Comparative Analysis of Differential and Directional Overcurrent Protection Schemes in a Ring-Structured Microgrid

Abstract

Protection systems face new issues as a result of significant changes in the grid structure, such as the addition of distributed generation (DG) resources. In microgrids, directional overcurrent relays (DOCR) are the favored option because of its ease of use, affordability, and ability to selectively handle bidirectional power flow. However, their effectiveness may be adversely affected by variations in fault current levels under various operating conditions. Faults can be detected fast with differential protection, but it costs more than overcurrent protection and needs a reliable communication infrastructure. This paper presents a comparative analysis of DOCR and differential protection applied to a microgrid modeled in PSS®Sincal and Gridscale X APA. Two scenarios are examined: grid-connected operation with DGs enabled and grid-fed operation with DGs disabled. The study results show that DOCRs are effective when fault currents are sufficiently high, while differential protection provides rapid fault clearance in both scenarios.