Aging model of polyethylene-based materials for HV cables founded on damage inception and growth from air-filled voids

In this paper, the aging of polyethylene-based materials for HV cables is addressed to inception and growth of damage from microscopic defects like air-filled microvoids. Such process is considered as divided in three subsequent phases: accumulation of electrons at PE-void interface and relevant injection in the air-filled void, hot-electron avalanche production in air, damage accumulation in PE due to avalanches. The rate of production of hot electrons inside the void is derived by solving the electron diffusion equation in the energy-time domain, and the growth rate of damage in polyethylene due to hot-electron discharges at the void-polymer interface is evaluated estimating local bond-breaking produced by hot electrons. An application of the proposed aging model to a PE-based material in typical working conditions for HVDC cables, including life estimation as a function of void size and applied electric field, is also presented.