CT Disconnection Identification of 3/2 Bus Differential Protection Based on Phase Current and Zero Sequence Current Variation Characteristics

Considering that the traditional 3/2 bus differential protection uses a single current measurement to detect CT circuit breakage, which is insufficient to handle complex fault scenarios, this paper proposes a more comprehensive strategy for CT circuit breakage detection. First, the current variation characteristics during CT circuit breakage and bus short-circuit faults are analyzed. Then, a CT circuit breakage detection criterion based on the abrupt changes in phase current and zero-sequence current is introduced, along with a bus short-circuit fault detection criterion. The paper also presents the logic for blocking the bus differential protection during CT circuit breakage and opening the protection during faults. Finally, the effectiveness of the proposed protection criteria under complex fault conditions is analyzed. Experimental results show that the proposed criteria can reliably detect CT circuit breakage and short-circuit faults under typical conditions, and can also ensure correct protection locking and unlocking during complex faults, such as CT circuit breakage combined with ground short-circuits.