Transformer partial discharge ultrasonic propagation simulation model construction method and system

Abstract

The invention provides a transformer partial discharge ultrasonic propagation simulation model construction method and system, and the method comprises the steps: defining a geometric model of a transformer, which is a three-dimensional model of an oil-filled transformer oil tank with a winding and an iron core; setting a sound field module and defining a sound source, and placing the sound source as a partial discharge source in the geometric model of the transformer; a hard boundary condition is applied to the surface of the geometric model tank of the transformer, reflection of the geometric model tank to sound pressure waves is obtained, and under the hard boundary condition, the normal derivative of pressure is zero at the boundary; performing grid division on the geometric model body of the whole transformer by adopting tetrahedral grid units; and after solving, further processing to obtain model parameters, wherein the model is used for displaying the distribution of the ultrasonic sound pressure in the transformer.

Description

Technical Field

[0001] The invention belongs to the technical field of transformer partial discharge simulation model construction, and in particular relates to a transformer partial discharge ultrasonic propagation simulation model construction method and system. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Oil-immersed power transformers are the main electrical equipment in power systems. Their operational reliability has an important impact on the safe operation of power systems. During production, installation and operation, their insulation structure may be damaged, resulting in partial discharge or even breakdown inside the transformer. Taking a three-phase oil-immersed transformer as the research object, the propagation characteristics of ultrasonic waves generated by partial discharge in the transformer in the time domain and frequency domain are simulated and analyzed.

[0004] Partial discharge is one of the important reasons for the long-term degradation of the insulation materials of high-voltage power transformers. In the long run, continued degradation will lead to failure. Therefore, early detection and location of partial discharge sources inside power transformers can reduce the risk of transformer failure.

[0005] The methods used for partial discharge monitoring in power transformers are electrical, chemical, acoustic and UHF. Acoustic and UHF methods are particularly convenient for locating the source of partial discharge in power transformers. For the three-dimensional location of the source of partial discharge, the commonly used technology in power transformers is the time difference of arrival (TDoA) method using acoustic signals or UHF signals.

[0006] Calibration and sensitivity are the main drawbacks of the UHF method. Although the UHF method is generally considered to be immune to external noise due to the shielding of the transformer tank, it can be affected by various sources such as WIFI, TV or radio signals. In contrast, the acoustic method is not affected by external electromagnetic noise. In the acoustic method, it is common to place four acoustic sensors on the tank surface to record the acoustic signals from the PD sources inside the transformer.

[0007] The time difference of the arrival of the acoustic signals detected by the sensors installed on the transformer box is used to locate the partial discharge source. Therefore, obtaining the precise PD source location using the TDoA method requires accurate estimation of the time when the acoustic signal arrives at each sensor. However, due to the presence of the power transformer windings and core, the acoustic PD signal faces multiple reflections and diffractions inside the transformer. These multiple reflections and diffractions change the time when the acoustic PD signal arrives at each sensor. Therefore, in the presence of the power transformer windings and core, it is difficult to accurately estimate the time when the acoustic partial discharge signal arrives at each sensor, which brings a large error to the localization of the partial discharge source.

