Method for improving anti-short-circuit capability of distribution transformer

Abstract

The invention relates to the technical field of transformers, and discloses a method for improving the anti-short-circuit capability of a distribution transformer, which can improve the anti-short-circuit capability of the distribution transformer and reduce the harm caused by a short-circuit fault. Based on the electrical parameters of the transformer, establishing an electromagnetic field simulation model of the transformer, simulating the condition when the transformer is short-circuited based on the established electromagnetic field simulation model, and performing finite element analysis on an electromagnetic field when the transformer is short-circuited to obtain simulated short-circuit stress on each part of the transformer; and the bearing capacity of each component of the transformer is verified through the simulated short-circuit stress borne by each part of the transformer, so that the weak part of the transformer is identified, and the weak part of the transformer is improved. According to the technical scheme, the anti-short-circuit capability of the distribution transformer can be effectively improved, and safe and stable operation of a power system is further guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of transformers, and particularly relates to a method for enhancing the short - circuit resistance of a distribution transformer. Background Art

[0002] With the continuous development of the power industry and the continuous expansion of the power grid scale, as the core equipment for power transmission and distribution, the stable and safe operation of distribution transformers plays a crucial role in ensuring the normal operation of the power system. However, during the actual operation process, distribution transformers often face various complex and changeable operating environments, especially the challenges of sudden events such as short - circuit faults, which pose severe requirements for the short - circuit resistance of distribution transformers.

[0003] When a short - circuit fault suddenly occurs in a transformer, a huge short - circuit current is generated in the winding. The interaction between the short - circuit current and the leakage magnetic field will generate a short - circuit electrodynamic force proportional to the square of the short - circuit current on the winding. Under the action of the huge electrodynamic force, if the structural components of the transformer cannot support and the insulation strength is low, that is, the short - circuit resistance is insufficient, the winding will be damaged. When a short - circuit fault occurs in the transformer, the deformation of the winding accumulates. The tolerance of the winding decreases under the impact of short - circuit, and it is more likely to appear bending deformation, and even the insulation is damaged, thus causing serious power accidents. Therefore, the present invention proposes a method for enhancing the short - circuit resistance of a distribution transformer to improve the short - circuit resistance of the distribution transformer. Summary of the Invention

[0004] The main object of the present invention is to provide a method for enhancing the short - circuit resistance of a distribution transformer to improve the short - circuit resistance of the distribution transformer.

[0005] The technical solution proposed by the present invention is as follows:

[0006] A method for enhancing the short - circuit resistance of a distribution transformer, comprising:

[0007] Based on the electrical parameters of the transformer, an electromagnetic field simulation model of the transformer is established;

[0008] Based on the electromagnetic field simulation model, simulate the situation when the transformer has a short - circuit, and perform finite - element analysis on the electromagnetic field when the transformer has a short - circuit to obtain the simulated short - circuit stresses received by each part of the transformer;

[0009] Verify the bearing capacity of each component of the transformer through the simulated short - circuit stresses received by each part of the transformer, so as to identify the weak parts of the transformer;

[0010] Improve the weak parts of the transformer.

[0011] Preferably, the step of establishing an electromagnetic field simulation model of the transformer based on the electrical parameters of the transformer includes:

[0012] Obtain the electrical parameters of the transformer, where the electrical parameters include: geometric dimensions;

[0013] Based on the electrical parameters of the transformer, establish a three-dimensional geometric model of the transformer, where the three-dimensional geometric model includes: a three-dimensional geometric model of the winding, a three-dimensional geometric model of the iron core, and a three-dimensional geometric model of the insulating layer;

[0014] Based on the three-dimensional geometric model of the transformer, establish an electromagnetic field simulation model when the transformer is operating.

[0015] Preferably, simulate the situation when the transformer undergoes a short circuit based on the electromagnetic field simulation model, and perform a finite element analysis on the electromagnetic field when the transformer undergoes a short circuit to obtain the short-circuit stresses received by each part of the transformer, including:

[0016] Adopt the equivalent circuit of a single-phase double-winding transformer and analyze according to the three-phase short-circuit situation at the outgoing line terminals of the transformer to obtain the simulated short-circuit stresses received by each part of the transformer, where the simulated short-circuit stresses include the short-circuit axial stress received by the winding, and the short-circuit radial stresses on the outer coil and the inner coil.

