UNITROL5000 digital excitation system developed by ABB was adopted in two 660 MW generating units of Jingdezhen Power Plant. It was studied and maintained as one of the most important electrical equipment by the Power Plant. The composition principles and device structure of the excitation system was briefly described by this article
several critical fault and failure cases of this excitation system was analyzed. Useful experience was provided to improve the security and stability of the excitation system in future.