Abstract: Bus external fault where is close to the bus, often leads to the extreme fast saturation of TA. That may cause the bus mal-operation. In order to solve this problem, a new TA saturation blocking and reopening scheme, on basis of superimposed distance protection（SDP） was proposed. And a new criterion for bus protection reopening was proposed in the paper. Theoretical analysis and simulation results show that the proposed blocking criterion can clearly distinguish internal faults, external faults and TA saturation from each other. Even the TA is super-fast deep saturated, the locking criterion can rapidly and reliably block bus protection. When an evolved fault happens, the reopening criterion can rapidly relieve blocking signal so that the fault can be quickly removed.