Mirko Cettolo’s scientific contributions

Induction motors are nowadays used more frequently than any other electric motor in various kinds of electric drives. Incipient fault diagnosis is very important because if the fault is undetected, small motor failure can lead to serious motor failure. Although several sophisticated fault detection methods can be found in literature and practice, the focus of this paper are two methods that could be used ldquoon-linerdquo in real-life situations, and can be performed in a short time. The experiments have been performed by analyzing the voltage in an external search coil, and the shaft voltage. In the case of the search coil voltage analysis, the tests were performed for six different search coil positions. The search coil voltage spectral analysis has also been performed. All tests were performed on 22 kW, 380 V, 1470 r/min induction motor, for the case of a healthy rotor and for the case of a rotor with different deliberately damaged rotor.

Induction motors have nowadays been more frequently used with frequency converters. The use of frequency converters affects the behavior of the machine and makes fault diagnosis more complicated. One of the widely used diagnostic methods is motor current signature analysis (MCSA). This method is based on measurement of sidebands in the stator current spectrum. Those sidebands are usually located close to the main supply frequency. Frequency converter causes supply frequency to slightly vary in time and, as a result, some additional harmonics in the current spectrum are induced and sidebands are reduced. Those harmonics can be easily misinterpreted as the sidebands caused by the rotor faults. Although the rotor faults in the case of frequency converter supply are not so often, precaution is still necessary. In this paper the experimental results of fault diagnosis carried out using standard supply and using frequency converter have been compared and presented. All tests were performed on 22 kW, 380 V, 1470 r/min induction motor. The current spectra are given for the motor with two broken bars with both types of supply.