A method for evaluating transformer short-circuit resistance

Abstract

The present disclosure belongs to the technical field of transformers and provides a method for evaluating the short-circuit resistance of a transformer, comprising the following steps: obtaining electrical parameters and a finite element simulation model of the transformer; constructing a transformer short-circuit model based on the obtained electrical parameters to simulate a sudden short-circuit fault of the transformer; calculating the short-circuit current of the transformer, the deformation distribution of the transformer winding, and the deformation amount of the transformer winding based on the finite element simulation model and the transformer short-circuit model, performing real-time updating of the transformer short-circuit model, and obtaining a frequency response curve of the transformer; and evaluating the short-circuit resistance of the transformer based on the obtained frequency response curve.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of transformers, and particularly relates to a method for evaluating the short-circuit resistance capability of a transformer. Background Art

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

[0003] Transformers occupy a crucial position in power systems, and their proper operation is crucial to the safe transmission of electrical energy. In recent years, transformer accidents have been numerous, and insufficient short-circuit resistance is the primary cause of damage. This can be caused by loose windings, improper transposition, insufficient winding preload, the cumulative effect of multiple shocks, and uncured conductors. If a transformer in a transmission line fails and becomes inoperable, it can severely impact the local power system and even trigger a large-scale power outage. Therefore, accurately detecting transformer winding deformation and assessing its short-circuit resistance are crucial for the safe and stable operation of the power grid.

[0004] When a transformer experiences a sudden short-circuit fault, a massive short-circuit current flows through the windings. The interaction between this short-circuit current and the leakage magnetic field generates a short-circuit electromotive force proportional to the square of the short-circuit current. If the transformer's structural components are unable to support this massive electromotive force, or if the insulation strength is low—in other words, if the transformer's short-circuit resistance is insufficient—the windings can be damaged. During a transformer short-circuit fault, winding deformation accumulates. The winding's resistance to the short-circuit shock decreases, making it more susceptible to bending and deformation, potentially damaging the insulation and causing severe discharge and short-circuiting. Currently, criteria for determining the severity of transformer winding deformation are based on experience and limiting factors and cannot be used as standard limits. Summary of the Invention

[0005] To solve the above problems, the present invention proposes a method for evaluating the short-circuit resistance of transformers. It adopts a combined diagnostic method of multiple criteria to judge the degree of deformation of the transformer winding under short-circuit conditions, and then judges the short-circuit resistance of the transformer under short-circuit conditions, providing a theoretical basis for accurately evaluating the short-circuit resistance of transformers.

[0006] According to some embodiments, the present disclosure provides a method for evaluating the short-circuit resistance of a transformer, using the following technical solutions:

[0007] A method for evaluating the short-circuit resistance of a transformer comprises the following steps:

[0008] Obtain the electrical parameters and finite element simulation model of the transformer;

[0009] Based on the obtained electrical parameters, a transformer short-circuit model is constructed to simulate the transformer's sudden short-circuit fault;

[0010] Based on the finite element simulation model and the transformer short-circuit model, the short-circuit current of the transformer, the deformation distribution of the transformer winding, and the deformation amount of the transformer winding are calculated, the transformer short-circuit model is updated in real time, and a frequency response curve of the transformer is obtained;

[0011] The short-circuit resistance of the transformer is evaluated based on the obtained frequency response curve.

[0012] As a further technical limitation, the process of obtaining the finite element simulation model is: based on the dimensional parameters of the transformer, a three-dimensional simulation model of the transformer is established in the finite element simulation software, a fixed constraint is applied to the lower end component of the three-dimensional simulation model of the transformer, a position constraint is applied to the upper end component of the three-dimensional simulation model of the transformer, and a specified acceleration is added to the three-dimensional simulation model of the transformer.

[0013] As a further technical limitation, the electrical parameters include at least resistance and inductance of the transformer.

[0014] As a further technical limitation, the Simulink module in MATLAB is used to build a transformer winding model under sudden short-circuit conditions. A three-phase grounding fault module is added to Simulink, and the short circuit is set between the fault phases or between the fault phase and the ground to simulate the sudden short-circuit fault of the transformer.

[0015] As a further technical limitation, in the process of evaluating the short-circuit resistance of the transformer according to the obtained frequency response curve, when the correlation coefficient R LF Less than the first threshold (ie R LF <0.6), the transformer winding is seriously deformed; when R LF The correlation coefficient R between the first threshold and the second threshold, or the frequency response curve in the mid-frequency band MF Less than the first threshold (ie 1.0>R LF ≥0.6 or R MF <0.6), the transformer winding is obviously deformed; when R LF Between the second threshold and the third threshold, and R MF Between the first threshold and the second threshold (ie 2.0>R LF ≥1.0 or 0.6≤R MF <1.0), the transformer winding is slightly deformed; when R LF Greater than the third threshold, and R MF Greater than the second threshold, and the correlation coefficient of the frequency response curve in the high frequency band is greater than the first threshold (ie R LF ≥2.0 and RMF ≥1.0 and R HF ≥0.6), the transformer winding is normal.

