A method for calculating the multi-medium thermal resistance coefficient of a cable group at the bottom of a fan tower

Abstract

The application discloses a kind of wind turbine tower bottom cable group multi-medium thermal resistance coefficient calculation method, belong to power system technical field.Method includes: constructing cable geometric model;According to array arrangement, construct cable group two-dimensional laying model;Divide the multi-layer medium thermal resistance module of inner core conductor, conductor shield layer, insulating layer, insulating shield layer, filling layer, protective sleeve and external environment;Each medium layer thermal resistance is connected in series to construct original steady-state thermal circuit control equation, introduce mutual heat thermal resistance matrix to quantitatively characterize the mutual heat effect of cable group, correct the original equation to obtain target thermal circuit control equation;Mutual heat temperature is substituted into target equation and each layer loss and thermal resistance is corrected, finally each medium thermal resistance coefficient is iteratively solved.The present application overcomes the defect that the error of existing simplified model is large by layered modeling and mutual heat correction, is suitable for single and any array arrangement cable group, and improves the thermal resistance coefficient calculation precision.

Description

Technical Field

[0001] This invention relates to the field of power system technology, specifically to a method for calculating the multi-medium thermal resistance coefficient of the cable group at the bottom of a wind turbine tower. Background Technology

[0002] The cables at the bottom of the wind turbine tower play a crucial role in power transmission, and their current-carrying capacity calculation directly affects the safe operation of the cables and the reliability of the wind turbine.

[0003] The thermal resistivity of the medium is one of the core parameters for calculating the current carrying capacity of cables. Cables at the bottom of wind turbine towers are typically in a mixed environment involving multiple media, including the cable's own insulation layer, cable protection layer (PVC pipe), surrounding soil, concrete bedding, and air. The thermal resistance characteristics of these different media vary significantly. Furthermore, with the continuous increase in wind turbine capacity, the number of cables at the bottom outlet of the turbine is constantly increasing, leading to thermal interaction between the cables and complex heat conduction, convection, and radiation processes involving multiple media.

[0004] Existing calculation methods often rely on empirical values ​​or simplified models, neglecting details such as dielectric layering and contact thermal resistance, leading to significant errors in the thermal resistance coefficient and consequently affecting the accuracy of current-carrying capacity calculations. The IEC 60287 standard serves as the theoretical foundation and basis for temperature monitoring and current-carrying capacity calculation of power cable lines. Studies have shown significant differences between cable thermal resistance parameters calculated according to the IEC 60287 standard and actual estimated values. For directly buried cable groups, the mutual heating effect between cables is a crucial factor affecting the accuracy of temperature field calculations. The IEC standard establishes a cable thermal path model by defining the thermal resistance of the insulation layer and the outer sheath, and uses equivalent thermal resistance to simulate the environment surrounding the cable. However, current technologies lack dedicated dielectric thermal resistance coefficient calculation models for the special environment at the bottom of wind turbine towers, failing to accurately reflect the actual heat dissipation path and posing a risk of misjudgment of current-carrying capacity. Summary of the Invention

[0005] This invention provides a method for calculating the thermal resistance coefficient of a multi-medium cable group at the bottom of a wind turbine tower, which improves the accuracy of current carrying capacity calculation for cables at the bottom of the wind turbine tower and overcomes the shortcomings of existing technologies that result in large errors in thermal resistance coefficient calculation due to neglecting medium layering and mutual heat effects between cables.

