Research On Stator Winding Interturn Short Circuit Faults Diagnosis Of Induction Motor

Induction motors are important drive equipments widely used in industrial and agricultural production. With the rapid development of modern industrial system, the capacity of a single motor keeps increasing and the load also becomes more complicated. The motor failures would not only result in damage to the motor, but also result in unscheduled machine downtime and the shutdown of a production line, which will cause huge financial losses. Statistical studies have shown that the stator winding interturn short circuit fault, which accounts for nearly 15% of total failures, is the most frequent fault for induction motors. Consequently, it's of significant social and economic benefits to do the research on the stator fault diagnosis technology which can detect stator fault at an incipient stage and also allow for carefully planed repair actions.Through the theoretical analysis and finite-element simulation, this paper mainly focuses on the diagnostic method of stator winding interturn short circuit fault in induction motors. Based on the analysis of some parameters which are sensitive to the stator asymmetry, such as zero sequence voltage, feature impedance, several effective methods are proposed.As the residual voltage in the stator winding after motor switch-off avoids the influence of supply, its fundamental zero sequence component could reflect the asymmetry of the stator directly. A diagnostic method based on the residual voltage after switch off is presented in this paper. Using the superiority of Hilbert-Huang Transformation in the non-steady signal analysis, the fundamental zero sequence voltage after switch off is extracted by empirical mode decomposition (EMD). For the sake of reducing the ending effect of EMD, the mirror extending approach is adopted in the signal process. The ratio between fundamental zero sequence voltage and corresponding phase voltage after switch-off is selected as the stator fault feature, that eliminate the influence of different load level effectively, has an impressive diagnosis precision.Online diagnostic method of stator fault based on the zero sequence voltage is researched. Through the analysis of the magnetic motive force (MMF) in the induction motor with the interturn short circuit fault, a conclusion is drawn that fundamental zero sequence voltage mainly comes from the three times harmonic MMF produced by the current in the short circuit cycle and asymmetrical windings. The equivalent supply voltage is defined for analyzing the influence on zero sequence voltage by the positive and negative sequence components respectively. The equivalent supply voltage is separated into positive and negative sequence voltage by use of the characteristic of Hilbert transform. Then, through detecting the relationship between the zero sequence voltage and other sequence voltage and load, a fault feature, which removes the influence of supply and load, is defined. And a method of online diagnostics on stator faults is presented.The applications of multiple reference frames theory in the motor fault diagnosis are discussed. The positive sequence voltage and their Hilbert transformation substituted for the elements of synchronous reference frame matrix, and the improved synchronous reference frame method is proposed. The current could be decomposed to positive and negative sequence components by the improved synchronous reference frame exactly. Based on these results, characteristic impedance and negative sequence current are used to diagnose the stator fault. The robust feature impedance is selected to detect the fault of unbalanced supply, and the negative sequence current is used for detecting the condition that the supply is balanced. Through the comparison between the actual data and the thresholds, the diagnosis can be achieved.The experimental results demonstrate the effectiveness and great engineering value of stator fault diagnosis techniques proposed in this paper.