The Influence of Thermal Ageing on the Electrical and Physiochemical Properties of Pressboard/Oil Interface

The pressboard/oil interface in transformer insulation is very vulnerable to creeping discharge. Therefore, the influences of thermal ageing of pressboard on the creeping discharge at pressboard/oil interface have been studied in the present contribution. Using a needle-plate electrode, long-term tests were carried out with differently-aged pressboard samples under constant voltages of 34 kV and 36 kV, respectively. The PD number and the average magnitude of PD pulses have been analysed to study PD activities of various test samples under different voltages. Moreover, it was found that the carbonization area is inversely proportional to the ageing degree of pressboard and the formation of white mark was jointly determined by the degree of thermal ageing and the intensity of electric field.…