A method for obtaining transient temperature rise between two cables in a trench considering nonlinear convection heat dissipation

Abstract

The present invention relates to a method for obtaining transient temperature rise between two cables in a groove considering nonlinear convection heat dissipation, comprising the following steps: 1) constructing a transient temperature rise heat circuit model between two cables in the groove; 2) using a finite element calculation method to identify the parameters of the transient temperature rise heat circuit model between the two cables; 3) obtaining the current of the two cables in the actual groove and obtaining the transient temperature rise between the two cables under mutual influence through iterative calculation according to the transient temperature rise heat circuit model between the two cables after parameter identification. Compared with the prior art, the present invention has the advantages of considering nonlinear convection heat dissipation and not relying on skin temperature measurement, being applicable to the case of two cables, having high reliability, high timeliness, and clear and definite calculation process.

Description

Technical Field

[0001] The invention relates to the technical field of power cable operation detection, and in particular to a method for obtaining transient temperature rise between two cables in a groove taking nonlinear convection heat dissipation into consideration. Background Art

[0002] At present, cables entering and exiting substations mostly use trenches. There is nonlinearity in the convective heat transfer and radiation heat transfer inside the trench, especially the lack of clear quantitative laws for convective heat dissipation. Therefore, the heating problem of trench cables is relatively complicated.

[0003] Due to the particularity of power cable operation, it is generally impossible to obtain the cable core temperature through direct measurement, especially the real-time transient temperature of the cable group core. Generally, engineering formula method based on test results, numerical algorithm or indirect measurement method is used to grasp the core temperature. Among them, the empirical formula method is mainly used to calculate the steady-state temperature rise of typical laying, and the scope of application is insufficient. The heat dissipation inside the groove involves thermodynamics and fluid mechanics. Its numerical calculation method has a large amount of calculation and a long calculation time when simulating the actual temperature rise of cables under multiple working conditions, and it is impossible to obtain the temperature rise change in time. The indirect measurement method first requires the installation of optical fiber temperature measurement or other devices to obtain the cable skin temperature, and then infer the core temperature. The reliability and economy are poor.

[0004] Therefore, a convenient and fast method is needed to obtain the transient temperature rise of the trench cable group, which is of great significance for the full utilization of existing cable resources and power grid planning and construction. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a method for obtaining the transient temperature rise between two cables in a groove taking into account nonlinear convection heat dissipation.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for obtaining transient temperature rise between two cables in a trench considering nonlinear convection heat dissipation comprises the following steps:

[0008] 1) Construct a transient temperature rise thermal circuit model between two cables in the trench;

[0009] 2) The finite element calculation method is used to identify the parameters of the transient temperature rise thermal circuit model between the two cables;

[0010] 3) The current of the two cables in the actual trench is obtained and the transient temperature rise between the two cables is obtained by iterative calculation based on the transient temperature rise thermal circuit model between the two cables after parameter identification.

[0011] The transient temperature rise thermal circuit model between the two cables in the groove is constructed according to the model, structure and layout of the two cables in the groove, and is used to describe the thermal transition process between the cables in the groove section.

[0012] In the step 1), the transient temperature rise thermal circuit model between the two cables in the groove is composed of the first thermal resistance R1, the first thermal inductance L1, the first branch where the heat load Q1 of the first cable is located, the second branch where the first thermal capacitance C1 is located, the third branch where the second thermal resistance R2 and the second thermal capacitance C2 are located, and the fourth branch where the comprehensive thermal resistance R3 of the second cable core to the environment is located. The common ends of the first branch, the second branch, the third branch and the fourth branch are all the groove environment temperature, the other ends of the third branch and the fourth branch are the outer skin temperature of the second cable affected by the heat of the first cable, the other ends of the third branch and the fourth branch are connected to the other ends of the third branch and the fourth branch through the first thermal resistance R1 and the first thermal inductance L1 respectively, and the temperature between the second thermal resistance R2 and the second thermal capacitance C2 on the third branch is the core temperature of the second cable affected by the heat of the first cable.

[0013] In the step 2), the parameters of the transient temperature rise thermal circuit model between the two cables include fixed parameters and variable parameters. The fixed parameter values ​​are determined by the model, structure and layout of the two cables in the groove, including the first thermal resistance R1, the first thermal sense L1, the first thermal capacitance C1, the second thermal resistance R2 and the second thermal capacitance C2. The variable parameter is the comprehensive thermal resistance R3 of the second cable core to the environment.

