Dynamic behavior of interconnected channels in water-treed polyethylene subjected to high voltage

While increasing a 500 Hz voltage from 300 V to 2000 V, the charging and ac loss currents of a water-treed XLPE are observed to increase more with voltage than those of a non-degraded XLPE. The fundamental and the third harmonic of the ac loss current have been numerically analyzed based on a model of water-treed insulation. In the model, a nonlinear voltage dependence of the conductance of a water-filled channel region is assumed. Magnitudes and phase angles of the fundamental and 3rd harmonic components of the ac loss current calculated from the model are compared with the observed ones. It was found that the length of water-filled channel region of a water tree grows with increasing voltage, and that this length approaches that of the water-treed region estimated by the pulsed electroacoustic (PEA) method