Experimental verification of the inhibiting effect of hydraulic pressure on point discharge in oil-paper insulation under constant AC voltage

This paper reports on experimental studies of point discharge in oil-paper insulation under different hydraulic pressures. The point partial discharge of oil-paper insulation under different hydraulic pressure was measured for the first time. With the help of a commercial partial discharge detector, five discharge parameters under constant AC voltage were recorded and plotted as curves. These show that the partial discharge under very low pressure developed very quickly after it was initiated. So, care should be taken with oil-paper equipment operating at high altitudes, because once the discharge is initiated, it would develop into a catastrophe in a relatively short time. The partial discharge inception voltage and breakdown voltage increased with pressure, but the rising rates decreased with the increase of pressure. The discharge parameters decreased with pressure but the difference between the adjacent curves became smaller and smaller, which is called the saturation characteristic of the hydraulic pressure's effect on discharge. Therefore, very high hydraulic pressure is not necessary for weakening the partial discharge in oil paper insulation. It is believed that the hydraulic pressure influences the discharge in the oil-paper insulation by changing the state of the gas in this compound insulation system. This paper provides a reference for the operation and maintenance of oil-paper insulation equipment running in high-altitude areas. Adjusting hydraulic pressure might be an effective and economical way to reduce the size and weight of oil-paper insulation equipment.