The Research Based On The Protection Strategy Of Micro-grid Isolated Network Operation

The micro-grid has the advantages such as low transmission and distribution costs, high reliability and low impact on the environment, which has become a popular topic. However, with the connection of DG, the micro-grid realizes a bidirectional current flow and changes the characteristics of the traditional one-way flow of distribution network. The connection of DG also brings many issues to the protection of traditional distribution network, such as miss operation, malfunction, lower sensitivity and the reclosing failures, and the traditional three-stage current protection cannot meet the requirements. But when the micro-grid entering the isolated network operation, it can achieve an uninterrupted power supply and improve the stability of system to supply power. Therefore, it is necessary to research into the isolated network under the condition of system fault, so as to make sure the power system more efficient and reliable.To solve the contradiction between the development bottleneck of micro-grid technology and the application limitation of the traditional distribution network protection, this paper uses 400 V low voltage power distribution network as an example, and establish a system model of micro-grid connected by DG. By researching the properties of internal interphase fault and grounding fault of micro-grid that under the isolated network operation to find out the difference between with traditional power grid failure. Then, this paper proposes a new protection scheme which is suitable for the micro grid. The positive and negative direction of impedance that starts by overcurrent install at the Feeder unit configured in the DG relay to protect the line fault. Use a new protection strategy based on voltage fluctuation as the protection of Micro-Grid. Meanwhile, paper used MATLAB/Simulink software to build a model of micro-grid which represented by photovoltaic power generation system, and simulate the properties of isolated network operation fault. Finally, the protection strategy of micro-grid under the isolated network operation is verified.