Extending Carter Factor to Slot Openings Equipped With Semimagnetic Slot Wedges

Abstract

Stator slotting increases the equivalent air gap as Frederick William Carter pointed out already in 1901. Since then, the Carter factor has provided a solution to the problem of analytically calculating the decrease in magnetic flux density under an electrical machine slot opening. Nowadays, semimagnetic wedges (SMWs) are often used to close the stator slots and to smooth the flux density behavior on the rotor surface. SMWs also partly compensate for the slotting-caused decrease in the magnetic flux making the equivalent air gap length shorter than in the case without SMWs. However, the original Carter factor does not take into account the effect of SMWs and should, therefore, be extended. This study offers a solution for extending the original Carter factor to calculate the equivalent slot opening in the presence of SMWs.