Protecting Motors Fed Through Adjustable Speed Drives: Practical Challenges and Solutions to Guard Against Thermal Damage

Motor protection is a well-established principle. A primary failure indicator for motors is heat, which can damage insulation, bearings, the frame, rotors, and more. Once this thermal damage occurs, it is only a matter of time until the failure reveals itself as a phase-to-ground or phase-to-phase fault, a bearing failure leading to the rotor impacting the stator, or other issues. If proper thermal protection is not provided, protection elements such as 50/51 phase and ground and 87 differential protection will clear any faults resulting from this damage. Still, it is basically too late; these protection elements can only limit the extent of the damage at that point.