[0014] In the step 2), multiple sets of data are obtained by simulating random working conditions using the finite element method, each set of data is composed of the ambient temperature T0, the heat load Q1 of the first cable, the heat load Q2 of the first cable, the core temperature T 1c and skin temperature T 1s and the core temperature of the second cable T 2c and skin temperature T 2s , and based on the data, the parameters of the calculation model for the temperature rise of the outer skin of the two cables in the trench are estimated.

[0015] The calculation model for the temperature rise of the outer skin of the two cables in the groove is specifically:

[0016] t1=Q 11 *[p1+p2*power(t0,k1)+p3*power(t1,k2)+p4*power(t2,k3)]+Q 21 *[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+t0=Q 11 *R 11 +Q 21 *R 21 +t0

[0017] t2=Q 12*[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+Q 22 *[pp5+pp6*power(t0,kk4)+pp7*power(t1,kk5)+pp8*power(t2,kk6)]+t0=Q 12 *R 12 +Q 22 *R 22 +t0

[0018] Among them, R 11 , R 22 are the thermal resistances of the first and second cables for self-heating, R 12 =R 21 are the thermal resistances of the first cable and the second cable that affect each other’s heating, that is, the comprehensive thermal resistance R3, Q 11 , Q 22 are the heat flux out of the outer skin of the first cable and the second cable due to self-heating, Q 12 , Q 21 are the outflow heat fluxes from the sheath under mutual influence obtained according to the transient temperature rise thermal circuit model between the two cables, that is, the heat flux flowing through the comprehensive thermal resistance R3. t1 and t2 are the sheath temperatures of the first cable and the second cable respectively. t0 is the trench ambient temperature. power(·) represents the power exponential operation of the base. p1, p2, p3, p4, p5, p6, p7, p8, k1, k2, k3, k4, k5, k6, pp5, pp6, pp7, pp8, kk4, kk5, and kk6 are all estimated parameters.

[0019] The step 3) specifically comprises the following steps:

[0020] 31) Setting the variable parameter in the transient temperature rise thermal circuit model between the two cables in the groove, that is, the initial value of the comprehensive thermal resistance R3, obtaining the cable self-heating values ​​of the two cables according to the currents of the two cables and the set initial core temperatures, respectively, and substituting them into the transient temperature rise thermal circuit model between the two cables in the groove after parameter identification, obtaining the initial core temperature of each cable under mutual influence and the initial outflow skin heat flux under mutual influence through thermal circuit calculation, and obtaining the initial skin temperature under mutual influence according to the initial outflow skin heat flux under mutual influence;

[0021] 32) In the kth step of the iteration, the self-heating value of each cable is updated according to the current of each cable in the current step and the core temperature of each cable obtained in the k-1th step, and the variable parameter is updated according to the outflowing outer skin heat flux under the mutual influence obtained in the k-1th step. The core temperature of each cable is obtained by adding and summing the core temperature caused by self-heating and the core temperature under the mutual influence;

[0022] 33) In the k+1th step of the iteration, the core temperature and heat flow under mutual influence of the k+1th step are obtained by continuing to calculate the heat path according to the cable's own heating value updated in the kth step and the updated variable parameters. Steps 32)-33) are repeated to obtain the core temperature and skin temperature of the two cables under mutual influence.

[0023] In the step 31), the initial wire core temperature is set to be the groove environment temperature.

[0024] In the step 33), the outer skin temperature under the mutual influence of the updated outflow outer skin heat flow is updated through the outer skin temperature rise calculation model of the two cables in the groove. 21 =Q 22 =0, then:

[0025] t1=Q 11 *R 11 +t0

[0026] t2=Q 12 *R 12 +t0.

[0027] In the step 32), the update formula of the variable parameter is:

[0028] R3=t2 / Q 12 .

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. The present invention establishes a rapid calculation model for transient temperature rise between two cables in a groove taking into account nonlinear convection heat dissipation, thereby overcoming the shortcomings of poor timeliness of numerical calculation methods and poor reliability of real-time monitoring methods, and providing a direct basis for subsequent research on rapid algorithms for transient temperature rise of groove cable groups and even actual operation control of cable equipment.

[0031] 2. In order to adapt to the nonlinear heat dissipation characteristics between trench cables, the nonlinear thermal resistance R3 representing the "skin temperature-heat generation" law is introduced into the transient temperature rise calculation model for the first time.

[0032] 3. The model itself has basically nothing to do with loss and only reflects the thermal properties of the cross section. It has a clear physical meaning and provides a direct basis for subsequent analysis and improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the transient calculation model between cables.

