Partial discharges of cavities in ethylene propylene rubber insulation

The aim of this paper is to investigate the characteristics of partial discharge (PD) within dielectric-bounded and electrode-bounded cavities which are embedded in Ethylene Propylene Rubber (EPR) by using plane to plane electrode. The theoretical analysis is carried on the electric field strength and PD inception voltage of cylindrical and ellipsoidal cavities in different dimensions. The samples with the different dimensions of artificial spherical cavities in EPR are made and the PD characteristics in the cavities, such as PD number, amplitude and phase, are measured by professional instrument in laboratory. It has been found by the experiments that the symmetric PD distribution changes from "rabbit-like" to "turtle-like" shape with the time of applied voltage. With the increase of applied voltage on the samples, the PD inception phase becomes prior to the zero crossing of positive and negative half-cycle. Meanwhile, PD pulse repetition rate has an increase trend with increasing the experimental voltage and the amplitude of PDs occurred in dielectric-bounded cavities changes from a higher value to normal during a short time. However, no obvious amplitude change of PDs occurred in electrode-bounded cavities has been observed in the experiment. As a result, internal PDs occurred in cavities is one of the prime reasons resulted in the degradation and corrosion of EPR.