Step Down Transformer

Inspected a commercial building today with four step down transformers. Three of the four were operating at between 80 and 85 deg f. The fourth was at 168 f. Two of the four are 25 kva @ 575 down to 240/120vac. the others are 15kva @ 575 down to 240/120vac.They are all located in the same mechanical room. I know they are all rated @80deg celcius and the 168 deg f falls within that but can anyone offer an expanation as to why the one is running at a higher temperature than the others. Is it possible that the load being drawn on the higher temp transformer is higher and causing the higher temperature reading.

That transformer is probably just drawing more current than the other two. The higher the load, the higher the temp.

What he said. These things can get pretty freaking hot when they’re loaded closer to their maximum rated capacity. Some are even rated to be overloaded for short periods of time. There can be some serious heat rolling out of them puppies sometimes and still be completely within spec.

Thanks guys

Remember also that the nameplate temperature rating is the allowable temperature RISE over a standard ambient (usually 40 deg C). As mentioned before that can result in very hot running temps for a heavily-loaded transformer.

Does the transformer in question have the proper clearances to walls to allow for ventilation? Typically 6 inches is minimum wall clearance. Also a very dusty/dirty transformer runs hotter.