Two new approaches to analysis of inner-fault of squirrel-cage rotor for three-phase induction motors

The paper details two new methods for analyzing inner-fault of squirrel-cage rotor for three-phase induction motors. The basic ideas of the first method we have developed in this paper are the "bi-directional revolving magnetic fields" concept and the superposition theorem. According to the procedures of the first method, we calculate the additional stator currents respectively at frequency f₁ and (1-2s)f₁, which are caused by breaking one rotor-bar. Then those stator currents are added to the original stator currents in the healthy case so as to form the total fault stator currents during the inner-fault of a squirrel-cage rotor. For the second method, based on the hybrid system of 1,2,0 axes and d,q, 0 axes, we find out the ratio between the amplitude of the stator current at frequency (1-2s)f₁ and that at frequency f₁. On the basis of these ideas, the mathematical models of these two new methods have been built. The simulation and experimental results have also been obtained and compared