Electrical properties propagation of exposed combined insulation

Power transformers are inconsiderable group of the electrical appliances with two components insulation system. One of the components - liquid insulating medium plays two roles- insulating and cooling. It can be mineral as well as synthetic based liquid. Second component is an organic based solid insulation usually of cellulose character. Organic materials of this structure are sensitive to an operational degradation factors (temperature, oxidation, humidity etc.). Their deterioration can endanger fail free operation of electrical appliances. Naturally, the observation of time dependencies of insulating component features is main interest of the appliance operators and researchers.