On-line Partial Discharge Monitoring System and Data Processing Using WTST-NST Filter for High Voltage Power Cable

Defects inside insulation of HV XLPE cable accessories can lead to partial discharge (PD) activity. When PD activity happens, leakage current may flow through the grounded line. To acquire the PD current signal, one practicable and effective method is placing a high frequency current transformer (HFCT) winding the grounded line. In order to measure the insulation degradation, a partial discharge on-line monitoring system is developed and reported in this paper. Through the field test, the presented monitoring system is effective and available for power cable in the condition based maintenance (CBM). However, on-site partial discharger detection on XLPE cables and cable accessories are very difficult of variable noise interference, which gives much trouble to partial discharge detecting. This paper introduced an adaptive filter stationary-non stationary filter based on the wavelet transform (WTST-NST) to de-noise the stationary noise interference in partial discharge detecting. The proposed method is a wavelet domain filtering technique, based on the iterative multiresolution decomposition reconstruction (MRD-MRR) with hard threshold, for extracting PD signals from stationary interference noise. Quantitative and qualitative analysis of the experimental results, while using the WTST-NST filter to PD signals recorded from power cables, prove that the ability to extract the PD from noise hidden in it. Key-words: Power cable, Adaptive WTST-NST filter, On-line monitoring, Partial Discharge, MRD-MRR Algorithm, Stationary noise interference, condition based maintenance(CBM)