CN112883615A - Method for acquiring transient temperature rise between two cables in groove by considering nonlinear convection heat dissipation - Google Patents
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Abstract
The invention relates to a method for acquiring transient temperature rise between two cables in a groove by considering nonlinear convection heat dissipation, which comprises the following steps of: 1) constructing a transient temperature rise thermal circuit model between two cables of the groove; 2) identifying parameters of a transient temperature rise thermal circuit model between two cables by adopting a finite element calculation method; 3) and obtaining the current of the two cables in the actual groove, and obtaining the transient temperature rise between the two cables under the mutual influence through iterative calculation according to the transient temperature rise thermal circuit model between the two cables after parameter identification. Compared with the prior art, the method has the advantages of considering nonlinear convection heat dissipation, not depending on skin temperature measurement, being suitable for the condition of two cables, high reliability, high timeliness, clear and definite calculation process and the like.
Description
Technical Field
The invention relates to the technical field of power cable operation detection, in particular to a method for acquiring transient temperature rise between two cables in a groove by considering nonlinear convection heat dissipation.
Background
At present, a groove mode is adopted for the cables to pass in and out of a transformer substation, the convection heat transfer and the radiation heat transfer in the groove are nonlinear, and particularly, the convection heat dissipation lacks of a definite quantitative rule, so that the heating problem of the groove cables is relatively complex.
Due to the particularity of the operation of the power cable, the temperature of the core of the cable cannot be obtained through direct measurement generally, particularly the real-time transient temperature of the core of a cable group can not be obtained through direct measurement, the core temperature is generally mastered through an engineering formula method, a numerical algorithm or an indirect measurement method based on test results, wherein the empirical formula method is mainly used for calculating the steady-state temperature rise of typical laying, the application range is insufficient, the heat dissipation inside a groove relates to thermodynamics and hydrodynamics, the numerical calculation method is large in calculation amount when the actual multi-working-condition cable temperature rise is simulated, the calculation time is long, the temperature rise change cannot be obtained in time, an optical fiber temperature measurement or other devices are additionally arranged to obtain the skin temperature of the cable firstly through the indirect.
Therefore, a convenient and fast method is needed to obtain the transient temperature rise of the groove cable group, and the method has important significance in the aspects of full utilization of existing cable resources, planning and construction of a power grid and the like.
Disclosure of Invention
The present invention is directed to overcome the above-mentioned drawbacks of the prior art, and to provide a method for obtaining a transient temperature rise between two cables in a trench by considering nonlinear convection heat dissipation.
The purpose of the invention can be realized by the following technical scheme:
a method for acquiring transient temperature rise between two cables in a groove by considering nonlinear convection heat dissipation comprises the following steps:
1) constructing a transient temperature rise thermal circuit model between two cables of the groove;
2) identifying parameters of a transient temperature rise thermal circuit model between two cables by adopting a finite element calculation method;
3) and obtaining the current of the two cables in the actual groove, and obtaining the transient temperature rise between the two cables through iterative calculation according to the transient temperature rise thermal circuit model between the two cables after parameter identification.
The transient temperature rise thermal circuit model between the two cables in the groove is constructed according to the model, the structure and the arrangement mode of the two cables in the groove and is used for describing the thermal transition process between the cables on the section of the groove.
In the step 1), the transient temperature rise heat circuit model between the two cables in the groove is composed of a first thermal resistance R1The first thermal sensation L1Thermal load Q of first cable1The first branch and the first heat capacity C1The second branch and the second thermal resistance R2And a second heat capacity C2Comprehensive thermal resistance R of the third branch and the second cable core to the environment3The heat insulation structure comprises a fourth branch, wherein the common ends of the first branch, the second branch, the third branch and the fourth branch are all groove environment temperature, the other ends of the third branch and the fourth branch are used for heating the first cable to influence the sheath temperature of the second cable, and the other ends of the third branch and the fourth branch sequentially pass through a first thermal resistor R1And a first sensation of heat L1Is connected with the other ends of the third branch and the fourth branch, and a second thermal resistance R is arranged on the third branch2And a second heat capacity C2The first cable generates heat to affect the temperature of the wire core of the second cable.
