Thermal Dependence of Electric Breakdown Strength of the Liquid Dielectrics

Except for the working parts there is an insulation, which is the inseparable component of the system in every high-voltage device. Insulation quality affects the lifetime of the whole device, therefore it is necessary to dimension the insulation so that it will be able to withstand not only the abnormal conditions like overloading or failures but also operative conditions. The combined oil-paper insulation is the most frequently used in the high-voltage transformer, while the liquid element offers the biggest demands. Besides an electroinsulating function, the transformer oil plays a key role in a cooling task, therefore it has to be able to resist to the high temperatures and retain the desired parameters in this condition, too. This paper deals with comparison of electric breakdown strength and its thermal dependence of the various oil types, including the natural esters, which have become a new phenomenon in the world of the electroinsulating liquids.