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This paper presents a wavelet-based method for real-time detection of voltage sags in transmission lines. The wavelet coefficient energies of the phase voltages and currents are used for real-time detection of the transients at both beginning and end times of voltage sags. On the other hand, the voltage sags are identified in real-time by means of the approximation coefficient energy analysis. The voltage sag diagnosis method was evaluated by using the Real Time Digital Simulation (RTDS).
Costa et al. (2010) studied this question.