Detection of brushless exciter rotating diodes failures by spectral analysis of main output voltage

Rotating rectifier is a basic part of synchronous generators. Inappropriate operation of this component can prove costly for the machine's owner. This paper presents theoretical analysis and experimental validation for detecting failure of brushless exciter rotating diodes that can fail either open circuit or short circuit. Harmonic analysis of the alternator output voltage waveform is performed when machine is unloaded as well as when it runs around its rated load. Apparition of characteristic frequencies can be useful to distinguish the rotating diodes state. By considering the relative amplitudes at specific harmonics, it is possible to discriminate short circuit diode failure case from open circuit diode breakdown.