[0016] Furthermore, if R LF Between the first threshold and the third threshold or R MF Less than the second threshold (ie 2.0>R LF ≥0.6 or R MF <1.0), the transformer winding deformation is not serious, and the transformer's short-circuit resistance must be determined by judging the relationship between the inductance parameters after short circuit and the initial parameters.

[0017] Furthermore, if the inductance parameter after the short circuit does not change by more than the set value compared with the initial parameter, the transformer has not lost its short-circuit resistance after the short circuit, and the short-circuit simulation analysis continues; if it exceeds the set value, the change relationship between the capacitance parameter and the initial parameter is determined;

[0018] If the capacitance parameter does not change by more than the set value compared with the initial parameter, the transformer has not lost its short-circuit resistance after the short circuit, and the short-circuit simulation analysis continues; if it exceeds the set value, the relationship between the hoop tensile stress and hoop compressive stress and the allowable stress is determined.

[0019] Furthermore, if the hoop tensile stress is not greater than the second stress threshold, and the hoop compressive stress is not greater than the first stress threshold (i.e., F CS ≤0.9×F ps And F CC ≤0.35×F ps ), the transformer does not lose its short-circuit resistance after the short circuit, and the short-circuit simulation analysis continues; if the hoop tensile stress is greater than the second stress threshold, or the hoop compressive stress is greater than the first stress threshold (i.e. F CS >0.9×F ps or F CC >0.35×F ps ), it is necessary to determine the relationship between the radial bending stress and the allowable stress of the conductor within the span between the stays.

[0020] Furthermore, if the radial bending stress of the wire within the span between the struts is not greater than the second stress threshold (i.e., F rf ≤0.9×F ps ), the transformer does not lose its short-circuit resistance after the short circuit, and the short-circuit simulation analysis continues; if the radial bending stress of the wire within the span between the supports is greater than the second stress threshold (i.e. F rf >0.9×F ps ), it is necessary to determine the relationship between the axial bending stress of the conductor within the span between the radial pads and the allowable stress; if the axial bending stress of the conductor within the span between the radial pads is not greater than the second stress threshold (i.e., F af ≤0.9×Fps ), the transformer does not lose its short-circuit resistance after the short circuit, and the short-circuit simulation analysis continues; if the axial bending stress of the conductor within the span between the radial pads is greater than the second stress threshold (i.e., F af >0.9×F ps ), then determine the safety factor.

[0021] Furthermore, if the safety factor is greater than the safety factor threshold (i.e., S>2.5), the transformer winding does not lose stability during short circuit, and the short circuit simulation analysis continues; if the safety factor is not greater than the safety factor threshold (i.e., S≤2.5), the value of the radial pad compressive stress is determined.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] Compared with the disclosed technology, the present invention has the following beneficial effects:

[0024] This paper addresses the shortcomings of previous methods for determining transformer winding deformation severity and short-circuit resistance, which were determined solely based on experience and consideration of limiting factors. This method, which cannot serve as a standard limit and therefore cannot accurately determine a transformer's short-circuit resistance, employs a combined diagnostic method using multiple criteria to determine a transformer's short-circuit resistance under short-circuit conditions. This method provides a theoretical basis for accurately assessing transformer short-circuit resistance and proposes improvement measures for insufficient short-circuit resistance. Furthermore, by leveraging Simulink's ability to accurately calculate the short-circuit current of a transformer winding during a sudden short circuit, the short-circuit current calculation results from Simulink are coupled to finite element simulation software to analyze the changes in the transformer's structural characteristics under the influence of short-circuit electrodynamic forces. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute a part of the present disclosure, are used to provide a further understanding of the present disclosure. The exemplary embodiments of the present disclosure and their descriptions are used to explain the present disclosure and do not constitute an improper limitation to the present disclosure.

[0026] Figure 1 is a flow chart of a method for evaluating the short-circuit resistance capability of a transformer in an embodiment of the present disclosure;

[0027] Figure 2 is a flow chart of transformer short-circuit capability evaluation in an embodiment of the present disclosure;

[0028] Figure 3 It is a Simulink power system simulation diagram combined with a finite element module in an embodiment of the present disclosure;

[0029] Figure 4 is a diagram of an actual calculation model of a transformer winding in an embodiment of the present disclosure;

[0030] Figure 5is a diagram showing radial leakage flux density of a low-voltage winding in an embodiment of the present disclosure;

[0031] Figure 6 is a diagram showing radial leakage flux density of a high-voltage winding in an embodiment of the present disclosure;

[0032] Figure 7 is a result diagram of radial short-circuit force density of a low-voltage winding in an embodiment of the present disclosure;

[0033] Figure 8 is a result diagram of the radial short-circuit force density of the high-voltage winding in the embodiment of the present disclosure;

[0034] Figure 9 is a low voltage winding deformation curve in the embodiment of the present disclosure;

[0035] Figure 10 is the high-voltage winding deformation curve in the embodiment of the present disclosure. DETAILED DESCRIPTION

[0036] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0037] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present disclosure belongs.

