A pilot-based distance protection scheme for meshed distribution systems with distributed generation

This paper proposes a pilot-based distance protection scheme for meshed distribution systems with a high penetration of distributed generation. The proposed scheme assumes distance relays installed at the opponent ends of each main line segment. A forward distance element is enabled in each relay to protect the main line segment, while, a reverse distance element is enabled in each relay for protecting adjacent buses and laterals. The relays protecting a main line segment or a bus/lateral communicate in a permissive logic, ensuring protection sensitivity and security at the same time. The scheme provides efficient primary and backup protection against faults of any type, even with a considerable fault resistance, and under weak-infeed conditions. It is also appropriate for both the grid-connected and the islanded mode of system operation. Coordination of the distance protection scheme with the lateral protection means is also addressed. Existing numerical distance relay technology is considered, to enhance the applicability of the proposed scheme. Offline setting of the distance relays is required, which has to be performed once. Only one setting group is ultimately extracted for each relay, suitable for different fault/system conditions, avoiding the need for adaptive protection techniques. The proposed scheme is applied to a test meshed distribution system and conclusions are drawn. Comparison with directional over-current and differential protection shows the advantages of the designed distance-based protection scheme.