Discrimination between internal fault and magnetising inrush currents of power transformers in the presence of a superconducting fault current limiter applied to the neutral point

Abstract

The phase-to-ground fault is the most probable fault in power systems. Generally, the neutral grounding resistor is utilised to limit the current for this fault. However, this resistor decreases the sensitivity of the differential protection. The fault current limiter (FCL) is an attractive candidate to be used instead of the regular grounding resistor. FCL only operates for high fault currents and has a negligible resistance for normal or low current faults conditions. Therefore, it reduces the high fault currents while not affecting the sensitivity of the differential protection. However, the signals used as inputs of the differential protection may be adversely affected by the FCL and this may lead to wrong operation of this protection. A comprehensive study is required to evaluate the performance of differential protection algorithms in the presence of a FCL in the neutral point. This study analyses the impact of high-temperature resistive superconducting FCLs (SFCLs) existed in the neutral point on transformer inrush current discrimination methods. Some well-known methods for discrimination of an internal fault from inrush current are evaluated in the presence of SFCLs. Furthermore, through extensive simulations, their performance is compared with and without the presence of SFCLs.