[0006] The technical solution adopted by this invention to solve its technical problem is a method for calculating the multi-medium thermal resistance coefficient of the cable group at the bottom of a wind turbine tower, including the following steps: S1. Construction of cable geometric model: Construct a geometric model of the cable. The structure of the cable includes an inner core conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, a filler layer, and a protective sheath. S2. Construction of a two-dimensional cable group laying model: Based on the cable geometry model, the cable group is arranged in an array pattern, resulting in a two-dimensional laying model including... The geometric model in which This refers to the number of geometric models arranged horizontally. This refers to the number of geometric models arranged vertically, and also includes the horizontal spacing between the geometric models. and longitudinal spacing ; S3. Division of the multilayer dielectric thermal resistance module: Sequentially determine the dielectric layer as inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, protective sleeve and external environment, and input the basic parameters of each dielectric layer; S4. Construction of the steady-state thermal circuit model: The thermal resistance units of each dielectric layer are connected in series. Each dielectric layer in the steady-state thermal circuit model corresponds to a different thermal resistance layer, and the original thermal circuit control equations are constructed. Mutual heating and temperature rise exist between cables in the cable group, so lateral spacing is introduced. and longitudinal spacing and the number of arrangements The mutual thermal resistance is corrected, and the original thermal circuit control equation is corrected to obtain the corrected target thermal circuit control equation. S5. Calculate the thermal resistance coefficient: Substitute the temperature value considering the mutual heating effect into the modified target thermal path control equation, and simultaneously modify the thermal resistance and loss values ​​of each dielectric layer. Based on the modified target thermal path control equation, and according to the formula for the thickness and thermal resistance of each dielectric layer, calculate the thermal resistance coefficient of each dielectric layer. .

[0007] Furthermore, the construction of the cable geometric model described in step S1 includes the following steps: S101, by inspecting the cable type at the bottom of the wind turbine tower, the internal structure of the cable is determined; S102, based on its internal cable structure, constructs a cable geometric model consisting of an inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, and protective sheath.

[0008] Furthermore, the construction of the two-dimensional cable group laying model in step S2 includes the following steps: S201, Determine the cable arrangement and arrange the cable group according to the array arrangement method; S202, Confirmed This refers to the number of geometric models arranged horizontally. The number of geometric models arranged vertically, where and All are positive integers, and satisfy the requirement of the total number of cable groups. ; S203, Determine the transverse spacing of the cables and longitudinal spacing The horizontal spacing Defined as the distance between the centers of adjacent cables in the lateral direction, and the longitudinal spacing between them. Defined as the distance between the centers of adjacent cables in the longitudinal direction; S204, construct a two-dimensional cable group laying model based on the arrangement method, where the first... Line 1 The coordinates of the cable position in the column are ,in , , , ; S205, Calculate the actual distance between any two cables. For the first root cable and the root cable The distance is: .

[0009] Furthermore, the division of the multilayer dielectric thermal resistance module in step S3 includes the following steps: S301, Determine the dielectric layer module: Sequentially determine the dielectric layer as the inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, protective sleeve, and external environment; S302, Boundary Condition Setting Module: Set the external ambient temperature to... Input the thermal properties of the external medium, including the thermal conductivity of soil, the thermal conductivity of concrete, and the air convection heat transfer coefficient; S303, set the basic parameters of each medium: set the thickness of the inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, and protective sleeve, as well as the initial value of the thermal conductivity of each material.

[0010] Furthermore, the construction of the steady-state thermal circuit model described in step S4 includes the following steps: S401, Constructing the original thermal path control equations: Connecting the thermal resistance units of each dielectric layer in series, according to the steady-state heat conduction law, the following equations are obtained:

[0011] in, The temperature of the inner conductor. Temperature of the conductor shielding layer Temperature of the insulation layer Temperature of the insulating shielding layer. Temperature of the filler layer To protect the temperature of the sleeve, External ambient temperature; These are the loss values ​​corresponding to each layer; These are the thermal resistance values ​​of the conductor shielding layer, insulation layer, insulation shielding layer, filling layer, protective sleeve, and external environment, respectively, and the total thermal resistance. ; S402, Introducing mutual heat rise: For any two cables in a cable group, the first... root cable to the first The mutual thermal temperature rise of the two cables is:

[0012] in For the first root cable to the first The mutual thermal resistance of the two cables is calculated using the following formula: For the first root cable and the first The spacing between the cables is calculated using the following formula:

[0013] In the formula For the first The row and column positions of the cables in a two-dimensional arrangement. For the first The row and column positions of the cables in a two-dimensional arrangement. The spacing is for horizontal arrangement. The vertical spacing is the distance between the rows. The equivalent thermal conductivity of the external medium. The outer radius of the cable; For any i The total mutual heat rise of the cable. The sum of the mutual heat rise generated by all other cables within the area:

[0014] in This represents the total number of cables; S403, for Arrangement Establish a mutual heat rise matrix for the root cable:

[0015] matrix elements Defined as: when hour, ;when hour, , ; S404, Modify the thermal control equation to obtain the target thermal control equation:

[0016] in , .

