Breakdown of Insulating Materials by Surface Discharge

"Round-robin" experiments for partial discharge degradation of polyethylene have been made by means of a parallelplate electrode system. Following this, a second round-robin was run using direct electrodes with the object of surveying some simple testing methods corresponding to actual phenomena such as local perforation by corona. Corona lifetimes of several insulating materials were measured by using two kinds of electrode systems, i.e., a hemisphere-plane configuration and a cylinder plane as recommended by the International Electrotechnical Commission (IEC). Precise differences between different materials cannot be defined because of the fluctuation of corona lifetime of the same material, but there may be some significance in the order of six kinds of materials. Several possible causes of the variability were examined with regard to the differences of test dates, humidities, airflows, and specimens\´ thicknesses and some information concerning relations between variability and experimental conditions was obtained. These results and considerations should be helpful relative to the adoption of the most reasonable electrode and the performance of test procedure.