Abstract: The performance of ultra-high voltage（UHV） transformer differential protection based on harmonic restraining method is seriously influenced by harmonics and its operation time is long.Aiming to solve this problem,this paper presented a novel protective scheme based on equivalent circuit model of transformer for UHV three-phase divided tank transformer.This paper established a T-type equivalent circuit model of transformer with its parameters calculated on-time.This model is not affected by transformer’s operation states,and its parameters can be uniquely determined.It proposed a transformer protection criterion,which was based on the balanced transformer equivalent circuit model equation and the variation of instantaneously measured equivalent excitation inductance.With Matlab simulation tool,this paper established a model according to the parameters of the first UHV power transmission system in China,simulated such situations as energizing,external faults,internal faults,normal operation in the model,and testified the feasibility of the proposed transformer protection in UHV transmission systems.The performance of the protection scheme is not affected by inrush currents,and the protection can operate quickly and has high sensitivity.