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Spectral analysis of induction motor current to detect rotor faults with reduced false alarms

  • US 5,049,815 A
  • Filed: 08/27/1990
  • Issued: 09/17/1991
  • Est. Priority Date: 04/20/1990
  • Status: Expired due to Term
First Claim
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1. A method of detecting rotor faults in an induction motor, wherein the motor includes a rotor having a multiplicity of conductive bars and a stator drawing motor current from a power supply, the method comprising the steps of:

  • A. deriving a current signal indicative of said motor current;

    B. sampling said current signal at a predetermined sampling rate to obtain a time succession of current values over a predetermined sampling period;

    C. transferring said current values to a frequency spectrum;

    D. determining the fundamental frequency of said motor current from said frequency spectrum;

    E. scanning said frequency spectrum in a lower sideband of said fundamental frequency for current peaks exceeding a threshold amplitude;

    F. ascribing the frequency of each said current peak as a candidate indicating the slip frequency of the motor;

    G. checking predetermined harmonic sidebands of said frequency spectrum at frequencies predicted from each said slip frequency candidate for matching current peaks until all but one of said slip frequency candidates are disqualified; and

    H. conducting a rotor fault analysis of said frequency spectrum using the determined fundamental frequency and the qualified remaining one of said slip frequency candidates as the motor slip frequency.

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