[0038] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0039] Example

[0040] like Figure 1 A method for evaluating the short-circuit resistance capability of a transformer is shown, comprising the following steps:

[0041] Obtain the electrical parameters and finite element simulation model of the transformer;

[0042] Based on the obtained electrical parameters, a transformer short-circuit model is constructed to simulate the transformer's sudden short-circuit fault;

[0043] Based on the finite element simulation model and the transformer short-circuit model, the short-circuit current of the transformer, the deformation distribution of the transformer winding, and the deformation amount of the transformer winding are calculated, the transformer short-circuit model is updated in real time, and a frequency response curve of the transformer is obtained;

[0044] The short-circuit resistance of the transformer is evaluated based on the obtained frequency response curve.

[0045] In view of the shortcomings that the criteria for the severity of transformer winding deformation in the relevant standards "Guidelines for Detection and Judgment of Power Transformer Winding Deformation by Reactance Method" and "Power Transformer Part 5: Ability to Withstand Short Circuits" cannot be used as standard limits, but are only determined based on experience and taking into account limiting factors, and thus cannot accurately judge the transformer's ability to withstand short circuits, a combined diagnostic method of multiple criteria is used to judge the transformer's ability to withstand short circuits under short-circuit conditions, providing a theoretical basis for accurately evaluating the transformer's ability to withstand short circuits, and proposing improvement measures for insufficient short-circuit resistance.

[0046] The transformer short-circuit resistance evaluation method in this embodiment mainly includes the following: building a transformer circuit in Simulink software, calculating the short-circuit current of the transformer under sudden short-circuit conditions, and importing it into finite element simulation software, establishing a three-dimensional transformer model in the finite element simulation software, and calculating the transformer winding leakage magnetic field, radial and axial short-circuit electromotive force distribution, winding deformation, and hoop tensile stress F CS and hoop compressive stress F CC , radial bending stress F of the conductor within the span between the braces rf , the axial bending stress F of the conductor within the span between radial pads af , radial critical instability strength F rc , radial electromotive force F re , radial pad compressive stress F pc And the compressive stress F of the transformer insulation end ring pe The updated value of the winding inductance parameter and the frequency response curve after the short circuit are also analyzed. A combined diagnostic method using multiple criteria is used to determine the transformer's deformation severity and short-circuit withstand capability under short-circuit conditions. This method addresses the drawback that the criteria for transformer winding deformation severity and short-circuit withstand capability are determined solely based on experience and consideration of limiting factors, which cannot be used as standard limits and, therefore, cannot accurately determine the transformer's short-circuit withstand capability. It provides a theoretical basis for accurately evaluating the transformer's short-circuit withstand capability and proposes improvement measures for insufficient short-circuit withstand capability.

[0047] like Figure 2 As shown, the specific steps of the transformer short-circuit resistance evaluation method in this embodiment are:

[0048] Step S01: Based on an actual power transformer, electrical parameters such as resistance and inductance of the transformer are calculated;

[0049] Step S02: Build a transformer short circuit model in Simulink software, use the short circuit module to impose a short circuit on the secondary side of the transformer to simulate the transformer short circuit fault, as shown in the following example: Figure 3As shown;

[0050] Step S03: Based on the actual size of the transformer, a finite element simulation model is established according to step S01, as shown in the following example: Figure 4 As shown;

[0051] Step S04: setting the physical field and solution type of the finite element simulation software, setting the transformer materials including soft iron, copper and transformer oil and corresponding coefficients;

[0052] Step S05: using the Simulink module to calculate the change in the short-circuit current of the transformer under the short-circuit condition;

[0053] Step S06: using finite element simulation software, importing the Simulink module to calculate and obtain the short-circuit current data of the short circuit;

[0054] Step S07: Analyze and calculate the leakage magnetic field and force field of the short circuit using finite element simulation software. The result diagrams of the radial leakage magnetic flux density of the low voltage winding and the radial leakage magnetic flux density of the high voltage winding are as follows: Figure 5 and Figure 6 As shown, the result diagrams of the radial short-circuit force density of the low-voltage winding and the radial short-circuit force density of the high-voltage winding are respectively as shown in Figure 7 and Figure 8 As shown;

[0055] Step S08: Using the solid mechanics part of the finite element simulation software, obtain the deformation distribution of the transformer winding under the short circuit and calculate the winding deformation amount.

[0056] The curves of low voltage winding deformation and high voltage winding deformation are shown as follows: Figure 9 and Figure 10 As shown;

[0057] Step S09: Calculate the hoop tensile stress F according to the axial force, radial force and deformation of the transformer winding. CS and hoop compressive stress F CC , radial bending stress F of the conductor within the span between the braces rf , the axial bending stress F of the conductor within the span between radial pads af , radial critical instability strength F rc , radial electromotive force F re , radial pad compressive stress F pc And the compressive stress F of the transformer insulation end ring pe and other parameters;

[0058] Step S10: updating the transformer model in the finite element simulation software based on the deformation of the winding after the short circuit, calculating the current density using the short-circuit current simulated in step S05, obtaining the magnetic vector potential of the winding based on the current density, and then obtaining the magnetic induction intensity and magnetic flux, and finally calculating the inductance parameters, capacitance parameters, and frequency response curve of the winding after the short circuit based on the updated transformer model according to the magnetic flux and the short-circuit current;

