Induction Motors Torque Analysis via Frequency Extraction for Reliable Broken Rotor Bar Detection

Conventional diagnostic methods applied to industrial induction motors, such as the Motor Current Signature Analysis may lead to false negative diagnostic outcomes is several cases, one of which is the case of non-adjacent broken rotor bars. So, alternatives have been proposed and concern the monitoring and analysis of the stator current or stray flux of the motor during the start-up with more advanced signal processing algorithms. Those methods work well in most cases, however the real issue is that many large industrial motors have very few start-ups during their operating life time. In that sense it is not possible to apply the transient analysis-based methods. In this paper, an alternative methodology is presented for the first time solving this issue for induction motors at steady state. The method relies on a two-stage signal processing and analysis of the harmonic index of the motor's torque during operation. The results are convincing that the fault can be very reliably be detected at steady state as well as its severity level.