[0017] Preferably, the step of adopting the equivalent circuit of a single-phase double-winding transformer and analyzing according to the three-phase short-circuit situation at the outgoing line terminals of the transformer to obtain the simulated short-circuit stresses received by each part of the transformer includes:

[0018] Calculate the short-circuit axial stress received by the winding, including:

[0019] Divide the winding into several winding regions in a centrosymmetric manner;

[0020] Calculate the ampere-turn imbalance between the high-voltage winding and the low-voltage winding in each winding region, and draw an ampere-turn distribution diagram in combination with the winding height of the corresponding winding region;

[0021] Divide the winding into several leakage magnetic groups according to the ampere-turn distribution diagram, and calculate the axial electrodynamic force of each leakage magnetic group;

[0022] Superimpose the axial electrodynamic forces of each leakage magnetic group to obtain the maximum axial electrodynamic force in the winding;

[0023] Calculate the stress generated by the maximum axial electrodynamic force, and use the stress generated by the maximum axial electrodynamic force as the short-circuit axial stress received by the winding.

[0024] Preferably, after calculating the short-circuit axial stress received by the winding, it further includes:

[0025] Calculate the short-circuit radial stresses on the outer coil and the inner coil respectively, including:

[0026] Calculate the total stress on the outer coil wire:

[0027] σ w = σ a + σ1;

[0028] Wherein, σ w is the total stress on the outer coil wire, σ a is the bending stress caused by the axial force, and σ1 is the tensile stress caused by the radial force on the wire;

[0029] Calculate the total stress on the inner coil wire:

[0030] σ n = σ a + σ2 + σ3;

[0031] Wherein, σ n is the total stress on the inner coil wire, σ2 is the compressive stress caused by the radial force on the wire, and σ3 is the bending stress caused by the radial force on the wire;

[0032] Take the total stress on the outer coil wire as the short - circuit radial stress of the outer coil, and take the total stress on the inner coil wire as the short - circuit radial stress of the inner coil.

[0033] Preferably, verifying the bearing capacity of each component of the transformer by the simulated short - circuit stress received by each part of the transformer, so as to identify the weak parts of the transformer, includes:

[0034] Compare the design strength value of the component bearing the short - circuit stress with the magnitude of the simulated short - circuit stress borne by the component;

[0035] If the design strength value of the component is greater than the simulated short - circuit stress borne by the component, determine that the component is a safe part of the transformer;

[0036] If the design strength value of the component is less than or equal to the simulated short - circuit stress borne by the component, determine that the component is a weak part of the transformer.

[0037] Preferably, improving the weak parts of the transformer includes:

[0038] Improving the weak parts of the transformer from the direction of electromagnetic characteristics includes:

[0039] Adopt a high - permeability iron core;

[0040] Increase the wire gauge used for the coil;

[0041] Adjust the coil ampere - turn distribution to improve the coil ampere - turn balance;

[0042] Increase the number and width of the coil axial spacers.

[0043] Preferably, improving the weak parts of the transformer further includes:

[0044] Improving the weak parts of the transformer from the mechanical property direction, including:

[0045] Adopting a pull-screw type pressing ring structure for the coil;

[0046] Increasing the section bending modulus of the coil pressing plate;

[0047] Increasing the contact area between the coil pressing plate and the coil;

[0048] During the process of winding the coil, winding the wire tightly, and applying a pre-tightening force after the iron core is sleeved with the coil. Preferably, based on the electromagnetic field simulation model, simulating the situation when the transformer short-circuits, performing a finite element analysis on the electromagnetic field when the transformer short-circuits to obtain the short-circuit stress received by each part of the transformer, and then further including:

[0049] Obtaining the simulated temperature of the transformer based on the electromagnetic field simulation model, and judging whether the simulated temperature of the transformer exceeds the safe operating temperature;

[0050] If so, improving the heat dissipation of the transformer.