[0008] In recent years, the literature "Sun Haofei, Gao Kun, Hua Xiaochang, et al. Research on ultrasonic positioning method of partial discharge in transformer based on path time difference [J]. Smart Electric Power, 2022, 50(03): 100-107" elaborated in detail the propagation characteristics and propagation paths of ultrasonic signals in the transformer through simulation. Combined with the simulation results, a numerical node model of the transformer was established, and the path-finding algorithm for the indirect wave path and the direct wave path of the ultrasonic signal was studied. The time difference between the two paths was used as a characteristic parameter and compared with the time difference of the measured waveform, and the particle swarm optimization algorithm was used to iteratively obtain the location of the discharge source. A positioning experiment was carried out on a 35kV experimental transformer to verify the accuracy of the algorithm. Reference "Qi Weiqiang, Li Jian, Chen Baichao, et al. Ultrasonic propagation characteristics in transformers based on COMSOL [J]. Transactions of the Chinese Society of Electrotechnical Engineering, 2015, 30(S2): 195-200. DOI: 10.19595 / j.cnki.1000-6753.tces.2015.s2.029." By establishing a transformer simulation model, the propagation law of sound pressure in space and its amplitude variation, the influence of the discharge source position on the signal propagation characteristics, and the attenuation law of sound waves when propagating in the core, winding and transformer oil are studied under the condition of fixed partial discharge source. This provides a basis for ultrasonic partial discharge detection in transformers. The document "Liu Xu. Simulation study on the propagation law of ultrasonic signals of partial discharge in transformers [D]. North China Electric Power University (Beijing), 2017. DOI: 10.27140 / d.cnki.ghbbu.2017.000036." takes the air gap discharge in the oil inside the transformer as an example to introduce the mechanism of partial discharge, the reason why partial discharge generates ultrasonic waves, and the propagation theory of ultrasonic waves. Based on this, relevant research is conducted on the propagation process of ultrasonic signals generated by partial discharge in transformers. A three-dimensional finite element model of a 35kV oil-immersed power transformer based on a real structure was built, and a time domain simulation study was conducted on the propagation process of ultrasonic signals inside the transformer. There have been certain research results on the simulation of the ultrasonic propagation process inside the transformer, but there are few studies on the ultrasonic propagation process under multiple fields in air and oil in the space-time dual process.

[0009] Partial discharge is an important cause of transformer failure and insulation breakdown. Traditional ultrasonic detection methods rely on external sensors, which are susceptible to noise and have limited detection range.

[0010] Due to the existence of power transformer windings and cores, partial discharge signals face multiple reflections and diffractions inside the transformer. These multiple reflections and diffractions change the time it takes for the ultrasonic signal to reach the sensor. At the same time, due to the different levels of mesh division and differences in physical models in model construction, it is difficult to achieve a balance between simulation time and accuracy. In addition, most existing partial discharge ultrasonic models use simplified models such as needle-plate electrodes, and there are few studies on the ultrasonic propagation mechanism through overall transformer modeling. Summary of the invention

[0011] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a method for constructing a transformer partial discharge ultrasonic propagation simulation model. The constructed model is used to study the propagation law of partial discharge ultrasonic signals in the transformer and guide the precise positioning of partial discharge signals.

[0012] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0013] In a first aspect, a method for constructing a transformer partial discharge ultrasonic propagation simulation model is disclosed, comprising:

[0014] Define the geometric model of the transformer, which is a three-dimensional model of the oil-filled transformer tank with windings and core;

[0015] Define the sound source, which is placed inside the transformer geometry as a local discharge source;

[0016] A hard boundary condition is imposed on the surface of the geometric model tank of the transformer to obtain its reflection of the sound pressure wave. Under the hard boundary condition, the normal derivative of the pressure is zero at the boundary.

[0017] The entire transformer geometric model is meshed using tetrahedral mesh units;

[0018] After solving, the model parameters are further processed to obtain the model parameters, which is used to show the distribution of ultrasonic sound pressure inside the transformer.

[0019] As a further technical solution, in setting boundary conditions, the first is the external boundary, where the transformer casing is assumed to be an "absolute soft boundary", that is, the sound pressure p = 0; the second is the internal boundary, where the contact surfaces between the oil, winding, and core are assumed to be continuous.

[0020] As a further technical solution, the model of the local discharge source is specifically:

[0021]

[0022] Where, Qs is the output function; t is the time variable; b and f are the time offset [s] and frequency; a is the shape coefficient of the rising part of the partial discharge pulse; φ is the compensation coefficient.

[0023] As a further technical solution, the propagation of sound waves in the numerical simulation model in the boundary conditions is governed by the following partial differential equations:

[0024]

[0025] In the formula, p is the sound wave pressure, c is the sound wave velocity, ρ is the material density, Q is the point source energy, t is the time, and qd A dipole radiation source.

[0026] As a further technical solution, when defining the geometric model of the transformer, the properties of mineral oil are used for transformer oil, and the materials and their properties used in different parts of the geometric model of the transformer are different.

