Research Strategy Of Current Protection Of Distribution Network Under Distributed Power Supply Intervention

The rapid rise of distributed power is an inevitable trend of sustainable development.With the intensification of the energy crisis,the deterioration of the natural environment,and the increasing maturity of DG technology,China has introduced policies and subsidies to support the development of DG in many places,promoting the rapid rise of distributed power.A large number of distributed power sources have brought challenges to the regional grid's power in grid planning,operation and maintenance,power quality,especially relay protection,etc.This paper focuses on exploring the impact of the current protection of distribution network after DG access.The main work is as follows:1.Discusses the current development trend of DG in the regional power grid,and takes Heze regional power grid as an example,analyzing the reasons for the rapid development of DG.Introduces the stability of the power grid in actual work,and analyzes the impact of DG on the regional power grid in early forecast and later operation,such as larger current fluctuations,increased difficulty in forecasting,insufficient reactive power support capacity,and reduced frequency adjustment capability,etc.Determine the key points as follows:the determination of the position and capacity of the DG,the impact on voltage and energy,and the impact on relay protection.Then based on an example of the local power grid in Heze area,proposes a solution of the power grid carrying capacity evaluation system after DG access,solving the problems besides relay protection.2.Analyzes theoretically through formulas on the influence of the distribution location,capacity,and fault location on the short-circuit current and protection settings after the DG is connected to the regional distribution network.By building a PSCAD/EMTDC-based transient simulation,the correctness of the theory was proved theoretically,and verify the consistency and reliability of theoretical analysis and simulation calculation by caculating the access capacity under different conditions of DG access.3.A new strategy of directional longitudinal protection combined with over current protection is proposed,which improves the original protection configuration.It partitions according to the connected location of one or more DG,and is equipped with different protection devices and directional element in upstream and downstream.Verify the effectiveness of the strategy and analyzes the advantages and disadvantages of this scheme by simulation analysis of a 10kV line.4.Developed a new and more economical strategy--an improved scheme of adaptive current quick-break protection.The disadvantages of traditional adaptive protection are discussed.Based on this,the calculation method of equivalent impedance and equivalent electromotive force in two-phase fault and three-phase fault is explored after the connection of DG to the back of the protection,forming a new self-adaptive protection formula.Combined this method with the system's operation mode and DG position,this paper develops a new adaptive current instantaneous trip protection flow chart.At the same time,in order to solve the problem of excessive data transmission in this method,a dual setting strategy for downstream DG access is proposed.Different protection settings are put in during DG access and disconnection to improve the protection sensitivity.Finally,the feasibility of the new method is verified by simulation.