Modulation of partial discharge activity in GIS insulators by X-ray irradiation

A system was assembled which can perform high-sensitivity partial discharge (PD) measurements under combined electric stress and X-ray irradiation on 138-kV class gas-insulated switchgear (GIS) post insulators. Under X-ray irradiation, the PD pulse repetition rate is increased and the discharge inception voltage (DIV) is sharply reduced. The DIV of these insulators under X-ray irradiation was recorded at values at low as 25 kV, although some samples could not be brought into discharge at 400 kV without X-rays. The modulation effect of X-rays on PD activity permits the location of the discharge side. In general, pulse-height and pulse-phase patterns are more tightly clustered with X-ray irradiation, but the patterns display a board range of features depending on the type of defect, voltage, and time on voltage