An improved technique for quantifying PD activity in cross-linked polyethylene (XLPE) power cables

Abstract

The presence of air-filled cavities within the insulation of active power cables affects the electric field distribution in the insulation bulk and increases the electrical stress inside and around the cavities. This causes accelerated ageing of the materials and creates regions for partial discharge (PD) development that may subsequently result in cable failure. In this paper, an improved PD quantifying technique applied for insulated power cables is first presented. Its effectiveness is demonstrated through an in-depth study of electric field distribution across a defective cross-linked polyethylene (XLPE) power cable with practical dimensions for HV applications and by analysing the PD behaviour under different ageing conditions. In realizing the aforementioned, the cable model with different arrangements, in series and parallel, of two discharging air-filled cavities was implemented in COMSOL software. The simulated cable fields are analysed for different separations and positions of the cavities before and after PD activity. The cavity fields are extracted in MATLAB and utilized for PD pattern characterization under three ageing conditions. Through the PD patterns and statistical quantities measured from simulated PD behaviour, the severity of PD in the cable model was quantified over the different ageing periods. It was found that the series configuration of the cavities was the most harmful configuration due to its high-field magnitude and greater tendency to initiate a PD propagation. Furthermore, the PD behaviour changes during ageing and the highest PD activity, greater PD magnitude and rate, were recorded at the most advanced ageing stage. Thus, indicating that PD characteristics can be used for inferring the ageing stage.