Novel protection schema for a radial microgrid system

摘要

The improved use of renewable power generation and the coordinated connection with electrical networks and loads bring a new concept, the microgrids. In general, a microgrid can operate in both grid connected mode and islanding mode. Ensuring the continuity of protection in both operation modes is a great technical challenge. Dealing with different short circuit currents level depending on the operation mode as well as ensuring selectivity and sensitivity are the issues of the proposed protection scheme. The present work presents a microgrid protection scheme for a three bus-bar radial microgrid which includes energy storage and a static compensator (STATCOM). Protection strategy is based on the implementation of bi-directional overcurrent relays and includes over- and under-voltage and frequency relays as back-up protection. The main restriction is perhaps a limitation in normal working at 80% of the rated current of the converter-based generator, leaving the 20% remaining to overcurrent detection. In the other hand, an impedance measurement method is used to perform the islanding protection. Results show that the protection scheme detect effectively the islanding condition and also isolate three-phase faults applied in each bus-bar.