Discriminating of Rotor Fault and Low Frequency Load Torque Oscillation Using Motor Square Current Signature Analysis

This paper proposes a method to discern broken bar rotor fault from low frequency load torque oscillation in induction motors. If a motor is subjected to load fluctuation, the sideband components show up in phase current and they can exhibit similar behavior that of broken bar which leads misleading diagnostics. Thus, broken rotor bar and load oscillation related harmonics may sometimes overlap in the same spot. In this study, Motor Square Current Signature Analysis (MSCSA) method is used to detect broken rotor bar fault when load torque oscillation frequency overlaps with that of broken bar fault. This method is quite simple, but effective for false positive indication. The 2D-FEM simulations and experiments are carried out to prove the efficacy of proposed method. Based on the presented results, it is shown that broken bar related signatures such as 4fs-2ksfs do exist, whereas there is no load oscillation related signatures at the sidebands of 4fs in the square of phase current spectrum.