In the step 2), the parameters of the transient temperature rise thermal circuit model between the two cables comprise fixed parameters and variable parameters, the numerical values of the fixed parameters are determined by the models, the structures and the arrangement modes of the two cables in the groove, and the parameters comprise a first thermal resistance R1The first thermal sensation L1First heat capacity C1A second thermal resistance R2And a second heat capacity C2The variable parameter isComprehensive thermal resistance R of two cable cores to environment3。
In the step 2), a finite element method is used for simulating random working conditions to obtain multiple groups of data, and each group of data is obtained by the ambient temperature T0Thermal load Q of first cable1Thermal load Q of first cable2Core temperature T of first cable1cAnd skin temperature T1sAnd core temperature T of the second cable2cAnd skin temperature T2sAnd according to the data, performing parameter estimation of a calculation model of the temperature rise of the two cable sheaths of the groove.
The temperature rise calculation model of the two cable sheaths in the groove is specifically as follows:
t1＝Q11*[p1+p2*power(t0,k1)+p3*power(t1,k2)+p4*power(t2,k3)]+Q21*[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+t0＝Q11*R11+Q21*R21+t0
t2＝Q12*[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+Q22*[pp5+pp6*power(t0,kk4)+pp7*power(t1,kk5)+pp8*power(t2,kk6)]+t0＝Q12*R12+Q22*R22+t0
wherein R is11、R22Thermal resistances, R, for self-heating of the first and second cables, respectively12＝R21Thermal resistances for mutual influence heating of the first cable and the second cable respectively, i.e. comprehensive thermal resistance R3，Q11、Q22Outflow sheath heat flow Q for the first and second cables, respectively, to heat themselves12、Q21Respectively, the heat flows of the outer skin under the mutual influence obtained according to a transient temperature rise heat circuit model between the two cables, namely the heat flows of the outer skin which flows through the comprehensive thermal resistance R3Heat flow of (t)1And t2Sheath temperatures, t, corresponding to the first and second cables, respectively0For trench ambient temperature, power (-) represents a power exponent operation of the base number, p1、p2、p3、p4、p5、p6、p7、p8、k1、k2、k3、k4、k5、k6、pp5、pp6、pp7、pp8、kk4、kk5、kk6Are all estimated parameters.
The step 3) specifically comprises the following steps:
31) setting a variable parameter in a transient temperature rise thermal circuit model between two cables of a groove, namely comprehensive thermal resistance R3Respectively obtaining the self heat productivity of the two cables according to the current of the two cables and the set initial core temperature, respectively substituting the self heat productivity into a transient temperature rise thermal circuit model between the two cables in the groove after parameter identification, respectively obtaining the initial core temperature of each cable under mutual influence and the initial outflow sheath heat flow under mutual influence through thermal circuit calculation, and obtaining the initial sheath temperature under mutual influence according to the initial outflow sheath heat flow under mutual influence;
32) in the iterative kth step, updating the cable self-heating value of each cable according to the current of each cable in the current step and the core temperature of each cable obtained in the kth-1 step, and updating the variable parameters according to the outflow sheath heat flow under the mutual influence obtained in the kth-1 step, wherein the core temperature of each cable is obtained by the superposition summation of the core temperature caused by the self-heating and the core temperature under the mutual influence;
33) and in the iterative k +1 step, the core temperature under the mutual influence and the heat flow under the mutual influence in the k +1 step are obtained by continuously calculating the heat circuit according to the self heating value of the cable updated in the k +1 step and the updated variable parameters, and the steps 32-33) are repeated, so that the core temperature and the skin temperature of the two cables under the mutual influence can be obtained.
In the step 31), the set initial wire core temperature is the groove environment temperature.
In the step 33), the sheath temperature under the mutual influence is updated through the temperature rise calculation model of the two cables in the groove according to the updated outflow sheath heat flow under the mutual influence, and when Q is reached21＝Q22When 0, then there are:
t1＝Q11*R11+t0
t2＝Q12*R12+t0。
in the step 32), the updating formula of the variable parameter is as follows:
R3＝t2/Q12。
compared with the prior art, the invention has the following advantages:
firstly, the invention establishes a rapid transient temperature rise calculation model between two cables of the groove considering nonlinear convection heat dissipation, thereby overcoming the defects of poor timeliness and poor reliability of a real-time monitoring method of a numerical calculation method, and providing a direct basis for the subsequent rapid algorithm research of the transient temperature rise of the groove cable group and even the actual operation control of cable equipment.
