Series Compensated Transmission Line Protection Using Distance Relays

Use of series capacitors on transmission lines has become popular due to a variety of factors such as rapid increase in electricity demand, delays in implementing new transmission facilities and interconnection of new generation facilities such as large scale wind-farms. Most of these transmission lines are protected using conventional phasor based distance relays that operate based on voltage and current signals, measured locally. The presence of series capacitors can create abnormal system conditions (voltage inversions, current inversions, sub-harmonics and DC offsets) that potentially lead to unintended operation of conventional distance relays. This paper describes how such factors can affect the performance of the conventional distance relays and outlines solutions to overcome these challenges.