Power Transformers Blog – Expert Safety and Usage Info

This blog concerns a very simple maintenance procedure MIDWEST performs on electrical arc furnace transformers. It has saved our customers tons of money over the years. First a little information on arc furnaces and arc furnace transformers. 

Electrical arc furnaces are basically monstrous arc welders. Instead of the electrodes being pencil thin, they might be 14 inches or more in diameter. And there are three electrodes. The arcing is extremely loud and creates a lot of dust. The dust collectors take care of most of the dust, but there always seems to be dust that gets on to the secondary bus bar of the arc furnace electrical transformers. Whether McGraw Edison, Pennsylvania Transformer, or many of the other arc furnace transformer manufacturers, dust can be a real enemy of the secondary bus bar.

On some arc furnace transformers, both ends of an individual winding come out of the transformer in such a configuration that there may be only a quarter of an inch between the end winding bus bar. In other words, two massive copper buses, separated by only a ¼”, may have 280 volts potential between them during operation of the electrical furnace transformer.  And the secondary windings are huge masses of bus bar. If these bus bars become coated with foundry dust and the dust is conductive enough, a massive arcing fault may occur at the secondary of the transformer. Unfortunately MIDWEST has responded to such emergencies, and they are a mess. Very expensive repairs.  And so easily preventable.

The unsophisticated solution is to clean the dust and any other contaminates from between the bus bars before they become a threat. One has to do this carefully so as not to damage the seal where the bus comes through the top of the transformer, for example. It may look simple, but only experienced and qualified electrical personnel, who know what they are doing, should do this. In the wrong hands, this maintenance procedure could easily be the cause of a major blowout rather than the prevention.

MIDWEST works a lot with electricians, maintenance mechanics, and other assorted electrical folks that have the every day job of keeping production machines running. When they call for help, for example when they suddenly need a replacement transformer, they want the short answer to their question. Sometimes you can tell from the edge in their voice that they are overwhelmed, in a real jam, and, if we put more burden on them by asking twenty questions about their old transformers, they are just going to stop listening, say thank you, and hang up. They want an immediate short answer to their immediate question.  This isn’t always possible or safe, but, since we have so much field service experience, we usually can get to the point quickly.

Sometimes the simplicity of the request can be amazing. For example, we had an electrician call during his lunch break and ask how he could tell if one of their old dry type transformers, used for production machines, was overheating. They had added a ton of equipment to it over recent years and he was worried the transformer was overloaded and would fail. His boss knew nothing about old, new, replacement electrical transformers and really didn’t want to be bothered with a “maybe problem.” The electrician needed something to get his bosses attention. He couldn’t measure the load, but he just knew it was overloaded.

Our unscientific suggestion was to put his hand on the top of the old power transformer enclosure. If he couldn’t hold it there for a few seconds, the transformer is in danger of being overloaded. The load should be measured and compared to the nameplate rating. If they don’t, they run the risk of the transformer failing when they least expect it, say the day before a holiday. Getting and installing a replacement transformer under emergency conditions can be a lot more expensive than scheduled transformer replacement. You don’t want to get burned.

Safety note. Be sure the transformer is grounded before touching it.

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.