[0059] Step S11: Import the updated parameters obtained in step S10 into the updated transformer model, repeat steps S05-S10, and obtain the radial and axial electromotive forces, deformation, and hoop tensile stress F of the winding under the transformer short-circuit condition. CS and hoop compressive stress F CC , radial bending stress F of the conductor within the span between the braces rf , the axial bending stress F of the conductor within the span between radial pads af , radial critical instability strength F rc , radial electromotive force F re , radial pad compressive stress F pc And the compressive stress F of the transformer insulation end ring pe , inductance parameters, capacitance parameters and frequency response curve after short circuit;

[0060] Step S12: Determine the transformer's short-circuit resistance according to the frequency response curve after short circuit. LF <0.6, at this time the winding is severely deformed and the transformer's ability to resist short circuits is insufficient. The short-circuit simulation analysis should be stopped immediately and the short-circuit cumulative deformation should be output.

[0061] Step S13: If 2.0>R LF ≥0.6 or R MF <1.0, at this time the winding deformation is not serious, and the relationship between the inductance parameters after the short circuit and the initial parameters should be further determined. Specifically:

[0062] Step S1301: If the inductance parameter after the short circuit does not change by more than ±2.0% compared to the initial parameter, it is considered that the transformer has not lost its short-circuit resistance after the short circuit, and step 11 is repeated to continue the short-circuit simulation analysis; if it exceeds ±2.0%, the relationship between the change of the capacitance parameter and the initial parameter should be further determined;

[0063] Step S1302: If the capacitance parameter changes by no more than ±2.0% compared to the initial parameter, it is considered that the transformer has not lost its short-circuit resistance after the short circuit, and step 11 is repeated to continue the short-circuit simulation analysis. If it exceeds ±2.0%, the relationship between the hoop tensile stress and the hoop compressive stress and the allowable stress should be further determined.

[0064] Step S14: If F CS≤0.9×F ps (Among them, F ps It refers to the tensile stress when the load continues to increase until the non-proportional stretch reaches 0.2% of the measured length. The tensile stress is related to the material properties of the winding and is determined according to the selected material. CC ≤0.35×F ps , it is considered that the transformer has not lost its short-circuit resistance after the short circuit, and step S11 is repeated to continue the short-circuit simulation analysis; if F CS >0.9×F ps or F CC >0.35×F ps , the relationship between the radial bending stress and the allowable stress of the conductor within the span between the supports should be further determined, specifically:

[0065] Step S1401: If F rf ≤0.9×F ps , it is considered that the transformer has not lost its short-circuit resistance after the short circuit, and step S11 is repeated to continue the short-circuit simulation analysis; if F rf >0.9×F ps , the relationship between the axial bending stress and the allowable stress of the conductor within the span between the radial pads should be further determined;

[0066] Step S1402: If F af ≤0.9×F ps , it is considered that the transformer has not lost its short-circuit resistance after the short circuit, and step S11 is repeated to continue the short-circuit simulation analysis; if F af >0.9×F ps , the safety factor S should be further determined;

[0067] Step S15: If S>2.5, it is considered that the transformer winding has not lost stability in this short circuit, and step S11 is repeated to continue the short circuit simulation analysis; if S≤2.5, the value of the radial pad compressive stress should be further determined, specifically:

[0068] Step S1501: If F pc ≤80MPa, it is considered that the transformer winding has not lost stability in this short circuit, and step S11 is repeated to continue the short circuit simulation analysis; if F pc >80MPa, the compressive stress of the transformer insulation end ring should be further determined.

[0069] Step S1502: If F pe ≤80MPa, it is considered that the transformer winding has not lost stability in this short circuit, and step S11 is repeated to continue the short circuit simulation analysis; if F pe>80MPa, it is considered that the transformer winding has lost stability in this short circuit and the transformer's short-circuit resistance is insufficient. The short-circuit simulation analysis should be stopped immediately and the short-circuit cumulative deformation should be output.

[0070] Step S16: If R LF ≥2.0 and R MF ≥1.0 and R HF ≥0.6, the winding is not deformed, and step S11 is repeated to continue the short-circuit simulation analysis;

[0071] Step S17: In view of the insufficient short-circuit resistance of the transformer, methods and measures for improving the short-circuit resistance of the transformer are proposed:

[0072] Step S1701: From the perspective of the transformer itself: Strengthen the radial short-circuit resistance: appropriately increase the number of struts and pads between the windings so that the windings are supported at multiple points, thereby strengthening the radial support strength of the windings; use high-strength epoxy fiberglass tubes or hard paper tubes to replace the weaker soft paper tubes to reduce the possible gaps between the windings; after the winding is severely deformed, it is necessary to consider replacing the entire winding and use wires with strong short-circuit resistance. For example, you can consider increasing the cross-sectional area of ​​the wire to increase the end stress of the winding. Before replacement, test the short-circuit resistance of the wire and make a choice based on comprehensive cost considerations. In addition, you can also use a wire tensioning device to increase the tightness of the winding. Strengthening axial short-circuit resistance: As with radial resistance, strengthening the conductor strength can also improve axial short-circuit resistance. Pay attention to ensuring that the heights of high- and low-voltage windings are consistent as much as possible. Consider using fastening devices to limit the height of the windings to within the allowable range of height error to avoid greater impact on the windings during a short circuit due to unbalanced ampere-turns of the windings. Use axial clamping devices to reduce the axial gap between the windings. Overall, the short-circuit impedance of the transformer can be appropriately increased to reduce the short-circuit current. This can be done by increasing the impedance of the transformer winding itself and by adding a reactor at the transformer outlet.

