On the estimation of AC behavior of field grading composites

In the present work, the Authors have analyzed the DC and AC conductivity behavior of five different ZnO filled Silicon Rubber field grading material (FGM) composites. To avoid thermal runaway under continuous high-amplitude AC stress, pulsed AC measurements are performed. In the absence of a systematic procedure to estimate AC conductivity, an earlier proposed ad hoc method is used to analyze the pulse measurement data at 50 Hz and at higher frequencies. It was observed that depending on the degree of non-linearity and the magnitude of the low field conductivity, this method sometimes fails to give a useful estimate of AC conductivity. Possible physical reasons for this behavior are discussed.