Systematic and reproducible partial discharge patterns during electrical tree growth in an epoxy resin

The partial discharge activity (the number of discharges per second) during electrical tree growth in the flexible epoxy resin CY1311 was measured using a phase-resolved synchronous counting system, The experimental conditions, voltage and pin-plane spacing were varied to produce a wide range of tree structures from branch to bush. Systematic and repeatable changes in the partial discharge activity occurred, depending on the experimental conditions and these correlated with the type of tree structure (branch density or fractal dimension) formed. The type of tree growth was principally determined by the applied electric field and the occurrence of regular changes (bursts) in the partial discharge activity which are associated with a sudden and temporary phase shift and broadening of the partial discharge phase distributions. The number of bursts an their dynamics determine the type of tree grown.