National Grid experience with partial discharges in gas insulated substations

The method of PD detection used by NGC is the UHF technique. Capacitive couplers are the most effective sensors. PD sources are located by time-of-flight measurement where signals from couplers on either side are displayed simultaneously on a 2 channel fast Digital Storage Oscilloscope (DSO). Better instrumentation and the collation of a database of transit times through different plant have improved accuracies. With this experience PD sources have been located to within plus or minus 0.5 m and confirmed by inspection. An ultrasonic PD detection system is being used to confirm locations and it is hoped that more precise location will be possible.<
>