Effect of Insulating Gases on Electrical Treeing in Epoxy Resin

Electrical trees initiated from defects in solid insulation are one of the main causes of cable insulation failure. Both the initiation and propagation of electrical trees are linked to PD activity in the free volume and interfaces between electrode, gaseous and solid dielectrics. This work investigates the potential of suppressing partial discharge (PD) during tree propagation by displacing air with a higher electron affinity gas. Epoxy resin samples with pre-existing trees were energized under 7 kVrms in atmospheric air and SF6 under 2 bar absolute for 3 hours. PD measurements indicate that the permeation of SF6 into the epoxy sample could significantly reduce the discharge energy and lead to a reduced number of discharges. However, the tree length growth was comparable for both gases. This is attributed to offsetting of reduced PD energy by SF6 within the tree channels and subsequent reaction between gas by-products and the epoxy.