[0027] In a second aspect, a system for constructing a transformer partial discharge ultrasonic propagation simulation model is disclosed, comprising:

[0028] The geometric model definition module of the transformer is configured to: define the geometric model of the transformer as a three-dimensional model of an oil-filled transformer tank with windings and an iron core;

[0029] The sound source definition module is configured to: define the sound source, which is placed inside the geometric model of the transformer as a local discharge source;

[0030] The boundary condition setting module is configured to: apply a hard boundary condition on the surface of the geometric model tank of the transformer to obtain its reflection of the sound pressure wave, and under the hard boundary condition, the normal derivative of the pressure is zero at the boundary;

[0031] The meshing module is configured to: mesh the geometric model of the entire transformer using tetrahedral mesh units;

[0032] The model parameter solving module is configured to: further process the solution to obtain the model parameters, and the model is used to show the distribution of ultrasonic sound pressure inside the transformer.

[0033] One or more of the above technical solutions have the following beneficial effects:

[0034] The present invention adopts the above method to realize the construction of the transformer partial discharge ultrasonic propagation simulation model, adds the partial discharge source model, can avoid the problem of multiple reflections and diffractions of the partial discharge signal inside the transformer, has appropriate grid division, high flexibility, strong adaptability, convenient grid subdivision, and high calculation efficiency. The boundary conditions adopted can obtain an accurate model.

[0035] The technical solution of the present invention adopts a three-dimensional finite element method, and the simulation model is in the form of tetrahedral mesh division to realize finite element segmentation of the model, study the propagation law of partial discharge ultrasonic signals in the transformer, and provide simulation model guidance for the subsequent positioning of partial discharge faults.

[0036] The simulation results show that the ultrasonic waves generated by partial discharge of the transformer propagate to the surroundings in the form of spherical waves. Whether analyzing the total sound pressure in the transformer from the time domain or the frequency domain, it can be seen that the ultrasonic waves inside the transformer often attenuate and oscillate with the point sound source, which conforms to the law of sound propagation. The simulation results can provide a reference for explaining the propagation characteristics of variable partial discharge ultrasound in transformers.

[0037] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0039] Figure 1 Schematic diagram of acoustic PD pulse signal;

[0040] Figure 2 A schematic diagram of a three-dimensional model of an oil-filled transformer tank with windings and a core is considered for an embodiment of the present invention;

[0041] Figure 3 Schematic diagram of the spatial distribution of ultrasound within the first 2 ms; (a)-(j) are schematic diagrams of the spatial distribution of 0.01 ms, 0.04 ms, 0.08 ms, 0.12 ms, 0.18 ms, 0.24 ms, 0.29 ms, 0.33 ms, 0.38 ms and 2 ms, respectively;

[0042] Figure 4 This is a schematic diagram of some probe points on the transformer;

[0043] Figure 5 Schematic diagram of the sound pressure signal at each observation point;

[0044] Figure 6 Schematic diagram of the maximum sound pressure changes in oil and air for simulation model analysis; (a) is a schematic diagram of the maximum sound pressure changes in air, and (b) is a schematic diagram of the maximum sound pressure changes in oil;

[0045] Figure 7 Schematic diagram of the change of the sound pressure intensity of each probe in the air and oil over time; (a) is a schematic diagram of the change of the sound pressure intensity of the probe in the air over time, and (b) is a schematic diagram of the change of the sound pressure intensity of each probe in the oil over time;

[0046] Figure 8 This is a schematic diagram of the distribution of pillars and point sources;

[0047] Fig. 9 Schematic diagram of the propagation of ultrasonic waves starting from the partial discharge point between the low-voltage and high-voltage windings;

[0048] Fig.10 Schematic diagram for comparing two different locations of PD point source;

[0049] Fig.11 A schematic diagram of a method flow chart of a model built according to an embodiment of the present invention. DETAILED DESCRIPTION

[0050] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0051] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0052] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0053] Embodiment 1

[0054] See attached Fig.11 As shown, this embodiment discloses a method for constructing a transformer partial discharge ultrasonic propagation simulation model, including:

[0055] Step 1: Define the geometric model;

[0056] A three-dimensional numerical model of a power transformer with a partial discharge ultrasonic source is established using the finite element method to analyze the propagation of acoustic waves inside the transformer.

