Brushless Three-Phase Synchronous Generator Under Rotating Diode Failure Conditions

In brushless excitation systems, the rotating diodes can experience open- or short-circuits. For a three-phase synchronous generator under no-load, we present theoretical development of effects of diode failures on machine output voltage. Thereby, we expect the spectral response faced with each fault condition, and we propose an original algorithm for state monitoring of rotating diodes. Moreover, given experimental observations of the spectral behavior of stray flux, we propose an alternative technique. Laboratory tests have proven the effectiveness of the proposed methods for detection of fault diodes, even when the generator has been fully loaded. However, their ability to distinguish between cases of diodes interrupted and short-circuited, has been limited to the no-load condition, and certain loads of specific natures.

1. Nomenclature

Instantaneous angle of the rectifier input voltage.

Fourier series coefficient.

Additional phase shifting due to short-circuit condition.

emf induced in stator phase under no-load condition.

Normalized amplitude of the frequency .

Maximal amplitude related to the harmonic of .

harmonic of fundamental frequency

Instantaneous excitation coil current.

DC component of the excitation coil current.

Ratio of characteristic defect frequencies .

Inductance of the excitation coil.

Mutual inductance linking excitation coil and phase .

Maximal amplitude related to the harmonic of .

Mechanical speed.

Fundamental frequency of the rectifier input voltage.

Prevailing sideband components under intact bridge.

Sideband frequencies.

Fundamental frequency of the main output voltage.

Number of pair–poles related to the exciter.

Number of pair–poles related to the main generator.

Phase shifting related to the excitation coil current.

Permanent flux embraced by stator phase .

Resistance of the excitation coil.

Maximal amplitude related to the frequency .

Maximal line to line input voltage of the rectifier bridge.

Instantaneous output voltage of the rectifier bridge.

rectifier input voltage.

Amplitudes ratio related to sidebands .