Eddy currents in medium power switched reluctance machines

Switched reluctance machines are characterized by high local flux densities in the core, high current gradients in the windings and relatively large winding areas for the nondistributed windings. In particular, in medium-, high-power and high-speed machines these characteristics may lead to thermal problems. Hot spots in the windings are a result of losses, which originated from high-frequency alternating magnetic fields. It is identified that proximity effects situated at the pole tips and across the entire winding area are causing significant current displacements and in consequence for a considerable amount of copper losses. This paper reports the phenomenon of eddy currents in the windings of switched reluctance machines. Experimental verification and finite-element-simulation are presented for a 4-phase 55 kW switched reluctance machine.