Research On Small Current Grounding System Single-phase Earth Fault Line Selection Algorithm And Design Of Fault Line Selection Deveice

Small current grounding system includes neutral non-grounded system andPetersen-coil grounded system,they are both neuteal un-effectual grounded systems.Powersystems with this kind of neuteal grounding mode have the advantage of the power supplyreliability.6-66kv power grids in our country widely use neuteal un-effectual groundedmode. Single-phase-to-ground fault for medium and low voltage distribution network isvery frequent, statistics shows that single-phase-to-ground fault accounts for more than80%of medium and low voltage power distribution line fault, intermittent arc groundingcaused by single-phase grounding fault will generate the arc grounding overvoltage whichmay be bad for insulation performance. So the study of single-phase-to-ground fault insmall current grounding system has important theory meaning and realistic meaning.This paper studies the fault characteristics of single-phase grounding fault in a typicalsmall current grounding system and the change laws of fault line’s current and voltage,andanalyses several kinds of fault line selection algorithm and their respective applicableoccasions. Based on the truth of that single-phase grounding faults are complicated andthe low accuracy of the onefold fault line selection algorithm,this paper constructs anintegrated fault line selection criterion according to the measure value, the criterion takesthe advantages of active power method、the first half wave method and the waveletanalysis method in order to improve the reliability of the fault line selection device.Current amplitude fault measure、current phase fault measure、wavelet coefficientfault measure、first half wave fault measure and active component fault measure arechosen to quantify the possibility of a specific line.For neutral non-grounded system andPetersen-coil grounded system,this paper uses different fault measures combinations toform a integrated fault line selection logic, so as to guarantee the accuracy of line selectionresults and improve the adaptability of the integrated line selection scheme;this paper alsoadd the PT wire break and ferro-resonance discriminant program,which can effectivelyprevent the device to mistake these two kinds of phenomena for single-phase-to-groundfault. The paper expounds the basic principle of wavelet analysis, on the basis of thesestudies,this paper realizes the C language of the wavelet analysis and writes the C code ofwavelet decomposition and reconstruction,they are successfully applied to the DSP chip.In addition, in order to meet the data record and offline analysis,the function of saving theraw data during the fault according to COMTRADE standard is added.Because of actual need, this device adopts the DSP+ARM multi-cpu-scheme, andcarried out modulares design in accordance with their different function,using the plugtype installation for the convenience of commissioning and maintenance. Logical softwareprocess design and excellent hardware anti-jamming capability ensure the overallperformance of the fault line selection device and the accuracy of the fault line selectionresults.