It is known in the related art to attach a high-current line, consisting of at least one generally water-cooled tube made of copper or another highly conductive material, high up on a center mast arm in order to achieve balance within a high-current system. It is further known, in the field of current-carrying mast arms, to achieve balance by bending the center mast arm at an elevated position, or by additional installation of balancing loops on the mast arms or on the transformer return line, as shown in European Patent No. 0 184 140 and its U.S. counterpart, U.S. Pat. No. 4,682,341, the contents of which are incorporated herein by reference for these teachings. In most of the cases put into practice, however, the center mast arm is bent upward, resulting in a so-called triangulated arrangement with which inductive balancing can be achieved.
Certain serious disadvantages, however, are associated with the triangulated arrangement of the mast arms. One disadvantage is in the high weight of the center mast arm as compared to the weight of the two outer mast arms. A further disadvantage is the increased weight of the lifting mast supporting the center mast arm which results from this approach. This unequal weight distribution results in extremely uneconomical operation of the three-phase arc furnace.
From theoretical considerations, it is also known to make the diameters of the mast arms different sizes (i.e., a modified coplanar arrangement) in order to balance the reactances of the three-phase arc furnaces, as shown in the journal "Elektrowarme International" 49 (November 1991), B4, pp. B201 to B211. Although the use of a form of coplanar current conductors was common in the first decades of use of three-phase arc furnaces, the prior art (as in the version cited in the journal) fails to teach a practical, fully balanced coplanar conductor layout in a three-phase arc furnace system.
USPTO Backgrounds
USPTO Backgrounds