Analytical on-line method of determining transient stability margin using protection information for asymmetric faults

The transient stability margin is affected by different fault locations, fault clearing time and fault types that could be provided by protection information. This study presents an analytical on-line method of determining transient stability margin quantitatively using protection information for multi-generator system. First, the multi-machine system is equivalent to a one-machine infinity-bus system with the help of complementary cluster centre of inertia-relative motion. Second, the asymmetric fault models are built using positive rule, and the transient stability margin is then deduced by modelling the piecewise models of generator angles. Third, the practical transient stability margin assessment algorithm is then obtained. The sensitivity and affection mechanism of stability margin affected by fault factors are further derived, and the analytical stability margin is put forward to online access the transient stability margin after fault with the acquisition of the protection information. Finally, four-generator system, New England system and a real large power grid are used as test systems to verify the effectiveness and accuracy of the proposed method.