Research On Modeling Analysis And Protection Scheme Of Complex Distribution Network With DG

As the growing shortage of fossil fuels and increasing development of the renewable energy technology, developing renewable sources becomes an important strategic plan of all the counties around the world. As a result, Distributed Generation(DG) technology has made a great progress in recent years. Although installing more DG in the power system make the compensation in its normal operation, at the same time, it brings great impacts on the system, especially in the distribution network protection. This dissertatio will focuse on the impacts of network protection after connecting DG by addressesing three aspects of system modeling, protection analysis and protection scheme. Firstly, to explore the model of complex distribution network with PV system, an equivalent source model based on PV-DG is proposed; Secondly, the impacts of distribution network protection with DG are analyzed from aspects of principle and simulation; Finally, this thsis suggests a new protection scheme due to the simulation results.For modeling complex distribution network, the load model and DG model are deeply discussed. The load model consisits of several common static load and asynchronous motor which represents dynamic model. The three-phase PV system is selected as a DG model. By discussing working principle of its parts and simulating on the software EMTDC\PSCAD, an equivalent source model based on PV-DG is proposed.Research on the impacts of protection due to the DG is discussed, specifically in the impact of three-zone current protection, fuse and recloser. By modeling a practical distribution network of Liaocheng, the simulation results tell the impact analysis for three-zone current protection by different sizes and placements of DG.According to the simulation results and existing protection scheme of distribution sytem, a new protection scheme is proposed. The scheme comprises of two sections, one is differential protection using current balance scheme on the connecting line between DG and distribution network, the other is an adaptive protection approach on the feeder line where DG is installed.At last, the research contents are summarized, and future research directions are prospected.