The influence of O2, N2 and H2O on space-charge accumulation in XLPE under DC fields

The development of space-charge in XLPE insulation of power cables was investigated using the LIPP technique on samples 85 cm long. Exposing the samples to 130 kPa of dry O₂ or dry N₂ at 80°C for 24 hr had little effect on space-charge accumulation under a dc field. Exposure to a high humidity environment for 24 hr at 90°C caused an increase in space-charge density near the outer electrode and in the bulk. When the polarity of the applied voltage was reversed the equilibrium space-charge profile was very similar to that observed before reversal, but with opposite polarity. This suggests an apparent space-charge originating from an inhomogeneous concentration of partially aligned permanent molecular dipoles