Space charge mapping and conduction current measurements in epoxy and polyethylene

Abstract

The study of the effect of space charge within dielectric materials is important with respect to understanding the mechanisms of aging and breakdown. Accumulation of space charge in insulation can accelerate degradation through local field enhancement, and consequent ionisation/excitation and electromechanical energy storage. Aging and breakdown of the polymers are related to the release of the electromechanical energy around trapped charges. In this work, space charge mapping and conduction current measurement are carried out on similar dielectric specimens. Quantitative information about the space charge within the dielectric volume are obtained from these experiments e.g. space charge distribution, charge transport mechanisms. These are expected to give us an insight into the aging and breakdown process in polymeric dielectrics. The space charge distribution is mapped using Pulsed Electroacoustic technique. Conduction current measurement is carried out using three electrode systems. In both these measurements, dielectric material is polarised for a given time and then depolarised for the same duration under dc field. Aluminium films are used as the electrode material. Two different types of polymeric materials are used in this work in order to understand the effect of material properties. These are epoxy resin which is an amorphous material, and polyethylene which is a semi crystalline material. The information obtained from these techniques about the charge trapping and detrapping are used to correlate the operative charge accumulation and transport processes. Further, the effect of electric field on these processes is studied.