High electromagnetic-interference immunity ability can be obtained in the on-line detection of partial discharges(PD)in gas-insulated-switchgear(GIS) by sensing the electro-magnetic signals electrically in UHF band Produced by the PD. Investigation are performed to sense the UHF signals from the outside of GIS. Based on the external UHF sensing technique
a PD detection device of GIS with movable sensors is developed
and its measuring and locating pro-cedures was established. It is been practically proved that the external UHF sensing technique is satisfactory in sensitivity
antiinterference ability and locating accuracy
and the movables of the sensors brings about some significant advantages.