To study the effect of accelerated thermal ageing on the propagation and partial discharge characteristics of electrical trees of 500 kV extra high voltage direct current(EHVDC)cross-linked polyethylene(XLPE)cable

cross-cut and ring-cut samples were prepared. Electrical tree initiation and growth experiments were conducted at three temperatures

using a real-time electrical tree observation system and partial discharge measurement setup. Combined with differential scanning calorimetry

conductivity tests and molecular dynamics simulations to analyze the effect of accelerated thermal ageing. Accelerated thermal ageing significantly reduces the tree initiation voltage

shortens initiation time

increases tree growth rate

and elevates both partial discharge magnitude and pulse repetition rate. The oxidation induction time and crystallinity decrease after ageing

in dicating molecular chain scission and enlarged amorphous regions due to antioxidant depletion

led to conductivity increase and activation energy decrease. Molecular dynamics simulations show an increase in the fraction of free volume. The expansion of amorphous region and enlarged inter-chain gaps enhance charge transport channels and reduce energy barriers

leading to higher partial electrical field strength

faster tree initiation

and more complex electrical tree branching structure.