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Posts Tagged ‘General Electric Circuit Breakers’

Arc Blast Damaged Westinghouse PC32000 Molded Case Circuit Breaker

December 29th, 2011 9 comments
Arc Damaged Westinghouse PC32000 Circuit Breaker

Arc Damaged Westinghouse PC32000 Circuit Breaker

If you want to see a good picture of a large circuit breaker that has been damaged by an arc blast, look at the pictures with this blog. The breaker was a Westinghouse PC32000 molded case circuit breaker. It was a 2000 amp circuit breaker that failed to interrupt a fault and blasted the inside of the breaker until it actually blew a hole through the side of the circuit breaker frame. If you look closely, you will see where a MIDWESTswitchgear service technician actually stuck a screwdriver through the hole. The close up picture shows the hole and shows the extensive arcing damage to the moveable arcing and main contacts. The phase barriers, arc chutes, pretty much the whole Westinghouse PC32000 circuit breaker, was arc blasted beyond repair. One picture shows the destroyed circuit breaker next to a MIDWEST inventory stock PC32000 circuit breaker. This is a tough Westinghouse molded case circuit breaker. It wouldn’t make any difference whether the breaker was Square D or GE General Electric. If the breaker contacts begin to open, but fail to interrupt the current, arc damage will quickly occur. If the breaker is trying to interrupt fault current, extensive arc damage occurs very fast and will quickly expand into a phase to phase fault with catastrophic destruction. The arcing fault may explode outside the case of the circuit breaker.  This is one of the reasons for wearing protective clothing and following safe work practices when operation circuit breakers. Bad things can happen very fast. Too fast for you to get out of the way.  We suggest being paranoid about safety when working around electrical power equipment.

Another View of a Arc Damanged Westinghouse PC32000 Circuit Breaker

Another View of a Arc Damanged Westinghouse PC32000 Circuit Breaker

Old or New Circuit Breaker Hearing Test

October 13th, 2010 No comments

  

PAL36200 Square D Molded Case Circuit Breaker

PAL36200 Square D Molded Case Circuit Breaker

How would you feel if you were an Engineering Technician and you had just spent over an hour maintaining and testing a Square D PAL362000 circuit breaker and the Engineer walked up, operated the PAL362000 one time and said “It’s junk, throw it out?”  You might think the Engineer should be thrown out. But actually, the Engineer was just confirming what the technician already knew. In this case the circuit breaker had been inspected for any deficiency. The cover had been removed, yes, carefully, and the contacts, arc chutes, operating mechanism were all checked and maintained. The line and load side terminals of the old Square D PAL362000 were clean and in good condition. There was no sign of rust, worn main contacts or arc damaged arcing contacts. The operating mechanism visually looked in good condition. There was discoloration to the movable contact fingers of each pole piece. 

 

Tests were performed on the PAL362000 over current devices.  The test results were all good.

 

The contact resistance test results and the insulation resistance test results were all good.  The reset tests were all good.  So what was wrong with this expensive PAL362000 Square D circuit breaker?  There were two things wrong with the breaker. One deficiency was suspected based on the inspection and test procedure. The other was determined based upon our experience servicing Square D PAL362000 and PAF362000 circuit breakersFirst of all the movable contact fingers, ie pole pieces, were discolored.  We have seen this before and it usually means the circuit was heavily loaded.  In this case the circuit breaker was on a feeder that routinely hit 1800 amps and occasionally the breaker had tripped due to the load.  The other thing that told us the breaker was defective was also based on experience.  The experience of operating Square D PAL361000, PAL361200, PAL361600, PAL362000, PAF361000, PAF361200, PAF361600 and PAF362000 circuit breakers has taught us to listen carefully to the closing and opening of the three pole pieces, the moveable contact assemblies. Circuit Breakers that have been in very harsh conditions or operated under continuous heavy load, have a tendency to not open and close all three pole pieces simultaneously. When the breaker is defective, you can hear two or more poles close or open at different times. You will hear two separate distinct contact closings or openings. We know, if the difference is very obvious, repair attempts tend to be very temporary. With proper cleaning, lubrication, and exercising, the breaker may seem to operate properly. But we know from experience, the following year, or even in a few months, the breaker will again not close or open properly.  In these days of real concern for arc flash hazard protection, this defect can not be ignored.

 

In the example discussed here, the Engineer just confirmed what the technician already knew. The Square D circuit breaker failed the hearing test. In this case experience rules. And it applies to Westinghouse, Cutler Hammer, GE General Electric circuit breakers also.

Circuit Breaker Retrofitting Shortcut Mistake

July 16th, 2010 No comments
For many years retrofitting General Electric circuit breakers and Westinghouse, now Cutler Hammer, circuit breakers was very common.  Replacing the old dashpot style over current devices with modern electronic over current protection greatly improved the reliability and the flexibility of the retrofitted circuit breaker. This was particularly true when using the newer generation electronic retrofit kits. We still run into many of these retrofitted circuit breakers today.  Typically the retrofits were well done. But sometimes we run across a circuit breaker that was retrofitted in the field, on site. This saved time and was often done quickly during shutdowns or to just save cost. Ignoring the need to maintain a circuit breaker to be retrofitted, MIDWEST never retrofitted circuit breakers on site because of the need to perform complete over current testing and special load testing after the retrofit was complete.  Companies that retrofitted breakers on site could test the breaker by secondary injection method. That would prove the new electronic device operated properly and it would prove the old Westinghouse circuit breaker would actually trip, but it did not proof test the complete system. Worse yet were occasions when we might see a General Electric circuit breaker, for example, that had been retrofitted on site and not even tested by secondary injection method by the contractor that did the work.  MIDWEST recognizes this when we are troubleshooting a circuit breaker that apparently failed to trip and we discover that it would never trip under any circumstances.  We do a positive trip test. Tough test, takes about 12 seconds. We simply confirm that the trip device will actually move the trip bar enough to trip the Westinghouse circuit breaker, for example.  And we find out it will not. This is typically just a mechanical adjustment.  But you can imagine the anger when a customer finds out that the breaker they paid 2 or 3 thousand dollars or more to retrofit fifteen years ago, was just a switch because the breaker would never trip under any conditions, other than pushing the trip button.  Period maintenance and testing would have found this. Experience and knowledge would have prevented it. Shortcuts cause problems. It wouldn’t make any difference if it was an old Allis Chalmers, Siemens, ITE, or Federal Pacific or General Electric or Westinghouse circuit breaker, the problem was with the service company procedure, not the manufacturer.