Space charge characteristics of oil-paper insulation in the electro-thermal aging process

High electric field and temperatures can result in electrical property degradation of oil-paper insulation and accelerate its aging process. This paper describes the regulation of space charge in the process of electro-thermal aging. Electric field distortion and differences in characteristic parameters during electro-thermal aging are analyzed, along with the effects of electro-thermal aging on space charge from the perspective of trap energy. High temperature and an electric field are used to accelerate the aging of oil-paper, and space charge characteristics are measured using the pulsed electro-acoustic (PEA) method throughout the electro-thermal aging. Based on results obtained, it can be concluded that homo-charge injection occurs at the anode and the type of the charge injection at the cathode varies throughout the electro-thermal aging; the decrease of permittivity during aging allows for space charge injection to take place; growth of trap depth makes the space charge accumulate in the middle of the sample; and space charge accumulation after electro-thermal aging results in inner electric field distortion, which leads to large current and decreased breakdown in voltages.