Partial discharge occurrence induced by crack defect on GIS insulator operated at 1100 kV

It was observed that partial discharges were not detected from GIS insulators with the crack defects operated at 1100 kV in the UHV substation in China. The question is that whether crack defects can induce partial discharge at the operated voltage. In order to obtain the relationships between PD occurrence and crack configuration on GIS insulator operated at 1100 kV, the electric field strengths in the crack, changed with crack length, crack depth, crack direction, crack position, were simulated on a 1100 kV GIS insulator at operation voltage. The simulated results indicated that the field strength in the cracks, which located on the surface of the insulator or paralleled to the electric field direction, were close to that in the insulator around the crack, and the crack cannot induce partial discharge. However, the field strength in the cracks, which located in the deep position of insulator and in perpendicular to the electric field direction, was much higher than that in the insulator around the crack. For example, in the case of the crack located close to high voltage conductor, field strength in deep crack perpendicular to electric field direction could be 5.6 times of the field strength in the insulator around the crack, and it close to the field criteria of gas discharge, leading partial discharge occurred at operation voltage. The simulated results were verified by the experiment conducted on the insulators with cracks. The experimental results indicated that the crack could produce partial discharge, only when it is located in deep insulator material and in perpendicular to the electric field direction, and close to high voltage conductor.