Method for analyzing influence of HEMP late period on transformer and related device

Abstract

The invention discloses a method and a related device for analyzing the influence of HEMP late period on a transformer, and the method comprises the steps: respectively constructing a transformer iron core vibration acceleration model, a transformer sound pressure model and a transformer heat conduction model caused by a magnetostrictive effect, and comprehensively analyzing the influence of DC magnetic bias on the transformer from the three aspects of vibration, noise and temperature rise. The harm caused by the HEMP late direct current magnetic bias to the transformer is known from multiple angles, an effective guiding means is provided for analyzing the harm caused by the HEMP late direct current magnetic bias to the transformer, and the problem that an effective analysis method for the influence of the HEMP late on the transformer is lacked in the prior art is solved. And guidance is difficult to provide for avoiding the damage to the transformer caused by direct-current magnetic bias caused by the late period of HEMP.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method for analyzing the influence of HEMP on transformers in the late stage and a related device. Background Art

[0002] High-altitude Electromagnetic Pulse (HEMP) is generated by a nuclear explosion at an altitude of more than 30 km above the ground. The radiation field generated by HEMP in near-Earth space can be divided into E1 (early), E2 (middle), and E3 (late) according to the time change. E3 is also called magnetic fluid electromagnetic pulse. E3 is a low-frequency (below 1Hz) and low-amplitude (about tens of volts per km) electromagnetic pulse that will cause drastic changes in the geomagnetic field, resulting in the formation of ground induced potential (Earth surface potential, ESP) on the ground surface. The ground induced potential, as a voltage source, forms a loop with the earth through long-distance conductors on the ground (rails, transmission lines, oil pipelines, etc.), generating geomagnetically induced current (GIC). Geomagnetically induced current can be regarded as a quasi-DC relative to the 50Hz power frequency current. Geomagnetically induced current will cause DC bias of the transformer in the power supply system, resulting in severe magnetic saturation of the transformer core and failure to work normally, ultimately affecting the safe and stable operation of the system. Therefore, analyzing how the DC bias magnetism caused by the late HEMP affects the transformer in order to better solve the harm caused by the DC bias magnetism to the transformer is a technical problem that needs to be solved urgently by technical personnel in this field. Summary of the invention

[0003] The present invention provides an analysis method and related device for the influence of late HEMP on transformers, which are used to solve the technical problem that the prior art lacks an effective analysis method for the influence of late HEMP on transformers and is difficult to provide guidance for avoiding the harm of DC bias magnetic field caused by late HEMP on transformers.

[0004] In view of this, a first aspect of the present invention provides a method for analyzing the impact of HEMP on transformers in the late stage, comprising:

[0005] A transformer core vibration acceleration model caused by magnetostrictive effect is constructed, and the transformer core vibration under DC bias is analyzed to obtain the first analysis result;

[0006] A transformer sound pressure model is constructed to analyze the transformer noise under DC bias and obtain a second analysis result;

[0007] Construct a transformer heat conduction model, analyze the transformer temperature under DC bias, and obtain the third analysis result;

[0008] The first analysis result, the second analysis result and the third analysis result are integrated to obtain the analysis result of the influence of HEMP in the late stage on the transformer.

[0009] Optionally, the transformer core vibration acceleration model is:

[0010]

[0011] in, is the transformer core vibration acceleration, t is the time, K is the size of the transformer core before deformation, is the maximum magnetostriction change, is the coercive force, is the maximum value of the transformer excitation voltage, l is the length of the transformer main magnetic circuit coil, R is the transformer equivalent resistance, is the angular frequency, L is the transformer equivalent inductance, is the magnetostriction coefficient under saturation state, N is the number of coil turns of the transformer, is the DC bias current.

[0012] Optionally, the transformer sound pressure model is:

[0013]

[0014] in, is the fluid density, q is the dipole source, Q is the monopole source, c is the speed of sound propagation in the fluid, p is the effective value of the transformer noise pressure, is the divergence, is the effective value gradient of transformer noise sound pressure.

[0015] Optionally, the transformer heat conduction model is:

[0016]

[0017] in, is the heat flow rate, T is the transformer temperature, is the temperature gradient along the x-axis, is the temperature gradient along the y-axis, is the temperature gradient along the z-axis, is the thermal conductivity of transformer oil in the x-axis direction, is the thermal conductivity of transformer oil in the y-axis direction, is the thermal conductivity of transformer oil in the z-axis direction, is the transformer oil density, is the specific heat of transformer oil.

