Reduction of PD in a void by additives of azobenzoic compound in HDPE insulating material

In order to reduce partial discharges (PD) in a void within an organic insulator, the material of the inner wall of the void was modified by additives, i.e. four types of azobenzo materials: azobenzene, p-nitro-azobenzene, p-amino-azobenzene and nitrobenzene-azo-resorcinol. The voids in the insulator specimens have a cylindrical configuration with a diameter of 1 mm diameter and a height of 100 μm. The materials of the top and bottom surfaces of the cylindrical void are high-density polyethylene (HDPE) with additive, prepared by the solution casting method. The specimen was placed between plane electrodes. It was found that the PD for the specimen with additive was reduced to as low as ~20% of that for the specimen without additive when the applied voltage was near the PD inception. The reduction of PD in the voids was observed for all four kinds of additives. The effective additive concentration was between 0.05 and 0.5% wt. The mechanisms for the reduction in PD were discussed, focusing on two factors: prevention against secondary electron emission from the void wall due to the excitation of the additive, and prevention of electron detachment from the void wall due to the charge traps by the additive, which may play significant roles in the reduction of the PD in the voids