Unraveling the “U-Shaped” Dependence of Surface Flashover Performance on the Surface Trap Level

Abstract

The effects of surface traps on surface flashover remain controversial. To clarify the relation between surface flashover and surface trap level, in this work, the surface trap level of epoxy composites was modified by nanoparticles incorporation, electron beam irradiation, and ozone treatment. Surface trap characteristics were analyzed by surface potential decay. Surface flashover voltages were measured in a vacuum for dc voltage and in SF 6 for ac voltage. The ''U-shaped'' curve is founded to describe the relation between surface flashover voltage and surface deep trap level, surface flashover voltage first decreases and then increases with surface deep trap level. Enhancement of surface flashover voltage is attributed to reduced surface charge density, which was calculated by a double-trap flashover model. The simulation results indicate that the surface charge density on left side of ''U-shaped'' curve is controlled by surface shallow traps, whereas that on the right side is determined by surface deep traps. The effects of surface shallow and deep traps on surface charge accumulation and dissipation are used to demonstrate the reduced surface charges and improved surface flashover voltage for the ''U-shaped'' curve. The proposed ''U-shaped'' curve offers a promising way to improve surface flashover performance for high-voltage applications by tailoring surface trap characteristics with surface modifications. INDEX TERMS Surface flashover, surface trap level, surface charge, epoxy composites.

Effect of mineral oil on flashover voltage of HTV silicone rubber under AC corona ageing: from the view of trap level distribution

“…Branched chain and tail groups would combine together to form molecular chain grid structure during the cross‐linking reaction, leading to the reduction of chemical groups. As deep traps are formed by chemical traps [16], which are generated by the existence of chemical groups, such as impurities, oxidation products, and additives, thus the density of deep trap decreases with increasing corona ageing time due to the cross‐linking reaction, as obtained in Section 3.2.2.…”

“…During the flashover process of HTV silicone rubber, the charge transport is mainly determined by external field distribution and the surface charge decay characteristics of insulation material. Du and Li [15, 16] found that the charge decay is closely related to the charge trapping and detrapping process, which is determined by the trap energy level distribution. However, the transportation process is quite different for electrons and positive ions, due to the different charge‐to‐mass ratio.…”

Improvement of surface flashover in vacuum

“…The flashover mechanism corresponding to different parts in the 'U-shaped' curve is stated in Fig. 19 [109]. In Fig.…”

“…The faster dissipation of surface charges contributes to relieving the distortion of electric field at CTJ, ultimately enhancing the surface flashover characteristics. In addition, authors apply ozone oxidation treatment technology to epoxy resin composite materials, and find that the surface flashover voltages both in vacuum and SF 6 (0.2 MPa) can be increased by more than 10%, after micro‐Al 2 O 3 /epoxy modified by ozone oxidation treatment [108, 109].…”

“…Fig.18'U-shaped' curves for the relationship between surface flashover voltage and surface trap level[109] (vacuum level: 3.0 × 10 −3 Pa; DC voltage; finger type electrodes space: 5 mm)…”