FEM Analysis of Electric Field Distribution Under Different Material Characteristics in Optical Fiber Insulator

Optical fiber current transformer (OFCT) is widely used in flexible DC transmission to improve the ability of information perception of power grid, and optical fiber insulator is the key component of OFCT to provide insulation and protection. However, discharges in optical fiber insulator seriously affect the stable operation of the power system. Here, the effect of material characteristics of different parts on the electric field distribution in insulator is explored to figure out the inner discharge mechanism. A ± 400 kV optical fiber insulator 3D simulation model is constructed in COMSOL Multiphysics, and differences in the electric field distribution in the insulator are compared and analyzed by finite element method under different conductivity of materials. The results show that the conductivity of the fiber coating and filling compound significantly affects the electric filed at interfaces in the insulator flange sections. The semiconducting fiber coating results in a mismatched potential into the flange sections at both terminals, which further leads to a remarkable electric field distortion on the inner wall of fiber sheath at the interface between the sheath and coating layer. The maximum electric field at the interface is even up to 84.5 kV/mm. The electric field distortion also occurs at the interface between epoxy tube and filling compound when the conductivity of the filling compound increases. Therefore, the increases in conductivity of the fiber coating and filling compound leads to electric field distortion at interfaces, which can cause discharges in the optical fiber insulator.