Remote diagnosis of overhead line insulation defects

High voltage insulation defects cause partial discharges (PD) which can be detected through the reception of radiated radio frequency (rf) impulses. The paper describes a method of detecting insulation defects on overhead lines using vehicle mounted rf measuring equipment. The equipment is based on a 4 antenna array that is directly sampled using digital equipment with a bandwidth of 1 GHz. The results are analysed by firstly estimating the time delays apparent between the 4 antennas. Secondly, using the time delays, bearing and RMS time delay error information is calculated that allows identification of the PD source. The equipment has been tested in the field on a 132 kV overhead line defect that was initially reported to a radio spectrum management agency. The results show that equipment has the sensitivity to identify the defective insulator string.