[0018] Optionally, the transformer heat conduction model further includes temperature boundary conditions, heat flow boundary conditions and convection boundary conditions;

[0019] The temperature boundary conditions are:

[0020]

[0021] in, is the boundary condition of the object, is the known wall temperature;

[0022] The heat flow boundary conditions are:

[0023]

[0024] in, is the known heat flux density, - is the direction in which heat flows to reduce temperature, is the thermal conductivity of the transformer, is the temperature gradient along the direction of heat flow toward decreasing temperature;

[0025] The convection boundary conditions are:

[0026]

[0027] Among them, - is the direction of heat flow towards lower temperature, is the thermal conductivity of the transformer, is the temperature gradient in the direction of heat flow and temperature decrease, h is the convective heat transfer coefficient, is the temperature of the fluid medium in contact with the object.

[0028] A second aspect of the present invention provides an analysis device for the influence of HEMP on transformers in the late stage, comprising:

[0029] A vibration analysis module is used to construct a transformer core vibration acceleration model caused by magnetostrictive effect, analyze the transformer core vibration under DC bias, and obtain a first analysis result;

[0030] A noise analysis module is used to construct a transformer sound pressure model, analyze the transformer noise under DC bias, and obtain a second analysis result;

[0031] The temperature analysis module is used to construct a transformer heat conduction model, analyze the transformer temperature under DC bias, and obtain a third analysis result;

[0032] The output module is used to integrate the first analysis result, the second analysis result and the third analysis result to obtain the analysis result of the influence of HEMP in the late stage on the transformer.

[0033] Optionally, the transformer core vibration acceleration model is:

[0034]

[0035] in, is the transformer core vibration acceleration, t is the time, K is the size of the transformer core before deformation, is the maximum magnetostriction change, is the coercive force, is the maximum value of the transformer excitation voltage, l is the length of the transformer main magnetic circuit coil, R is the transformer equivalent resistance, is the angular frequency, L is the transformer equivalent inductance, is the magnetostriction coefficient under saturation state, N is the number of coil turns of the transformer, is the DC bias current;

[0036] The transformer sound pressure model is:

[0037]

[0038] in, is the fluid density, q is the dipole source, Q is the monopole source, c is the speed of sound propagation in the fluid, p is the effective value of the transformer noise pressure, is the divergence, is the effective value gradient of transformer noise sound pressure;

[0039] The transformer heat conduction model is:

[0040]

[0041] in, is the heat flow rate, T is the transformer temperature, is the temperature gradient along the x-axis, is the temperature gradient along the y-axis, is the temperature gradient along the z-axis, is the thermal conductivity of transformer oil in the x-axis direction, is the thermal conductivity of transformer oil in the y-axis direction, is the thermal conductivity of transformer oil in the z-axis direction, is the transformer oil density, is the specific heat of transformer oil.

[0042] Optionally, the transformer heat conduction model further includes temperature boundary conditions, heat flow boundary conditions and convection boundary conditions;

[0043] The temperature boundary conditions are:

[0044]

[0045] in, is the boundary condition of the object, is the known wall temperature;

[0046] The heat flow boundary conditions are:

[0047]

[0048] in, is the known heat flux density, - is the direction in which heat flows to reduce temperature, is the thermal conductivity of the transformer, is the temperature gradient along the direction of heat flow toward decreasing temperature;

[0049] The convection boundary conditions are:

[0050]

[0051] Among them, - is the direction of heat flow towards lower temperature, is the thermal conductivity of the transformer, is the temperature gradient in the direction of heat flow and temperature decrease, h is the convective heat transfer coefficient, is the temperature of the fluid medium in contact with the object.

[0052] A third aspect of the present invention provides a device for analyzing the impact of HEMP on transformers in the late stage, the device comprising a processor and a memory:

[0053] The memory is used to store program code and transmit the program code to the processor;

[0054] The processor is used to execute the analysis method of the late HEMP impact on the transformer as described in any one of the first aspects of the present invention according to the instructions in the program code.

[0055] A fourth aspect of the present invention provides a computer-readable storage medium for storing program code, wherein the program code is used to execute the method for analyzing the late-stage impact of HEMP on a transformer as described in any one of the first aspects of the present invention.

