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Space charge dynamics in oil-paper insulation under the combination influence of moisture and temperature

The main insulation system in HVDC transformer consists of oil-paper insulation. The formation of space charge in oil/paper insulation system can not only affect the dielectric strength, but also relate to the stability and security of HVDC transformer. Moisture and temperature has detrimental effect on the electrical breakdown strength and insulation life of oil-paper insulation. Thus a better understanding the combination influence of the moisture and temperature on the charge distribution in multi-layer oil-paper insulation system becomes increasingly practical importance. In the present study, the space charge dynamics in three layers oil-paper insulation system with three different moisture concentrations (0.28%, 1.32% and 4.96%) under 15 °C and 55 °C were investigated using the PEA technique under 20 kV/mm . The combination influence of the moisture and temperature on the charge distribution in multi-layer oil-paper insulation system was provided. Results show that the higher the moisture content and the temperature of the oil-paper sample, the higher the mobility of the trapped charges in the sample, and the more obvious the positive charge injection and negative charge injection were observed.