Effect of relative humidity on surface dielectric breakdown of epoxy based nanocomposites under repeated pulses

In this work, epoxy based nanocomposites was prepared to investigate the effect of relative humidity on surface dielectric breakdown under repeated pulses. Two kinds of inorganic nano particles, i.e. silica and alumina, were used as fillers. The experiment was carried out at room temperature with relative humidity varied from 50% to 90%. A pair of needle-plate electrodes that was tightly pressed on the sample surface made the electrode pattern. By applying repeated pulses with voltage magnitude of -30 kV at a frequency of 100 Hz between the electrodes, surface discharge was initiated and thereby the dielectric breakdown was allowed. The time from voltage application to the formation of the breakdown was measured. Obtained results indicated that the time to the breakdown was strongly dependent upon the concentration of nano particle, which was also varied as a function of the relative humidity. It is suggested that behaviors of water absorption and charge transportation are changed as a consequence of the addition of nano particles as compared to the neat epoxy, which results in the variation in the resistance to the breakdown of epoxy resin.