Microcosmic parameter-based XLPE thermo-oxidative aging structure evolution and insulating property correlation mechanism analysis method

Abstract

The invention discloses an analysis method of an XLPE thermo-oxidative aging structure evolution and insulating property correlation mechanism based on microscopic parameters. The analysis method comprises the following steps: step 1, constructing a periodic structure model of an oxygen-containing cross-linked XLPE and carrying out geometric optimization; step 2, acquiring XLPE structure models under different thermo-oxidative aging degrees by utilizing de novo molecular dynamics; 3, on the basis of a density functional theory (DFT), calculating microcosmic parameters, related to insulation performance, of XLPE of different structures under different electric field intensities by utilizing Gaussian software; and 4, depicting a'thermal oxidation aging degree-microscopic parameter 'radar map based on the change rule of the microscopic parameters of the XLPE under different thermal oxidation aging degrees, and constructing a structure-function relationship between the microscopic parameters and the different thermal oxidation aging degrees. According to the method, the thermo-oxidative aging process of the XLPE is simulated on the basis of AIMD, differences of microcosmic parameters of the XLPE under different aging degrees are compared, and the structure-function relationship between the thermo-oxidative aging degrees and the microcosmic parameters of the cross-linked XLPE is constructed more accurately.

Description

Technical Field

[0001] The present invention relates to the field of cable insulation, and more specifically to an analysis method for the correlation mechanism between XLPE thermal oxidation aging structure evolution and insulation performance based on microscopic parameters. Background Art

[0002] Cables are like the lifeblood of the power system, playing a vital role in ensuring the safe operation of the power grid and the reliability of power transmission. Since 1955, cross-linked polyethylene (XLPE) has become the main material for cables due to its excellent insulation and mechanical properties. During the operation of the cable, XLPE will inevitably be subjected to comprehensive electrical, thermal and mechanical stresses, resulting in aging and degradation of its insulation performance. This degradation poses a major risk to the reliability of cables in the power system, thus affecting the safe transmission of electric energy. The thermal oxidation aging of XLPE is the main cause of its performance failure. In response to this problem, many scholars at home and abroad have conducted extensive research on the thermal oxidation aging characteristics of XLPE. C. Kim et al. conducted accelerated thermal aging tests on XLPE in the temperature range of 105-150 ° C, focusing on the insulation properties of XLPE under thermal aging under AC electric fields. Some studies have shown that with the increase of aging, the mechanical properties of XLPE gradually deteriorate at extreme temperatures. Some research groups have conducted multi-dimensional analysis of the thermal oxidation aging process of ultra-high voltage submarine cables, revealing the differences in the thermal decomposition mechanisms of XLPE in the early and late stages of thermal aging.

[0003] However, many studies have not clarified the specific structure of XLPE during the thermal oxidative aging process, and the microstructure of insulating materials is the key to determining their macroscopic properties. Therefore, obtaining the structure of XLPE at each stage of thermal oxidative aging is crucial to understanding the evolution of its performance during the thermal oxidative aging process. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an analysis method for the correlation mechanism between the thermal oxidation aging structure evolution and insulation performance of XLPE based on microscopic parameters.

[0005] To achieve the above objectives, the present invention provides an analysis method for the correlation mechanism between the thermal oxidation aging structural evolution and insulation performance of XLPE based on microscopic parameters, and uses molecular simulation technology to explain the structural changes of XLPE during thermal oxidation aging at the atomic scale.

[0006] To achieve the above purpose, an analysis method for the correlation mechanism between the thermal oxidation aging structure evolution and insulation performance of XLPE based on microscopic parameters includes the following steps:

[0007] Step 1, constructing a periodic structure model of oxygen-containing cross-linked XLPE and performing geometric optimization;

[0008] Step 2, using ab initio molecular dynamics to obtain the XLPE structural model under different degrees of thermal oxidation aging;

[0009] Step 3, based on density functional theory (DFT), Gaussian software was used to simulate and calculate the microscopic parameters related to the insulation performance of XLP E with different structures under different electric field strengths.

