Research On N-k Contingency Operational Risk In Transmission System

Nowadays, worldwide blackouts are happening frequently, which has brought tremendous negative impact to the society and economic development. N-k contingency is one of the main reasons of blackout. So it is necessary to do comprehensive evaluation and research on N-k contingency.The main work is listed as follow.1. Based on the reliability theory, at first, transmission lines’ own factors,real-time load condition and external environment factors are taken into consideration to establish the multi-factor outage model of transmission line.Combined with Markov theory, the working logic of hidden fault in protection facilities is analyzed. Hidden fault probability model of relay protection system is built. Then the path searching method of N-k contingency in transmission system is improved. Combined with risk theory,this method can assess the risk of N-k contingency risk in transmission system under different wind speed.2. Probabilistic power flow is introduced into the transmission system including wind farm. At first, point estimate method and Gram-Charlier are elaborated. Point estimate method and Gram-Charlier are used in the calculation of power flow. Then, based on Weibull wind speed probabilistic distribution model, the probabilistic distribution output model of wind turbine is established. At last, the calculation process of probabilistic power flow in transmission system including wind farm is obtained. And the influence to power flow and bus voltage by the randomness of wind power is proved in the case.3. To qualitatively analyze N-k contingency risk in transmission system influenced by wind farm, the risk analysis model of N-k contingency in transmission system based on probabilistic power flow is proposed.Probabilistic modeling and algorithm combining point estimate method and Gram-Charlier are applied to calculate the probabilistic distribution of power flow so that the impact by the wind farm to the reliability of transmission system can be analyzed. Based on Utility theory, risk assessment model of N-k contingency is established. The proposed method is proved to be feasible on IEEE Reliability Test System 79.