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Evaluating the electric power quality (EPQ) becomes very important task due to the widespread use of nonlinear loads, distributed energy resources (DERs) and the economic impact of poor EPQ. In a deregulated environment, having different power quality indices (PQIs) with different values has no significance unless they are combined into single value that could represent them. In this paper, a new fuzzy-wavelet packet transform based PQI is introduced that amalgamates the recommended PQIs after being redefined in the time-frequency domain using wavelet packet transform for compatibility purposes with nonstationary disturbances. In order to handle the uncertainties associated with the electric power system operations, fuzzy systems are used in this paper. In order to study the effect of wavelet filter length and the choice of the best wavelet basis function, the new fuzzy developed modules along with the reformulated PQIs are used in three case studies considering electric arc furnace load supplied from stationary low distorted voltage, stationary high distorted voltage and nonstationary distorted voltage (voltage dip) in addition to a real case study considering variable speed drive.