[0051] Preferably, after improving the weak parts of the transformer, it further includes:

[0052] Judging whether the short-circuit resistance ability of the improved transformer meets the preset safety requirements, where the preset safety requirements are that the design strength values of all components of the transformer are greater than the simulated short-circuit stress borne by the components;

[0053] If not, execute the steps of establishing an electromagnetic field simulation model of the transformer based on the electrical parameters of the transformer and subsequent steps.

[0054] Through the above technical solutions, the following beneficial effects can be achieved:

[0055] The method for improving the short - circuit resistance of a distribution transformer proposed by the present invention can simulate the short - circuit stresses borne by each part of the transformer during a short - circuit through the established electromagnetic field simulation model, determine the weak links of the transformer based on the short - circuit stresses borne by each part, and improve the weak links of the transformer. In specific applications, based on the electrical parameters of the transformer, an electromagnetic field simulation model of the transformer is established through simulation software. The situation when the transformer undergoes a short - circuit is simulated through the electromagnetic field simulation model, and a finite - element analysis is performed on the electromagnetic field when the transformer undergoes a short - circuit, so as to obtain the short - circuit stresses received by each part of the transformer. Furthermore, by comparing the short - circuit stresses received by each part of the transformer with the bearing capacity of each component of the transformer, the weak parts of the transformer are identified. Finally, the weak parts of the transformer are improved to enhance the short - circuit resistance of the transformer. In summary, the method for improving the short - circuit resistance of a distribution transformer proposed by the present invention can effectively improve the short - circuit resistance of the distribution transformer, which is beneficial to ensuring the safe and stable operation of the power system. Brief Description of the Drawings

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0057] Figure 1 It is a flowchart of the steps of the method for improving the short - circuit resistance of a distribution transformer of the present invention;

[0058] Figure 2 It is an equivalent circuit diagram of a single - phase double - winding transformer of the method for improving the short - circuit resistance of a distribution transformer of the present invention.

[0059] The realization of the objectives, functional characteristics, and advantages of the present invention will be further described in conjunction with the embodiments and with reference to the drawings. Detailed Embodiments

[0060] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0061] It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the attached drawings). If the specific posture changes, the directional indications will also change accordingly.

[0062] In addition, in the present invention, descriptions such as "first" and "second" are only for descriptive purposes and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0063] In the present invention, unless otherwise clearly specified and limited, terms such as "connection" and "fixation" should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and can be the internal communication of two components or the interaction relationship between two components, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0064] In addition, the technical solutions between various embodiments of the present invention can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0065] The present invention provides a method for enhancing the short-circuit resistance of a distribution transformer.

[0066] Please refer to Figures 1 to 2 , in the first embodiment of a method for enhancing the short-circuit resistance of a distribution transformer proposed by the present invention, this embodiment includes the following steps:

[0067] Step S110: Based on the electrical parameters of the transformer, establish an electromagnetic field simulation model of the transformer;

[0068] To establish the electromagnetic field simulation model, simulation software is required. The simulation software can specifically be: ANSYS Maxwell, COMSOL Multiphysics, Opera, JMAG, etc. After establishing the electromagnetic field simulation model, it is also necessary to simulate working conditions, such as voltage, resistance, etc., and refine the mesh near the key parts (such as windings, iron cores) of the electromagnetic field simulation model to improve the calculation accuracy.

[0069] Step S120: Based on the electromagnetic field simulation model, simulate the situation when the transformer undergoes a short circuit, and perform finite element analysis on the electromagnetic field when the transformer undergoes a short circuit to obtain the simulated short-circuit stresses received by each part of the transformer.

[0070] Specifically, the edge element method is used to analyze the electromagnetic field model. The edge element method has stronger solving ability and higher accuracy for time-harmonic fields and transient fields. For inhomogeneous media, the tangential continuity of its vectors is automatically satisfied without additional constraints.

[0071] Specifically, obtaining the short-circuit stresses received by each part of the transformer includes short-circuit current calculation, short-circuit electrodynamic force calculation, and short-circuit stress calculation, which can be specifically obtained through a solver.

[0072] Step S130: Verify the bearing capacity of each component of the transformer through the simulated short-circuit stresses received by each part of the transformer, so as to identify the weak parts of the transformer.