[0073] Step S1702: From the perspective of external factors: attention should be paid to possible collision problems of the transformer during movement and transportation; in addition, the transformer application environment should be kept dry to minimize the short circuit problem of the transformer caused by the influence of external factors.

[0074] As one or more implementation modes, the specific content of step S01 is: calculating electrical parameters such as resistance and inductance of the transformer.

[0075]

[0076] Among them, U e and I e is the rated voltage and rated current, Z kis the short-circuit impedance percentage. The rated voltage, rated current and short-circuit impedance percentage are all obtained from the transformer nameplate parameters.

[0077]

[0078] Calculate the transformer impedance value according to formula (1) and substitute it into formula (2) to obtain the value of L1+L2:

[0079]

[0080]

[0081] The inductance value L1 of the primary side of the transformer is obtained according to formula (3), and the value of the inductance L2 is calculated according to formula (4).

[0082] In one or more implementation methods, the specific content of step S02 is: using the Simulink module in MATLAB to build a transformer winding model under sudden short-circuit conditions, adding a three-phase grounding fault module in Simulink, and setting the short circuit between the faulty phases or between the faulty phase and the ground to simulate the short-circuit fault type;

[0083] As one or more implementation methods, the specific content of step S03 is: based on the dimensional parameters of the transformer, a three-dimensional simulation model of the transformer is established in the finite element simulation software, and in combination with actual conditions, a fixed constraint is applied to the lower end component of the model, a position constraint is applied to the upper end component of the model, and a specified acceleration is added to the entire model as the gravity acceleration -g_const.

[0084] As one or more implementation methods, the specific content of step S04 is: setting the low-voltage and high-voltage windings to copper materials under the material node in the finite element simulation software, and setting the magnetic core to lossless soft iron; adding the physical field as the magnetic field, adding Ampere's law under the physical field node, the corresponding domain is the magnetic core, and selecting the BH curve in the magnetization model list of the constitutive relationship; adding coil 1 and coil 2 nodes under the magnetic field node, setting coil 1 to the high-voltage winding with 508 turns, and coil 2 to the low-voltage winding with 32 turns; adding the study type as transient in study 1, the time unit as s, and the time step as range (0, 0.002, 0.2), indicating that the finite element simulation software calculation start time is 0s, the step size of each step is 0.002s, and the simulation ends at 0.2s; defining the grid size according to the research focus, customizing the maximum unit size of the winding part to 50mm, and predefining the magnetic core part as ultra-coarsening.

[0085] As one or more implementation methods, the specific content of step S05 is: setting the Simulink simulation start time to 0s, the short-circuit current start time to 0.02s, and the simulation end time to 0.2s, keeping the Simulink start time, simulation step size, and end time consistent with the finite element simulation software, and after the simulation is completed, obtaining the short-circuit current waveform.

[0086] In one or more embodiments, step S06 specifically includes exporting the short-circuit current data calculated by Simulink to generate an Excel spreadsheet, then defining an interpolation function in a finite element simulation software file to couple the short-circuit current data to achieve a co-simulation. After the simulation is complete, the finite element simulation software calculates the magnitude distribution of the short-circuit transient electromotive force acting on the transformer windings and core.

[0087] In one or more implementations, step S07 specifically includes: utilizing the plotting function in the magnetic field module of the finite element simulation software, selecting a one-dimensional plot group, and plotting the magnetic flux density component in the magnetic module under the magnetic field node, corresponding to radial and axial leakage flux density curves. Plotting the Lorentz force contribution component in the mechanical module under the magnetic field node, corresponding to radial and axial short-circuit electromotive force curves acting on the winding.

[0088] As one or more implementation methods, the specific content of step S08 is: using the drawing function in the solid mechanics module of the finite element simulation software, selecting the one-dimensional drawing group, drawing the total displacement in the displacement module under the solid mechanics node, and obtaining the deformation variable curves of the high-voltage and low-voltage windings.

[0089] As one or more implementation methods, the specific content of step S09 is: according to the axial force, radial force and deformation amount of the transformer winding, the hoop tensile stress F is calculated. CS and hoop compressive stress F CC , radial bending stress F of the conductor within the span between the braces rf , the axial bending stress F of the conductor within the span between radial pads af , radial critical instability strength F rc , radial electromotive force F re , radial pad compressive stress F pc And the compressive stress F of the transformer insulation end ring pe and other parameters.

