Four Inches (4”) of Water in Transformer
MIDWEST is frequently asked about some of our unusual experiences over the years. Things that happened that had no text book solution. Here is one of those experiences, having to do with an old outdoor askarel (PCB) filled transformer. The transformer was a transplant from indoor to outdoor. A little crazy, even in those days. This happened decades ago. Back when old askarel transformers were still sampled. The fluid dielectric strength test results were horrible, 14 Kv. During their next plant shutdown, we inspected the transformer and found about 4” of water layered and floating on top of the askarel fluid. Askarel fluid weighed about 12.7 lbs. per gallon, so the lighter water, about 8 lbs per gallon, just mostly floated on the top of the dielectric fluid, askarel. The exposed glass rupture disk on top of the old power transformer had cracked when rained turned to ice during the winter. The internal high voltage (13,800 volts) leads, from the high voltage bushings to the transformer windings, actually passed through the layer of water. These leads were insulated, but not insulated against water. The secondary bushing leads were below the free water level. The plant would be in crisis without this transformer. They had no spare replacement transformer. It would take too long to get a reconditioned, rebuilt or new transformer. So the plant engineer said, “It was working when we turned it off, so, when you’re done, we’re turning it back on.” We removed the layer of free water; Added R-Temp Transformer Fluid to the proper level; Turned the transformer back on; and no noise, good. All the PCB contaminated fluid and debris was properly disposed at an EPA authorized facility.
MIDWEST told the customer the transformer needed to be replaced as soon as possible. There was an incipient, even imminent, failure. The next time we heard from the customer was seven months later when the 1000 kva transformer failed. Our advice was ignored. But we were amazed the transformer lasted that long.