[0073] Specifically, compare the short-circuit stresses received by each part of the transformer with the design strength values of the components. The weak parts of the transformer show structural damage or deformation when a short circuit occurs.

[0074] Step S140: Improve the weak parts of the transformer.

[0075] Specifically, improvements can be made from two directions: electromagnetic characteristics and mechanical characteristics. From the direction of electromagnetic characteristics, the anti-short-circuit ability of the transformer is improved by improving the internal leakage magnetic field distribution to reduce the induced magnetic field strength of the leakage magnetic field, thereby reducing the short-circuit electrodynamic force. From the direction of mechanical characteristics, by calculating the mechanical strength requirements of the relevant components that bear the short-circuit electrodynamic force, using appropriate materials and frame structures, and taking necessary reinforcement measures for the weak areas, the anti-short-circuit ability of the transformer is improved.

[0076] The method for improving the short-circuit resistance of a distribution transformer proposed by the present invention can simulate the short-circuit stresses borne by various parts of the transformer during short-circuit through the established electromagnetic field simulation model, judge the weak links of the transformer based on the short-circuit stresses borne by various parts, and improve the weak links of the transformer. When specifically applied, based on the electrical parameters of the transformer, an electromagnetic field simulation model of the transformer is established through simulation software, the situation when the transformer undergoes a short circuit is simulated through the electromagnetic field simulation model, and a finite element analysis is performed on the battery field when the transformer undergoes a short circuit, so as to obtain the short-circuit stresses received by various parts of the transformer. Furthermore, by comparing the short-circuit stresses received by various parts of the transformer with the bearing capacities of various components of the transformer, the weak parts of the transformer are identified, and finally the weak parts of the transformer are improved to enhance the short-circuit resistance of the transformer. In summary, the method for improving the short-circuit resistance of a distribution transformer proposed by the present invention can effectively improve the short-circuit resistance of the distribution transformer, which is beneficial to ensuring the safe and stable operation of the power system.

[0077] In the second embodiment of a method for improving the short-circuit resistance of a distribution transformer proposed by the present invention, based on the first embodiment, step S110 includes the following steps:

[0078] Step S210: Obtain the electrical parameters of the transformer, where the electrical parameters include: geometric dimensions;

[0079] Specifically, the geometric dimensions include: winding geometric dimensions, core dimensions, number of winding turns, coil shape, insulation layer structure, etc. Further, the electrical parameters also include winding materials, resistance and inductance of the transformer, etc.

[0080] Step S220: Based on the electrical parameters of the transformer, establish a three-dimensional geometric model of the transformer, where the three-dimensional geometric model includes: a three-dimensional geometric model of the winding, a three-dimensional geometric model of the core, and a three-dimensional geometric model of the insulation layer;

[0081] Step S230: Based on the three-dimensional geometric model of the transformer, establish an electromagnetic field simulation model when the transformer is operating.

[0082] In the third embodiment of a method for improving the short-circuit resistance of a distribution transformer proposed by the present invention, based on the first embodiment, step S120 includes the following steps:

[0083] Step 310: Adopt the equivalent circuit of a single-phase double-winding transformer and analyze according to the three-phase short-circuit situation at the transformer outlet end to obtain the simulated short-circuit stresses received by various parts of the transformer, where the simulated short-circuit stresses include the short-circuit axial stress received by the winding, and the short-circuit radial stresses on the outer coil and the inner coil.

[0084] Please refer to Figure 2 , U1 is the primary side phase voltage, LK are the leakage inductance coefficients of the high- and low-voltage coils; R K is the equivalent resistance of the high- and low-voltage coils, and i K is the short-circuit current.

[0085] Specifically, analyzing the transient process of the current in a sudden short circuit using the equivalent circuit of a single-phase double-winding transformer can simplify the calculation. The three-phase short-circuit situation is the most severe among several short-circuit situations, with the largest short-circuit current. Calculating the short-circuit current according to the three-phase short-circuit situation at the transformer outlet terminal, obtaining the short-circuit stress, and designing and checking the short-circuit withstand capacity of the distribution transformer based on this can provide a certain safety margin.

