Font Size: a A A

Research On Fault Line Selection In Neutral Un-effectual Grounded System Based On S-Transform

Posted on:2013-08-25Degree:MasterType:Thesis
Country:ChinaCandidate:J F SuFull Text:PDF
GTID:2232330374476247Subject:Power system and its automation
Abstract/Summary:PDF Full Text Request
Neutral un-effectual grounded system is widely used in Chinese medium voltagedistribution network. In distribution networks, single-phase grounding fault is the mostfrequent in all faults. However, the fault detection of neutral un-effectual grounded systemwhen single-phase grounding fault occurs has never been effectively solved because faultcurrent is weak and fault arc is unstable.This paper aims to solve this problem based onS-transform.First, this paper introduces the domestic and international fault line selection researchresults in neutral un-effectual grounded system, summarizes the current fault line selectionapproaches and analyses the problems of the existing methods. And then, the transient andsteady-state failure characteristics of neutral un-effectual grounded system is analyzed. Byanalyzing the input impedance characteristics of lines in the zero sequence network, selectedfrequency band in which transient zero sequence current of fault and non-fault line presentedin opposite polarity is found for line selection. After analyzing the time-frequencycharacterization capabilities, S-transform is used to extract the transient zero sequence currentamplitude and phase angle information. Selecting the lines which has the largest and thesecond equivalent current amplitudes in selected frequency band as candidacies. For eachcandidacy, by calculating the phase angle unbiased variance of the rest lines, and the phaseangle difference between candidacy and rest lines’ mean value, candidacy could be real faultline or not can be decided. When the feature of phase angle is not so sharp, by calculating thecorrelation coefficient of each line in the selected frequency band, smaller mean value ofcorrelation coefficient of the candidate line is selected as the fault line. Finally, Using theHypersim to establish simulation model of neutral un-effectual grounded system whichineludes ovetheadlines, cables and ovethead line-cable mixed line. A various simulations ofdifferent lines, different fault distance, different fault resistance and different fault close angleare done to obtain a large number of fault data, and using them to test the accuracy of thealgorithm and capacity of resisting disturbance.
Keywords/Search Tags:neutral un-effectual grounded system, fault line selection, transient zero sequencecurrent, S-transform, Hypersim
PDF Full Text Request
Related items