Method and system for evaluating insulating property of insulating oil based on microscopic physical property parameters

Abstract

The invention discloses a method and system for evaluating the insulating property of insulating oil based on microscopic physical property parameters, and relates to the field of insulating property evaluation, and the method comprises the following steps: respectively establishing an ion-containing mineral oil molecule model and a natural lipid molecule model; calculating ionization energy and electron affinity of insulating oil molecules under different electric field intensities; calculating and analyzing the dynamic characteristics of each ion in mineral oil and natural ester systems; and carrying out direct current conductivity test on mineral oil and natural ester. According to the method, the molecular ionization energy and the electron affinity of the insulating oil are calculated in a simulating manner, the dynamic characteristics of typical ions in the insulating oil are analyzed, and the direct current conductivity of different types of insulating oil is tested to test and verify the prediction result, so that the insulating property of the insulating oil under the action of a direct current electric field is accurately and efficiently evaluated; and theoretical guidance is provided for designing a converter transformer valve side wire outlet device with excellent insulating performance.

Description

Technical Field

[0001] The present invention relates to the field of insulation performance evaluation, and in particular to a method and a system for evaluating the insulation performance of insulating oil under a direct current electric field based on microscopic physical property parameters. Background Art

[0002] UHV DC transmission projects can achieve long-distance, large-capacity power transmission, and are an important means to solve the problem of reverse distribution of energy resources and energy demand in my country. As a key device connecting the AC side and DC side of the high-voltage DC transmission system, the insulation performance of the valve-side outlet device of the converter transformer is directly related to the overall safe and stable operation of the power system. According to statistics, valve-side winding faults of converter transformers account for a high proportion of total faults, among which the failure rate caused by oil-paper insulation discharge and local overheating is particularly prominent. Therefore, how to accurately evaluate the insulation performance of the oil-paper insulation system of the valve-side outlet device, so as to guide the design of insulation materials in the converter transformer, is the primary problem that needs to be solved to ensure the safe operation of my country's UHV DC transmission projects.

[0003] Unlike traditional AC transformers, the valve-side outlet device of the converter transformer needs to withstand high-amplitude AC, DC and polarity reversal voltages during operation, among which the DC component has a particularly significant impact on the oil-paper insulation performance. Studies have shown that when the DC conductivity of the insulating oil changes, it will directly affect the electric field distribution inside the valve-side outlet device, which may lead to local field concentration and increase the risk of insulation failure. In the past, advanced test techniques such as the recovery voltage method and polarization / depolarization current method were usually used to test the DC conductivity of insulating oil, but the construction and process of the test platform were complex and time-consuming, and there was a lack of microscopic analysis and evaluation of the conductivity characteristics of insulating oil molecules under the action of a DC electric field, so the effect of predicting the conductivity of insulating oil was poor. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the problem to be solved by the present invention is that the construction and process of the prior art test platform are complex and time-consuming, and lack the ability to analyze and evaluate the conductivity characteristics of insulating oil molecules under the action of a DC electric field at the microscopic level, thereby failing to predict the conductivity of the insulating oil.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters, which includes respectively establishing models of mineral oil molecules and natural lipid molecules containing ions; calculating the ionization energy and electron affinity of insulating oil molecules under different electric field strengths; calculating and analyzing the kinetic characteristics of each ion in the mineral oil and natural ester system; and performing DC conductivity testing on the mineral oil and natural ester.

[0007] As a preferred embodiment of the method for evaluating the insulating properties of insulating oil under a DC electric field based on microscopic physical property parameters described in the present invention, the steps of separately establishing the models of mineral oil molecules and natural lipid molecules containing ions include constructing models of mineral oil molecules, natural ester molecules and ions based on Materials Studios software, separately establishing a mineral oil system and a natural ester system containing ions through an Amorphous Cell module, and finally, geometrically optimizing, annealing and dynamically balancing the mineral oil system and the natural ester system to minimize the energy of the system.

[0008] As a preferred embodiment of the method for evaluating the insulating properties of insulating oil under a DC electric field based on microscopic physical property parameters described in the present invention, the mineral oil molecules are composed of monoalkanes, dialkanes, trialkanes, tetraalkanes, aromatic hydrocarbons and chain hydrocarbons, the natural ester molecules are composed of glyceryl trilinolenate, glyceryl trilinoleate, glyceryl tristearate, glyceryl trioleate and glyceryl tripalmitate, and the ions are composed of H3O+, Cu2+, OH- and Cl-.