[0086] In the fourth embodiment of a method for improving the short-circuit resistance of a distribution transformer proposed in the present invention, based on the third embodiment, step S310 includes the following steps:

[0087] Step S410: Calculate the short-circuit axial stress on the winding, including the following steps:

[0088] Step S411: Divide the winding into several winding regions in a centrosymmetric manner;

[0089] Specifically, when dividing the winding regions, it should be divided according to the actual structure of the winding and the principle that the regions are as equal in height as possible and the ampere-turn distribution is uniform.

[0090] Step S412: Calculate the ampere-turn imbalance between the high-voltage winding and the low-voltage winding in each winding region, and draw an ampere-turn distribution diagram in combination with the winding height of the corresponding winding region;

[0091] Step S413: Divide the winding into several leakage magnetic groups according to the ampere-turn distribution diagram, and calculate the axial electrodynamic force of each leakage magnetic group;

[0092] Specifically, the calculation formula for the axial electrodynamic force is:

[0093] F s = B m lI

[0094] where F s is the axial electrodynamic force under the instantaneous short-circuit current, B m is the average leakage magnetic intensity of the m-th ampere-turn partition, l is the effective length of the winding, and I is the instantaneous short-circuit current.

[0095] Step S414: Superimpose the axial electrodynamic forces of each leakage magnetic group to obtain the maximum axial electrodynamic force in the winding;

[0096] Specifically, the calculation formula for the maximum axial electrodynamic force is:

[0097] F max = ∑F s

[0098] Among them, F max is the maximum axial electrodynamic force.

[0099] Step S415: Calculate the stress generated by the maximum axial electrodynamic force, and use the stress generated by the maximum axial electrodynamic force as the short - circuit axial stress.

[0100] Specifically, the calculation formula for the short - circuit axial stress is:

[0101]

[0102] Among them, σ y is the short - circuit axial stress, and Z is the section modulus.

[0103] Specifically, the short - circuit axial force pulls the coil upward, jacks up the upper pressure plate, or presses the coil downward, generating pressure on the lower pressure plate. The axial force is conducted through the coil ends to the pressure plate, yoke, and core clamping parts. When the axial force exceeds the mechanical strength of any structural member during its conduction, it will cause irreversible deformation of the structural member.

[0104] In the fifth embodiment of a method for improving the short - circuit resistance of a distribution transformer proposed by the present invention, based on the fourth embodiment, after step S410, the following steps are further included:

[0105] Step S510: Calculate the short - circuit radial stresses on the outer coil and the inner coil respectively, including the following steps:

[0106] Step 511: Calculate the total stress on the outer - coil conductor:

[0107] σ w =σ a +σ1;

[0108] Among them, σ w is the total stress on the outer - coil conductor, σ a is the bending stress caused by the axial force, approximately 0, and σ1 is the tensile stress caused by the radial force on the conductor;

[0109] Specifically, σ w should satisfy σ w ≤0.9R P0.2 , where R P0.2 is the stress when the plastic elongation rate of the conductor is 0.2%.

[0110] Step S512: Calculate the total stress on the inner - coil conductor:

[0111] σ n =σ a +σ2 + σ3;

[0112] Among them, σn σ is the total stress on the inner coil wire, σ2 is the compressive stress caused by the radial force on the wire, and σ3 is the bending stress caused by the radial force on the wire;

[0113] Specifically, σ n should satisfy σ n ≤0.9R P0.2 , where R P0.2 is the stress when the plastic elongation of the wire is 0.2%.

[0114] Step S513: Take the total stress on the outer coil wire as the short-circuit radial stress of the outer coil, and take the total stress on the inner coil wire as the short-circuit radial stress of the inner coil.

[0115] Specifically, the distribution characteristic of the radial force on the winding is that: in the horizontal direction, the closer to the main oil duct, the greater the force; in the vertical direction, the closer to the middle of the winding, the greater the force. The short-circuit radial force squeezes the inner coil inward and stretches the outer coil outward. Under the action of the compressive stress, the inner coil may have deformation failures such as free warping, forced warping, and spiral deformation. Under the action of the tensile stress, the outer coil expands outward, deforming the coil, damaging the inter-turn insulation, and even breaking the wire severely in severe cases.

