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 ρ θ 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 ρ θ 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.INDEX TERMS Ethylene propylene rubber (EPR), AC electric field, space charge, direct detection, electric field distortion, impurity.
In this paper, the effect of moisture on the charge behaviour in oil-impregnated pressboard is analysed based on the characteristics of the interface and the bulk. Space charge behaviour and infrared spectra are acquired from a sample with a high moisture content of 1.92% and another with low moisture content of 0.13%. The results show that a greater number of hydrogen bonds form in the high-moisture sample. The threshold fields of charge injection are 1 and 0.6 kV/mm in the low-and high-moisture samples, respectively. The dynamic charge transport in bulk is significantly accelerated by moisture. The drop in the injection barrier at the interface and the accelerated transport of charge in bulk in the high-moisture sample may be associated with the mediating effect of a water layer at the interface and the lower trap energy in bulk caused by the hydrogen bonds, respectively. The combined changes in the interface and the bulk led to the dominant position of negative charges inside the high-moisture sample, regardless of the distribution area or the charge amount.
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