[0057] The geometric model is a solid model of a three-phase power transformer; a three-dimensional model of an oil-filled transformer tank with windings and core is established, such as Figure 2 As shown. Different situations are studied based on the design model of 100kVA distribution transformer. The transformer tank size is 900mm×335mm×905mm, the side wall thickness is 3.15mm, and the upper and lower wall thickness is 5mm. The size of the winding and core is considered as shown in Table 1. Figure 2 The modeled acoustic partial discharge point source is considered as a partial discharge source and is placed inside the transformer. The acoustic signal generated by the partial discharge source is realized by a measuring probe placed on the outer surface of the tank wall of the geometric model device. This measuring probe is used as an acoustic sensor.

[0058] Table 1 Dimensional parameters of each part of the transformer

[0059]

[0060] Material properties: The materials used in different parts of the transformer model and their properties are shown in Table 2. In this transformer model, the properties of mineral oil are used for the transformer oil. In order to avoid computational burden, memory requirements and reduce the overall computational time, the insulating paper and the pressure plate are not modeled in this simulation. It can also be noted that the insulating paper and the pressure plate do not significantly distort the shape of the acoustic signal, but slightly attenuate the size of the acoustic signal received at the sensor location. Therefore, if the received acoustic signal strength is sufficient, some methods can be used to locate the partial discharge source in the transformer, such as the arrival time difference method TDOA, the acoustic time reversal method ATR, etc.

[0061] Table 2 Physical properties of each material used in the model

[0062]

[0063]

[0064] Step 2: Set up the sound field module and define the sound source;

[0065] The acoustic field module of COMSOL Multiphysics software is used to establish a simulation model to simulate the changes in sound. The numerical model provides a mathematical basis for the simulation model.

[0066] About the partial discharge source model:

[0067] In the sub-technical solution of this embodiment, a point source Q is selected as the acoustic partial discharge source. The value of the point source is as a time-dependent partial discharge pulse as expressed in Formula 2:

[0068]

[0069] Where, Qs(t) is the output function; t is the time variable; b and f are the time offset [s] and frequency; a is the shape coefficient of the rising part of the partial discharge pulse; φ is the compensation coefficient.

[0070] The simulation uses pulse pulse, f = 20kHz, b = 100μs, a = 10 6 .

[0071] The schematic diagram of acoustic PD pulse signal is as follows: Figure 1 As shown, this formula is the sound source formula of the simulation model, a point source.

[0072] This sound source can better reflect the ultrasonic process generated in the short pulse process of partial discharge. It is placed at point 1 and is part of the geometric model. It is the source of the sound wave and is subsequently simulated through the acoustic source of the partial discharge.

[0073] Step 3: Set boundary conditions;

[0074] This mathematical model does not consider any fluid dynamics or other acoustic physics issues. Therefore, the fluidity, thermal conductivity and electromagnetic field coupling characteristics of transformer oil are not taken into account. In addition, it is assumed that the medium is a lossless medium, and there is no loss in the propagation of sound waves in the core, winding or transformer oil.

[0075] First: in setting boundary conditions, the first is the external boundary, and the transformer casing is assumed to be an "absolute soft boundary", that is, the sound pressure p = 0; the second is the internal boundary, and the contact surfaces between the oil, winding, and core are assumed to be continuous.

[0076] Secondly, the governing equations of ultrasonic propagation belong to the initial conditions of the simulation model.

[0077] The propagation of sound waves within the numerical simulation model is governed by the following partial differential equation:

[0078]

[0079] Among them, p is the sound wave pressure, c is the sound wave velocity, ρ is the material density, Qs(t) is the output function, t is the time, q d A dipole radiation source.

[0080] Finally, regarding the hard boundary condition: the hard boundary condition Equation 3 is applied to the surface of the transformer tank to obtain its reflection of the sound pressure wave.

[0081]

[0082] In wave problems, the hard boundary condition is that the wave function must be zero at the boundary, so the normal derivative of the pressure is zero at the boundary.

[0083] When setting boundary conditions in this embodiment, the boundary conditions, ultrasonic wave propagation control equations and hard boundary conditions are included. The above settings are in line with the sound wave propagation process, and the medium characteristics and source characteristics are taken into account, and all factors are considered.

[0084] Step 4: Grid division;

[0085] Meshing: The entire geometry is meshed using tetrahedral mesh units, which provides high flexibility, strong adaptability, convenient mesh subdivision, and high computational efficiency. The maximum size of the mesh unit is 17.38 mm. The model has 1,072,600 degrees of freedom. The entire mesh has 788,944 domain elements, 81,400 boundary elements, and 3,876 edge elements. The total length of the simulation model is 6,000 μs, and the computational time step is 0.833 μs.