[0056] It can be seen from the above technical solutions that the analysis method of the influence of HEMP in the late stage on the transformer provided by the present invention has the following advantages:

[0057] The analysis method of the influence of late HEMP on transformer provided by the present invention respectively constructs a transformer core vibration acceleration model caused by magnetostrictive effect, a transformer sound pressure model and a transformer heat conduction model, comprehensively analyzes the influence of DC bias on transformer from three aspects of vibration, noise and temperature rise, understands the harm caused by DC bias in late HEMP to transformer from multiple angles, provides effective guidance means for analyzing the harm caused by DC bias in late HEMP to transformer, solves the technical problem that the prior art lacks an effective analysis method for the influence of late HEMP on transformer and is difficult to provide guidance for avoiding the harm caused by DC bias in late HEMP to transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0059] Figure 1 A schematic flow chart of a method for analyzing the influence of HEMP in the late stage on a transformer provided in an embodiment of the present invention;

[0060] Figure 2 A force and mass flow diagram of a unit small volume element provided in an embodiment of the present invention;

[0061] Figure 3 It is a structural schematic diagram of a device for analyzing the influence of HEMP in the late stage on a transformer provided in an embodiment of the present invention;

[0062] Figure 4 It is a schematic structural diagram of a device for detecting the influence of HEMP on transformer in the late stage provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0063] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] For easier understanding, see Figure 1 The present invention provides an embodiment of a method for analyzing the influence of HEMP on transformers in the late stage, comprising:

[0065] Step 101: construct a transformer core vibration acceleration model caused by magnetostrictive effect, analyze the transformer core vibration under DC bias, and obtain a first analysis result.

[0066] It should be noted that when the transformer is operating normally, the total current flowing into the transformer is greater than the excitation current generated, but when DC bias occurs, the opposite is true. It can be seen that the DC bias has a more obvious effect on the vibration of the transformer core, and the vibration characteristics can be used to study the impact of HEMP on the transformer in the late stage.

[0067] The vibration on the surface of the transformer mailbox is mainly caused by the magnetostrictive effect and electromagnetic force of the core material (generally silicon steel sheets), so the acceleration of the core vibration can be calculated to represent the displacement of the core vibration. With the continuous optimization and upgrading of the stacking method of the core silicon steel sheets (such as the use of stepped joints, etc.), the gaps between the core silicon steel sheets will become smaller and smaller, resulting in a significant reduction in magnetic leakage, so the core vibration of the power transformer caused by electromagnetic force can be ignored.

[0068] Apply power frequency voltage to the transformer :

[0069]

[0070] in, is the maximum value of the transformer excitation voltage, is the angular frequency, , , t is the time.

[0071] Assume that in the transformer equivalent circuit, the impedance is , R is the transformer equivalent resistance, L is the transformer equivalent inductance, and the AC current is , the DC bias current is , then under normal circumstances, the AC current can be expressed as:

[0072]

[0073] Through Fourier transform and then inverse transform, we can get:

[0074]

[0075] The DC bias state of the transformer is simulated by assuming that the current in the transformer winding is a superposition of AC and DC quantities. At this time, the current i in the transformer winding can be expressed as:

[0076]

[0077] When the transformer is running at no load, the current i in the transformer winding is:

[0078]

[0079] According to the total current law, we have:

[0080]

[0081] Among them, N is the number of turns of the transformer coil, and H is the magnetic field strength.

[0082] Therefore, the magnetic field strength H can be expressed as:

[0083]

[0084] according to , as well as , we can get:

[0085]

[0086] Where A is the cross-sectional area, is the main magnetic flux, B is the magnetic flux density, l is the length of the transformer main magnetic circuit coil, is the transformer core magnetic permeability.

[0087] It can be seen that the main magnetic flux of the iron core is composed of AC and DC magnetic fluxes, the front part is the DC component, and the back part is the AC component.

[0088] The tiny deformation of the core silicon steel sheet due to the magnetostrictive effect meets the following conditions:

[0089]

[0090] Among them, K is the size of the transformer core before deformation, is the maximum magnetostriction change, is the coercive force, is the magnetostriction coefficient in the saturation state.

[0091] Magnetostriction of core silicon steel sheet It can be expressed as:

[0092]

[0093] Substitute the expression of magnetic field intensity H into the magnetostriction of the core silicon steel sheet The formula is:

[0094]

[0095] Taking the second-order derivative of the maximum magnetostrictive change, the core vibration acceleration caused by the magnetostrictive effect can be obtained as:

[0096]

[0097] in, is the transformer core vibration acceleration.

[0098] It can be seen from the above transformer core vibration acceleration that when no DC current flows in, the transformer core vibration acceleration only includes the first term in the expression, and when DC current flows in, it includes the entire expression.

[0099] In summary, when DC bias occurs in the transformer, the core vibration acceleration spectrum includes both even and odd multiples of the power supply voltage frequency (industrial frequency 50Hz).

