The Effect of Insulation Oil on the Electrical and Dielectric Properties of Epoxy Resin

It is well known that thermal and electrical stresses have a strong influence on the degradation of insulation, but the effect of insulation oil is not yet well analysed. There are different electrical apparatus operating with insulation oil as cooling system and epoxy resin as the insulation system. So it is very important to be cleared, how the oil will affect the electrical and dielectric properties of the solid insulation material. On this account thermal stress was applied to a number of castresin samples with the presence of insulation oil and its effect was evaluated via partial discharge inception voltage, loss factor, capacitance and breakdown voltage measurements. Starting point of the investigations for this study was the question of how far the insulation oil at higher temperatures affects the electrical and dielectric properties of the epoxy resin. To evaluate this influence, several samples were produced considering a special geometry, so that the possibility of diffusion of oil in epoxy resin can be increased. Then after different ageing periods, breakdown voltage, partial discharge inception voltage and loss factor of the specimens were measured as key parameters.