Improvement of operation of power transformer protection system during sympathetic inrush current phenomena using fault current limiter

Power transformer protection has a high sensitivity due to its important role in power systems. Various factors such as inrush and sympathetic inrush currents may result in the inappropriate performance of protective relays and cause problems such as power outage or blocking of sensitive loads. Until now, several studies have been performed on the detection and reduction of inrush current, however, the effect of sympathetic inrush current on transformer protection has not been addressed. In this study, the operation of the protection system during the sympathetic inrush current is comprehensively analysed. Furthermore, the use of a fault current limiter is proposed to reduce the undesirable effects of the phenomena. The effects of the limiter on the saturation of power and current transformers are investigated. A real transmission station is simulated using DIgSILENT Power Factory Software to perform these studies by considering the resistive and impedance fault current limiter.‏ Results show that protective relays do not have an improper operation during the phenomena with limiters. Moreover, with the resistive fault current limiter, sympathetic inrush and inrush currents are decreased by 5 and 15% more than the impedance fault current limiter, respectively. Saturation of power and current transformers is significantly reduced with limiters, especially with a resistive fault current limiter.