Painting Transformer Tanks

Q. I was puzzled by the question in your June column from A.S., who produced oil-filled transformers. Usually they are cleaned and painted after filling. If this is so, I wonder what temperature the sealed unit can take. If this is the case, he would have no choice but to use an epoxy primer and two-part polyurethane system. If the tanks are painted before filling, he should use a suitable primer and an acrylic bake material, especially if the transformers are used in an outside environment. —S.B.

A. At my company, depending on their size and the plant that produced them, we sometimes painted our transformer tanks before filling with oil, while I think another Pittsburgh company painted its pole-mounted distribution transformers after filling. I remember that the transformers were still warm when they were crated for shipment. If so, they were painted using force-dried paints. Since both procedures are still being used, I guess it’s six of one and a half dozen of the other.

Regarding the baking temperature that oil-filled transformers can withstand, normal baking cycles should pose no problem. Baking cycles of 20 to 30 minutes at 300º to 350ºF is common for the types of tank finishes used. The enamel on magnet wire used in modern transformer windings will withstand these and higher temperatures in continuous service. Other materials of construction are equally heat-resistant.