Research On Risk Assessment Of Cascading Failure Based On Power System Operational Reliability

The interconnection of regional power grids reduces the spare capacity of the power system effectively and improves the economic performance of running. However, the tre nd also increases the difficulty of control and the risks of safety, which results in blackou ts once partial failure is operated or controlled improperly. Cascading failure is a major manifestation of blackouts, therefore it has a very important practical significance to stre ngthen the study of power system cascading failures and detect the cascading failure risk.The paper proposes a risk analysis method of cascading failure based on operational reliability, the main contents of which are as follows:The process of three typical blackouts worldwide is demonstrated, and the reasons o f them are excavated deeply. On the above basis the entire development process of casca ding failure is divided, and characteristics of each stage are point out, which reveals the g eneral laws of cascading failures development.According to the mechanism of cascading failure, the model of fault chain is chosen to represent cascading failure paths. Considering the impact on the remaining branches a fter some branch breaks and the ability of anti-load-fluctuation, the consequences vulnera bility indicator, the impact vulnerability indicator, and the composite vulnerability indicat or of branches are defined by the entropy theory, which makes the quantitative analysis o f branch vulnerability possible. On this basis the reasonable threshold of composite vulne rability indicator is set, and the branches whose composite vulnerability index value is lar ger than threshold or the severe overload branches are selected to form the initial failure s et of cascading failures.According to the relevant features of the adjacent failure links, the relevance indicators are defined considering the load rate of branches, the power flow fluctuation and coupling relationship with the superior breaking branch. The relevance indicator is analyzed by fuzzy C-means to get the branches whose relevance indicator value is larger in order to get the next failure link. The stability-lose and splitting of power system is a criterion to end the search, and the cascading failure path tree is used to form fault chains, which overcomes the shortcomings of existing fault chain algorithm.Consider the impact of transmission line's own health, operating conditions and external environment for its outage probability, and establish transmission line's operational reliability model to accurately calculate the probability of cascading failures. Then select branch overload index and bus voltage exceeding as the consequence severity index of cascading failures. Finally, the model of operational risk assessment on power system cascading failure based on risk theory is proposed. The model can be more accurately reflecting the system's operational status as well as possible operational risks, providing early warning information to the dispatcher.