Formulas for calculating short-circuit forces between channels located back to back

IN 1937 Arnold¹ published an analytic procedure enabling the designer of a single-phase two conductor bus to determine combinations of conductor spacing and cross section that render the proximity effect zero — hence combinations that render the a-c resistance, and thus the eddy current loss, a minimum. For explicit details the reader is referred to Arnold´s paper. For our purpose it suffices to remark that in general the designer is afforded an indefinite number of combinations (of conductor spacing and cross section) from which to choose; that the exact cross sections determined by the theory are not simple in shape; that as the ratio of conductor spacing to perimeter of conductor cross section increases, the equivalent structural shape associated with a particular conductor spacing shifts from rectangular strap to channel to circular or square tubular conductor, that the ac resistance, and hence the eddy-current loss, can be calculated from a given simple formula; and that the accuracy of this formula and the correctness of the general theory are verified by experimental data set forth in the paper.