Determining Critical Clearing Time Based on Critical Trajectory Method using Unbalance Fault

Transient stability has an essential role in the electric power system. When a disturbance occurs, the minimum protection relay will operate in about 0.22 seconds. However, this condition does not guarantee the system will return to steady state condition because of its Critical Clearing Time (CCT). If the fault is isolated before the value of CCT, the generator will return to stable. Otherwise, the generator becomes unstable if the fault is isolated after the value of CCT. This paper proposed the calculation of CCT on generators using an energy function method to determine the control of Unstable Equilibrium Point (CUEP) by considering unbalance fault. The result of this method has an allowable error in 0.0108% for the calculation in critical clearing time. Moreover, this method has faster calculation time than time domain simulation method with the difference in calculation time is 116.243 seconds.