[0116] In the sixth embodiment of a method for improving the short-circuit resistance of a distribution transformer proposed by the present invention, based on the fifth embodiment, step S130 includes the following steps:

[0117] Step S610: Compare the design strength value of the component bearing the short-circuit stress with the magnitude of the simulated short-circuit stress borne by the component;

[0118] Step S620: If the design strength value of the component is greater than the simulated short-circuit stress borne by the component, determine that the component is a safe part of the transformer;

[0119] Step S630: If the design strength value of the component is less than or equal to the simulated short-circuit stress borne by the component, determine that the component is a weak part of the transformer.

[0120] Specifically, the design strength value of the component should be greater than the short-circuit stress borne by the component, and a certain redundancy design is also required to ensure safety and reliability.

[0121] In the seventh embodiment of a method for improving the short-circuit resistance of a distribution transformer proposed by the present invention, based on the sixth embodiment, step S140 includes the following steps:

[0122] Step S710: Improve the weak part of the transformer from the direction of electromagnetic characteristics, including the following steps:

[0123] Step S711: Adopt a high magnetic permeability iron core;

[0124] Specifically, the high magnetic permeability core can reduce the leakage flux, thereby reducing the electromotive force generated by the leakage flux.

[0125] Step S712: increasing the wire gauge used in the coil;

[0126] Specifically, increasing the wire gauge used in the coil can reduce the short-circuit current density, thereby reducing the short-circuit electromotive force. At the same time, increasing the wire gauge used in the coil is beneficial to the thermal stability of the transformer during short circuit and prevents the coil from burning out.

[0127] Step S713: adjusting the coil ampere-turn distribution to improve the coil ampere-turn balance;

[0128] Specifically, the ampere-turn distribution of the coil should be as uniform as possible to reduce the ampere-turn area of the leakage magnetic group, and at the same time, the distribution position of the high-voltage coil taps should be adjusted. It is best to place the taps symmetrically in the middle or at the ends of the winding.

[0129] Step S714: Increase the number and width of the coil axial struts.

[0130] Specifically, the more stays are used and the wider they are, the less likely forced buckling failure will occur.

[0131] This embodiment provides measures for improving the transformer from the perspective of electromagnetic characteristics, and there is no particular order for the above steps.

[0132] In an eighth embodiment of a method for improving the short-circuit resistance of a distribution transformer proposed by the present invention, based on the seventh embodiment, step S140 further includes the following steps:

[0133] Step S810: improving the weak parts of the transformer from the perspective of mechanical properties, including the following steps:

[0134] Step S811: adopting a screw-type coil pressing structure for the coil;

[0135] Specifically, the pressure plate of the screw-type pressure ring structure has a support beam, and the maximum bending stress of the pressure plate caused by the axial electric force is significantly reduced compared with the pressure nail type pressure ring structure.

[0136] Step S812: increasing the cross-sectional bending modulus of the coil pressing plate;

[0137] Specifically, without affecting heat dissipation, the contact area between the pressure plate and the coil should be increased, and the use of an integral pressure plate (non-independent pad) is better than the use of dispersed independent pads.

[0138] Step S813: increasing the contact area between the coil pressing plate and the coil;

[0139] Specifically, increasing the contact area between the coil pressing plate and the coil can improve mechanical stability, enhance heat dissipation performance, and ensure that the coil does not displace during operation due to vibration or electromagnetic force.

[0140] Step S814: Tightly wind the wire during the coil winding process and apply a pre-tightening force after the iron core is sleeved with the coil.

[0141] Specifically, tightly winding the wire and applying a pre-tightening force can ensure accurate geometric dimensions of the coil, reduce electromagnetic interference, further improve the mechanical strength of the coil, and prevent the coil from displacing during operation.

[0142] This embodiment provides measures for improving the transformer from the mechanical characteristics aspect, and there is no sequence requirement for the above steps.

