Changes in overcurrent protection paradigms of low and medium-voltage smart grids

The use of Smart Grids with high penetration of renewable distributed generation introduces several new issues. Distribution systems are changing in various aspects such as: increase of fault currents of non-constant values, protective devices not strictly in series, and new protection tasks. The new issues that are analyzed here are islanding operation and its detection, effect of unbalance and harmonics on distributed generators, changing of overcurrent values due to the type and power of the distributed generator, current limiters application and reclosing and out-of-phase connection. The changes in protection paradigms are presented studying the technical aspects, and concluding with the need of careful analysis and gradual adoption of new technologies.