This presentation was made at the 2019 NAFEMS World Congress in Quebec Canada
In the interrupting chambers of high-voltage circuit breakers (HVCB), shown schematically in the Figure 1, insulating material which is mostly Teflon or poly-tetra-fluoro-ethylene (PTFE) is used to confine the electric arc between the electrodes and to guide the gas flow toward the thermal volume and exhaust tubes. The ablation of PTFE due to the radiated energy from the electric arc mixes with insulating gas, thereby modifies the thermodynamics and chemistry of the problem. Another important phenomenon in these type of arcing flows is the self-induced magnetic field which results from the electric current between the electrodes.
The purpose of present work is a computational investigation of thermal plasma flows in a mixture of working gas and ablated vapors in the presence of a magnetic field. Therefore, a numerical simulation to model ablation-radiation- magnetic field coupling in real gas flows has been provided and verified. The basic flow solver is a finite volume algorithm using Roe’s Riemann solver, coupled to mass addition and ohmic source terms in the continuity and energy equations due to the ablation and electric arc, respectively. In this work, the ablation effect is modelled by injecting a mass flux to the boundary cells through the corresponding faces representing the ablative walls. The multi-component module of the code can model the mixture composed of multiple species in the chamber. The ohmic source is computed using the Joule’s heating which is a function of electrical conductivity and also the electric field. In addition, the Lorentz forces caused by the arc’s current are added to the momentum equations. These forces are obtained from the self-induced magnetic fields by solving the Maxwell’s equations. The energy added to the domain due to the Joule’s heating, has to be transferred to its surrounding parts. The dominant energy transfer in this application is radiation which is modelled using the P1 method. The presence of Lorentz forces due to the magnetic field has a consequence on the pressure field followed by the electrical conductivity in the plasma region. Increasing in pressure due to the self-magnetic pressure effect, increases the electric arc’s energy that leads more radiated energy toward the PTFE parts. This causes an increase in the ablation rate and boundary recession which is studied comprehensively in this paper.
|Date||18th June 2019|
|Organisation||Montreal Ecole Polytechnique|