Electromagnetic theory predicts that a dielectric sample in which a steady DC current of density ε is flowing, and in which the ratio of permittivity ε to conductivity σ varies with position, will acquire a space charge density j·grad(ε/σ). A simple and convenient way to generate an ε/σ gradient in a homogeneous sample is to establish a temperature gradient across it. The resulting spatial variation in ε is usually small in polymeric insulators, but the variation in σ can be appreciable. Laser induced pressure pulse (LIPP) measurements were made on 1.5 mm thick plaques of ultra pure LDPE equipped with vacuum-evaporated aluminium electrodes. Temperature differences up to 27°C were maintained across the samples, which were subjected to DC fields up to 20 kV/mm. Current density was measured as a function of temperature and field. Negligible thermally generated space charge was observed. The charge carrier mobility in the bulk of the samples was estimated to be of order 10-8 cm2 V-1 s-1.
|Title of host publication||Conference on Electrical Insulation and Dielectric Phenomena|
|Place of Publication||Victoria, Canada|
|Publication status||Published - 2000|
|Event||69th Annual Conference on Electrical Insulation and Dielectric Phenomena - Victoria, Canada|
Duration: 15 Oct 2000 → 18 Oct 2000
|Conference||69th Annual Conference on Electrical Insulation and Dielectric Phenomena|
|Period||15/10/2000 → 18/10/2000|