Effects of high thermal conductivity on temperature rise of epoxy cast winding for power transformer

Epoxy resin is widely used for insulation in cast dry-type transformers, in spite of its weak ability of thermal conduction. One approach to obtain a higher thermal conductivity is to introduce inorganic fillers with high thermal conductivity. The purpose of this paper is to study the effect of high thermal conductivity on temperature rise of epoxy cast windings. In this paper, micro and nano boron nitride (BN) particles were mixed into epoxy with idfferent mass fraction. Then the composite was cast into mold to make different transformer windings. Thermal distribution was calculated and simulated by finite element analysis. An then experiments were carried out to verify the simulation results and investigate the effects of the improved thermal conductivity on temperature rise. Obtained results showed that the thermal conductivity had a significant effect on temperature rise. With increasing the thermal conductivity, the maximum temperature decreased obviously. The maximum temperature difference and time to reach thermal equilibrium state were decreased. It is concluded that the ability of thermal conduction of the transformer can be improved by using the epoxy with high thermal conductivity. Dielectric breakdown strength (BD strength) of different windings were also investigated and it was found that pure epoxy resin had the highest BD strength, while the composites filled with BN particles were all lower than neat epoxy.