[0086] Step 5: Solve the equation - set up the solver;

[0087] In this implementation example, by running the simulation, COMSOL selects the finite element method (FEM) to solve the sound field according to the set physical field and boundary conditions; and solves the sound pressure changes in the model.

[0088] Step 6: Post-processing analysis, verify the model, and adjust the parameters of the previous steps based on the results of the model verification.

[0089] After the above processing, we get: the distribution of ultrasonic sound pressure inside the transformer output by the running model. The subsequent analysis is based on the change of the sound field inside the transformer.

[0090] The following is the validation model process in steps.

[0091] The spatial distribution of sound pressure changes:

[0092] Figure 3 The spatial distribution of ultrasonic waves in the first 2ms. The sound pressure change is caused by the local discharge sound source placed in the No. 1 transformer winding, where (a)-(j) are the spatial distribution diagrams of 0.01ms, 0.04ms, 0.08ms, 0.12ms, 0.18ms, 0.24ms, 0.29ms, 0.33ms, 0.38ms and 2ms respectively. Figure 3 It can be clearly seen that within 0.3ms after the occurrence of the local discharge acoustic explosion, the spatial distribution of the sound pressure inside the transformer changes rapidly, but there is no obvious change after 0.4ms. At the same time, it can be found that in the transformer core and winding, since the propagation speed of sound is about 3 to 4 times that of transformer oil, the change amplitude of the sound pressure is greater than that in oil. It can be seen that in a medium with a faster sound wave propagation speed, the gradient of the sound pressure change is steeper. In addition, Figure 3 a~ Figure 3 It can be seen that the local discharge acoustic explosion propagates to the surroundings in the form of a spherical wave front.

[0093] Time variation of sound pressure:

[0094] The location of the local discharge source remains unchanged, but the location of the observation point is changed: the side view of the transformer is as follows: Figure 4 As shown, in the transformer core-winding structure, the local discharge source position is set at 1 in the center of the core, and observation points 2-9 are set at the inner wall of the transformer, the top and side of the core, and the inside and surface of the winding.

[0095] The sound pressure signal at each observation point is as follows: Figure 5As shown in the figure, it can be clearly seen that in the whole process of sound wave propagation, the sound pressure value at A1 is higher than that at A2, and that at A2 is higher than that at A3. It can be seen that the signal amplitude decays with the increase of propagation distance. At the same time, the same type of peaks show obvious time lag with the passage of distance. This is because the slow propagation speed of the sound wave signal leads to obvious lag in observation. The location of the local discharge source can be achieved by observing the arrival time difference at different points. Observe the local discharge signal at 2 points.

[0096] It can be seen that the frequency and waveform of the sound wave look similar in all probes, which means that the sound source is generated by 1 potential, so the signal changes generated by radiation to points 2-9 are very similar. The farther the probe is from the sound source, the more likely it is that there will be a slight delay in the time it receives the sound wave. This is because it takes time for the sound wave to propagate.

[0097] Sound pressure in transformer oil versus propagation changes in air:

[0098] The sound pressure level decreases with increasing propagation distance. The distance between the source point and the measuring probe was measured in mm at different locations on the transformer model. The distance was measured based on two reference values ​​for air and oil. The reference air pressure value was 20 μP. The reference pressure of the transformer oil was estimated based on the acoustic impedance ratio of oil and air in order to keep a similar scale and facilitate the comparison of the sound pressure decibels.

[0099] Considering that the acoustic impedance of oil is about 3098 times that of air, the reference pressure used in the transformer oil sound pressure calculation is:

[0100] Z oil =ρ oil ×c oil =890kg / m 3 ×1420m / s=1263800Rayl(4)

[0101] Z air =ρ air ×c air =1.2kg / m 3 ×340m / s=408Rayl(5)

[0102] Among them, ρ is the medium density, c is the speed of sound wave propagation in the medium, and this formula includes two media, oil and air. The reference pressure ratio is:

[0103]

[0104] p ref,oil =20μPa×3097.55=0.061951Pa(7)

[0105]

[0106] By analyzing the maximum sound pressure changes in oil and air through the simulation model, we can get the following Figure 6 The curves shown, among which (a) is a schematic diagram of the maximum sound pressure change in air, and (b) is a schematic diagram of the maximum sound pressure change in oil.

