Mechanical Stresses in Busbar Supports During Short Circuits

With the increased magnitudes of short-circuit current obtained in modern busbar circuits, it becomes a matter of great importance to determine the mechanical stresses imposed on busbar supports during short circuits. The stresses are due to the electromagnetic force produced by the current flowing in adjacent conductors in the bus structure. When usefully applied, the electromagnetic force propels electric motors, or sends the pointer of a voltmeter along the scale; but the same electromagnetic force when destructively applied may bring about rupture of bus supports, distortion of conductors or even shut-down of stations. In the days when currents were low, or when large spacings between conductors were maintained, a support sufficiently strong to carry the weight of the conductors often was sufficient to withstand the stresses due to the electromagnetic forces, but with large short-circuit currents and with reduced spacing between conductors a more accurate knowledge of the stresses due to the electromagnetic forces is absolutely essential to the designer. The electromagnetic force has been the subject of investigations in the past not only for the case of busbars but also for transformers, current-limiting reactors, and disconnecting switches. In the case of busbars, as well as in some of the other cases mentioned, the stresses resulting from the action of the forces applied are very materially affected by the mechanical vibrations produced.