A power conversion system for ac furnace with enhanced arc stability

This paper proposes a criterion for ac arc stability and an optimal converter topology for a non-ferrous metal ac arc furnace. The ac arc furnace rated for 36kA/224V/21MW has been investigated. The key parameters of modified Cassie-Mayr arc model have been calculated by the electromagnetic and flow simulations for electric arc. The used arc simulation model has been validated by a laboratory free-burning arc setup. It has been shown that the steepness of arc current at zero-crossing determines the arc stability, and the associated peak arc resistance can be used as its quantitative measure. Among the evaluated three power converter systems, the forced commutated inverter topology with a six-step modulation realizes the steepest current at zero-crossing resulting in the best arc stability. The proposed converter topology having a high degree of arc stability is expected to bring about reliable operation of ac arc furnace and enhanced productivity of the total furnace system.