A finite element simulation method for external field distribution of transformer core vibration noise

Abstract

The present invention discloses a finite element simulation method for the external field distribution of the core vibration noise of an oil-immersed transformer based on COMSOL. The three-dimensional physical model of the transformer is used to simulate the transient electromagnetic field of the transformer, and the transient electromagnetic force of the transformer core under no-load operation is calculated. The result is used as the excitation source of the structural field, and the transient displacement of the core vibration is calculated. Then, the transient core surface vibration acceleration is calculated, and the transient data is exported for FFT transformation. The result is used as the initial value of the sound field analysis to simulate the external sound field of the transformer. The sound pressure level of a certain point in the external sound field at different frequencies is compared, and the main harmonic components in the transformer radiation noise are analyzed. A no-load experiment is performed on a 220kV oil-immersed transformer, and an acoustic sensor is placed at the corresponding position in the model to collect sound pressure data. The sound pressure data in the measured time domain is FFT transformed to be close to the simulation value, which verifies the superiority of the simulation model in the calculation of the sound pressure external field.

Description

Technical Field

[0001] The present invention relates to the technical field of simulation calculation of power system operation control, and in particular to a finite element simulation method based on COMSOL oil-immersed transformer core vibration noise external field distribution. Background Art

[0002] The vibration and noise of the transformer not only pollutes people's living environment, but also affects the service life of laminated core products. Effectively simulating the vibration and noise generation mechanism of the transformer core under the influence of different harmonics and different compression factors, obtaining the propagation characteristics of the vibration vector in the internal and external space of the transformer and the vibration distribution law of each component, provides a reasonable theoretical basis for equipment vibration reduction and noise reduction, is conducive to the design of high-performance laminated core products, and is of great significance to the protection and operation of the transformer. The magnetostrictive characteristics of the transformer core are the main cause of transformer noise. There are many numerical calculation methods for the problem of magnetostriction, which are based on different methods to measure the strain of the core, and on this basis, calculate the magnetostrictive force and vibration displacement of the core. The numerical calculation method can effectively explain the harmonic components in the transformer noise signal from the mechanism. In addition, some scholars have adopted the finite element analysis method considering the magneto-mechanical weak coupling problem of magnetostriction, which can simulate the vibration noise caused by the magnetostriction of the core, but the magnetic anisotropy of the silicon steel sheet and the influence of mechanical vibration on the magnetic field distribution are ignored in the analysis, and no magneto-mechanical strong coupling model that can be promoted and applied has been established. Summary of the invention

[0003] In view of the above problems, the present invention proposes a finite element simulation method for the external field distribution of vibration noise of the iron core of an oil-immersed transformer based on COMSOL. Through the coupling of electromagnetic field, structural force field and acoustic field, the vibration distribution of magnetostriction of the iron core is accurately simulated, and the distribution of sound pressure in the external field is calculated by taking into account the weakening of sound pressure during the propagation process.

[0004] To achieve the purpose of the present invention, a finite element simulation method for the external field distribution of vibration noise of an oil-immersed transformer core based on COMSOL is provided, comprising the following steps:

[0005] Step 1: Establish a three-dimensional simulation model of the transformer, simulate the transient electromagnetic field of the three-dimensional simulation model of the transformer, and calculate the transient electromagnetic force of the transformer core under no-load operation;

[0006] Step 2: Using the transient electromagnetic force as the excitation source of the structural field, the transient displacement of the transformer core vibration is calculated, and then the transient core surface vibration acceleration is calculated and the data is exported for fast Fourier transform (FFT) to obtain the core surface acceleration in the frequency domain;

[0007] Step 3: Use the core surface acceleration in the frequency domain as the initial value of the sound field analysis, simulate the external sound field of the transformer, compare the sound pressure levels of typical positions in the external sound field at different frequencies, and analyze and obtain the main harmonic components in the transformer radiation noise;

[0008] Step 4: Perform a no-load test on a 220kV oil-immersed transformer, place an acoustic sensor at the corresponding position in the model to collect acoustic signals, and perform a fast Fourier transform (FFT) on the sound pressure data in the measured time domain;

[0009] Step 5: Compare the processed measured data with the simulation value to verify the performance of the simulation model in the sound pressure field calculation.

[0010] Step one includes:

[0011] The material and electromagnetic parameters of the three-dimensional physical model of the transformer are adjusted and set according to the errors of the transformer technical parameters and factory test parameters, and a simplified three-dimensional model of the oil-immersed transformer is established.

