Study On Fault Line Selection Of Small Current Grounding System Based On EMD And Fractal Theory

Electricity is one of the most important energy resources in People’s Daily life, and thestability of power system related to the national economic development and nationalsecurity. So, to prevent and eliminate power failures is extremely important. The presentour country mainly adopts the small current grounding system, of which, the greatest riskof failure is the single-phase grounding fault. Nevertheless, the single-phase ground faultline selection of small current grounding system has not been well solved because manyreasons, such as the fault steady state current is small, the current transformer is notbalanced, the irregular change of the power load, and the unstable fault of arc. So, theresearch of single-phase fault line selection of small current grounding system has beenbecoming the current hot and difficult.This paper first introduces the research status of single-phase earth fault line selectionfor small current grounding system at home and abroad, and summarizes the line selectionprinciples. The principle of the small current grounding system grounding method to formfault is analyzed systematically. Then, the EMD (Empirical Mode Decomposition) theoryand fractal theory and their applications are elaborated in detail. On this basis, the researchfocuses on the fractal theory and correlation dimension algorithm. Combined with EMD,and then put forward a new method that EMD and correlation dimension are used in smallcurrent grounding system in the single-phase ground fault line selection.Finally, in this paper a10.5kV transmission line is built through ATP-EMTP powersystem simulation software and the zero sequence current signals is analyzed byMATLAB. The zero sequence current is processed by EMD and extracted the harmoniccomponents to calculate the correlation dimension. Through the contrastive analysis of thecorrelation dimension, a criterion based on EMD and correlation dimension is reached forfault line selection of small current grounding system.In order to test the reliability of the line selection method and the criterion, in thisarticle, a large number of simulation examples are carried, and the factors, such as thegrounding, grounding resistance, fault switching angle and fault phase etc, affecting thesingle-phase ground fault line selection of small current grounding system are fullyconsidered. The results show that the method is not affected by the above factors, and canselect the fault line correctly and reliability, it can be used as a kind of new method for practical application.