Power Transformers Blog – Expert Safety and Usage Info

Transformers come in many different flavors of course. One popular type found in and out of industry is the pad mount transformer. Most people have seen these without knowing what they were seeing. If you look outside an apartment complex, grocery store, or small industrial facility you might see a green colored rectangular shaped enclosure sitting on a concrete pad at ground level. That more than likely would be a pad mount transformer. What makes these unique in the family of transformers is their placement outside of a secure restricted access area such as that of a typical electrical substation. These units are designed to be placed in public access areas eliminating the need for a fenced secure area. These units are fully enclosed and have locking cabinet doors preventing public access to high voltage cable connections.

Although these transformers are fully enclosed and locked, it would be misleading to say they were safe since they are still energized. Concrete posts or steel guard rails are often placed around pad mount transforms to protect them from vehicle traffic. Pad mount transformers are reliable and aesthetically pleasing units with typically underground cable feeds. Although they can be fed from the side or from overhead. These transformers are for outdoor use and as such are usually mineral oil filled.

If you have questions about old pad mount transformers, call MIDWEST. They sell, rent, repair and buy them. They would be more than happy to speak to you.

The best test to predict the reliable operating condition of an oil filled transformer is the combustible gas-in-oil analysis. Using a syringe, 40 cc of oil is taken from the transformer and analyzed. When threshold levels of specific gases in the oil are reached, protocol demands appropriate action be taken.  This is an extreme oversimplification of a combustible gas-in-oil analysis.

One such case involved a 3000 kva, 25 kv primary, 600 volt secondary, foundry furnace transformer.  The oil test results indicated the transformer began generating high levels of acetylene.  Additional tests were performed and the transformer was shut down and taken out of service. A temporary transformer was put in its place to continue plant production. The defective transformer was sent out to be rebuilt.

Furnace transformers are special breeds of cats, designed to withstand the stresses of heavy shifting loads. Often times these transformers are pushed to the max in terms of load limits. Based on secondary ampere readings, this transformer was pushed to over 100% of rated load capacity, creating high thresholds of heat in the windings. Transformers don’t much like that too well. Heat puts all kinds of funny stresses on the internals of transformers.

In two months time the rebuilt transformer was put back in service and life continued on.