Secondly, in order to adapt to the nonlinear heat dissipation characteristic among the groove cables, the nonlinear thermal resistance R representing the sheath temperature-heat productivity rule is introduced into the transient temperature rise calculation model for the first time3。
And the model is basically independent of loss, only reflects the thermal characteristics of the section, has clear physical significance and provides direct basis for subsequent analysis and improvement.
Drawings
Fig. 1 is a model of transient calculation between cables.
FIG. 2 is a schematic diagram of a finite element calculation model of temperature rise of two cables in a groove.
Fig. 3 is a histogram of the sheath temperature rise error of the cable 1.
Fig. 4 is a temperature rise error histogram of the sheath of the cable 2.
Fig. 5 shows the temperature rise process of the core and the sheath of the cable 1.
Fig. 6 shows the temperature rise process of the core and the sheath of the cable 2.
Fig. 7 is a comparison of the temperature rise process of the core and the sheath of the cable 2.
Fig. 8 is a comparison of temperature rise processes of the core and the sheath of the cable 2 under the checking working condition.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Example (b):
the invention provides a method for acquiring transient temperature rise between two cables in a groove by considering nonlinear convection heat dissipation, which has the following principle:
the heating of the cable mainly depends on the loss of the cable and the thermal characteristics of the section where the cable is located, the loss of the cable has a clear corresponding relation with the running current and the running temperature, and the cable can be directly applied; the latter depends mainly on the geometrical parameters of the section and the physical parameters of each part. According to the analysis of heat transfer science, the thermal resistance of the cable body is related to the specific structure of the cable, and the thermal resistance can be regarded as unchanged in calculation; the radiation heat dissipation capacity, the radiation heat dissipation thermal resistance and the convection heat dissipation thermal resistance are related to factors such as the ring temperature, the heat productivity and the like, wherein the rules of the radiation heat dissipation capacity, the radiation heat dissipation thermal resistance and the convection heat dissipation thermal resistance are known and can be obtained by a determined formula; for the latter, it will be sought to represent it in some mathematical form by mathematical modeling, thus providing the possibility of fast calculation.
Aiming at the influence of the transient temperature rise between two cables in the groove, the transient temperature rise model (thermal circuit model) between the two cables is provided, as shown in fig. 1, and the temperature reference point of the model is the groove environment temperature.
In FIG. 1, Q1Is a thermal load for the cable 1; r3The comprehensive thermal resistance of the wire core of the cable 2 to the environment is provided; r1、L1、R2、C1And C2All parameters are parameters for generating different transition processes, have no clear physical significance, and reflect the thermal transition process between the cables with the groove sections.
The determination of the model does not depend on the heat generation quantity or the current magnitude of the cable, is only related to the heat characteristic of the material around the cable, and is generally carried outWithin a range of line temperatures except for R3Furthermore, such properties may be considered to be substantially unchanged; for a particular cross-section, R can be modeled mathematically3The method is expressed in a certain mathematical form, so that after the model is established, numerical calculation such as finite elements is not required to be repeated when the cable current is converted, and a satisfactory result can be obtained directly through simple iteration.
The method mainly comprises the following steps:
1.1 finite element calculation model
The method adopts finite element calculation, and other numerical calculation or test methods can also be adopted in practical application. The finite element calculation model in this example is shown in FIG. 2.
The calculation adopts a finite element method, the grooves are selected to be 1m x 0.5m, the air is selected to be ideal gas information, the cables 1 and 2 are selected to be non-uniform heat conductivity coefficients, and the heat conductivity coefficient of the copper conductor is selected to be 380W/(m)2K), the heat conductivity coefficient of the XLPE material is selected to be 0.3W/(m)2K), conductor diameter 5cm, insulation thickness 2.5 cm.
1.2 Hot Path model building
R in the thermal circuit model3The parameter rule can be extracted through steady-state calculation, and other parameters are obtained through transient calculation data.
(1) Fitting of skin temperature-heat productivity law
Calculating the random selection of the working condition, namely the ring temperature is 0-30 ℃, and the body heat flow changes randomly; and (3) steady state calculation: the iteration step number is 500 steps, and the relaxation factor is 0.5; different ring temperatures T0Cable 1 heat flow Q1Cable 2 heat flow Q2Under the condition, the core temperature T of the cables 1 and 2 under 60 working conditions1cAnd T2cTemperature T of outer skin1sAnd T2sThe steady state calculation results are shown in table 1.
