Detection of high field AC conduction loss current in polymeric insulating materials

A novel method for the detection of high-field AC conduction loss current in polymeric insulating materials is developed. It uses the unbalanced operation of a current-comparator-type high-field tan-δ-capacitance bridge and the deconvolution technique for signal processing. Examples of the transfer function of this detection system for different amplifier gain levels are shown. Under certain conditions, the high-field AC conduction current of LDPE (low-density polyethylene) film evaluated with this method contains both an in-phase fundamental sine wave component which correlates with tan δ and harmonics caused by the nonlinear electric-field dependence of the conduction current. In epoxy resin, however, only the fundamental sinusoidal wave component of the dissipation current is detected