In order to study the initiation and growth of electrical trees in XLPE cable influenced by local air pressure

using samples of XLPE cable with artificial defect made with needle and square-cut XLPE slices as examples

we built up a test system to investigate the growth regularity and partial discharge features of the electrical trees in the inner insulation layers or the channels of the trees with local air pressure on. The results show that the air pressure acting on the inner insulation layers has no significant influence on the initiation and early growth of electrical tree

but in the later growth stage

it promotes the trees’ growth rate

decreases the trees’ dimension and increases the trees’ expanding coefficient. On the other hand

the pressure acting on the channels of a tree alters the discharge pattern into streamer discharge while the discharge pulses distribute nearly in all phases. Further analysis indicates that the deformation of softening area at high temperatures under the air pressure is the main factor that promotes the electrical tree growth

and the increased gas density which causes more violent collision ionization will primarily cause the earlier streamer discharge.