[0012] Furthermore, step one includes:

[0013] (1) Establish a three-dimensional physical model of the transformer in the finite element simulation software COMSOL;

[0014] (2) Set the material type and properties of the core, winding, and transformer oil in COMSOL;

[0015] (3) Mesh the three-dimensional physical model of the transformer in COMSOL;

[0016] (4) Applying excitation under no-load conditions to the transformer model;

[0017] (5) Set the study time and time step of the transient solver to calculate the transient electromagnetic force of the transformer core under no-load operation.

[0018] Furthermore, the excitation under no-load condition is applied to the transformer model including:

[0019] The primary side of the transformer is set to be connected to a three-phase industrial frequency AC voltage source of rated size, and the current on the secondary side is 0.

[0020] Furthermore, step 2 includes:

[0021] Taking the transient electromagnetic force as the excitation source of the structural field, the transient displacement of the transformer core vibration is calculated according to formula (1), and then the surface acceleration of the transformer core vibration is calculated according to formula (2). The time domain acceleration data is transformed by fast Fourier transform FFT to obtain the core surface vibration acceleration in the frequency domain:

[0022]

[0023] Where M is the mass matrix, C is the damping matrix, D is the stiffness matrix, u is the node displacement, and P(t) is the equivalent magnetostrictive force;

[0024]

[0025] Where x, y, and z are the three directions of the three-dimensional physical model, a is the vibration acceleration, and t is the calculation time.

[0026] Furthermore, step three includes:

[0027] The core surface acceleration in the frequency domain is used as the initial value of the sound field analysis to simulate the external sound field of the transformer. Formula (3) is obtained by Fourier transforming the Helmholtz wave equation. The sound pressure value in the frequency domain is calculated according to formula (3):

[0028]

[0029] coefficient

[0030] Where ρ0 is the fluid density, P is the sound pressure, ω is the angular frequency, and C c is the bulk modulus.

[0031] The finite element simulation method of the external field distribution of the vibration noise of the core of the oil-immersed transformer based on COMSOL uses a pre-established three-dimensional simplified physical model of the oil-immersed transformer to perform transient electromagnetic field simulation on the transformer. The material properties and electromagnetic parameters of the three-dimensional physical model of the transformer are set according to the errors of the transformer technical parameters and factory test parameters to establish a three-dimensional simulation model of the transformer to calculate the magnetostrictive force on the core of the transformer under no-load operation, and the force is introduced into the structural field of the three-dimensional transformer simulation model established above to perform transient structural field simulation on the transformer to obtain the distribution results of the vibration displacement of the core of the transformer under no-load operation. The vibration acceleration of the core surface can be calculated through the displacement data, and the acceleration data in the frequency domain is obtained after the surface vibration acceleration data in the time domain is transformed by FFT. The data is used as the initial condition for the sound field calculation to calculate the distribution of the vibration noise of the core of the transformer. By conducting a no-load experiment on a 220kV oil-immersed transformer, placing a microphone at the corresponding position to take the sound pressure data, and comparing it with the simulation data, the superiority of the simulation model in the calculation of the sound pressure external field is verified.

[0032] Compared with the prior art, the above-mentioned finite element simulation method of the external field distribution of vibration noise of the oil-immersed transformer core based on COMSOL has the following beneficial effects: Based on the finite element method and electromagnetics, structural mechanics and acoustics theory, a simple and effective transformer simulation modeling method is provided by performing electromagnetic-structural-acoustic field coupling simulation on the oil-immersed transformer; and the main components of the transformer core vibration and noise signals under normal conditions are analyzed. And based on the comparison of the acoustic signal components collected by the no-load experiment of the existing transformer, the superiority of the simulation model in the calculation of the sound pressure external field is verified. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flow chart of a finite element simulation method for external field distribution of core vibration noise of an oil-immersed transformer based on COMSOL in one embodiment;

[0034] Figure 2 is a three-dimensional schematic diagram of a physical model of a transformer in one embodiment;

[0035] Figure 3 is a schematic diagram of grid division of a transformer physical model in an embodiment;

[0036] Figure 4 is a magnetic flux density simulation diagram in an electromagnetic field simulation when a transformer is running at no-load in an embodiment;

[0037] Figure 5 is a vibration displacement diagram of the transformer when it is running at no-load when t=0.02s in one embodiment;

[0038] Figure 6 The figure is a sound pressure level diagram when freq=200Hz when the transformer is running at no-load in one embodiment. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0040] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0041] refer to Figure 1 As shown, Figure 1The flowchart of the finite element simulation method of oil-immersed transformer core vibration noise based on COMSOL in one embodiment includes the following steps:

[0042] Step 1: Establish a three-dimensional simulation model of the transformer, simulate the transient electromagnetic field of the three-dimensional simulation model of the transformer, and calculate the transient electromagnetic force of the transformer core under no-load operation;

