The backup protection of UHV large capacity transformers consisted of three single phase transformers is studied. The overreach permissive type and the overreach blocking type impedance pilot protection scheme, used as backup protection of these transformers is proposed. The feasibility and superiority of the proposed scheme are proved. Such impedance protections are less affected by magnetizing inrush currents and the correctness of the conclusion is testified by digital simulations. The simulation model of UHV transformer is established. Simulation results prove that the magnetizing inrush current caused by transformer no-load switching and external fault clearing will not make the impedance protection maloperation, while the fault can be cleared fast at interphase short-circuit of transformer exit. The proposed protection scheme can improve the reliability of protection of large capacity UHV transformers.