Discharge energy and dc tracking resistance of organic insulating materials

As an evaluation test method for surface insulation degradation of organic insulating materials, the tracking test method is described in IEC Publ.112 as a safe and reliable evaluation. This publication has now been applied to the material selection. Due to the fact that the experimental values of the comparative tracking index (CTI), have wide variations, problems in reliability testing are abundant. In this paper, the correlation is investigated between discharge energy and tracking resistance of organic insulating materials. The test method resembles the IEC Publ.112 method, but with the application of dc voltages. The number of drops to tracking failure was measured with samples of paper based phenolic laminate, polybutylene terephthalate and epoxy resin. Discharge currents were detected when discharge occurred on the sample surface. A Gaussian wavelet analysis was applied to show energy levels of discharge currents. It was found that the tendency of discharge energy on organic insulating materials corresponded to the CTI of dc tracking resistance, and the results were an improvement on the IEC Publ.112 method for grading materials. The tracking resistance of organic insulating materials could be deduced from the discharge energy