Method for evaluating short circuit resistance of amorphous alloy transformer

Abstract

The application provides a kind of amorphous alloy transformer short circuit resistance evaluation method, it is related to amorphous alloy transformer technical field. Including: determining the design parameter of amorphous alloy transformer, according to design parameter corresponding electromagnetic calculation model and structure calculation model are established;Set the material attribute, coil turns of electromagnetic calculation model and boundary condition, carry out eddy current field calculation, obtain the leakage magnetic distribution and Lorentz force distribution in coil under different short circuit fault conditions;Set the material attribute, contact relationship and boundary condition of structure calculation model;According to conservative interpolation method, short circuit force density distribution is mapped to structure calculation model, statics analysis is executed, and the stress and strain corresponding to coil position are obtained;The short circuit resistance of amorphous alloy transformer under each short circuit fault condition is evaluated, and the corresponding evaluation result is obtained.The application solves the problem of long time consumption and low efficiency in the prior art of amorphous alloy transformer short circuit resistance evaluation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of amorphous alloy transformer, and particularly relates to an amorphous alloy transformer short-circuit resistance evaluation method. BACKGROUND

[0002] With the rapid development of smart grid construction and new energy grid connection technology, the short-circuit resistance of power transformers as key power transmission and transformation equipment has become a core index for measuring the reliability of the equipment. Amorphous alloy transformers have been widely used in modern power systems due to their low loss and high efficiency, but the evaluation of their short-circuit resistance faces special challenges.

[0003] 1. The amorphous alloy transformer is a shell-type transformer, and the coil is a non-circular structure, and the fastening structure of the coil is completely different from that of the traditional transformer. The mainstream analytical algorithm in the transformer industry is not applicable to the short-circuit resistance calculation of the amorphous alloy transformer.

[0004] 2. The existing electromagnetic-structure coupling analysis generally adopts a transient dynamics calculation method, which needs to solve a nonlinear equation set in the time domain. The nonlinear characteristics of the anisotropic parameters and the dynamic yield strength of the material changing with the strain rate significantly increase the convergence difficulty, resulting in a single simulation time of more than 60 hours, which seriously affects the product design iteration efficiency and is difficult to meet the engineering actual demand. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide an amorphous alloy transformer short-circuit resistance evaluation method, which solves the problems of long time consumption and low efficiency in the prior art.

[0006] To achieve the above purpose, the present application provides the following scheme:

[0007] An amorphous alloy transformer short-circuit resistance evaluation method comprises the following steps:

[0008] determining the design parameters of the amorphous alloy transformer, wherein the design parameters include electromagnetic design parameters and structural design parameters;

[0009] establishing corresponding electromagnetic calculation models and structural calculation models according to the design parameters based on a preset three-dimensional software;

[0010] presetting the offset of the axial center height of the high-voltage coil and the low-voltage coil based on the short-circuit test results to obtain the coil position to be calculated;

[0011] setting the material properties, the number of turns of the coil and the boundary conditions of the electromagnetic calculation model based on the coil position to be calculated, performing eddy current field calculation, and obtaining the magnetic flux leakage distribution and the Lorentz force distribution in the coil under different short-circuit fault conditions;

[0012] determine a short-circuit force density distribution according to the magnetic flux leakage distribution and the Lorentz force distribution;

[0013] set material properties, contact relations and boundary conditions of the structure calculation model;

[0014] map the short-circuit force density distribution to the structure calculation model according to a conservative interpolation method, perform a static mechanics analysis to obtain stress and strain corresponding to the coil position;

[0015] evaluate the short-circuit resistance of the amorphous alloy transformer under each short-circuit fault condition according to the stress and strain corresponding to the coil position, and obtain a corresponding evaluation result.

[0016] Preferably, the material properties of the electromagnetic calculation model include:

[0017] magnetic permeability and electrical conductivity.

[0018] Preferably, the material of the structure calculation model includes:

[0019] copper wire, copper foil and Q235 steel.

