Abstract: All current and voltage sampling data of 220 kV smart substation are obtained by merging unit. Once the merging unit is abnormal, protection misoperation and rejection will be caused. In this paper, a protection false action caused by abnormal large number of merging unit on voltage side of 220 kV main transformer protection is analyzed. The test shows that abnormal large number of double AD is caused by single event upset of logical array block (LAB) failing which Including logic element of Different AD chips. And three corrective measures are proposed, which are optimizing logic element distribution, dual sampling components, increasing redundant processing and anomaly detection.