Non-communication Protection for Single-Phase-to-Ground Fault Feeder in Neutral Non-Effectively Grounded Distribution System

The traditional non-communication protection for distribution system is only applicable to fault feeders in neutral effectively grounded distribution system or the phase-to-phase fault feeders in neutral non-effectively grounded distribution system. For single-phase-to-ground fault feeders in the latter system, the protection will fail to operate because the magnitude of the current flow in the fault-to-ground connection is too small. To solve this problem, this paper presents a new non-communication protection compatible with the fault detection principle based on comparing the polarities of the initial voltage and current traveling waves. In this technique, when a single-phase-to-ground fault occurs, the relays which detect the fault is in the forward direction will operate based on the conventional time grading coordination at first, after one relay makes tripping decision which has the fastest time setting, the relay on the opposite side will detect the sound phase current changes in a time window to accelerate the operation. Extensive Electromagnetic Transients Program (EMTP) simulation studies with respect to a typical double end feeder system whose neutral is non-effectively grounded show that the proposed technique is able to fast and accurately remove a single-phase-to-ground fault line section from both ends.