Method and system for calculating diffusion of internal fault dissolved gas of oil immersed current transformer

Abstract

The invention discloses a method and system for calculating diffusion of dissolved gas in an oil immersed current transformer internal fault, and belongs to the technical field of electric power systems. The method comprises the steps that a three-dimensional solid model is established according to the structure of the inverted oil-immersed current transformer, and an internal multi-physical field model is established based on the three-dimensional solid model; building a coupling model on the basis of the internal multi-physical field model, and determining the internal temperature distribution condition of the inverted oil-immersed current transformer during normal operation on the basis of the coupling model; and on the basis of the coupling model, according to the distribution condition, the diffusion of the dissolved gas in the inverted oil-immersed current transformer is calculated, and finite element mesh division is carried out on the coupling model. According to the method, the prediction precision is improved, and the dissolved gas change of the inverted oil-immersed current transformer under the actual fault condition can be predicted more accurately.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and more particularly, to a method and system for calculating the diffusion of dissolved gases in the event of an internal fault of an oil-immersed current transformer. Background Art

[0002] In the operation of power equipment, the condition monitoring and fault diagnosis of inverted oil-immersed current transformers are crucial. As a key component in the power system, it plays a core role in the process of electric energy transmission and distribution. To ensure the reliability and safety of its operation, it is necessary to monitor the equipment status in real time in order to timely evaluate and diagnose potential faults. For example, problems such as local overheating and power supply interruption may be caused by dissolved gases in the insulating oil, and the accumulation of these gases not only accelerates the deterioration of the insulation system, but may also lead to equipment failure, thus threatening the stability of the power grid and the safety of personnel.

[0003] The generation of dissolved gases has a complex and multi-faceted impact on inverted oil-immersed current transformers. The accumulation of gases in the oil may form local bubbles, which will gather in the high electric field regions inside the equipment, thus triggering partial discharge or arc discharge, further exacerbating insulation damage. In addition, the continuous generation of gases will reduce the electrical strength of the insulating oil and increase the risk of breakdown voltage. Especially after a high-energy short-circuit fault, the generation of a large amount of gases such as acetylene will significantly deteriorate the insulation performance of the oil, resulting in the gradual failure of the insulation layer of the current transformer. If the gas accumulates to a certain extent and is not processed in time, it may trigger serious secondary faults such as arc discharge and tank explosion, which not only damage the current transformer itself, but also pose a threat to the safety of surrounding equipment and the entire power system.

[0004] Currently, the research on the diffusion of dissolved gases inside inverted oil-immersed current transformers mainly focuses on empirical models and experimental methods. However, these methods often have difficulty accurately predicting the changes in gas diffusion under actual fault conditions. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a method for calculating the diffusion of dissolved gases in the event of an internal fault of an oil-immersed current transformer, including:

[0006] According to the structure of the inverted oil-immersed current transformer, a three-dimensional solid model is established, and based on the three-dimensional solid model, an internal multi-physical field model is built;

[0007] Based on the internal multi-physical field model, a coupling model is built, and based on the coupling model, the internal temperature distribution condition of the inverted oil-immersed current transformer during normal operation is determined;

[0008] Based on the coupling model, according to the distribution, calculate the diffusion of dissolved gases inside the inverted oil-immersed current transformer, and perform finite element mesh division on the coupling model.

[0009] Optionally, the coupling model is a three-dimensional electro-thermal-fluid coupling model.

[0010] Optionally, the coupling model includes: a solver.

[0011] Optionally, after building the coupling model, set the solver to a transient-frequency domain solver, and set the material properties, number of calculation steps, calculation step size, and boundary conditions of the inverted oil-immersed current transformer structure.

[0012] Optionally, according to the distribution, calculating the diffusion of dissolved gases inside the inverted oil-immersed current transformer includes:

[0013] In the calculation step size, calculate the viscosity of the insulating oil, and based on the viscosity and temperature distribution of the insulating oil, calculate the diffusion coefficient of the dissolved gas in the insulating oil through the Stokes-Einstein equation. And based on the diffusion coefficient, through the double-film mass transfer theory equation, transfer the dissolved gas in the gas field to the liquid field through the gas-liquid coupling surface to obtain the dissolved gas concentration in the liquid field until all calculation step sizes are calculated, that is, complete the calculation of the diffusion of dissolved gases inside the inverted oil-immersed current transformer.

[0014] Optionally, the Stokes-Einstein equation is as follows:

[0015]

[0016] Among them, D is the diffusion coefficient, k is the Boltzmann constant, μ is the solvent viscosity, r is the radius of the diffusing particle, and T is the temperature.

[0017] Optionally, the double-film mass transfer theory equation is as follows:

[0018] m g =k_m(c * -c)M a

[0019] Among them, m g is the mass transfer rate of the gas, k_m is the mass transfer coefficient, c * is the saturation concentration, c is the actual concentration of the dissolved gas, and M a is the molar mass of the mass transfer gas.

[0020] Optionally, the boundary conditions include:

[0021] Set a heat source, perform heat dissipation and heat radiation simulations of the internal temperature field, calculate the viscosity of the insulating oil affected by temperature, set the external temperature to 25 °C, set the contact surface between the gas field and the liquid field as the gas-liquid coupling surface, and set the remaining surfaces of the fluid domain as wall surfaces. Set the fixed constraints, calculation time, number of calculation steps, and calculation step size required for the calculation.

[0022] Optionally, the calculation formula for electromagnetic-thermal field coupling in the coupling model is as follows:

[0023] Calculate through the following formula:

[0024]

[0025] Q e = J·E

[0026]

[0027] Among them, E is the internal electric field of the inverted oil-immersed current transformer, V is the electric potential at each point inside, J is the input current density, C p is the constant-pressure heat capacity of the material, u is the internal coordinate vector, Q e is the heating power, is the temperature gradient, and ρ is the material density.

