An equivalent method for thermal conductivity in temperature field analysis of Roebel transposed conductors

Abstract

The present invention discloses an equivalent method for thermal conductivity in temperature field analysis of a Roebel transposed conductor. First, the periodic structure of the transposed conductor (a single sintered flat copper wire) is separated as a typical representative volume element, and simplified physical models (a series model and a parallel model) are established to obtain its equivalent thermal conductivity. Subsequently, the thermal conductivity of the transposed conductor in the main direction is derived using the series model and the parallel model, respectively, based on the specific structure of the transposed conductor. The present invention considers both series and parallel thermal diffusion between different materials in the Roebel transposed conductor, and takes into account the combined influence of both series and parallel thermal diffusion on the thermal conductivity. This method is closer to the actual structure and has higher accuracy.

Description

Technical Field

[0001] The invention belongs to the field of temperature field analysis, and in particular relates to an equivalent method for thermal conductivity in temperature field analysis of a Roebel transposed conductor. Background Art

[0002] In the manufacturing of motors and power transformers, in addition to the trend toward higher voltages and larger capacities, recent developments have significantly improved transformer performance, with significant results. These efforts include increasing efficiency and reducing losses, increasing power density, and lowering vibration and noise levels. For certain specialized motors (such as high-speed motors and those with high magnetic loads) or power transformers, the use of transposed conductors in winding coils can significantly reduce circulating and eddy current losses, improving operational reliability and lifespan. The smaller the diameter of the transposed conductor strands, the more beneficial this is for reducing AC losses.

[0003] Transposed conductors are enameled copper wires that are continuously transposed during the stranding process. They typically consist of a copper conductor, insulating varnish, an insulating layer, and an impregnating varnish. They are a composite structure with anisotropic physical properties. When analyzing coil temperature fields, detailed modeling of the transposed conductors—that is, establishing the detailed strand structure—inevitably results in a finite element analysis model with a large number of meshes, posing challenges to computer hardware and analysis time.

[0004] There are various approaches to analyzing the temperature field of transposed coils. A relatively simple approach for transposed conductors is to treat them as a single, isotropic copper conductor. This approach offers advantages in terms of simple modeling and material assignment, as well as fast computation. However, since it ignores the anisotropy caused by the combination of dissimilar materials, its material equivalent parameters differ significantly from the actual material properties, making it inaccurate in assessing the actual temperature distribution of the transposed conductor. Furthermore, some researchers have used composite material micromechanics homogenization analysis methods to derive the equivalent thermal conductivity of the transposed conductor in the principal direction. These analytical methods often simplify the physical model to a simple parallel or series model, failing to properly account for the influence of longitudinal heat diffusion between different materials on the thermal conductivity, resulting in a certain degree of error. However, heat flow within a Roebel transposed conductor involves both series and parallel heat diffusion between different materials. Therefore, the equivalent parameters derived using simple parallel or series models do not reflect the actual structure, impacting the accuracy of simulation results. Therefore, in the derivation of the thermal conductivity of the actual Roebel transposed conductor, the joint influence of the series and parallel conditions on the thermal conductivity should be taken into account. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing method for equivalent thermal conductivity of transposed conductors in temperature field analysis of motors or transformers, and to provide an equivalent method for thermal conductivity in temperature field analysis of Roebel transposed conductors.

[0006] The technical solution adopted by the present invention to solve the technical problem is: an equivalent method for thermal conductivity in Roebel transposed conductor temperature field analysis, comprising the following steps:

[0007] Step 1, preparation process of Roebel transposed conductor: First, copper rods are drawn into a flat copper wire with a width × thickness (wmm × bmm). Then, the wmm × bmm flat copper wire is sintered with a polyimide film with a double-sided thickness of tmm to obtain a w1mm × b1mm sintered flat copper wire, where w1 = w + t and b1 = b + t. Finally, n w1mm × b1mm sintered flat copper wires are transposed to obtain a Roebel transposed conductor.

[0008] Step 2: Calculate the volume fractions of the flat copper wire and polyimide film based on their thermal conductivity and dimensions including width, height, and single-side thickness of the film. The Roebel transposed conductor separates the periodic structure of the flat copper wire, i.e., a single flat copper wire, as a typical representative volume element. The volume fraction of the flat copper wire is defined as: w1 = w f +w m , V f +V m =1, where subscripts c, f, and m represent sintered flat copper wire, flat copper wire, and polyimide film, respectively. V f ,V m are the volume fractions of the flat copper wire and polyimide film, A f ,A c ,A m are the areas of flat copper wire, sintered flat copper wire and polyimide film respectively;

[0009] Step 3: Establish physical models (series model and parallel model) of a single sintered flat copper wire. Based on the mechanical parameters and volume fraction obtained in step 2, derive the equivalent thermal conductivity expressions of the sintered flat copper wire under the series model and the parallel model, respectively.