[0020] Preferably, the material properties of the structure calculation model include:

[0021] elastic modulus and Poisson's ratio.

[0022] Preferably, the short-circuit fault conditions include:

[0023] three-phase short-circuit condition, two-phase short-circuit condition, single-phase short-circuit condition and ground short-circuit condition.

[0024] Preferably, the calculation expression of the stress is:

[0025] S=S inel +S el ;

[0026] wherein S inel is plastic stress and S el is elastic stress.

[0027] Preferably, the calculation expression of the strain is:

[0028] ε=ε inel +ε el ;

[0029] wherein ε inel is plastic stress and ε el is elastic stress.

[0030] The present application discloses the following technical effects:

[0031] The application provides a kind of amorphous alloy transformer short circuit resistance evaluation method, comprising: determining the design parameters of amorphous alloy transformer, the design parameters include: electromagnetic design parameters and structural design parameters;Based on the preset three-dimensional software, the corresponding electromagnetic calculation model and structural calculation model are established according to the design parameters;Based on short circuit test results, the axial center height of high and low voltage coil is preset offset, and the coil position to be calculated is obtained;The coil position to be calculated, the material properties, coil turns and boundary conditions of electromagnetic calculation model are set, eddy current field calculation is carried out, the leakage magnetic distribution and Lorentz force distribution in the coil under different short circuit fault conditions are obtained;The short circuit force density distribution is determined according to the leakage magnetic distribution and Lorentz force distribution;The material properties, contact relationship and boundary conditions of structural calculation model are set;According to the conservative interpolation method, the short circuit force density distribution is mapped to the structural calculation model, the static mechanics analysis is executed, and the stress and strain corresponding to the coil position are obtained;The short circuit resistance of amorphous alloy transformer under each short circuit fault condition is evaluated according to the stress and strain corresponding to the coil position, and the corresponding evaluation result is obtained.The application uses static structural mechanics to replace transient structural mechanics to evaluate short circuit resistance, which converts complex transient mechanics problem into static mechanics problem, and greatly shortens the calculation time. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0033] Figure 1 A flow chart of the amorphous alloy transformer short circuit resistance evaluation method provided by the embodiment of the present application is provided.

[0034] Figure 2 A general assembly schematic diagram of the amorphous alloy transformer provided by the embodiment of the present application is provided.

[0035] Figure 3 A front view of the amorphous alloy transformer body provided by the embodiment of the present application is provided.

[0036] Figure 4 A body force density distribution schematic diagram provided by the embodiment of the present application is provided.

[0037] Figure 5 A pre-tightening force load schematic diagram on the screw provided by the embodiment of the present application is provided.

[0038] Figure 6 A first equivalent stress nephogram provided by the embodiment of the present application is provided.

[0039] Figure 7A second equivalent stress nephogram provided by the embodiment of the present application.

[0040] Explanation of reference numerals:

[0041] 1, tank cover; 2, tank wall; 3, tank cover suspension shaft; 4, upper clamp; 5, pressing plate; 6, supporting plate; 7, lower clamp; 8, shell transformer core; 9, shell winding; 10, body suspension shaft. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0043] In order to make the above objectives, characteristics and advantages of the present application more apparent, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0044] As shown in the drawings, Figure 1 The present application provides a method for evaluating short-circuit resistance of an amorphous alloy transformer, comprising:

[0045] Step 100: determining design parameters of the amorphous alloy transformer, wherein the design parameters include electromagnetic design parameters and structural design parameters;

[0046] Step 200: establishing corresponding electromagnetic calculation models and structural calculation models according to the design parameters based on a preset three-dimensional software;

[0047] Step 300: presetting an offset of an axial center height of high-voltage and low-voltage coils based on short-circuit test results, and obtaining a coil position to be calculated;

