A new approach to analysis of inter-turns faults of three-phase induction motors

During practical operation of 3 - phase induction motors in industry, some internal faults occur in their stator windings. For instance, the short - circuit between stator winding coils (inter - turns) of any phase, the carelessly inverted - connection of one phase and short circuit between two phases are all the common problems of internal faults. These kinds of faults will make serious influence on the operation of the motor. Among these faults, it is most serious when the inter - turns of stator winding are short - circuited due to some reason, say, the insulation of individual turns is deteriorated. Zhang Linzheng and other colleagues have presented an analytical method of internal faults of 3 - phase induction motors and it was published in "Proceedings of the International Conference on Electric Machines "1995, in which by running the FORTRAN program on a personal computer all the characteristics and parameters can be known when a fault happens, but there are some deviations between the simulation results and experimental data. In order to improve the internal - fault simulation of 3 - phase induction motors, we present this paper. The basic idea we have developed in this paper is the "Bi-directional Revolving Magnetic Fields" concept, i.e. each coil carrying AC current will produce pulsating MMF that can be decomposed into two opposite - directional revolving MMF's and then synthesize the effects of all coil MMF's according to actual inner - faults to take the place of Symmetrical Components Method to solve internal faults of induction motors. In addition, the motor parameters are influenced by internal faults, for example, the slot leakage reactances, even if referred to the same number of turns, are still unequal, and the same is true of the resistances, which has been considered in this paper. On the basis of those ideas, a new mathematical model and corresponding computation program have been built, and the simulation results have also been gotten. The simulation results are quite approximate to the measured data. This analysis method is accurate enough and simpler than other methods, such as multi - loop method.