A Short-Circuit Protection System Considering the Negative Sequence of Fault Current Available to Long Distribution Lines

A fault current measured at a distribution substation is small in case of a two-phase short-circuit fault near the end of a long distribution line. This characteristic makes it difficult to settle the overcurrent relay installed at the root of line because the load current could hardly be distinguished from the fault current. On the other hand, a negative-sequence current relay likely isolates such a two-phase short-circuit fault, but it may not operate properly due to effects of load on the distribution line. This study sets a proposal of short-circuit protection system considering the negative sequence of fault current that can be applied to long distribution lines. It also demonstrates how useful the proposed system is for isolating such a two-phase short-circuit fault on a long distribution line. © 2023 The Institute of Electrical Engineers of Japan.