LAUSR

Reliable protection of modern distribution systems is challenging due to various technical difficulties, mainly related to the need for more efficient use of existing networks (e.g., shorter interruption durations and fewer affected customers, integration of distributed generation, meshed network operation, etc.). Such challenges require, among others, the reconsideration of conventional protection techniques. A potential solution under examination concerns the adoption of distance protection for distribution feeders, due to its advantages compared to overcurrent protection. However, as distance relays are mainly designed for transmission networks, there are several issues to deal with in distribution applications, such as the proper setting of the zero-sequence compensation factor (K 0). The latter issue is critical in order to guarantee correct relay operation during single-line ground faults. This paper examines the effect of K0 on the operation accuracy of distance relays protecting inhomogeneous distribution feeders. Theoretical analysis, as well as investigation of various influencing factors, result in the determination of a pattern, which relates relay accuracy to K 0. Based on this analysis, a simple methodology for setting K0 properly is proposed, which is implementable with commercially available relays. The methodology is applied on a test distribution feeder and meaningful conclusions are derived.