Abstract:The backup automatic switch device is an effective means to improve the power supply reliability and ensure the continuity of power supply in power system. It is mainly used in substations of 110kV and below voltage level. Substation backup automatic switch devices with conventional bridge connection, single-parent-double (multiple) segment connection and the same capacity transformers are relatively simple in logic and easy to design in function. However, the transformer capacities in some old substations are not uniform, and the connection mode is special, which results in that the conventional operation logic of backup automatic switch cannot be applied. Therefore, more factors must be considered in the design of substation backup automatic switch with different transformer capacities and special connection modes, and the logic is more complex. This paper analyses the design principle of 10kV backup automatic switch in special connected substations, and makes a logical analysis of 10kV backup automatic switch under different operating modes, which provides reference for the logical design of 10kV backup automatic switch.