[0010] The equivalent thermal conductivity coefficients under the series-parallel physical model are: c A c =λ f A f +λ m A m , Where δ is the conductor thickness (m), A is the conductor cross-sectional area (m 2 ), λ is the thermal conductivity of the conductor (W / mK);

[0011] The equivalent thermal conductivity coefficients under the series-parallel physical model are: c A c =λ f A f +λ m A m , Where δ f ,δ c ,δ m are the thicknesses (m) of the flat copper wire, sintered flat copper wire, and polyimide film, respectively. f ,λ c ,λ m The thermal conductivity (W / mK) of flat copper wire, sintered flat copper wire and polyimide film respectively;

[0012] The equivalent thermal conductivity of a single sintered flat copper wire in the length, width and thickness directions are

[0013]

[0014]

[0015]

[0016] Where λ epoxy ,λ cu are the thermal conductivity of polyimide film and flat copper wire respectively;

[0017] The equivalent thermal conductivity of the Roebel transposed conductor in the length, width and thickness directions are

[0018]

[0019]

[0020]

[0021] Step 4: For the specific structure of the Roebel transposed conductor, based on the obtained specifications and dimensions of the Roebel transposed conductor, including the number of turns of the sintered flat copper wire, the width and height of the transposed conductor, and the single-side thickness of the outer insulation of the transposed conductor, a series model and a parallel model of the Roebel transposed conductor along the three main directions of length, width, and thickness are established respectively. Based on the thermal conductivity expressions of the sintered flat copper wire under the series model and the parallel model obtained in Step 3, the equivalent thermal conductivity of the Roebel transposed conductor along the three main directions of length, width, and thickness is derived using the series model and the parallel model respectively.

[0022] Furthermore, in step 1, 19 sintered flat copper wires with a size of w1mm×b1mm are transposed to obtain a Roebel transposed conductor with a size of Wmm×Bmm.

[0023] Furthermore, in step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide films are defined as I and III, and the flat copper wire is defined as II. When the three parts I, II, and III form a parallel relationship, the formula λ is derived from the parallel model of a single sintered copper flat wire. c A c =λ f A f +λ m A m The equivalent thermal conductivity in the 1-axis direction is λ1=λ I V I +λ II V II +λ III V III ,in

[0024]

[0025] λ I =λ III =λ Expoy ,λ II =λ Cu

[0026] Substituting into the above formula we can get

[0027] Furthermore, in step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide films are I and III, and the flat copper wire is II. When parts I, II, and III form a parallel relationship and parts II is formed in series by parts A, B, and C, the equivalent thermal conductivity in the 2-axis direction can be obtained from the parallel model of a single sintered flat copper wire:

[0028]

[0029] Furthermore, in step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide films are I and III, and the flat copper wire is II. When parts I, II, and III form a parallel relationship and parts II is formed in series by parts A, B, and C, the equivalent thermal conductivity in the three-axis direction can be obtained from the parallel model of a single sintered flat copper wire:

[0030]

[0031] Furthermore, in the step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide film is I, and the flat copper wires are II to X. When I to X form a parallel relationship, I is formed by parts A, B, and C in series, and II to X are formed by parts D and E in parallel, the equivalent thermal conductivity of the Roebel transposed conductor in the axis 1 direction can be obtained from the parallel model of a single sintered flat copper wire:

[0032] Furthermore, in the step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide film is I, and the flat copper wires are II to X. When I to X form a parallel relationship, I is formed by parts A, B, and C in series, and II to X are formed by parts D and E in series, the equivalent thermal conductivity of the Roebel transposed conductor in the 2-axis direction can be obtained from the parallel model of a single sintered flat copper wire:

[0033] Furthermore, in step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide film is I, and the flat copper wires are II to X. When I to X form a parallel relationship, I is formed by parts A, B, and C in series, and II to X are formed by parts D and E in series, the equivalent thermal conductivity of the Roebel transposed conductor in the three-axis direction can be obtained from the parallel model of a single sintered flat copper wire:

[0034] The beneficial effects of the present invention are as follows: the equivalent method disclosed in the present invention can consider both the series heat diffusion and the parallel heat diffusion between different materials in the heat flow in the Roebel transposed conductor, and can take into account the joint influence of the series heat diffusion and the parallel heat diffusion on the thermal conductivity coefficient. The equivalent method is closer to the actual structure and has a higher equivalent accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic structural diagram of a single sintered flat copper wire according to the present invention;

[0036] Figure 2 This is a schematic structural diagram of the Roebel transposed conductor of the present invention;

[0037] Figure 3 This is the heat conduction model of the sintered flat copper wire of the present invention;

[0038] Figure 3 (a) is the parallel heat conduction model of sintered flat copper wires of the present invention;

[0039] Figure 3 (b) is the heat conduction model of the sintered flat copper wire in series according to the present invention;

[0040] Figure 4 Schematic diagram of thermal resistance of the parallel heat conduction model of sintered flat copper wires according to the present invention;

[0041] Figure 5 Schematic diagram of thermal resistance of the sintered flat copper wire series thermal conduction model of the present invention;

[0042] Figure 6 Schematic diagram of the thermal resistance in one direction of a single sintered flat copper wire according to the present invention;

[0043] Figure 7 Schematic diagram of the thermal resistance in two directions of a single sintered flat copper wire of the present invention;

[0044] Figure 8 Schematic diagram of the thermal resistance in three directions of a single sintered flat copper wire of the present invention;

[0045] Figure 9 Schematic diagram of the thermal resistance of the Roebel transposed conductor in one direction of the present invention;

[0046] Figure 10 Schematic diagram of the thermal resistance of the Roebel transposed conductor in two directions according to the present invention;

[0047] Figure 11 Schematic diagram of the thermal resistance of the Roebel transposed conductor in three directions of the present invention. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0049] The present invention proposes an equivalent method for thermal conductivity in Roebel transposed conductor temperature field analysis. This method can take into account the combined effects of series and parallel connections on thermal conductivity. By using a homogenization method, the transposed conductor is simplified and defined as an anisotropic material. This simplifies the finite element analysis model of the transposed conductor, improves work efficiency, and enhances the accuracy of simulation analysis results. The steps are as follows.

[0050] Step 1, the preparation process of Roebel transposed conductor: first, the copper rod is prepared into a width × thickness (wmm × bmm) flat copper wire through a wire drawing process, and then the wmm × bmm flat copper wire is sintered with a polyimide film. The thickness of the polyimide film on both sides is tmm, and a w1mm × b1mm sintered flat copper wire is obtained, where w1=w+t, b1=b+t. Finally, n w1mm × b1mm sintered flat copper wires are transposed to obtain a Roebel transposed conductor. Figure 1 As shown in the figure, 19 w1mm×b1mm sintered flat copper wires are transposed to obtain a Wmm×Bmm Roebel transposed conductor (W=2×w1, B=10×b1). It should be noted that it is assumed that there is no gap between the sintered flat copper wires during transposition, that is, there is only a polyimide film with a thickness of tmm between the flat copper wires. To simplify the analysis, the length direction of the Roebel transposed conductor is defined as axis 1, the width direction of the Roebel transposed conductor is defined as axis 2, and the thickness direction of the Roebel transposed conductor is defined as axis 3, as shown in the figure. Figure 2 shown.

[0051] Step 2: Calculate the volume fraction of the flat copper wire and the paint film based on the thermal conductivity of the single sintered flat copper wire and the paint film and the dimensions including the width, height, and thickness of the paint film on one side.

[0052] The Roebel transposed conductor periodic structure (single sintered flat copper wire) is isolated as a typical representative volume element. For uniformity, the subscripts c, f, and m represent the sintered flat copper wire, flat copper wire, and polyimide film, respectively. The volume fraction of the sintered flat copper wire is defined as:

[0053] w1=w f +w m , V f +V m =1.

[0054] V f ,V m are the volume fractions of the flat copper wire and polyimide film, A f ,A c ,A m are the areas of flat copper wire, sintered flat copper wire and polyimide film respectively.

[0055] Step 3: Establish a physical model (series model and parallel model) of a single sintered flat copper wire. Based on the mechanical parameters and volume fraction obtained in step 2, derive the equivalent thermal conductivity expressions of the sintered flat copper wire under the series model and parallel model, respectively.

