During operation

unpredictable insulator flashovers occur frequently in the gas insulated transmission line (GIL) and gas insulated switchgear (GIS). Metal particles are considered an important cause of flashover. However

the partial discharge (PD) and flashover characteristics of metal particles on the ultra/extra-high voltage GIL/GIS insulator surface have not been fully understood

thereby hindering condition diagnosis and fault warning. In this paper

a test platform for an actual 550 kV GIL triple insulator and metal particles with different lengths at different positions are set. The ultra-high frequency (UHF) method

pulse current method

and ultrasonic method are used for PD detection. The flashover characteristics of different defects are studied

and the PD development before flashover is investigated. The results indicate that the closer the defect to the particle trap

the lower the flashover voltage

and the smaller the ratio of flashover voltage to PD inception voltage. Before flashover

the PRPD and φ-N patterns also change significantly. There is a significant change in the proportion of discharge during the positive and negative half cycles. The apparent charge

UHF signal amplitude

and discharge repetition rate fluctuate significantly without exhibiting any significant upward trend.