Modelling of a high-impedance arcing fault due to a leaning tree in medium voltage (MV) networks was experimentally verified and the network transients due to this fault were also investigated. Even though the tree had a very high resistance value, the initial transients were periodically caused by the arc reignitions after each zero-crossing. In this paper, these features are extracted from residual currents using discrete wavelet transform (DWT) to localise this fault event. The DWT performance at different measuring nodes throughout an unearthed 20 kV network can be gathered at the base station using wireless sensors concept. So, the DWT is evaluated for a wide area of the network and the fault detection is confirmed by numerous DWT extractors. Due to the periodicity of arc reignitions, the initial transients are localised not only at fault starting instant but also during the fault period that will enhance the detection security. The term of locating the faulty section is determined based on ratios of the residual current amplitudes. The fault cases are simulated by ATP/EMTP and the arc model is implemented using the universal arc representation. the residual waveforms is obvious and can be used for detecting the fault. The most suitable signal processing technique for localising these initial transients is DWT.
DWT-BASED FAULT DETECTIONWavelets are families of functions generated from one single function, called the mother wavelet, by means of scaling and translating operations. The scaling operation is used to dilate and compress the mother wavelet to obtain the respective high and low frequency information of the function to be analysed. Then the translation is used to obtain the time information. In this way a family of scaled and translated wavelets is created and it serves as the base for representing the function to be analysed [19]. Figure 4. Enlarged view of residual current waveforms (i r ) when the fault occurred in section EF.Figure 7. The detector S di of the details shown in Figure 6. (a) S di of the residual current details in section AB (i r(AB) ), (b) S di of the residual current details in section Bc (i r(BC) ), (c) S di of the residual current details in section BD (i r(BD) ), (d) S di of the residual current details in section BE (i r(EB) ), (e) S di of the residual current details in section EK (i r(EK) ), (f) S di of the residual current details in section EF (i r(EF) ).