The undetermined surface flashover of insulators limits the development of ultra-high voltage AC gas insulated equipment. In this paper, we report a micro discharge potentially triggered surface flashover phenomenon, which is revealed directly by luminescence activities of samples with different micro morphologies. The results show that sandblasted samples, which are prone to a lower surface flashover voltage, present luminescence pulses corresponding to micro discharge activities over the surface. Polished samples have the mold release agent layer removed and inhibit local micro ionization, which eliminates the pulse luminescence and improves the surface flashover voltage. This paper brings novel ideas to insulation surface flashover mechanism under AC voltage and lays a foundation for further developing high reliable gas insulted equipment.

To suppress the charge accumulation on the spacer surface in direct current (DC) gas insulated transmission line (GIL) is an important and emergent issue for the development of a clean, safe and economic smart grid. A design method of the DC spacer is proposed, and a spacer prototype is prepared and evaluated both by simulation and type test. The DC withstand voltage test and polarity reversal test are performed using the new DC spacer compared with a commercialised 220 kV AC spacer. The simulation results indicate that the surface electric field and surface charge of the DC spacer are lower than those of the alternating current (AC) spacer under DC voltage. The test results verify that the surface flashover voltage of this DC spacer is higher than that of the AC spacer. The potential feasibility of the spacer design for HVDC is discussed. It is hoped that the content of this paper can bring new ideas in the development of HVDC gas insulated equipment.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.