Short circuit forces acting on the shielded three-phase supply

Summary

One of the serious tasks, that designer of heavy current equipment has to solve, is a sufficient mechanical fixing of electrical supply when exposed to short circuit forces. One method of reducing the values of the short circuit forces is the shielding of current-carrying conductors. Shielding is usually realized in such a way that the conductors are put in steel pipes of appropriate forms. This causes that short-circuit current carrying conductors are in a relatively weak magnetic field and, therefore, the Lorentz force acting on them is substantially weaker compared with unshielded conductors. The calculation of short-circuit forces for such a case was carried out for three-phase symmetrical line. The main disadvantage of the above method of shielding consists in the fact that eddy current losses produced in the shielding pipes contribute to heating of wires. Between the pipe and conductor, there is an air gap preventing the transfer of heat. The Lorentz forces acting on the wires were calculated for two types of shielding differing in the thickness of the shielding shells. The calculation of the electromagnetic field was performed by the FEM-based code QuickField 5.0. Mapping of the heating process is not included in this work and will be published later.

Additional informations

Authors

Kai Wu, Liu Kai, Wang Wenhao