Simulation calculation and analysis on three-dimensional electrothermal coupling of a new type of current transformer for distribution network

In recent years, the new type current transformer with bushing structure has been widely used in the distribution network system due to its advantages of miniaturization, high mechanical strength, maintenance-free, safety and environmental protection. The distribution of electric field and temperature field inside the transformer are important characteristic parameters to characterize its electrical insulation and aging performance. Then, the electric field distribution of inner conductor, secondary winding and insulating medium of CT is mainly determined by the applied voltage and relative dielectric constant, while the distribution of the temperature field mainly comes from ohmic heat of primary current and joule heat of insulating medium. Therefore, the study on the electro-thermal coupling field of CT is more complicated and necessary. In this paper, a 3D simulation model of a new type of current transformer for distribution network based on electric-thermal coupling is established by using finite element software. Considering that the actual thermal conduction process of CT is mainly by conduction, convection and radiation, three different kinds of boundary conditions such as solid heat transfer boundary condition, heat convection boundary condition and surface radiation boundary condition are applied to the CT. Through the model created above, the temperature rise process and the distribution characteristics of temperature of the CT under different current conditions are studied. Meanwhile, the maximum field strength and the hottest temperature of the CT are calculated. According to this, the position of weak insulation of the transformer is determined. The research results can provide a reference for the factory production of new type current transformer.