Method for judging transformer oil paper insulation deterioration through multiple sulfides

Abstract

A method for judging transformer oil paper insulation deterioration through multiple sulfides comprises the steps that the actual operation condition of an oil-immersed power transformer is monitored and analyzed, and parameter information of a dangerous source is determined; and analyzing the parameter information of the dangerous source quality according to a pre-constructed simulation analysis model to obtain deterioration data of the transformer oil paper. Wherein the simulation analysis model is constructed on the basis of data obtained based on the simulation experiment steps. According to the application of analog simulation data in actual detection, a reliable basis is provided for accurate detection and protection of oil paper insulation degradation, actual maintenance work can be effectively guided, oil paper insulation faults caused by sulfide are reduced, and safe and stable operation of the oil paper insulation transformer is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of transformer insulation monitoring and fault diagnosis, and in particular to a method for judging transformer oil-paper insulation degradation through multiple sulfides. Background Art

[0002] Transformers are the core equipment for energy transmission and conversion in power systems, and are of great significance to the safe and stable operation of the entire power grid. In recent years, many transformer insulation failures caused by corrosive sulfides have occurred at home and abroad. Insulation failures caused by sulfur corrosion reactions have seriously affected the safe and stable operation of oil-immersed power transformers. The existing simulation model only incorporates the insulation paper and does not include the influence of oil, while the actual transformer is an oil-paper hybrid insulation system.

[0003] Therefore, it is urgent to establish an oil-paper hybrid model to analyze the impact mechanism of sulfides on the oil-paper insulation system. Summary of the invention

[0004] The present invention provides a method for judging the degradation of transformer oil-paper insulation through multiple sulfides. Based on the application of simulation data in actual detection, it provides a reliable basis for accurately detecting and preventing the degradation of oil-paper insulation, can effectively guide actual maintenance work, reduce oil-paper insulation failures caused by sulfides, and ensure the safe and stable operation of oil-paper insulated transformers.

[0005] To achieve the above object, the present invention adopts the following technical solutions: Monitor and analyze the actual operation of oil-immersed power transformers to determine the parameter information of hazardous sources; According to the pre-built simulation analysis model, the parameter information of the hazardous source is analyzed to obtain the degradation data of the transformer oil-paper; Among them, the hazardous substances include: one or more combinations of dibenzyl disulfide, hexadecanethiol and benzothiophene.

[0006] Furthermore, the construction of the simulation analysis model is based on the data obtained from the simulation experiment steps, wherein the simulation experiment steps are as follows: Establish an insulating oil-sulfide composite insulation system consisting of a mineral oil and a sulfide model; Constructing a cellulose model; The insulating oil-sulfide model was combined with the cellulose model to construct an oil-sulfide-paper hybrid model and optimized; Conduct molecular dynamics simulation analysis; Calculate the Young's modulus, shear modulus, Poisson's ratio and bulk modulus of cellulose; construct hydrogen bonds and calculate the number of hydrogen bonds in cellulose; calculate the mean square displacement of cellulose molecular chains; calculate electrostatic energy; calculate the van der Waals energy and shear viscosity of insulating oil.

[0007] Furthermore, the insulating oil-sulfide composite insulation system composed of mineral oil and sulfide model includes: Using 60 , 30 With 10 Molecular oil model, oil density is set to 0.9 g / cm 3 ; 2.58%, 5.15% and 7.73% of multiple sulfides were added into the oil model respectively to form 7 groups of insulating oil-sulfide composite insulation systems.

[0008] Furthermore, a cellulose model is constructed, including: Build glucose monomers, use the Build polymers function to combine glucose monomers into cellulose chains, use the Amorphous cell module to build an amorphous model, and set the cellulose density to 1.5 g / cm3.

[0009] Furthermore, the insulating oil-sulfide model is combined with the cellulose model to construct an oil-sulfide-paper hybrid model and optimize it, including: Use the build layer module to build the model, select Crystal as the building method, select Default for the section attribute, select a fixed volume for the built model, use the average value of the original lattice for the new lattice contact surface parameters, and then perform 500 steps of geometric optimization.

