Modelling of Enhancement of Electric Field and Temperature on Partial Discharge in the XLPE Cavity Model under Positive DC Voltage

Abstract

Performing partial discharge (PD) detection under DC voltage can help to find out insulation defects of the high-voltage direct current (HVDC) cable systems. Partial discharges highly depend on the field strength at the defect, which is determined by the dielectric conductivity under DC voltage. As is known the polymer conductivity is significantly influenced by electric field strength and temperature, and over the cable working temperature range the conductivity of cable insulation material could change by orders of magnitude. This phenomenon will result in locally enhanced electric field distortion when there is a defect inside the cable insulation. And it will have some influences on the detection of partial discharge. To investigate the field distortion caused by the field and temperature dependent insulation conductivity and its influences on the partial discharge under DC, a sandwich model with an internal cylindrical cavity is established using finite element method (FEM). The electric field distribution in the crosslinked polyethylene (XLPE) sandwich sample is calculated with existence of an internal air-filled cavity. And the results are compared with and without the consideration of the field and temperature dependent material characteristics. The caculation results show that at ambient temperature, the electric field in the cavity is enhanced by considering of the field dependence of conductivity. And at the maximum working temperature, the field distribution at the cavity is dominated by temperature. In addition, sandwich cavity samples are made using cable insulation slices from the commercial 320 kV HVDC cable. Partial discharge tests under positive DC voltage are conducted to verify the calculations.