The application of light emission techniques to study the spatial and temporal development of partial discharge activity during initiation and growth of electrical trees

Electrical treeing is the main long term failure process in synthetic resin insulators. Void formation at a region of local electrical stress enhancement (tree initiation), is followed by the growth of fine erosion channels (tree growth stage) driven by partial discharge (PD) activity. In this paper we report on ultra-sensitive non-evasive light detection techniques (using a photomultiplier and liquid nitrogen and Peltier cooled charge coupled device (CCD) cameras) which we have used to study i) the tree initiation processes which lead to PD and ii) the spatial and temporal development of PD activity and its relationship to damage accumulation during tree growth