Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene
Journal article, 2017

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.







ray computed-tomography




Electrical tree



L. K. H. Pallon

Royal Institute of Technology (KTH)

F. Nilsson

Royal Institute of Technology (KTH)

S. Yu

Royal Institute of Technology (KTH)

D. M. Liu

Royal Institute of Technology (KTH)

A. Diaz

Paul Scherrer Institut

M. Holler

Paul Scherrer Institut

Xiangrong Chen

Chalmers, Materials and Manufacturing Technology, High Voltage Engineering

Stanislaw Gubanski

Chalmers, Materials and Manufacturing Technology, High Voltage Engineering

M. S. Hedenqvist

Royal Institute of Technology (KTH)

R. T. Olsson

Royal Institute of Technology (KTH)

U. W. Gedde

Royal Institute of Technology (KTH)

Nano Letters

1530-6984 (ISSN) 1530-6992 (eISSN)

Vol. 17 3 1402-1408

Areas of Advance


Materials Science

Subject Categories

Materials Chemistry

Other Electrical Engineering, Electronic Engineering, Information Engineering

Condensed Matter Physics



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