Space Charge Behavior in Ethylene Propylene Rubber Under a 50-Hz AC Electric Field

In this study, the space charge behavior in ethylene propylene rubber (EPR) under a 50-Hz AC field is studied based on the variation of space charge response, FTIR spectra and impurity contents inside EPR with thermal treatment. The space charge was detected with the pulsed electroacoustic (PEA) method and the phase shift of detecting pulse under 50 Hz AC field was realized according to the automatic equal phase shift (AEPS) principle. The results show three main types of impurities in untreated EPR. Three distinct regions of space charge distribution are seen in untreated EPR under a 50-Hz AC field. The mean phase density of space charge $\rho _{\theta }$ is increased with the enhancement of the applied field from 15 to 61 kV/mm. The maximum electric field distortion rate of untreated EPR tends to rise first and then decrease, ranging from 6.65% to 31.87%. The impurity content and the $\rho _{\theta }$ decreased significantly for EPR thermal treated at 150 °C for 18 h. Corresponding, the maximum electric field distortion rate is effectively reduced to 0.66%. Finally, the space charge source and migration process are speculated based on the diffusion trend of the space charge isodensity line and the migration direction of various charges under the electric field.