Detection and experimental investigation of open conductor and single-phase earth return faults in distribution systems

Abstract

This paper presents a new and reliable detection approach for different crucial faults in distribution systems. These faults are one-open conductor faults at the far side of the feeder or simultaneous faults that are an open conductor followed by an earth fault at either the source side or load side (downed conductor-return faults). Under downed conductor-return faults, there is no zero-sequence current at the conventional protection point. Furthermore, the negative-sequence component is less than the normal unbalance component of the conventional protection point under one-open conductor faults at the far side of the feeder. Therefore, the presented detection approach is based on the measurements at the low voltage side of the load transformers. The proposed method detects such faults by monitoring only the magnitude of the measured three-phase voltage at the load side without installing voltage transformers. A robust threshold value is proposed to guarantee dependability against all fault conditions and security against the normal unbalance. Also, the security of the proposed approach against external faults (at the low voltage side) is verified by monitoring the magnitude of the three-phase current. Fortunately, the proposed system identifies the faulted section. The faulted feeder isolation and the faulted section isolation are accomplished by a proposed autonomous control method with the aid of the infrastructure of smart grids (available communication system). Extensive investigations are done based on a detailed simulation of the selected distribution feeder using the ATP-EMTP program. For verification purposes, recorded faulted cases are experimentally applied on a real distribution feeder to visualize such fault conditions and confirm the detection impossibility of earth-return faults by conventional protection, significantly if the fault faraway the substation. On the other hand, all applied test results corroborate the efficacy of the proposed detection method under the considered faults.