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Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene

L. K. H. Pallon ; F. Nilsson ; S. Yu ; D. M. Liu ; A. Diaz ; M. Holler ; Xiangrong Chen (Institutionen för material- och tillverkningsteknik, Högspänningsteknik) ; Stanislaw Gubanski (Institutionen för material- och tillverkningsteknik, Högspänningsteknik) ; M. S. Hedenqvist ; R. T. Olsson ; U. W. Gedde
Nano letters (1530-6984). Vol. 17 (2017), 3, p. 1402-1408.
[Artikel, refereegranskad vetenskaplig]

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.

Nyckelord: Electrical tree, ptychography, DC-tree, HVDC, polyethylene, ray computed-tomography, conductivity, initiation, breakdown, polymer, samples, model

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Denna post skapades 2017-03-31. Senast ändrad 2017-10-18.
CPL Pubid: 248739


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Institutionen för material- och tillverkningsteknik, Högspänningsteknik (2005-2017)


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