Power Transformers Blog – Expert Safety and Usage Info

Here is an example of the success of an Unlimited RCM (Reliability Centered Maintenance) program for large kva and Mva oil filled power transformers. Our Engineering Technicians and Engineers know what the most common problems are for oil filled electrical power transformers, whether 1000 Kva, 5000 kva or 25 Mva. We do the more glamorous transformer tests, but most of these require an outage, which has become unheard of for many large manufacturing facilities and some small municipal utilities. Fluid samples for routines and GCs on dielectric fluid still can be taken safely in some cases. But a hard focused inspection by an experienced, trained, and knowledgeable expert will find many of the probable, but unapparent, deficiencies in oil filled power transformers. Someone following a simple TC Checklist is nearly useless. By TC Checklist, MIDWEST means a “Training Chimpanzee” Checklist. The person performing the service has to think. They have to focus or they will miss subtle things that individually may mean nothing, but collectively may reveal a serious problem or danger. We find things others have looked right at and missed. Some of the things we look for are hard to explain. Others, that seem obvious to the pros, may be invisible to the inexperienced. MIDWEST’s Unlimited RCM Services have saved customers more money than all the transformer testing put together. Here is a simple example of a fluid filled transformer oil leak discovered only by the not so sophisticated “look and feel” test. It wasn’t the ordinary transformer oil weepage or leakage that allowed plenty of time to correct. It was invisible because the transformer was a large pad mount unit and it was leaking into the cable entrance pit under the cable connection compartment. The tank was fire hot, but the cooling tubes and top headers were not unreasonable hot. We could tell the oil level was so low that we were worried the high voltage cables inside the transformer or the core or even the coils might be exposed. Usually a fatal problem. A quick outage was arranged, despite production’s pleas to wait. We found the lowest high voltage bushing was actually cracked and fluid was coming out in a steady little stream. Not just weeping or slowing dripping. A quick temporary repair was made in order to get production back up until a replacement bushing could be purchased. We’ve seen this crisis before. Emergency outage, drop the oil, remove the bushing, make a crazy careful temporary epoxy repair, refill, test, and energize. The only other safe choice was to leave power off until a replacement bushing could be delivered. Terror for production. Later the new bushing was delivered and installed during a scheduled outage. A gas sample was taken and all was well. The transformer was days, if not hours, from failing. If we were not performing Unlimited RCM inspections, they would have had a failure, at great cost to critical production. One additional note. We have a customer who, against our advice, operated a transformer for over 20 years with the temporary repair. Our technical term for that is ‘luck.’ The Unlimited Services by experts works. If you don’t have an electrical power transformer expert, consider starting by using a qualified electrician. A safety note, before you touch an energized transformer, make sure it is properly grounded.