[0017] Furthermore, step S5 involves calculating the thermal resistance coefficient, including the following steps: S501, substitute the temperature value considering the mutual heating effect into the modified target thermal path control equation, and at the same time modify the thermal resistance and loss values ​​of each dielectric layer: for For the cable group, first calculate the distance between any two cables according to step S205. :

[0018] Then construct the mutual heating thermal resistance matrix. The matrix elements are calculated according to the following rules: when hour, ; when hour, ; Next, calculate the mutual heat rise vector. :

[0019] in The loss vector of each cable ; S502, based on the modified target thermal path control equation, and according to the formulas for the thickness and thermal resistance of each dielectric layer, calculate the thermal resistance coefficient of each dielectric layer. ; The specific calculation steps are as follows: (1) Input parameters: Determine the cable geometry parameters, i.e., the thickness of each layer. Layout parameters ( ), ambient temperature Thermal conductivity of external medium ; (2) Calculate the cable spacing matrix: according to the formula Calculate the distance between all cable pairs; (3) Construct the mutual heating thermal resistance matrix: according to the formula and Build The mutual thermal resistance matrix; (4) Calculate the mutual heat rise: based on Calculate the mutual temperature rise of each cable; (5) Simultaneous thermal circuit equations: Substitute the mutual heat temperature rise into the modified thermal circuit control equations to obtain a complete set of equations that include the mutual heat effects. (6) Solving for the thermal resistance coefficient: Solve the system of equations using an iterative method, and apply the thermal resistance formula. Inversely calculate the thermal resistance coefficient of each dielectric layer ; For thickness, The thermal resistance coefficient, For heat dissipation area; (7) Verification and optimization: Substitute the calculated thermal resistance coefficient into the original equation for verification. If the error exceeds the threshold, readjust the parameters and perform iterative calculations until the accuracy requirements are met. S503, when , At this time, the mutual heating effect is zero. The thermal control equation degenerates into the steady-state heat conduction equation of a single cable; when or At this time, the mutual heating effect cannot be ignored. The thermal coupling effect between cables must be considered.

[0020] The beneficial effects of this invention are as follows: This invention meticulously divides the cable structure into seven dielectric layers: inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, protective sheath, and external environment. Each dielectric layer is assigned independent thermal resistance parameters, and a steady-state thermal path model is constructed according to the series relationship of heat flow through each layer. This overcomes the shortcomings of existing technologies that simplify cables to a single dielectric or ignore dielectric layering, and can more accurately reflect the actual heat dissipation path, significantly improving the calculation accuracy of the thermal resistance coefficient of each dielectric layer. Taking XLPE insulated cable as an example, through layered modeling, the independent thermal resistance coefficients of each layer, such as the conductor shielding layer, insulation layer, and insulation shielding layer, can be obtained separately, avoiding the cumulative error caused by using an equivalent uniform thermal resistance coefficient. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the present invention; Figure 2 This is a schematic diagram of the cable structure at the bottom of the wind turbine tower; Figure 3 Schematic diagram of the cable group laying method at the bottom of the wind turbine; Figure 4 Steady-state thermal equivalent circuit diagram. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0023] See Figure 1 The following is a detailed process for calculating the multi-medium thermal resistance coefficient of the cable group at the bottom of a wind turbine tower according to the present invention.

[0024] S1. Construction of the cable geometric model

[0025] like Figure 2 As shown, the structure of the cable at the bottom of the wind turbine tower includes an inner conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, a filler layer, and a protective sheath.

[0026] The internal structure of the cable is determined by inspecting the cable type at the bottom of the wind turbine tower. For example, for a certain type of YJV22-8.7 / 15kV-3×95 cross-linked polyethylene (XLPE) insulated power cable, its internal structure is as follows: Inner conductor: Copper conductor, cross-sectional area Approximately ; Conductor shielding layer: Semiconductor layer, approximately [thickness missing] ; Insulation layer: XLPE insulation, thickness approximately ; Insulating shielding layer: semi-conductive layer, approximately [thickness missing] ; Filler layer: Water-blocking tape and filler rope to fill gaps in the cable cores; Protective Case: PVC sheath, approximately [thickness missing] .

