Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene
2017 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, no 3, 1402-1408 p.Article in journal (Refereed) Published
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.
Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017. Vol. 17, no 3, 1402-1408 p.
Electrical tree, ptychography, DC-tree, HVDC, polyethylene
IdentifiersURN: urn:nbn:se:kth:diva-204068DOI: 10.1021/acs.nanolett.6b04303ISI: 000396185800013PubMedID: 28177252ScopusID: 2-s2.0-85014927866OAI: oai:DiVA.org:kth-204068DiVA: diva2:1085510
QC 201703292017-03-292017-03-292017-03-29Bibliographically approved