[0028] Optionally, the heat source is set and calculated through the following formula:

[0029] P1 = I1 2 R1

[0030] P2 = I1 2 R2

[0031] P3 = U 2 ωC tanδ

[0032] Among them, P1 is the joule heat of the primary conductor of the inverted oil-immersed current transformer, R1 is the resistance of the primary conductor, I1 is the primary-side current, P2 is the joule heat of the secondary winding of the inverted oil-immersed current transformer, R2 is the resistance of the secondary winding, I2 is the secondary-side current, P3 is the overall dielectric loss of the inverted oil-immersed current transformer, U is the withstand voltage of the insulation structure, ω is the angular frequency, C is the dielectric capacitance, and tanδ is the dielectric loss factor.

[0033] Optionally, the convective heat flux with the outside is set as:

[0034] q0 = h * (T ext - T)

[0035] Among them, T ext is the external temperature, h is the convective heat transfer coefficient, and T is the temperature.

[0036] Optionally, the viscosity of the insulating oil varies with temperature, and the formula is as follows:

[0037]

[0038] Where η(T) is the dynamic viscosity of the insulating oil at temperature T.

[0039] Optionally, the calculation formula for the Henry's constant of the dissolved gas is as follows:

[0040]

[0041] Where G is the universal gas constant, ρ1 is the solvent density, M1 is the average molecular weight of the solvent, and K is the Ostwald equilibrium constant related to temperature T.

[0042] Optionally, the grid update formula is as follows:

[0043]

[0044] In the formula, D is the diffusion coefficient, is the moving speed of the grid, is the Laplace operator.

[0045] Optionally, the conservation principle on the gas-liquid coupling surface is:

[0046] v l ·n = v g ·n

[0047] σ l ·n = σ g ·n + f interface

[0048]

[0049] Where v l and v g are the velocity vectors of the liquid phase and the gas phase respectively, n is the normal vector of the interface, σ l and σ g are the stress tensors of the liquid phase and the gas phase respectively, f interface is the force on the interface, q l and q g are the heat conduction fluxes of the liquid phase and the gas phase respectively, h l and h g are the enthalpies of the liquid phase and the gas phase respectively, is the mass flow rate per unit area.

[0050] On the other hand, the present invention also proposes a system for calculating the diffusion of dissolved gases in the internal fault of an oil-immersed current transformer, including:

[0051] A modeling unit, configured to establish a three-dimensional solid model according to the structure of an inverted oil-immersed current transformer, and based on the three-dimensional solid model, build an internal multi-physical field model;

[0052] A first calculation unit, configured to build a coupling model based on the internal multi-physical field model, and based on the coupling model, determine the internal temperature distribution of the inverted oil-immersed current transformer during normal operation;

[0053] A second calculation unit, configured to perform calculations on the diffusion of dissolved gases inside the inverted oil-immersed current transformer based on the distribution and perform finite element mesh division on the coupling model.

[0054] Optionally, the coupling model is a three-dimensional electro-thermal-fluid coupling model.

[0055] Optionally, the coupling model includes a solver.

[0056] Optionally, after building the coupling model, set the solver to a transient-frequency domain solver, and set the material properties, number of calculation steps, calculation step size, and boundary conditions of the structure of the inverted oil-immersed current transformer.

[0057] Optionally, performing calculations on the diffusion of dissolved gases inside the inverted oil-immersed current transformer based on the distribution includes:

[0058] During the calculation step size, calculate the viscosity of the insulating oil, and based on the viscosity of the insulating oil and the temperature distribution, calculate the diffusion coefficient of the dissolved gas in the insulating oil through the Stokes-Einstein equation, and based on the diffusion coefficient, through the double-layer film mass transfer theory equation, transfer the dissolved gas in the gas field to the liquid field through the gas-liquid coupling surface to obtain the dissolved gas concentration in the liquid field until all calculation step sizes are calculated, that is, complete the calculation of the diffusion of dissolved gases inside the inverted oil-immersed current transformer.

[0059] Optionally, the Stokes-Einstein equation is as follows:

[0060]

[0061] Where D is the diffusion coefficient, k is the Boltzmann constant, μ is the solvent viscosity, r is the radius of the diffusing particle, and T is the temperature.

[0062] Optionally, the double-layer film mass transfer theory equation is as follows:

[0063] m g =k_m(c * -c)M a

[0064] Where m gis the mass transfer rate of the gas, \(k_m\) is the mass transfer coefficient, \(c\) * is the saturation concentration, \(c\) is the actual concentration of the dissolved gas, \(M\) a is the molar mass of the mass transfer gas.

[0065] Optionally, the boundary conditions include:

[0066] Set the heat source, heat dissipation, and heat radiation to simulate the internal temperature field, calculate the viscosity of the insulating oil affected by temperature, set the external temperature to 25 °C, set the contact surface between the gas field and the liquid field as the gas-liquid coupling surface, and set the remaining surfaces of the fluid domain as the wall surfaces. Set the fixed constraints, calculation time, number of calculation steps, and calculation step size required for the calculation.

[0067] Optionally, the calculation formula for electromagnetic-thermal field coupling by the coupling model is as follows:

[0068] It is calculated by the following formula:

[0069]

[0070] Q e = J·E

[0071]

[0072] where \(E\) is the internal electric field of the inverted oil-immersed current transformer, \(V\) is the electric potential at each point inside, \(J\) is the input current density, \(C\) p is the constant-pressure heat capacity of the material, \(u\) is the internal coordinate vector, \(Q\) e is the heating power, is the temperature gradient, \(\rho\) is the material density.

[0073] Optionally, the heat source is set and calculated by the following formula:

[0074] \(P1 = I1\) 2 \(R1\)

[0075] \(P2 = I1\) 2 \(R2\)

[0076] \(P3 = U\) 2 \(\omega C \tan\delta\)

[0077] where \(P1\) is the joule heat of the primary conductor of the inverted oil-immersed current transformer, \(R1\) is the resistance of the primary conductor, \(I1\) is the primary-side current, \(P2\) is the joule heat of the secondary winding of the inverted oil-immersed current transformer, \(R2\) is the resistance of the secondary winding, \(I2\) is the secondary-side current, \(P3\) is the overall dielectric loss of the inverted oil-immersed current transformer, \(U\) is the withstand voltage of the insulation structure, \(\omega\) is the angular frequency, \(C\) is the dielectric capacitance, and \(\tan\delta\) is the dielectric loss factor.

