Diode Open-Circuit Fault Detection for Rotating Rectifiers of Brushless Exciters

The rotating rectifier represents a vulnerable link within the brushless excitation generator and is prone to diode open-circuit faults. A multi-diode fault will lead to significant fluctuations in the generator's excitation current, thereby inducing power oscillations in the unit. Investigating the characteristics and detection approaches of open-circuit diode faults is of great significance. In this study, a typical brushless exciter is taken as an example for examination. First, an analysis is conducted on the diode conduction behavior of the rotating rectifier in the exciter. According to the variations in the air-gap magnetic field of the exciter under normal and single-diode open circuit conditions of the rotating rectifier, it is observed that the fault might introduce fractional harmonics into the air-gap magnetic field. Based on the structural characteristics of the exciter stator and the spillover effect of the main magnetic field, a U-shaped iron core wound with coils is placed in the vicinity of the stator shell to achieve magnetic flux diversion and signal collection. The diode open-circuit fault is identified by the variations in harmonic components of the voltage induced in the coil. Subsequently, a two-dimensional finite element simulation model for a 5.8 MW three-phase brushless exciter is established. A three-phase, 14-pole brushless exciter and a rotating rectifier experimental platform were built for method validation. The results indicate that the induced voltage in the U-shaped core coil can effectively reflect the characteristics of diode open-circuit faults. This method is applicable to the online diagnosis of diode open-circuit faults in brushless exciters, enabling non-invasive detection, reducing the complexity of sensor installation, and exhibiting significant advantages in terms of high convenience and low risk.