Partial discharge measurements as a source of information about the technical condition of PILC insulated MV cables

Abstract

The paper focuses on the new possibilities of managing a key element of the power supply system: the power cable network. The possibilities are created by the technical condition assessment of power cables based on partial discharge diagnosis at damping (self-extinguishing) AC voltage. Both cable manufacturers and their users pursue to obtain a high technical reliability of the power network. Modern IT and measurement systems make it possible to acquire data enabling a better assessment of the line technical condition. Undoubtedly, among the new data sources there is also diagnostics based on partial discharge (PD) measurement (PD inception voltage, PD extinguishing voltage, the PD apparent charge value for different voltage levels, PD intensity, PD distribution as a function of cable length). Providing a unique data set which describes an insulation technical condition of particular line elements, such a diagnostics creates an opportunity to change the current method of power cable network management to a new more effective one, both technically and economically. Measurements of partial discharges in MV cable network were carried out in one of the distribution companies in Poland in the years 2005-2010. They were intended to develop an optimal method for the use of partial discharges diagnosis in the assessment of technical condition of power cables. The main area of research covered MV cable lines of a total length of 590 km.. The studies on power cables provided a group of measurements for Paper Insulated Lead Covered power cables (PILC). From all the measurements there were selected 18 cases where a cable failure was recorded and the measurements of partial discharges were carried out both before the failure and immediately after the repair of the failure. Basing on the carried research work and analysis it has been found that: Basic parameters indicating the risk of the failure are: reduced PD inception voltage and the occurrence of increased PD intensity in a power cable. The study shows that, the lower the PD inception voltage, the higher the percentage of cable sections of an increased PD intensity. Consequently, a greater number of cable sections which can be included to the group of increased risk of failure. No correlation between the increase of PD value and increasing probability of the failure occurrence has been found.. (5 pages)