Type I: (
a) power-angle relation of
PE versus
δ, (
b) stability index for different clearing times showing a bipartite behaviour and (
c) time-series diagrams. In (
a), the red (blue) area A (B) denotes acceleration (deceleration) energy. Based on the EAC, we get the critical clearing angle
and the corresponding CCT ≈ 0.136, as shown in (
b), where if the fault clearing time is less than the CCT, the system could be stable, indicated by 0, or otherwise, indicated by 1. In (
c), numerical results for two different clearing times (higher or lower than the CCT) prove this point well. The parameters here are:
Pm = 0.65 and
Pd = 0.6. The other two key parameters,
Pb and
Pp, are fixed throughout the paper:
Pb = 1.3 and
Pp = 0.8. The critical conditions obtained in the paper for various patterns of CCT should be carefully examined by moving the position of
δc. In addition, we use solid grey lines in (
a) for these critical conditions from analyses, where the definitions of
α and
β are in equations (3.4) and (3.8).