Water and Energy Research Digest

This paper presents a new approach for transmission line protection using a time-frequency transform technique. The transform known as S-Transform (ST) is used for fault detection from the current and voltage signal at the relaying point. ST is an extension of wavelet transform and possesses superior property over the latter as the moving functions are fixed with respect to time axis while the localizing scalable Gaussian window dilates and translates, providing excellent time localization property for different signals. The spectral energy of the ST of the current and voltage signals gives the indication of fault and no-fault condition. Also the phasor estimation is done to find out the magnitude and phase of the faulted current and voltage signals which provide accurate results even with noisy conditions. Using the magnitude and phase of current and voltage signal, the impedance to the fault point is calculated. After the fault detection, fault location is calculated using polynomial curve fitting from an index obtained from the spectral energy of the voltage and current signals.