Transient Stability Assessment Using Individual Machine Equal Area Criterion PART III: Reference Machine

The analysis of the transient stability of a multimachine system via the use of a few machines is a promising technique for transient security assessment. This paper proposes a genuine nonglobal direct-time-domain method that is developed from the previous COI-reference-based IMEAC method. In this paper, the reference machine (RM) is chosen as a real machine that does not separate from the system after fault clearing. The key concept of this paper is to select the reference machine (RM) first and then replace the COI with the RM during the post-fault period in the transient security assessment. In this manner, the motions of all machines in the system are redefined in RM reference. Furthermore, it is found that the Kimbark curve of the RM-reference-based critical machine has a distinctive quasi-sinusoidal characteristic, and thus the curve is predictable after fault clearing. Following the individual-machine thinking, the stability analysis of the multimachine system is transformed into monitoring the stability state of a few RM-reference-based critical machines, which completely avoids the usage of COI. The simulation results show the effectiveness of the proposed method in the transient stability analysis of multimachine systems.