Effects of atmospheric pressure on DC resistance to tracking of polymer insulating materials

Polymer insulating materials are required for use in high altitude regions. For the use of polymer insulating materials in such regions, it must be confirmed whether the resistance to tracking at high altitudes is different from that at altitudes near the sea level. In this paper, an artificial atmospheric chamber was set up to investigate the resistance to tracking on a polymer insulating surface at DC voltage application under a reduced pressure. The tests were carried out in accordance with IEC 60112. The test results showed that the dependences of the resistance to tracking for polymer insulating materials upon the decrease in ambient pressure could be classified into three types. One type is for paper-based phenolic laminate and polycarbonate, where the resistance increases with the decreasing ambient pressure; the second is for polybutylene terephthalate where the resistance decreases with the decreasing ambient pressure; the last type is for epoxy resin where the resistance is almost independent of the decrease in the pressure. A Gaussian wavelet analysis was applied to discharge currents to discuss correlations among the resistance to tracking, the discharge energy level and the ambient pressure. It was found that the data of resistance to tracking with some of the materials obtained at altitudes near sea level are inadequate for use in a high-altitude environment. Problems may occur with respect to the safety and reliability of polymer insulating materials when the DC resistance to tracking decreases under low-pressure conditions.