[0010] Furthermore, the model is subjected to molecular dynamics simulation analysis, including: The temperature was set to 343 K, the pressure was 1×10-4 Pa, the pcff force field was used, the temperature control method was Andersen, the pressure control method was Berendsen, the electrostatic interaction method adopted the Ewald method, the step size was set to 1fs, the trajectory was output every 5000 steps, and each model finally obtained a 21-frame molecular trajectory file.

[0011] Furthermore, the Mechanical Properties function of the Forcite module was used to obtain the Cij elastic coefficient matrix of the composition, from which the Young's modulus, shear modulus, Poisson's ratio and bulk modulus of cellulose can be derived; The mean square displacement (MSD) of the cellulose molecular chain was calculated using the analysis function of the Forcite module; The electrostatic energy of different composite insulation models is calculated by the Forcite module; The van der Waals energy and shear viscosity of the insulating oil are calculated using the Forcite module.

[0012] Further, constructing hydrogen bonds and calculating the number of hydrogen bonds in cellulose include: The Build module in the molecular dynamics simulation was used to construct hydrogen bonds, and the number of hydrogen bonds in cellulose was calculated to measure the degree of deterioration of the insulating paper.

[0013] This paper successfully reveals this complex process by deeply exploring the microscopic mechanism of multiple sulfides on oil-paper insulation degradation, which is of great significance for the application of simulation data to actual detection. It has strongly promoted the exploration of effective sulfur corrosion protection technology, brought new hope for the maintenance of oil-paper insulated transformers, and greatly helped to extend their service life.

[0014] From the actual test results, when the three sulfides coexist, the weakening of the mechanical properties of cellulose materials reaches the most serious level, and the hydrogen bonds are also greatly damaged. When only a single thiol is present, although the destructive effect on hydrogen bonds is relatively weak, it will greatly intensify the movement of cellulose chains. Under the influence of sulfides, the viscosity of insulating oil generally shows an increasing trend, among which hexadecanethiol is the main factor affecting viscosity. It is particularly important to note that when DBDS and hexadecanethiol act synergistically, the increase in the viscosity of the insulating oil reaches the maximum. In contrast, thiophene has a smaller effect on the viscosity of insulating oil. Only when it acts together with hexadecanethiol at medium and low concentrations will the viscosity of the insulating oil be significantly increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Flow chart to study the mechanism of action of multiple sulfides on transformer oil-paper insulation degradation; Figure 2-5 The trend diagram of Young's modulus, shear modulus, Poisson's ratio and bulk modulus of cellulose under the action of different sulfides; Figure 6 The diagram of the number of hydrogen bonds in cellulose under the action of different sulfides; Figure 7-9 The mean square displacement trend of cellulose under the influence of different sulfides ( Figure 7 The sulfide concentration is 2.58%, Figure 8 The sulfide concentration is 5.15%, Fig. 9 Sulfide concentration is 7.73%); Fig.10 The trend diagram of electrostatic energy of cellulose under the influence of different sulfides; Fig.11 The trend diagram of the van der Waals energy of insulating oil under the influence of different sulfides; Fig.12 This is a trend chart of the shear viscosity of insulating oil under the influence of different sulfides. DETAILED DESCRIPTION

[0016] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions 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. The preferred implementations described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0017] The present invention provides a method for judging the degradation of transformer oil-paper insulation through multiple sulfides, which is used to explore the interaction mechanism between multiple sulfides. First, the actual operation of the oil-immersed power transformer is monitored and analyzed to determine the parameter information of the hazardous source. Then, according to a pre-constructed simulation analysis model, the parameter information of the hazardous source is analyzed to obtain the degradation data of the transformer oil-paper.

[0018] Among them, the hazardous substances include: one or more combinations of dibenzyl disulfide, hexadecanethiol and benzothiophene.

[0019] Furthermore, different concentrations of sulfides (2.58%, 5.15% and 7.73%) were selected and the number of sulfur atoms was used as the variable to control seven groups of sulfide insulation models.

