Study Of Distributed Generation Islanding Detection Criterion

Recent years, distributed generation (DG) units are rapidly increasing and they make a contribution to improve quality of power, minimize peak loads and help solve environmental problems. Most DGs may be connected in parallel with the utility network and supply power into power grid as well as local load. This causes a series of problems as well as islanding. Islanding operation of DG usually occur when power supply from the main utility is interrupted due to several reasons but the DG keeps supplying power into the distribution networks. These kinds of islanding conditions cause negative impacts on the network, electrical equipment and on line workers; therefore, it is necessary to effectively detect the islanding conditions and swiftly disconnect DG from distribution network. This thesis studies islanding phenomenon and islanding detection thoroughly, and presents a new method for islanding detection.The studied project includes three main parts: analysis and simulation of the changes between pre and after islanding; research and comparison of current islanding detection methods; a new islanding detection technique based on a GPS synchronized measurement system and its simulation using MATLAB.The thesis analyzes the changes of electric data pre and after islanding, indicates that the frequency variation, voltage magnitude variation and angular variation while islanding can be used in anti-islanding detection. The dissertation also introduces the status and principle of the current islanding detection methods. Through comparing and analyzing ,the paper points out the advantages and shortcomings of the current methods, and summarizes the VS method especially. At last, the paper presented a new islanding detection method based on the research into traditional VS technique. The proposed scheme is a double terminals method by making use of the GPS and...