Circuit breaker trip circuit (also known as control circuit) is the most important secondary circuit for relay protection. Among them, the “communication triple trip” (CTT) hard contact connected to the operation exit circuit of the protection device increases the complexity of the trip circuit and the difficulty of analyzing the trip circuit failure. When the system runs normally, the signal of “control circuit disconnection” cannot be accurately and timely uploaded to the operation monitoring background. When the system short-circuit fault occurs, the circuit breaker cannot operate correctly due to the trip circuit break, so the adjacent interval is connected by the near backup protection, thus causing the expansion of the accident scope. In this paper, it is proposed for the first time that the CTT hard contact protected by circuit breaker should be replaced by the soft CTT (i.e. the control word) of the protection device, so as to make the trip circuit reliable, clear and simple, and at the same time ensure the accuracy of the “control circuit break” signal.
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