Practical experiences with on-line PD monitoring and interpretation for MV cable systems

PD monitoring on-line with location (PD-OL) is one of the successful diagnostic tools for MV cable networks which has been recently introduced to the main utilities in the Netherlands and also a few worldwide. Data acquired by PD-OL need to be correctly interpreted in order to identify the upcoming faults in MV cable networks and possibly forecast the remaining life of the component. Interpretation of the measured signals by means of statistical analysis of various PD patterns as well as trend watching in the patterns, which is considered as the prominent advantage of the on-line monitoring, enables us to estimate the degradation stage in insulation systems. In this paper, we present the result of such analysis applied on two life circuits. The data was obtained over a period of over two years continuous monitoring of the circuits including PILC/ XLPE cables and oil-filled / grease / polymer joints. The results of analyses on several weak spots which were detected before failure are presented. Besides, results of failed accessories are discussed in relation to their prior PD behavior as diagnosed by PD-OL.