Identification of charge injection and conduction properties of epoxy resin from polarization current measurements

Accumulation of space charge is a very important issue in the design and development of high voltage insulation systems. The formation of space charge is intrinsically related to charge injection, trapping and conduction in a dielectric. In case of polar dielectrics like epoxy resin, in addition to space charge injection and accumulation, dipolar polarization also plays a prominent role in determining its behavior at high electric fields. In this work, a method has been proposed to separately identify charge injection conduction and dipolar polarization from polarization current measurements performed on thin epoxy resin samples. The samples were stressed at 10 kV/mm and 20 kV/mm electric fields prior to depolarization. The time domain measurements were correlated with frequency domain measurements using Hamon approximation. It was found that at both electric fields, the observed polarization current was highly influenced by charge injection.