This paper describes an algorithm to detect and classify electrical events related to power quality. The events detection is based on monitoring the statistical characteristics of the energy of the error signal, which is defined as the difference between the monitored waveform and a sinusoidal wave generated with the same magnitude, frequency, and phase as the fundamental sinusoidal component. The system novel feature is the event recognition based on a neural network that uses the error signal as input. Multi-rate techniques are also employed to improve the system operation for on-line applications. Software tests were performed showing the good performance of the sytem. © 2005 IEEE. 54175420Arrillaga, J., Watson, N.R., Bollen, M.H.J., Power quality following deregulation (2000) Proc. of the IEEE, 88 (2), pp. 246-261. , FebDugan, R.C., McGranaghan, M.F., Beaty, H.W., (1996) Electrical Power Systems Quality, , McGraw-HillPoisson, O., Rioual, P., Meunier, M., Detection and measurement of power quality disturbances using wavelet transform (2000) IEEE Trans. on Power Delivery, 15 (3), pp. 1039-1044Ibrahim, W.R.A., Morcos, M.M., Artificial intelligence and advanced mathematical tools for power quality applications: A survey (2002) IEEE Trans. on Power Delivery, 17 (2), pp. 668-673Santoso, S., Grady, W.M., Powers, E.J., Lamoore, J., Bhatt, S.C., Characterization of distribution power quality events with fourier and wavelet transforms (2000) IEEE Trans. on Power Delivery, 15 (1), pp. 247-254Ribeiro, M.V., Duque, C.A., Romano, J.M.T., An improved method for signal processing and compression in power quality evaluation (2004) IEEE Trans. on Power Delivery, 19 (2), pp. 464-471Ramos, F.R., Ribeiro, M.V., Romano, J.M.T., Duque, C.A., On signal processing approach for event detection and compression applied to power quality evaluation (2002) Proc. of the IEEE 10th International Conference on Harmonic and Quality of Power, pp. 133-138Lippmann, R.P., A critical overview of neural network pattern classifiers (1991) IEEE workshop on Neural Network for Signal Processing, pp. 266-275Santoso, S., Powers, E., Grady, W.M., Parsons, A.C., Power quality disturbance waveform recognition using wavelet-based neural classifier-part 1: Theoretical foundation (2000) IEEE Trans. on Power Delivery, 15 (1), pp. 222-228Santoso, S., Powers, E., Grady, W.M., Parsons, A.C., Power quality disturbance waveform recognition using waveletbased neural classifier-part 2: Application (2000) IEEE Trans. on Power Delivery, 15 (1), pp. 229-235