The formal commissioning Jindongnan-Nanyang-Jingmen UHV demonstration project identifies that the construction of special high-voltage power grid has entered a rapid development stage, but the increase of UHV two system time constant makes the CT become tailing phenomenon can not be ignored. On the one hand, it puts forward a new problem for the selection of UHV circuit breaker CT current transformer, namely selecting only the TPY secondary will deteriorate further CT tailing phenomenon and selecting the P secondary will increase the cost. On the other hand, CT trailing influences breaker failure protection, making it unable to right action. In view of this situation, it studies the failure protection under the wiring mode of 3/2 breaker in UHV and proposes an improved scheme. The contrast analysis, simulation and RTDS experimental results prove that the modified scheme is feasible, which can both effectively solve the problems of the selection of UHV circuit breaker CT current transformer and CT tailing hazard failure protection.