[0027] Based on this internal structure, a corresponding cable geometric model is constructed using computer-aided design software (such as AutoCAD or ANSYS). The dimensions of each layer are set according to the actual cable parameters and are used as geometric input for the subsequent thermal circuit model. In this embodiment, the cable outer radius... .

[0028] S2. Construction of a two-dimensional cable group laying model

[0029] like Figure 3As shown, the cable group is arranged in an array according to the cable geometry model.

[0030] The cable arrangement is determined, and the cable group is arranged according to an array pattern. In this embodiment, there are a total of 6 cables at the bottom of a wind turbine tower, arranged according to... (3 columns horizontally) Arranged in an array of 2 vertical rows, i.e. Determine the horizontal spacing. Longitudinal spacing The array arrangement includes, but is not limited to, regular arrangements such as horizontal "I" lines, vertical arrangements, and rectangular arrays. A two-dimensional cable group laying model is constructed based on the arrangement. Line 1 The coordinates of the cable position in the column are ,in: , .

[0031] Therefore, the planar coordinates of the six cables are as follows: Cable 1: ,coordinate ; Cable 2: ,coordinate ; Cable 3: ,coordinate ; Cable 4: ,coordinate ; Cable 5: ,coordinate ; Cable 6: ,coordinate .

[0032] For the 1 cable (location is) ) and the 1 cable (location is) ), its distance is:

[0033] For example, cable 1 ( ) and cable 5 ( The distance between them is:

[0034] The distance between each cable constitutes The distance matrix provides input for subsequent calculations of mutual thermal resistance.

[0035] S3, Division of Multilayer Dielectric Thermal Resistance Module

[0036] The dielectric layer is sequentially defined as the inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, protective sheath, and external environment.

[0037] S301. Determine the dielectric layer module: Sequentially determine the dielectric layer as the inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, protective sleeve, and external environment.

[0038] S302, Setting Boundary Conditions Module: Set the external ambient temperature to... Input the thermal properties of the external medium: Soil thermal conductivity: ; Thermal conductivity of concrete: ; Air convection heat transfer coefficient: .

[0039] Equivalent thermal conductivity of external medium Taking into account the combined effects of soil, concrete, and air, this example adopts... .

[0040] S303. Set the basic parameters for each medium: Set the initial values ​​of the thickness of the inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filler layer, and protective sleeve, as well as the initial values ​​of the thermal conductivity of each material. In this example: Inner conductor: copper, thermal conductivity Cross-sectional area ; Conductor shielding layer: Semiconducting material, thermal conductivity ,thickness ; Insulation layer: XLPE, thermal conductivity (Initial value, to be iterated and corrected), thickness ; Insulating shielding layer: semi-conductive material, thermal conductivity ,thickness ; Filler layer: Water-blocking tape, thermal conductivity ; Protective cover: PVC, thermal conductivity ,thickness .

[0041] S4. Construction of Steady-State Thermal Circuit Model

[0042] like Figure 4 As shown, the thermal resistance units of each dielectric layer are connected in series (heat flows through each layer in sequence), and each dielectric layer in the steady-state thermal circuit model corresponds to a different thermal resistance layer.

[0043] S401. Construct the original thermal circuit control equations

[0044] According to the steady-state heat conduction law: The original thermal circuit control equations were constructed.

[0045] With a certain cable (cable) For example, assuming the rated current... Under operating conditions, the temperature values ​​of each layer are obtained through measurement or calculation: Inner conductor temperature: ; Conductor shielding temperature: ; Insulation layer temperature: ; Temperature of insulating shielding layer: ; Filler layer temperature: ; Protective sleeve temperature: ; External ambient temperature: .

[0046] The loss values ​​for each layer are calculated according to the IEC 60287 standard: Conductor loss ; Shielding layer loss Insulation layer loss The loss angle is calculated from the tangent of the dielectric loss angle.

