Method and apparatus to detect and isolate faults in rotary machines

An off-line method for fault detection and isolation in a rotary machine having a rotor and at least two stator windings, the rotary machine having a number of pole pairs, the method comprising the steps of:

• (a) generating, with a signal generator, an input signal and applying the input signal to a stator winding or a set of stator windings of the rotary machine while the rotor is locked at a rotor position;
• (b) measuring a current and a voltage, with an ADC and a computing and control unit, from the stator winding or the set of stator windings while the rotor is locked at the rotor position;
• (c) applying Fourier transform, with the computing and control unit, to the current and the voltage to obtain a frequency response of the stator winding or the set of stator windings at the rotor position;
• (d) rotating the rotor to a new rotor position by a rotation angle and locking the rotor at the new rotor position;
• (e) repeating the method from step (a)-(c) to obtain a new frequency response at the new rotor position;
• (f) repeating the method from step (d)-(e) till the rotor is rotated for at least a complete cycle to obtain a frequency response function of the rotation angle;
• (g) applying Fourier transform, with the computing and control unit, to the frequency response function to obtain a two-dimension frequency response in terms of a frequency and a spatial frequency;
• (h) comparing, with the computing and control unit, a magnitude or a phase difference between the two-dimension frequency response and a reference two-dimension frequency response;
• (i) determining, with the computing and control unit, that there is a fault in the rotary machine if the magnitude or the phase difference exceeds a threshold number;
• (j) repeating the method from step (a)-(i) for all stator windings or all sets of stator windings.