Computation On The Transport Properties Of Switchcear Arc Plasma

The arc plasma is inevitably occurred during the interruption of the circuit breaker.For describ ing the dynamic variations of the arc and the influence on the electric fielddistribution in arc quenching chamber because of the existence of arc, investigation on thethermodynamic properties and the transport properties of various particles composing thearc plasma becomes the key to study the internal microscopic process of the circuitbreakers. For obtaining the quantitative description of the internal micro change process ofthe arc, Eindhoven model is used for calculating the particle number density distribution ofthe arc plasma, to analyze the influences of the temperature, the pressure and the particlecollision on the electrical conductivity. Based on the solution and analyses ofthermodynamics equilibrium and Boltzmann equation model, the change rules of theelectrical conductivity with the temperature and the pressure has been obtained, and thequantitative description has been achieved. From the modeling theory, SF6 and vacuum arcplasma parameters according to the features of different circuit breakers has beeninvestigated, and the micro-arc plasma model is derived, including vacuum, pure SF6 andhybrid SF6 with copper vapor both in equilibrium state and two-temperature cases, basedon the Dalton's law, the mass action law, the charge neutral law and the Stoichiometricequilibrium condition. Moreover, the vacuum, SF6 and SF6 mixed Cu micro-arc plasmamodel under equilibrium state and two-temperature cases are derived. And the nonlinearequations of various particle number densities are obtained and the electrical conductivityof the arc under different conditions have been calculated.During the process from the arc burning to the arc dielectric recovery, there existscharged particles with a certain conductivity and metal vapor within break, the contactsand the nozzle, the dynamic change with the potential gradient, temperature gradient andthe pressure gradient, meanwhile, the electric field distribution is different from the finalelectrostatic field after the interruption. According to the characteristics of the chargedparticles and metal vapor comes with a certain electrical conductivities, based on Maxwellequation for numerical analyses of the distribution of the interior electric field of the arc quenching chamber, the equation of the electric field during the SF6 arc burning process inthe chamber is deduced, the 2-D electric field is simulated using the finite element method,and the visualization of the field distribution has been realized.