[0078] Optionally, set the convective heat flux with the outside world to:

[0079] q0 = h * (T ext - T)

[0080] where T ext is the external temperature, h is the convective heat transfer coefficient, and T is the temperature.

[0081] Optionally, the viscosity of the insulating oil varies with temperature, and the formula is as follows:

[0082]

[0083] where η(T) is the dynamic viscosity of the insulating oil at temperature T.

[0084] Optionally, the calculation formula for the Henry's constant of the dissolved gas is as follows:

[0085]

[0086] where G is the universal gas constant, ρ1 is the solvent density, M1 is the average molecular weight of the solvent, and K is the Ostwald equilibrium constant related to temperature T.

[0087] Optionally, the formula for updating the grid is as follows:

[0088]

[0089] In the formula, D is the diffusion coefficient, is the moving speed of the grid, is the Laplace operator.

[0090] Optionally, the conservation principle on the gas-liquid coupling surface is:

[0091] v l ·n = v g ·n

[0092] σ l ·n = σ g ·n + f interface

[0093]

[0094] where v l and v g are the velocity vectors of the liquid phase and the gas phase respectively, n is the normal vector of the interface, σ l and σ g are the stress tensors of the liquid phase and the gas phase respectively, f interface is the force on the interface, q l and q g are the heat conduction fluxes of the liquid phase and the gas phase respectively, h l and h gare the enthalpies of the liquid phase and the gas phase respectively, is the mass flow rate per unit area.

[0095] On the other hand, the present invention also provides a computing device, including: one or more processors;

[0096] The processor is configured to execute one or more programs;

[0097] When the one or more programs are executed by the one or more processors, the method as described above is implemented.

[0098] On the other hand, the present invention also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed, the method as described above is implemented.

[0099] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0100] The present invention provides a method for calculating the diffusion of dissolved gases in an oil-immersed current transformer during internal faults, including: establishing a three-dimensional solid model according to the structure of an inverted oil-immersed current transformer, and building an internal multi-physical field model based on the three-dimensional solid model; building a coupling model based on the internal multi-physical field model, and determining the internal temperature distribution of the inverted oil-immersed current transformer during normal operation based on the coupling model; calculating the diffusion of dissolved gases inside the inverted oil-immersed current transformer based on the distribution condition by the coupling model, and performing finite element mesh division on the coupling model. The present invention improves the prediction accuracy and can more accurately predict the change of dissolved gases in the inverted oil-immersed current transformer under actual fault conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Figure 1 is the calculation flow chart of the embodiment of the present invention;

[0102] Figure 2 is the solid model modeling of the inverted oil-immersed current transformer in the embodiment of the present invention, where (a) is the overall combination of the inverted oil-immersed current transformer, (b) is the outer shell of the inverted oil-immersed current transformer, (c) is the internal insulating paper of the inverted oil-immersed current transformer, (d) is the combination of the primary busbar and the iron core, and (e) is the secondary winding;

[0103] Figure 3 is the mesh division diagram of the multi-physical field model of the inverted oil-immersed current transformer in the embodiment of the present invention;

[0104] Figure 4 is the schematic diagram of gas-liquid coupling calculation in the embodiment of the present invention;

[0105] Figure 5Dissolved gas diffusion diagram of an embodiment of the present invention, where (a) is at t = 0 h, (b) is at t = 5 h, (c) is at t = 10 h, (d) is at t = 15 h, (e) is at t = 30 h, and (f) is at t = 50 h;

[0106] Figure 6 Concentration diagram of three points of dissolved gas diffusion of an embodiment of the present invention, where (a) is the selected point of an inverted oil-immersed current transformer, (b) is the dissolved hydrogen concentration at point a, and (c) is the dissolved hydrogen concentration at point b. Detailed implementation manners

[0107] Now, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely, and to fully convey the scope of the present invention to those skilled in the art. The terms in the exemplary embodiments shown in the drawings are not intended to limit the present invention. In the drawings, the same units / components are denoted by the same reference numerals.

[0108] Unless otherwise specified, the terms (including scientific and technical terms) used herein have the ordinary meaning understood by those skilled in the art. Additionally, it can be understood that the terms defined in the commonly used dictionary should be understood to have a meaning consistent with the context of their related fields, and should not be understood as having an idealized or overly formal meaning.

[0109] Embodiment 1:

[0110] The present invention provides a method for calculating the diffusion of dissolved gases in the internal faults of an oil-immersed current transformer, as Figure 1 shown, including the following steps:

[0111] (1) According to the structure of the inverted oil-immersed current transformer, a three-dimensional solid model of the inverted oil-immersed current transformer is established;

[0112] (2) According to the three-dimensional solid model of the inverted oil-immersed current transformer, a multi-physical field model of the inverted oil-immersed current transformer is designed, and a three-dimensional electro-thermal-fluid coupling model of the inverted oil-immersed current transformer is established in the model calculation software. The solver is set as a transient-frequency domain solver, and the material properties, number of calculation steps, calculation step size, and boundary conditions of the structure of the inverted oil-immersed current transformer are set;

[0113] (3) Immediately afterwards, according to the electro-thermal coupling model, the internal temperature distribution of the inverted oil-immersed current transformer under normal operation is calculated;

[0114] (4) According to the internal temperature distribution of the inverted oil-immersed current transformer under normal operating conditions, in the first calculation step, calculate the viscosity of the insulating oil. Based on the viscosity of the insulating oil and the temperature distribution, calculate the diffusion coefficient of the dissolved gas in the insulating oil through the Stokes-Einstein equation; transfer the dissolved gas in the gas field to the liquid field through the gas-liquid coupling surface by the double-layer film mass transfer theory to obtain the dissolved gas concentration in the liquid field.

