In this paper, quantum chemical calculation and isothermal relaxation current (IRC) measurement are performed on thermally aged XLPE cables to investigate the effect of defects on dielectric properties and trap energy distribution of XLPE insulation. Samples of XLPE cables are thermally aged at 135 °C up to 45 days. Microscopic experiments including gel permeation chromatography, differential scanning calorimetry, and Fourier transform infrared spectrometer show that the molecular weight and crystallinity of XLPE decreases with aging time. The IRC results show that both the trap density and the trap depth increase with aging. To quantitatively calculate the trap depth variation due to physical and chemical defects by thermal aging, a quantum chemical calculation is carried out based on Gaussian 09. It is found that the broken cross-linking bonds between molecular chains weaken the stability of the molecular network structure, introducing the shallow physical trap (0.3 eV) in the aged XLPE. The molecular chain is thermally oxidized, the carbonyl group is introduced as a deep chemical trap (1.44 eV) in the XLPE. The chemical defect not only changes the localised energy state, but also significantly decreases the intrinsic breakdown strength of XLPE molecule from 0.62 to 0.51 V/Angstrom in quantum chemistry calculation.

中文翻译：

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基于量子化学计算的交联聚乙烯电缆绝缘老化特性研究

本文通过对热老化交联聚乙烯电缆进行量子化学计算和等温弛豫电流 (IRC) 测量，研究缺陷对交联聚乙烯绝缘的介电性能和陷阱能量分布的影响。XLPE 电缆样品在 135 °C 下热老化长达 45 天。凝胶渗透色谱法、差示扫描量热法和傅里叶变换红外光谱仪等显微实验表明，交联聚乙烯的分子量和结晶度随着老化时间的延长而降低。IRC 结果表明陷阱密度和陷阱深度都随着老化而增加。为了定量计算热老化引起的物理和化学缺陷引起的陷阱深度变化，基于Gaussian 09进行了量子化学计算。发现分子链间断裂的交联键削弱了分子网络结构的稳定性，在老化的 XLPE 中引入了浅层物理陷阱（0.3 eV）。分子链被热氧化，羰基作为深层化学陷阱 (1.44 eV) 引入 XLPE。化学缺陷不仅改变了局域能态，而且在量子化学计算中显着降低了 XLPE 分子的固有击穿强度从 0.62 到 0.51 V/埃。