Abstract

A microgrid embraces a low-voltage distribution grid with distributed energy resources and controllable loads. In the last years, there has been a growing awareness in exploiting microgrids to facilitate DER integration in electric power systems as well as to improve reliability and power quality in distribution grids. A microgrid can operate connected to the upstream medium voltage grid—utility grid—or islanded in a controlled and coordinated way. A major challenge associated with the implementation of microgrids is to design a suitable protection system scheme for different operating conditions. To overcome this challenge, different approaches have been proposed in the literature.The protection systems applied at microgrids must work both in utility grid faults and microgrid faults. Faults on the utility grid could lead to a protection response that isolates the microgrid from the utility grid as fast as required to keep the microgrid safety. On the other hand, faults in the own microgrid require the smallest sector removal of the microgrid to isolate the fault. Due to the presence of several DER in microgrids, the protection systems are also needed to cope with the bidirectional energy flows. Thus, the traditional protection devices and standard solid-state relays are designed for selectivity purposes, making them inapt to ensure the protection of microgrids. These protection devices do not provide flexibility for setting the tripping characteristics neither the current direction sensitivity feature.Some problems related to protections sensitivity and selectivity arises when a microgrid is in islanded operation. Thus, this new paradigm of distribution facilities requires a protection system based on microprocessor relaying and communications. Protecting microgrids in both modes can be achieved by using different communication architectures associated with protections. Using centralized or distributed architectures means that the relay protection settings are modified centrally or locally regarding microgrid operating conditions.This chapter aims to provide the key highlights of the available protection schemes used to address microgrid protection issues.