[0143] In the ninth embodiment of a method for improving the short-circuit resistance of a distribution transformer proposed by the present invention, based on the first embodiment, after step S120, the following steps are further included:

[0144] Step S910: Obtain the simulated temperature of the transformer based on the electromagnetic field simulation model and determine whether the simulated temperature of the transformer exceeds the safe operating temperature;

[0145] Specifically, use computer-aided engineering (CAE) software for thermal simulation analysis.

[0146] Step S920: If so, improve the heat dissipation of the transformer.

[0147] The Joule heat generated by the short-circuit current cannot be dissipated in a short time, which will cause the winding to quickly heat up, possibly causing irreversible thermal damage to the inter-turn insulation or inter-layer insulation of the winding, and further developing into an internal short circuit of the winding, or even burning out the coil. Specifically, the improvement methods can be: optimizing design parameters, such as optimizing the wiring method of the winding, using a larger wire gauge, etc.; improving material properties, such as using high thermal conductivity materials, etc., using a cooling system, such as an air-cooling system, a water-cooling system, etc.

[0148] In the tenth embodiment of a method for improving the short-circuit resistance of a distribution transformer proposed by the present invention, based on the eighth embodiment, after step S140, the following steps are further included.

[0149] Step S1010: Determine whether the short-circuit resistance of the improved transformer meets the preset safety requirements, where the preset safety requirements are that the design strength values of all components of the transformer are greater than the simulated short-circuit stress borne by the components;

[0150] Specifically, a certain margin should be left when improving the transformer. The improved transformer should meet the requirements of not generating structural damage and deformation during short circuit. Further, the improved transformer will not suffer thermal damage during short circuit.

[0151] Step S1020: If not, execute the steps of establishing an electromagnetic field simulation model of the transformer based on the electrical parameters of the transformer and subsequent steps.

[0152] The serial numbers of the embodiments of the present invention above are only for description and do not represent the superiority or inferiority of the embodiments.

[0153] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made under the concept of the present invention by using the content of the specification and drawings of the present invention, or direct / indirect application in other related technical fields is included in the patent protection scope of the present invention.

Claims

1. A method for enhancing the short-circuit withstand capacity of a distribution transformer, characterized in that, Including: Based on the electrical parameters of the transformer, establish an electromagnetic field simulation model of the transformer; Based on the electromagnetic field simulation model, simulate the situation when the transformer has a short circuit, and perform finite element analysis on the electromagnetic field when the transformer has a short circuit to obtain the simulated short-circuit stress on each part of the transformer; Verify the bearing capacity of each component of the transformer through the simulated short-circuit stress on each part of the transformer, so as to identify the weak parts of the transformer; Improve the weak parts of the transformer.

2. The method for enhancing the short-circuit withstand capacity of a distribution transformer according to claim 1, wherein The establishing of the electromagnetic field simulation model of the transformer based on the electrical parameters of the transformer includes: Obtain the electrical parameters of the transformer, where the electrical parameters include: geometric dimensions; Based on the electrical parameters of the transformer, establish a three-dimensional geometric model of the transformer, where the three-dimensional geometric model includes: a three-dimensional geometric model of the winding, a three-dimensional geometric model of the iron core, and a three-dimensional geometric model of the insulating layer; Based on the three-dimensional geometric model of the transformer, establish an electromagnetic field simulation model when the transformer is working.

3. The method for enhancing the short-circuit withstand capacity of a distribution transformer according to claim 1, characterized in that, The simulating the situation when the transformer has a short circuit based on the electromagnetic field simulation model and performing finite element analysis on the electromagnetic field when the transformer has a short circuit to obtain the short-circuit stress on each part of the transformer includes: Adopt the equivalent circuit of a single-phase double-winding transformer and analyze according to the three-phase short-circuit situation at the outgoing line end of the transformer to obtain the simulated short-circuit stress on each part of the transformer, where the simulated short-circuit stress includes the short-circuit axial stress on the winding and the short-circuit radial stress on the outer coil and the inner coil.

