Effect of liquid impregnation on electrical tree initiation in XLPE

The tree initiation voltage of impregnated crosslinked polyethylene (XLPE) with a dielectric liquid is drastically improved compared to normal XLPE for both ac and impulse voltage application. It is considered that liquid fills the polymer free volume, and removes space for electrons to be accelerated to high energy. The experimental results support that collision impact of electrons accelerated in polymer free volume is the dominant cause of electrical tree initiation, and also show that liquid impregnation is a promising way to improve performance and prolong the life of polymeric insulating materials.