Charge decay on polymers subjected to ageing by partial discharges

The decay of the surface potential of corona-charged 23-25 mu m thick polyimide, polyethyleneterephthalate and polyetherimide samples, degraded by partial discharges, was determined. The samples were first subjected in their centre part to A.C. voltages by a sphere-plane electrode system at relative humidities from 10 to 80%. This resulted in partial discharges and thus ageing of the samples. After various extents of ageing, the samples were corona charged over their entire area to a surface potential of about 250 V. The decay of the surface potential, measured with a scanning probe over periods of several days, was found to be more pronounced in the central, aged area and depended on the ageing extent and on the relative humidity at which the ageing was performed. (C) 1998 SCI.