Overload protection for medium voltage motors controlled by switchgear starters

The author addresses the application of traditional types of overload protective devices, notes some of the difficulties in doing so, and then recommends the better types. It is suggested that a combination of relays may be the best answer. Microprocessor relays, with good memory characteristics, are probably the best protection that can be applied, but they must be studied closely to be properly set. Some of them are furnished with the possibility of custom-building the protection curve. It is noted that this is much easier then to fit the curve including overload, start, and stall protection between the motor start run curve and the motor thermal withstand curve, which is the ultimate overload protection