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Research On Single Phase-to-Ground Fault Line Selection Of Small Current Ground System Based On Mathematical Morphology

Posted on:2012-11-25Degree:MasterType:Thesis
Country:ChinaCandidate:X M LongFull Text:PDF
GTID:2132330332998504Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
ABSTRACT:With economic development and urban construction, the distribution network structure become increasingly complex and a large number of cables have been used, therefore, in order to guarantee the reliability of power supply, it must debugging accurately and rapidly. The low and medium voltage distribution network in our country mainly adopts the small current neutral grounding system, single phase fault account for 80% of the small current neutral grounding system fault, and fault line selection has received much concern. There are already so many principles and methods of fault line selection, but overall, these methods have some defects, and should be improved furtherly.Based on the analysis of single phase grounding fault's features in small current neutral grounding system, and according to the mutation of transient information after fault, the paper proposes a new method to fulfill fault line selection which is based on SMMG transform in mathematical morphology. Specific criterions are:the current signal in fault line is transformed by SMMG, the polarity of the first modulus maximum obtained by the transformation is opposite to that in non-fault line, and it's the maximum value, the ratio of the maximum value:the second largest value is always greater than K1(the threshold value is setted by concrete line), the ratio of the SMMG coefficient's max spectrum energy value:the second largest value is always greater than K2(the threshold value is setted by concrete line). For the small current neutral grounding system which install zero sequence current transformer directly, zero sequence current in each line is transformed by SMMG directly; for the small current neutral grounding system which install only A-C two-phase current transformer, when the A or C phase is fault, choose the current signal perform SMMG transformation, when the B phase is fault, construct characteristics modulus Iy by A, C phase current Iy=(Ia+Ic)/3, Iy is transformed by Wavelet, then distinguish the fault line.This paper chooses Matlab's. m language to construct mathematical morphology filter, and proper structure element to perform de-noising processing of the collected signals, it can make effectively filter and retain transient signals; construct SMMG to fulfill the detection and line selection of fault information's catastrophe point. Using PSCAD/EMTP simulation software to build the small current neutral grounding system model, through a large number of simulation experiments indicate that:the mathematical morphology line selection Algorithms which are based on zero sequence current and the fault phase current in are less affected by grounding resistance, fault time, fault location and other factors, it can do line selection accuratly and reliably in a variety of fault conditions, simple calculation, and fast.
Keywords/Search Tags:Small Current Neutral Grounding System, Single Phase Grounding Fault, Mathematical Morphology, SMMG, Fault Line Selection, Zero Sequence Current, Fault Phase Current
PDF Full Text Request
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