Study On Distance Protection On Double-Circuit Line With UPFC

With China’s economic development and increasing demand for electricity resources, the need of transmission capacity of the grid development is increasing. This means the grid scale should be expanded and have higher voltage, EHV transmission line should be constructed to increase the transmission power, so the same pole line developed rapidly. At the same time, the application of FACTS devices in power system increased fast. UPFC is widely used in the transmission lines to control fast and effective active and reactive power flow fast and effectively, so double circuit line with UPFC has good prospects for development. But the input of UPFC will lead to changes in the parameters of the line and affect the performance of distance protection.Paper establishes the simulation model of the same pole with UPFC. In the injection of voltage control mode of UPFC, the transmission power effect of the system simulation will be analyzed, Simulation results show that UPFC can control the transmission line trend flexibly and accurately.When the same pole with UPFC occurs short circuit fault, due to the effect of zero-sequence mutual of the same pole, UPFC-series and UPFC-shunt side additional impedance, traditional distance protection has failed to comply. The paper analyzes the different type effect to traditional distance protection of fault occurred at different point.By derivation of the respective components in the additional impedance expression, Each component is showed as the time-function of the distance to fault. An adaptive algorithm is proposed to be designed to correct the measured impedance. The results show that this adaptive protection scheme can react all kinds of short-circuit fault in the same pole with UPFC accurately, so the safe operation of the transmission line can be ensured.