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Posts Tagged ‘Cutler Hammer Circuit Breakers’

Circuit Breaker Arc Chute Missing – Remove the Cover

April 4th, 2011 No comments

MIDWEST has its own internal blogosphere that especially hums away when something unusual happens, like when one of the Engineers or Engineering Technician discovers something important or rare or both with the electrical equipment they are working on. Here is an example of some internal buzz that also proved the

MA31000 Square D Circuit Breakers For Sale

MA31000 Square D Circuit Breakers For Sale

importance of removing the covers from electrical power circuit breakers, whether Square D circuit breakers, Cutler Hammer circuit breakers or GE General Electric circuit breakers. The need is not related to the manufacturer. In this example, the Engineering Technician was reconditioning and testing a 1000 amp Square D circuit breaker. When he removed the cover of the circuit breaker, he was amazed to find the center pole arc chute was gone. Completely missing. Fortunately the arcing and main contacts appeared undamaged. There was some arcing marks on the arcing contacts, but nothing serious. One could do high current tests, contact resistance tests, and insulation resistance tests and never catch this defect. But the first time this breaker tried to interrupt a large fault current, it could have failed, with the resulting arcing causing an eventual phase to phase arcing fault on the line side of a large circuit breaker. This arcing fault might not be large enough to trip the main breaker immediately. If for some reason the panel board was a MLO, main lugs only, the protective device might be the main breaker or fused switch on the line side of an upstream transformer. This is a worst case environment, but it does happen. It is especially dangerous because the arcing fault may last several minutes before the main protective device operates. And more scary is the possibility of someone being injured by the fault. This is an incipient failure. Also an insidious failure. It is another example of the reason to properly recondition replacement power circuit breakers. Testing alone is not enough. 

Circuit Breaker Large Over Current Time Delays

December 29th, 2010 4 comments

In MIDWEST’s training classes for qualified personnel, there is a segment where we explain the long time delay range within which a Square D 1000 amp circuit breaker should trip due to an overload. This information is received with anything from amazement to skepticism to outright disbelief, even though we show the Square D circuit breaker characteristic trip curve.  The overload time delay information is not restricted to Square D circuit breakers. It’s the same with Cutler Hammer, GE General Electric, Siemens, ITE, Westinghouse, Merlin Gerin, or Federal Pacific circuit breakers.

 

In our training example we use an old Square D 1000 amp MA type circuit breaker.  If we tested this circuit breaker at 3000 amps, that’s 300%, the minimum to maximum trip range is about 45 seconds to 340 seconds. It might trip in 45 seconds or it might not trip for 340 seconds.  This is an old thermo-magnetic circuit breaker, which typically works by heating a bi-metal in the over current trip device. Many newer breakers use electronic over current devices which have more repeatable overload time delay test results.

 

The illusion is that these Square D, Cutler Hammer, Westinghouse circuit breakers are designed to directly protect people. They are not. The breakers protect the equipment connected to them and they protect the electrical system. They are designed for the characteristics of the equipment connected, such that connected equipment will not be damaged by an overload or fault. This is a basic limited explanation. So, when you think of molded case circuit breakers, power circuit breakers or air circuit breakers, it’s important to know these breakers don’t just trip right at the breaker trip device rating.       

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.