Impacts of transient instability on power system reliability

This paper addresses the effects of transient instability on power system reliability. Composite system reliability evaluation has been performed based on steady-state estimation of load curtailments. In composite reliability evaluation, after each contingency, faulted components are assumed to be isolated from the rest of the system immediately and the system is assumed to return to a stable state with proper generation rescheduling for minimum load curtailments. In this context, minimum load curtailments are usually performed by solving linear/non-linear programming optimization problems. Although the optimization problem with minimum load curtailment may find a steady-state feasible solution, a stable transition to a post-fault stable equilibrium point is not guaranteed. In this paper, three probabilistic transient stability indices are proposed to assess system robustness against transient contingencies and update the reliability indices. Transient stability direct methods are used in assessing system stability and determining the probabilistic stability indices. This method is applied on the reduced WECC (Western Electricity Coordinating Council) system and the results showed that the effect of transient instability should not be ignored.