[0009] As a preferred embodiment of the method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters described in the present invention, the calculation of the ionization energy and electron affinity of the insulating oil molecules under different electric field strengths includes, based on density functional theory, geometrically optimizing the constructed insulating oil molecular model, applying electric fields of different electric field strengths along the x-axis to the insulating oil molecular model, and obtaining the optimal structure of the insulating oil molecules under different electric field strengths.

[0010] As a preferred embodiment of the method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters of the present invention, the calculation of the ionization energy and electron affinity of insulating oil molecules under different electric field strengths also includes, based on the optimized insulating oil molecular model, calculating the ionization energy IP and electron affinity EA of insulating oil molecules based on density functional theory, wherein the calculation formulas of IP and EA are expressed as follows:

[0011] IP=E M+ -E M

[0012] EA=E M -E M-

[0013] Among them, E M Expressed as the energy calculated when the molecule is neutral, E M+ Expressed as the energy calculated when the molecular charge is +1, E M- Expressed as the energy calculated when the molecular charge is -1.

[0014] As a preferred embodiment of the method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical parameters of the present invention, the calculation and analysis of the dynamic characteristics of each ion in the mineral oil and natural ester system includes: using the SteepestDescent method to geometrically optimize the mineral oil system and the natural ester system, and performing a 100ps molecular dynamics simulation of the two optimized insulating oil system models under the conditions of a pressure of 1atm and a temperature of 340K using a constant pressure and constant temperature ensemble. The pressure and temperature during the entire simulation process are respectively controlled by a Berendsen barostat and a Nose thermostat, and a time step of 1fs is set to integrate the Verlet motion equation; the mobility of ions in the insulating oil molecules is characterized by the mean square displacement MSD, which is expressed as follows:

[0015] MSD=<|r i (t)-r i (0)| 2 >

[0016] Among them, r i (t) and r i (0) represents the position vector of the i-th atom at time t and time 0 respectively.

[0017] As a preferred embodiment of the method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical parameters of the present invention, the DC conductivity test of mineral oil and natural ester includes building a three-electrode polarization or depolarization current test platform to measure the DC conductivity of mineral oil and natural ester under the condition of an electric field strength of 0-5kV / mm. The calculation formula of the DC conductivity of the insulating oil is expressed as follows:

[0018]

[0019] Among them, σ represents conductivity, ε0 ​​represents vacuum dielectric constant, C0 represents geometric capacitance of insulating material, U0 represents polarization voltage, i c Expressed as the stable value of the polarization current.

[0020] Another object of the present invention is to provide a system for evaluating the insulating properties of insulating oil under a DC electric field based on microscopic physical parameters, which system can predict the conductivity of the insulating oil.

[0021] In order to solve the above technical problems, the present invention provides the following technical solutions: a system for evaluating the insulating performance of insulating oil under a direct current electric field based on microscopic physical property parameters, comprising: a model building module, a molecular energy calculation module, a kinetic characteristic module and a conductivity testing module; the model building module respectively establishes models of mineral oil molecules and natural fat molecules containing ions; the molecular energy calculation module calculates the ionization energy and electron affinity of insulating oil molecules under different electric field strengths; the kinetic characteristic module calculates and analyzes the kinetic characteristics of each ion in the mineral oil and natural ester system; the conductivity testing module performs a direct current conductivity test on the mineral oil and the natural ester.

[0022] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters are implemented.

[0023] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for evaluating the insulating performance of insulating oil under a direct current electric field based on microscopic physical property parameters as described above.

[0024] The beneficial effects of the present invention are as follows: the valve-side outlet device of the converter transformer needs to withstand high-amplitude AC, DC and polarity reversal voltages simultaneously during operation, among which the DC component has a particularly significant effect on the oil-paper insulation performance. Therefore, when designing the insulating material of the valve-side outlet device of the converter transformer, its insulation performance under the action of the DC electric field must be fully considered to ensure the safe, stable and efficient operation of the transformer. The DC conductivity of the insulating oil has an important influence on the DC insulation performance of the valve-side outlet device. In the past, advanced testing techniques were usually used to test the DC conductivity of the insulating oil, but there was a lack of microscopic analysis and evaluation of the conductivity characteristics of the insulating oil molecules under the action of the DC electric field, so as to predict the conductivity of the insulating oil. Therefore, the present invention proposes a method for evaluating the insulating performance of insulating oil under a DC electric field using microscopic physical property parameters, by simulating and calculating the ionization energy and electron affinity of insulating oil molecules, analyzing the kinetic characteristics of typical ions in insulating oil, and experimentally verifying the prediction results by testing the DC conductivity of different types of insulating oils, thereby accurately and efficiently evaluating the insulating performance of insulating oil under a DC electric field, and providing theoretical guidance for designing a valve-side outlet device of a converter transformer with excellent insulation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0026] Figure 1 This is a flow chart of the method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters in Example 1.

