Research On Optimal Allocation Methods For Fault Current Limiting Measures Based On Ward Equivalence

With the growing capacity of power supply and the strengthening structure of the power grid, the short-circuit capacity is increasing rapidly as well. So there are a considerable number of sites whose short-circuit current is approaching or even greater than the rated interrupting capacity of the breakers. So the faulty component can’t be removed promptly. The oversized short-circuit current increasingly becomes a significant threat to the safety and stability of the power grid. It’s urgent and necessary to take current limiting measures and study specific decision making methods.As an actual grid is large in general, this paper firstly simplified the grid’s network based on ward equivalence method, so as to reduce the scale of the optimal current limiting measures allocation model and improve the model’s solving efficiency while the calculation precision was guaranteed. Then formed a mixed integer linear programming model which corresponded to the circuit opening measure and a mixed integer quadratic constraint programming model which corresponded to the FCL installation measure based on Node-Voltage method. Then introduced some mature deterministic algorithms that could solve the formed models, such as the linera programming simplex method, branch and bound method and the original dual interior point method. Finally by applying the two models in specific calculation cases, the effectiveness of the proposed models was confirmed.As for the optimal circuit opening allocation model, the network’s connectivity and the grid’s N-1security were guaranteed by analysis of the grid’s topology. Further, added power balance equation constraints, branch flow constraints and N-1security constraints. By calculating the expected faults’ affected domains, the reserved part of the equivalent grid was accordingly enlarged. As for the optimal FCL allocation model, because FCL would not change the power flow distribution, the main concern of the model was short-circuit current limiting results and contacts between variables, and established an mixed integer quadratic constraint programming model and was solved by the branch and bound method and the original dual interior point method. This paper made a derivation of the application of the original dual interior point method in quadratic constraint programming model. When the candidate FCL installation branch was a small reactance branch or a transformer branch, there may came up a numerical convergence problem, it was solved by introducing the concept of virtual line.This paper elaborated the modeling and its solving method of the optimum allocation of current limiting measures in theory, and also developed an application program on the platform of Visual Studio2005in C++. Through the calculation of the short-circuit current limiting problem of the IEEE39Bus system and Zhejiang power grid, the correctness and solving efficiency of the proposed optimal current limiting measures allocation model was verified.