An Overview of Protection Techniques for Microgrid and the Factors Involved
Mahmud, Syed Golam
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Microgrids are the emerging component of smart grid system. The power transfer losses from transmission end to distribution end are aimed to reduce due to the implementation of microgrid network at distribution level and to increase the network reliability. Microgrid is a distribution network consisting of DG technologies, which can operate in parallel with utility grid to meet the required demand. However, the main criteria to isolate microgrid from active distribution network is that, it can operate independently in islanded mode. The main challenge of microgrid is that to tackle the dynamic behavior of microgrid sources such as solar cell, wind turbine generation etc. and the fault current contribution from these sources. Fault current level also varies according to the mode of operation: grid connected mode and islanded mode. These challenges make the traditional protection schemes less effective. Hence, an advance microgrid protection techniques are required to meet the above challenges for smoother and secured operation of microgrid. In this thesis, an extensive literature review is presented about microgrid and its protection. The impact of embedded DG units in microgrid network is analyzed and their role towards network protection is presented in this thesis. There are certain impacts such as LOM, sympathetic tripping etc. which are found from research work that need to be addressed to ensure proper protection of microgrid. One of the key findings of this research is that there are several key factors affecting to design and implement an effective microgrid protection technique. The key factors include microgrid topology and type, type of DG unit, relay type, communication type and type of faults in microgrid. Then the thesis focus on different protection strategies of microgrids based on above key factors. A communication assisted adaptive protection strategy is analyzed in detail among them. It is found from the research that adaptive protection provides accurate and secured protection with advanced facilities. Moreover, a literature based case study is presented at the end of this thesis to prove the effectiveness of adaptive protection strategy in microgrid network operated in both grid connected and islanded mode.