Three-stage voltage stability contingency screening and ranking

Mid-long term voltage instability is an important category of voltage instability, but mid-long term analysis has difficulty dealing with large number of contingencies. To address this problem, a systemic approach of three-stage voltage stability contingency screening and ranking is proposed. Contingencies are screened through three stages of static, transient, and mid-long term analysis. Static and transient analysis methods are first used to shortlist a number of probably critical contingencies form a large list of credible contingencies; mid-long term analysis method is then used to identify contingencies that cause mid-long term voltage instability from the shortlist. Testing on a practical power system shows that the proposed approach can identify the contingencies causing mid-long term voltage instability, while mid-long term analysis deals with only a short list of contingencies. Under voltage instability causing contingencies, control strategies are made on critical nodes and are able to mitigate voltage instability.