The influence of switching impulse voltage superimposition on partial discharge characteristics of oil impregnated paper insulation system and conditions inside its oil gap defect

The authors have evaluated the possibility of deterioration diagnosis of Oil-filled (OF) cable systems by PD measurement so far. In our previous studies, we confirmed continuous occurrence of PDs even under the design electric field of 275 kV OF cables. Also we confirmed the progress of intermittent occurrence of PDs to continuous one by repeated superimpositions of lightning impulse voltage corresponding to switching surge. However, correlation between PD characteristics and internal conditions of the oil gap defect was not obtained. Therefore, in this study, we experimentally investigated the effects of the switching impulse voltage superimposition that can occur in practical operation of 275 OF cable systems on PD characteristics and we observed the conditions inside the oil gap defect by a CCD camera.