[0107] Figure 7 The following is a schematic diagram of the change of sound pressure intensity of each probe in air and oil over time; (a) is a schematic diagram of the change of sound pressure intensity of each probe in air over time, and (b) is a schematic diagram of the change of sound pressure intensity of each probe in oil over time; the logarithmic scale diagram shows that the sound pressure level at probe 2 is the highest, because probe 2 is closest to the local emission source. In the air, the maximum sound pressure shows a downward trend with increasing distance. This is consistent with the physical phenomenon that the energy of sound waves gradually decays when propagating in the air. Points of different colors represent different probes (prob2 to prob9), and the data of all probes show a similar downward trend, but the specific sound pressure values ​​are different. Similar to the air, the maximum sound pressure in the oil also shows a downward trend with increasing distance, but the overall sound pressure value is lower than that in the air. Both figures show the trend of sound pressure decaying with increasing distance, which is a general characteristic of sound wave propagation. The sound pressure values ​​in oil are generally lower than those in air. This is because the density and viscosity of oil are different from those of air, which causes the propagation speed and attenuation characteristics of sound waves in oil to be different from those in air, which is manifested as faster propagation speed and less attenuation in oil, so the overall sound pressure intensity in the air is lower.

[0108] The sound waves received by all probes present similar waveforms in time, but the sound pressure values ​​are different. The sound pressure rises rapidly at the beginning, then gradually decreases and stabilizes. Probe 2 (closest to the sound source) receives the highest sound pressure, and the sound pressure received by other probes gradually decreases as the distance increases. Similar to the air, the sound waves received by all probes present similar waveforms in time, but the sound pressure values ​​are different. The sound pressure rises rapidly at the beginning, then gradually decreases and stabilizes. 6 The influence of the internal winding structure of the transformer on the attenuation of the acoustic signal

[0109] In order to further study the attenuation effect of the winding on the ultrasonic signal during propagation, a point sound source was placed in the oil circuit between the high-voltage and low-voltage windings. Prop 2 was placed at the same position of the point source at 150 mm, while the other two props were placed, as Figure 8 shown.

[0110] Fig. 9 Propagation of ultrasonic waves starting from the partial discharge point between the low-voltage and high-voltage windings; Fig.10 Two different locations of the PD point source are compared. The internal is the point source location between the low voltage and high voltage windings, while the external is the point source location outside the transformer winding.

[0111] In the transformer core and winding, the gradient of sound pressure change is steeper than that in oil, and the local discharge acoustic explosion propagates to the surroundings in the form of a spherical wave front.

[0112] (1) The spatial distribution of sound pressure caused by local discharge is different at different times, and the greater the sound speed, the greater the gradient of sound pressure change.

[0113] (2) From the perspective of the attenuation of the signal amplitude at different observation points, the farther away from the local discharge source, the greater the attenuation of the sound pressure; at the same time, for the same observation position, the longer the signal propagation path, the more serious the signal amplitude attenuation.

[0114] The technical solution of the present invention adopts a three-dimensional finite element method to study the propagation law of partial discharge ultrasonic signals in a transformer and guide the precise positioning of partial discharge signals.

[0115] The simulation results show that the ultrasonic waves generated by partial discharge of the transformer propagate to the surroundings in the form of spherical waves. Whether analyzing the total sound pressure in the transformer from the time domain or the frequency domain, it can be seen that the ultrasonic waves inside the transformer often attenuate and oscillate with the point sound source, which conforms to the law of sound propagation. The simulation results can provide a reference for explaining the propagation characteristics of variable partial discharge ultrasound in transformers.

[0116] Embodiment 2

[0117] The purpose of this embodiment is to provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0118] Embodiment 3

[0119] The purpose of this embodiment is to provide a computer-readable storage medium.

[0120] A computer-readable storage medium stores a computer program, which executes the steps of the above method when executed by a processor.