4. The method for enhancing the short-circuit withstand capacity of a distribution transformer according to claim 3, characterized in that The adopting of the equivalent circuit of a single-phase double-winding transformer and analyzing according to the three-phase short-circuit situation at the outgoing line end of the transformer to obtain the simulated short-circuit stress on each part of the transformer includes: Calculate the short-circuit axial stress on the winding, including: Divide the winding into several winding regions in a centrosymmetric manner; Calculate the ampere-turn imbalance between the high-voltage winding and the low-voltage winding in each winding region, and draw an ampere-turn distribution diagram in combination with the winding height of the corresponding winding region; Divide the winding into several leakage magnetic groups according to the ampere-turn distribution diagram, and calculate the axial electrodynamic force of each leakage magnetic group; Superimpose the axial electrodynamic forces of each leakage magnetic group to obtain the maximum axial electrodynamic force in the winding; Calculate the stress generated by the maximum axial electrodynamic force, and take the stress generated by the maximum axial electrodynamic force as the short-circuit axial stress on the winding.

5. The method for enhancing the short-circuit withstand capacity of a distribution transformer according to claim 4, wherein After calculating the short-circuit axial stress on the winding, it further includes: Calculate the short-circuit radial stress on the outer coil and the inner coil respectively, including: Calculate the total stress on the outer coil wire: σ w = σ a + σ1; Among them, σ w is the total stress on the outer coil wire, σ a is the bending stress caused by the axial force, and σ1 is the tensile stress caused by the radial force on the wire; Calculate the total stress on the inner coil wire: σ n = σ a + σ2 + σ3; Among them, σ n is the total stress on the inner coil wire, σ2 is the compressive stress caused by the radial force on the wire, and σ3 is the bending stress caused by the radial force on the wire; Take the total stress on the outer coil wire as the short-circuit radial stress of the outer coil, and take the total stress on the inner coil wire as the short-circuit radial stress of the inner coil.

6. The method for enhancing the short-circuit withstand capacity of a distribution transformer according to claim 5, characterized in that The verifying the bearing capacity of each component of the transformer through the simulated short-circuit stress on each part of the transformer and thus identifying the weak parts of the transformer includes: Compare the design strength value of the component bearing the short-circuit stress with the magnitude of the simulated short-circuit stress borne by the component; If the design strength value of the component is greater than the simulated short-circuit stress borne by the component, determine that the component is a safe part of the transformer; If the design strength value of a component is less than or equal to the simulated short-circuit stress borne by the component, determine that the component is a weak part of the transformer.

7. The method for enhancing the short-circuit withstand capacity of a distribution transformer according to claim 6, wherein The improvement of the weak part of the transformer includes: Improving the weak part of the transformer from the electromagnetic characteristic direction includes: Adopting a high magnetic permeability iron core; Increasing the wire gauge used for the coil; Adjusting the coil ampere-turn distribution to improve the coil ampere-turn balance; Increasing the number and width of the coil axial spacers.

8. The method for enhancing the short-circuit withstand capacity of a distribution transformer according to claim 7, characterized in that, The improvement of the weak part of the transformer further includes: Improving the weak part of the transformer from the mechanical characteristic direction includes: Adopting a pull-screw type pressing ring structure for the coil; Increasing the section bending modulus of the coil pressing plate; Increasing the contact area between the coil pressing plate and the coil; Tightly winding the wire during the coil winding process and applying a pre-tightening force after the iron core is sleeved with the coil.

9. The method for enhancing the short-circuit withstand capacity of a distribution transformer according to claim 1, wherein After performing the finite element analysis on the electromagnetic field when the transformer undergoes a short circuit based on the electromagnetic field simulation model to obtain the short-circuit stress received by each part of the transformer, the following steps are further included: Obtaining the simulated temperature of the transformer based on the electromagnetic field simulation model and determining whether the simulated temperature of the transformer exceeds the safe operating temperature; If so, perform heat dissipation improvement on the transformer.

10. The method for enhancing the short-circuit withstand ability of a distribution transformer according to claim 8, characterized in that, After the improvement of the weak part of the transformer, the following steps are further included: Judging whether the short-circuit resistance ability of the improved transformer meets the preset safety requirements, where the preset safety requirement is that the design strength value of all components of the transformer is greater than the simulated short-circuit stress borne by the components; If not, execute the steps of establishing the electromagnetic field simulation model of the transformer based on the electrical parameters of the transformer and the subsequent steps.

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