Electrical tree growth in epoxy resin under DC voltages

This work investigates electrical tree propagation in a glassy epoxy resin under constant DC voltages of +60 kV and -60 kV, using samples with classical needle-plane electrodes but having small AC trees (henceforth called `initial trees') incepted prior to the DC tests. The characteristics of DC trees propagating from an initial tree is analysed via a sequence of 2-D projections of trees captured using a CCD camera during the test. The experimental results suggest that DC tree growth rate is polarity dependent even when initiated by the presence of an initial AC tree. The shape of the initial AC tree does not have a profound influence on the shape of the DC tree. The length of the initial tree, however, may have a determinant influence on the growth of DC tree. DC treeing exhibits a runway propagation and statistical analysis suggests that tree growth starts to accelerate after reaching a certain distance across the insulation.