TABLE 1 finite element calculation results of temperature rise of grooved cables 1 and 2
The invention provides a temperature rise calculation model of two cable sheaths in a groove, which is shown as a formula (1).
t1＝Q11*[p1+p2*power(t0,k1)+p3*power(t1,k2)+p4*power(t2,k3)]+Q21*[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+t0＝Q11*R11+Q21*R21+t0
t2＝Q12*[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+Q22*[pp5+pp6*power(t0,kk4)+pp7*power(t1,kk5)+pp8*power(t2,kk6)]+t0＝Q12*R12+Q22*R22+t0
(1)
Wherein R is11、R22Thermal resistance for self-heating of the cables 1, 2, R12＝R21Thermal resistance, Q, for the mutual influence of the heating of the cables 1, 211、Q22Outflow sheath heat flow, Q, obtained for the self-heating model of the cables 1, 212、Q21The resulting outflow sheath heat flow for the heating model is influenced by the cables 1, 2.
The parameters are estimated by using a Marquardt method (Levenberg-Marquardt) + general global optimization method, the estimation result is shown in Table 2, the error histograms are shown in FIGS. 3-4, and the error statistics are shown in Table 3.
TABLE 2 Cable 1, 2 convective thermal resistance parameter estimation
| Parameter(s) | Best estimate | Parameter(s) | 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 |
Table 3 statistical table for temperature error of cable 1, 2 sheath
| N | Minimum | Maximum | Mean | Std.Deviation | |
| Cable 1 crust (K) | 60 | -2.80 | 2.79 | 0.0175 | 1.18046 |
| |
60 | -2.68 | 3.64 | 0.0348 | 1.14302 |
Statistics shows that the whole normal distribution is met, the maximum deviation is not more than 4K, the variance is 1.18K and 1.14K, and the actual operation requirement can be met.
The parameters in the table 2 are substituted into the formula (1), and then a quantitative rule representing the relationship among the temperature of the two cables in the groove, the environment temperature of the groove and the heat productivity can be obtained. When Q is21＝Q22When 0, formula (1) is converted to formula (2).
t1＝Q11*[p1+p2*power(t0,k1)+p3*power(t1,k2)+p4*power(t2,k3)]+t0＝Q11*R11+t0
t2＝Q12*[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+t0＝Q12*R12+t0
(2)
(2)C1、C2、R1、R2、L1Isotransient parameter extraction
Calculating working condition selection: the environment temperature is 15 ℃, the cable 1 is subjected to step excitation, the cable 2 is subjected to 0 input, and the body heat flow is 75W/m; the step size is 1000s, the calculation time length is 300 × 1000s, the number of steps of single step iteration is 250 steps, and the relaxation factor is 0.5. The calculation results are shown in fig. 5 and 6.
Transient parameters were solved by genetic algorithm based on the transient model between two cables in the trench as shown in fig. 1. The above parameters reflect the thermal transition of the trench profile.
1) Setting parameter ranges
Get C1、C2∈(0,100)，L1∈(0,500)，R1、R2Belongs to (0,50), binary coding, the number of initial populations is 200, the maximum genetic algebra is 100, the cross probability is 0.75, and the mutation probability is 0.25.
2) Setting fitness function
Line core transient temperature rise response m according to the model shown in FIG. 1c(i) Response m to transient temperature rise of outer sheaths(i) And calculating the transient temperature rise response T of the core of the cable 2 under the excitation of the cable 1 as shown in FIG. 6c(i) Transient temperature rise response T with outer sheaths(i) And the deviation of the two groups of curves is taken as a fitness function, and is shown as a formula (3).
3) Setting convergence criterion
When the fitness function reaches the maximum genetic algebra, the fitness function is less than 300 × 0.1 × 2 — 6, i.e., convergence is considered.
4) Application of 'skin temperature-heat productivity' rule
a. Set up R3Initial value is 1. Note that, since C is1、C2、L1、R1、R2In the presence of R3The setting of the initial value does not affect the subsequent calculation.
b. R was calculated using the model and set heat flow shown in FIG. 13Heat flow Q of the branch12＝IR3。
c. Using the formula (2), the skin temperature rise t can be obtained2。
d. Correction of R3＝t2/Q12The model shown in fig. 1 was parameter adjusted.
e. And d, repeating the steps b-d until the transient process is finished.
