Background. At present, induction motors are increasingly being operated as part of variable‑frequency drives. One of the common types of faults leading to failures is damage of rotor windings. Spectral analysis of the stator current appears to be a promising method for detecting such faults. However, available studies do not pay sufficient attention to frequency converters, although different settings of these converters can yield significantly different spectra in the presence of rotor winding damage. Thus, the ongoing research investigates the influence of the frequency converter on the stator current spectra of induction motors during their startup.
Materials and methods. The study of the operation of AIR71A6 type induction motor integrated into a frequency-controlled drive has been carried out on an experimental stand. A Vesper E4‑8400‑010H frequency converter has been employed as the frequency control unit. To capture the stator current signal, an ENMU device has been utilized. The acquired signals have been transmitted to a laptop via a media converter. To validate the results, the motor’s rotational speed has been simultaneously recorded using an encoder.
Results. Time‑frequency spectra of stator current signals have been obtained for various frequency converter settings. It has been found that the higher the voltage, the closer the harmonic frequency from the fictitious rotor winding is to the fundamental harmonic of the signal during startup. Also, it has been established that the rate of frequency increase at the converter output, depending on the U(f) curve setting, can significantly affect the physical configuration of the spectrum of the induction motor. Harmonics from the fictitious rotor winding appear only in the presence of rotor winding damage, regardless of the frequency converter setting.
Conclusions. The obtained results must be taken into account both during implementation and development of new methods to diagnose the condition of the induction motor rotor winding.