The correlation between the partial discharge behaviour and the spatial and temporal development of electrical trees grown in an epoxy resin

Combined partial discharge detection and video monitoring of the tree growth have shown a strong correlation between the partial discharge activity and the spatial and temporal development of electrical tree growth in CY1311 epoxy resin. CCD imaging of the spatial distribution of light emitted, due to partial discharges in the tree structure, has shown that the different modes of partial discharge behaviour reflect their different spatial distribution within the existing tree structure, with new growth occurring at those parts of the tree in which the partial discharges are active. The dynamics of the partial discharge behaviour, namely the frequency and duration of two modes of activity, is controlled by the experimental conditions (voltage and pin-plane spacing) and determines the type (fractal dimension) of the resultant tree. During one mode of activity, rapid low-fractal-dimension radial growth of the tree occurs. During the other mode, new growth occurs at a slower rate from the tree structure near the pin electrode, leading to an increase in the overall fractal dimension of the tree structure.