Abstract: An arc furnace for quickly and continuously melting directly reduced iron ore so as to make steel, wherein the furnace wall above the hearth line and the furnace roof have partly spherical inner surfaces, the spherical surface defining these inner surfaces having the center located adjacent to the point equidistantly spaced apart from the lower ends of electrodes, and the electrodes are inclined at an angle to the vertical so that the distance between the lower ends thereof may be reduced to a minimum.

Abstract: An electric smelting furnace in which a hollow electrode with the wall thickness depending upon the depth of current penetration is disposed vertically within the furnace and spaced by a desirable distance from the furnace bottom, and the top of the hollow electrode is connected to a duct for discharging the furnace off-gases and charging the raw materials into the furnace after they are preheated by the furnace off-bases in the duct and prereduced in the hollow electrode.

Abstract: A power control system is disclosed for an electric arc or refining furnace circuit to which is supplied power directly from an independent power generating unit or units installed independently of a publicly available power supply system or any other power generating unit. Depending upon the operating conditions of the furnace, the power supply is controlled by the suitable adjustment of the generator voltage or frequency or by the combination thereof based upon the relations V = K..PHI..n where V = generator voltage, K = constant, .PHI. = flux density and n = operating speed of a prime mover mechanically coupled to each generator, and f = p.n/60 where f = frequency, and p = number of poles in each generator.