[0115] (5) Transfer the dissolved gas in the liquid field of this step to the gas field through the gas-liquid coupling surface, and obtain the diffusion coefficient of the gas field through the gas field control equation. After this step is completed, the change of the gas field boundary condition is transmitted back to the liquid field, and then the flow field calculation of the next step is carried out, and so on in a cycle. After the set number of steps is calculated, the calculation of the diffusion of the dissolved gas in the fault of the inverted oil-immersed current transformer based on gas-liquid coupling is completed.

[0116] (6) Carry out finite element mesh division on the established three-dimensional electro-thermal-fluid three-dimensional coupling model of the inverted oil-immersed current transformer.

[0117] Further, the specific content of step (1) is as follows:

[0118] Use a modeling tool to establish a three-dimensional model of the inverted oil-immersed current transformer. When establishing the model, the physical model should be reasonably simplified, which can not only reduce the calculation amount of the model but also meet the accuracy requirements of the calculation results.

[0119] Further, step (2) includes the following steps:

[0120] Set the heat source, heat dissipation, and thermal radiation of the multi-physical field model of the inverted oil-immersed current transformer to simulate the internal temperature field. The external temperature is set to 25 °C, the contact surface between the gas field and the liquid field is set as the gas-liquid coupling surface, and the rest of the surfaces of the fluid domain are set as wall surfaces. Set the fixed constraints, calculation time, number of calculation steps, and calculation step length required for the calculation.

[0121] Further, the boundary conditions of step (3) include:

[0122] The coupling of the internal electromagnetic-thermal field of the inverted oil-immersed current transformer is calculated by the following formula:

[0123]

[0124] Q e =JE (2)

[0125]

[0126] In the formula, E is the internal electric field of the inverted current transformer (V / m), V is the electric potential at each point inside (V), J is the input current density (A / m²), which is the heating power (W / m²), C p is the constant-pressure heat capacity of the material (J / kg·K), and u is the internal coordinate vector.

[0127] After that, the heat source is calculated by the following formula:

[0128] P1 = I1 2 R1 (4)

[0129] P2 = I1 2 R2 (5)

[0130] P3 = U 2 ωC tanδ (6)

[0131] In the formula, P1 is the Joule heat of the primary conductor of the inverted current transformer, R1 is the resistance of the primary conductor, and I1 is the primary-side current. P2 is the Joule heat of the secondary winding of the inverted current transformer, R2 is the resistance of the secondary winding, and I2 is the secondary-side current. P3 is the overall dielectric loss of the inverted current transformer, U is the withstand voltage of the insulation structure (V), ω is the angular frequency (rad / s), C is the dielectric capacitance (F), and tanδ is the dielectric loss factor.

[0132] After that, the convective heat flux with the outside is set as:

[0133] q0 = h * (T ext - T) (7)

[0134] In the formula, T ext is the external temperature, and the emissivity is set to 0.9.

[0135] Furthermore, the boundary conditions of step (4) include:

[0136] The formula for the change of insulating oil viscosity with temperature is:

[0137]

[0138] Among them, η(T) is the dynamic viscosity of the insulating oil at temperature T.

[0139] After that, the diffusion coefficient of the dissolved gas described in step (5) is calculated, and the Stokes-Einstein equation is:

[0140]

[0141] In the above formula, k is the Boltzmann constant, μ is the solvent viscosity, and r is the radius of the diffusing particle.

[0142] Then, calculate the mass transfer of the dissolved gas and the insulating oil. The double-film theory equation is as follows:

[0143] m g =k(c * -c)M a (10)

[0144] Wherein, m g is the mass transfer rate of the gas, k is the mass transfer coefficient, expressed as k = (D * d b / H), where D is the diffusion coefficient, H is the Henry constant, d b is the characteristic diameter, c * is the saturation concentration, calculated by the formula c * =(p2 + p ref ) / H, representing the concentration of the dissolved gas under the given pressure p2, p ref is the reference pressure, c is the actual concentration of the dissolved gas, and M a is the molar mass of the mass transfer gas.

[0145] Among them, the calculation formula for the Henry constant of the dissolved gas is:

[0146]

[0147] Wherein, G is the universal gas constant, ρ1 is the solvent density, M1 is the average molecular weight of the solvent, and K is the Ostwald equilibrium constant related to the temperature T.

[0148] Then, calculate that the Ostwald equilibrium constant can be expressed as:

[0149]

[0150] By substituting Formula (11) and Formula (12) into Formula (10), the mass transfer coefficient of the dissolved gas in the insulating oil can be obtained, and then the mass transfer rate of the gas can be obtained.

[0151] Update the grid in real time through Formula (13):

[0152]

[0153] In the formula, D is the diffusion coefficient, is the movement speed of the grid, is the Laplace operator.

[0154] Furthermore, step (6) is specifically to describe the conservation principle on the gas-liquid coupling surface, that is:

[0155] v l ·n=v g ·n (2)

[0156] σ l ·n = σ g ·n + f interface (3)

[0157]

[0158] In the formula, v l and v g are the velocity vectors of the liquid phase and the gas phase respectively, n is the normal vector of the interface, σ l and σ g are the stress tensors of the liquid phase and the gas phase respectively, f interface is the force on the interface (including the contribution of surface tension), q l and q g are the heat conduction fluxes of the liquid phase and the gas phase respectively, h l and h g are the enthalpies of the liquid phase and the gas phase, is the mass flow rate per unit area.

[0159] Furthermore, step (6) includes the following steps:

[0160] Perform mesh division on the inverted oil-immersed current transformer, and use tetrahedral meshes with relatively good quality. Refine the meshes in the more complex areas of the model, check and adjust the mesh quality, and perform calculations according to the set calculation time, number of calculation steps, and calculation step size

[0161] To better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0162] Take the LVB220W3 inverted current transformer as the research object below.

