Investigations on the magnetic field convection effects in the discharge in SF/sub 6/ circuit breakers

Summary form only given. A model which includes electrodynamics, gas-dynamics, plasma physics and plasma chemistry is needed for the design of the SF/sub 6/ circuit breakers. The model is an essential tool for the understanding of the operations of the considered device, in order to improve its efficiency and reliability during nominal operation and during faults. The Lorentz force has been included in the momentum equation, and the radiation effects are taken into account in the energy equation. The equation describing the electrodynamics is the convection diffusion equation for the magnetic flux density, obtained from the Maxwell equations and Ohm's law. The induced electromotive force is neglected. A finite volume time dependent formulation has been adopted in order to numerically solve the fluid dynamic problem. The electrodynamics is solved by means of a finite element method. The fluid dynamic code is iteratively coupled to the electrodynamic code in order to obtain the time evolution of the discharge. The radiation term, the conductivity and the thermodynamic parameter of the plasma are evaluated assuming local thermal equilibrium. The high current phase of a discharge during the switch off process in an SF/sub 6/ circuit breakers has been considered. The magnetic convection effects on the discharge regime have been analyzed. The MHD interactions have an important role in the discharge behaviour. The values of the Lorentz force appear to be comparable to the applied electric field and the discharge is constricted in a channel of transverse dimension of about one centimeter.