[0034] Figure 2 Schematic diagram of the finite element calculation model for temperature rise of two cables in the trench.

[0035] Figure 3 It is the histogram of cable 1 outer skin temperature rise error.

[0036] Figure 4 It is the histogram of temperature rise error of cable 2 outer skin.

[0037] Figure 5 This is the temperature rise process of cable 1 core and sheath.

[0038] Figure 6 This is the temperature rise process of cable 2 core and outer sheath.

[0039] Figure 7 Comparison of the temperature rise process of cable 2 core and sheath.

[0040] Figure 8 To compare the temperature rise process of cable 2 core and sheath under verification working conditions. DETAILED DESCRIPTION

[0041] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] Example:

[0043] The present invention provides a method for obtaining transient temperature rise between two cables in a groove considering nonlinear convection heat dissipation, and the principle is as follows:

[0044] The heating of the cable mainly depends on the cable loss and the thermal characteristics of the section. The former has a clear correspondence with the operating current and operating temperature and can be directly applied; while the latter mainly depends on the geometric parameters of the section and the physical parameters of each part. According to the analysis of heat transfer, the thermal resistance of the cable body is related to the specific structure of the cable and can be regarded as unchanged in the calculation; the radiation heat dissipation, radiation heat dissipation thermal resistance, and convection heat dissipation thermal resistance are related to factors such as ambient temperature and heat generation. The laws of the first two are known and can be obtained by determining the formula; for the latter, we will seek to express it in a certain mathematical form through mathematical modeling, so as to provide the possibility of rapid calculation.

[0045] Aiming at the transient temperature rise between the two cables in the trench, the present invention takes this as the main idea to carry out work. The present invention proposes a transient temperature rise model (thermal circuit model) between the two cables, such as Figure 1 As shown, the temperature reference point of the model is the trench ambient temperature.

[0046] Figure 1 In the figure, Q1 is the heat load of cable 1; R3 is the comprehensive thermal resistance of cable 2 core to the environment; R1, L1, R2, C1 and C2 are all parameters used to produce different transition processes and have no clear physical meaning. These parameters reflect the thermal transition process between cables in the groove section.

[0047] The determination of this model does not depend on the heat generated by the cable itself or the current size, but is only related to the thermal properties of the materials surrounding the cable. Except for R3, such properties can be considered to be basically unchanged within the general operating temperature range. For a specific cross-section, R3 can be expressed in a certain mathematical form through mathematical modeling. Therefore, after the model is established, there is no need to repeat numerical calculations such as finite element when transforming the cable current, and satisfactory results can be obtained directly through simple iterations.

[0048] This method mainly includes the following steps:

[0049] 1.1 Finite element calculation model

[0050] This method uses finite element calculation, and other numerical calculation or experimental methods can also be used in practical applications. Figure 2 shown.

[0051] The calculation adopts the finite element method, the groove is selected as 1m*0.5m, the air is selected as ideal gas information, the cables 1 and 2 are selected as non-uniform thermal conductivity, and the thermal conductivity of the copper conductor is selected as 380W / (m 2 *k), the thermal conductivity of XLPE material is selected as 0.3W / (m 2 *k), conductor diameter 5cm, insulation thickness 2.5cm.

[0052] 1.2 Thermal circuit model establishment

[0053] The R3 parameter law in the thermal circuit model can be extracted through steady-state calculation, and other parameters can be obtained through transient calculation data.

[0054] (1) Fitting the law of “skin temperature-heat generation”

[0055] The calculation conditions randomly select the ambient temperature of 0~30℃, and the body heat flux changes randomly; steady-state calculation: the number of iterations is 500 steps, and the relaxation factor is 0.5; under different ambient temperature T0, cable 1 heat flux Q1, cable 2 heat flux Q2, the core temperature T of cable 1 and cable 2 of 60 groups of working conditions 1c With T 2c , skin temperature T 1s With T 2s The steady-state calculation results are shown in Table 1.

[0056] Table 1 Finite element calculation results of temperature rise of trench cables 1 and 2

[0057]

[0058]

[0059] The present invention proposes a calculation model for the temperature rise of the outer skins of two cables in a groove, as shown in formula (1).

