Table 1 shows the average components at (1 ± 2 s) f Hz. In each fault, the components at 50 - 6.67 Hz, that is, (1 - 2 s) f Hz, are approximately the same as those at 50 + 6.67 Hz, that is, (1 + 2 s) f Hz. This speed vibration and the forward current produce a stator current frequency of (1 - s) f ± 2 sf + sf = (1 ± 2 s) f. The torque produces a vibration of 2 sf, and thus, the rotor speed becomes (1 - s) f ± 2 sf. Then, a torque with a frequency of 2 sf is developed because the stator current has two frequencies f and (1 - 2 s) f. In contrast, the backward current frequency of - sf is considered as a stator frequency of (1 - 2 s) f because - sf + (1 - s) f = (1 - 2 s) f. Because the rotor is running at (1 - s) f, the frequency recognized at the stator is sf + (1 - s) f = f. The forward current frequency sf in the rotor is considered as frequency f at the stator. If the rotor has a defect, such as a broken bar or broken end ring, a backward current frequency of - sf can flow in the rotor. When the rotor is running at slip s and the supply frequency is f, the frequency of the forward current in the rotor is sf. Let us explain the frequency of (1 ± 2 s) f Hz. We found 50 ± 6.67 Hz components, that is, (1 ± 2 s) f Hz as expected. Therefore, three sets of measured results were slightly different. To take this slight difference into account, the experimental system was set up for every measurement. We expected a slight difference in the mechanical loss because the connection of the motor, the torque meter, and the servo motor could not be perfect even under the same situation. However, because the measured results are sensitive to the experimental setup, the experiment was performed three times. Therefore, the effect of the inverter source and the load equipment on this measurement was very small. Because the servo motor is a synchronous motor with surface permanent magnets, the torque ripple is very small. Therefore, the Fourier analysis of the stator voltage did not include the (1 ± 2 s) f Hz components, where s is the slip and f is the fundamental supply frequency. 3, the inverter rating is 1.1 kVA, which is a sufficient capacity for the 400-W experimental induction motor. Moreover, the stator voltage and current waveforms in a transient response are analyzed by the wavelet analysis.įourier analysis of the measured stator current at the rated speed. The electromagnetic field in the rotor is analyzed to clarify the effect of the number of broken bars and broken end ring segments on the motor performance. Next, the difference between the broken end ring segments and broken bars is verified by MCSA. First, we manufacture some rotors with broken bars or end rings. This chapter addresses not only broken bar but also broken end ring faults. They dealt with broken rotor bars but not a broken end ring. analyzed the stator current under different numbers of broken bars and different loads of an induction motor. analyzed the flux distribution in the air gap of an induction motor with one and two broken rotor bars. studied the broken rotor bar and stator faults using FE and discrete wavelet analyses.

Concerning the FE analysis of rotor failures in induction motors, several papers have been presented. dealt with the fault diagnosis of induction machines with broken rotor bars and end ring segment and loss of stator phase during operation using DWT. However, most of the literature has studied only broken-bar faults, and broken end ring faults have been marginally dealt with. carried out diagnosis of induction machines using DWT under a time-varying condition. proposed a time-scale method based on DWT to make the broken-bar fault diagnosis slip independent. proposed a method based on the identification of characteristic patterns introduced by fault components in the wavelet signals obtained from the discrete wavelet transformation of transient stator currents. developed an automatic online diagnosis algorithm for broken-rotor-bar detection, which was optimized for single low-cost field-programmable gate array implementation. proposed a method to diagnose rotor bar failures in induction machines based on the analysis of the stator current during start-up using the discrete wavelet transform (DWT). Several studies have carried out diagnosis of induction machines using motor current signature analysis (MCSA). Induction motor faults are summarized in and, and rotor failures account for approximately 10% of the total induction motor failures. Therefore, early detection of motor faults is highly desirable. However, production will stop if these motors fail. Squirrel-cage induction motors are widely used in many industrial applications because they are cost effective and mechanically robust.

Squirrel cage