There encountered repeated electrical failures such as burning-up of closing coil or contact adhesion of closing relay with respect to a 6 kV switch in an actual plant owing to mechanism inaction or sticking,etc.This paper analyzes the reasons for closing coil burning-up or closing relay contact adhesion by clarifying the principle of the secondary closing con-trol circuit of the 6 kV switch.It then proposes and designs a retrofit scheme of adding time relay to the closing circuit to realize the function of delayed block.
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