Research On Adaptive Protection Method Of Distribution Network With Distributed Power

As the world ' s environment gradually deteriorates and fossil energy sources are depleted,countries around the world are turning their attention to clean and pollution-free new energy sources.Under the call of energy conservation and emission reduction,China began to vigorously develop clean energy represented by photovoltaic and wind power.The connection of distributed generation(DG)based on clean energy to the distribution network has become an inevitable trend in the development of the power grid.However,a large number of distributed power sources are connected to the distribution network,which makes the distribution network change from a traditional single power radiation network to a distribution network with a multi-terminal power structure.The access of distributed power makes the distribution network structure more complex,and it also brings huge challenges to power system failure analysis and relay protection.Therefore,it is of great significance to study the fault analysis methods and protection strategies for distributed power sources after they are connected to the distribution network.The development situation of China's distribution network and the impact of DG access on the distribution network are introduced in this article.The current status of domestic and foreign research on the protection methods of DG access to distribution networks is introduced.The control strategy of DG integration into distribution network is analyzed in detail and the equivalent model of DG is established.The effects of DG integration capacity and access location on the short-circuit current of the distribution network are analyzed through simulation and general conclusions are drawn.The principle and shortcomings of the existing adaptive current instantaneous protection are analyzed.an adaptive positive sequence current quick-break protection(I stage protection)method is established by analyzing the relationship between the positive sequence voltage and the positive sequence current at each protection installation.In order to protect the full length and improve the sensitivity of the traditional time-limited current instantaneous trip protection,an adaptive time-limited positive sequence current instantaneous trip protection(Section II protection)method is proposed in this paper.Thefeasibility of this protection is verified by simulation.In order to solve the problem that the traditional overcurrent protection acts too long when it is close to the head end of the power supply,the inverse time overcurrent protection method is used as the third-stage current protection.By improving the cooperation relationship between the inverse time overcurrent protection and the operation time limit of the traditional three-stage current protection,the operation time of the protection is significantly shortened,and the rapidity of the protection is improved.This method is proved to be equally applicable in a distribution network system with two distributed power sources through an example analysis.