[0047] The original thermal control equations are as follows:

[0048] in, The temperature of the inner conductor. Temperature of the conductor shielding layer Temperature of the insulation layer Temperature of the insulating shielding layer. Temperature of the filler layer To protect the temperature of the sleeve, External ambient temperature; These are the loss values ​​corresponding to each layer; These are the thermal resistance values ​​of the conductor shielding layer, insulating layer, insulating shielding layer, filling layer, protective sleeve, and external environment, respectively. Determined based on cable laying conditions: For directly buried cables ,in The equivalent radius of the external environment (such as the radius of the soil isotherm). This represents the equivalent thermal conductivity of the external medium. Correspondingly, the equivalent thickness of the external environment... Total thermal resistance .

[0049] For example, if Then the thermal resistance of the conductor shielding layer is:

[0050] S402, Introducing mutual heat temperature rise

[0051] In a direct-buried cable group, adjacent cables exhibit thermal coupling due to their spacing, and the temperature rise of each cable is affected by the superposition of heat flow from other cables within the area. Based on this superposition relationship, mutual thermal resistance is introduced into the thermal circuit control equation to characterize the thermal coupling effect between cables.

[0052] For any two cables in the cable group, let the first one be the second one. root cable and the first Taking the first cable as an example, the first root cable to the first The mutual thermal temperature rise of the two cables is:

[0053] in For the first root cable to the first The mutual thermal resistance of the two cables is calculated using the following formula: For the first root cable and the first The spacing between the cables is calculated using the distance formula in S2.

[0054] Taking two cables (cable 1 and cable 2) as an example, the mutual temperature rise between cable 2 and cable 1 is:

[0055] Among them, mutual heating thermal resistance for:

[0056] From S2, we can see that the distance between cable 1 and cable 2 is... , , ,but:

[0057] If the loss of cable 2 Then the mutual temperature rise between cable 2 and cable 1 is:

[0058] The expression for the mutual heat rise when two cables interact is:

[0059] in , The total thermal resistance of the cable itself (obtained by connecting the thermal resistances of each layer in S401 in series), ).

[0060] For any i The total mutual heat rise of the cable. The sum of the mutual heat rise generated by all other cables within the area:

[0061] in This represents the total number of cables.

[0062] S403, Establish the mutual heat rise matrix

[0063] for Arrangement Root cable (in this embodiment) Establish a mutual heat rise matrix:

[0064] matrix elements Defined as: when hour, (Self-thermal resistance); when hour, .

[0065] For example, the distance between cable 1 and cable 6 is ,but:

[0066] For example, the distance between cable 1 and cable 4 is ,but:

[0067] In this embodiment, because The mutual thermal resistances of cable 1 and cable 2 (laterally adjacent) and cable 1 and cable 4 (vertically adjacent) are equal, both being... .

[0068] For the total thermal resistance of the cable itself Taking cable 1 as an example, if Then, in the mutual heat rise matrix:

[0069] like Then the total mutual heat rise of cable 1 is:

[0070] Substitute the values:

[0071] Similarly, the total mutual heat rise between cables 2 and 6 can be calculated to obtain the complete... vector.

[0072] S404. Modify the thermal circuit control equation to obtain the target thermal circuit control equation.

[0073] The physical essence of mutual heating temperature rise is that it effectively raises the external ambient temperature of the cable. Therefore, when performing thermal circuit correction, only the thermal circuit equation of the outermost layer (from the protective sheath to the external environment) is corrected, while the temperature difference equation between the layers inside the cable remains unchanged.

[0074] The revised target thermal circuit control equations are as follows:

[0075] in , .

[0076] For the six cables in this embodiment, taking cable 1 as an example, its target thermal control equation is:

[0077] in .

[0078] In this embodiment, Compare the outermost equations of the original thermal circuit equation (before modification) with the target thermal circuit equation (after modification): Before revision: external ambient temperature ; Revised version: .

[0079] After correction, the temperature of the protective sleeve Increased under the same loss conditions The equivalent external ambient temperature is from Become That is, the mutual heating effect is equivalent to raising the external ambient temperature. This is consistent with the physical reality that the temperature of the surrounding soil rises due to the heat generated by adjacent cables in a group of directly buried cables.

[0080] S5. Calculate the thermal resistance coefficient

[0081] S501, Input Parameters and Construction of Mutual Heating Resistance Matrix

[0082] The temperature values ​​that take into account the mutual heating effect are substituted into the modified target thermal circuit control equation, and the thermal resistance and loss values ​​of each dielectric layer are modified at the same time.

