Posts Tagged ‘Retrofitting’

3 Second Sophisticated Circuit Breaker Test

August 23rd, 2010 Comments off

Here is another MIDWEST real world experience. This time dealing with circuit breakers, specifically three old power air circuit breakers.  Because of the extremely difficult location of the breakers, getting equipment to test the old circuit breakers was nearly impossible. And the cost would have been astronomical. There seemed to be serious problems with the circuit breakers. These were bolted in place generator breakers and the switchboard they were in had to provide power at all times.  A short outage could be catastrophic. But the breakers were tripping and the generator operators needed to know if the breakers were the problem or if they had load problems somewhere in their power system. The circuit breakers had old oil dashpot type over current devices and the operators wanted to know if retrofitting the circuit breakers with new electronic over current devices would make their problem go away. So, during a rather tense meeting, MIDWEST recommended the following three tests on two poles of each breaker.  The first test would take about 3 seconds. The second test would take about 8 seconds. And the third test could take as long as 90 seconds. We thought these tests would be nearly 100% as effective as actual high current testing in determining the condition of the dashpot over current devices. These were not calibration tests. They were function tests. The first sophisticated test procedure was to look at the oil dashpots. If we saw signs of oil weepage out of the circuit breaker oil filled dashpots, the breaker over current protective devices, ie the oil dashpots, were deficient and the breaker should be retrofitted. Simple. The second test involved manually pushing the instantaneous lever of the old oil dashpots.  If the action and resistance was normal and the dashpot reset properly, no nuisance problem.  The third and last test was to simulate an over current condition by a slow steady push on the delay component of the dashpots on the outside phases. For a veteran in the maintenance, repair and testing of these old air circuit breakers, these checks are very simple and very reliable in detecting defective oil dashpots. The actual test time per circuit breaker took us less than 45 seconds. We were not calibrating anything, but we did determine that all three circuit breakers had defective over current protective devices and needed to be retrofitted with new electronic over current protection. This was done and their problem was solved. How the retrofitting was done is a good subject for another blog. By the way, these circuit breakers were located in Antarctica.

Circuit Breaker Retrofitting Shortcut Mistake

July 16th, 2010 Comments off
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.