[0090] As one or more implementation methods, the specific content of step S10 is: updating the transformer model in the finite element simulation software according to the deformation of the winding after the short circuit, first using the short-circuit current simulated in step S05 to calculate the current density, and then obtaining the magnetic vector potential of the winding through the current density.

[0091]

[0092] Where c is the electrical conductivity, ρ is the magnetic permeability, I s is the current density in the conductor.

[0093] After calculating the magnetic vector potential A in the winding according to formula (5), the curl of the magnetic vector potential A is calculated to obtain the magnetic induction intensity B.

[0094]

[0095] According to formula (7), Gauss's magnetic field law, the magnetic flux is obtained

[0096]

[0097] According to formula (8), the updated calculation of the inductance after the short circuit is completed.

[0098]

[0099] As one or more implementation methods, the specific content of step S11 is: importing the updated parameters obtained in step S10 into the updated transformer model, repeating steps S05-S10, and obtaining the radial and axial electromotive forces, deformation, and hoop tensile stress F of the winding under the transformer short-circuit condition. CS and hoop compressive stress F CC , radial bending stress F of the conductor within the span between the braces rf , the axial bending stress F of the conductor within the span between radial pads af , radial critical instability strength F rc , radial electromotive force F re , radial pad compressive stress F pc And the compressive stress F of the transformer insulation end ring pe , inductance parameters, capacitance parameters and frequency response curve after short circuit.

[0100] As one or more implementation methods, the specific content of step S12 is: according to the provisions of DL / T911-2016 "Frequency Response Analysis Method of Power Transformer Winding Deformation" on the deformation of power transformer windings, when R LF When <0.6, the winding is severely deformed; when 1.0>R LF ≥0.6 or R MF When <0.6, the winding is obviously deformed; when 2.0>R LF ≥1.0 or 0.6≤R MF When <1.0, the winding is slightly deformed; when R LF ≥2.0 and R MF ≥1.0 and R HFWhen the value is ≥0.6, the winding is normal. When the winding is severely deformed, the transformer's short-circuit resistance is insufficient. The short-circuit simulation analysis should be stopped immediately and the short-circuit cumulative deformation should be output.

[0101] As one or more implementation methods, the specific content of step S13 is: if 2.0>R LF ≥0.6 or R MF <1.0, at this time the winding deformation is not serious, and the relationship between the inductance parameters after the short circuit and the initial parameters should be further determined.

[0102] Furthermore, step S13 includes step S1301, the specific content of which is as follows: according to the provisions on the relative change of power transformer winding parameters in DL / T1093-2018 "Guidelines for Detection and Judgment of Power Transformer Winding Deformation by Reactance Method", the relative change ratio of the winding parameters of power transformers with a capacity of 100MVA and below and a voltage of 220kV and below should not be greater than ±2.0%, that is, the change of the inductance and capacitance parameters of the windings compared with the initial parameters should not exceed ±2.0%. If it does not exceed ±2.0%, it is considered that the transformer has not lost its short-circuit resistance, and step S11 is repeated to continue the short-circuit simulation analysis; if it exceeds ±2.0%, the severity of the winding deformation should be comprehensively analyzed in combination with the supplementary judgment results. Therefore, if the inductance parameters after the short circuit do not change by more than ±2.0% compared with the initial parameters, it is considered that the transformer has not lost its short-circuit resistance after the short circuit, and step S11 is repeated to continue the short-circuit simulation analysis; if it exceeds ±2.0%, the change relationship between the capacitance parameters and the initial parameters should be further determined.

[0103] The step S13 also includes a step S1302. The specific content of step S1302 is: if the capacitance parameter changes by no more than ±2.0% compared with the initial parameter, it is considered that the transformer has not lost its short-circuit resistance after the short circuit, and step 11 is repeated to continue the short-circuit simulation analysis; if it exceeds ±2.0%, the relationship between the hoop tensile stress and the hoop compressive stress and the allowable stress should be further determined.

[0104] As one or more implementation methods, the specific content of step S14 is: according to the provisions of GB1094.5-2018 "Power Transformer Part 5: Ability to Withstand Short Circuit" on the mechanical parameters of power transformer windings, if F CS ≤0.9×F ps And F CC ≤0.35×F ps , it is considered that the transformer can withstand the dynamic stability effect of the short circuit; otherwise, a comprehensive analysis should be conducted in combination with the supplementary results. ps It refers to the tensile stress when the load continues to increase until the non-proportional stretch reaches 0.2% of the measured length. The tensile stress is related to the material properties of the winding and is determined according to the selected material. Therefore, if FCS ≤0.9×F ps And F CC ≤0.35×F ps , it is considered that the transformer has not lost its short-circuit resistance after the short circuit, and step S11 is repeated to continue the short-circuit simulation analysis; if F CS >0.9×F ps or F CC >0.35×F ps , the relationship between the radial bending stress and the allowable stress of the conductor within the span between the supports should be further determined.

[0105] The step S14 further includes step S1401, the specific content of step S1401 is: if F rf ≤0.9×F ps , it is considered that the transformer has not lost its short-circuit resistance after the short circuit, and step S11 is repeated to continue the short-circuit simulation analysis; if F rf >0.9×F ps , the relationship between the axial bending stress and the allowable stress of the conductor within the span between the radial pads should be further determined.

