Effect of AC Electric Field on Space Charge Distribution in Ethylene Propylene Diene Monomer

In this paper, the space charge behavior in ethylene propylene diene monomer (EPDM) samples under AC electric field is studied. Space charge profiles of EPDM were obtained by using a space charge measurement system based on the pulsed electroacoustic (PEA) method. The automatic equipartition phase shift principle (AEPS) was adopted to achieve high phase resolution of the space charge signal under 50-Hz electric field. Two kinds of samples were studied, one unaged and another thermal-aged at 150°C for 18 h. Space charge was obviously detected at the electric field of 5kV/mm and higher electric field inside both unaged and aged EPDM samples. It means that the threshold electric field for obvious space charge accumulation is above 5 kV/mm for EPDM. Heterocharge and homocharge accumulation are significant near the upper electrode and lower electrode in unaged EPDM, respectively. The heterocharge accumulation significantly decreased after being thermal-aged at 150°C for 18 h. It seems that the heterocharge accumulation in EPDM is associated with the impurities dissociation under high electric field, and the amount of impurities can decrease under high temperature.