A correction method for two-dimensional thermal model of corrugated aluminum sheathed cable

Abstract

The present invention provides a method for correcting a two-dimensional thermal model of a corrugated aluminum sheath cable, including: collecting the structural parameters and thermophysical parameters of the corrugated aluminum sheath cable; establishing a finite element model based on the collected structural parameters and thermophysical parameters; calculating the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheath cable based on the collected structural parameters and thermophysical parameters; calculating the total equivalent thermal resistance R of the three-dimensional model all ; according to the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheath cable and the total equivalent thermal resistance R of the three-dimensional model all , calculating the equivalent air thermal conductivity λ of the two-dimensional equivalent model air1 ; establishing a two-dimensional finite element model of the cable according to the total equivalent thermal resistance R of the three-dimensional model all and the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheath cable. The present invention corrects the air thermal conductivity in the two-dimensional model equivalent to the average value of the corrugated aluminum sheath, making the core temperature calculated by the two-dimensional model more accurate.

Description

Technical Field

[0001] The invention relates to the field of high-voltage cable temperature field calculation, in particular to a correction method for a two-dimensional thermal model of a corrugated aluminum sheathed cable. Background Art

[0002] Corrugated aluminum sheathed cables are widely used in urban power transmission, and their safe and economical operation is of great significance to urban construction. The hottest point temperature inside the cable determines the current carrying capacity of the cable, and the rapid and accurate calculation of the hottest point temperature has become the main goal at this stage. The cable body temperature model mainly includes the one-dimensional thermal path model provided by the IEC60287 standard, the two-dimensional cross-sectional model equivalent to the average radius of the corrugated aluminum sheath, and the three-dimensional model. However, the existing one-dimensional and two-dimensional models are only applicable to straight aluminum sheathed cables. The corrugated aluminum sheathed cables are regarded as straight aluminum sheathed cables only by the average value equivalent method, which cannot guarantee the accuracy of the overall equivalent thermal resistance. In the temperature model under complex environments such as cable conduit laying and tunnel laying, it is necessary to reduce the three-dimensional cable body model to two dimensions to greatly reduce the calculation time while ensuring accuracy.

[0003] The Chinese utility model patent specification CN105928969A introduces a method for calculating the thermal resistance of the corrugated aluminum sheath of a high-voltage single-core cable. This method regards the air gap as pure heat conduction to calculate its equivalent thermal resistance. However, due to the fluid and body-penetrating properties of air, the convection heat transfer between the air and the cable wrapping tape and the corrugated aluminum sheath, as well as the radiation heat transfer between the cable wrapping tape and the corrugated aluminum sheath cannot be ignored. In order to ensure the accuracy of the temperature calculation, it is necessary to perform a three-dimensional modeling of the cable, consider the effects of various heat transfer methods, and then modify the two-dimensional cross-sectional model. Summary of the invention

[0004] In view of the above-mentioned deficiencies of the prior art, the present invention proposes a method for correcting the two-dimensional thermal model of a corrugated aluminum sheathed cable, so as to correct the existing two-dimensional cable cross-section model which uses the average value of the corrugated aluminum sheath radius as the equivalent radius, thereby improving the accuracy of the cable temperature and current-carrying capacity calculation.

[0005] A method for correcting a two-dimensional thermal model of a corrugated aluminum sheathed cable comprises the following steps:

[0006] Step 1, collecting structural parameters and thermophysical parameters of the corrugated aluminum sheathed cable;

[0007] Step 2: Based on the structural parameters and thermophysical parameters collected in step 1, a three-dimensional COMSOL finite element model of the corrugated aluminum sheathed cable is established;

[0008] Step 3, calculating the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable based on the structural parameters and thermophysical parameters collected in step 1;

[0009] Step 4: Calculate the total equivalent thermal resistance R of the three-dimensional model all ;

[0010] Step 5: According to the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable calculated in step 3 and the total equivalent thermal resistance R of the three-dimensional model calculated in step 4 all , calculate the air equivalent thermal conductivity λ of the two-dimensional equivalent model air1 ;

[0011] Step 6: Calculate the equivalent thermal conductivity of air in the two-dimensional equivalent model according to step 5 air1 The structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable obtained in step 3 are used to establish a two-dimensional finite element model of the cable.

[0012] Furthermore, the structural parameters of the corrugated aluminum sheathed cable include the outer diameter D of each layer of insulating material. 1 ~D 8 , corrugated aluminum sheath pitch l and thickness d, the thermal physical parameters include the thermal conductivity λ of each layer of insulating medium 1 ~λ 8 .

[0013] Furthermore, the step 2 specifically includes: based on the parameters collected in step 1, using COMSOL finite element simulation software to establish a three-dimensional COMSOL finite element model of the electrical corrugated aluminum sheathed cable, wherein the boundary condition of the outer surface of the cable is set to the first type of boundary and the temperature is constant at T w ; Assume that the internal copper core conductor is the heat source, and its power is P; the boundary between the corrugated aluminum sheath and the cable wrapping tape is set to surface-to-surface radiation, and the air domain is set to be transparent; consider the convection heat transfer between the air and the wall, assume that the air flow state is laminar and compressible, and consider the air gravity.