[0048] Step 400: setting material properties, coil turns and boundary conditions of the electromagnetic calculation models, performing eddy current field calculation, and obtaining leakage magnetic distribution and Lorentz force distribution in the coils under different short-circuit fault conditions for the coil position to be calculated;

[0049] Step 500: determining short-circuit force density distribution according to the leakage magnetic distribution and the Lorentz force distribution;

[0050] Step 600: setting material properties, contact relationships and boundary conditions of the structural calculation models;

[0051] Step 700: mapping the short-circuit force density distribution to the structural calculation models according to a conservative interpolation method, performing static mechanics analysis, and obtaining stress and strain corresponding to the coil position;

[0052] Step 800: According to the stress and strain corresponding to the coil position, the short-circuit resistance of the amorphous alloy transformer under each short-circuit fault condition is evaluated, and the corresponding evaluation result is obtained.

[0053] Specifically, a liquid-immersed amorphous alloy transformer is taken as an example, and the model number is SBH21-M-400-10-NX2. The amorphous alloy transformer is a double-winding amorphous alloy transformer, and the cooling medium is mineral oil. Figure 2 The main structure assembly drawing of the amorphous alloy transformer is shown in the figure. The model hides two walls of the oil tank, including tank cover 1, oil tank wall 2, tank cover hanging shaft 3, and body hanging shaft 10 fixed together with tank cover 1 through a screw rod.

[0054] After the amorphous alloy transformer starts to operate, the main heat source in the oil tank exchanges heat with the transformer oil. The transformer oil starts to circulate in the oil tank and exchanges heat with the air through the tank cover 1 and the oil tank wall 2 of the transformer. The main view of the internal structure of the amorphous alloy transformer, i.e., the body, is shown in Figure 3 The body structure of the amorphous alloy transformer is a shell type transformer structure. The coil is a non-circular structure. The high-voltage coil and the low-voltage coil are tightly fixed in the middle of the body by the upper clamp 4 and the lower clamp 7 through the pressing plate 5 and the supporting plate 6. The shell type transformer core 8 is like a shell and stands in the middle of the body. The shell winding 9 lies down, as shown in Figure 3 Table 1 is a table of basic performance parameters of the SBH21-M-400-10-NX2 amorphous alloy transformer, and is shown as follows:

[0055] Table 1

[0056] Parameter Value Transformer model SBH21-M-400-10-NX2 Phase number 3 Short-circuit impedance 4% Insulation level HV LI75AC35 Winding material Copper Cooling method Liquid-immersed Rated voltage 10 / 0.4 kV Rated current 23.1 / 577.4A

[0057] The following are the detailed steps of the present example. The main purpose of the present example is to show the calculation method of the short-circuit resistance of the amorphous alloy transformer under the three-phase symmetrical short-circuit condition.

[0058] S1: Determine the electromagnetic design parameters and structure design parameters of the amorphous alloy transformer;

[0059] Specifically, the electromagnetic design parameters of the amorphous alloy transformer include but are not limited to the number of phases, short-circuit impedance, coil electrical parameters, rated capacity, rated voltage, voltage regulation range, body arrangement parameters, and core parameters.

[0060] According to the determined parameters of the amorphous alloy transformer, a corresponding three-dimensional model is constructed.

[0061] S2: According to the design parameters of the amorphous alloy transformer, a corresponding electromagnetic calculation model and structure calculation model are established and input into the system to be solved;

[0062] Specifically, the transformer model established in S1 is a complete three-dimensional design model, which can be simplified to a magnetic permeability close to air insulation material, only the coil and the electromagnetic calculation model composed of ferromagnetic material are reserved; corresponding to the structure calculation model, part of the insulation that does not participate in the support can be simplified.

[0063] S3: preset the relative axial displacement amount of the high-voltage coil and the low-voltage coil based on the short-circuit test result, and input the system to make the axial center height of the high-voltage coil and the low-voltage coil produce a certain offset;

[0064] Specifically, in the embodiment of the present application, the capacity of the amorphous alloy transformer is 400kVA, the rated voltage is 10 / 0.4kV, and the rated current is 23.1 / 577.4A. According to the inversion of the test results, the maximum axial relative displacement of the high-voltage coil and the low-voltage coil of the amorphous alloy transformer with the capacity and voltage grade is 0.59%.

