High-resistance faults on a multi-terminal line: analysis, simulated studies and an adaptive distance relaying scheme

The presence of a T-connection to a third terminal can drastically affect the performance of a distance relay at the other terminals. Fault resistance, especially high fault resistance, makes this problem more severe and complicated. Detailed analysis of the apparent impedance for these cases as seen from the relaying point is derived and, based on extensive simulations of the infeed/outfeed and fault-resistance effects on the relay characteristics, an adaptive distance relaying scheme is proposed. A microprocessor based distance relay using this new technique can quickly respond to very-high-resistance faults with maximum coverage of the protected line. The validity of this new scheme has been confirmed by real-time testing on a prototype hardware scheme