期刊
NANO LETTERS
卷 17, 期 3, 页码 1402-1408出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.6b04303
关键词
Electrical tree; ptychography; DC-tree; HVDC; polyethylene
类别
资金
- Swedish Foundation for Strategic Research [EM11-0022]
- Knut and Alice Wallenberg Foundation
- Swiss National Science Foundation (SNF) [145056]
- Swedish Foundation for Strategic Research (SSF) [EM11-0022] Funding Source: Swedish Foundation for Strategic Research (SSF)
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.
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