Changing the dielectric dissipation factor of transformer fluid based on synthetic ester in the condition of a concentrated heat flux

The problem of the influence of concentrated heat flux on the dielectric dissipation factor (DDF) of synthetic ester is presented in this article. Some industrial practice has shown that in the result of action of concentrated heat flux of high intensity on the synthetic ester, the dielectric dissipation factor of this ester changes, rising to the level disqualifying this ester as a useful for the insulation in power transformers. The preliminary experimental studies, which had in view a verification of the practical observations, indicate that the DDF increase with the growth of the unitary surface load of heating elements used in the heating process. For the certain values of unitary surface load, the DDF of synthetic ester may increase even above the specified in the standard IEC 61099 level of 0.03. In the case of presented experimental works such value is about 1.1 W/cm² and is lower than the value of 2 W/cm², which is typical for the heating elements used in the heating process of mineral oil. It means that the influence of concentrated heat flux on the properties of synthetic ester is visible and taking into account this result and also the industrial experiences, it seems to be important the continuation of initiated experiments.