Non-destructive methods for detection and localisation of partial discharges

Abstract

The use of plastic dielectric components in the high voltage insulation is being imposed to reduce the maintenance costs to the detriment of the fluid insulation technology cables (mainly paper-fluid oil). It could prevent not-expected problems such as the appearance of defects in the manufacturing process of: the cables (lack of symmetry, impurities, cavities) or accessories for the power cable (terminals and splices). These defects produce small partial breaks of insulation (partial discharges) which causes the breakage of the cable and accessories. It entails the temporary loss of service and the unavailability of the network ‎. International and national regulations try to mitigate these defects, either in manufacturing or in their installation in the field, but it is difficult to detect them in an early stage. To know the status of an installation cable and accessories, there are systems for detection of partial discharges, which is the main method for detection of potential failures. The inspection can be carried out in an installation disconnected from the electrical grid (offline inspection) and in a connected installation (online inspection). The requirement to maintain a continuous service, has forced to develop predictive maintenance methods that avoid the disconnection of the installation.