Newtonian Mechanics Based Transient Stability PART IV: Equivalent Machine

This paper analyzes the mechanisms of the equivalent machine and also its advantages in TSA. Based on the two group separations, an equivalent machine is modeled through the equivalence of the motions of all machines inside each group. This "motion equivalence" fully ensures the modeling of the two-machine system and the corresponding Newtonian energy conversion. Against this background, the original system becomes the equivalent system. It is clarified that the equivalent machine strictly follows the machine paradigms. These strict followings bring the two advantages in the equivalent-machine based TSA: (i) the stability of the equivalent machine is characterized precisely, and (ii) the equivalent-machine trajectory variance is depicted clearly. The two advantages are fully reflected in the precise definitions of the equivalent-machine based transient stability concepts. In particular, the equivalent machine swing is clearly depicted through the EDSP or EDLP of the machine, and the critical stability of the equivalent system is strictly defined as the critical stability of the equivalent machine. Simulation results show that the effectiveness of the equivalent-machine in TSA.