The continuous torque density of conventional electric machines is determined by the size of the air-gap area and the back-iron depth, which are determined by the power rating of the armature winding set, the speed of the machine, and the achievable air-gap flux density before core saturation. Despite the high coercivity of neodymium or samarium-cobalt PMs, continuous torque density is virtually the same amongst electric machines with optimally designed armature winding sets. Continuous torque density relates to <answer>method of cooling and permissible period of operation before destruction by overheating</answer> of windings or PM damage.
What does continuous torque density refer to?
method of cooling and permissible period of operation before destruction by overheating