[0010] Step 4: Based on the changing rules of the microscopic parameters of XLPE under different degrees of thermal oxidation aging, a radar chart of "degree of thermal oxidation aging-microscopic parameters" is drawn to construct the structure-activity relationship between microscopic parameters and different degrees of thermal oxidation aging.

[0011] Preferably, in step 1, the construction of the cross-linked XLPE structure is achieved by setting the carbon atoms between a plurality of basic XLPE chains as cross-linking points and placing them in a simulation box with periodic boundary conditions.

[0012] Preferably, in step 1, the geometry optimization of the cross-linked XLPE is achieved by using the M062X functional in the CP2K software in combination with the 6-311G (d, p) basis set.

[0013] Preferably, in step 2, the AIMD (ab initio molecular dynamics) simulation process is performed using CP2K software at the PBE functional and DZVP-MOLOPT-SR-GTH-D3 basis set level.

[0014] Preferably, in step 2, the XLPE structural models under different thermal oxidative aging degrees include typical structures under five different aging degrees, namely, unaged and 1-4 grade aged, including both saturated molecular structures and unsaturated molecular structures.

[0015] Preferably, in step 3, the microscopic parameters related to the insulation performance include dipole moment, ionization energy, electron affinity, excitation process, molecular orbital and molecular surface electrostatic potential.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention provides an analysis method for the correlation mechanism between the thermal oxidation aging structure evolution and insulation performance of XLPE based on microscopic parameters, and studies the reaction kinetics of XLPE based on ab initio molecular dynamics theory to more accurately describe the thermal oxidation aging process of XLPE; density functional theory is used to simulate and analyze the variation law and difference of discharge-related microscopic parameters of 5 different XLPE structures under different electric field strengths, and the influence of electric field on XLPE molecular structure and microscopic parameters is judged based on ionization energy, electron affinity, excitation process and conductivity. The present invention can provide theoretical guidance for analyzing the discharge process of XLPE from a microscopic level; at the same time, it also opens up new ideas for subsequent related research on judging the operation status of cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the typical structure of cross-linked XLPE at five different aging stages;

[0019] Figure 2 is the graph of the change of dipole moment of different XLPE structures with electric field strength;

[0020] Figure 3 It is a graph showing the variation of ionization energy and electron affinity of different XLPE structures with electric field strength;

[0021] Figure 4 are the molecular orbitals of different XLPE structures at 0 kV / mm; DETAILED DESCRIPTION

[0022] The following is a clear and complete description of the technical solution in the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The present invention provides an analysis method for the correlation mechanism between the thermal oxidation aging structure evolution and the insulation performance of XLPE based on microscopic parameters, comprising the following steps:

[0024] Step 1, constructing a periodic structure model of oxygen-containing cross-linked XLPE and performing geometric optimization;

[0025] Step 2, using ab initio molecular dynamics to obtain the XLPE structural model under different degrees of thermal oxidation aging;

[0026] Step 3, based on density functional theory (DFT), Gaussian software was used to simulate and calculate the microscopic parameters related to the insulation performance of XLP E with different structures under different electric field strengths.

[0027] Step 4: Based on the changing rules of the microscopic parameters of XLPE under different degrees of thermal oxidation aging, a radar chart of "degree of thermal oxidation aging-microscopic parameters" is drawn to construct the structure-activity relationship between microscopic parameters and different degrees of thermal oxidation aging.

[0028] Embodiment 1

[0029] A periodic structural model of oxygen-containing cross-linked XLPE was constructed and its geometry was optimized.

[0030] In the specific implementation, based on density functional theory, a single basic XLPE molecular chain was constructed in CP2K software. Through the carbon atoms between XLPE, 20 XLPE chains were polymerized to construct a cross-linked XLPE model and placed in a periodic structure. Subsequently, an electric field was applied to the molecular model along the y-axis, and the electric field strength ranged from 0 to 408 kV / mm. Finally, the cross-linked XLPE structure was optimized at the M062X / 6-311G (d, p) basis set level to obtain the optimized structural model.

