We proposed an online fault diagnosis method for solving the fault of straight-through switch in the segment-powered linear induction motor.By analyzing the characteristics of the structure of the segmented-power supply system

the characteristic impedance was calculated by using the envelope of ABC three-phase voltage and current

and the relationship between the characteristic and the power supply frequency was studied by the method of linear regression.Meanwhile

the distribution law of the regression equation error was studied by the method of statistical analysis

and the fault criterion was obtained.According to the variance of the driving pulse signal to the regression equation

the fault location was realized.The method was verified by the experiments finally.The results show that the characteristic impedance calculated according to ABC three-phase voltage and current envelope can approximate to linear with the power supply frequency

and this relationship will cause obvious change when direct through faults arise.This rule can be used for diagnosis and orientation for direct through faults.