[0027] Figure 2 This is a flow chart of the model construction of the method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters in Example 1.

[0028] Figure 3 This is a module structure diagram of the system for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters in Example 2. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] Example 1, reference Figure 1 and Figure 2 , which is the first embodiment of the present invention, and provides a method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical parameters, including: Figure 1 As shown:

[0032] Step 1: Establish models of mineral oil molecules and natural lipid molecules containing ions respectively.

[0033] First, the Materials Studios software was used to construct models of mineral oil molecules, natural ester molecules, and ions. The mineral oil molecules are composed of monoalkanes, dialkanes, trialkanes, tetraalkanes, aromatic hydrocarbons, and chain hydrocarbons; the natural ester molecules are composed of glyceryl trilinolenate, glyceryl trilinoleate, glyceryl tristearate, glyceryl trioleate, and glyceryl tripalmitate; and the ions are composed of H3O+, Cu2+, OH-, and Cl-. Then, the mineral oil system and natural ester system containing ions were established respectively through the Amorphous Cell module. Finally, the mineral oil system and natural ester system were geometrically optimized, annealed, and dynamically balanced to minimize their energy and make them more reasonable. The model construction process is as follows: Figure 2 shown.

[0034] Step 2: Calculate the ionization energy and electron affinity of insulating oil molecules under different electric field strengths.

[0035] Based on density functional theory, the Gaussian 16W software was used to optimize the geometry of the insulating oil molecular model using the M062X functional combined with the 6-311G (d, p) basis set. Electric fields of 0, 5.14 kV / mm, 10.28 kV / mm, 15.42 kV / mm, and 20.56 kV / mm were applied to the insulating oil molecular model along the x-axis to obtain the optimal structure of the insulating oil molecule under different electric field strengths. Based on the optimized insulating oil molecular model, the M062X functional combined with the 6-311G (d, p) basis set was used to calculate the ionization potential (IP) and electron affinity (EA) of the insulating oil molecule according to formula (1) and formula (2):

[0036] IP=E M+ -E M (1)

[0037] EA=E M -E M- (2)

[0038] Among them, E M Expressed as the energy calculated when the molecule is neutral, E M+ Expressed as the energy calculated when the molecular charge is +1, E M- Expressed as the energy calculated when the molecular charge is -1.

[0039] Step 3: Calculate and analyze the kinetic characteristics of each ion in the mineral oil and natural ester system.

[0040] Materials studios software was used to perform molecular dynamics simulation based on COMPASS force field. First, the SteepestDescent method was used to perform geometric optimization on the mineral oil system and the natural ester system. Then, the two optimized insulating oil models were simulated for 100ps using a constant pressure and constant temperature ensemble (NPT) at a pressure of 1atm and a temperature of 340K. The pressure and temperature during the entire simulation process were controlled by the Berendsen barostat and the Nose thermostat, respectively, and the time step was set to 1fs to integrate the Verlet motion equation.

[0041] The mobility of ions in insulating oil molecules is characterized by mean square displacement (MSD):

[0042] MSD=<|r i (t)-r i (0)| 2 > (3)

[0043] Among them, r i (t) and r i (0) represents the position vector of the i-th atom at time t and time 0 respectively.

[0044] Step 4: DC conductivity test of mineral oil and natural ester.

[0045] A three-electrode polarization / depolarization current test platform was built to measure the DC conductivity of mineral oil and natural ester under the condition of electric field strength of 0-5kV / mm. The DC conductivity of insulating oil is calculated by formula (4):

[0046]

[0047] Among them, σ represents conductivity, ε0 ​​represents vacuum dielectric constant, C0 represents geometric capacitance of insulating material, U0 represents polarization voltage, i c Expressed as the stable value of the polarization current.

[0048] Before the test, the insulating oil samples were dried: the insulating oil was placed in a vacuum drying oven at a drying temperature of 90°C, a vacuum degree of 0.95MPa, and a drying time of 48h. The dried insulating oil was tested and measured. The measurement temperature was 40°C, the test polarization time was 1000s, the depolarization time was 300s, and each group of tests was discharged for 10 minutes to ensure sufficient discharge.

[0049] Example 2, reference Figure 3, which is the second embodiment of the present invention, and is different from the first embodiment in that: a system for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters, comprising a model building module, a molecular energy calculation module, a kinetic characteristic module and a conductivity testing module; the model building module respectively establishes models of mineral oil molecules and natural fat molecules containing ions; the molecular energy calculation module calculates the ionization energy and electron affinity of insulating oil molecules under different electric field strengths; the kinetic characteristic module calculates and analyzes the kinetic characteristics of each ion in the mineral oil and natural ester system; the conductivity testing module performs a DC conductivity test on the mineral oil and natural ester.

