Unified Power Flow Controller And Its Effects On Protection Relay

As the flexible controller of the Flexible AC Transmissions System(FACTS),an Unified Power Controller(UPFC) can control concurrently or selectively the transmission voltage, impedance and angle or alternatively, the real and reactive power flow in the line. However the presence of UPFC significantly affects the operation of protection relays in the power system. , This paper presents UPFC concept , its modeling technology and the basic control strategies: the effects of UPFC on protection system also were analyzed under symmetric and non-symmetric conditions, some adaptive schemes have been proposed. Results of simulation with EMTDC/PSCAD are given.