Dealing with noise polluting electric signals acquired from a large power group

The paper is focused on finding appropriate procedures of denoising electrical signals (SN) acquired from the secondary winding of the excitation transformer in a large power group and evaluating their benefits. The signals were affected by white Gaussian noise with relatively high Signal to Noise ratios. The currents have significant harmonic contents (total harmonic distortions exceeding 25%). Two sets of 30 consecutive periods from quasi-stationary data, corresponding to different active powers, were analyzed. Firstly “average” signals (AS) of one period length were determined in order to obtain estimated values for the power of noise (EPN). Computations were made afterward by using the 1-st periods from the acquired signals in order to establish the best denoising parameters, considering the EPN and the root mean square differences relative to the AS when compared to signals denoised (SD) in different ways. Once determined the denoising parameters, the 1-st periods from SN, AS and SD were analyzed by using original FFT based programs in order to evaluate power quality (PQ) indices of all types of signals. Conclusions were drawn relative to the effects of denoising over the accuracy in evaluating PQ indices.