Minimizing the three-phase unbalance in an electric arc furnace

A method is proposed to reduce impedance imbalance in the electrode arms of an arc furnace. Conducting plates or tubes are used to shield the magnetic fields around busbars in order to minimize the mutual inductance. The volume integral equation method is used to calculate bus impedances, current distribution, and eddy current losses. The numerical results indicate a significant improvement in system balance even during bus movement. Two types of shields are investigated. Shielding the center phase by using a large tube reduces the unbalance at the coplanar bus positions, but it has little effect when one bus is offset. Shielding by two conducting plates standing between buses yields good balance and constant reactance for all bus positions. The power loss in the shields is only a small percentage of the bus loss, the shields can be replaced by parallel conducting bars bounded at ends. By combining the new method with a smaller center bus diameter, better results have been achieved