Is motor cooling adequate for extended operation at very low speeds?
Cooling often depends on motor speed, such as with totally enclosed fan-cooled (TEFC) motors. To meet constant torque loads, therefore, a motor should not be operated at less than 30 percent speed without additional cooling. Consider a larger motor, constant speed cooling or a totally enclosed non-ventilated (TENV) motor for these conditions. Motor thermal protection devices will prevent high-temperature damage when motors operate continuously at very low speeds. With variable torque loads such as centrifugal machines, the rapidly decreasing power at low speed reduces cooling problems.