Operational Reliability Modeling And Simulation For Generation And Transmission System

The development of power system towards long distance, high voltage, large capacity and area interconnection, the gradual establishment of the power market, and the application of new technologies and equipment, which are potential risk to the power system. In recent years, blackouts in interconnected power system frequently happened at home and abroad, so the researchers pay more and more attention on reliability assesment of power system.The inaccurate prediction of load demand, the random failure in transformer or transmission line, and the effect of bad weather condition on transmission system, which lead to randomness in the power system operation. Moreover, with the fast expanding in scale of power grid, the power transmission mode has changed markedly. The VSC-HVDC (Voltage Source Converter based High Voltage Direct Current) based on the advanced power electronics technology has been used operationally in power system, which will bring unneglectable effect on power system. Major work and contributions about operational planning reliability assesment in power system are summeried as follows.(1) State transition diagram spaces of different generation unit are presented, which considers system requirements rate, unit’s start-up delay, start-up failure probability and postponable outage. The definition of condition forced outage rate(CFOR) is built. The CFOR characterizes the unit’s outage which occurs in case of system’s need. The formula of CFOR for different unit models are given, which reveals the correlation between unit’s reliability and system’s requirement. Based on the proposed unit model, a new unit commitment model is carried out and the impact of unit parameter varying, subsection dispatching and different load curve on generation unit’s reliability are discussed.(2) Aiming the deficiency of load model used for operational planning reliability assessment, this paper proposes a new integrative clustering algorithm based on K-means clustering model. The clustering model considers bus characteristics information such as load type, power outage, so the accuracy of the integrative K-means clustering algorithm is higher than that of other load clustering model. Based on the load clustering model, the multi-dimension correlation sampling technique considering bus load correlation and load forecasting uncertainty is adopted to determine load value for different buses. On the basis of the proposed load model and cumulative probability load model, a new calculation method of frequency index incorporating load transferring is deduced, which solves the problem of frequency index calculated in nonsequential Monte Carlo simulation.(3) The effect of bad weather on transmission grid is studied, and a multi-state model is built to illustrate the line failure rate under different weather state (normal and bad). A state space diagram for a two component system with the three weather state model is presented and the reliability indices are calculated.Considering the uncertainty of weather state, a new outage model for transmission line is put foreward based on the interval probability theory. Based on the proposed model, this paper uses interval arithmetic and state enumeration method to calculate reliability indices of composite system. Furthermore, affine arithmetic is used to solved the large overestimate problem in interval arithmetic.(4)The work principle and construction of VSC-HVDC system are studied in this paper. The subsystems of VSC-HVDC division model is presented according to function of different module in VSC-HVDC and need of reliability evaluation, and the reliability models of subsystems are established by state space method. Moreover, combining the proposed reliability model of subsystems, the equivalent model of whole VSC-HVDC system is built and the reliability parameters are calculated. The reliability assessment model of AC and DC hybrid system including VSC-HVDC is put foreward, and the effect of VSC-HVDC’s access on power grid is analyzed. Aiming the application of VSC-HVDC in wind grid connected, the reliability evaluation is carried out according the wind grid connected model by parallel AC/DC system is studied.