Thickness dependence of space charge in XLPE and its nanocomposites under temperature gradient

The effect of the introduction of nano-fillers into polyethylene on space charge accumulation is usually studied in electric fields reaching 100kV/mm using thin 100 gm samples, which is much thinner than the insulation in actual HVDC cables. Our previous work showed that space charge distributions in LDPE and its nanocomposites have different thickness dependences at isothermal temperature (20 degrees C and 60 degrees C). This was explained using the bipolar model and trapping potential model. However, in actual cables the temperature is not isothermal, but has a gradient, so we have investigated the space charge distribution in unfilled XLPE and its SiO2 nanocomposites under different temperature gradients at 50kV/mm. It is found that the unfilled XLPE space charge distributions definitely have thickness dependence under a temperature gradient. The XLPE/SiO2 nanocomposites also show strong thickness dependence: the thin samples accumulate large heterocharge densities, but the thicker the sample is, the less the heterocharge accumulates and even under a temperature gradient the 0.5mm nanocomposites still suppress most of the hetero charge.