Experimental investigation of positional accuracy for UHF partial discharge location

UHF methods for locating partial discharges (PD) in power transformers are under development and are increasingly being applied in the field. Due to the complexity and variation of internal structures in power transformers, a useful starting point is to assess the accuracy of PD location in a simple environment. Therefore, tests have been carried out in a metal tank to assess the difference between calculated and actual positions of a PD source when the source is located at various positions within the tank. The tank was fitted with three UHF sensors. A contact discharge test cell was used to generate PD-type current pulses that excite UHF signals. Signals from each sensor were captured and their recorded differences in arrival time at the sensors were compared with expected time differences based on the known coordinates of the PD source and sensors. Two methods for estimating the onset point of the UHF signal at each sensor were evaluated, using experimental data as a basis for determining which technique might be most useful for locating PD.