THE DECOMPOSITION OF SIGNAL OF ELECTROMOTIVE FORCE OF THE STATOR WINDINGS FOR DIAGNOSTICS OF BROKEN ROTOR BARS OF INDUCTION MOTORS

Development of induction motor broken rotor bars diagnostics method basing on the analysis of the electromotive force induced in stator windings after disconnecting the motor from the network is presented. Basing on the calculation of the magnetic field in an induction motor air gap, it is shown that informational features corresponding to magnetic field distortions caused by broken rotor bars are lost in the signal of the stator phase electromotive force. It was pro-posed to use a decomposition of electromotive force of the stator winding phase by electromotive force signals of coil active sides using z-transform theory, which allows extracting features of rotor bars damages, which is impossible to detect analyzing phase electromotive signal. Wavelet analysis of the extracted electromotive force of one active coil side allows increasing the reliability of induction motor rotor bars fault detection. Using decomposition of the diagnostic signal, which is the sum of wavelet expansion of the stator phase electromotive force, makes it possible to simplify extraction of the rotor bars faults features. The effectiveness of the proposed diagnostic method is confirmed by exper-iments.