[0043] Step 2: Using the transient electromagnetic force as the excitation source of the structural field, the transient displacement of the transformer core vibration is calculated, and then the transient core surface vibration acceleration is calculated and the data is exported for fast Fourier transform (FFT) to obtain the core surface acceleration in the frequency domain;

[0044] Step 3: Use the core surface acceleration in the frequency domain as the initial value of the sound field analysis, simulate the external sound field of the transformer, compare the sound pressure levels of typical positions in the external sound field at different frequencies, and analyze and obtain the main harmonic components in the transformer radiation noise;

[0045] Step 4: Perform a no-load test on a 220kV oil-immersed transformer, place an acoustic sensor at the corresponding position in the model to collect acoustic signals, and perform a fast Fourier transform (FFT) on the sound pressure data in the measured time domain;

[0046] Step 5: Compare the processed measured data with the simulation value to verify the performance of the simulation model in the sound pressure field calculation.

[0047] In one embodiment, the finite element simulation method for the external field distribution of the vibration noise of the oil-immersed transformer core based on COMSOL further includes:

[0048] A simplified three-dimensional physical model of oil-immersed transformer is established.

[0049] Specifically, this embodiment can establish a three-dimensional physical model of the transformer (a three-dimensional physical model of the transformer) according to the actual structure and size of the transformer.

[0050] In one example, when building a 3D physical model of a transformer, the simplifications and assumptions that can be made include:

[0051] (1) Ignore the inter-turn insulation of the winding, simplify the winding into a cylindrical type, and assume that the number of coil turns is evenly distributed;

[0052] (2) Ignore the metal structural parts such as the iron yoke and splint inside the transformer;

[0053] (3) It is assumed that the material distribution of each part of the transformer is uniform and isotropic.

[0054] In one embodiment, a pre-established three-dimensional physical model of a transformer is used to perform transient electromagnetic field simulation on the transformer. The material properties and electromagnetic parameters of the three-dimensional physical model of the transformer are set according to the errors of the transformer technical parameters and factory test parameters to establish a three-dimensional simulation model of the transformer. The transient electromagnetic field of the transformer model is simulated to calculate the transient electromagnetic force of the transformer core under no-load operation:

[0055] (1) Establish a three-dimensional physical model of the transformer in the finite element simulation software COMSOL;

[0056] (2) Set the material type and properties of the core, winding, and transformer oil in COMSOL;

[0057] (3) Meshing of transformer model in COMSOL;

[0058] (4) Applying excitation under no-load conditions to the transformer model;

[0059] (5) Set the study time and time step of the transient solver to calculate the transient electromagnetic force of the transformer core under no-load operation.

[0060] Specifically, the excitation applied to the transformer under rated conditions includes:

[0061] Set up the external circuit under no-load conditions, connect the primary side of the transformer to a three-phase industrial frequency AC voltage source of rated size, and the current on the secondary side is 0.

[0062] In one embodiment, the transient electromagnetic force of the electromagnetic field research result is used as the excitation source of the structural field, and the transient displacement of the core vibration is calculated according to the vibration formula:

[0063]

[0064] Where M is the mass matrix, C is the damping matrix, D is the stiffness matrix, u is the node displacement, and P(t) is the equivalent magnetostrictive force.

[0065] Then calculate the surface acceleration of the core vibration:

[0066]

[0067] Where x, y, and z are the three directions of the three-dimensional physical model, a is the vibration acceleration, and t is the calculation time.

[0068] Finally, the acceleration data in the time domain is transformed by FFT to obtain the surface acceleration in the frequency domain.

[0069] In one embodiment, the core surface acceleration in the frequency domain of the structural field research result is used as the initial value of the acoustic field analysis to simulate the external acoustic field of the transformer. The sound pressure value is calculated according to the frequency domain equation after Fourier transformation of the Helmholtz wave equation:

[0070]

[0071] In the formula, ρ0 is the fluid density, p is the sound pressure, c is the sound speed, ω is the angular frequency, C c is the bulk modulus, the coefficient

[0072] In one embodiment, a no-load test was conducted on a 220kV oil-immersed transformer, a microphone was placed at the corresponding position in the model to collect sound pressure data, and the sound pressure data in the measured time domain was FFT transformed. Compared with the simulation data, the superiority of the simulation model in the calculation of sound pressure field was verified.

