Spectral Power Analysis of Partial Discharges Waveforms During Electrical Tree Growth Under Different Excitation Frequencies

Electrical trees are the main mechanism of failure in solid polymeric insulation. Their growth is associated to partial discharge (PD) activity. Measuring and analyzing PDs during tree growth is crucial for the insulation condition assessment and thus, the risk of failure of power equipment. Here, PD pulse waveforms are analyzed using power ratios maps. The aim of the study is to evaluate the ability of power ratio maps to determine the state of progression of electrical trees. Electrical trees were grown in epoxy resin samples at different frequencies, while PDs were measured using very-high frequency (VHF) and ultra-high frequency (UHF) techniques. The progression of the tree was observed using an optical camera and it was correlated with PD data. The results showed that power ratio maps obtained from VHF and UHF signals yield similar patterns. Especially in VHF, it was observed that the centroids of the clusters associated to each stage of tree-growth moved with tree-progression. PDs at the beginning of tree-growth were located at the top-right of power maps, while in more advanced stages, they were located more to the bottom-center of the maps. This means that the PD pulse waveform had higher frequency content in the beginning than in the end of tree growth. In base of this initial results, it is concluded that power ratio maps are sensitive to the state of growth of electrical trees, and thus, can be used for assessing the risk of failure of insulation subjected to electrical treeing degradation mechanism.