[0014] Furthermore, the step 3 specifically includes: using the parameters collected in step 1, using the average value equivalent method to obtain the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable, that is, the two-dimensional cross-sectional equivalent diameter D 1 * ~D 8 * , where D 1 * ~D 5 * , D 8 * With D 1 ~D 5 , D 8 Equal, D 6 * , D 7 * for:

[0015]

[0016] Furthermore, the step 4 specifically includes: using the three-dimensional COMSOL finite element model of the corrugated aluminum sheathed cable established in step 2 to calculate the cable core temperature T n , then the total equivalent thermal resistance R all The calculation formula is shown in formula (3):

[0017]

[0018] Furthermore, the step 5 specifically includes:

[0019] The total equivalent thermal resistance of a coaxial cylindrical structure is:

[0020]

[0021] The equivalent thermal conductivity λ of air in the two-dimensional cross-sectional model can be calculated by formula (4): air1 .

[0022] The present invention takes into account the influence of convective heat transfer in the air gap between the corrugated aluminum sheath cable wrapping tape and the metal sheath and the thermal radiation of the walls on both sides of the air gap on the equivalent thermal resistance. Based on this, the thermal conductivity of air in a two-dimensional model equivalent to the average value of the corrugated aluminum sheath is corrected, so that the cable core temperature calculated by the two-dimensional model is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of a method for correcting a two-dimensional thermal model of a corrugated aluminum sheathed cable according to the present invention;

[0024] Figure 2 It is a schematic diagram of the structure of the corrugated aluminum sheathed cable;

[0025] Figure 3 It is the equivalent two-dimensional cross-sectional structure diagram of the corrugated aluminum sheathed cable;

[0026] Figure 4 This is the COMSOL model diagram of the corrugated aluminum sheathed cable. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution 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 part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] See also Figure 1The embodiment of the present invention provides a method for correcting a two-dimensional thermal model of a corrugated aluminum sheathed cable, comprising the following steps:

[0029] Step 1: Collect the structural parameters and thermophysical parameters of the corrugated aluminum sheathed cable; the structural parameters of the corrugated aluminum sheathed cable include the outer diameter D of each layer of insulating material 1 ~D 8 , corrugated aluminum sheath pitch l and thickness d, the thermal physical parameters include the thermal conductivity λ of each layer of insulating medium 1 ~λ 8 .

[0030] Step 2: Based on the structural parameters and thermophysical parameters collected in step 1, a three-dimensional COMSOL finite element model of the corrugated aluminum sheathed cable is established; specifically, based on the parameters collected in step 1, a three-dimensional COMSOL finite element model of the corrugated aluminum sheathed cable is established using COMSOL finite element simulation software, wherein the boundary condition of the outer surface of the cable is set to the first type of boundary and the temperature is constant at T w ; Assume that the internal copper core conductor is the heat source, and its power is P; the boundary between the corrugated aluminum sheath and the cable wrapping tape is set to surface-to-surface radiation, and the air domain is set to be transparent; consider the convection heat transfer between the air and the wall, assume that the air flow state is laminar and compressible, and consider the air gravity.

[0031] Step 3: Calculate the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable based on the structural parameters and thermophysical parameters collected in step 1; Specifically, the parameters collected in step 1 are used to obtain the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable using the average value equivalent method, that is, the two-dimensional cross-sectional equivalent diameter D 1 * ~D 8 * The equivalent two-dimensional cross section is Figure 3 As shown. 1 * ~D 5 * , D 8 * and Figure 2 Middle D 1 ~D 5 , D 8 Equal, D 6 * , D 7 * for

[0032]

[0033] Step 4: Calculate the total equivalent thermal resistance R of the three-dimensional model allSpecifically, the three-dimensional COMSOL finite element model of the corrugated aluminum sheathed cable established in step 2 is used to calculate the cable core temperature T n , then the total equivalent thermal resistance R all The calculation formula is shown in formula (3):

[0034]

[0035] Step 5: According to the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable calculated in step 3 and the total equivalent thermal resistance R of the three-dimensional model calculated in step 4 all , calculate the air equivalent thermal conductivity λ of the two-dimensional equivalent model air1 .

[0036] Since the total equivalent thermal resistance of the coaxial cylindrical structure is

[0037]

[0038] The equivalent thermal conductivity λ of air in the two-dimensional cross-sectional model can be calculated by formula (4): air1 .

[0039] Step 6: Calculate the equivalent thermal conductivity of air in the two-dimensional equivalent model according to step 5 air1 The cable two-dimensional finite element model is established with the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable obtained in step 3. Specifically, the corresponding cable two-dimensional cross-sectional model can be established in COMSOL software.

[0040] The present invention is described in detail below with a specific example:

[0041] Step 1: Take the conductor cross-sectional area of ​​110kV transmission line as 630mm 2 The XLPE cable model is YJW03. The cable core structure and thermal properties of related materials are shown in Table 1.

[0042] Table 1 Cable structure and thermal properties

[0043]

[0044] In addition, the pitch l of the corrugated aluminum sheath is 20 mm and the thickness d is 2 mm.

