부산대학교 도서관

This article presents an experimental comparative study of streamer currents propagating in mineral oil (MO), natural esters [olive oil (OO) and rapeseed oil (NE)], and synthetic ester (SE, tetra-ester) under both positive and negative lightning impulse voltages. Because of the similarity in the shapes of streamer currents in investigated liquids, it is difficult to differentiate between the current signals corresponding to each liquid. For that purpose, two techniques are used for the analysis of these signals. The first one is the fast Fourier transform (FFT) technique, which is based on the frequency spectrum analysis. The second one is the discrete wavelet transform (DWT) method, which has demonstrated its ability for the analysis of the nonstationary signals. The obtained experimental results show spectral signature specific to each liquid, thus making it possible to differentiate the various streamer currents. Overall, the two techniques show good performance. However, the accuracy and effectiveness of the DWT method are better than those of the FFT technique.