Mechanical Protection of Induction Motors by Off-the-Shelf Electrical Protective Relays

Abstract

In this paper, a novel idea is presented to apply off-the-shelf commercial protective relays, widely used to protect induction motors against different electrical and thermal faults, to detect mechanical faults as a complementary capability. In other words, the available protective relays can be configured to protect induction motors against mechanical abnormalities in addition to their normal duty to detect electrical and thermal faults. To support the idea, the current and vibration signals are generated by sophisticated modeling of the motor for different faults and then the simulated signals are injected to a numerical relay simulator designed in full detail to resemble a commercial relay. It is shown that some mechanical faults like broken rotor bars and shorted stator windings can be diagnosed by the relay using the Motor Current Signature Analysis (MCSA). Other mechanical abnormalities harder to detect by MCSA would be diagnosed by using vibration analysis as a complementary tool to MCSA. In the latter case, an extra input (vibration) is needed to be delivered to the relay. Simulation results verify the presented analysis used for modeling healthy/faulty motor and the designed relay simulator.