[0045] Step 2: Based on the structural parameters and thermophysical parameters collected in step 1, a three-dimensional COMSOL finite element model of the corrugated aluminum sheathed cable is established. The specific model is as follows: Figure 4 shown.

[0046] Step 3: Calculate the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable based on the structural parameters and thermophysical parameters collected in step 1, where the equivalent diameter of the two-dimensional section D 1* ~D 5 * , D 8 * and Figure 2 Middle D 1 ~D 5 , D 8 are equal, the equivalent diameter of the two-dimensional cross section D 6 * , D 7 * for

[0047]

[0048]

[0049] Available D 6 * =79.5mm; D 7 * =83.5mm

[0050] Step 4: Calculate the cable core temperature T using the finite element model established in step 2 n , the total equivalent thermal resistance is shown in Formula 3.

[0051]

[0052] Calculate R all =0.948K / W.

[0053] Step 5: Based on the total equivalent thermal resistance R obtained in step 4 all And the structural parameters obtained in step 3, calculate the equivalent thermal conductivity of air λ air1 .

[0054] Since the total equivalent thermal resistance of the coaxial cylindrical structure is

[0055]

[0056] The equivalent thermal conductivity λ of air in the two-dimensional cross-sectional model can be calculated by formula 4: air1 After calculation, λ air1 =0.074W / (m·K).

[0057] Step 6: Calculate the equivalent thermal conductivity of air based on step 5 air1 The corresponding two-dimensional finite element model of the cable is established in COMSOL software based on the structural parameters obtained in step 3.

[0058] Using the finite element model after correcting the air thermal conductivity, when the external ambient temperature is 20°C and the cable heating power is 20W, the calculated cable core temperature is 312.1K; if the uncorrected two-dimensional cross-section model is used, the calculated cable core temperature is 315.6K.

[0059] In comparison, the cable core temperature obtained using the three-dimensional model is 312.1K, which is consistent with the corrected two-dimensional model, and the Celsius error compared with the uncorrected two-dimensional model is 9%, indicating that the corrected model is more accurate.

[0060] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A correction method for the two-dimensional thermal model of corrugated aluminum sheathed cable, Features The steps include: Step 1, collecting structural parameters and thermophysical parameters of the corrugated aluminum sheathed cable; Step 2: Based on the structural parameters and thermophysical parameters collected in step 1, a three-dimensional COMSOL finite element model of the corrugated aluminum sheathed cable is established; Step 3, calculating the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable based on the structural parameters and thermophysical parameters collected in step 1; Step 4: Calculate the total equivalent thermal resistance R of the three-dimensional model all ; Step 5: According to the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable calculated in step 3 and the total equivalent thermal resistance R of the three-dimensional model calculated in step 4 all , calculate the air equivalent thermal conductivity λ of the two-dimensional equivalent model air1 ; Step 6: Calculate the equivalent thermal conductivity of air in the two-dimensional equivalent model according to step 5 air1 Establish a two-dimensional finite element model of the cable based on the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable obtained in step 3; The structural parameters of the corrugated aluminum sheathed cable include the outer diameter D of each layer of insulation material 1 ~ D 8 , corrugated aluminum sheath pitch l and thickness d, the thermal physical parameters include the thermal conductivity λ of each layer of insulating medium 1 ~ λ 8 ; The step 2 specifically includes: based on the parameters collected in step 1, using COMSOL finite element simulation software to establish a three-dimensional COMSOL finite element model of the electrical corrugated aluminum sheathed cable, wherein the boundary condition of the outer surface of the cable is set to the first type of boundary and the temperature is constant at T w ; Assume that the internal copper core conductor is the heat source, and its power is P; the boundary between the corrugated aluminum sheath and the cable wrapping tape is set to surface-to-surface radiation, and the air domain is set to be transparent; consider the convection heat transfer between the air and the wall, assume that the air flow state is laminar and compressible, and consider the air gravity.

2. The method for correcting the two-dimensional thermal model of the corrugated aluminum sheathed cable according to claim 1, Features: The step 3 specifically includes: using the parameters collected in step 1, using the average value equivalent method to obtain the structural parameters of the equivalent two-dimensional model of the corrugated aluminum sheathed cable, that is, the two-dimensional cross-sectional equivalent diameter D 1 * ~ D 8 * , where D 1 * ~ D 5 * , D 8 * With D 1 ~ D 5 , D 8 Equal, D 6 * , D 7 * for: （1） （2）。 3. The method for correcting the two-dimensional thermal model of the corrugated aluminum sheathed cable according to claim 2, Features: The step 4 specifically includes: using the three-dimensional COMSOL finite element model of the corrugated aluminum sheathed cable established in step 2 to calculate the cable core temperature T n , then the total equivalent thermal resistance R all The calculation formula is shown in formula (3): （3）。 4. The method for correcting the two-dimensional thermal model of the corrugated aluminum sheathed cable according to claim 3, Features: The step 5 specifically includes: The total equivalent thermal resistance of a coaxial cylindrical structure is: （4）； The equivalent thermal conductivity λ of air in the two-dimensional cross-sectional model can be calculated by formula (4): air1 .

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