[0100] Step 102: construct a transformer sound pressure model, analyze the transformer noise under DC bias, and obtain a second analysis result.

[0101] It should be noted that the sources of transformer noise are mainly divided into two parts: the transformer body noise composed of the transformer core, winding and oil tank, and the transformer cooling device noise caused by the transformer cooling fan and submersible oil pump. For transformer noise using water coolers, the noise of the water cooler is very small, so it can be ignored.

[0102] The transformer body noise is generated by the body vibration. Since the transformer cooling device is difficult to model and analyze, the noise of the transformer cooling device can be ignored here. The magnetostrictive vibration of the core is the most important element causing the transformer body noise. The magnetostrictive vibration of the core can be transmitted from its feet to the mailbox (solid path) or to the mailbox through the insulating oil (liquid path). The vibration energy transmitted by these two parts causes the transformer mailbox wall to vibrate and generate noise. For the air path, the noise of the transformer body is transmitted to the surroundings in the form of sound waves.

[0103] In acoustic theory, the vibration of objects is the source of sound. Frequency can describe the height of sound, and sound pressure, sound intensity, and sound power can describe the strength of sound. The propagation of sound waves is essentially the propagation of energy. The transmission of sound waves will cause changes in the energy of surrounding air particles. The change in atmospheric pressure caused by air is defined as the effective value of the transformer noise sound pressure. In continuous media, sound pressure can be used to characterize the pressure and operating state of any point in the sound field. Sound pressure can be used to describe the strength of sound. Normally, the size of sound pressure varies with the noise, so the size of sound pressure can be used as a physical quantity of noise, and the unit is Pa ( ). 20 Indicates the reference sound pressure. It is the pain valve sound pressure.

[0104] Since the sound pressure of the pain valve is much different from the reference sound pressure, the concept of sound pressure level is introduced to indicate the level of noise. The unit of sound pressure level is decibel (dB). For the study of transformer noise, the sound pressure level The expression is:

[0105]

[0106] Where p is the effective value of transformer noise sound pressure, is the reference sound pressure.

[0107] Unit mass impulse velocity potential The following wave equation exists for the effective value p of the transformer noise pressure:

[0108]

[0109] in, is the transformer oil density, in .

[0110] Unit mass impulse velocity potential The propagation speed c of sound in the medium satisfies:

[0111]

[0112] in, is the Laplace operator, and we define .

[0113] For high-voltage transformers, the sound pressure is transmitted from the core and winding as solid vibration through the transformer oil, which can be expressed as:

[0114]

[0115] in, is the sound pressure and n is the particle area.

[0116] The displacement of a solid particle is represented by d, and the normal velocity of the solid particle is It can be expressed as:

[0117]

[0118] The fluid particle velocity for:

[0119]

[0120] in, is the gradient operator, and we define .

[0121] The unit mass impulse velocity potential is obtained by solving the wave equation , the particle velocity can be obtained through simple differential operation And the effective value of transformer noise sound pressure p.

[0122] like Figure 2 As shown in the figure, take any volume element in the medium and consider the motion characteristics of the element under the action of sound waves. It can be known that the effective value p of the transformer noise pressure is related to the particle vibration velocity The relationship is:

[0123]

[0124] in, is the particle vibration velocity Component along the x-axis.

[0125] Integrating the previous formula, we get:

[0126]

[0127] Depend on , is the density increment, which means that the fluid density can be decomposed into the sum of the average density of the fluid and the density increment, where:

[0128]

[0129] The first term on the right side of the above formula is the local velocity, and the second term on the right side is the migration velocity. Substitute into the above formula.

[0130] After neglecting higher-order traces, the one-dimensional equation of motion of an ideal gas is linear, namely:

[0131]

[0132] In the acoustic field, the mass increment caused by the density change of the volume element is equal to the mass difference of the fluid flowing into the unit, such as Figure 2 As shown in the force and mass flow diagram of a small unit volume element, the mass flowing in on the left is equal to the mass flowing out on the right. According to the law of conservation of mass, the one-dimensional continuity equation in an ideal fluid is:

[0133]

[0134] According to the basic assumption of acoustics, sound waves propagate adiabatically. Based on the relationship between sound pressure and density, the relationship between the effective value p of transformer noise sound pressure and space-time variation can be obtained as follows:

[0135]

[0136] For three-dimensional space, we can use the equation Generalization of the one-dimensional to three-dimensional wave equation:

[0137]

[0138] For the calculation of transformer acoustic field, the transformer core (the main source of noise) can be regarded as a combination of monopole and dipole. Then the domain control equation to be solved in the acoustic field calculation is:

[0139]

[0140] Among them, q is a dipole source, Q is a monopole source, c is the propagation speed of sound in the fluid, is the divergence, is the effective value gradient of transformer noise sound pressure.

