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Archive for April, 2011

Draw Out Air Circuit Breaker Lubrication Problem

April 20th, 2011 Comments off

 

DS-420 Westinghouse Low Voltage Air Circuit Breakers For Sale by MIDWEST

DS-420 Westinghouse Low Voltage Air Circuit Breakers For Sale by MIDWEST

 

The over lubrication of low voltage draw out air circuit breakers drives the MIDWEST Switchgear Shop crazy. Sometimes MIDWEST gets these circuit breakers after the owner’s maintenance folks finally give up trying to permanently fix them. They usually do not have the luxury of time, which we have in the switchgear shop. But they are correct in one sense and it’s that they know most of the problems with air circuit breakers are actually mechanical and not electrical at all. But the solution of choice too often is to spray the mechanical operating mechanism with some aerosol type cleaner and lubricant. Then exercise the breaker, spray a little more lub, until the breaker opens and closes mechanically without a problem. But three months later or six or nine, whenever they actually operate it again, the breaker does not open and close properly. So eventually they get sick of this and send it to MIDWEST’s Switchgear Shop. Our job is to take the operating mechanism apart, clean everything, properly lubricate, and reassemble. Concerning lubrication, it is important to know three things. What lubricant to use. Where to put it. And how much to use. Or, as the shop says, how much not to use. The problem of too much lubricant might seem counter intuitive to some folks, but excessive lubricant collects dust and dirt. The wrong lubricant gets hard. And the wrong lubricant in the wrong amount in the wrong place just about guarantees an eventual problem.  Whether an old Cutler Hammer or Westinghouse 1600 amp DA 50 circuit breaker or an old GE AK-1-50, or more modern air circuit breaker, we find most problems are mechanical and most are caused by OE (ie Operator Error), especially when racking in and out, and by poor maintenance. In the real world one sometimes must get the breaker to operate and back in service as soon as possible.  But don’t confuse the temporary fix for a permanent reliable repair.

 

Circuit Breaker Arc Chute Missing – Remove the Cover

April 4th, 2011 Comments off

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.