[0060] t1=Q11 *[p1+p2*power(t0,k1)+p3*power(t1,k2)+p4*power(t2,k3)]+Q 21 *[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+t0=Q 11 *R 11 +Q 21 *R 21 +t0

[0061] t2=Q 12 *[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+Q 22 *[pp5+pp6*power(t0,kk4)+pp7*power(t1,kk5)+pp8*power(t2,kk6)]+t0=Q 12 *R 12 +Q 22 *R 22 +t0 (1)

[0063] Among them, R 11 , R 22 R is the thermal resistance of cables 1 and 2 due to self-heating. 12 =R 21 Q is the thermal resistance of cables 1 and 2 that affect each other’s heat generation. 11 , Q 22 is the heat flux out of the outer skin obtained by the self-heating model of cables 1 and 2, Q 12 , Q 21 The heat flux out of the outer skin obtained by the mutual heating model of cables 1 and 2.

[0064] The Levenberg-Marquardt method + general global optimization method is used to estimate the parameters. The estimation results are shown in Table 2 and the error histogram is shown in Figures 3-4 The error statistics are shown in Table 3.

[0065] Table 2 Estimation of convection thermal resistance parameters of cables 1 and 2

[0066] parameter Best estimate parameter Best estimate p1 0.084689 pp5 0.762479302 p2 0.023745 pp6 0.000578866 p3 0.376664 pp7 -4.42E-05 p4 -0.0184 pp8 -0.220953453 p5 -4.56032 kk4 1.494985708 p6 5.253385 kk5 1.91283647 p7 0.273104 kk6 0.197923798 p8 -0.72497 k1 0.615466 k2 -0.0988 k3 0.684237 k4 -0.00395 k5 0.230338 k6 0.116568

[0067] Table 3 Cable 1 and 2 outer skin temperature error statistics

[0068] N Minimum Maximum Mean Std. Deviation Cable 1 sheath (K) 60 -2.80 2.79 0.0175 1.18046 Cable 2 sheath (K) 60 -2.68 3.64 0.0348 1.14302

[0069] Statistics show that the overall normal distribution is satisfied, the maximum deviation is no more than 4K, and the variance is 1.18K and 1.14K, which can meet the actual needs of operation.

[0070] Substituting the parameters in Table 2 into equation (1), we can obtain the quantitative law that characterizes the relationship between the temperature of the two cables in the trench, the trench ambient temperature and the heat generation. 21 =Q 22 When =0, equation (1) is transformed into equation (2).

[0071] t1=Q 11 *[p1+p2*power(t0,k1)+p3*power(t1,k2)+p4*power(t2,k3)]+t0=Q 11 *R 11 +t0

[0072] t2=Q 12 *[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+t0=Q 12 *R 12 +t0 (2)

[0074] (2) Extraction of transient parameters such as C1, C2, R1, R2, and L1

[0075] The calculation conditions are: ambient temperature 15℃, "cable 1 step excitation, cable 2 0 input", body heat flux 75W / m; step length 1000s, calculation time 300*1000s, single-step iteration number 250 steps, relaxation factor 0.5. The calculation results are as follows: Figure 5 and Figure 6 shown.

[0076] according to Figure 1 The transient model between two cables in the trench is shown in Figure 1. The transient parameters are solved by genetic algorithm. The above parameters reflect the thermal transition process of the trench section.

[0077] 1) Set parameter range

[0078] Take C1, C2∈(0,100), L1∈(0,500), R1, R2∈(0,50), binary coding, the initial population size is 200, the maximum genetic generation is 100, the crossover probability is 0.75, and the mutation probability is 0.25.

[0079] 2) Set the fitness function

[0080] according to Figure 1 The transient temperature rise response of the line core of the model shown is m c (i) Transient temperature rise response of outer sheath ms (i), and Figure 6 The transient temperature rise response T of cable 2 core under the excitation of cable 1 is shown in the figure. c (i) Transient temperature rise response of outer sheath T s (i), the deviation of the two sets of curves is used as the fitness function, as shown in formula (3).

[0081]

[0082] 3) Set convergence criteria

[0083] When the fitness function reaches the maximum genetic generation number, it is less than 300*0.1*0.1*2=6, which is considered to be converged.

[0084] 4) Application of the “skin temperature-calorific value” rule

[0085] a. Set the initial value of R3 to 1. It should be noted that due to the existence of C1, C2, L1, R1, and R2, the setting of the initial value of R3 does not affect subsequent calculations.

[0086] b. Utilization Figure 1 The model shown and the set heat flow are used to calculate the heat flow Q of the branch where R3 is located. 12 =I R3 .

[0087] c. Using formula (2), the skin temperature rise t2 can be obtained.

[0088] d. Correction R3 = t2 / Q 12 ,right Figure 1 The model shown is subjected to parameter adjustment.

