 1200/2000A circuit breakers.

In January, 1983, a report of some cracked / broken puffer piston rods at the Mohave Generating Station of Southern California Edison in Lauglin, Nevada was received. These circuit breakers are SHK 350-1200A supplied on S.O.

33-44107 and have been in operation since about 1970. The cracks / breakage of the puffer piston rods occurs at the operating pin hole. The conditions were noted while performing an overhaul on the circuit breakers, with some twenty (20) circuit breakers in Unit No. 1 and twenty (20) in Unit No. 2. thus a total of 120 puffer pistons are in operation at this station. A total of eight (G) puffer piston rods were found to be broken. The number of puffar piston rods that were cracked is not known, however the user ordered a total of twenty (20) replacement parts.

The average ambient temperature at this station is about 80*F. Temperature excursions normally vary between 35*F and 125'F, but extremes to a low of

+30*F and a high of 135'F have occurred. The humidity is normally between 10% and 15%. No more than one broken puffer piston rod per breaker was found during any inspection.

A March 17, 1983 report received from Detroit Edison (Fermi) indicates that one (1) broken puffer piston rod and nine (9) cracked rods in 5HK 350-1200A circuit breakers were found. These circuit breakers were manufactured in 1973 on S.O. 33-47196 and the reported conditions were noted in a total of five (5) circuit breakers. No operation count was reported on these breakers.

A BBE Service Engineering Report dated August, 1983 identifies that some SHK 250-1200A and 2000A at the Salt River Project, Navajo Generating Station manufactured between 1972 and 1980 were examined for puffer piston rod cracks.

There are approximately eighty-six (86) circuit breakers at this location, some of which have over 10,000 operations. This inspection showed that there were no cracks or breakage in any of the puffer piston rods. The environ-mental conditions at this station are similar to those noted at the Mohave Generating Station.

Switchgear Systems Division Spring House, PA 19477 e (215) 628 7400

W B_B_C srown sovsri eiectr;c, inc.

Interim Report 5HK Circuit Breakers

' Puffer Piston Rods -

October 3, 1983

.Page 2 The'5HK circuit breakers have been in production since 1960 with essentially the same design configuration and materials used today. The puffer piston tube was originally made with Zytel-101 unfilled material. This material was used until 1980 when:the vendor and material was changed to Nylafil El-30-EM.

Puffer piston rods of both the Zytel and Nylafil material have been subjected to thermal' aging tests with no.significant degradation trend being noted after initial " drying out" of ' the nylon material. When humidified after long

, exposure at high temperature the material returns to essentially the same strength characteristics as when'new. Thermally aged puffer piston rods in the dry condition were subjected to endurance testing of over 5000 operations.

Subsequent inspection of these items disclosed no cracking or damage to the puffer piston rods.

Three (3) puffer piston. rods with cracks were obtained from Detroit Edison LFermi 2 Station. These were subjected to mechanical endurance testing in a test breaker to investigate the tendency for existing cracks to progress into failures. After-1200 operations, the inspection indicated that the cracks

did not propagate nor did any. parts break. One of the puffer piston rods for this test was modified wherein the holes for the operating pin were redrilled

in a smaller diameter to determine if this interference fit of the pin could.

! result in a test failure. The inspection of this part upon the completion of the endurance test (1200 operations) indicated that cracks had not devel-oped.

A puffer piston in the 5HK circuit breaker performs two functions. For low L current interruptions the puffer is needed to assist the magnetic forces to

-move the arc into the interrupting chamber. -A puffer piston also provides a

' pneumatic cushion which reduces the shock forces imposed on the mechanism and

. -current carrying parts on opening. For lower values of current, arc inter-ruption could be adversely affected by failure of one puffer piston with failure to extinguish the arc. Mechanically,-loss of a puffer could reduce I: 'the number of operations before maintenance would be necessary.

BBE has never. experienced a circuit breaker failure due to a broken puffer piston rod.

uAt this time, the BBE evaluation of data indicate that aging is not a likely cause for the~ puffer. piston rod cracks. Also, BBE testing and the sampling

-inspections conducted to'date also indicate that the cracking'is not a generic defect.

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e BBC BROWN BOVf RI Brown Bovari Electric, Inc.

Interim Report SHK Circuit Breakers Puffer Piston Rods October 3, 1983 Page 2 Efforts are under way to obtain additional aged samples from the field and consultations with other materials experts are planned. At the time of this interim report there is no clear explanation for the presence of puffer piston rod cracks at Fermi 2. Information gathered to date also indicates that no more than one broken puffer piston rod per breaker has been found at any I

inspection.

BBE is continuing its evaluation of this situation and will keep you advised of any significant findings.

The BBE recommendation at this time is to inspect for this condition at normal maintenance intervals and to replace cracked or broken assemblies. The assembly part number is 193989-T2.

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