[0083] for For the cable group arrangement, first calculate the distance between any two cables according to the distance formula in S2. :

[0084] Then construct the mutual heating thermal resistance matrix. The matrix elements are calculated according to the following rules: when hour, ; when hour, (That is, the sum of the thermal resistance of each layer of the cable in series).

[0085] Next, calculate the mutual heat rise vector. :

[0086] in The loss vector of each cable .

[0087] S502, Calculate the thermal resistance coefficient of each medium.

[0088] Based on the revised target thermal path control equation, and according to the formulas for the thickness and thermal resistance of each dielectric layer... Calculate the thermal resistance coefficient of each medium. .

[0089] in The thickness of the dielectric layer (unit: m). Thermal resistivity (unit: K·m / W). The heat dissipation area (unit: m², for cylindrical cables) is the area of ​​heat dissipation. Take the unit length ).

[0090] Taking the insulating layer as an example, the thickness of the insulating layer is known. Inner radius of the insulation layer outer radius Take the logarithmic average area .

[0091] If obtained by solving the thermal circuit equation Then the thermal resistance coefficient of the insulating layer is:

[0092] Calculated The result is consistent with the standard thermal resistance coefficient of XLPE material, verifying the accuracy of the calculation method.

[0093] Similarly, for conductor shielding layers, if The area was calculated using the logarithmic mean area method. Substitute Then it can be obtained For each of the other layers, the same calculation process is followed. .

[0094] The specific calculation steps are as follows: (1) Input parameters: Determine the cable geometry parameters (thickness of each layer) : , , , The equivalent thickness of the filler layer. , (Equivalent thickness for external environment), layout parameters () Boundary conditions (ambient temperature) Thermal conductivity of external medium ).

[0095] (2) Calculate the cable spacing matrix: according to the formula Calculate the distance between all cable pairs to obtain Distance matrix :

[0096] (3) Construct the mutual heating thermal resistance matrix: according to the formula (when (time) and (when (Time) Construction Mutual thermal resistance matrix .

[0097] Based on the thermal resistance of cable 1 For example, substituting the cable spacing into the calculation of mutual thermal resistance:

[0098] Corrected mutual thermal resistance matrix: (4) Calculate the mutual heat rise: based on Calculate the mutual temperature rise of each cable. Assume that the loss of each cable is zero. Then the mutual heat rise vector of each cable can be obtained:

[0099] In this embodiment, with a symmetrical arrangement, the mutual thermal temperature rise of each cable is equal. If the arrangement is asymmetrical, the mutual thermal temperature rise of each cable will be different.

[0100] (5) Simultaneous thermal equations: Substitute the mutual heat rise into the modified thermal control equations (only the outermost equations are superimposed). ), resulting in a complete set of equations including mutual heating effects, totaling There are 6 equations in each group.

[0101] Taking cable 1 as an example, the complete system of equations is:

[0102] (6) Solving for the thermal resistance coefficient: Solve the system of equations using an iterative method. The iterative process is as follows: First iteration: Input the initial values ​​of the thermal conductivity of each medium, including , , Calculate the thermal resistance of each layer. ; Substituting into the target thermal path control equation, the temperature of each layer is calculated. ; Update the thermal conductivity based on the empirical relationship between temperature and thermal conductivity (provided in the material handbook). ; Repeat the calculation until the temperature difference between two consecutive iterations is less than a set threshold (e.g., ).

[0103] Based on the final convergence thermal resistance value ,Depend on Inversely calculate the thermal resistance coefficient of each dielectric layer .

[0104] (7) Verification and Optimization: Substitute the calculated thermal resistance coefficient into the original thermal circuit control equation for verification, and compare the calculated temperature values ​​of each layer with the measured values ​​(or finite element simulation values). If the error exceeds the threshold (e.g. If the initial values ​​of the thermal conductivity of each medium are readjusted, iterative calculations are performed until the accuracy requirements are met.

