Channel model for AC electric arc
Abstract
This report contains the results from calculations of freeburning AC electric arcs in argon. In order to calculate the arc current and arc voltage, the external electric circuit must be taken into consideration. The external circuit is modeled by an equivalent circuit consisting of an ideal AC voltage source, a loss resistance, and an inductance. The qualitative behavior of the currentvoltage characteristic is in agreement with observed characteristics, but experimental data are necessary in order to check whether the calculated power loss is reasonable. Nonsymmetry was modeled by introducing different anode and cathode falls in the two half periods. An attempt at taking into account different cathode current densities in the two half periods, depending on whether the electrode or silicon melt is cathode, did not give satisfactory results. Thermionic emission was assumed in both half periods, but this may not be the right mechanism when the silicon melt is cathode. The time delay of the AC arc compared to the DC case is modeled by a time constant. It was shown that this preset time constant must be in agreement with the mean 'mechanical' relaxation time in the arc in order to fulfill the energy balance. By updating the time constant until this is achieved, the time constant is eliminated as a parameter that must be chosen a priori.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 June 1993
 Bibcode:
 1993STIN...9427327L
 Keywords:

 Alternating Current;
 Anodes;
 Arc Melting;
 Cathodes;
 Current Density;
 Electric Arcs;
 Electric Potential;
 Electrodes;
 Equivalent Circuits;
 Inductance;
 Melts (Crystal Growth);
 Thermionic Emission;
 Argon;
 Electric Current;
 Electric Discharges;
 Fourier Analysis;
 Mathematical Models;
 Time Constant;
 Tungsten;
 Electronics and Electrical Engineering