Abstract: This paper takes the failure of the automatic bus transfer (ABT) device to operate during a fault in a 10 kV dual-switch cabinet and switching station as an example. A comprehensive analysis is conducted on the operation mode, charging/discharging logic, blocking conditions, protection setting values, fault recording data and event records of the device. The results show that the charging logic of the ABT device has significant defects, which creates a large protection blind zone. Corresponding improvement measures for the protection setting values are proposed accordingly.