In order to guarantee that no whole transformer substation power outage will occur but partial load is certain to run when the bus coupler dead-zone goes faulty in the double bus operation mode，the differential protection of both the bus and the bus coupler dead-zone is studied.The existing bus protection scheme is improved so that it will act correctly during bus fault.Even though fault should occur in the bus dead-zone，it can still correctly disconnect the bus coupler breaker and the related bus.Finally，by estimating the action time of the bus coupler breaker，the feasibility of the scheme is proved.