Effects of instrument transformers location on measured impedance by distance relay in presence of UPFC

Abstract

This paper presents the measured impedance at the relaying point in the presence of a flexible alternating current transmission system (FACTS) device, i.e. unified power flow controller (UPFC). The presence of UPFC on a transmission line has a great influence on the tripping characteristic of distance relays. Distance relay tripping characteristic itself depends on the power system structural conditions (short circuit levels at the line ends), pre-fault operational conditions (load angle and voltage magnitude ratio at the line ends), and especially the ground fault resistance. In the presence of UPFC, its controlling parameters as well as the connection point of the instrument transformers of distance relay affect the tripping characteristic. Here, the measured impedance at the relaying point is calculated due to concerning parameters.