Effects of instrument transformers connection point on measured impedance by distance relay in presence of SSSC

This paper presents the measured impedance at the relaying point in the presence of a series connected Flexible Alternating Current Transmission System (FACTS) device, i.e. Static Synchronous Series Compensator (SSSC). The presence of SSSC 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 fine 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 SSSC, 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.