The effects of flexible AC transmission systems device on protective relay

The paper introduces the basic structure and equivalent circuit model of unified power flow controller (UPFC) and then analyzes its effects on the transmission line distance relay in two cases. Different location of the UPFC, fault resistance, parameters of UPFC, the location of the fault and system operation conditions all affect the measured apparent impedance to some degree. The presence of UPFC will make the relay under-reach or over-reach. In order to eliminate the effects of a UPFC device on protective relay, two methods are given in this paper. One is to equip protective relay devices in which the UPFC device is equipped. In this way the UPFC device is always beyond the fault loop. The other is to use an artificial neural network to eliminate the effects of UPFC device.