Directional Element Studies For Distribution System Protection With Distributed Generation

With the vigorous development of new energy,distributed generation(DG)represent by wind energy and solar energy bring the reliability of energy supply as well as economy,environmental protection advantages,and DG has been promoted.However,the access to DG has brought many problems to the traditional protection of distribution network.The traditional protection configuration scheme,the protection action setting and the protection action cooperation will be affected to some extent and can't meet the requirements of the distribution network with DG.How to quickly and accurately judgment the fault direction of distribution network with DG has become a key problem in the study of distribution system protection.In this paper,firstly,the fault characteristics of DG to distribution network are analyzed,and the effect of distributed power supply on distribution network protection is studied at different fault locations,and focus on fault bus current characteristics of information.Based on the analysis above,aiming at the protection configuration of the traditional distribution network,the operation characteristics of the distribution network protection configuration represented by the current protection are analyzed.It is pointed out that the traditional distribution network protection cannot meet the requirements of distribution network protection with DG.Then the paper has done some research on the principle,operation characteristic and operation scope of the existing directional elements,the power direction element,the power-frequency component variation directional element,the transient energy direction element.The three directional elements in the distributed power distribution network Adaptability issues have been researched.Based on the analysis and research,this paper proposes a directional element using the current phase characteristics for two or more lines of the distribution network under phase to phase fault.The phase to phase fault characteristic was analyzed.The current phase difference between two non-fault lines are close to zero degrees,but the current phase difference between non-fault line and fault line are close to ninety degrees on the same bus.Experiments show that the directional element can quickly and accurately judge the fault direction,but the performance of the transient transition will be affected to a certain extent at the bus exit due to the phase fault.Therefore,in order to compensate for the lack of directional elements based on the current phase characteristics,this paper proposes a faulted directional element using waveform characteristic.The current phase characteristics of the fault component distribution network with DG are analyzed.The time-domain correlation analysis is used to analyze the relationship between the fault line current and the modulus of non-fault line fault component.According to that,the directional element can distinguish the fault direction.The use of the directional elements of the current waveform effectively preserves the phase information while overcoming the large influence of the transition resistance of the distribution network and avoids the problem of malfunctioning of the directional elements due to inaccurate extraction phasor.A typical model of distribution network with DG simulation system is established in MATLAB,and the reliability and effectiveness of the fault directional elements in different situations are verified.The two directional elements proposed in this paper only use the current information of the line,and adapt to the working conditions of the distribution network with DG,and reduce the configuration requirements of the installation of voltage transformers on the line side,which has well engineering application significance.