[0065] S4: set the material properties, excitation conditions and boundary conditions of the electromagnetic calculation model;

[0066] In step S4, the specific method is:

[0067] A1: set the electromagnetic material parameters of different materials, mainly permeability and conductivity, the material of the coil is electrical copper, the calculation domain material is air (the insulation material has been simplified in S2, which does not affect the magnetic field part calculation), and the core is a nonlinear ferromagnetic material with a magnetic permeability of B-H curve. Table 2 is the electromagnetic calculation material property table, and table 2 is as follows:

[0068] Table 2

[0069] Material Permeability Electrical conductivity [S / m] Electrical copper 1 46700000 Silicon steel sheet Nonlinear B-H curve 1 Air 1 1

[0070] A2: set the number of turns of the low-voltage coil and the high-voltage coil;

[0071] A3: calculate the eddy current field, set the analysis frequency to 50Hz according to the technical parameters, and set the boundary condition as the magnetic field calculation boundary parallel to the calculation domain;

[0072] S5: set the material properties, contact parameters and boundary conditions of the structure calculation model

[0073] The method of the present application simplifies the transient calculation to static calculation, greatly reduces the calculation time and computer resources occupied by the calculation, and therefore can optimize the modeling accuracy of the coil and the compression structure (fine modeling of the compression structure at key positions, including the body compression plate, the supporting plate 6, the screw rod, the connection structure between the body and the box cover 1, etc.) and the contact parameters (except the welding structure, the rest of the contact structure is friction contact), further improving the accuracy and reliability of the calculation.

[0074] In step S5, the specific method is:

[0075] B1: Set the material properties of various structural components, including copper, Q235 steel, epoxy resin and laminated wood, the main material properties are elastic modulus and Poisson's ratio, Table 3 is the structural calculation material property table, and Table 3 is as follows:

[0076] Table 3

[0077] Material Elastic modulus [MPa] Poisson's ratio Copper 110000 0.35 Q235 steel 200000 0.3 Epoxy resin 2000 0.35 Laminated wood 9000 0.2

[0078] B2: Set the contact relationship between different structural components, mainly binding contact and friction contact, and the friction coefficient needs to be determined according to the material;

[0079] B3: Apply a fixed constraint to a reasonable position of the amorphous alloy transformer;

[0080] In this embodiment, the transformer is a liquid-immersed transformer, so the fixed constraint position is the bottom of the oil tank.

[0081] S6: Set the input under different short-circuit fault conditions as the electromagnetic field calculation excitation;

[0082] Specifically, the short-circuit fault conditions include three-phase short-circuit conditions, two-phase short-circuit conditions, single-phase short-circuit conditions and ground short-circuit conditions. In the specific calculation process, according to the determined amorphous alloy transformer impedance and line equivalent impedance, the peak short-circuit current of each short-circuit fault condition is determined, that is:

[0083]

[0084] In the formula, I is the peak short-circuit current; U is the rated voltage or the tapping voltage of the coil; Z t is the transformer impedance; Z s is the system short-circuit impedance; k is the initial current offset coefficient.

[0085] Specifically, the short-circuit current values under a plurality of different short-circuit fault conditions are taken as the excitation, and the short-circuit current values are loaded to each coil winding in the finite element model of the transformer, so that each coil winding is sequentially given current excitation from phase A to phase B to phase C.

[0086] S7: Calculate the coil internal leakage magnetic distribution and Lorentz force distribution corresponding to the specified short-circuit condition

[0087] The magnetic field finite element analysis follows Maxwell's equations.