[0089] e. Repeat steps b to d until the transient process ends.

[0090] 5) Calculation results

[0091] The calculation results are: C1=12.648W*s / (K*m), C2=7.101W*s / (K*m), L1=186.979K*s*m / W, R1=7.695K*m / W, R2=4.069K*m / W, and the fitness function fitness=1.738 is less than the convergence criterion, so the calculation is considered to have converged.

[0092] According to the obtained parameters, the temperature rise of the cable 2 core and the outer skin is calculated, and the results are directly calculated by ANSYS (such as Figure 6 Compared with Figure 7 The error statistics are shown in Table 4.

[0093] Table 4 Statistical table of cable 2 core and sheath temperature rise process errors

[0094] Minimum Maximum Mean Std. Deviation Core error (K) -0.12 0.16 -0.0001 0.05283 Skin error (K) -0.10 0.10 -0.0001 0.05511

[0095] 1.3 Application steps and verification of thermal circuit model

[0096] 1.3.1 Model application steps

[0097] 1) Establish the model according to the parameters required in Section 2.2 and set the initial value of R3 = 1.

[0098] 2) Utilize Figure 1 The model shown and the set initial heat flow calculate the core temperature rise and the heat flow Q of the branch where R3 is located. 12 =I R3 .

[0099] 3) Using formula (2), the skin temperature rise t2 relative to the groove ambient temperature can be obtained.

[0100] 4) Correction R3 = t2 / Q 12 ,right Figure 1 The model shown is subjected to parameter adjustment.

[0101] 5) Correct according to core temperature and real-time current Figure 1 Cable heat load Q1 in.

[0102] 6) Repeat steps 2) to 5) until the transient process ends.

[0103] 1.3.2 Verification conditions

[0104] The above model is applied to the working conditions shown in Table 5, the groove ambient temperature is 20℃, and compared with the finite element calculation, the temperature rise comparison between the cable core and the outer sheath is Figure 8 The error statistics are shown in Table 6.

[0105] Table 5 Cable working conditions

[0106]

[0107] Table 6 Statistical table of cable 2 core and outer sheath temperature rise process errors

[0108] Minimum Maximum Mean Std. Deviation Core error (K) -3.66 1.85 -0.4140 1.46392 Skin error (K) -1.69 1.19 0.0712 0.77832

Claims

1. A method for obtaining transient temperature rise between two cables in a trench considering nonlinear convection heat dissipation, characterized in that: The following steps are involved: 1) Construct a transient temperature rise thermal circuit model between two cables in the trench; 2) The finite element calculation method is used to identify the parameters of the transient temperature rise thermal circuit model between the two cables; 3) Obtain the current of the two cables in the actual trench and obtain the transient temperature rise between the two cables under mutual influence through iterative calculation based on the transient temperature rise thermal circuit model between the two cables after parameter identification; In the step 1), the transient temperature rise thermal circuit model between the two cables in the groove is composed of the first thermal resistance R1, the first thermal inductance L1, the first branch where the heat load Q1 of the first cable is located, the second branch where the first thermal capacitance C1 is located, the third branch where the second thermal resistance R2 and the second thermal capacitance C2 are located, and the fourth branch where the comprehensive thermal resistance R3 of the second cable core to the environment is located. The common ends of the first branch, the second branch, the third branch and the fourth branch are all the groove environment temperature, the other ends of the third branch and the fourth branch are the outer skin temperature of the second cable affected by the heat of the first cable, the other ends of the third branch and the fourth branch are connected to the other ends of the third branch and the fourth branch through the first thermal resistance R1 and the first thermal inductance L1 respectively, and the temperature between the second thermal resistance R2 and the second thermal capacitance C2 on the third branch is the core temperature of the second cable affected by the heat of the first cable.

2. According to the method for obtaining transient temperature rise between two cables in a groove considering nonlinear convection heat dissipation according to claim 1, it is characterized in that: The transient temperature rise thermal circuit model between the two cables in the groove is constructed according to the model, structure and layout of the two cables in the groove, and is used to describe the thermal transition process between the cables in the groove section.

3. The method for obtaining transient temperature rise between two cables in a groove considering nonlinear convection heat dissipation according to claim 1 is characterized in that: In the step 2), the parameters of the transient temperature rise thermal circuit model between the two cables include fixed parameters and variable parameters. The fixed parameter values ​​are determined by the model, structure and layout of the two cables in the groove, including the first thermal resistance R1, the first thermal sense L1, the first thermal capacitance C1, the second thermal resistance R2 and the second thermal capacitance C2. The variable parameter is the comprehensive thermal resistance R3 of the second cable core to the environment.

