Location of Faults on Transmission Lines Using Wavelet Transforms

Waveforms of voltages and currents in electrical power systems may include higher harmonics, transient components and random noise due to faults and other disturbances. For the control and protection devices, it is necessary to estimate in real-time parameters of the basic waveforms. Various digital algorithms have been developed for real-time estimation of the phasors of fundamental components. The most known methods are basing on the Fourier technique. By on-line estimation the phasors of the currents and voltages main component do not rotate under stationary conditions. When using Fourier algorithms under transient conditions the estimated phasors change their positions. However, the trajectories of the estimated parameters are not monotonous. The estimated phasors can be applied to calculating the impedance of a faulted transmission line, for protection devices. To predict the desired parameters of a protected line under transient conditions we need a monotonous behaviour of the transient response of algorithms for impedance calculating. Different wavelets have been investigated. In this paper some investigation results of the complex Morlet wavelet are shown. On the basis of extensive investigations, using Morlet wavelet with the scale coefficient a = 0.01 for the both current and voltage filtering is proposed.