Research On Relay Protection Of Distribution Network With DG

In recent years, the energy and environmental issues have become increasinglyprominent because of the rapid economic development of China. However, the drawbacks ofthe traditional centralized bulk power grid mode of "large unit, high voltage power grid isobvious. As a supplement of large power grid, distributed generators are developing rapidlyfor its high efficiency and environmental protection. However, after DG is connected to thedistribution network, the traditional single-source radial-network will become to be a doubleterminal or multi-terminal power network, and the direction of the trend will change, too. Thiswill bring a series of problems for the relay protection, such as misoperation and malfunction,and will affect the automatic reclosing. The effect will be more obvious, especially whenlarge-scale distributed generators are connected. Studying the distribution network relay withthe interaction of DG and proposing a new protection scheme have an important significance.Firstly, this paper introduces the application of several distributed generators which areused more widely. Based on the fact that the majority of DG is connected to distributionnetwork by the power electronic devices, this paper analyses the working principle and failureresponse of inverter interfaced distributed generators as a key and determines the model andcontrol mode of inverter interfaced distributed generators to provide a theoretical foundationfor the following work.Secondly, starting from the type, capacity and location of distributed generators, thispaper analyzes the effect on protection and automatic reclosing of distribution network withthe interaction of DG. By using the electromagnetic transient simulation softwarePSCAD/EMTDC, this paper builds the typical model of10kV distribution network to tests thetheoretical analysis further.Finally, based on the wide area protection, this paper puts forward to a new protectionprinciple which can be divided into two steps: first, the branch where fault occurs is identifiedto locate the fault direction in a relatively small range with the practical criterion for the faultdirection of the nodes with multi-branch; second, in view of fault direction, by building acommunication unit between the first line and the second one, the fault will be locatedaccurately. In this way can we reduce the processing of useless node information in thenetwork effectively. Finally, by simulating of the new protection principle with thePSCAD/EMTDC, the results show that the new protection principle can be used to determinethe fault range, and has a good application prospect.