[0105] S503, Single cable vs. multiple cable scenarios

[0106] when (For a single cable): the mutual thermal resistance matrix degenerates to matrix ,in This represents the cable's total thermal resistance. A single cable does not experience mutual thermal influence from other cables, therefore the total mutual thermal temperature rise is... The thermal control equations degenerate into the steady-state heat conduction equations for a single cable:

[0107] when or (With multiple cables): mutual heat effects cannot be ignored. The thermal coupling effect between cables must be considered. Mutual thermal resistance matrix. Since it is a non-diagonal matrix, the mutual thermal temperature rise of each cable is determined by matrix multiplication. The calculations are performed, and the results are substituted into the modified target thermal control equations for solution.

[0108] For example, in this embodiment In the case of 6 cables, the total mutual heat rise of cable 1 is:

[0109] Substituting the outermost equation of the target thermal circuit control equation:

[0110] This accurately reflects the effect of the heating of the adjacent cable on the temperature rise of the external environment of cable 1.

[0111] For example, regarding The four cables are arranged in a square array, and the mutual thermal resistance matrix is ​​as follows: The mutual thermal temperature rise of each cable in the matrix is ​​calculated using the same method:

[0112] for The three cables are arranged in a vertical array, and the mutual thermal resistance matrix is ​​as follows: matrix:

[0113] All of the above array arrangements fall within the scope of protection of this invention, and the thermal resistance coefficient can be accurately calculated through a unified target thermal path control equation framework.