4. The method for obtaining transient temperature rise between two cables in a groove considering nonlinear convection heat dissipation according to claim 3 is characterized in that: In the step 2), multiple sets of data are obtained by simulating random working conditions using the finite element method, each set of data is composed of the ambient temperature T0, the heat load Q1 of the first cable, the heat load Q2 of the first cable, the core temperature T 1c and skin temperature T 1s and the core temperature of the second cable T 2c and skin temperature T 2s , and based on the data, the parameters of the calculation model for the temperature rise of the outer skin of the two cables in the trench are estimated.

5. The method for obtaining transient temperature rise between two cables in a groove considering nonlinear convection heat dissipation according to claim 4 is characterized in that: The calculation model for the temperature rise of the outer skin of the two cables in the groove is specifically: t1=Q 11 *[p1+p2*power(t0,k1)+p3*power(t1,k2)+p4*power(t2,k3)]+ Q 21 *[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+t0 =Q 11 *R 11 +Q 21 *R 21 +t0 t2=Q 12 *[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+ Q 22 *[pp5+pp6*power(t0,kk4)+pp7*power(t1,kk5)+pp8*power(t2,kk6)]+t0 =Q 12 *R 12 +Q 22 *R 22 +t0 Among them, R 11 , R 22 are the thermal resistances of the first and second cables for self-heating, R 12 =R 21 are the thermal resistances of the first cable and the second cable that affect each other’s heating, that is, the comprehensive thermal resistance R3, Q 11 , Q 22 are the heat flux out of the outer skin of the first cable and the second cable due to self-heating, Q 12 , Q 21 are the outflow heat fluxes from the sheath under mutual influence obtained according to the transient temperature rise thermal circuit model between the two cables, that is, the heat flux flowing through the comprehensive thermal resistance R3. t1 and t2 are the sheath temperatures of the first cable and the second cable respectively. t0 is the trench ambient temperature. power(·) represents the power exponential operation of the base. p1, p2, p3, p4, p5, p6, p7, p8, k1, k2, k3, k4, k5, k6, pp5, pp6, pp7, pp8, kk4, kk5, and kk6 are all estimated parameters.

6. A method for obtaining transient temperature rise between two cables in a groove considering nonlinear convection heat dissipation according to claim 5, characterized in that: The step 3) specifically comprises the following steps: 31) Setting the variable parameter in the transient temperature rise thermal circuit model between the two cables in the groove, that is, the initial value of the comprehensive thermal resistance R3, obtaining the cable self-heating values ​​of the two cables according to the currents of the two cables and the set initial core temperatures, respectively, and substituting them into the transient temperature rise thermal circuit model between the two cables in the groove after parameter identification, obtaining the initial core temperature of each cable under mutual influence and the initial outflow skin heat flux under mutual influence through thermal circuit calculation, and obtaining the initial skin temperature under mutual influence according to the initial outflow skin heat flux under mutual influence; 32) In the kth step of the iteration, the self-heating value of each cable is updated according to the current of each cable in the current step and the core temperature of each cable obtained in the k-1th step, and the variable parameter is updated according to the outflowing outer skin heat flux under the mutual influence obtained in the k-1th step. The core temperature of each cable is obtained by adding and summing the core temperature caused by self-heating and the core temperature under the mutual influence; 33) In the k+1th step of the iteration, the core temperature and heat flow under mutual influence of the k+1th step are obtained by continuing to calculate the heat path according to the cable's own heating value updated in the kth step and the updated variable parameters. Steps 32)-33) are repeated to obtain the core temperature and skin temperature of the two cables under mutual influence.

7. A method for obtaining transient temperature rise between two cables in a groove considering nonlinear convection heat dissipation according to claim 6, characterized in that: In the step 31), the initial wire core temperature is set to be the groove environment temperature.

8. The method for obtaining transient temperature rise between two cables in a groove considering nonlinear convection heat dissipation according to claim 7, characterized in that: In the step 33), the outer skin temperature under the mutual influence of the updated outflow outer skin heat flow is updated through the outer skin temperature rise calculation model of the two cables in the groove. 21 =Q 22 =0, then: t1=Q 11 *R 11 +t0 t2=Q 12 *R 12 +t0。 9. The method for obtaining transient temperature rise between two cables in a groove considering nonlinear convection heat dissipation according to claim 7, characterized in that: In the step 32), the update formula of the variable parameter is: R3=t2 / Q 12 。

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