[0020] Furthermore, the construction of the simulation analysis model is based on the data obtained from the simulation experiment steps, such as Figure 1 As shown, the simulation experiment steps are as follows: Firstly, an insulating oil-sulfide composite insulation system consisting of mineral oil and sulfide models is established; In order to establish a practical oil-immersed power transformer model, the actual operation of the oil-immersed power transformer and the material composition of the transformer insulating oil and insulating paper are determined. In the present invention, in order to meet the corresponding parameters of the actual oil-immersed power transformer, the actual operation should take into account the working conditions of the actual operation of the transformer, such as temperature, pressure, electric field, etc.

[0021] The mineral oil in the actual oil-immersed power transformer is a mixture of three major hydrocarbons: 60% by mass of alkanes, 10% to 40% by mass of cycloalkanes, and 5% to 15% by mass of aromatic hydrocarbons. Therefore, the composition of the insulating oil model in this simulation adopts 60 , 30 With 10 Molecular oil model, oil density is set to 0.9 g / cm 3 .

[0022] Furthermore, multiple sulfides of different concentrations are added to the established oil model, and periodic boundary conditions (PBC) are used in the model establishment process, which can ensure that the atoms at the boundary of the model are uniformly stressed, so that the influence of boundary effects can be ignored.

[0023] Furthermore, a cellulose model was constructed.

[0024] Since cellulose is divided into 30% amorphous region and 70% crystalline region, the amorphous region has a disordered structure, bonds are easily broken, and mechanical properties are easily changed. Therefore, the amorphous region was selected as the aging research object.

[0025] This simulation uses 10 cellulose chains with a degree of polymerization of 20 to form a cellulose model and conduct molecular dynamics simulation of the amorphous region of cellulose. Specifically, first build the glucose biose monomer, then use the Build polymers function to assemble it into a cellulose chain, and finally use the Amorphous cell module to build its amorphous model. The cellulose density is set to 1.5g / cm 3 .

[0026] Furthermore, the insulating oil-sulfide model was combined with the cellulose model to construct an oil-sulfide-paper hybrid model and optimized.

[0027] Use the build layer module to build the model, select Crystal as the building method, select Default as the section attribute, select a fixed volume for the built model, use the average value of the original lattice for the new lattice contact surface parameters, and then perform 500 steps of geometric optimization to ensure that the energy in the unit cell is at the lowest state.

[0028] Furthermore, molecular dynamics simulation analysis is performed.

[0029] To ensure the accuracy of the simulation, the starting position of the atoms is kept at the lowest potential energy possible. Therefore, for the complex system composed of macromolecules that appears in this simulation, an energy minimization step is required to keep the system energy at the lowest point.

[0030] Therefore, molecular dynamics simulation (MD) was used to relax the model for 20 ps under the constant temperature and pressure (NPT) ensemble to make the model in a stable state; Then, the model was subjected to 100 ps molecular dynamics calculations in the NVT ensemble; The temperature of the entire simulation process was 343 K and the pressure was 1×10-4 Pa. The pcff force field was used, the temperature control method was Andersen, the pressure control method was Berendsen, the electrostatic interaction method adopted the Ewald method, the step size was set to 1 fs, the trajectory was output every 5000 steps, and each model finally obtained a 21-frame molecular trajectory file.

[0031] Furthermore, the Young's modulus, shear modulus, Poisson's ratio and bulk modulus of cellulose are calculated; hydrogen bonds are constructed and the number of hydrogen bonds in cellulose is calculated; the mean square displacement of the cellulose molecular chain is calculated; the electrostatic energy is calculated; and the van der Waals energy and shear viscosity of the insulating oil are calculated.

[0032] Among them, the generalized Hooke's law can be used to derive the relationship between stress and strain of solid materials. Through the Mechanical Properties function of the Forcite module, the Cij elastic coefficient matrix of the composition can be obtained, and then various mechanical parameters of cellulose can be derived. Young's modulus is used to measure its stiffness. Young's modulus is defined as the ratio of uniaxial stress to uniaxial deformation. Shear modulus characterizes the ratio of shear stress to shear strain of a material under shear stress. Poisson's ratio can be used to reflect the magnitude of the lateral deformation of a material. It refers to the absolute value of the lateral normal strain divided by the absolute value of the axial normal strain after the material is subjected to unidirectional tension or compression, also known as the lateral deformation coefficient. Bulk modulus is also called volume modulus. It is used to reflect the macroscopic properties of a material and to characterize the magnitude of the deformation of a material caused by pressure around the surface. It is defined as the pressure required to produce a unit relative volume contraction.

