Simulation study on abnormal discharge in insulator of fiber optical current transformer

When the multi-terminal hybrid DC transmission project is put into operation, it is found that the failure rate of FOCT increases. In this paper, the finite element simulation model of FOCT is built. The influence of different fiber sheath materials and gel conductivity parameters on the electric field distribution characteristics is studied by simulation. The causes of abnormal discharge are summarized, and the improvement measures and suggestions are given. The results show that The internal discharge near the fittings is mainly due to the introduction of potential in the shielding area and the mismatch of gel and fiber material parameters. Measures such as selecting appropriate conductivity materials in multilayer media and appropriately increasing the length of insulators are proposed. The research results can provide reference and support for fault analysis and structural improvement

I. Introduction

UHVDC transmission technology has the advantages of long transmission distance, large transmission capacity and low operation loss. It is widely used in cross regional transmission projects to solve the contradiction between uneven distribution of energy and resources [1]–[2]. Furthermore, it has developed into multi-terminal Hybrid DC and flexible DC transmission technology, which provides an important support for the flexibility, stability and safety operation of power grid [3]–[4]. But the increase in voltage levels and transmission capacity has brought challenges to power equipment. The traditional electromagnetic current transformer can't meet the requirements, so a new technical route needs to be adopted. Fiber Optic Current Transformer (FOCT) is a new type of current transformer based on Sagnac interferometry, which has the characteristics of wide dynamic range, good insulation performance and high measurement accuracy [5]–[7]. Its application plays an important role in ensuring the reliable operation of DC system.