Comparing TCSC placements on mid-point and ends of second circuit of double circuit line from measured impedance point of view

Distance relays are widely used as the main and back-up protection for transmission lines. They operate based on measured impedance at the relaying point, which is affected by several factors including pre-fault line loading and short circuit levels at the line ends. Introduction of Flexible Alternating Current Transmission System (FACTS) devices imposes further changes on the measured impedance at the relaying point. This paper studies the effect of the presence of Thyristor Controlled Series Compensator (TCSC) on the second circuit of a double circuit transmission line, on the measured impedance at the relaying point. In the presence of TCSC, the measured impedance at the relaying point is affected not only with its compensation degree, but also with its installation point. Here, the measured impedance at relaying point is compared when a lumped TCSC is installed at the mid-point of the second circuit and once two part TCSC is at the line ends.