Power Transformers Blog – Expert Safety and Usage Info

MIDWEST was called to check out an old 3750 kva oil filled transformer. The owner was trying to decide whether to reclaim the oil in the old power transformer or to go ahead and replace it with a new 5000 Kva transformer. They actually needed a 5 Mva replacement power transformer. They had the history of the oil test results. It was apparent the transformer had slowly absorbed moisture over the years and there was serious paper degredation. They wanted MIDWEST to do an under the cover inspection to see if there were visual signs of sludge and tank rust. Pretty straight forward stuff. Their electricians asked if they could look inside the transformer while we had the access cover open. They had to follow our safety precautions.  They were absolutely amazed to see all the wood used inside the transformer. Almost the entire top of the core and coils was hidden under wood.  The wood was used for blocking, for support of the tap changer, and for making the high voltage connects going to the line side of the windings. The electricians were a little skeptical when we explained how much wood was actually used in transformer construction. How common it was. And that 15 Kv high voltage terminations were made on the wood. They were also surprised how clean the inside of the transformer looked, even though the oil was dark and there was visible sludge on flat surfaces, especially on the wood. For the electricians, seeing was believing. High voltage oil filled power transformers are made with wood.

MIDWEST replaced the old main electrical power transformers for a manufacturing facility.  When we were done, the outdoor substation looked barren. It looked like the power capacity went way down.  We removed one 1000 kva oil filled three phase Westinghouse transformer, one 1000 kva oil filled three phase GE General Electric Transformer, and three 167 kva single phase oil filled transformers. We replaced all these transformers with one new oil filled 3750 Kva transformer. We replaced the concrete pad, of one of the old 1000 kva transformers, with a larger pad. Installed a new grounding system and replaced the fencing. But the new installation made the substation look bare.  Where there were five old oil filled transformers, there was now one new oil filled power transformer. The new 3750 kva transformer wasn’t much larger than one of the old scrap 1000 kva transformers. But, when you looked at the substation, you saw four abandoned concrete pedestals for the removed transformers. And that made the place look like it was going out of business, rather than growing.

The size of many very old GE General Electric, Westinghouse, and especially Allis Chalmers oil filled electrical power transformers was a third to even 100% larger than a new same Kva power transformer. Pad mount transformers are especially smaller because of their low profile.  The low profile green box pad mount transformers got extensive early use in subdivision developments, where the new owners of dream homes didn’t want ugly electrical overhead lines and transformers outside their windows. The little green boxes were small and everywhere, but there were barely noticeable because of their size and color.

So, for electrical power transformers, new is less, less space that is.