Abstract:As the impulse withstanding test for GIS is widely used in field, the PD detection under impulse is considered as a new diagnosis method for insulation of GIS. Some studies and statistics showed that the impulse voltage had greater efficiencies in finding local enhanced defects comparing with AC voltages due to its limitation effect on corona stabilization. In this paper, a wideband PD detection system was built, by which the pulse current signal could be obtained. The PD behaviors and the statistical distributions were investigated under standard oscillating light impulse(OLI) and oscillating switching impulse(OSI). Based on that, an actual GIS with artificial insulator air gap defect was tested. By experiments, three PD sequences were summarized and their occurrence probabilities were found to vary with the voltage level, the gas pressure and the dimension of air gap defect. And the first discharge decides the other two partial discharge. The PD tests on actual GIS demonstrated that OLI and OSI voltages could efficiently excite PDs from insulator air gap defects in GIS.