-On the basis of a previously developed mathematical model of electromagnetic power transfer between phases, an investigation of effectiveness of the functioning of the arc steel furnace EAF-100 with coplanar construction of the secondary current lead in the modes of "short", "medium" and "long" arc discharges was carried out. It was ascertained that the electromechanical processes in EAF are defined not only by the gradients of potential in arc discharges, but also by the electromagnetic processes of interaction between phases, which lead to rearrangement of integral power, generated by arc discharges. Recommendation on the employment of a reactor with separately controlled phases for the operation of the furnace in the long arc mode was formulated.Keywords-arc steel furnace, power transfer between phases, "short" and "long" arc discharges, optimization of power.