Internal partial discharge in cavity of polyurethane

Parameters and time development of internal partial discharges in insulation material - polyurethane were studied. The internal defect was created by a needle, which was moved back by 1 mm in order to create an air filled cavity in addition to the micro-cavity at the tip of the needle. In the experiment polyurethane pattern was stressed by high AC voltage and parameters of the partial discharges until breakdown of insulation material were recorded. The discharge activity generated in the air cavity, the point of the greatest stress degrades gradually the insulation. This degradation is connected with growth of an electrical tree, which parameters are described. The apparent charge magnitude, voltage and the time of occurrence of each PD event were recorded by LDS- 6.