Influence of cavity size and cavity location on partial discharge frequency dependence [polymer insulation]

Variable frequency phase resolved partial discharge analysis (VF-PRPDA) is a partial discharge measurement technique where the frequency of the applied voltage is variable. In this paper, the VF-PRPDA technique is applied to a test object containing a cylindrical cavity in an otherwise homogeneous insulation of polycarbonate. The frequency is varied in the range 10 mHz-100 Hz. It is shown how the frequency dependence of PD is influenced by the cavity diameter and the cavity location in relation to the electrodes. The PD frequency dependence is also numerically modeled for an isolated cylindrical cavity with diameter 1.5 mm using a field model.