Research On Fault Location In Non-effectively Grounded New Distribution Network With DG

With the continuous development of society,the grid-connected operation of distributed generation(DG)and the use of cable hybrid lines have brought great economic benefits to the community,but also changed the flow structure of the traditional distribution network.At the same time,the power grid in our country mainly adopts the small-current grounding method,and the fault characteristic is not obvious when the single-phase grounding fault occurs;the distribution of zero sequence current will be changed by the arc suppression coil connected to the neutral point,all these factors bring new challenges to the single-phase grounding fault location problem.Therefore,this paper presents a fault line selection method and a section location method suitable for the new distribution network,which is of great significance to maintain the safe and stable operation of the system.In this paper,the transient fault characteristics of a single-phase-to-ground fault in a traditional resonant-resonant distribution system are studied.Based on the analysis,the influence of DG on the single-phase-to-ground fault characteristics is analyzed.Through the simulation model of the new distribution network with wind turbines,the correctness of theoretical analysis mentioned above is verified,which lays a theoretical foundation for the following fault line selection method.When a single-phase ground fault occurs in a new distribution network,the transient energy of the faulty line is far greater than that of a healthy line.Based on this feature,a fault line selection method based on improved HHT modal energy is proposed.The method uses the complete ensemble empirical mode decomposition(CEEMDAN)to decompose the transient zero-sequence current of each line,and then calculates the high-frequency and low-frequency modal energy separately.When the energy of the transient capacitor current in the system is large,the fault line selection is completed by using the high-frequency modal energy weighting coefficient;when the attenuation DC component is large in the system,the low-frequency modal energy weighting coefficient is used to select the fault line.At the same time,in order to eliminate the noise pollution in the environment of the recorded wave environment,this paper proposes a denoising method based on CEEMDAN and SVD to extract the pure fault component before the line selection.Through the simulations and experiments,it can be proved that the proposed method has good accuracy and adaptability,and is not affected by factors such as fault distance,arc suppression coil compensation,fault angle,grounding resistance,noise and arc fault.After accurately identifying the faulty line,this paper further proposes a method of fault section location for new distribution network with DG.When the single-phase ground fault occurs in the new distribution network,the spectral energy distributions on both sides of the fault point are different.According to this feature,the relative entropy of CEEMDAN energy with symmetry is defined to identify this difference so as to find the fault section.The method uses CEEMDAN to decompose the transient zero-sequence current information uploaded by each segment device,and reflects the difference of energy distribution between the two ends by energy relative entropy.The segment w:ith the largest entropy value can be judged as the fault segment.The simulation analysis shows that the proposed method has high accuracy and reliability,and is not affected by factors such as hybrid lines,fault location,fault closing angle,transition resistance,noise and arc fault.