On-line Identification Method Of Short-circuit Transfer Impedance And Its Application

With the rapid development of economy and society,the electricity demand of China keeps continuous growth.In order to meet the growing demand for electricity,the scale of power grid continues to expand.While the developing of highly interconnected power system has improves the power supply capacity and economy of the grid,it has also brings about the problem of short-circuit current levels in the grid.As the short-circuit current changes with the change of the grid operation mode,it is difficult to accurately grasp the short-circuit current level in actual engineering,resulting in the decisions based on the short-circuit current being conservative or optimistic,which may lead to increased investment in power grid,and the power supply capacity is wasted,or it may lead to hidden dangers that threaten the safe and stable operation of the power grid.Therefore,accurately grasping the short-circuit current level and short-circuit current variation law is an important practical engineering problem that must be solved in power system.This paper takes the short-circuit transfer impedance as a starting point.Based on the system identification theory,and the data resources of the power data platform,this paper research on online identification of short-circuit transfer impedance and real-time monitoring of short-circuit current,in order to provide an effective technical means for the practical engineering to accurately grasp the short-circuit current level and short-circuit current variation law.Firstly,in view of the limitations of the conventional solution method of short-circuit transfer impedance in large-scale power grids,a short-circuit transfer impedance identification method based on line information before and after the short-circuit is proposed.This method combines the power flow information before the short-circuit and the information on short-circuit current decay curves after the short-circuit of the lines,and uses the system identification principle to solve for the short-circuit transfer impedance;An improved particle swarm algorithm based on the adaptive change of weighted particle and learning factors is proposed to optimize the identification of transfer impedance,which improves the calculation speed and efficiency.It is not necessary to know the parameter information of each element in the power grid as a known condition,and can realize the online monitoring of short-circuit current,which solves the engineering problem that the short-circuit current is not easy to be accurately grasped,adapts to any complex power grid,and has good engineering practicality.Then,the proposed method is used to further explore the value of short-circuit transfer impedance in solving short-circuit current problems in practical power grid engineering.Aiming at the problem of determining the importance of short-circuit current influencing factors in power grid engineering,a quantitative analysis method of shortcircuit current influencing factors based on the principal component analysis method is proposed,using short-circuit transfer impedance as an index.The degree of each shortcircuit current influencing factor on the short-circuit current is quantified by the shortcircuit transfer impedance,which provides a method for determining the main influencing factors of the short-circuit current in the power grid.Aiming at the difficulty of formulating open-loop schemes in power grid where short-circuit current exceeds the standard,a research method of open-loop scheme based on short-circuit transfer impedance is proposed.Identifying the short-circuit transfer impedances of the lines connected to the short-circuit point under different open-loop schemes,analyzing the change trend and degree,and combining with sensitivity analysis method,the open-loop points that effectively limit the short-circuit current can be summarized.Short-circuit transfer impedance can be used to provide reference for the evaluation and selection of open-loop schemes.Based on the above theoretical research,this paper provides theoretical guidance and technical means for a provincial power grid to solve the problem of short-circuit current exceeding standard.