Abstract: When a serious internal fault occurs in a power transformer, serious consequences such as explosion and combustion may occur. Conventional current-based protection schemes often fail to meet the rapid response requirements for preventing such explosion accidents. To address this issue, this article proposes an ultra-fast and sensitive transformer differential tripping principle. By utilizing the post-fault time-domain characteristics of the sampling values, a one-point starting method and an absolute-value integration method for the sampling value variation are designed. The former is based on the time difference characteristics of ferromagnetic saturation, utilizing the time difference characteristics of voltage and current sampling values at the moment of change, and can achieve inrush current identification and locking at the startup point. The latter achieves ultra-high sensitivity start-up and fault tripping, guarantees operation within 3ms, and maintains exceptional sensitivity even under low-magnitude fault conditions. A simulation system for converter transformers based on hardware-looped dynamic simulation physics platform is built, and the operation of the new protection principle under different fault scenarios is simulated to verifying its feasibility and superiority. It can be seen that this protection principle can significantly improve the action speed of transformer differential tripping protection and effectively reduce the risk of explosion accidents.