Effects of temperature on characteristics of creepage discharge in oil-impregnated pressboard insulation under combined AC-DC voltage

The characteristics of oil-impregnated pressboard (OIP) insulation in converter transformer are different with that in traditional AC transformers due to the complication of voltage applied on valve side windings of converter transformers. There is a serious lack of empirical research on effect of temperature on creepage discharge in OIP under combined AC-DC voltage. Therefore, this study investigates the characteristics spectrum of creepage discharge in OIP under combined AC-DC voltage, and explores the effect of temperature on characteristics of creepage discharge under different temperature from 70 to 110°C. The experimental results show that the partial discharge inception voltage and flashover voltage decrease as temperature increase. The times of low amplitude discharge (LAD) decrease and amplitude of LAD increase. Meanwhile, the times of high amplitude discharge (HAD) gradually increase at each stage of creepage discharge with higher temperature. The analysis indicates that the charge carriers easily accumulate and quickly migrate directional movement along the electric field ahead of discharging. The residual charge carriers are more easily dissipated after discharging. The ‘hump’ region of LAD moves to the direction of higher discharge magnitude. The interval time between two consecutive discharges drastically shorten. The HAD intensively appear, result in accelerating the development of creepage discharge in OIP insulation.