Prestrike modeling in SF6 circuit breakers

Abstract

Prestrike is a common phenomenon in Circuit Breakers (CB) when the moving contact approaching to the fixed contact during the closing operation. This paper focuses on prestrike modeling in SF6 circuit breakers. A multi-physics method is developed to accurately modeling the prestrikes in SF6 circuit breakers. In this study, a model is developed for a simultaneous solution of the MHD equations and the governing equations of the circuit feeding the plasma in order to consider mutual effects of the circuit and the plasma. Navier-Stoke equations, turbulent flow equations, and the equation of heat transfer in fluids, coupled with Maxwell's equations are physical equations governing the circuit breakers. Kirchhoff's voltage and current laws equations are governing equations of the external electric circuit. The Electric-Circuit-Constrained Magnetohydrodynamic (ECC-MHD) model developed in this paper is able to study the electromagnetic properties of conducting fluids fed by electrical circuits. Motion of moving contact and temperature dependency of SF6 gas properties are considered during the solving of this multi-physics problem. Finite Element Method (FEM) is used to solve the multi-physics equations governing the circuit breaker. Finally a 72 kV single pressure puffer type SF6 circuit breaker is used for numerical studies. To investigate the mutual effects of the feeding circuit parameters and generated plasma in the circuit breaker, numerical studies are performed for different values of resistance and inductance in the arc current path.