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Three-Dimensional Nanometer Features of Direct Current Electrical Trees in Low-Density Polyethylene
Love K H Pallon1, Fritjof Nilsson1, Shun Yu1
1School of Chemical Science and Engineering, Fibre and Polymer Technology, KTH Royal Institute of Technology , SE-100 44 Stockholm, Sweden.
Nano Letters
|February 9, 2017
Summary
Electrical trees in insulating materials grow in steps via prechannel structures, not partial discharges. This finding is crucial for developing reliable high voltage direct current (HVDC) power grids.
Area of Science:
- Materials Science
- Electrical Engineering
- Physics
Background:
- Electrical trees cause insulation breakdown in power systems.
- Understanding electrical tree growth is vital for reliable high voltage direct current (HVDC) power grids up to 1 MV.
Purpose of the Study:
- To visualize the 3D structure of electrical trees in low-density polyethylene (LDPE).
- To elucidate the growth mechanism of electrical trees at the nanoscale.
Main Methods:
- X-ray ptychographic tomography was used for 3D visualization of an electrical tree in LDPE at 92 nm resolution.
- Simulations were performed to investigate the role of electro-mechanical stress.
Main Results:
- 3D imaging revealed nanoscale prechannel formations with lower density around the main electrical tree branch.
- Prechannel structures were connected to the main tree via lower-density paths, indicating step-by-step growth.
- Prechannel structures were too small to be formed by partial discharges, suggesting electro-mechanical stress and impact ionization as the cause.
Conclusions:
- Electrical tree growth in LDPE occurs in a step-by-step manner through prechannel structures.
- Electro-mechanical stress and impact ionization are the likely mechanisms for prechannel formation, not partial discharges.
- This research provides critical insights for enhancing the reliability of HVDC power systems.
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