Modeling of a Centralized Microgrid Protection System and Distributed Energy Resources According to IEC 61850-7-420

Microgrids have been proposed in an effort to handle the impact of distributed generators (DGs) and make conventional grids suitable for large scale deployments of DGs. However, the introduction of microgrids brings some challenges such as the protection of a microgrid and its entities. Due to the existence of generators at all levels of the distribution system, the fault currents vary substantially. Furthermore, grid connected and islanded modes introduce two different sets of fault currents. Consequently, the traditional fixed current relay protection schemes need to be improved. The authors developed a new protection system which utilizes extensive communication to monitor the microgrid and update relay fault currents according to the variations in the system. This system is designed to respond to dynamic changes in the system such as connection/disconnection of DGs. This paper presents the modeling of a microgrid protection system with logical nodes provided in IEC61850 and IEC61850-7-420 communication standards. It also demonstrates how the proposed communication takes place through logical nodes. Firstly, models for different DGs are provided to detail the implementation of the said logical nodes. Then, a case study is given on a sample microgrid to show how the proposed protection scheme can be run based on these models.