Hybrid method of determining the transient stability margin of a power system

A hybrid method of determining the transient stability margin of a power system for a given fault clearing time is presented. The method combines the desirable features of the transient energy function method and the output results of the conventional time domain simulation method to find the stability margin, which in the present case is determined for only one of the machines in the system called the critical machine. The critical machine is considered to be the one that initially runs out of synchronism and it is identified by checking the variation of machine angles generated by the time domain simulation method. The stability margin obtained by the proposed method would be very useful for guiding the selection of fault clearing time in subsequent case studies by the time domain simulation method. The proposed method was successfully demonstrated on the 7-machine CIGRE system and 17-machine reduced Iowa system