Space charge behaviour in LDPE after AC electrical ageing

Space charge accumulation after ac ageing and its effect on dc poling has been studied in low-density polyethylene (LDPE). LDPE film samples with thickness of around 180 μm were aged at an electric stress of 50 kV/mm under 50 Hz ac voltage for various times at ambient temperature. Space charge dynamics in the samples after ageing were monitored using the pulsed electroacoustic (PEA) technique. Except the presence of considerable amount of space charge accumulation in the aged sample, the ageing has also brought a significant influence into the space dynamic under dc poling voltage. The ageing extent was previously investigated by chemical analysis (i.e. Fourier Transform Infrared FTIR and Raman spectrum) revealed little change taken place in the bulk of the material after ac ageing in the time frame studied. This indicates that the space charge measurement may be an effective method for diagnosing the early stage of material deterioration. It also provides additional information about charge mobility and trap depth that can be extracted from space charge profile.