Studies shows that the WRSM is a lower energy density machine comparing to a SPM machine, therefore the designed stator for a 2hp SPM machine will have a lower volume comparing to the designed stator for a 2hp WRSM machine.If we create two similar WRSM and SPM with the same shaft radius, air gap length, and same stator the current density in the field winding of the WRSM exceed from normal values.
If we limit the current in the field winding of WRSM, then for keeping the power rating of the machine, an increase in the stator current and therefore the required area for conductor is required.The studies shows that the slot area should be determined based upon the maximum air gap length for wound rotor machine in radial direction. The studies shows that the back iron and teeth width in common stator should be determined based upon the minimum air gap length for PM rotor machine.