Effects of temperature and techniques of measurement on the intrinsic electric strength of polythene

The electric strength of polythene has been measured under intrinsic conditions in the temperature range 20¿85°C. Values are obtained using a new type of specimen, developed by McKeown, and also with the conventional recessed specimen. The McKeown specimen gives results which are greater at all temperatures than conventional values, and for these specimens, the temperature dependence of the intrinsic electric strength agrees with Frohlich´s `amorphous¿ or high-temperature theory of breakdown. Experiments are described which show that this increase of electric strength achieved with the McKeown specimens at room temperature is attributable to the presence of the solid epoxide resin in which the polythene and spherical electrodes are set, though the reason for the increase is, as yet, unknown.