[0106] The step S14 further includes step S1402, the specific content of step S1402 is: if F af ≤0.9×F ps , it is considered that the transformer has not lost its short-circuit resistance after the short circuit, and step S11 is repeated to continue the short-circuit simulation analysis; if F af >0.9×F ps , the safety factor S should be further determined.

[0107] As one or more implementation methods, the specific content of step S15 is: if the radial critical instability strength F of the winding rc Greater than the radial electromotive force F during short circuit re , proving that the winding's mechanical strength can withstand the force generated by this short circuit, meaning the winding did not lose mechanical stability during this short circuit. However, due to limitations in the assembly process, there are gaps when assembling the transformer body insulation, and some braces cannot play a supporting role, resulting in a critical buckling strength lower than the calculated value. Therefore, the safety factor S is selected as:

[0108]

[0109] The value of S depends on the material and structural properties of the conductor, and a threshold of 2.5 is selected. Therefore, if S > 2.5, it is assumed that the transformer winding has not lost stability during this short circuit, and step S11 is repeated to continue the short-circuit simulation analysis. If S ≤ 2.5, the value of the radial spacer compressive stress should be further determined.

[0110] The step S15 further includes step S1501, the specific content of step S1501 is: if F pc ≤80MPa, it is considered that the transformer winding has not lost stability in this short circuit, and step S11 is repeated to continue the short circuit simulation analysis; if F pc >80MPa, the compressive stress of the transformer insulation end ring should be further determined.

[0111] The step S15 further includes step S1502, the specific content of step S1502 is: if F pe ≤80MPa, it is considered that the transformer winding has not lost stability in this short circuit, and step S11 is repeated to continue the short circuit simulation analysis; if F pe >80MPa, it is considered that the transformer winding has lost stability in this short circuit and the transformer's short-circuit resistance is insufficient. The short-circuit simulation analysis should be stopped immediately and the short-circuit cumulative deformation should be output.

[0112] As one or more implementation methods, the specific content of step S16 is: when R LF ≥2.0 and R MF ≥1.0 and R HF When ≥0.6, the winding is normal and not deformed, and step S11 is repeated to continue the short-circuit simulation analysis.

[0113] This embodiment addresses the shortcomings of previous criteria for determining transformer winding deformation severity and short-circuit resistance, which were determined solely based on experience and consideration of limiting factors, and therefore could not serve as standard limits, thereby failing to accurately determine the transformer's short-circuit resistance. This embodiment employs a combined diagnostic method using multiple criteria to determine the transformer's short-circuit resistance under short-circuit conditions, providing a theoretical basis for accurately assessing the transformer's short-circuit resistance and proposing improvement measures for insufficient short-circuit resistance. Furthermore, leveraging Simulink's ability to accurately calculate the short-circuit current of the transformer winding during a sudden short circuit, the short-circuit current calculation results from Simulink are coupled to finite element simulation software to analyze the changes in the transformer's structural characteristics under the influence of short-circuit electrodynamic forces.

[0114] Although the above describes the specific implementation methods of the present disclosure in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present disclosure. Those skilled in the art should understand that on the basis of the technical solution of the present disclosure, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present disclosure.

Claims

1. A method for evaluating transformer short-circuit resistance, characterized in that: The following steps are involved: Obtain the electrical parameters and finite element simulation model of the transformer; Based on the obtained electrical parameters, a transformer short-circuit model is constructed to simulate the transformer's sudden short-circuit fault; Based on the finite element simulation model and the transformer short-circuit model, the short-circuit current of the transformer, the deformation distribution of the transformer winding, and the transformer winding deformation are calculated, and the transformer short-circuit model is updated in real time to obtain a frequency response curve of the transformer, specifically: By using the solid mechanics part of the finite element simulation software, the deformation distribution of the transformer winding under the short circuit is obtained and the winding deformation is calculated. Based on the axial force, radial force and deformation of the transformer winding, the hoop tensile stress and hoop compressive stress, the radial bending stress of the conductor in the span between the stays, the axial bending stress of the conductor in the span between the radial spacers, the radial critical instability strength, the radial electromotive force, the radial spacer compressive stress and the compressive stress parameters of the transformer insulation end ring are calculated; The finite element simulation model is updated based on the deformation of the winding after the short circuit. The current density is calculated using the short-circuit current simulated by the transformer short-circuit model. The magnetic vector potential of the winding is obtained from the current density, and then the magnetic induction intensity and magnetic flux are obtained. Finally, based on the magnetic flux and short-circuit current, the inductance parameters, capacitance parameters and frequency response curve of the winding after the short circuit are calculated based on the updated finite element simulation model. The transformer's short-circuit resistance is determined based on the frequency response curve after short circuit, the hoop tensile stress, the hoop compressive stress, the radial bending stress of the conductors in the span between the stays, the axial bending stress of the conductors in the span between the radial pads, the radial critical instability strength, the radial electromotive force, the radial pad compressive stress, and the compressive stress parameters of the transformer insulation end ring. If the transformer's short-circuit resistance is insufficient, the short-circuit simulation analysis is immediately stopped and the short-circuit cumulative deformation is output. If the transformer has not lost its short-circuit resistance, the finite element simulation model and the transformer simulation model are updated according to the updated parameters calculated after the short circuit, and the short-circuit simulation analysis is continued.

