Abstract: To solve the problem that the sensitivity of the starting element is limited by the data window, a bus protection starting element based on the sampling value of the three-phase current mutation at the same time is proposed. Started using differential current components and zero sequence current components for fast identification of faults in the area, adopt the mode of data pre-processing, bus current can be divided into two groups, using the grouping current construction starting criterion, accurate identification of busbar fault zone, at the same time, according to the start of domestic components action sequence criterion of current transformer saturation, greatly improves the sensitivity of bus start element, at the same time improve the reliability of busbar protection. RTDS is used to build the simulation system, and the simulation results verify the sensitivity and rapidity of the starting element。