不同温度热老化对XLPE电缆绝缘材料晶体结构的影响研究

Effects of Thermal Aging on the Crystal Structures of the XLPE Cable Insulating Material at Different Temperatures

交联聚乙烯(cross-linked polyethylene,XLPE)电力电缆由于优良的电气和理化性能而被广泛应用于电力传输系统。为了研究不同温度热老化对XLPE电缆绝缘晶体结构的影响,该文对商用110 k V XLPE电缆绝缘在100和160℃进行加速热老化实验,采用X射线衍射(X-ray diffraction,XRD)分析、差示量热扫描(differential scanning calorimetry,DSC)分析和扫描电子显微镜(scanning electron microscopy,SEM)观察等实验手段对不同热老化试样的晶体结构进行表征,并采用DSC法对不同热老化试样中的残余抗氧化剂含量进行表征。实验结果表明,根据抗氧化剂是否消耗完毕,XLPE试样的热老化过程可以分为物理老化阶段和化学老化阶段。物理老化阶段中,重结晶过程使得不完善的晶体趋于完善,结晶度升高;化学老化阶段中,氧化反应引发XLPE分子链断裂,结晶度下降。100℃热老化条件下,相比无定形区,结晶区具有更致密的结构,不利于O2的侵入,因此热老化主要破坏XLPE试样的无定形区。160℃热老化条件下,XLPE试样中的晶体处于熔融状态,热老化对已熔融的结晶区造成严重破坏,使得重结晶后的球晶数目减少、组成球晶的片晶数目减少、片晶间距增大、球晶结构的完整性被破坏。

The cross-linked polyethylene（XLPE） has been extensively used as an electrical insulating material for medium and high voltage power distribution cables for its outstanding physical, chemical and electrical properties. In order to study the influence of thermal aging at different temperatures on the crystal structures of XLPE cable insulation, thermal aging was conducted on 110 k V XLPE cable insulation at 100℃ and 160℃ respectively. The crystal structures of the aged samples were characterized by X-ray diffraction（XRD）, differential scanning calorimetry（DSC） and scanning electron microscopy（SEM）, and the concentration of antioxidants in different aged samples was quantitatively measured by DSC method. It is deduced by the experiment results that the thermal aging process can be divided into the physical aging stage and the chemical aging stage depending on the concentration of antioxidants in XLPE. At the physical aging stage, the re-crystallization process lead to the improvement of crystal structure and the increase in crystallinity. At the chemical aging stage, drastic chain scission lead to sharp breakage of intramolecular and intermolecular bonds, leading to the decrease in crystallinity. At 100℃, the thermal aging mainly affects the amorphous regions because of the much denser structures of crystalline regions, which may make the oxygen diffusion more difficult. At 160 ℃, the thermal aging affects the molten spherulites, resulting in decreased lamellae, increased interlamellar spacing and destruction of spherulites.