[0141] The sound pressure level distribution of transformer noise can be obtained through multi-physics field coupling calculation.

[0142] Step 103: construct a transformer heat conduction model, analyze the transformer temperature under DC bias, and obtain a third analysis result.

[0143] It should be noted that DC bias magnetization causes an increase in eddy current loss in the transformer box, which in turn leads to an increase in temperature. Using indirect coupling, the eddy current loss unit results of the magnetic field analysis are used as the excitation of the thermal field analysis unit to perform steady-state thermal analysis.

[0144] Transformer temperature rise refers to the temperature difference between a certain part of the transformer and the cooling medium. In order to ensure safe and reliable operation of the transformer, its temperature rise cannot exceed the limit. The normal temperature rise limit of the oil-immersed transformer at rated capacity is: the average temperature rise of the top oil temperature to the surrounding air is 60K, and the average temperature rise of the winding to the surrounding air is 65K. For the core, the electrical connection wires outside the winding, or the structural parts in the mailbox, there is no temperature rise limit, but the temperature rise is still required not to be too high, usually below 80K, to avoid excessive aging of the oil or thermal damage to adjacent parts.

[0145] The temperature rise of the transformer will cause the insulation of the transformer to age faster, thus shortening the life of the transformer. The life of the insulating material determines the service life of the transformer. The temperature rise of the transformer windings, core pressure plates and other components increases, which increases the working temperature of the insulating materials in contact with them, speeds up the oxidation process, leads to faster aging of the transformer insulation, reduces the mechanical strength and electrical strength of the insulating materials, and thus shortens the service life of the transformer.

[0146] There are three basic types of heat transfer in a transformer: heat conduction, heat convection and heat radiation.

[0147] Heat conduction follows Fourier's law:

[0148]

[0149] in, is the known heat flux density in units of , “-” means that heat flows in the direction of decreasing temperature, is the thermal conductivity of the transformer, in units of , is the temperature gradient in the direction of decreasing temperature along the heat flow.

[0150] Thermal convection refers to the heat exchange between a solid surface and the fluid in contact with it due to the temperature difference. Thermal convection is divided into forced convection and natural convection. Convection is generally applied as a surface boundary condition and can be described using the Newton cooling equation as:

[0151]

[0152] in, is the surface heat transfer coefficient, in units of , is the temperature of the solid surface, is the temperature of the surrounding fluid.

[0153] In the case of air cooling, for a smooth surface, we have: , for non-smooth surfaces, we have: , where v is the average velocity of the circulating oil. When the average temperature of the cooling surface and the inlet air is 50 degrees, v The above formula is applicable to the heat calculation with air blowing cooling, because only a part of the air blown from the fan falls on the cooling pipe, and the air speed is different at different positions of the cooling pipe.

[0154] The convection heat transfer coefficient between transformer oil and box is:

[0155]

[0156] in, is the transformer oil density, in , is the specific heat of transformer oil, in , v is the average velocity of the circulating oil, generally , H is the temperature reached by the cooling oil as it continues to rise along the heat dissipation surface.

[0157] Thermal radiation refers to the heat exchange in which other objects convert the electromagnetic energy emitted by an object into heat. The amount of heat radiated per unit time increases as the temperature of the object increases. Both thermal convection and thermal conduction require a heat transfer medium, but thermal radiation does not require any medium, and the thermal radiation efficiency is highest in a vacuum. Thermal analysis involving thermal radiation is highly nonlinear.

[0158] In engineering, radiation between two or more objects is usually considered. Each object in the system radiates and absorbs heat at the same time. The net heat transfer between them can be expressed by the following formula:

[0159]

[0160] in, is the heat flow rate, is the absorption rate, is the Sronpen-Boltzmann constant, is the area of ​​the radiation surface 1, is the shape coefficient from radiation surface 1 to radiation surface 2, is the thermodynamic temperature of the radiation surface 1, is the thermodynamic temperature of the radiation surface 2.

[0161] In general three-dimensional problems, the temperature field of an object changes with coordinate position and time, that is, According to the principle of thermal equilibrium, the heat stored in any microelement in an object during any time dt is equal to the sum of the heat transferred into the microelement and the heat generated by the heat source in the microelement. The stored heat is The difference between the heat transferred out and into the microelement along the x-axis at the same time is:

[0162]

[0163] in, is the heat flux in the x direction.

