In electric motors with buried magnet rotors have circumferential magnetization and are installed in deep grooves. Due to this type of magnetization, the magnet height is in the tangential orientation. The effective arc coefficient is restricted by the slot.
The synchronous reactance of the q axis is higher than the d axis. The thickness of the bridge between the shaft and the adjacencies of the magnets must be meticulously chosen. This was the type of configuration selected for project design. This setting is also referred to as “buried” or “spoke.”
In this configuration, a means must be employed which prevents the flow from being closed by means of the shaft. The application of a non-ferromagnetic material is fundamental. With a ferromagnetic axis, much of the flow lies in a way to close without crossing the engine air gap and as a result this flow does not generate torque on the motor shaft.
With the principle of raising the magnetic flux in the air gap, the axis must be of non-ferromagnetic compound or a ring of non-ferromagnetic material should be applied between the magnets and the ferromagnetic axis. https://www.mrosupply.com/motors/ac-motors/general-purpose-motors/2840760_sum76004-4_baldor/