Study on Surface Charge Accumulation Mechanism of DC-GIL Insulator Based on Charge Behavior

Surface charge accumulation on insulator is one of the main restrictive factors of DC gas insulated pipeline transmission line (DC-GIL). The current research has been a great concern to volume and surface conductance while the trap effect always been neglected. In this paper, we focus on the effect of both surface and bulk traps mechanism on surface charge accumulation on insulator. Firstly, we establish the physical model of disc spacer including surface thin layer and bulk layer and the theoretical mathematical model of micro-dynamic behavior of space charge consisting of charge landing, injection, trapping and detrapping. In addition, the probability coefficient is introduced to characterize the change of the accumulated charges in the surface thin layer in each physical process. Meanwhile, the effect of trap mechanism on the accumulation of surface charge has been calculated by simulation. It was found that surface accumulated charge is easily trapped by surface traps, which reduces the charge density accumulated on the upper surface and increases the charge density accumulated on the lower surface. With the increase of accumulation time, the effect of trapping mechanism will make the surface charge distribution more uneven and the peak value increase. The probability coefficient of charge injection is strongly dependent on the carrier mobility, and is also closely related to the accumulation time.