Study On Auto-adaptive Distance Protection For Transmission Line With UPFC

In recent years, the rapid development of power electronics technology enables a growing number of FACTS devices to be applied into power systems. As a typical FACTS device, UPFC can flexibly adjust the power flow in power system, but it will also change the parameters of transmission line which will affect the action of traditional protection.This Paper studied the research of UPFC technology at home and abroad in recent years, the mathematical model and working principle of UPFC, and established a double-annular power supply system through MATLAB. Simulation results show that the UPFC have the flexible control capabilities in active and reactive power.With the two case of the transmission line not containing and containing UPFC, this paper analyzes the impact to the distance protection of traditional impedance measurement when occurring all kinds of short-circuit fault (single-phase to ground, two-phase to ground, two-phase-to-phase short-circuit, and three-phase short-circuit faults) at different fault location. Simulation results show that when the short-circuit fault occurred in the line behind UPFC, the measurement of impedance contains two incremental impedance which caused by UPFC series injected voltage and shunt reactive current, then the traditional distance protection can not act properly.Through the analysis of the algorithm and the realization of the adaptive Protection in recent years, this paper presents two adaptive programs coping with incremental impedance for adding a result of UPFC. A auto-adaptive distance protection program is to automatically adjust the impedance setting value of the protection with operation of UPFC after short-circuit fault, making the protection setting as a variable impedance.Another program is to amend the value of measurement impedance, then ,determine the protection action in the traditional setting impedance circle.The results shows that these two programs will enable the protection correctly respond to all kinds of short-circuit fault in case of having UPFC.So that they can ensure the safety of the power system.