Feasibility of detection partial discharges in bushings using UHF method

It is bushing faults that cause most of transformer unplanned outages. Until now, preventive test methods are widely used for estimating the insulation condition of bushings. Since the preventive test cycle is too long, it is difficult to find out latent defects effectively. In this paper, on-line partial discharge (PD) detection method and a TDOA location method based on ultra-high frequency (UHF) signals are presented. Firstly, the fundamental of UHF location method is demonstrated; then, experiments are carried out to verify this method. Test results show that: (1) in the tests of poor connection in bushing tap and suspended discharge on bushing's top cap, the rise time of UHF signals is short with small dispersions, which shows accurate location results; (2) in the tests of surface discharge and floating discharge lying on the bottom of bushing, both of the rise time and last time of UHF signals is longer with bigger dispersions, and the location results are both focused around the bottom of the upper porcelain insulator. The research result is valuable and meaningful for on-line PD detection and location for bushings.