Research On On-line Security Monitoring Approach Of Large Scale Interconnected Power Network Based On Steady-state Security Region

In recent years, large-scale blackouts happen in succession worldwide which brings severe consequence to the industrial production and household life. Thus, more and more attention has been paid to the research on power network security issues. In the process of failure development, a fast and visual estimation of the distance between current operating point and security boundary is favorable to the power grid real-time monitoring and evaluation. The security region method can effectively solve these problems. Therefore it is necessary to deeply research on the theory and application of the security region method, which is of great significance on improving operation security of large-scale interconnected power network.Based on the analysis of the general theory and model of steady-state security region, this thesis studies its practical mathematical model and application method on power system on-line security monitoring and analysis with the practical demand of power grid considered. The main research efforts are listed as follow:1. A novel dynamic searching method of key transmission line-set is proposed. These lines, which reflect power system operation risk, are studied as the monitoring focus of the security region. The direction of line flow can not be fully considered using the traditional cut-set, while it isn't easy to deal with the problem of non-key transmission line. Therefore, the concept of key transmission line-set is introduced with the consideration of three factors such as line flow margin, the impact on the whole grid when line tripping and the characteristics of the transfer of power flow. These key transmission lines dynamically change with the system state, which are more favorable to the power grid real-time monitoring and evaluation.2. The whole region model of steady-state security region has a high-dimensional form that is difficult for practical application, so a practical mathematical model of steady-state security region based on dynamic division technology is presented in this dissertation. Firstly, according to the network topology, a dynamic division method is proposed, which ensures that the area tie-lines reflect power system operation risk. Then the mathematical model based on security region dimensional reduction is constructed, which reduces the model from high dimensions to three dimensions. By monitoring the pathway of the operating point with the change of node power, the trend analysis of the security state can be performed.3. The approaches of on-line security monitoring, security analysis and region visualization based on steady-state security region are proposed. The application study on steady-state security region is developed from two aspects. One is that when the security region exists, three-dimensional or two-dimensional visualization approach is proposed, and security margin between current operating point and security boundary is derived based on security quantitative analysis which breaks the limitation of point-by-point method that can not characterize the overall security of power system and helps to make the right judgments to the security state of power system. The other is that when the security region doesn't exist, the "bottlenecks" which cause the security region to disappear is identified, which provide useful information for the restoration of the security region. 4. Based on the above theories and methods, the software architecture of steady-state security region integrated analysis and visualization system is completed. Then the specific function of each module and their coordination are described. Finally, the reasonableness and validity of the proposed methods have been proven by the test results of the IEEE39-bus testing system, which is of great significance on the on-line security monitoring and evaluation.In this dissertation, key transmission lines that reflect power system operation risk are regarded as the monitoring focus of the security region. Then the paper proposes the practical mathematical model of the steady-state security region based on dynamic division and consideration of load uncertainty and three-dimensional or two-dimensional visualization approach that gives the system overall security estimation. And the on-line security monitoring and analysis approaches based on the steady-state security are developed. Finally, the integrated analysis and visualization system software architecture design of the steady-state security region is completed. The study is to some extent to meet observability requirements for the power system security, which helps operating personnel make the right judgments to the security state of power system.