5) Calculation results
The calculation result is as follows: c1＝12.648W*s/(K*m)，C2＝7.101W*s/(K*m)，L1＝186.979K*s*m/W，R1＝7.695K*m/W，R24.069K m/W, the fitness function, fit, is 1.738 is less than the convergence criterion, and the calculation may be considered to be converged.
According to the obtained parameters, the temperature rise of the core and the sheath of the cable 2 is calculated and compared with the result of direct calculation of ansys (as shown in fig. 6), as shown in fig. 7. The error statistics are shown in table 4.
Table 4 cable 2 core, sheath temperature rise process error statistical table
| Minimum | Maximum | Mean | Std.Deviation | |
| Core error (K) | -0.12 | 0.16 | -0.0001 | 0.05283 |
| Outer skin error (K) | -0.10 | 0.10 | -0.0001 | 0.05511 |
1.3 application procedure and verification of Hot Path model
1.3.1 application procedure of the model
1) Modeling according to parameters obtained in section 2.2, and setting R3Initial value is 1.
2) Calculating core temperature rise and R by using the model shown in FIG. 1 and setting the initial heat flow3Heat flow Q of the branch12＝IR3。
3) By using the formula (2), the skin temperature rise t relative to the trench ambient temperature can be obtained2。
4) Correction of R3＝t2/Q12The model shown in fig. 1 was parameter adjusted.
5) Correcting cable thermal load Q in figure 1 according to core temperature and real-time current1。
6) And repeating the steps 2) -5) until the transient process is finished.
1.3.2 checking working conditions
The above model was applied to the conditions shown in table 5, with a trench ambient temperature of 20 ℃, and compared with finite element calculations, the cable core to sheath temperature rise ratio is shown in fig. 8, with error statistics shown in table 6.
TABLE 5 Cable working condition table
Table 6 statistics table for temperature rise process error of cable 2 core and sheath
| Minimum | Maximum | Mean | Std.Deviation | |
| Core error (K) | -3.66 | 1.85 | -0.4140 | 1.46392 |
| Outer skin error (K) | -1.69 | 1.19 | 0.0712 | 0.77832 |
Claims (10)
1. A method for acquiring transient temperature rise between two cables in a groove by considering nonlinear convection heat dissipation is characterized by comprising the following steps:
1) constructing a transient temperature rise thermal circuit model between two cables of the groove;
2) identifying parameters of a transient temperature rise thermal circuit model between two cables by adopting a finite element calculation method;
3) and obtaining the current of the two cables in the actual groove, and obtaining the transient temperature rise between the two cables under the mutual influence through iterative calculation according to the transient temperature rise thermal circuit model between the two cables after parameter identification.
2. The method for acquiring the transient temperature rise between two cables in the groove considering the nonlinear convective heat dissipation according to claim 1, wherein the transient temperature rise thermal circuit model between two cables in the groove is constructed according to the model, the structure and the layout of the two cables in the groove, so as 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 trench considering nonlinear convective heat dissipation as claimed in claim 1, wherein in step 1), the transient temperature rise thermal path model between two cables in a trench is defined by a first thermal resistance R1The first thermal sensation L1Thermal load Q of first cable1The first branch and the first heat capacity C1The second branch and the second thermal resistance R2And a second heat capacity C2Comprehensive thermal resistance R of the third branch and the second cable core to the environment3The heat insulation structure comprises a fourth branch, wherein the common ends of the first branch, the second branch, the third branch and the fourth branch are all groove environment temperature, the other ends of the third branch and the fourth branch are used for heating the first cable to influence the sheath temperature of the second cable, and the other ends of the third branch and the fourth branch sequentially pass through a first thermal resistor R1And a first sensation of heat L1Is connected with the other ends of the third branch and the fourth branch, and a second thermal resistance R is arranged on the third branch2And a second heat capacity C2The first cable generates heat to affect the temperature of the wire core of the second cable.
4. The method for obtaining the transient temperature rise between two cables in the trench considering the nonlinear convective heat dissipation as recited in claim 3, wherein in the step 2), the parameters of the transient temperature rise thermal circuit model between two cables include fixed parameters and variable parameters, and the values of the fixed parameters are determined by the model, structure and layout of the two cables in the trench, including the first thermal resistance R1The first thermal sensation L1First heat capacity C1A second thermal resistance R2And a second heat capacity C2And the variable parameter is the comprehensive thermal resistance R of the second cable core to the environment3。
5. A method of heat dissipation considering nonlinear convection as recited in claim 4The method for acquiring the transient temperature rise between two cables in the groove is characterized in that in the step 2), a finite element method is used for simulating random working conditions to obtain a plurality of groups of data, and each group of data is obtained by the environmental temperature T0Thermal load Q of first cable1Thermal load Q of first cable2Core temperature T of first cable1cAnd skin temperature T1sAnd core temperature T of the second cable2cAnd skin temperature T2sAnd according to the data, performing parameter estimation of a calculation model of the temperature rise of the two cable sheaths of the groove.
