An Analytical Method of Determining Transient Stability Margin Considering Unbalanced Fault Factors

Maintaining the transient stability of the power system is very important for the stable and safe operating. This paper presents an analytical method of determining transient stability margin quantitatively using protection information for multi-generator system. First, the additional impedance of unbalanced fault is calculated by positive sequence equivalent rule. Based on the complementary cluster center of inertia-relative motion, the multi-machine system is equivalent to a one-machine infinity-bus system. Then, through the piecewise models of generator angles, the analytical expression of the equivalent fault clearing angle and the transient stability margin are obtained. Furthermore, the analytical stability margin is put forward to quantize the transient stability after fault occurred with the acquisition of the protection information, and the effects of fault location and fault clearing time on the stability margin under unbalanced faults are analyzed. Finally, four- machine two-area system is used as test system to investigate the effectiveness and accuracy of the proposed method.