1.NARI Group Corporation (State Grid Electric Power Research Institute), Nanjing 211106, China;2.State Key Laboratory of Smart Grid Protection and Control, Nanjing 211106, China

Since large-scale renewable energy and power electronic equipment accessing grids, as well as AC and DC hybrid connection, the dynamic characteristics of power systems become more complicated. Based on the quantitative ability of transient stability using extended equal area criterion (EEAC), the mechanism of the influence of discrete control time such as fault clearing time and generator-tripping time on the transient angle stability margin is analyzed in this paper. Transient angle stability margin is represented by the area on the extended phase plane (P-δ), which is composed of the unbalanced power and power angle of the dominant image. It not only shows clear geometric relationship, but also has clear physical meaning. Therefore, the impact of the control time on transient angle stability margin can be decomposed into P-axis and δ-axis effects of the control variable. For non-Hamiltonian system, some phenomena inconsistent with the previous cognitions may exist. The above analysis is verified by several practical examples.