[0088]

[0089]

[0090]

[0091]

[0092] where D is the electric displacement vector with unit of C / m; J is the current density vector with unit of A / m 2 ; B is the magnetic induction vector with unit of T; E is the electric field vector with unit of V / m; H is the magnetic field vector with unit of A / m; p is the charge density with unit of C / m 3 .

[0093] The constitutive equation of electromagnetic calculation is:

[0094]

[0095]

[0096]

[0097] where s represents the dielectric constant of medium with unit of F / m; μ is the permeability of medium with unit of H / m; represents the conductivity of medium with unit of S / m.

[0098] The top view of electromagnetic volume force density distribution of a certain phase angle at short circuit is shown in Figure 4 The electromagnetic force in the high-voltage coil makes it have a tendency to expand outward, and the electromagnetic force in the low-voltage coil makes it have a tendency to contract inward.

[0099] S8: mapping the short-circuit force density distribution calculated by the electromagnetic calculation model to the structural calculation model

[0100] Specifically, since the mesh partitioning results of the electromagnetic calculation model and the mesh partitioning results of the structural calculation model are not consistent, a conservative interpolation method is adopted to realize the transfer of the volume force density from the electromagnetic calculation model to the structural calculation model. The process is to integrate each element of the source grid (magnetic field grid) to the coverage area of the target grid (structural grid), and ensure the total force conservation, that is:

[0101] ;

[0102] where represents the total force after mapping of the structural calculation model; is the volume of the i th element; is the volume of a certain region of the load to be mapped; is the volume force density distribution in the grid of the electromagnetic calculation model.

[0103] Specifically, after the volume force density distribution of the electromagnetic calculation model is mapped to the structural calculation model by the conservative difference method.

[0104] S9: calculate the stress condition of amorphous alloy transformer coil and body compression structure under the action of equivalent static peak short-circuit force;

[0105] The structural mechanics calculation adopts static structural mechanics, and from the stress point of view, Newton's second law can be expressed as:

[0106] ;

[0107] Wherein, p is the density, u is the displacement field, Indicates acceleration, s is the stress tensor, and Fv is the volume force.

[0108] When the calculation is a static field, the mechanical system is in static equilibrium state, and the displacement field is 0, and the above formula can be simplified as

[0109]

[0110] In the formula, s is the stress tensor matrix, and each element in the matrix represents the force component on the unit area of the material.

[0111] The material model is an elastic-plastic model, which describes two different stress and strain conditions below and above the yield point of the material. The material model refers to the mathematical model for calculating the stress of different materials in solid mechanics.

[0112] S=S inel +S el ;

[0113] Wherein, S inel is the plastic stress, and S el is the elastic stress.

[0114] The calculation expression of the strain is:

[0115] ε=ε inel +ε el ;

[0116] Wherein, ε inel is the plastic stress, and ε el is the elastic stress.

[0117] In the embodiment of the application, in addition to the short-circuit force in the coil in the structural calculation model, there is also a pre-tightening force in the fastening structure, that is, a pre-tightening force is applied on each screw rod, and under the static field convergence condition, the stress on the screw rod also needs to be checked, and the pre-tightening force load applied in the model is as shown in Figure 5 .

[0118] The size of the pre-tightening force is usually determined by the applied torque, and the relationship is:

[0119]

[0120] In the formula, T is the applied torque; K is the torque coefficient (related to factors such as friction, thread geometry, etc.); is the pre-tightening force; d is the nominal diameter of the bolt.

[0121] Under the static equivalent calculation method, the equivalent stress nephogram of the A-phase coil is shown in Figure 6 The maximum equivalent stress of the high-voltage coil is 74 MPa < 110 MPa (the high-voltage coil is a copper wire), and the maximum equivalent stress of the low-voltage coil is 35 MPa < 60 MPa (the low-voltage coil is a copper foil), both of which are less than the material yield strength. Even if the structure deforms to a certain extent, it will quickly rebound.