[0056] For the above-mentioned Roebel transposed conductor, according to its spatial structure, there are two models for analyzing and calculating its representative volume element sintered flat copper wire: Type II, parallel heat conduction model; Type II, series heat conduction model. Among them, the representative volume element sintered flat copper wire is a parallel heat conduction model in the 1-axis direction, such as Figure 3 (a) shows the representative volume element sintered flat copper wire in the 2-axis and 3-axis directions as a series heat conduction model, as shown in Figure 3 (b) shown.

[0057] for Figure 3 (a) The parallel heat conduction model described, the thermal resistance diagram of the sintered flat copper wire parallel heat conduction model is shown in Figure 4 As shown. According to Fourier's law, the heat generated by the conductor is

[0058] Due to the formula λ c A c =λ f A f +λ m A m The expression is similar to Ohm's law I=UR in electricity, so the thermal resistance R of a homogeneous conductor can be written as Where δ is the conductor thickness (m), A is the conductor cross-sectional area (m 2 ), λ is the thermal conductivity of the conductor (W / mK). Figure 4 The thermal resistance of the parallel heat conduction model is derived similarly to the resistance formula in physics, so we have

[0059] Will Bring in Then there is

[0060] For the parallel model, due to δ c =δ f =δ m , then λ c A c =λ f A f +λ m A m .

[0061] Like the parallel heat conduction model, the thermal resistance method can still be used to describe the heat conduction series model of sintered flat copper wire. Figure 3 (b) The series heat conduction model described, the thermal resistance diagram of the sintered flat copper wire series heat conduction model is shown in Figure 5 Its derivation is similar to the resistance formula in physics, so R c =R f +R m .

[0062] Will Bring in R c =R f +R m Then there is

[0063] For the series model, since A c =A f =A m , then

[0064] Where δ f ,δ c ,δ m are the thicknesses of the flat copper wire, sintered flat copper wire, and polyimide film (m); λ f ,λ c ,λ m These are the thermal conductivity coefficients (W / mK) of flat copper wire, sintered flat copper wire, and polyimide film, respectively.

[0065] Equivalent thermal conductivity of a single sintered copper flat wire in the 1-axis direction

[0066] Its equivalent thermal conductivity in the 2-axis direction is

[0067] Its equivalent thermal conductivity in the three-axis direction

[0068] Where λ epoxy ,λ cu are the thermal conductivity of polyimide film and flat copper wire, respectively.

[0069] Equivalent thermal conductivity of Roebel transposed conductor in the 1-axis direction

[0070]

[0071] Its equivalent thermal conductivity in the 2-axis direction

[0072] Its equivalent thermal conductivity in the three-axis direction

[0073] Step 4: For the specific structure of the Roebel transposed conductor, based on the obtained specifications and dimensions of the Roebel transposed conductor, including the number of turns of the sintered flat copper wire, the width and height of the transposed conductor, and the single-side thickness of the outer insulation of the transposed conductor, a series model and a parallel model are established along the three main directions of length, width, and thickness. Based on the thermal conductivity expressions of the sintered flat copper wire under the series model and the parallel model obtained in Step 3 and the obtained specifications and dimensions of the Roebel transposed conductor, the equivalent thermal conductivity of the Roebel transposed conductor along the three main directions of length, width, and thickness is derived using the series model and the parallel model.

[0074] for Figure 3 (a) The parallel heat conduction model described, the thermal resistance diagram of the sintered flat copper wire parallel heat conduction model is shown in Figure 4 As shown. According to Fourier's law, the heat generated by the conductor is

[0075] Due to the formula λ c A c =λ f A f +λ m A m The expression is similar to Ohm's law I=UR in electricity, so the thermal resistance R of a homogeneous conductor can be written as Where δ is the conductor thickness (m), A is the conductor cross-sectional area (m 2 ), λ is the thermal conductivity of the conductor (W / mK). Figure 4 The thermal resistance of the parallel heat conduction model is derived similarly to the resistance formula in physics, so we have

[0076] Will Bring in Then there is

[0077] For the parallel model, due to δ c =δ f =δ m , then λ c A c =λ f A f +λ m A m .

[0078] Like the parallel heat conduction model, the thermal resistance method can still be used to describe the heat conduction series model of sintered flat copper wire. Figure 3 (b) The series heat conduction model described, the thermal resistance diagram of the sintered flat copper wire series heat conduction model is shown in Figure 5 Its derivation is similar to the resistance formula in physics, so R c =Rf +R m .

