Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene
Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene
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DOI：
10.1021/acs.nanolett.6b04303
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发表时间：
2017-03-01
期刊：
影响因子：
10.8
通讯作者：
Gedde, Ulf W.
中科院分区：
文献类型：
--
作者：
Pallon, Love K. H.;Nilsson, Fritjof;Gedde, Ulf W.
电树枝是电力系统中绝缘材料击穿的原因之一。了解电树的生长在发展可靠的高压直流（HVDC）电网系统中起着至关重要的作用，其传输电压高达1 MV。一个部分，包含一个电树在低密度聚乙烯（LDPE）已被可视化的三维（3D）的分辨率为92 nm的X射线重叠关联断层扫描。3D成像显示，在电树的主要分支周围形成了具有较低密度的几百纳米宽度的预通道形成物。前通道结构通过穿过密度较低的材料的路径与主树部分连接，证明树通过在主通道前面形成的前台阶结构以逐步的方式生长。所有的预通道结构的尺寸远低于帕邢定律的限制，因此不是由局部放电形成的。相反，有人建议，prechannel结构形成的机电应力和碰撞电离，其中前者被证实是一个潜在的解释与机电应力张量几乎相同的数量级的低密度聚乙烯的短期模量的模拟。
Electrical trees are one reason for the breakdown of insulating materials in electrical power systems. An understanding of the growth of electrical trees plays a crucial role in the development of reliable high voltage direct current (HVDC) power grid systems with transmission voltages up to 1 MV. A section that contained an electrical tree in low-density polyethylene (LDPE) has been visualized in three dimensions (3D) with a resolution of 92 nm by X-ray ptychographic tomography. The 3D imaging revealed prechannel-formations with a lower density with the width of a couple of hundred nanometers formed around the main branch of the electrical tree. The prechannel structures were partially connected with the main tree via paths through material with a lower density, proving that the tree had grown in a step-by-step manner via the prestep structures formed in front of the main channels. All the prechannel structures had a size well below the limit of the Paschen law and were thus not formed by partial discharges. Instead, it is suggested that the prechannel structures were formed by electro-mechanical stress and impact ionization, where the former was confirmed by simulations to be a potential explanation with electro-mechanical stress tensors being almost of the same order of magnitude as the short-term modulus of low-density polyethylene.