The S-Transform (ST) is an extension of wavelet transform which posses 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. Phase spectrum obtained in this transform is always with respect to fixed reference point and the real and imaginary spectrum can be localized independently. Such a transform with moving and scalable localizing Gaussian window, therefore, provides excellent time localization property for different nonstationary signals. In this paper the ST of fault current signal is analyzed for an advanced series compensated transmission system. The time-frequency analysis of the current signals at different fault conditions of the system clearly classifies the faulty sections and phases.