High-impedance fault detection in EHV transmission lines

The automatic detection of high impedance faults (HIFs) on transmission systems has been one of the most persistent and difficult problems facing utilities as a major safety concern. The paper presents two approaches to HIF detection in extra high voltage transmission lines. Both schemes analyze the nature and dynamics of the arc phenomenon related to HIFs using voltage waveforms at the relaying point. The first scheme is based on discrete wavelet transform (DWT) analysis while the second analyzes the three phase voltages using high frequency tap of the coupling capacitor voltage transformers. To ensure development of reliable algorithms, an accurate modeling of HIF is utilized with its complex characteristics such as buildup, shoulder as well as nonlinearity and asymmetry. Results of computer simulation using ATP/EMTP on 345 kV transmission line system clearly reveal that each of the proposed methods can accurately detect HIFs in the EHV transmission lines as well as their ability to discriminate clearly between HIFs and various switching conditions.