Abstract: Aiming at the problem that traditional differential protection of transformers cannot operate in the case of early faults such as winding deformation and slight inter-turn short circuit, this paper proposed a novel early fault protection strategy for transformers based on the transformer multi-operating state model. Firstly, the state space equation of three-phase three-column transformer was established under normal operation, various out-of-area faults, and the no-loaded closing conditions, and the discrete iteration method was used to solve the state equations. The predicted current waveform of the model and the measured current waveform were converted to a grayscale image. The optimal segmentation value of foreground and background of the picture was calculated. The difference was obtained and compared with the protection threshold. A new solution for early winding fault protection of transformers was formed. In this scheme, only the voltage and current of the transformer port can be collected to detect the transformer winding deformation and minor inter-turn faults sensitively, without adding additional sensors. Finally, the effectiveness of the scheme was verified by simulation and dynamic model experiments.