High-Frequency Analysis and Measurement Techniques with Mixed-Mode Conversion of Induction Machine for Shaft-Voltage Prediction

This paper shows high-frequency measurement techniques including phase windings and shaft-ends of a three-phase electrical machine rotating at its rated-rpm, and mixed-mode conversion method for impedance parameters. For the purpose, an external torque source mechanically drives the induction machine, while measuring phase windings and shaft-ends with a vector network analyzer. To investigate common-mode, differential-mode, and inter-phase differential-mode components of drive signals with each shaft-end, we converted the measured impedance parameters to mixed-mode impedance parameters. To verify the converted results, transfer impedances between shaft ends and common-mode component of the mixed-mode parameters are compared with time-domain shaft voltage waveforms that are generated by sinusoidal CM input signals of different frequencies. The comparison showed the mixed-mode impedance parameters match the time-domain waveforms. Also, the mixed-mode parameters showed that common- and differential-mode are more responsible for shaft end-to-end voltage, while common-mode and inter-phase differential-mode are more responsible for shaft-to-frame voltage, for the induction machine. Also, frequency ranges of each mode over which each voltage are more susceptible are specified from the results.