MODELING OF POLYPHASE BRUSHLESS EXCITER BEHAVIOR FOR FAILING DIODE OPERATION

This paper describes an original numerical method for modeling the rec tified polyphase salient pole synchronous machines which are commonly utilized for large turbo-generator brushless excitation systems. Simul ating this kind of systems under normal and especially abnormal operat ing conditions, would be of great help for designers and operators in order to improve their reliability and availability. The proposed meth od is especially convenient to represent actual machines without almos t any restrictive assumption. It makes possible the evaluation of the stress of semi-conductors when diode failures occur. Results show that good operation of the exciter with short-circuited diodes is almost i mpossible since its output voltage and current are noticeably weakened . However, its operation can be acceptably maintained if one or more d iodes are open.