Effect of defect size on PD pulse characteristics measured with high frequency current transformer in XLPE insulation

This paper presents study aimed at understanding the effect of defect size on characteristics of partial discharge (PD) pulse measured with high frequency current transformer (HFCT) in XLPE insulation. Four typical defects are established to introduce internal, surface, corona and floating discharges, the dimensions of the defects are varied in a certain range. The experiment is carried out at room temperature with relative humidity of ~ 40%. PDs are generated by applying a series of AC voltages to the defects, and are measured by the HFCT. The pulse shape parameters, including rise time, pulse width, magnitude and frequency distribution, are extracted. Obtained results show that the pulse shape is changed with the defect pattern. The parameters are dependent upon the defect size and are varied as a function of the voltage applied. It is suggested that the variation of defect size leads to the change in electric field and thereby results in the alteration of both initiation and formation processes of the discharge.