Feasible Region Of Fault Current Constrained OPF And Optimal Placement Of Fault Current Limiters

With the continuous expansion of the scale of power system,the completion of interconnection between large regional power grids,the continuous increasing of loading levels,power plant capacity,substation capacity,many power systems are now facing the problem of short-circuit current exceeding the standard,limiting short-circuit current is imminent,the problem of limiting short-circuit current is taken into account both in operation and planning in the paper.In operation,fault current constraints are added to the constraints set of the OPF problem to form the fault current constrained OPF problem.The fault current level is limited by adjusting the control variables of the system,so as to ensure that the system can satisfy the possible fault current threat and improve the reliability.Based on the dynamic system theory,equivalence is established between the feasible regions of the fault current constrained OPF problem and the union of regular stable equilibrium manifolds of a particular quotient gradient system(QGS),so as to get the characterization method of feasible regions of fault current constrained OPF.Feasible region is used as a tool to analyze the impact of fault current constraints on the OPF solution at different loading levels,and a dynamic trajectory-based optimal power flow algorithm is used to solve the optimal solution.This algorithm can avoid the two disadvantages of nonlinear local solvers: convergence to local optimal solution or divergence.Then the impact of fault current constraints on the economic operation of the system is analyzed under different loading levels and fault current threshold.The modified IEEE 9-bus system shows that the higher the loading levels and the lower the threshold of fault current,the greater the impact of fault current constraints on the economic operation of the system,leading to higher operation cost.In planning,the fault current limiter is adopted in transmission lines to limit short-circuit current.Considering the total cost of fault current limiter and the fault level reduction of the entire network,a multi-objective model of fault current limiter optimization problem is established,and a four-stage method including assessment stage,screening stage,optimization stage and decision stage is proposed to solve the problem.The effectiveness of the proposed method is verified in IEEE 30-bus system with different loading levels,and the robustness of the compromising solution to short-circuit current margin is also examined for different loading levels.