[0163] The internal fault dissolved gas diffusion calculation method for the gas-liquid coupled inverted oil-immersed current transformer in this embodiment specifically includes the following steps:

[0164] Step (1): As Figure 2 shown, establish a three-dimensional solid model of the inverted oil-immersed current transformer with actual size in the modeling software;

[0165] Step (2): According to the three-dimensional solid model of the inverted oil-immersed current transformer, design a multi-physical field model of the inverted oil-immersed current transformer and set the relevant parameters of the internal structural materials of the inverted oil-immersed current transformer. The structural material parameters are: (a) The primary conductor rod material is steel, with a thermal conductivity of 238 (W / (m * K)), the primary current is 2000 A, and the primary resistance is 20.72 μΩ; (b) The secondary winding is copper, with a thermal conductivity of 400 (W / (m* K)), secondary current of 5 A, secondary resistance of 4.44 Ω; (c) The insulating oil selected is No. 25 insulating oil with a thermal conductivity of 0.13 - 8 -5T , where T is the oil temperature.

[0166] Step (3): To solve the operating conditions of the inverted oil-immersed current transformer under normal conditions, a three-dimensional electro-thermal-fluid coupling model of the inverted oil-immersed current transformer is established;

[0167] Step (4): In the inverted oil-immersed current transformer, first, the physical fields of dilute mass transfer and bubble flow are used to simulate the gas-liquid coupling phenomenon, and the fault area is set, and high-temperature boundary conditions are applied. According to the internal temperature distribution of the transformer under normal operating conditions, the viscosity of the insulating oil is first calculated in the first calculation step. Subsequently, based on the viscosity and temperature distribution, the diffusion coefficient of the dissolved gas in the insulating oil is calculated through the Stokes-Einstein equation. Using the double-film mass transfer theory in the bubble layer, the dissolved gas in the gas phase is transferred to the liquid phase through the gas-liquid coupling surface, and then the concentration distribution of the dissolved gas in the liquid phase is obtained through the reaction interface in the dilute mass transfer;

[0168] Step (5): Set the calculation data transfer between the gas field and the liquid field of the multi-physical field model of the designed inverted oil-immersed current transformer. The gas-liquid coupling calculation process is as Figure 4 shown. When the dissolved gas in the liquid field of one step is transferred to the gas field through the gas-liquid coupling surface, the diffusion coefficient of the gas field is obtained through the gas field control equation. After this step is completed, the change of the gas field boundary conditions is transferred back to the liquid field, and then the flow field calculation of the next step is carried out, and so on in a cycle. After the set number of steps is calculated, the calculation of the diffusion of the dissolved gas in the fault of the inverted oil-immersed current transformer based on gas-liquid coupling is completed.

[0169] Step (6): Finally, mesh division is performed on the inverted oil-immersed current transformer, the solver is set to a transient-frequency domain solver, the solution time is set to 50 h, and the solution step is set to 1 h for solution.

[0170] Taking hydrogen as an example, the characteristics of the dissolved hydrogen concentration at different times when an internal fault occurs in the inverted oil-immersed current transformer are as Figure 5 shown in (a), (b), (c), (d), (e) and (f) therein. As Figure 5 can be seen. At the initial state (0 h), the concentration of the dissolved gas inside the transformer is low and evenly distributed, and no obvious gas accumulation or diffusion phenomenon is observed, indicating that the system has not been affected by an internal fault. After 5 h, the hydrogen concentration in the fault area increases significantly, exceeding 10 mol / m 3, and begins to spread from the local area to the surrounding. By 10 hours, the diffusion of hydrogen is further intensified, and the overall concentration tends to be uniform, maintaining between 10-12mol / m 3 . After 15 hours, the hydrogen concentration in the fault area approaches the peak value (about 12mol / m 3 ). Although the concentration near the fault point is relatively high, the growth rate of hydrogen concentration in the area far from the fault point is relatively slow. After 30 hours, the diffusion range of hydrogen continues to expand, but the fault area still maintains a relatively high hydrogen concentration, while the concentration in other areas still rises slowly, showing an obvious concentration gradient. After 50 hours, the hydrogen concentration in the fault area remains at a high level, and the hydrogen concentration in other areas also increases, but the diffusion rate is still uneven. Generally speaking, the calculation results show that under fault conditions, hydrogen accumulates rapidly in the fault area, forming a local high concentration, while the diffusion of hydrogen in other oil areas is relatively slow, resulting in significant regional concentration differences. This situation of excessive local hydrogen concentration may trigger a series of disasters, including partial discharge, insulation breakdown, thermal runaway, explosion caused by gas accumulation, pressure increase and equipment rupture, etc., seriously affecting the safety and operation reliability of equipment.

[0171] The present invention first establishes a three-dimensional solid model and a three-dimensional electro-thermal-fluid coupling model of an inverted oil-immersed current transformer, and performs precise mesh division on the model. Subsequently, the electro-thermal thermodynamics and fluid mechanics of the multi-physical field model of the inverted oil-immersed current transformer are calculated and analyzed, and two-way coupling is realized through the gas-liquid coupling surface to simulate the diffusion process of dissolved gases in the inverted oil-immersed current transformer under internal fault conditions. This method not only significantly improves the accuracy of fault prediction, but also provides an important reference for the design and maintenance of inverted oil-immersed current transformers. The specific advantages are as follows:

[0172] (1) Improve prediction accuracy. By using the calculation method of gas-liquid coupling, the change of dissolved gases in the inverted oil-immersed current transformer under actual fault conditions can be predicted more accurately. This accuracy is crucial for identifying potential fault points and taking timely preventive measures.

[0173] (2) Optimize the design of the inverted oil-immersed current transformer. This method can help engineers better understand the dynamic response inside the inverted oil-immersed current transformer under fault conditions, so as to optimize the design of the inverted oil-immersed current transformer and reduce the risk of faults caused by improper design.

[0174] (3) Support fault diagnosis and prevention. This calculation method can not only be used for the design of inverted oil-immersed current transformers, but also for the fault diagnosis and prevention of existing inverted oil-immersed current transformers. By simulating fault conditions, preventive measures and emergency response plans can be better formulated.

