Non-direct-ground System Single Line-to-earth Fault Location With Wavelets Analysis Method

Non-ground and Peterson-coil-grounded neutral systems are also called non-direct ground systems. They are widely employed in distribution net~vorks. However, when a single line-to-ground fault occurs, it is rather difficult to identify the fault feeder because the fault currents are much too small. Several methods have been developed to solve the problem, but none? of them can perform well under various fault conditions. This paper introduces a method utilizing the strong transient components in the fault currents. While an appropriate signal-processing tool is keenly need. Wavelet transform, also called wavelet analysis, is a set of new and promising theories in mathematics, and has been proved to be very efficient for transient signal analysis. It consists in building a new representation of the analyzed signal, according to a set of damped oscillations named avelets? Each wavelet is derived from an original function, i.e. the other wavelet? by translation and scaling. By transforming the fault signals of single-line-to-ground faults into their corresponding details, we can tell easily on which line the faults have occurred. The major point here is to compare the maximum points of the details, either their magnitudes or directions can be used to identify the fault line. We have also dealt with some problems about the issue, including the unbalanced currents caused by unsymmetry of three phase current transformers, the high resistance of the fault, zero-crossing-faults, etc.