2. A method for evaluating transformer short-circuit resistance as claimed in claim 1, characterized in that: The process of obtaining the finite element simulation model is as follows: based on the dimensional parameters of the transformer, a three-dimensional simulation model of the transformer is established in the finite element simulation software, a fixed constraint is applied to the lower end component of the three-dimensional simulation model of the transformer, a position constraint is applied to the upper end component of the three-dimensional simulation model of the transformer, and a specified acceleration is added to the three-dimensional simulation model of the transformer.

3. A method for evaluating transformer short-circuit resistance as claimed in claim 1, characterized in that: The electrical parameters include at least the resistance and inductance of the transformer.

4. A method for evaluating transformer short-circuit resistance as claimed in claim 1, characterized in that: use MATLAB in Simulink The module builds a transformer winding model under sudden short circuit conditions. Simulink Add a three-phase grounding fault module to simulate a transformer short circuit fault by setting the short circuit between the faulty phases or between the faulty phase and the ground.

5. A method for evaluating transformer short-circuit resistance as claimed in claim 1, characterized in that: In the process of evaluating the short-circuit resistance of the transformer according to the obtained frequency response curve, when the correlation coefficient of the frequency response curve in the low frequency band is less than the first threshold value, the transformer winding is severely deformed; when the correlation coefficient of the frequency response curve in the low frequency band is between the first threshold value and the second threshold value, or the correlation coefficient of the frequency response curve in the mid-frequency band is less than the first threshold value, the transformer winding is obviously deformed; When the correlation coefficient of the frequency response curve in the low frequency band is between the second threshold and the third threshold, and the correlation coefficient of the frequency response curve in the mid-frequency band is between the first threshold and the second threshold, the transformer winding is slightly deformed; when the correlation coefficient of the frequency response curve in the low frequency band is greater than the third threshold, and the correlation coefficient of the frequency response curve in the mid-frequency band is greater than the second threshold, and the correlation coefficient of the frequency response curve in the high frequency band is greater than the first threshold, the transformer winding is normal.

6. A method for evaluating transformer short-circuit resistance as claimed in claim 5, characterized in that: If the correlation coefficient of the frequency response curve in the low frequency band is between the first threshold and the third threshold or the correlation coefficient of the frequency response curve in the mid-frequency band is less than the second threshold, the transformer winding deformation is not serious. In this case, it is necessary to determine the transformer's short-circuit resistance by judging the relationship between the change in the inductance parameters after the short circuit and the initial parameters.

7. A method for evaluating transformer short-circuit resistance as claimed in claim 6, characterized in that: If the inductance parameter after short circuit does not change by more than the set value compared with the initial parameter, the transformer has not lost its short circuit resistance after short circuit, and the short circuit simulation analysis continues; if it exceeds the set value, the relationship between the change of the capacitance parameter and the initial parameter is determined; If the capacitance parameter does not change by more than the set value compared with the initial parameter, the transformer has not lost its short-circuit resistance after the short circuit, and the short-circuit simulation analysis continues; if it exceeds the set value, the relationship between the hoop tensile stress and hoop compressive stress and the allowable stress is determined.

8. A method for evaluating transformer short-circuit resistance as claimed in claim 7, characterized in that: If the hoop tensile stress is not greater than the second stress threshold, and the hoop compressive stress is not greater than the first stress threshold, the transformer has not lost its short-circuit resistance after the short circuit, and the short-circuit simulation analysis continues; If the hoop tensile stress is greater than the second stress threshold, or the hoop compressive stress is greater than the first stress threshold, then the relationship between the radial bending stress of the conductor within the span between the stays and the allowable stress needs to be determined.

9. A method for evaluating transformer short-circuit resistance as claimed in claim 8, characterized in that: If the radial bending stress of the conductors within the span between the stays is not greater than the second stress threshold, the transformer has not lost its short-circuit resistance after the short circuit, and the short-circuit simulation analysis can continue. If the radial bending stress of the conductors within the span between the stays is greater than the second stress threshold, the relationship between the axial bending stress of the conductors within the span between the radial spacers and the allowable stress must be determined. If the axial bending stress of the conductor within the span between the radial spacers is not greater than the second stress threshold, the transformer has not lost its short-circuit resistance after the short circuit, and the short-circuit simulation analysis continues. If the axial bending stress of the conductor within the span between the radial spacers is greater than the second stress threshold, the safety factor is determined.

10. A method for evaluating transformer short-circuit resistance as claimed in claim 9, characterized in that: If the safety factor is greater than the safety factor threshold, the transformer winding does not lose stability during the short circuit, and the short circuit simulation analysis continues; if the safety factor is not greater than the safety factor threshold, the value of the radial pad compressive stress is determined.

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