[0050] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0051] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0052] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0053] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0054] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for evaluating the insulating properties of insulating oil under a DC electric field based on microscopic physical parameters, characterized in that: include, Establish models of mineral oil molecules and natural lipid molecules containing ions respectively; Calculate the ionization energy and electron affinity of insulating oil molecules under different electric field strengths; Calculate and analyze the kinetic characteristics of various ions in mineral oil and natural ester systems; Conduct DC conductivity tests on mineral oils and natural esters.

2. The method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters according to claim 1, characterized in that: The method of separately establishing the models of mineral oil molecules and natural lipid molecules containing ions includes constructing models of mineral oil molecules, natural ester molecules and ions based on MaterialsStudios software, separately establishing the mineral oil system and natural ester system containing ions through the Amorphous Cell module, and finally, geometrically optimizing, annealing and dynamically balancing the mineral oil system and the natural ester system to minimize the system energy.

3. The method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters according to claim 2, characterized in that: The mineral oil molecules are composed of monoalkanes, dialkanes, trialkanes, tetraalkanes, aromatic hydrocarbons and chain hydrocarbons; the natural ester molecules are composed of glyceryl trilinolenate, glyceryl trilinoleate, glyceryl tristearate, glyceryl trioleate and glyceryl tripalmitate; and the ions are composed of H3O+, Cu2+, OH- and Cl-.

4. The method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters according to claim 3, characterized in that: The calculation of the ionization energy and electron affinity of the insulating oil molecules under different electric field strengths includes, based on density functional theory, geometrically optimizing the constructed insulating oil molecular model, applying electric fields of different electric field strengths to the insulating oil molecular model along the x-axis, and obtaining the optimal structure of the insulating oil molecules under different electric field strengths.

5. The method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters according to claim 4, characterized in that: The calculation of the ionization energy and electron affinity of the insulating oil molecules under different electric field strengths also includes, based on the optimized insulating oil molecular model, calculating the ionization energy IP and the electron affinity EA of the insulating oil molecules based on density functional theory, wherein the calculation formulas of the IP and EA are expressed as follows: IP=E M+ -E M YES=Yes M -Yes M- Among them, E M Expressed as the energy calculated when the molecule is neutral, E M+ Expressed as the energy calculated when the molecular charge is +1, E M- Expressed as the energy calculated when the molecular charge is -1.

6. The method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters according to claim 5, characterized in that: The computational analysis of the kinetic characteristics of each ion in the mineral oil and natural ester systems includes: using the SteepestDescent method to perform geometric optimization on the mineral oil system and the natural ester system, and performing a 100ps molecular dynamics simulation of the optimized two insulating oil system models under the conditions of a pressure of 1atm and a temperature of 340K using a constant pressure and constant temperature ensemble, wherein the pressure and temperature during the entire simulation process are respectively controlled by a Berendsen barostat and a Nose thermostat, and a time step of 1fs is set to integrate the Verlet motion equation; The mobility of ions in insulating oil molecules is characterized by the mean square displacement (MSD), which is expressed as: MSD=<|r i (t)-r i (0)| 2 > Among them, r i (t) and r i (0) represents the position vector of the i-th atom at time t and time 0 respectively.

7. The method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters according to claim 6, characterized in that: The DC conductivity test of mineral oil and natural ester includes building a three-electrode polarization or depolarization current test platform to measure the DC conductivity of mineral oil and natural ester under the condition of electric field strength of 0-5kV / mm. The calculation formula of the DC conductivity of insulating oil is expressed as: Among them, σ represents conductivity, ε0 ​​represents vacuum dielectric constant, C0 represents geometric capacitance of insulating material, U0 represents polarization voltage, i c Expressed as the stable value of the polarization current.

8. A system using the method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical parameters as claimed in any one of claims 1 to 7, characterized in that: Including model building module, molecular energy calculation module, kinetic characteristics module and conductivity test module; The model building module respectively builds models of mineral oil molecules and natural lipid molecules containing ions; The molecular energy calculation module calculates the ionization energy and electron affinity of insulating oil molecules under different electric field strengths; The kinetic characteristics module calculates and analyzes the kinetic characteristics of each ion in the mineral oil and natural ester system; The conductivity test module performs a direct current conductivity test on mineral oil and natural ester.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters described in any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for evaluating the insulating performance of insulating oil under a DC electric field based on microscopic physical property parameters described in any one of claims 1 to 7 are implemented.

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