[0122] The equivalent stress nephogram of the coil is shown in Figure 7 The equivalent stress in the rest of the structure except the screw rod is very small, all of which are less than the material yield strength. Even if the structure deforms to a certain extent, it will quickly rebound. Table 4 is the coil external electromagnetic thrust table, which is as follows:

[0123] Table 4

[0124] Single low-voltage coil axial outward electromagnetic thrust [kN] Single high-voltage coil axial outward electromagnetic thrust [kN] 43 -42

[0125] The bolt used in the axial fixer body structure is a single-sided 4.8.8 strength screw rod, model M12. The pre-tightening force P0 corresponding to the screw rod is (0.5~0.7)σs×As=27~38kN, and there are 8 screw rods on both sides of the body, i.e. 216-304kN of compression force is provided to the entire three-phase coil. By comparing the numerical calculation of the coil external electromagnetic thrust in Table 4, the pre-tightening force provided by the screw rod is much larger than the coil electromagnetic thrust under the condition that the axial position of the coil does not shift. Among them, σs is the yield limit of the bolt material, and As is the calculation diameter of the dangerous section of the thread.

[0126] Table 5 is a calculation time comparison table, which is shown as follows:

[0127] Table 5

[0128] Part The method of the present application Traditional transient electromagnetic-structure coupling field Calculation time length [h] 2 60

[0129] S10: return to S6 to continue calculating the remaining short-circuit conditions.

[0130] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other.

[0131] The principles and implementation manners of the present application are described by using specific examples in the present application, and the above examples are only used to help understand the method of the present application and its core idea; meanwhile, for the general technical personnel in the art, the specific implementation manners and application ranges will be changed according to the idea of the present application. In conclusion, the content of the present specification should not be understood as the limitation of the present application.

Claims

1. A method for evaluating the short-circuit withstand capability of an amorphous alloy transformer, characterized in that, include: Determine the design parameters for the amorphous alloy transformer, including electromagnetic design parameters and structural design parameters; Based on the preset 3D software, corresponding electromagnetic calculation models and structural calculation models are established according to the design parameters; Based on the short-circuit test results, the axial center height of the high and low voltage coils is preset to offset, and the coil position to be calculated is obtained. Based on the location of the coil to be calculated, the material properties, number of coil turns and boundary conditions of the electromagnetic calculation model are set, and eddy current field calculation is performed to obtain the leakage magnetic field distribution and Lorentz force distribution in the coil under different short-circuit fault conditions. The short-circuit force density distribution is determined based on the leakage magnetic field distribution and the Lorentz force distribution. Set the material properties, contact relationships, and boundary conditions of the structural calculation model; Based on the conservative interpolation method, the short-circuit force density distribution is mapped to the structural calculation model, and static mechanical analysis is performed to obtain the stress and strain corresponding to the coil position; The expression for calculating the stress is: S=S inel +S el ; Among them, S inel For plastic stress, S el It is elastic stress; The expression for calculating the strain is: ε=ε inel +ε el ; where ε inel For plastic stress, ε el It is elastic stress; Based on the stress and strain corresponding to the coil position, the short-circuit withstand capability of the amorphous alloy transformer under various short-circuit fault conditions is evaluated, and the corresponding evaluation results are obtained. The material properties of the electromagnetic calculation model include: Magnetic permeability and electrical conductivity; The materials used in the structural calculation model include: Copper wire, copper foil, Q235 steel; The material properties of the structural calculation model include: Elastic modulus, Poisson's ratio; The contact relationship between different structural components is set, mainly as binding contact and frictional contact. The frictional contact requires the corresponding friction coefficient to be determined according to the material. Apply fixed constraints to the appropriate positions of the amorphous alloy transformer.

2. The method for evaluating the short-circuit withstand capability of an amorphous alloy transformer according to claim 1, characterized in that, Short-circuit fault conditions include: Three-phase short circuit condition, two-phase short circuit condition, single-phase short circuit condition, and ground short circuit condition.

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