[0073] In one embodiment, a S13-M-200 / 10 distribution transformer is used as a research object. The transformer has a rated voltage of 10±2×2.5% / 0.4kV, a rated current of 11.5 / 288.7A, and a Dyn11 connection. The finite element simulation method for vibration noise of an oil-immersed transformer core based on COMSOL provided in this embodiment is as follows: Figure 2 As shown, the following steps are included:

[0074] Step 1: Establish a simplified three-dimensional physical model of the oil-immersed transformer;

[0075] This embodiment first makes reasonable simplifications and assumptions about the transformer structure:

[0076] (1) Ignore the inter-turn insulation of the winding, simplify the winding into a cylindrical type, and assume that the number of coil turns is evenly distributed;

[0077] (2) Ignore the role of metal structural parts such as iron yokes and splints inside the transformer;

[0078] (3) It is assumed that the material distribution of each part of the transformer is uniform and isotropic;

[0079] The transformer core of this embodiment is a three-phase three-column structure, which is made of stacked silicon steel sheets; the winding is circular and uniform with multiple turns; the actual size of each part of the transformer is provided by the manufacturer; finally, the three-dimensional model schematic diagram is established using the modeling function of COMSOL software as shown in the figure Figure 2 As shown, Figure 2 (a) represents the front view, (b) represents the top view, and (c) represents the right view.

[0080] Step 2: According to the transformer technical parameters and factory test parameter errors, the material properties and electromagnetic parameters of the transformer 3D physical model are set to establish a transformer 3D simulation model, the transient electromagnetic field of the transformer model is simulated, and the transient magnetostrictive force of the transformer core under no-load operation is calculated;

[0081] Specifically, the transient electromagnetic field simulation of the transformer includes the following steps:

[0082] (1) Establish a simplified three-dimensional model of the transformer in the geometry module of the finite element simulation software COMSOL;

[0083] (2) Mesh the physical model of the transformer in COMSOL, such as Figure 3 As shown, the core is divided into free tetrahedral grids, the winding is divided into swept grids, and the transformer oil and air bag are divided into coarser grids, which simplifies the calculation while ensuring the accuracy of the calculation.

[0084] (3) Set the material properties of the transformer tank, core, winding, and transformer oil in COMSOL, such as conductivity, magnetic permeability, density, etc.

[0085] (4) Excite the transformer model under no-load conditions. Apply rated current I in the primary winding. N = 11.5A three-phase AC power supply, as shown in the formula. Set the number of turns of the primary winding N p =693, the number of turns of the secondary winding is N s =32.

[0086]

[0087] I B =I N sin(2πf*t)

[0088]

[0089] Among them I A , I B ,I C Indicates three-phase current.

[0090] (5) Set the study time and time step of the transient solver to calculate the transient electromagnetic force of the transformer core under no-load operation, which is used as the excitation source of the structural field. Set the study time to 0.06s and the time step to 0.0005s.

[0091] (6) Ensure that the magnetic flux of the core is around 1.5-1.8T. In the unsaturated state, the magnetic flux density simulation diagram in the electromagnetic field simulation when the transformer is running at no load is as follows Figure 4 shown.

[0092] Step 3: Using the transient electromagnetic force as the excitation source of the structural field, the transient displacement of the core vibration is calculated, and then the transient core surface vibration acceleration is calculated and the data is exported for FFT transformation to obtain the core surface vibration acceleration in the frequency domain; specifically, the structural field simulation of the transformer includes the following steps:

[0093] (1) Continue to use the simplified three-dimensional transformer model established in the electromagnetic field;

[0094] (2) Add and set the structural properties of the transformer oil tank, iron core, winding and transformer oil in the material library: In this embodiment, the density, Young's modulus and Poisson's ratio of the iron core are set as constants. The specific property settings are shown in Table 1:

[0095] Table 1 Transformer core material property settings

[0096] Material <![CDATA[Density (kg / m 3 )]]> Young's modulus (Pa) Poisson's ratio (W / (m·K)) Iron Core 7870 <![CDATA[2×10 11 ]]> 0.45

[0097] (3) Continue to use the simplified three-dimensional transformer model established in the electromagnetic field to divide the grid.

[0098] (4) Setting initial and boundary conditions: In this embodiment, the core is set to be a magnetostrictive material, and the magnetostrictive model adopts nonlinear isotropic magnetoelastic properties. The upper boundary of the core is set as a fixed constraint, and roller supports are set on the side and the bottom.

[0099] (5) The transient calculation of the structural field obtains the vibration displacement of the core surface. Figure 5 The vibration displacement diagram at t=0.02s when the transformer is running at no-load is shown.

[0100] The “time domain to frequency domain (FFT)” function of the COMSOL simulation software was used to set the maximum conversion frequency to 1000 Hz, and the calculation results of 0-0.06s in the time domain were converted into frequency domain data. Figure 6 The figure shows the sound pressure level diagram when the transformer is running at no-load and freq=200Hz.

