Method for determining whether secondary circuit of current transformer is left open-circuited and corresponding determining apparatus

The invention relates to a method for determining whether a secondary circuit of a current transformer is left open-circuited and a corresponding determining apparatus. The determining method acquires analog quantities of protection coils and measurement coils through a combination unit, and determines whether the secondary circuit of the current transformer is left open-circuited. The determining method includes the following steps: determining whether the combination unit is operating normally; acquiring the analog quantities of the protection coils and the measurement coils; determining whether a power grid is operating normally and whether the combination unit has been connected at the same time to secondary sampling circuits of the protection coils and the measurement coils of the current transformer; determining whether the secondary circuit of the current transformer is left open-circuited by respectively comparing the A, B, C phase sampling values of the protection coils with corresponding A, B, C phase sampling values of the measurement coils. According to the invention, the problem that the cut-off of the secondary circuit of the current transformer under light load often fails to be noticed in time can be effectively addressed, and the determination of the open circuit status in the secondary circuit of the current transformer in a more sensitive and effective manner can be achieved.