[0033] Depend on Figure 2-5 It can be seen that with the increase of sulfide content, the Young's modulus of each model generally shows a downward trend. Among them, the modulus of thiophene is not obviously decreasing due to its low activity. The hexadecanethiol group decreases more at the beginning, but it is more gentle when the sulfur content is high. DBDS decreases more when the sulfur content is high. Thiophene enters the late aging stage in advance when the sulfur content is high, resulting in its molecular ring opening and conversion into corrosive sulfides. The shear modulus, bulk modulus and Young's modulus have similar rules. The modulus of the mixed group of three sulfides decreases the most. For a single sulfide, the degree of modulus decrease is: DBDS>hexadecanethiol>thiophene, and the effect of the DBDS+hexadecanethiol group is greater than that of the single DBDS. At the intermediate concentration, the DBDS+hexadecanethiol group has the strongest corrosion effect, and at high concentrations, the modulus decreases most significantly under the synergistic effect of the three. It can be inferred that the corrosion effects of different types of sulfides will promote each other.

[0034] Furthermore, the Build module in the molecular dynamics simulation was used to construct hydrogen bonds, and the number of hydrogen bonds in cellulose was calculated to measure the degree of degradation of the insulating paper, and the effects of different sulfides and changes in different sulfide concentrations on the degradation characteristics of cellulose were explored.

[0035] Depend on Figure 6 It can be seen that with the increase of sulfide content, the number of hydrogen bonds destroyed by corrosive sulfur generally shows a decreasing trend. When corrosive sulfides are added with DBDS, the destructive effect on hydrogen bonds is stronger, and hexamethylenethiol has a weaker destructive effect on hydrogen bonds. The DBDS + hexamethylenethiol group has the greatest destructive effect on hydrogen bonds. When the sulfur concentration is high, the three sulfides will also cause greater damage to hydrogen bonds. In addition, it is noted that in the benzothiophene group, the number of hydrogen bonds increases abnormally with the increase of the added sulfide concentration. It is speculated that this may be due to the low activity of thiophene, which is not enough to damage the hydrogen bonds of cellulose. As the number of added thiophene molecules increases, thiophene and cellulose in the model form more sulfur-hydrogen intermolecular hydrogen bonds. As the hydrogen bonds are destroyed, the mechanical strength of cellulose will also be weakened, thereby exacerbating the aging phenomenon.

[0036] Furthermore, molecular dynamics analysis was used to study the synergistic mechanism of sulfide in the oil-paper insulation system. The mean square displacement (MSD) of the cellulose molecular chain was calculated using the analysis function of the Forcite module to explore the motion strength of the cellulose chain in the insulation paper, and then analyze its mechanical properties and thermal stability.

[0037] Depend on Figure 7 , Figure 8 , Fig. 9 It can be seen that under the three concentrations, the mean square displacement value of the hexadecanethiol group is larger, followed by the DBDS+hexadecanethiol group. It can be seen that these two sulfides have a greater weakening effect on the stability of the cellulose chain, reducing its mechanical properties and deformation resistance, thereby leading to aging breakdown of the insulating medium. Thiophene has a greater weakening effect on the cellulose chain at low concentrations, and its destructive effect is far less than that of DBDS and hexadecanethiol at higher concentrations. The effect of DBDS alone is not as good as that of hexadecanethiol. It is speculated that due to the characteristics of its long-chain molecule, the size of a single molecule of hexadecanethiol is larger than that of DBDS and thiophene, and the number of atoms in a single molecule is also more. After incorporation, it is more likely to cause instability in the geometric structure of cellulose in the amorphous region.

[0038] Furthermore, the electrostatic energy of different composite insulation models was calculated by the Forcite module to evaluate the effects of different sulfide combinations on the degradation of insulation paper.

