An improved method based on double-end phase difference system for on-line cable PD location

Conventional Phase Difference method pinpoints the PD location by analysing the phase difference of the primary arriving signals at both terminals in power cable, however it lacks consideration of signal separation in noisy environment and fails to ensure location accuracy when defect is close to cable end. Based on the analysis of PD pulse propagation character in cable system presented in the first part of this paper, an improved on-line PD location method is then proposed. Measuring instruments are installed at both terminals to collect real-time pulse signals and deliver measured signals to the processing center. On the basis of the cross-correlation function analysis, the direct and the first reflected waves measured at both ends are identified and separated from interference. Implementing the cross spectral density function, the phase differences of two pairs of signals are then obtained and the defect is finally determined by integrating the two location results. The situation when PD locates near the cable end is as well analyzed on considering the mechanism of wave reflection and overlapping, so as to increase the accuracy and reliability of the PD pulse location. The performance of the proposed technique is tested by simulation under ATP-EMTP on considering the noisy environment and the situation when the defect is close to the cable terminal. The comparison with other methods and the analysis are presented at the end of the paper.