Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Patent
1987-08-31
1988-08-02
Paschall, M. H.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
361 31, 361 78, 318798, 318806, H02H 708
Patent
active
047617039
ABSTRACT:
A method and apparatus for detecting rotor faults in an induction motor. A flux sensor generates a flux signal corresponding to the magnetic flux at a predefined flux detection point external to the motor. A current sensor generates a current signal proportional to the current drawn by said motor. A time series of data points is stored, representing the values of the flux signal and the current signal over a period of time. The time series are transformed by FFT into a set of flux spectra and into a set of current spectra. Then the line frequency of the motor's power supply is determined by finding the maximum of the current spectra. Similarly, the slip frequency of the motor is determined by finding the maximum of the flux spectra in a predefined spectral range (e.g., below 2 Hz). The analysis of the rotor is then performed by comparing the amplitude of the current spectra, at a set of rotor fault harmonic frequencies, with specified fault threshold criteria. Each rotor fault harmonic frequency is a predefined function of the line frequency and the slip frequency. The presence of a rotor fault is denoted if the amplitude of any of said current spectra exceed a corresponding fault threshold criteria.
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Grabkowski Stephen E.
Kliman Gerald B.
Koegl Rudolph A. A.
Schulz, Jr. Max W.
Electric Power Research Institute Inc.
Paschall M. H.
Wysocki A. Jonathan
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