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Molecular Simulation Study on the Effect of Moisture on Micr

  The water molecules added in the insulating paper cellulose system mainly destroyed the hydrogen bond network between the cellulose molecules, which resulted in the decrease of the mechanical strength of the insulating paper, but the hydrogen bond on the cellulose had no significant effect on the tensile strength.

  Power transformer inside the main use of oil and paper combination of insulation, insulation paper performance directly determines the performance of the transformer life. In the transformer operating conditions are vulnerable to electricity, heat and many other factors in the role of cellulose chain breakage, resulting in the degradation of insulating paper aging. Moisture has an accelerating effect on the aging of insulating paper.

  As a third kind of research method, molecular simulation technology can study the phenomena and microphysical processes that can not be observed at the molecular level, and have achieved great success in the fields of chemical industry, energy and pharmaceutical industry. The influence of moisture on the mechanical properties, the hydrogen bond and the Mulliken population of insulating paper was studied by using molecular simulation technology to study the effect of moisture on the cellulose fiber aging mechanism. The

  The modeling of the model was carried out using the amorphous polymer construction method proposed by Theodorou using the Materals Studio 4.0 package Amorphous Cell module, which contains a cellulose chain containing 20 cellobiose units and added mass Fraction of 5% of the water, the number of water molecules is about 20. Figure 1 is an initial model with a moisture content fraction of 5%.

  The initial model was dynamically relied on the NVT (canonical ensemble) system, and the annealing was carried out at 200K, from 1000K to 400K and then to 1000K. After the annealing process, select the transformer operating temperature 343K, the cellulose model in the NPT (constant-pressure, constant temperature) and NVT system for MD simulation. After the kinetic relaxation, the internal stress of the model is reduced, the hole distribution in the system is close to the real material, and the thermodynamic equilibrium state is reached.

  Young's modulus is the ratio of stress to strain, which is used to describe the elastic modulus of the solid material against deformation. Young's modulus as a measure of the rigidity of the material parameters, the greater the value that the stronger the rigidity of the material, the ability to resist deformation is stronger, can directly characterize the mechanical strength of the material.

  The internal hydrogen bond network of cellulose is an important index to measure the mechanical strength of cellulose insulating paper. The change of hydrogen bond inside cellulose not only directly affects the mechanical properties of insulating paper, but also has a profound effect on the aging resistance of insulating paper.

  In the actual transformer operating environment, the moisture does not change the chemical bond type leading to the ring opening of the pyran ring. The water mainly plays a large role in the bond strength of the CO bond on the pyran ring, which in turn affects the ring opening of the pyran ring Easy degree.

  The polymer cellulose is linked by a cellulose monomer through a glycosidic bond, and the cleavage of the glycosidic bond will directly lead to a decrease in the degree of polymerization of the insulating paper cellulose chain. The intensity of the corresponding chemical bond (O-H or C-O bond) will be weakened after the water molecules react with the hydroxyl groups on the cellulose chain to produce new hydrogen bonds.

  in conclusion

  (1) With the increase of moisture content, the Young's modulus will be reduced, that is, the tensile strength of the insulating paper cellulose is weakened, the plasticity is enhanced and the ductility is enhanced.

  (2) the addition of water molecules makes the hydrogen bonds in the intramolecular hydrogen bonds and intermolecular hydrogen bonds destroyed, thus affecting the mechanical properties of insulating paper cellulose.

  (3) water will lead to cellulose glycosidic bond chemical strength decreased, thereby promoting glycosidic bond breakage.

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