An analysis of the relationship between induction motor current and shaft speed fluctuations
For induction motors, motor shaft speed variations accompany motor load torque variations and motor torque variations. Hence, shaft speed fluctuation detection can serve as a warning of undesirable motor load conditions. This paper presents a theoretical foundation for the relationship between motor shaft speed fluctuations and stator current fluctuations when the shaft speed is perturbed by any cause. In addition, it shows that amplitude and frequency demodulation of motor current enhance the observed current fluctuations. The equations presented herein are derived in an as-yet unpublished work. Differential equations and basic electromagnetic equations, rather than phasors, are emphasized in their derivation. Fourier spectra of motor current, amplitude-demodulated motor current, and frequency-demodulated motor current are given for motor shaft speed modulated simultaneously with 13- and 17-Hz perturbations. We conclude that frequency demodulation is potentially a much better method to detect shaft speed fluctuations than is amplitude demodulation but that better methods of frequency demodulation are needed. The best presently available methods of frequency demodulation alias interference lines down into the spectra of interest below 60 Hz. There, they mask the valid spectral lines.
- Research Organization:
- Oak Ridge National Lab., TN (United States)
- Sponsoring Organization:
- DOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 5761759
- Report Number(s):
- CONF-920474-1; ON: DE92007234
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
426000* -- Engineering-- Components
Electron Devices & Circuits-- (1990-)
99 GENERAL AND MISCELLANEOUS
990200 -- Mathematics & Computers
ANALYTICAL SOLUTION
ANGULAR VELOCITY
ELECTRIC MOTORS
FAILURES
FOURIER ANALYSIS
FREQUENCY MODULATION
INDUCTION
MACHINE PARTS
MODULATION
MONITORING
MOTION
MOTORS
ROTATION
SHAFTS
STATORS
TORQUE
VELOCITY