In this paper

both open and short circuit of the rotating diodes in brushless synchronous excitation machines with rotating diode phase compound excitation are is analyzed in detail. The diesel generation unit of my company is selected to study. The principle of its rotating diodes monitoring circuit is investigated. The diode in the monitoring circuit can send a delayed signal when open

and disconnect the generator from system at once for protection when short. The performance of the monitoring circuit is illuminated and discussed briefly at the end of this paper.