[0039] Depend on Fig.10The electrostatic energy of different sulfide models can be obtained. Electrostatic energy is converted from external force to overcome the electric field force. The total electrostatic energy is obtained by adding the self-energy of each charge and the mutual energy between other charges. For most sulfide models, due to the presence of sulfur atoms, the polarizability of the molecule is improved, which leads to a slight increase in the electrostatic energy in cellulose with the increase of sulfide concentration. Among them, the DBDS + thiophene + hexadecanethiol group increased the most, followed by the DBDS + hexadecanethiol group, and the thiophene group was relatively stable. For the hexadecanethiol group, due to its long-chain molecular characteristics, the charge of the tail functional group will decrease, so compared with other groups, its intermolecular electrostatic energy decreases, while the remaining groups generally show an upward trend.

[0040] Furthermore, the Forcite module is used to calculate the van der Waals energy of insulating oil, analyze the microscopic aging characteristics of the insulation model, and reveal the microscopic effects of different sulfide combinations on insulating oil molecules.

[0041] Van der Waals force, also known as intermolecular force, is a weak mutual attraction between molecules, which is composed of orientation force, induction force, and dispersion force. Evaluate the effect of different sulfides on the shear viscosity of insulating oil, calculate the shear viscosity of insulating oil, and explore its thermal conductivity. Viscosity is used to measure the viscosity of fluids, which can be expressed as the ability of the fluid to hinder its relative flow. Electrical insulating oil needs to conduct heat through itself, so the viscosity should be kept as moderate as possible to ensure the effective flow and heat dissipation of transformer oil, while not reducing the flash point due to being too small. When ensuring that the flash point is high enough, the lower the viscosity, the more beneficial it is for transformer operation.

[0042] Depend on Fig.11It can be seen that the van der Waals energy generally decreases with the increase of sulfur concentration. However, when the three sulfides act synergistically, the decrease in van der Waals energy is small at high sulfur concentrations. It is speculated that at low concentrations, there is no orientation force between the sulfide molecules and the non-polar alkane molecules in the oil and the sulfide, while at high concentrations, the orientation forces between different sulfide molecules begin to stand out, reducing the decrease in van der Waals energy. The synergistic effect of the DBDS+hexamercaptan group significantly weakens the van der Waals energy more than the single effect of DBDS and hexamercaptan. Similarly, the weakening of the van der Waals energy of insulating oil under the synergistic effect of DBDS and thiophene is also greater than the single effect of the two. It is speculated that when the total number of sulfur atoms is the same, among DBDS, hexamercaptan, and benzothiophene, the number of hexamercaptan molecules is larger and the molecular weight of the single molecule is larger, which is easier to deform, resulting in hexamercaptan having a higher dispersion force, while the single DBDS and thiophene have a higher induction force due to their strong polarity, which slows down the decrease in van der Waals energy. Although the carbon atoms of hexamethylenethiol form bonds in the SP3 hybrid mode with low polarity, and its long chain weakens the influence of the terminal thiol on the molecular polarity, the molecular polarity is low, making its induction force lower than that of DBDS and thiophene, but since the dispersion force in the van der Waals force occupies a dominant position, the decrease in the van der Waals energy of the DBDS and thiophene group is still greater than that of the hexamethylenethiol group. Furthermore, the shear viscosity of the insulating oil is calculated, the effect of different sulfides on the shear viscosity of the insulating oil is evaluated, its thermal conductivity is explored, and the effect of different sulfide combinations on the stability of the oil-paper insulation system is analyzed.

[0043] like Fig.12 As shown in the figure, the viscosity of insulating oil generally increases with the addition of sulfides, among which DBDS and hexadecanethiol have a synergistic effect on the viscosity of insulating oil, and it can be seen that hexadecanethiol has a great influence on the viscosity of insulating oil. It is speculated that hexadecanethiol may have a large internal friction due to its large molecular weight and more carbon-hydrogen bonds, which leads to a significant increase in the viscosity of insulating oil.

[0044] In summary, the present invention constructs 7 groups of sulfide-oil-paper models composed of three sulfides, DBDS, hexadecanethiol and benzothiophene, and performs molecular dynamics simulation analysis on the mechanical properties of insulating paper and insulating oil. According to the mechanical properties parameters of insulating paper, the number of hydrogen bonds, the stability of cellulose chain motion, and the van der Waals energy and viscosity data of insulating oil, among the seven models and three sulfides, the synergistic effect of the BDS+hexadecanethiol group is the strongest, which will accelerate the degradation process of the oil-paper composite insulation system.

