Research On Limiting Short-circuit Current Optimization Of The Power Grid Based On A Multi-objective Method

With the rapid development of China's power grid scale, grid structures increasingly close, and 500kV transmission main network gradually formed, and all the electrical distance between adjacent stations continue to be narrowed. Considering the electromagnetic loop network operation between 500 kV and 200 kV networks, and meeting the demand of reliability under the rapid growth of the power supply, power system short-circuit current level is rapidly increasing, which brings security hidden danger to the stable operation of the power grid. In the power system, therefore, how to reduce the large grid short-circuit current level to ensure that the system can run safely, reliably and economically, is one of the important subjects should be further research, and it has the vital significance.Combining the research present situation about existing short-circuit current limiting measures and optimization schemes of the power grid in the domestic and foreign, this paper studies the multi-objective decision that can be taken to limit the short-circuit current of large power grids.Firstly, this paper research on excessive short-circuit current of 500 kV power grid. We can adjust the network frame structure of 500 kV power grid, which can increase the electrical distance between overweight sites to limit short-circuit current by breaking some of lines in the end power grid. And the paper proposes a multi-objective line-outage optimization method based on a comprehensive sensitivity analysis to limit short-circuit current, by considering of the relationship among the suppression effect, the main network integrity and security and stability of the system voltage.Secondly, the paper derives, detailedly, the sensitivities calculation process of breaking-lines to excessive site self-impedance, three-phase short-circuit current and node voltage at the end of the grid, building a multi-objective optimization model of comprehensive sensitivity, which considers a number of constraint conditions, such as the equality constraint, branch node tide capacity constraints, the voltage of the power generation pattern, and generator power injection constraints.Then, getting the sensitivity normalized, it obtains the comprehensive sensitivity values by means of a combination weighting factor and the definition of Pareto optimal front set. Descending the values to get the priority of measures of the best combined effect, we quickly find the optimal line-outage measure after checking the short-circuit current.Finally, the effectiveness of this method is verified by case analysis and simulation calculation results of a 500 kV simplify network in Guangdong power grid, and the method can quickly obtain the optimal line-outage measure to limit short-circuit current based on the multi-objective decision.