[0164] Then the net heat input to the microelement is:

[0165]

[0166] in, is the heat flux in the y direction, is the heat flux in the z direction.

[0167] According to the law of heat conduction, the heat flux is proportional to the temperature gradient, but in the opposite direction, that is:

[0168]

[0169] in, is the temperature gradient along the x-axis, is the temperature gradient along the y-axis, is the temperature gradient along the z-axis, is the thermal conductivity of transformer oil in the x-axis direction, is the thermal conductivity of transformer oil in the y-axis direction, is the thermal conductivity of transformer oil in the z-axis direction.

[0170] The net heat input to the microelement is:

[0171]

[0172] The heat source density in the microelement is , then the heat supplied by the heat source in time dt is , then the differential equation for heat conduction is:

[0173]

[0174] There are countless solutions that satisfy the above equation. The initial transient temperature distribution must be determined, and the law of heat exchange between the surface of the object and the surrounding medium, that is, the boundary conditions, also needs to be known.

[0175] In order to make the solution of the heat balance equation at each node unique, temperature boundary conditions, heat flow boundary conditions and convection boundary conditions are attached.

[0176] The temperature boundary conditions are:

[0177]

[0178] or

[0179]

[0180] in, is the boundary condition of the object, is the known wall temperature, is a known function of temperature that varies with position and time.

[0181] The heat flow boundary conditions are:

[0182]

[0183] or

[0184]

[0185] in, is the known heat flux density, - is the direction in which heat flows to reduce temperature, is the thermal conductivity of the transformer, is the temperature gradient along the direction of heat flow and temperature decrease, is a known function of heat flux that varies with position and time.

[0186] The convection boundary conditions are:

[0187]

[0188] or

[0189]

[0190] Among them, - is the direction of heat flow towards lower temperature, is the thermal conductivity of the transformer, is the temperature gradient in the direction of heat flow and temperature decrease, h is the convective heat transfer coefficient, is the temperature of the fluid medium in contact with the object, and h can be constants or functions that vary with position and time, is the convective heat transfer coefficient of radiation surface 1, Convective heat transfer coefficient of radiation surface 2.

[0191] Based on the above transformer heat conduction differential equation, temperature boundary conditions, heat flow boundary conditions and convection boundary conditions, the temperature rise of the transformer can be determined.

[0192] HEMP E3 will cause a dramatic change in the geomagnetic field, resulting in the formation of ground induced electromotive force on the surface of the earth, forming a loop with the earth, and generating geomagnetic induced current. This current can be regarded as quasi-DC relative to the 50Hz power frequency current. This forms a DC bias effect, which in turn causes transformer vibration, noise and temperature rise. Therefore, the present invention comprehensively evaluates and analyzes the impact of HEMP late DC bias on the transformer through vibration, noise and temperature rise, which can better solve the analysis problem of the harm of DC bias to the transformer.

[0193] Step 104: Integrate the first analysis result, the second analysis result and the third analysis result to obtain an analysis result of the impact of HEMP on the transformer in the late stage.

[0194] It should be noted that, by analyzing the transformer core vibration under DC bias according to the transformer core vibration acceleration model caused by magnetostrictive effect, the influence of DC bias on transformer core vibration in the late HEMP period can be obtained. By analyzing the transformer noise under DC bias according to the transformer sound pressure model, the influence of DC bias on transformer noise in the late HEMP period can be obtained. By analyzing the temperature rise of the transformer under DC bias according to the transformer heat conduction model, the influence of DC bias on transformer temperature in the late HEMP period can be obtained.

[0195] The analysis method of the influence of late HEMP on transformer provided by the present invention respectively constructs a transformer core vibration acceleration model caused by magnetostrictive effect, a transformer sound pressure model and a transformer heat conduction model, comprehensively analyzes the influence of DC bias on transformer from three aspects of vibration, noise and temperature rise, understands the harm caused by DC bias in late HEMP to transformer from multiple angles, provides effective guidance means for analyzing the harm caused by DC bias in late HEMP to transformer, solves the technical problem that the prior art lacks an effective analysis method for the influence of late HEMP on transformer and is difficult to provide guidance for avoiding the harm caused by DC bias in late HEMP to transformer.