[0121] Embodiment 4

[0122] The purpose of this embodiment is to provide a transformer partial discharge ultrasonic propagation simulation model construction system, including:

[0123] The geometric model definition module of the transformer is configured to: define the geometric model of the transformer as a three-dimensional model of an oil-filled transformer tank with windings and an iron core;

[0124] The sound source definition module is configured to: define the sound source, which is placed inside the geometric model of the transformer as a local discharge source;

[0125] The boundary condition setting module is configured to: apply a hard boundary condition on the surface of the geometric model tank of the transformer to obtain its reflection of the sound pressure wave, and under the hard boundary condition, the normal derivative of the pressure is zero at the boundary;

[0126] The meshing module is configured to: mesh the geometric model of the entire transformer using tetrahedral mesh units;

[0127] The model parameter solving module is configured to: further process the solution to obtain the model parameters, and the model is used to show the distribution of ultrasonic sound pressure inside the transformer.

[0128] The purpose of this embodiment is to provide a computer program product containing instructions, which, when running on a computer, enables the computer to execute the methods and functions involved in any of the above embodiments.

[0129] The steps involved in the apparatus of the above embodiment correspond to the method embodiment 1, and the specific implementation method can refer to the relevant description part of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0130] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0131] 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 method for constructing a transformer partial discharge ultrasonic propagation simulation model, characterized in that: include: Define the geometric model of the transformer, which is a three-dimensional model of the oil-filled transformer tank with windings and core; Define the sound source, which is placed inside the transformer geometry as a local discharge source; A hard boundary condition is imposed on the surface of the geometric model tank of the transformer to obtain its reflection of the sound pressure wave. Under the hard boundary condition, the normal derivative of the pressure is zero at the boundary. The entire transformer geometric model is meshed using tetrahedral mesh units; After solving, the model parameters are further processed to obtain the model parameters, which is used to show the distribution of ultrasonic sound pressure inside the transformer.

2. The method for constructing a transformer partial discharge ultrasonic propagation simulation model according to claim 1, characterized in that: include: For the external boundary, the transformer shell is assumed to be an "absolute soft boundary", that is, the sound pressure p = 0; secondly, for the internal boundary, the contact surfaces between the oil, winding and core are assumed to be continuous.

3. The method for constructing a transformer partial discharge ultrasonic propagation simulation model according to claim 1, characterized in that: The model of the local discharge source is specifically: Where, Qs(t) is the output function; t is the time variable; b and f are the time offset [s] and frequency; a is the shape coefficient of the rising part of the partial discharge pulse; φ is the compensation coefficient.

4. The method for constructing a transformer partial discharge ultrasonic propagation simulation model according to claim 1, characterized in that: The propagation of acoustic waves in the numerical simulation model with boundary conditions is governed by the following partial differential equation: Among them, p is the sound wave pressure, c is the sound wave velocity, ρ is the material density, Qs(t) is the output function, t is the time, q d A dipole radiation source.

5. The method for constructing a transformer partial discharge ultrasonic propagation simulation model according to claim 1, characterized in that: When defining the geometric model of the transformer, the properties of mineral oil are used for the transformer oil, and the materials and their properties used in different parts of the geometric model of the transformer are different.

6. A system for constructing a transformer partial discharge ultrasonic propagation simulation model, characterized in that: include: The geometric model definition module of the transformer is configured to: define the geometric model of the transformer as a three-dimensional model of an oil-filled transformer tank with windings and an iron core; The sound source definition module is configured to: define the sound source, which is placed inside the geometric model of the transformer as a local discharge source; The boundary condition setting module is configured to: apply a hard boundary condition on the surface of the geometric model tank of the transformer to obtain its reflection of the sound pressure wave, and under the hard boundary condition, the normal derivative of the pressure is zero at the boundary; The meshing module is configured to: mesh the geometric model of the entire transformer using tetrahedral mesh units; The model parameter solving module is configured to: further process the solution to obtain the model parameters, and the model is used to show the distribution of ultrasonic sound pressure inside the transformer.

7. A transformer partial discharge ultrasonic propagation simulation model construction system as claimed in claim 1, characterized in that: The model of the local discharge source is specifically: Where b and f are the time offset [s] and frequency, and a is the shape factor of the rising part of the PD pulse.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method according to any one of claims 1 to 5 is implemented.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps of the method described in any one of claims 1 to 5 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method described in any one of claims 1 to 5 are performed.

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