Research On Load Carrying Capacity Of Power Grid Based On Vulnerable Links Evaluation

Under the background of rapid development of global economy,the connection between power industry and society is increasingly close.Network interconnection increases the complexity and operation risk of power system while improving the operation efficiency of power system.When some links in the network fail to operate,it will lead to cascading failure and cause inestimable serious impact.Therefore,it is necessary to identify these vulnerable links in timely and accurate methods in the current operating state of the system,so as to provide targeted preventive control measures,improve the carrying capacity and ensure the safe operation of the power system.Firstly,improved tenacity index is proposed by utilizing line load ratio and power supply capacity to make a distinction between attack difficulty and attack effectiveness.GA-PSO hybrid particle swarm algorithm is adopted to eliminate links that have relatively small impact on the system,so as to preliminarily screen vulnerable links of the power system and lay a foundation for further judgment and identification of weak links.Case studies were carried out respectively on the IEEE 39-bus test system to demonstrate the validity of the proposed method.Secondly,a category differentiation method of power grid vulnerable lines is proposed by analyzing the causes of the line vulnerability,considering the emphases of line vulnerability assessment in various system states.The easy-breakdown line and easy-affected line are differentiated to distinguish the source with the intermediate link during cascading failure,and the method is realized by complex network and Theil theory.Firstly,structural relative vulnerability is proposed by improved tenacity index.Then,state evaluation model is proposed by the impact Theil entropy and anti-impact Theil entropy considering residue consumptive ability of transmission lines.Finally,comprehensive evaluation model of vulnerable lines is established to realize category identification overall combining the structural relative vulnerability and state evaluation model.Case studies were carried out respectively on the IEEE 39-bus and the IEEE 118-bus test system to demonstrate the validity of the proposed method.Finally,the line load coefficient and interval coefficient are defined to identify the weak line,and two defense model models are established:a homogeneous dispatching optimization model and a planning model of the preferred upgrading.The homogeneous dispatching optimization model uses load entropy as the objective function to measure the operating uniformity of the system,and N-1 security constraints are embedded to to ensure N-1 reliability,so as to eliminate the vulnerable links in the normal operation of the grid.The planning model is based on the improved OPA model.which slow dynamic process was optimized to be the preferred upgrading based on the vulnerable transmission line identification.Case studies were carried out respectively on the IEEE 39-bus and the results show that the established models reduce the power failure risk and improves load carrying capacity,the safety and reliability of power grid from the perspectives of scheduling and planning.