Advanced technique for partial discharge detection and analysis in power cables

Polymeric cables are the most common choice for transmission and distribution in populated areas, as well as for the connection of components (transformers, GIS, etc.) in new power stations, replacing paper-oil cables. Indeed, they do possess superior characteristics with respect to oil-filled cables. As an example, they do require lower maintenance, they are lighter (easier to deploy) and, in case of breakdown, they are not flammable and do not cause polluting leaks. The drawback of polymeric cables is their scarce ability to withstand partial discharge activity over long periods of time. Therefore, partial discharge measurements performed soon after cable laying (generally during the 1-hour AC withstand test) or on aged cables are getting a key tool to ensure reliable performance of transmission lines. This paper introduces a novel technique for partial discharge detection, processing and diagnosis. The technique is based on the use of the information borne by the partial discharge pulse waveforms. It enables noise rejection and dealing with contribution of different sources separately and, therefore, allows accurate diagnosis to be carried out. The Measurement results enable, moreover, localization of partial discharge sources to be performed. Some practical examples of on-field partial discharge measurements and partial discharge source localization, performed applying the here presented technique, are reported and commented. Introduction: High voltage (HV) and medium voltage (MV) polymeric extruded power cables have achieved insulating properties comparable to those of oilpaper cables (e.g. high dielectric strength and resistivity, low dielectric losses and permittivity, low thermal resistance, chemical stability). The easy installation due to the absence of oil in the system (resulting in lower costs) made the polymeric extruded cables to replace oil-paper cables in many plants during