Research On Strategy For Transient Stability Probability Assessment Of Power Systems

Stability evaluation has long been recognized as a fundamental part of power system planning, design, operation and control. Traditionally, power systems have been planned and operated using deterministic transient stability criteria. However, stability analysis is basically a probabilistic rather than deterministic problem. Deterministic assessment can not reflect the essence of power system transient stability exactly. Compared with deterministic transient stability assessment of power systems, the result of probabilistic stability assessment can provide a realistic appraisal on instability level of the expected transient performance of systems using stochastic data of systems. Currently, a series of probabilistic approaches have been proposed. However, a challenging problem is the probabilistic approach allows too heavy computation to satisfy the demand of stability assessment on-line.As for this problem, a new analytical model described the uncertainty of the fault clearing time for probabilistic transient stability assessment of power systems is proposed in this paper. With the model, a Corrected Transient Energy Function (CTEF) based hybrid analysis strategy is developed to evaluate probabilistic instability index of systems. In this analysis strategy, trajectory simulation incorporating with CTEF energy margin of contingencies is conducted to judge the stability or to evaluate Critical Clearing Time (CCT) and then the probabilistic instability index of contingency is evaluated with the stability information or with the CCT. An outstanding advantage of this approach is that the CCT evaluation is only conducted for very severe contingencies which are only a fraction for the all contingencies considered in the probability assessment of over all systems. Hence, the computation burden on the instability probability assessment of systems has been remarkably reduced. Case studies on the New England test power system and a representation of North China power system are reported to show the effect and the potential application of the strategy.