| Neutral un-effectual grounding system (NUGS) is widely used in 6-66kVdistribution networks in China because of its high reliability. With the increase of netcapacity and length of transmission lines, the grounding capacitance current becomeslarger which leads to inevitable arc's earthing faults. As a result it raises the difficultyof line detection for single-phase-to-earth fault.After theoretical analyzing on traditional arc model which is based on physicalconcept and mathematical derivation, arc simulation model for NUGS is established.Two parameters, which are the peak value of steady state arc current and arc length,are introduced in this model. By setting these two parameters, various arcs can beeasily obtained under different steady state arc current. With the model embedded inthe NUGS simulation model, research on line detection for single-phase-to-earth faultin NUGS can be implemented.Fault features of single-phase arc's earthing in NUGS are analyzed, and then theoperating behavior of"Principle of Fault line-detection based on wavelet packetsreconstruction algorithm in NUGS"for arc's earthing fault is studied. As a result ofthe nonlinear, dynamic and damping behavior of arc, the above methodology fails todetect the fault line at the extreme case of arc's earthing fault that happens near zeropoint of the phase voltage and with the arc's length exceeding 100cm. Consideringthis extreme case, improved measure is proposed in this paper. It extracts thecharacteristic frequency bands, which compose arc transient feature, fromzero-sequence current of each line via wavelet packets decomposition algorithm. Thenreconstructed coefficients are utilized to detect the faulty line. Simulation resultsprove that it is reliable under whatever arc's earthing fault condition.
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