[0031] Embodiment 2

[0032] Ab initio molecular dynamics was used to obtain the structural model of XLPE under different degrees of thermal oxidative aging.

[0033] In the specific implementation, the optimized cross-linked XLPE structure model was simulated for 50ps at a high temperature of 3000K in the CP2K software based on the ab initio molecular dynamics (AIMD) method at the PBE / DZVP-MOLOPT-SR-GTH-D3 basis set level. By comprehensively considering the length of simulation time, the length of the molecular chain, and the difference between the existing structure and the initial XLPE structure, five representative thermal oxidation aging models were screened and marked as: Unaged, Aging Level 1, Aging Level 2, Aging Level 3, and Aging Level 4.

[0034] Embodiment 3

[0035] Based on density functional theory (DFT), Gaussian software was used to simulate and calculate the microscopic parameters related to the insulation performance of XLPE with different structures under different electric field intensities.

[0036] In the specific implementation, based on density functional theory, the M062X / def2-tzvp method was used in Gaussian software to calculate the dipole moment, ionization energy, electron affinity, excitation process, molecular orbital and molecular surface electrostatic potential of XLPE molecules under different structural models, and output them in the form of wave function.

[0037] Embodiment 4

[0038] Based on the changing law of microscopic parameters of XLPE under different degrees of thermal oxidative aging, a radar chart of "degree of thermal oxidative aging-microscopic parameters" was drawn, and the structure-activity relationship between microscopic parameters and different degrees of thermal oxidative aging was constructed.

[0039] In the specific implementation, the wave function results calculated by Gaussian software are input into Multiwfn, and Multiwfn and VMD are used to perform visual analysis on parameters such as electron density, molecular orbital, and molecular surface electrostatic potential. The differences and change patterns of microscopic parameters of XLPE structures with different aging levels under different electric field intensities are compared, and the structure-activity relationship between microscopic parameters and the degree of thermal oxidation aging is constructed, and the microscopic parameters of XLPE are used to reflect the macroscopic performance.

[0040] The above content is merely an illustration of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific structure described. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. An analytical method for the correlation mechanism between the thermal oxidation aging structural evolution and insulation performance of XLPE based on microscopic parameters, characterized in that: The following steps are involved: Step 1, constructing a periodic structure model of oxygen-containing cross-linked XLPE and performing geometric optimization; Step 2, using ab initio molecular dynamics to obtain the XLPE structural model under different degrees of thermal oxidation aging; Step 3, based on density functional theory (DFT), Gaussian software was used to simulate and calculate the microscopic parameters related to the insulation performance of XLP E with different structures under different electric field strengths. Step 4: Based on the changing rules of the microscopic parameters of XLPE under different degrees of thermal oxidation aging, a radar chart of "degree of thermal oxidation aging-microscopic parameters" is drawn to construct the structure-activity relationship between microscopic parameters and different degrees of thermal oxidation aging.

2. The method according to claim 1, characterized in that: In the step 1, the construction of the cross-linked XLPE structure is achieved by setting the carbon atoms between multiple basic XLPE chains as cross-linking points and placing them in a simulation box with periodic boundary conditions.

3. The method according to claim 1, characterized in that: In step 1, the geometry optimization of the cross-linked XLPE is achieved by using the M062X functional in the CP2K software in combination with the 6-311G (d, p) basis set.

4. The method according to claim 1, characterized in that: In step 2, the AIMD (ab initio molecular dynamics) simulation process is performed using CP2K software at the PBE functional and DZVP-MOLOPT-SR-GTH-D3 basis set levels.

5. The method according to claim 1, characterized in that: In the step 2, the XLPE structure models under different thermal oxidation aging degrees include typical structures under five different aging degrees, namely, unaged and 1-4 grade aged, including both saturated molecular structures and unsaturated molecular structures.

6. The method according to claim 1, characterized in that: In step 3, the microscopic parameters related to the insulating performance include dipole moment, ionization energy, electron affinity, excitation process, molecular orbital and molecular surface electrostatic potential.

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