6. The method for obtaining the transient temperature rise between two cables in the groove by considering the nonlinear convective heat dissipation according to claim 5, wherein the calculation model of the temperature rise of the two cables in the groove is specifically as follows:
t1＝Q11*[p1+p2*power(t0,k1)+p3*power(t1,k2)+p4*power(t2,k3)]+Q21*[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+t0
＝Q11*R11+Q21*R21+t0
t2＝Q12*[p5+p6*power(t0,k4)+p7*power(t1,k5)+p8*power(t2,k6)]+Q22*[pp5+pp6*power(t0,kk4)+pp7*power(t1,kk5)+pp8*power(t2,kk6)]+t0
＝Q12*R12+Q22*R22+t0
wherein R is11、R22Thermal resistances, R, for self-heating of the first and second cables, respectively12＝R21Are respectively the firstThermal resistance of root cable and second cable mutually influencing heating, i.e. comprehensive thermal resistance R3，Q11、Q22Outflow sheath heat flow Q for the first and second cables, respectively, to heat themselves12、Q21Respectively, the heat flows of the outer skin under the mutual influence obtained according to a transient temperature rise heat circuit model between the two cables, namely the heat flows of the outer skin which flows through the comprehensive thermal resistance R3Heat flow of (t)1And t2Sheath temperatures, t, corresponding to the first and second cables, respectively0For trench ambient temperature, power (-) represents a power exponent operation of the base number, p1、p2、p3、p4、p5、p6、p7、p8、k1、k2、k3、k4、k5、k6、pp5、pp6、pp7、pp8、kk4、kk5、kk6Are all estimated parameters.
7. The method for obtaining the transient temperature rise between two cables in a trench considering nonlinear convective heat dissipation according to claim 6, wherein the step 3) specifically comprises the following steps:
31) setting a variable parameter in a transient temperature rise thermal circuit model between two cables of a groove, namely comprehensive thermal resistance R3Respectively obtaining the self heat productivity of the two cables according to the current of the two cables and the set initial core temperature, respectively substituting the self heat productivity into a transient temperature rise thermal circuit model between the two cables in the groove after parameter identification, respectively obtaining the initial core temperature of each cable under mutual influence and the initial outflow sheath heat flow under mutual influence through thermal circuit calculation, and obtaining the initial sheath temperature under mutual influence according to the initial outflow sheath heat flow under mutual influence;
32) in the iterative kth step, updating the cable self-heating value of each cable according to the current of each cable in the current step and the core temperature of each cable obtained in the kth-1 step, and updating the variable parameters according to the outflow sheath heat flow under the mutual influence obtained in the kth-1 step, wherein the core temperature of each cable is obtained by the superposition summation of the core temperature caused by the self-heating and the core temperature under the mutual influence;
33) and in the iterative k +1 step, the core temperature under the mutual influence and the heat flow under the mutual influence in the k +1 step are obtained by continuously calculating the heat circuit according to the self heating value of the cable updated in the k +1 step and the updated variable parameters, and the steps 32-33) are repeated, so that the core temperature and the skin temperature of the two cables under the mutual influence can be obtained.
8. The method for obtaining transient temperature rise between two cables with grooves considering nonlinear convective heat dissipation of claim 7, wherein in the step 31), the initial core temperature is set to be the groove ambient temperature.
9. The method according to claim 8, wherein in step 33), the calculation model of the sheath temperature under the mutual influence is updated according to the updated outflow sheath heat flow under the mutual influence, and when Q is reached, the calculation model of the sheath temperature of the two cables in the groove is updated21＝Q22When 0, then there are:
t1＝Q11*R11+t0
t2＝Q12*R12+t0。
10. the method for obtaining transient temperature rise between two cables with grooves considering nonlinear convective heat dissipation of claim 8, wherein in the step 32), the updating formula of the variable parameters is:
R3＝t2/Q12。
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