Claims

1. A method for judging transformer oil-paper insulation degradation by multiple sulfides, characterized in that: include: Monitor and analyze the actual operation of oil-immersed power transformers to determine the parameter information of hazardous sources; According to the pre-built simulation analysis model, the parameter information of the hazardous source is analyzed to obtain the degradation data of the transformer oil-paper; Among them, the hazardous substances include: one or more combinations of dibenzyl disulfide, hexadecanethiol and benzothiophene.

2. The method for judging transformer oil-paper insulation degradation by multiple sulfides according to claim 1, characterized in that: The construction of the simulation analysis model is based on the data obtained from the simulation experiment steps, where the simulation experiment steps are as follows: Establish an insulating oil-sulfide composite insulation system consisting of a mineral oil and a sulfide model; Constructing a cellulose model; The insulating oil-sulfide model was combined with the cellulose model to construct an oil-sulfide-paper hybrid model and optimized; Conduct molecular dynamics simulation analysis; Calculate the Young's modulus, shear modulus, Poisson's ratio and bulk modulus of cellulose; construct hydrogen bonds and calculate the number of hydrogen bonds in cellulose; calculate the mean square displacement of cellulose molecular chains; calculate electrostatic energy; calculate the van der Waals energy and shear viscosity of insulating oil.

3. The method for judging transformer oil-paper insulation degradation by multiple sulfides according to claim 2, characterized in that: An insulating oil-sulfide composite insulation system consisting of a mineral oil and sulfide model is established, including: Using 60 , 30 With 10 Molecular oil model, oil density is set to 0.9 g / cm 3 ; 2.58%, 5.15% and 7.73% of multiple sulfides were added into the oil model respectively to form 7 groups of insulating oil-sulfide composite insulation systems.

4. The method for judging transformer oil-paper insulation degradation by multiple sulfides according to claim 2, characterized in that: Construct a cellulose model, including: Build the glucose monomers and use the Build polymers function to combine the glucose monomers into cellulose chains. Use the Amorphous cell module to build an amorphous model. The cellulose density is set to 1.5 g / cm 3 .

5. The method for judging transformer oil-paper insulation degradation by multiple sulfides according to claim 2, characterized in that: The insulating oil-sulfide model is combined with the cellulose model to build an oil-sulfide-paper hybrid model and optimize it, including: Use the build layer module to build the model, select Crystal as the building method, select Default for the section attribute, select a fixed volume for the built model, use the average value of the original lattice for the new lattice contact surface parameters, and then perform 500 steps of geometric optimization.

6. The method for judging transformer oil-paper insulation degradation by multiple sulfides according to claim 2, characterized in that: Conduct molecular dynamics simulation analysis, including: The temperature was set to 343 K, the pressure was 1×10-4 Pa, the pcff force field was used, the temperature control method was Andersen, the pressure control method was Berendsen, the electrostatic interaction method adopted the Ewald method, the step size was set to 1fs, the trajectory was output every 5000 steps, and each model finally obtained a 21-frame molecular trajectory file.

7. The method for judging transformer oil-paper insulation degradation by multiple sulfides according to claim 2, characterized in that: The Mechanical Properties function of the Forcite module is used to obtain the Cij elastic coefficient matrix of the composition, from which the Young's modulus, shear modulus, Poisson's ratio and bulk modulus of cellulose can be derived; The mean square displacement (MSD) of the cellulose molecular chain was calculated using the analysis function of the Forcite module; The electrostatic energy of different composite insulation models is calculated by the Forcite module; The van der Waals energy and shear viscosity of the insulating oil are calculated using the Forcite module.

8. The method for judging transformer oil-paper insulation degradation by multiple sulfides according to claim 2, characterized in that: Constructing hydrogen bonds and calculating the number of hydrogen bonds in cellulose include: The Build module in the molecular dynamics simulation was used to construct hydrogen bonds and calculate the number of hydrogen bonds in cellulose.

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