[0196] For easier understanding, see Figure 3 The present invention provides an embodiment of an analysis device for the influence of HEMP on transformers in the late stage, comprising:

[0197] A vibration analysis module is used to construct a transformer core vibration acceleration model caused by magnetostrictive effect, analyze the transformer core vibration under DC bias, and obtain a first analysis result;

[0198] A noise analysis module is used to construct a transformer sound pressure model, analyze the transformer noise under DC bias, and obtain a second analysis result;

[0199] The temperature analysis module is used to construct a transformer heat conduction model, analyze the transformer temperature under DC bias, and obtain a third analysis result;

[0200] The output module is used to integrate the first analysis result, the second analysis result and the third analysis result to obtain the analysis result of the influence of HEMP in the late stage on the transformer.

[0201] In one embodiment, the transformer core vibration acceleration model is:

[0202]

[0203] in, is the transformer core vibration acceleration, t is the time, K is the size of the transformer core before deformation, is the maximum magnetostriction change, is the coercive force, is the maximum value of the transformer excitation voltage, l is the length of the transformer main magnetic circuit coil, R is the transformer equivalent resistance, is the angular frequency, L is the transformer equivalent inductance, is the magnetostriction coefficient under saturation state, N is the number of coil turns of the transformer, is the DC bias current;

[0204] The transformer sound pressure model is:

[0205]

[0206] in, is the fluid density, q is the dipole source, Q is the monopole source, c is the speed of sound propagation in the fluid, p is the effective value of the transformer noise pressure, is the divergence, is the effective value gradient of transformer noise sound pressure;

[0207] The transformer heat conduction model is:

[0208]

[0209] in, is the heat flow rate, T is the transformer temperature, is the temperature gradient along the x-axis, is the temperature gradient along the y-axis, is the temperature gradient along the z-axis, is the thermal conductivity of transformer oil in the x-axis direction, is the thermal conductivity of transformer oil in the y-axis direction, is the thermal conductivity of transformer oil in the z-axis direction, is the transformer oil density, is the specific heat of transformer oil.

[0210] In one embodiment, the transformer heat conduction model further includes temperature boundary conditions, heat flow boundary conditions, and convection boundary conditions;

[0211] The temperature boundary conditions are:

[0212]

[0213] in, is the boundary condition of the object, is the known wall temperature;

[0214] The heat flow boundary conditions are:

[0215]

[0216] in, is the known heat flux density, - is the direction in which heat flows to reduce temperature, is the thermal conductivity of the transformer, is the temperature gradient along the direction of heat flow toward decreasing temperature;

[0217] The convection boundary conditions are:

[0218]

[0219] Among them, - is the direction of heat flow towards lower temperature, is the thermal conductivity of the transformer, is the temperature gradient in the direction of heat flow and temperature decrease, h is the convective heat transfer coefficient, is the temperature of the fluid medium in contact with the object.

[0220] For easier understanding, see Figure 4 The present invention provides an embodiment of a device for analyzing the influence of HEMP on transformers in the late stage, the device comprising a processor and a memory:

[0221] The memory is used to store the program code and transmit the program code to the processor;

[0222] The processor is used to execute any one of the methods in the embodiments of the method for analyzing the influence of the late HEMP on the transformer in the present invention according to the instructions in the program code.

[0223] The present invention also provides an embodiment of a computer-readable storage medium, which is used to store program code, and the program code is used to execute any method in the embodiments of the analysis method of the late HEMP impact on the transformer in the present invention.

[0224] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for analyzing the impact of HEMP on transformers in the late stage, characterized in that: include: A transformer core vibration acceleration model caused by magnetostrictive effect is constructed, and the transformer core vibration under DC bias is analyzed to obtain the first analysis result; A transformer sound pressure model is constructed to analyze the transformer noise under DC bias magnetization to obtain a second analysis result; A transformer heat conduction model is constructed to analyze the transformer temperature under DC bias and obtain the third analysis result; The first analysis result, the second analysis result and the third analysis result are integrated to obtain the analysis result of the influence of HEMP in the late stage on the transformer.

2. The method for analyzing the influence of HEMP on transformer in late stage according to claim 1, characterized in that: The transformer core vibration acceleration model is: in, is the transformer core vibration acceleration, t is the time, K is the size of the transformer core before deformation, is the maximum magnetostriction change, is the coercive force, is the maximum value of the transformer excitation voltage, l is the length of the transformer main magnetic circuit coil, R is the transformer equivalent resistance, is the angular frequency, L is the transformer equivalent inductance, is the magnetostriction coefficient under saturation state, N is the number of coil turns of the transformer, is the DC bias current.

