Electrical Tree Growth Under Very Low Frequency (VLF) Voltage Excitation

Electrical trees are a mechanism of failure of high voltage polymeric insulation. Their growth is associated to partial discharges (PD). Conventionally, PD are analyzed using phase-resolved PD plots and statistical parameters. An alternative is to exploit the tools of nonlinear time series analysis to analyze PD as a nonlinear dynamical process. Standards for field testing of power cable include the measurement of PD under very low frequency (VLF) voltage excitation. Here we calculated the correlation dimension of the reconstructed dynamic object obtained from the time series of PD during tree propagation. Also, conventionally PD analysis was carried out to compare with the alternative approach. Electrical trees grown at 0.1 Hz 14, 16 and 18 kV have been analyzed, along a tree grown at 50 Hz 14 kV for comparison. Different PD dynamics were found, depending on the applied voltage and frequency, and the stage of tree-growth. The results show that the approach using nonlinear time series analysis can be an alternative method of analyzing tree growth and PD under VLF voltage excitation.