The temperature gradient in oil immersed transformers

High temperatures are objectionable in transformers for several reasons. The first of these is their effect on the insulating materials, which are subject to gradual deterioration at temperatures of about 100 deg. cent. and to rapid destruction at temperatures greatly in excess of that figure. A second reason, which is not nearly so important, but nevertheless a valid objection, is their effect upon copper loss, which increases about 10 per cent with an increase of 25 deg. cent. in the temperature. Another reason, with oil-insulated transformers, lies in the effect of high temperatures upon some oils, in the deposition of solid hydrocarbons. This forms a coating on the surface of the coils and core, and clogs the ducts, thus increasing the temperature in the windings. The temperature at which this process begins depends upon the character of the oil used. A fourth objection to high temperatures existed formerly in the aging effect of temperatures exceeding about 70 deg. cent. upon the iron used in the core, thus increasing the core loss. This objection does not exist in connection with the present improved steel, which is non-aging.