Abstract: On June 26, 2022, a bus voltage unbalance incident occurred in the 35 kV I-phase bus of a certain 220 kV substation. Investigation revealed that the neutral point of the transformer's low-voltage winding was not grounded, resulting in capacitive imbalane in the transformer. Additionally, the C-phase fuse of the 35 kV I-phase bus was blown, leading to bus voltage unbalance. This paper analyzes the issues, summarizes the problems in on-site operations and scheduling, and provides recommendations for reference by operation and maintenance personnel.