[0175] Example 2:

[0176] The present invention also provides a system 200 for calculating the diffusion of dissolved gases in the event of an internal fault in an oil-immersed current transformer, comprising:

[0177] A modeling unit 201, configured to establish a three-dimensional solid model according to the structure of an inverted oil-immersed current transformer, and build an internal multi-physical field model based on the three-dimensional solid model;

[0178] A first calculation unit 202, configured to build a coupling model based on the internal multi-physical field model, and determine the internal temperature distribution of the inverted oil-immersed current transformer during normal operation based on the coupling model;

[0179] A second calculation unit 203, configured to calculate the diffusion of dissolved gases inside the inverted oil-immersed current transformer based on the distribution condition according to the coupling model, and perform finite element mesh division on the coupling model.

[0180] Wherein, the coupling model is a three-dimensional electro-thermal-fluid coupling model.

[0181] Wherein, the coupling model includes a solver.

[0182] Wherein, after building the coupling model, the solver is set as a transient-frequency domain solver, and the material properties, number of calculation steps, calculation step size and boundary conditions of the structure of the inverted oil-immersed current transformer are set.

[0183] Wherein, calculating the diffusion of dissolved gases inside the inverted oil-immersed current transformer according to the distribution condition includes:

[0184] In the calculation step size, calculate the viscosity of the insulating oil, and calculate the diffusion coefficient of the dissolved gas in the insulating oil according to the viscosity of the insulating oil and the temperature distribution. Based on the diffusion coefficient, transfer the dissolved gas in the gas field to the liquid field through the gas-liquid coupling surface through the double-layer film mass transfer theory equation to obtain the concentration of the dissolved gas in the liquid field until all calculation step sizes are calculated, that is, complete the calculation of the diffusion of the dissolved gas inside the inverted oil-immersed current transformer.

[0185] Wherein, the Stokes-Einstein equation is as follows:

[0186]

[0187] Wherein, D is the diffusion coefficient, k is the Boltzmann constant, μ is the solvent viscosity, r is the radius of the diffusing particle, and T is the temperature.

[0188] Wherein, the double-layer film mass transfer theory equation is as follows:

[0189] m g= k_m(c * - c)M a

[0190] where m g is the mass transfer rate of the gas, k_m is the mass transfer coefficient, c * is the saturation concentration, c is the actual concentration of the dissolved gas, and M a is the molar mass of the mass transfer gas.

[0191] Among them, the boundary conditions include:

[0192] Set the heat source, heat dissipation, and heat radiation to simulate the internal temperature field, calculate the viscosity of the insulating oil affected by temperature, set the external temperature to 25 °C, set the contact surface between the gas field and the liquid field as the gas-liquid coupling surface, and set the remaining surfaces of the fluid domain as the wall surfaces. Set the fixed constraints, calculation time, number of calculation steps, and calculation step size required for the calculation.

[0193] Among them, the calculation formula for electromagnetic-thermal field coupling by the coupling model is as follows:

[0194] It is calculated by the following formula:

[0195]

[0196] Q e = J·E

[0197]

[0198] where E is the internal electric field of the inverted oil-immersed current transformer, V is the electric potential at each internal point, J is the input current density, C p is the constant-pressure heat capacity of the material, u is the internal coordinate vector, and Q e is the heating power, is the temperature gradient, and ρ is the material density.

[0199] Among them, the heat source is set and calculated by the following formula:

[0200] P1 = I1 2 R1

[0201] P2 = I1 2 R2

[0202] P3 = U 2 ωC tanδ

[0203] Among them, P1 is the joule heat of the primary conductor of the inverted oil-immersed current transformer, R1 is the resistance of the primary conductor, I1 is the primary side current, P2 is the joule heat of the secondary winding of the inverted oil-immersed current transformer, R2 is the resistance of the secondary winding, I2 is the secondary side current, P3 is the overall dielectric loss of the inverted oil-immersed current transformer, U is the withstand voltage of the insulation structure, ω is the angular frequency, C is the dielectric capacitance, and tanδ is the dielectric loss factor.

[0204] Among them, the convective heat flux set with the outside is:

[0205] q0 = h * (T ext - T)

[0206] Among them, T ext is the external temperature, h is the convective heat transfer coefficient, and T is the temperature.

[0207] Among them, the viscosity of the insulating oil changes with temperature, and the formula is as follows:

[0208]

[0209] Among them, η(T) is the dynamic viscosity of the insulating oil at temperature T.

[0210] Among them, the calculation formula of the Henry constant of the dissolved gas is as follows:

[0211]

[0212] Among them, G is the universal gas constant, ρ1 is the solvent density, M1 is the average molecular weight of the solvent, and K is the Ostwald equilibrium constant related to temperature T.

[0213] Among them, the formula for updating the grid is as follows:

[0214]

[0215] In the formula, D is the diffusion coefficient, is the moving speed of the grid, is the Laplace operator.

[0216] Among them, the conservation principle on the gas-liquid coupling surface is:

[0217] v l ·n = v g ·n

[0218] σ l ·n = σ g ·n + f interface

[0219]

[0220] wherein, v l and v g are the velocity vectors of the liquid phase and the gas phase respectively, n is the normal vector of the interface, σ l and σ g are the stress tensors of the liquid phase and the gas phase respectively, f interface is the force on the interface, q l and q g are the heat conduction fluxes of the liquid phase and the gas phase respectively, h l and h g are the enthalpies of the liquid phase and the gas phase respectively, is the mass flow rate per unit area.

[0221] The present invention improves the prediction accuracy and can more accurately predict the change of dissolved gases in an inverted oil-immersed current transformer under actual fault conditions.

[0222] Example 3:

[0223] Based on the same inventive concept, the present invention also provides a computer device, which includes a processor and a memory. The memory is used to store a computer program, and the computer program includes program instructions. The processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, and is suitable for implementing one or more instructions. Specifically, it is suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of the method in the above embodiments.

