Diode Monitoring by Field Winding Axial Stray Flux in Brushless Synchronous Machines

Brushless excitation system is one of the most used, mainly due to the reduced maintenance, thanks to the absence of slip rings and brushes. The field current of the synchronous machine is supplied by a rotating diode bridge, which is fed from an auxiliary machine called exciter. The ripple of the field current is produced by the diodes. It has a dominant frequency which depends on the diode bridge pulses and the rated frequency of the exciter. This operation conditions can be dangerous for the exciter in case of long-time operation. In this paper the supervision of the rotating diodes is performed through the analysis of the axial stray flux of the field windings. Numerous experimental tests have been carried out in a brushless synchronous machine at healthy conditions and with one open diode with satisfactory results.