Electromagnetic forces in three-phase rigid busbars with rectangular cross-sections

A three-phase busbar arrangement with straight rigid conductors carrying short-circuit currents is investigated. Calculations are made assuming steady-state ac current with a peak value equal to the peak value of the short-circuit current. This assumption is used in the related IEC Standards 865/92. In this paper, the electromagnetic forces and current densities are calculated by solving the electromagnetic field diffusion equation numerically, using finite elements. The results are compared with results calculated according to the IEC Standards 865/86, as well as with the corresponding technical revision IEC 865/92. The comparison involves arrangements with rectangular cross-sections, as used in ac indoor installations of medium and low voltage. The forces calculated, especially in cases of multiple sub-conductors per main conductor, were greater than those calculated according to the above Standards. In older Standards this difference is up to fifty per cent, while in the revision this difference is smaller. The differences are probably due to proximity effects.