[0224] Example 4:

[0225] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory). The computer-readable storage medium is a memory device in a computer device, used to store programs and data. It can be understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and, of course, the extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space, and this storage space stores the operating system of the terminal. And, in this storage space, there are also stored one or more instructions suitable for being loaded and executed by the processor. These instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. One or more instructions stored in the computer-readable storage medium can be loaded and executed by the processor to implement the steps of the method in the above embodiments.

[0226] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes. The solutions in the embodiments of the present invention can be implemented in various computer languages. For example, object-oriented programming languages such as Java and interpreted scripting languages such as JavaScript.

[0227] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, and the combination of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the specified functions in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0228] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means that implement the function specified in the flowchart(s) Figure 1 or flowcharts and / or block diagram(s) Figure 1 or block diagrams.

[0229] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing steps for implementing the function specified in the flowchart(s) Figure 1 or flowcharts and / or block diagram(s) Figure 1 or block diagrams.

[0230] Although the preferred embodiments of the present invention have been described, additional changes and modifications can be made by those skilled in the art once they learn of the basic inventive concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0231] It is apparent that those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for calculating the diffusion of dissolved gases in the event of an internal fault of an oil-immersed current transformer, characterized in that, Including: Establish a three-dimensional solid model according to the structure of the inverted oil-immersed current transformer, and based on the three-dimensional solid model, build an internal multi-physical field model; Based on the internal multi-physical field model, build a coupling model, and based on the coupling model, determine the internal temperature distribution of the inverted oil-immersed current transformer during normal operation; Based on the coupling model, according to the distribution, calculate the diffusion of dissolved gases inside the inverted oil-immersed current transformer, and perform finite element mesh division on the coupling model.

2. The method according to claim 1, wherein The coupling model is a three-dimensional electro-thermal-fluid coupling model.

3. The method according to claim 1, characterized in that, The coupling model includes: a solver.

4. The method according to claim 1, wherein After building the coupling model, set the solver to a transient-frequency domain solver, and set the material properties, number of calculation steps, calculation step size, and boundary conditions of the structure of the inverted oil-immersed current transformer.

5. The method according to claim 1, wherein The calculation of the diffusion of dissolved gases inside the inverted oil-immersed current transformer according to the distribution includes: During the calculation step, calculate the viscosity of the insulating oil, and according to the viscosity of the insulating oil and the temperature distribution, calculate the diffusion coefficient of the dissolved gas in the insulating oil through the Stokes-Einstein equation, and based on the diffusion coefficient, through the double-layer film mass transfer theory equation, transfer the dissolved gas in the gas field to the liquid field through the gas-liquid coupling surface to obtain the concentration of the dissolved gas in the liquid field until all calculation steps are completed, that is, complete the calculation of the diffusion of dissolved gases inside the inverted oil-immersed current transformer.

6. The method according to claim 5, characterized in that, The Stokes-Einstein equation is as follows: Where D is the diffusion coefficient, k is the Boltzmann constant, μ is the solvent viscosity, r is the radius of the diffusing particle, and T is the temperature.

7. The method according to claim 5, wherein The double-layer film mass transfer theory equation is as follows: m g = k_m(c * - c)M a Among them, m g is the mass transfer rate of the gas, k_m is the mass transfer coefficient, c * is the saturation concentration, c is the actual concentration of the dissolved gas, M a is the molar mass of the mass transfer gas.

8. The method according to claim 4, wherein The boundary conditions include: Set heat sources, heat dissipation, and thermal radiation to simulate the internal temperature field, calculate the viscosity of the insulating oil affected by temperature, set the external temperature to 25°C, set the contact surface between the gas field and the liquid field as the gas-liquid coupling surface, set the remaining surfaces of the fluid domain as wall surfaces, and set the fixed constraints, calculation time, number of calculation steps, and calculation step size required for the calculation.

9. The method according to claim 1, characterized in that, The calculation formula for the electromagnetic-thermal field coupling of the coupling model is as follows: Calculated by the following formula: Q e = J·E Among them, E is the internal electric field of the inverted oil-immersed current transformer, V is the electric potential at each point inside, J is the input current density, C p is the constant-pressure heat capacity of the material, u is the internal coordinate vector, Q e is the heating power, is the temperature gradient, and ρ is the material density.

10. The method according to claim 8, wherein The heat source setting is calculated by the following formula: P1 = I1 2 R1 P2 = I1 2 R2 P3 = U 2 ωCtanδ Where P1 is the Joule heat of the primary conductor of the inverted oil-immersed current transformer, R1 is the resistance of the primary conductor, I1 is the primary-side current, P2 is the Joule heat of the secondary winding of the inverted oil-immersed current transformer, R2 is the resistance of the secondary winding, I2 is the secondary-side current, P3 is the overall dielectric loss of the inverted oil-immersed current transformer, U is the withstand voltage of the insulation structure, ω is the angular frequency, C is the dielectric capacitance, and tanδ is the dielectric loss factor.

11. The method according to claim 8, wherein Set the convective heat flux with the outside as: q0 = h*(T ext - T) where, T ext is the external temperature, h is the convective heat transfer coefficient, and T is the temperature.

12. The method according to claim 5, wherein The viscosity of the insulating oil changes with temperature, and the formula is as follows: Where η(T) is the dynamic viscosity of the insulating oil at temperature T.

13. The method according to claim 5, wherein The calculation formula for the Henry constant of the dissolved gas is as follows: Where G is the universal gas constant, ρ1 is the solvent density, M1 is the average molecular weight of the solvent, and K is the Ostwald equilibrium constant related to temperature T.

14. The method according to claim 5, characterized in that The formula for updating the mesh is as follows: where D is the diffusion coefficient, is the moving velocity of the grid, is the Laplace operator.

