Partial discharge and noise separation in combined cable-OHLs based on three-phase power ratios

Partial discharge (PD) detection has been proved as an effective tool for monitoring the insulation condition of high-voltage cables. However, the detection can be seriously affected by pulse-shaped interference from overhead lines (OHLs) when carried out at the cable termination of a combined cable-OHL. In this study, a novel scheme is presented for separating the PD pulses and interference in a combined cable-OHL. First, the characteristics of the currents from different pulse sources are investigated mathematically. On the basis of these characteristics, separation of multiple pulse sources can be realised by projecting the three-phase power ratios extracted from detected signals onto a ternary plot and then constructing maps using the power ratios of the defective phase. The performance of the scheme is subsequently evaluated by both numerical simulations and field applications. Furthermore, a comparison with the well-known time-frequency mapping method is provided. The results demonstrate that by using the proposed scheme, different pulse sources can be effectively identified without requiring stable pulse shapes and a better separation could be achieved compared with the conventional waveform-based approaches.