Condition based maintenance of MV power cable systems on the basis of advanced PD diagnostics

From the point of view of a power utility, insight in the condition of their medium voltage power cable network becomes more and more important to guarantee a reliable and secure power supply. For several years, detection and localisation of partial discharges (PD) using AC voltages is internationally accepted as a symptomatic, reliable diagnostic method for determination of the quality of insulation systems. In this paper, several ageing aspects in medium voltage power cables are discussed, supported by several diagnostic field examples. The following conclusions are drawn: studying fault statistic of components results in the identification of dominant faults; old 'diagnostics' are still very useful for some of these fault causes; using PD diagnostics on cables, important information of a cable section is collected in the PD 'fingerprint' of the measured cable section; standard interpretation rules are used for optimal decision-making for cable repair before failure occurs; the PD inception voltage, PD magnitudes, PD location, PD intensity and PD mapping together can give a good insight in the condition of a cable section; discharge defects can be related to different insulation systems of a cable section, either the cable accessories or the cable insulation itself; from PD mappings important information can be collected concerning PD source types in the paper insulated lead cable, e.g. either concentrated PD or scattered PD; and for determination of PD activity in XLPE cable insulation, combined analysis of PD quantities is necessary.