Influence of volume and surface conductivity on the transient surface charge characteristics of DC‐GIL insulator under thermal–electric coupled fields

Abstract

Here, the transient surface charge distribution of a basin-type insulator is investigated under thermal-electric coupled fields. Horizontally installed ±200 kV direct current gasinsulated transmission lines (DC-GIL) are employed, and a 3D geometric model is applied. An improved method is introduced in the transient simulation under coupled fields, which involves simplifying geometric model, decoupling calculation, applying weak form partial differential equation, and simplifying ion transport equation. The influence of volume and surface electric conductivity on the transient surface charge and electric field distribution is discussed. With increasing volume conductivity, the transient charge accumulation is accelerated due to the promotion of conduction through the insulator. With increasing volume conductivity, the polarity of the charge on convex surface changes from negative to positive, while it changes from positive to negative with increasing surface conductivity. This is the consequence of the transition in dominant conduction mechanism. Nonmonotonic variation of charge density is observed attributing to the variation transient field distribution. It can be concluded that the influence of volume and surface conductivity should be focused on when evaluating the insulation characteristics of DC-GIL insulators, and the thermal gradient should be considered in dealing with the long-term operating insulators. INTRODUCTIONThe insulator in gas-insulated equipment, for example gasinsulated transmission lines (GIL), acts as the supporting and insulating medium [1]. Usually, the insulator is made of epoxy resin composites with excellent insulating properties. Inside the enclosure, insulating gas is filled up to 4-7 bars. It is reported that flashover would occur at the gas/insulator interface which may be due to the electric field distortion [2, 3]. With the development of high voltage direct current (HVDC) transmission technology, DC-GIL attracts much attention. More obvious surface charge would accumulate on the insulator surface under DC voltage compared with the condition under alternating current (AC) voltage, and this may cause more serious field distortion in DC-GILs [4].

Effects of volume and surface conductivity on the surface charge and electric field characteristics of the tri‐post insulator in SF 6 ‐filled ± 500 kV DC‐GIL

“…The results indicated that both the volume and surface conductivities showed obvious influence on the surface charge distribution. It involves the transition of dominative conduction between bulk and interface conductions in charge accumulation process when varying the conductivity [13].…”