Diagnosis of rotor faults of induction motors, operated in non-rated conditions

Since the number of different induction motor applications is continuously increasing, the questions of current interest are those regarding the diagnosis of their technical condition. There are many different methods for on-line diagnostics of incipient rotor faults (broken rotor bars, rings etc.) that occur during their operation. One of the most frequently used method is the frequency analysis of the stator current using the FFT-transformation (MCSA) method. This is easy to apply and is non-invasive with respect to the motor construction. The subject of consideration in the following material is the application of this method when the motor has an asymmetrical power supply and is also using an autonomous power invertor. Also presented are the characteristic frequencies from experiments with a broken induction motor rotor bar as well as possible ways for diagnosis of this condition. Different ways to implement this method are given when the induction motor has a frequency converter supply.