Study on space charge characteristics of oil-paper insulation at breakdown moment

During the long-term operation of electrical equipment of HVDC system, accumulated space charge in oilpaper insulation can greatly distort the local electric field, which can cause the aging and breakdown of the equipment. Therefore, it is important to understand the influence of the space charge on breakdown characteristics of oil-paper insulation dielectrics under DC voltage. In this paper, four kinds of oil-paper samples with different aging status are obtained by accelerating thermal aging. At room temperature, each sample is applied with DC voltage till breakdown. During the processes of the breakdown, the space charge distribution is measured using pulsed electro-acoustic (PEA) method, and space charge distribution is analyzed at the breakdown moment. The experimental results show that positive space charge moved towards to opposite electrode under DC voltage and the more serious deterioration of the oil-paper insulation dielectrics, the deeper positive space charges moved. At breakdown moment, space charge and electric field polarity are reversed, and space charge density and electric field decrease with the delay time after breakdown.