Calculation of Slot Losses in High Frequency Electrical Machines

As new magnetic materials as well as applications emerge in electromechanical conversion systems, one finds that electrical machines are increasingly moving away from the mainstream power frequency to much higher frequencies. This shift is mostly being driven by the fact that for the same power a higher speed machine is smaller in size. Operating at higher frequencies has its advantages on size however one must ensure that this advantage is not offset by larger losses in the core as well as in the conductors carrying the high frequency currents. This paper discusses a method of calculating the slot losses in conductors. There are two aspects to this loss calculation, (a) most machines will have parallel conductors in a single coil, one must know the current distribution in these individual parallel paths and (b) the current in each conductor is not uniformly distributed through the cross-section but is skewed due to proximity and skin effects. Both these considerations must be accounted for when determining the dynamic loss factors.