Circuit breakers 9. Touchup painting 11. Considerable misunderstanding exists regarding the cooling effect that can be obtained by painting transformers with different types and colors of paint. It is thought by some that, as aluminum paint is a good reflector, that transformers painted with aluminum will operate considerably cooler than those painted with gray or black paint. This is true only for sources of heat outside the transformer and overlooks the fact that heat inside the transformer must be dissipated.
Heat is dissipated from the transformer by conduction, radiation, and convection.
In a transformer the heat must pass from the conductors and core iron through the insulation, oil, the steel case, and the paint coating. The thickness of the paint will add only an infinitesimal amount to either the length of the path or the combined thermal resistivity of the material through which the heat must pass. Any type or color of paint will therefore have a negligible effect on heat loss by conduction. The type and color of paint have no effect on convection. As there is no reflection of the sun's rays to be considered with transformers located indoors, the type and color of paint will effect only the heat loss by radiation.