Abstract
The influence of the thermal field of a transformer during operation on the thermal stability of meta-aramid insulation paper was studied through molecular dynamics simulations. Models of the crystalline and amorphous regions of meta-aramid fibers were constructed using known parameters. The model of the crystalline area was verified by comparing X-ray diffraction results with experimental data. The reasonableness of the simulation results was judged by the variation of energy, temperature, density, and cell size in relation to the dynamic time. The molecular dynamics simulations revealed that the modulus values in the crystalline regions were two to three times higher than those in the amorphous regions at various temperatures. In addition, the incompressibility, rigidity, deformation resistance, plasticity, and toughness of the crystalline regions were obviously higher than those of amorphous regions, whereas the toughness of the amorphous regions was better than that of the crystalline regions. The mechanical parameters of both the crystalline and amorphous regions of meta-aramid fibers were affected by temperature, although the amorphous regions were more sensitive to temperature than the crystalline regions. The molecular chain motion in the crystalline regions of meta-aramid fibers increased slightly with temperature, whereas that of the amorphous regions was more sensitive to temperature. Analyzing hydrogen bonding revealed that long-term operation at high temperature may destroy the structure of the crystalline regions of meta-aramid fibers, degrading the performance of meta-aramid insulation paper. Therefore, increasing the crystallinity and lowering the transformer operating temperature may improve the thermal stability of meta-aramid insulation paper. However, it should be noted that increasing the crystallinity of insulation paper may lower its toughness. These study results lay a good foundation for further exploration of the ways to improve the performance of meta-aramid insulation paper.
Highlights
Aramid paper was developed by Du Pont in the 1960s and called Nomex paper
It is known from X-ray diffraction (XRD) analysis that the crystal structure of meta-aramid fibers is triclinic with specific unit cell parameters of a = 0.527 nm, b = 0.525 nm, c = 1.13 nm, α = 111.5◦, β = 111.4◦, and γ = 88.0◦ [28,29]
Our results indicated that the aging of meta-aramid insulation paper starts from amorphous regions with relatively poor thermal stability, and the speed of aging is influenced by the thermal field
Summary
Aramid paper was developed by Du Pont in the 1960s and called Nomex paper. Aramid paper was produced from Nomex short-cut fibers and aramid pulp as raw materials using an oblique net papermaking wet method [1]. The aging process and its mechanism on oil–paper in transformers have been investigated [8,9,10,11,12,13,14,15,16,17,18], the thermal stability of meta-aramid insulation paper in transformers at operating temperature has not been analyzed. It remains important to examine the thermal stability and thermal aging mechanism of crystalline and amorphous regions in meta-aramid insulation paper. A molecular dynamics simulation method [19,20,21,22,23,24,25,26,27] is used to conduct a comparative analysis of the influence of a thermal field on the thermal stability of crystalline and amorphous regions of meta-aramid fiber from the perspective of an actual thermal field environment inside a transformer. This paper lays a foundation for further study on how to improve the performance of meta-aramid insulation paper
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