Research On Active Distribution Network Protection Scheme Considering Distributed Generation

ABSTRACT:As the appearance of traditional energy shortage and environmental pollution problems, the distributed power generation technology which is based on renewable energy, good environmental compatibility and high energy efficiency got rapid development and has become the new trend of the development of future power generation technology. When distributed generation (DG) access to distribution network, it can lead to the change of the distribution network topology structure, flow direction, and affect the protection and control of distribution network. So the traditional protection configuration will no longer apply. Therefore, the study of distribution network protection including distributed generation has important significance. This paper centers on this research direction and the main work contents are as follows:Firstly, it introduces the distribution network structure characteristics and the principle of three-step current protection, then summarized the current research status of distributed power generation technology and active distribution network and its key technology at home and abroad recently. It introduces the working principle, classification, operation mode and characteristics of DG, the technical features of active distribution network and its difference from passive distribution network.Secondly, this paper theoretically analyses the influence of original distribution network protection and automatic reclosing when DG access to distribution network. It mainly analyses the influence of protection and automatic reclosing which is caused by such factors as the differences of fault location, DG’s capacity and the position of access. Then it establishes simulation models through PSCAD/EMTDC simulation software to simulate the theoretical analysis above. In this way, the correctness of the theoretical analysis is verified. Moreover, this paper does a classified summary of current protection scheme for distribution network containing distributed generation and analyses the advantages and disadvantages of them. Based on these analysis, this paper points out that the protect action after excision of DG and allow the DG island operation plans are the development direction of the future.Finally, this paper proposes a protection scheme which is based on the cooperation of longitudinal protection and overcurrent protection. In view of the open loop operation of distribution network, depending on the position of DG access, the scheme separates the feeder into different partitions. In the upstream of DG area, there is equipped with a circuit breaker and longitudinal protection configure and other protection devices have to be kept. Considering the uncertainty of DG’s output, weak feed protection is installed in DG access points by the way of voltage components, to make sure that no matter how DG’s output changes, the longitudinal protection can be reliable action. Because current distribution network is designed based on closed-loop and operated based on open-loop, and with the increasing of DG’s permeability, closed-loop operation is the development trend of the future, so this paper also puts forward a longitudinal and overcurrent protection scheme which is suitable for closed-loop operation distribution network containing DG and is similar to open-loop operation distribution network. The principle of protection scheme above is simple and can solve the impact of DG access to distribution network protection effectively. Finally, this paper verifies the validity and feasibility of the scheme through the establishment of simulation model for the simulation analysis.