[0079] Will Bring in R c =R f +R m Then there is

[0080] For the series model, since A c =A f =A m , then

[0081] According to the characteristics of a single sintered flat copper wire when it is subjected to heat flow in the 1-axis direction, it can still be simplified into three parts: I, II, and III. They exist in the form of "parallel connection". The schematic diagram of the thermal resistance of a single sintered flat copper wire in the 1-axis direction is shown as follows: Figure 6 shown.

[0082] Formula λ is derived from the parallel model c A c =λ f A f +λ m A m The equivalent thermal conductivity in the 1-axis direction is:

[0083] λ1=λ I V I +λ II V II +λ III V III ,

[0084] in Substituting into the above formula we can get:

[0085]

[0086] According to the characteristics of a single sintered flat copper wire when it is subjected to heat flow in the two-axis direction, it can still be simplified into three parts: I, II, and III. They exist in the form of "parallel connection", among which II is "series connection" of three parts: A, B, and C. That is, a single sintered flat copper wire adopts a parallel-series model in the two-axis direction. Its thermal resistance diagram is shown as follows Figure 7 shown.

[0087] The derivation process is the same as that in the 1-axis direction, and the equivalent thermal conductivity in the 2-axis direction is:

[0088]

[0089] According to the characteristics of a single sintered flat copper wire when it is subjected to heat flow in the three-axis direction, it can still be simplified into three parts: I, II, and III. They exist in the form of "parallel connection", among which II is "series connection" of three parts: A, B, and C. That is, a single sintered flat copper wire adopts a parallel-series model in the three-axis direction. Its thermal resistance diagram is shown as follows Figure 8 shown.

[0090] The derivation process is the same as that in the 1-axis direction, and the equivalent thermal conductivity in the 3-axis direction is:

[0091]

[0092] against Figure 2 The characteristics of the Robel transposed conductor shown in the figure when subjected to heat flow in the 1-axis direction can still be simplified into ten parts: I, II, III, IV, V, VI, VII, VIII, IX, and X. These ten parts exist in a "parallel" form, where I is composed of three parts "in parallel" of A, B, and C, and nine parts II, III, ... X are composed of two parts "in parallel" of D and E. The thermal resistance diagram is shown below. Figure 9 shown.

[0093] The derivation process is the same as that in the 1-axis direction, and the equivalent thermal conductivity in the 1-axis direction is:

[0094]

[0095] against Figure 2 The characteristics of the Robel transposed conductor shown in the figure when subjected to heat flow in the two axial directions can still be simplified into ten parts: I, II, III, IV, V, VI, VII, VIII, IX, and X. These ten parts exist in a "parallel" form, where I is composed of three parts A, B, and C in "series", and the nine parts II, III, ... X are composed of two parts D and E in "series". The thermal resistance diagram is shown below. Figure 10 shown.

[0096] The derivation process is the same as that in the 1-axis direction, and the equivalent thermal conductivity in the 2-axis direction is:

[0097]

[0098] against Figure 2 The characteristics of the Robel transposed conductor shown in the figure when subjected to heat flow in the three axial directions can still be simplified into ten parts: I, II, III, IV, V, VI, VII, VIII, IX, and X. These ten parts exist in a "parallel" form, where I is composed of three parts A, B, and C in "series", and nine parts II, III, ... X are composed of two parts D and E in "series". The thermal resistance diagram is shown below. Figure 11 shown.

[0099] The derivation process is the same as that in the 1-axis direction, and the equivalent thermal conductivity in the 3-axis direction is:

[0100]

[0101] Based on the above three formulas and the relevant dimensions of the transposed conductor, the equivalent thermal conductivity of the Roebel transposed conductor along the three main directions of length, width and thickness can be derived.

