Partial discharges in electrical trees grown at 0.1 (VLF) and 50 Hz analyzed using PRPD and NLTSA

Electrical treeing is one of the main degradation mechanisms in high voltage polymeric insulation that could lead to electrical equipment failure. Electrical trees grow under partial discharge (PD) activity; therefore, PD measurement is a fundamental tool for electrical insulation diagnosis. In this paper, PDs are analyzed for electrical trees grown in epoxy resin needle-plane samples at very low frequency (VLF) 0.1 Hz and 50 Hz excitation voltages. PD analysis was carried out through the traditional PRPD analysis and with nonlinear time series analysis (NLTSA) tools, which is more recent in this context. For PRPD analysis at VLF, the discharge power and the 95th percentile of PD amplitude showed a nearly linear increase with the tree length. However, at 50 Hz, these parameters showed an oscillatory behavior which could be a consequence of a more conductive structure. For NLTSA, we calculated the correlation dimension and Lyapunov exponent. This last parameter showed positive values for VLF and 50 Hz tests, indicating a deterministic chaotic behavior for both cases.