[0114] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for calculating the multi-medium thermal resistance coefficient of the cable group at the bottom of a wind turbine tower, characterized in that, Including the following steps: S1. Construction of cable geometric model: Construct a geometric model of the cable. The structure of the cable includes an inner core conductor, a conductor shielding layer, an insulation layer, an insulation shielding layer, a filler layer, and a protective sheath. S2. Construction of a two-dimensional cable group laying model: Based on the cable geometry model, the cable group is arranged in an array pattern, resulting in a two-dimensional laying model including... The geometric model in which This refers to the number of geometric models arranged horizontally. This refers to the number of geometric models arranged vertically, and also includes the horizontal spacing between the geometric models. and longitudinal spacing The construction of the two-dimensional cable group laying model includes the following steps: S201, Determine the cable arrangement and arrange the cable group according to the array arrangement method; S202, Confirmed This refers to the number of geometric models arranged horizontally. The number of geometric models arranged vertically, where and All are positive integers, and satisfy the requirement of the total number of cable groups. ; S203, Determine the transverse spacing of the cables and longitudinal spacing The horizontal spacing Defined as the distance between the centers of adjacent cables in the lateral direction, and the longitudinal spacing between them. Defined as the distance between the centers of adjacent cables in the longitudinal direction; S204, construct a two-dimensional cable group laying model based on the arrangement method, where the first... Line 1 The coordinates of the cable position in the column are ,in , , , ; S205, Calculate the actual distance between any two cables. For the first root cable and the root cable The distance is: ； S3. Division of the multilayer dielectric thermal resistance module: Sequentially determine the dielectric layer as inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, protective sleeve and external environment, and input the basic parameters of each dielectric layer; S4. Construction of the steady-state thermal circuit model: The thermal resistance units of each dielectric layer are connected in series. Each dielectric layer in the steady-state thermal circuit model corresponds to a different thermal resistance layer, and the original thermal circuit control equations are constructed. Mutual heating and temperature rise exist between cables in the cable group, so lateral spacing is introduced. and longitudinal spacing and the number of arrangements The mutual thermal resistance is corrected, and the original thermal circuit control equation is corrected to obtain the corrected target thermal circuit control equation. The construction of the steady-state thermal circuit model includes the following steps: S401, Constructing the original thermal path control equations: Connecting the thermal resistance units of each dielectric layer in series, according to the steady-state heat conduction law, the following equations are obtained: in, The temperature of the inner conductor. Temperature of the conductor shielding layer Temperature of the insulation layer Temperature of the insulating shielding layer. Temperature of the filler layer To protect the temperature of the sleeve, External ambient temperature; These are the loss values ​​corresponding to each layer; These are the thermal resistance values ​​of the conductor shielding layer, insulation layer, insulation shielding layer, filling layer, protective sleeve, and external environment, respectively, and the total thermal resistance. ; S402, Introducing mutual heat rise: For any two cables in a cable group, the first... root cable to the first The mutual thermal temperature rise of the two cables is: in For the first root cable to the first The mutual thermal resistance of the two cables is calculated using the following formula: ； For the first root cable and the first The spacing between the cables is calculated using the following formula: In the formula For the first The row and column positions of the cables in a two-dimensional arrangement. For the first The row and column positions of the cables in a two-dimensional arrangement. The spacing is for horizontal arrangement. The vertical spacing is the distance between the rows. The equivalent thermal conductivity of the external medium. The outer radius of the cable; For any i The total mutual heat rise of the cable. The sum of the mutual heat rise generated by all other cables within the area: in This represents the total number of cables; S403, for Arrangement Establish a mutual heat rise matrix for the root cable: matrix elements Defined as: when hour, ;when hour, , ; S404, Modify the thermal control equation to obtain the target thermal control equation: in , ; S5. Calculate the thermal resistance coefficient: Substitute the temperature value considering the mutual heating effect into the modified target thermal path control equation, and simultaneously modify the thermal resistance and loss values ​​of each dielectric layer. Based on the modified target thermal path control equation, and according to the formula for the thickness and thermal resistance of each dielectric layer, calculate the thermal resistance coefficient of each dielectric layer. Calculate the thermal resistivity, including the following steps: S501, substitute the temperature value considering the mutual heating effect into the modified target thermal path control equation, and at the same time modify the thermal resistance and loss values ​​of each dielectric layer: for For the cable group, first calculate the distance between any two cables according to step S205. : Then construct the mutual heating thermal resistance matrix. The matrix elements are calculated according to the following rules: when hour, ; when hour, ; Next, calculate the mutual heat rise vector. : in The loss vector of each cable ; S502, based on the modified target thermal path control equation, and according to the formulas for the thickness and thermal resistance of each dielectric layer, calculate the thermal resistance coefficient of each dielectric layer. ; The specific calculation steps are as follows: (1) Input parameters: Determine the cable geometry parameters, i.e., the thickness of each layer. Layout parameters ( ), ambient temperature Thermal conductivity of external medium ; (2) Calculate the cable spacing matrix: according to the formula Calculate the distance between all cable pairs; (3) Construct the mutual heating thermal resistance matrix: according to the formula and Build The mutual thermal resistance matrix; (4) Calculate the mutual heat rise: based on Calculate the mutual temperature rise of each cable; (5) Simultaneous thermal circuit equations: Substitute the mutual heat temperature rise into the modified thermal circuit control equations to obtain a complete set of equations that include the mutual heat effects. (6) Solving for the thermal resistance coefficient: Solve the system of equations using an iterative method, and apply the thermal resistance formula. Inversely calculate the thermal resistance coefficient of each dielectric layer ; For thickness, The thermal resistance coefficient, For heat dissipation area; (7) Verification and optimization: Substitute the calculated thermal resistance coefficient into the original equation for verification. If the error exceeds the threshold, readjust the parameters and perform iterative calculations until the accuracy requirements are met. S503, when , At this time The thermal control equation degenerates into the steady-state heat conduction equation of a single cable; when or At this time Consider the thermal coupling effect between cables.

2. The method for calculating the multi-medium thermal resistance coefficient of the cable group at the bottom of a wind turbine tower as described in claim 1, characterized in that, The construction of the cable geometric model described in step S1 includes the following steps: S101, by inspecting the cable type at the bottom of the wind turbine tower, the internal structure of the cable is determined; S102, based on its internal cable structure, constructs a cable geometric model consisting of an inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, and protective sheath.

3. The method for calculating the multi-medium thermal resistance coefficient of the cable group at the bottom of a wind turbine tower as described in claim 1, characterized in that, The division of the multilayer dielectric thermal resistance module in step S3 includes the following steps: S301, Determine the dielectric layer module: Sequentially determine the dielectric layer as the inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, protective sleeve, and external environment; S302, Boundary Condition Setting Module: Set the external ambient temperature to... Input the thermal properties of the external medium, including the thermal conductivity of soil, the thermal conductivity of concrete, and the air convection heat transfer coefficient; S303, set the basic parameters of each medium: set the thickness of the inner core conductor, conductor shielding layer, insulation layer, insulation shielding layer, filling layer, and protective sleeve, as well as the initial value of the thermal conductivity of each material.

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