Effect of Color of Tank on the Temperature of Self-Cooled Transformers under Service Conditions

The effect of color on the temperature of oil-immersed self-cooled transformers under service conditions has been a mooted question for a great many years. Based upon the relative absorption powers of the various colors often used in painting transformer tanks the lighter colors should give appreciably lower temperatures in hot climate sections. The results of three series of field tests conducted on actual transformers are given in the paper. The results, however, do not show the advantages for the light colors that would be expected, based solely upon the absorption powers of the colors. A method of calculation is used to check the test results, taking into consideration the various factors which apply to a transformer and do not apply to, say, a piece of metal painted and exposed to the sun's rays, such as the ratio of the area of the surface exposed to the sun to the total surface dissipating heat, the difference in thermal capacities, and the condition where in one case the test piece is dissipating heat, as well as receiving heat from the sun, whereas in the other case it only receives heat from the sun. It is shown that when all the factors are taken into consideration the calculated results check very closely the observations.