Summary of useful concepts about the coordination of directional overcurrent protections

Abstract

This paper summarizes some useful concepts about the coordination of directional overcurrent protections. The following key topics are described: the analysis of systems in a ring configuration and only one source of short-circuit currents; the impossibility of obtaining selectivity for all the possible system configurations with multiple sources; the need for inverse functions in order to obtain selectivity in systems with multiple sources; the coordination with protections for radial loads; the coordination between instantaneous and delayed functions; the considerations to select the pickup values; the influence of contributions from motors to short circuit currents; the transient configurations due to sequential trips at both line ends; the influence of dynamic behavior of overcurrent functions; the influence of stability constraints; other specific considerations for ground functions; some specific considerations for systems with distributed generation. A summary of these points and their effect on the coordination of directional overcurrent protections is not available in the current literature. This novel description should facilitate the inclusion of these key points in research and coordination studies related to these protective functions.

Keywords

• Coordination of protective relays
• directional overcurrent protection
• directional overcurrent relays
• directional overcurrent functions