Investigation of power swing phenomenon and verification of critical clearing time through theoretical calculations and simulated studies

Power swing or transient stability commonly pose serious threat to the power system reliability. As such, the equal area criterion is used to identify the critical clearing time. However, the equal area criterion neglected the resistance in the power system and only considered pure reactance in the theoretical calculations. As a result, this paper will consider both the resistance and reactance present in the power system, in order to achieve a realistic transient stability study. A comparison in critical clearing time between the theoretical calculation and realistic simulation were conducted in this paper. It was found that neglecting the resistance in the theoretical assumptions will produce a conservative estimates for the critical clearing time. It was further demonstrated that a realistic power system with resistances can actually withstand a longer critical clearing time before the generator experiences out of step condition. In addition, this paper will also present the co-relation between the active power and rotor angle during a power swing event.