The residual ac breakdown voltage of 6.6 kV dry-cured XLPE power cable under wet-accelerated aging tests

The residual ac breakdown voltage decreased to about half of the initial breakdown voltage after 3 months of accelerated aging test under immersion. This decrease was found to be caused mainly by a trace amount of moisture existing in the insulation. However, the breakdown voltage did not further decrease with increasing moisture content. In order to clarify the influence of moisture, the state of water existing in the insulation was investigated using FTIR (Fourier transform infrared spectroscopy) and optical microscopy. From these results, it was concluded that the moisture in the amorphous region and/or at the interface next to the crystal region caused the reduction of the ac breakdown voltage.