Discharge Inception by Particles near Insulator Surfaces: the Proximity Effect

The influence of isolated conducting particulates which are in proximity to dielectric interfaces was investigated theoretically and experimentally. Localized enhancement of applied electric fields were calculated including effects of particle shape, distance to dielectric interface, and permittivity. The results showed significantly greater field enhancement can occur when particles are within a distance of about one partile radius from the interface and are stronger the greater the dielectric discontinuity. Experimental studies revealed that the discharge inception voltage was reduced as particles were brought close to an interface, in correspondence to the increase in local field enhancement. The effect was confirmed for three dielectrics: polyethylene, Delrin, and epoxy in SF6 gas from 100 to 700 kPa.