Effect of cavity sub-corona current on polymer insulation life

Calculations and experiments applying voltage to a test cell simulating a high-resistance conducting path in series with a cavity in polyethylene are discussed. These experiments generated chemical changes on the surface wall of the cavities for both subcorona currents (currents produced by voltage below critical inception voltage) and corona currents in different cavities. X-ray photoelectron spectroscopy (XPS) spectra of the cavity surface chemical species indicate similar moieties (functional groups), implying that subcorona current or discharge causes failures similar to corona insulation failures. The longer time for the subcorona species to develop is consistent with field failure occurrence within a few months to a few years. Electric field conditions favorable to the existence of subcorona currents at relatively low voltage are developed