Effect Of Fault Current Limiter On Voltage Sag And Optimal Allocation Method

With the increase of power load and the scale-up of power network, short circuit current increases rapidly. In order to reduce the dangers caused by the short circuit current. More and more attention is taking on the research of fault current limiter (FCL). At the same time, with the development of innovative and high technology and industry, more and more new kind load access in the power grid constantly. The new load is sensitive to voltage sag, in order to reduce various losses caused by voltage sag, power supply department and users looking actively for a variety of measures. Short circuit fault is the main reason for causing voltage sag. FCL can limit the short circuit current effectively and the voltage sag will be mitigating at the same time.When Fault Current Limiter install in the power grid, the effect depends on three parameters:the installation position, the current limiting impedance value and the action thresholds. This paper analysis the effect on voltage sags with various parameters of FCL in a simple radiant grid and loop grid respectively. By theory and simulation analysis, the effect of FCL for voltage sag mitigation is understood comprehensively, the cause of bad influence is analyzed and the solution measures are put forward.The influence of FCL on voltage sag in complex grid is analyzed; the analytic expressions for calculation of voltage sag with FCL are derived. The parameters of the grid will be changed after the FCL translating into high resistive state when fault occurs, the node impedance matrix is changed when derive the analytic expression for the voltage sag. When calculating the voltage sag with FCL in three-phase action, the install endpoint on the branch is considered. When FCL acting in non-threephase, the parameters of the system is asymmetric in fault state. So, the calculation method of multi-port network is adopted. Every FCL installation position serve as a port and the boundary equation is deduced. The multiport network equation included the FCL ports and fault ports is formed by hybrid parameter matrix. The relation between bus voltage and the fault position is got by the simultaneous solution for multiport network equation and boundary equation. The area of vulnerability with FCL is determined by using the calculation method of the voltage sag with FCL. The method developed was applied to the IEEE 39-bus test system. The mitigation effect of FCL is assess intuitively.This paper presents a new problem formulation for allocation of FCL for reducing fault current and mitigation of voltage sag. A new optimal model is established for allocating the installation location, impedance values and action current of FCL. The optimal objective function includes the voltage sag amplitude and frequency. The constraints include the target of reducing fault current and investment planning of FCL. This problem is formulated as a mixed integer nonlinear programming (MINLP). The improved discrete particle swarm optimization (DPSO) algorithm is adopted to search the optimal installation line. The enumeration method is used to choose to install in the beginning or end of the line. The chaotic particle swarm optimization algorithm is used to search the optimal impedance and acting current value. Finally the fault model is constructed by Monte Carlo method in the IEEE test system. The mitigation effect of FCL adopt the optimal allocation scheme is evaluated, the validity and practicability of the proposed method is validated.