Power Transformers Blog – Expert Safety and Usage Info

Large Enclosure for General Purpose Dry Type Transformers

For those who have never seen the inside of a general purpose dry type power transformer, you will probably be surprised at how much open space there is inside the enclosure.  The attached image of a dry type general purpose transformer shows just how much space there might be to properly cool off a transformer if it is heavily loaded. The image shows the transformer with panels removed, which allows you to see how much open space there is.  This transformer is special because of the voltages, 3810 volts three phase primary to 240 volts three phase secondary. Power transformers need a lot of space to keep cool.  Even when the transformer is not under load, the iron core still generates a lot of heat.   On the sides of the transformer enclosure, near the bottom and near the top, are vents which allow air to circulate through the enclosure removing the excess heat of the transformer core and coils.  Air is heated by the transformer, rises up and out the top vents while pulling cooler air in through the bottom vents.  Sometimes the vents have filters to keep dust out of the transformer.  If the transformer becomes covered with dust, it will not cool as well.  In serious cases, the transformer may get extremely hot, to the point of eventual failure.  Poor ventilation that results in overheating, shortens the life of the transformer.  Whether a 50 kva, 150 kva, or 500 kva 480 volt to 208 volt, the need to properly cool the transformer is important.  A safety tip, don’t stand near the vents of a general purpose transformer. An electrical fault could cause you serious harm.