The multi loop model of the independent end ring double squirrel cage motor with the skin effect was established by using the layered method and multiloop method in this paper.Based on the model,the time-frequency characteristics of the stator current in the starting process of the unloaded shearer uncovered in broken bars situations were investigated.The synchro extracting short-time Fourier transform was used to analyze of the time-frequency of the starting current.For broken bar identification,the amplitude-frequency angle was defined in the amplitude-frequency plane,and the time-frequency angle was defined in the time-frequency plane.The simulation results show that the amplitude-frequency angle can be used to distinguish whether the fault belongs to the upper cage or the lower cage,and the time-frequency angle can be used to roughly determine the number of broken bars.