[0102] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

Claims

1. An equivalent method for thermal conductivity in Roebel transposed conductor temperature field analysis, characterized by: Includes the following steps Step 1: First, a copper rod is drawn into a flat copper wire with a width of w mm and a thickness of b mm. The flat copper wire is then sintered with a polyimide film with a thickness of t mm to obtain a sintered flat copper wire with a size of w1 mm × b1 mm, where w1 = w + t and b1 = b + t. Finally, n sintered flat copper wires are transposed to obtain a Roebel transposed conductor. Step 2: Calculate the volume fraction of the flat copper wire and polyimide film based on the mechanical parameters and dimensions of the single sintered flat copper wire and polyimide film, including width, height, and thickness of the paint film on one side: Wherein, subscripts c, f, and m represent sintered flat copper wire, flat copper wire, and polyimide film, respectively. f ,V m are the volume fractions of the flat copper wire and polyimide film, A f ,A c ,A m are the areas of flat copper wire, sintered flat copper wire and polyimide film respectively; Step 3: Establish a series-parallel physical model of a single sintered flat copper wire, and derive the equivalent thermal conductivity expression of the sintered flat copper wire under the physical model based on the thermal conductivity and volume fraction; The equivalent thermal conductivity coefficients under the series-parallel physical model are: Where δ f ,δ c ,δ m are the thickness of the flat copper wire, sintered flat copper wire and polyimide film, respectively, f ,λ c ,λ m are the thermal conductivity coefficients of flat copper wire, sintered flat copper wire and polyimide film respectively; The equivalent thermal conductivity of a single sintered flat copper wire in the length, width and thickness directions are Where λ epoxy ,λ cu are the thermal conductivity of polyimide film and flat copper wire respectively; The equivalent thermal conductivity of the Roebel transposed conductor in the length, width and thickness directions are Step 4: Based on the specifications of the Roebel transposed conductor and the dimensions including the number of turns of the sintered flat copper wire, the width and height of the transposed conductor, and the thickness of the single side of the outer insulation of the transposed conductor, a series-parallel physical model of the Roebel transposed conductor is established along the three main directions of length, width, and thickness. Based on the thermal conductivity expression of the sintered flat copper wire under the series-parallel physical model, the equivalent thermal conductivity of the Roebel transposed conductor along the length, width, and thickness directions is derived.

2. The equivalent method for thermal conductivity in Roebel transposed conductor temperature field analysis according to claim 1, characterized in that: In step 1, 19 sintered flat copper wires with a size of w1mm×b1mm are transposed to obtain a Roebel transposed conductor with a size of Wmm×Bmm.

3. The equivalent method for thermal conductivity in Roebel transposed conductor temperature field analysis according to claim 1 or 2, characterized in that: In step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide films are defined as I and III, and the flat copper wire is defined as II. When the three parts I, II, and III form a parallel relationship, the equivalent thermal conductivity in the axis 1 direction can be obtained from the parallel model of a single sintered copper flat wire as λ1=λ I V I +λ II V II +λ III V III ,in l I =λ III =λ Expoy ,l II =λ Cu Substituting into the above formula we can get 4. The equivalent method for thermal conductivity in Roebel transposed conductor temperature field analysis according to claim 3, characterized in that: In step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide films are I and III, and the flat copper wire is II. When parts I, II, and III form a parallel relationship and parts II is formed in series by parts A, B, and C, the equivalent thermal conductivity in the 2-axis direction can be obtained from the parallel model of a single sintered flat copper wire:

5. The equivalent method for thermal conductivity in Roebel transposed conductor temperature field analysis according to claim 3, characterized in that: In step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide films are I and III, and the flat copper wire is II. When parts I, II, and III form a parallel relationship and parts II is formed in series by parts A, B, and C, the equivalent thermal conductivity in the three-axis direction can be obtained from the parallel model of a single sintered flat copper wire:

6. The equivalent method for thermal conductivity in Roebel transposed conductor temperature field analysis according to claim 1 or 2, characterized in that: In the step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide film is I, and the flat copper wires are II to X. When I to X form a parallel relationship, I is formed by parts A, B, and C in series, and II to X are formed by parts D and E in parallel, the equivalent thermal conductivity of the Roebel transposed conductor in the axis 1 direction can be obtained from the parallel model of a single sintered flat copper wire:

7. The equivalent method for thermal conductivity in Roebel transposed conductor temperature field analysis according to claim 1 or 2, characterized in that: In the step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide film is I, and the flat copper wires are II to X. When I to X form a parallel relationship, I is formed by parts A, B, and C in series, and II to X are formed by parts D and E in series, the equivalent thermal conductivity of the Roebel transposed conductor in the 2-axis direction can be obtained from the parallel model of a single sintered flat copper wire:

8. The equivalent method for thermal conductivity in Roebel transposed conductor temperature field analysis according to claim 1 or 2, characterized in that: In step 3, the length, width, and thickness directions of the Roebel transposed conductor are defined as axis 1, axis 2, and axis 3, respectively. The polyimide film is I, and the flat copper wires are II to X. When I to X form a parallel relationship, I is formed by parts A, B, and C in series, and II to X are formed by parts D and E in series, the equivalent thermal conductivity of the Roebel transposed conductor in the three-axis direction can be obtained from the parallel model of a single sintered flat copper wire:

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