Factors affecting transient stability

Transient stability is the ability of a system to remain in synchronism after a large sudden disturbance. From the swing equation $\frac{2H}{\omega_s}\frac{d^2\delta}{dt^2} = P_m - P_{max}\sin\delta$ and the equal area criterion, it depends on how much the rotor accelerates during the fault and how much decelerating power is available afterwards. The main factors are:

1. Pre-fault loading: heavier loading means a larger initial angle $\delta_0$ and less margin.
2. Type of fault: 3-phase faults are most severe, then LLG, LL and LG.
3. Location of fault: a fault near the generator reduces power transfer to almost zero.
4. Fault clearing time: the longer the fault stays, the larger the accelerating area; clearing must be faster than the critical clearing time.
5. Network reactance during and after the fault: higher post-fault reactance (e.g. one of two lines lost) lowers $P_{max}$.
6. Inertia constant $H$: a larger $H$ slows the rotor swing.
7. Generator internal voltage and excitation response: higher $E$ and fast excitation increase power transfer.
8. Reclosing scheme: fast and single-pole reclosing restores transfer capability quickly.