Abstract: The defect of 220 kV Ⅲ/Ⅳbus bar longitudinal differential protection and Ⅲbus bar line protection CVT line broken is studied in this article.The site inspection is ordered.The fault point is analyzed based on the secondary loop drawings and protection instructions.Then the best safety measure request is put forward according to the regulations and standards. Based on this, the information reporting process of "two reports" in improved, the inspection for CVT abnormal conditions is ordered, and the special emergency disposal card is made.