15. The method according to claim 8, wherein The conservation principle on the gas-liquid coupling surface is: v l ·n = v g ·n σ l ·n = σ g ·n + f interface where v l and v g are the velocity vectors of the liquid and gas phases respectively, n is the normal vector of the interface, σ l and σ g are the stress tensors of the liquid and gas phases respectively, f interface is the force on the interface, q l and q g are the heat conduction fluxes of the liquid and gas phases respectively, h l and h g are the enthalpies of the liquid and gas phases respectively, is the mass flow rate per unit area.

16. A system for calculating the diffusion of dissolved gases in an oil-immersed current transformer during internal faults, characterized in that, Including: A modeling unit, which is used to establish a three-dimensional solid model according to the structure of an inverted oil-immersed current transformer, and based on the three-dimensional solid model, build an internal multi-physical field model; A first calculation unit, which is used to build a coupling model based on the internal multi-physical field model, and based on the coupling model, determine the internal temperature distribution of the inverted oil-immersed current transformer during normal operation; A second calculation unit, which is used to calculate the diffusion of dissolved gases inside the inverted oil-immersed current transformer based on the distribution and perform finite element mesh division on the coupling model.

17. The system according to claim 16, wherein The coupling model is a three-dimensional electro-thermal-fluid coupling model.

18. The system according to claim 16, characterized in that, The coupling model includes: a solver.

19. The system according to claim 16, wherein After building the coupling model, set the solver to a transient-frequency domain solver, and set the material properties, number of calculation steps, calculation step size, and boundary conditions of the structure of the inverted oil-immersed current transformer.

20. The system according to claim 16, wherein The calculation of the diffusion of dissolved gases inside the inverted oil-immersed current transformer according to the distribution includes: During the calculation step, calculate the viscosity of the insulating oil, and according to the viscosity of the insulating oil and the temperature distribution, calculate the diffusion coefficient of the dissolved gas in the insulating oil through the Stokes-Einstein equation, and based on the diffusion coefficient, through the double-layer film mass transfer theory equation, transfer the dissolved gas in the gas field to the liquid field through the gas-liquid coupling surface to obtain the dissolved gas concentration in the liquid field until all calculation steps are completed, that is, complete the calculation of the diffusion of dissolved gases inside the inverted oil-immersed current transformer.

21. The system according to claim 20, wherein The Stokes-Einstein equation is as follows: Where D is the diffusion coefficient, k is the Boltzmann constant, μ is the solvent viscosity, r is the radius of the diffusing particle, and T is the temperature.

22. The system according to claim 20, wherein The double-layer film mass transfer theory equation is as follows: m g = k_m(c * - C)M a where m g is the mass transfer rate of the gas, k_m is the mass transfer coefficient, c * is the saturation concentration, c is the actual concentration of the dissolved gas, M a is the molar mass of the mass transfer gas.

23. The system according to claim 19, wherein The boundary conditions include: Set heat sources, heat dissipation, and thermal radiation to simulate the internal temperature field, calculate the viscosity of the insulating oil affected by temperature, set the external temperature to 25 °C, set the contact surface between the gas field and the liquid field as the gas-liquid coupling surface, and set the remaining surfaces of the fluid domain as wall surfaces, and set the fixed constraints, calculation time, number of calculation steps, and calculation step size required for the calculation.

24. The system according to claim 16, wherein The calculation formula for the electromagnetic-thermal field coupling of the coupling model is as follows: Calculate through the following formula: Q e = J·E Among them, E is the internal electric field of the inverted oil-immersed current transformer, V is the electric potential at each point inside, J is the input current density, C p is the constant-pressure heat capacity of the material, u is the internal coordinate vector, Q e is the heating power, is the temperature gradient, and ρ is the material density.

25. The system according to claim 23, wherein The calculation of the heat source setting is through the following formula: P1 = I1 2 R1 P2 = I1 2 R2 P3 = U 2 ωCtanδ Where p1 is the Joule heat of the primary conductor of the inverted oil-immersed current transformer, R1 is the resistance of the primary conductor, I1 is the current on the primary side, P2 is the Joule heat of the secondary winding of the inverted oil-immersed current transformer, R2 is the resistance of the secondary winding, I2 is the current on the secondary side, P3 is the overall dielectric loss of the inverted oil-immersed current transformer, U is the withstand voltage of the insulation structure, ω is the angular frequency, C is the dielectric capacitance, and tanδ is the dielectric loss factor.

26. The system according to claim 23, wherein Set the convective heat flux with the outside world as: q0 = h*(T ext - T) where, T ext is the external temperature, h is the convective heat transfer coefficient, and T is the temperature.

27. The system according to claim 20, wherein The viscosity of the insulating oil changes with temperature, and the formula is as follows: Where η(T) is the dynamic viscosity of the insulating oil at temperature T.

28. The system according to claim 22, wherein The calculation formula for the Henry constant of the dissolved gas is as follows: Where G is the universal gas constant, ρ1 is the solvent density, M1 is the average molecular weight of the solvent, and K is the Ostwald equilibrium constant related to temperature T.

29. The system according to claim 20, wherein, The formula for updating the mesh is as follows: where D is the diffusion coefficient, is the moving velocity of the grid, is the Laplace operator.

30. The system according to claim 23, wherein, The conservation principle on the gas-liquid coupling surface is as follows: v l ·n = v g ·n σ l ·n = σ g ·n + f interface where, v l and v g are the velocity vectors of the liquid phase and the gas phase respectively, n is the normal vector of the interface, σ l and σ g are the stress tensors of the liquid phase and the gas phase respectively, f interface is the force on the interface, q l and q g are the heat conduction fluxes of the liquid phase and the gas phase respectively, h l and h g are the enthalpies of the liquid phase and the gas phase respectively, is the mass flow rate per unit area.

31. A computer device, characterized in that, Including: One or more processors; The processor is used to execute one or more programs; When the one or more programs are executed by the one or more processors, the method described in any one of claims 1-15 is implemented.

32. A computer-readable storage medium, characterized in that, A computer program is stored thereon, and when the computer program is executed, the method described in any one of claims 1-15 is implemented.

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