3. The method for analyzing the influence of HEMP on transformer in late stage according to claim 1, characterized in that: The transformer sound pressure model is: in, is the fluid density, q is the dipole source, Q is the monopole source, c is the speed of sound propagation in the fluid, p is the effective value of the transformer noise pressure, is the divergence, is the effective value gradient of transformer noise sound pressure.

4. The method for analyzing the influence of HEMP on transformer in late stage according to claim 1, characterized in that: The transformer heat conduction model is: in, is the heat flow rate, T is the transformer temperature, is the temperature gradient along the x-axis, is the temperature gradient along the y-axis, is the temperature gradient along the z-axis, is the thermal conductivity of transformer oil in the x-axis direction, is the thermal conductivity of transformer oil in the y-axis direction, is the thermal conductivity of transformer oil in the z-axis direction, is the transformer oil density, is the specific heat of transformer oil.

5. The method for analyzing the influence of HEMP on transformer in late stage according to claim 4, characterized in that: The transformer heat conduction model also includes temperature boundary conditions, heat flow boundary conditions and convection boundary conditions; The temperature boundary conditions are: in, is the boundary condition of the object, is the known wall temperature; The heat flow boundary conditions are: in, is the known heat flux density, - is the direction in which heat flows to reduce temperature, is the thermal conductivity of the transformer, is the temperature gradient along the direction of heat flow toward decreasing temperature; The convection boundary conditions are: Among them, - is the direction of heat flow towards lower temperature, is the thermal conductivity of the transformer, is the temperature gradient in the direction of heat flow and temperature decrease, h is the convective heat transfer coefficient, is the temperature of the fluid medium in contact with the object.

6. An analysis device for the late impact of HEMP on transformers, characterized in that: include: A vibration analysis module is used to construct a transformer core vibration acceleration model caused by magnetostrictive effect, analyze the transformer core vibration under DC bias, and obtain a first analysis result; A noise analysis module is used to construct a transformer sound pressure model, analyze the transformer noise under DC bias, and obtain a second analysis result; The temperature analysis module is used to construct a transformer heat conduction model, analyze the transformer temperature under DC bias, and obtain a third analysis result; The output module is used to integrate the first analysis result, the second analysis result and the third analysis result to obtain the analysis result of the influence of HEMP in the late stage on the transformer.

7. The analysis device for the late HEMP impact on transformer according to claim 6, characterized in that: The transformer core vibration acceleration model is: in, is the transformer core vibration acceleration, t is the time, K is the size of the transformer core before deformation, is the maximum magnetostriction change, is the coercive force, is the maximum value of the transformer excitation voltage, l is the length of the transformer main magnetic circuit coil, R is the transformer equivalent resistance, is the angular frequency, L is the transformer equivalent inductance, is the magnetostriction coefficient under saturation state, N is the number of coil turns of the transformer, is the DC bias current; The transformer sound pressure model is: in, is the fluid density, q is the dipole source, Q is the monopole source, c is the speed of sound propagation in the fluid, p is the effective value of the transformer noise pressure, is the divergence, is the effective value gradient of transformer noise sound pressure; The transformer heat conduction model is: in, is the heat flow rate, T is the transformer temperature, is the temperature gradient along the x-axis, is the temperature gradient along the y-axis, is the temperature gradient along the z-axis, is the thermal conductivity of transformer oil in the x-axis direction, is the thermal conductivity of transformer oil in the y-axis direction, is the thermal conductivity of transformer oil in the z-axis direction, is the transformer oil density, is the specific heat of transformer oil.

8. The device for analyzing the influence of HEMP on transformer in late stage according to claim 7, characterized in that: The transformer heat conduction model also includes temperature boundary conditions, heat flow boundary conditions and convection boundary conditions; The temperature boundary conditions are: in, is the boundary condition of the object, is the known wall temperature; The heat flow boundary conditions are: in, is the known heat flux density, - is the direction in which heat flows to reduce temperature, is the thermal conductivity of the transformer, is the temperature gradient along the direction of heat flow toward decreasing temperature; The convection boundary conditions are: Among them, - is the direction of heat flow towards lower temperature, is the thermal conductivity of the transformer, is the temperature gradient in the direction of heat flow and temperature decrease, h is the convective heat transfer coefficient, is the temperature of the fluid medium in contact with the object.

9. An analysis device for the late effects of HEMP on transformers, characterized in that: The device comprises a processor and a memory: The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the analysis method of the late HEMP impact on the transformer according to any one of claims 1-5 according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium is used to store program codes, and the program codes are used to execute the method for analyzing the influence of HEMP in the late stage on the transformer according to any one of claims 1 to 5.

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