Investigation of the impacts of the refill valve diameter on prestrike occurrence in gas circuit breakers

Abstract

In puffer type Sulfur Hexafluoride (SF6) Circuit Breakers (CBs), the refill valve is the main inlet duct for the SF6 gas to enter the puffer volume. When the CB is closing and moving contacts and the nozzle are moving toward fixed contacts, the SF6 gas enters the puffer volume via the refill valve. Since changing the refill valve diameter can alter the direction of the SF6 gas motion in the closing operation of CBs, understanding its effects on CBs' function and performance may help to improve the CB design. This paper has focused on the effects of refill valve diameter on prestrike occurrence in the closing operation of puffer type SF6 CBs. In order to accurately study these effects, some equations are used in the developed multiphysics model, including the Navier–Stokes equations and standard K–ε turbulent model for modeling the motion of the SF6 gas, heat equation for calculation of the gas temperature, Maxwell equations for electromagnetic fields modeling, and gas state equation for taking into account the severe dependence of the SF6 gas properties on temperature. Numerical studies have been performed on a 72.5 kV CB. Performance and functionality of this CB have been investigated for four different refill valves from several physical aspects. Numerical studies show that the refill valve diameter has a considerable influence on the prestrike occurrence instant.