Electric field analysis of oil-paper insulation in converter transformer under different environmental factors

In order to study the influence of multiple environmental factors on the electric field distribution of the typical oil-paper insulation structure on the valve side of the converter transformer, the electrical conductivity and relative mediation of transformer oil and oil-impregnated paperboard were measured at -20℃-80℃ with temperature and moisture as variables. The oil-paper insulated valve side winding model of the converter transformer was established, and the material attribute was assigned as a dynamic value with temperature and moisture according to measured data. Through simulation, the electric field distribution of the oil-paper insulation structure under different temperature, moisture and applied voltage amplitude of 800 kV pure AC, 83% DC content, 87.5% DC content and pure DC conditions are obtained. Research indicates: When the temperature is -20℃ or 0, the electrical conductivity of oil-impregnated cardboard decreases first and then rises as the electric field strength increases, and conductivity increases with electric field strength when the temperature is 20℃ or 80℃. Temperature, moisture and DC content of the applied voltage all affect the electric field distribution of the oil-impregnated paper insulation, and the position of the maximum field strength is changed with the DC content of the applied voltage and the moisture content of the oil-impregnated paper. The field strength of the main insulation of the converter transformer at operating temperature is higher than that at room temperature. Moisture increases conductivity of oil-impregnated cardboard significantly or even higher than the conductivity of the insulating oil, resulting in higher electric field strength in the oil than in the oil-impregnated cardboard. © 2021, Harbin University of Science and Technology Publication. All right reserved.