[0101] Step 4: Use the core surface acceleration in the frequency domain as the initial value of the acoustic field analysis to simulate the external acoustic field of the transformer.

[0102] By comparing the sound pressure levels of typical locations in the external sound field at different frequencies, the main harmonic components of the transformer radiated noise are analyzed. The sound propagation velocities of transformer oil and air are set as shown in Table 2.

[0103] Table 2 Sound propagation velocity

[0104] Material Transformer oil (m / s) Air (m / s) Speed ​​of sound 1324 340

[0105] Step 5: Perform a no-load test on a 220kV oil-immersed transformer, place a microphone at the corresponding position in the model to collect sound pressure data, and perform FFT transformation on the sound pressure data in the measured time domain.

[0106] Specifically, the rated three-phase AC voltage is connected to the primary side of the transformer, and the secondary side is open. The acoustic sensor is placed 1 meter in front of the transformer, and the acquisition frequency is set to 64kHz and the acquisition time is set to 2s. The collected acoustic signal is subjected to spectrum analysis.

[0107] Step 6: Compare the processed measured data with the simulation values ​​to verify the superiority of the simulation model in the calculation of the sound pressure field.

[0108] Compared with the prior art, the above-mentioned finite element simulation method of the external field distribution of vibration noise of the oil-immersed transformer core based on COMSOL has the following beneficial effects: Based on the finite element method and electromagnetics, structural mechanics and acoustics theory, a simple and effective transformer simulation modeling method is provided by performing electromagnetic-structural-acoustic field coupling simulation on the oil-immersed transformer; and the main components of the transformer core vibration and noise signals under normal conditions are analyzed. And based on the comparison of the acoustic signal components collected by the no-load experiment of the existing transformer, the superiority of the simulation model in the calculation of the sound pressure external field is verified.

[0109] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A finite element simulation method for the external field distribution of vibration noise of oil-immersed transformer core based on COMSOL, characterized in that: The steps include: Step 1: Establish a three-dimensional simulation model of the transformer, simulate the transient electromagnetic field of the three-dimensional simulation model of the transformer, and calculate the transient electromagnetic force of the transformer core under no-load operation; Step 2: Using the transient electromagnetic force as the excitation source of the structural field, the transient displacement of the transformer core vibration is calculated according to formula (1), and then the transient core surface vibration acceleration is calculated according to formula (2) and the data is exported for fast Fourier transform (FFT) to obtain the core surface acceleration in the frequency domain; Where M is the mass matrix, C is the damping matrix, D is the stiffness matrix, u is the node displacement, and P(t) is the equivalent magnetostrictive force; In the formula, x, y, z are the three directions of the three-dimensional physical model, a is the vibration acceleration, and t is the calculation time; Step 3: Use the core surface acceleration in the frequency domain as the initial value of the sound field analysis, simulate the external sound field of the transformer, compare the sound pressure levels of typical positions in the external sound field at different frequencies, and analyze the main harmonic components in the transformer radiation noise; Formula (3) is obtained by Fourier transforming the Helmholtz wave equation. The sound pressure value in the frequency domain is calculated according to Formula (3): coefficient Where ρ0 is the fluid density, P is the sound pressure, ω is the angular frequency, and C c is the bulk modulus; Step 4: Perform a no-load test on a 220kV oil-immersed transformer, place an acoustic sensor at the corresponding position in the model to collect acoustic signals, and perform a fast Fourier transform (FFT) on the measured sound pressure data in the time domain; Step 5: Compare the processed measured data with the simulation value to verify the performance of the simulation model in the sound pressure field calculation.

2. The method according to claim 1, characterized in that Step one includes, The material and electromagnetic parameters of the three-dimensional physical model of the transformer are adjusted and set according to the errors of the transformer technical parameters and factory test parameters, and a simplified three-dimensional model of the oil-immersed transformer is established.

3. The method according to claim 1, characterized in that Step one includes: (1) Establish a three-dimensional physical model of the transformer in the finite element simulation software COMSOL; (2) Set the material type and properties of the core, winding, and transformer oil in COMSOL; (3) Mesh the three-dimensional physical model of the transformer in COMSOL; (4) Applying excitation under no-load conditions to the transformer model; (5) Set the study time and time step of the transient solver to calculate the transient electromagnetic force of the transformer core under no-load operation.

4. The method according to claim 3, characterized in that The excitation under no-load condition applied to the transformer model includes: The primary side of the transformer is set to be connected to a three-phase industrial frequency AC voltage source of rated size, and the current on the secondary side is 0.

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