The effect of inclusions in XLPE insulations on electrical trees generated by ac and grounded dc voltage

The effects of peroxide decomposition products and antioxidant in XLPE (cross-linked polyethylene) insulation on the initiation of ac tree (the tree generated by ac voltage) and the grounded dc tree (the tree generated by the grounded dc voltage) was investigated. Both inclusions were confirmed to have the effect of suppressing ac and the grounded dc tree. The peroxide decomposition products and antioxidant were confirmed to have almost the same effect in ac tree suppression at ambient temperature, while in grounded dc tree suppression peroxide decomposition products showed a greater effect than the AO. The ac tree inception voltage of XLPE containing peroxide decomposition products decreases with the increase of temperature. This decrease could be due to the loss of the decomposition products at elevated temperature. The tree inception voltage of degassed XLPE at high temperature is found to be almost equal to the inception voltage at ambient temperature. The mechanism of tree suppression and polarity effect of the grounded dc tree was examined.