CN111814323B - Method for acquiring transient temperature rise of row single cable under consideration of nonlinear action of air convection - Google Patents
Method for acquiring transient temperature rise of row single cable under consideration of nonlinear action of air convection Download PDFInfo
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Abstract
The invention relates to a method for acquiring transient temperature rise of a row single cable under the consideration of nonlinear action of air convection, which comprises the following steps: 1) Constructing a transient temperature rise lumped parameter model of the wall of the cable duct and constructing a transient temperature rise lumped parameter model of the cable core with the reference point as the wall temperature; 2) Setting an initial variable thermal resistance value and an initial cable core temperature at an initial moment, calculating according to the initial cable core temperature to obtain an initial cable heat flow, obtaining an initial calandria wall temperature, obtaining the heat flow of a branch where the variable thermal resistance is located, calculating and updating the cable core temperature at the next moment, and updating the cable heat flow and the variable thermal resistance value at the next moment; 3) Obtaining the heat flow of a branch where the variable thermal resistance is located at the next moment and the wall temperature of the pipe at the moment, and updating the cable heat flow and the variable thermal resistance value; 4) And repeating the step 3) until the calculation time length is finished, and finally obtaining the transient temperature rise of the single cable. Compared with the prior art, the method has the advantages of high calculation efficiency, high calculation accuracy and the like.
Description
Technical Field
The invention relates to the technical field of power cable operation, in particular to a method for acquiring lean transient temperature rise of a single cable in a calandria by considering the nonlinear action of air convection.
Background
A large number of power cables exist in urban power grids represented by Beijing, shanghai, guangzhou and Shenzhen, and power utilization regions of 110kV or below, particularly within the range of urban areas, soil direct burial and pipe arrangement are adopted as main laying modes. The cables laid in the calandria have obvious heat transfer effect because of close distance, generally adopt relatively conservative current-carrying capacity selection in a planning and designing stage, give fixed values aiming at different voltages and different cross sections, and do not consider the actual conditions of operation of other cables in the calandria.
Due to the particularity of the operation of the power cable, the temperature of the core of the power cable cannot be obtained through direct measurement, so technical personnel provide various methods for calculating the temperature of the core of the power cable, and the methods are all engineering formulas or approximate formulas based on numerical solutions and test results. For example, the method is a classic calculation method for calculating the temperature of a core of the power cable and a current-carrying capacity solving method based on numerical calculation based on IEC60287 standard. However, the existing similar research is mostly directed at single-loop cables, and the multiple-loop cables in actual operation are mostly solved by adopting a numerical method, so that the complexity of working conditions is considered, the required calculation amount is huge, and the efficiency in specific implementation is very low. Therefore, the operation is generally arranged by adopting a method of uniformly discounting the current of the cable in the calandria group according to the current of a single cable, the actual load current in the operation of different cables is not considered, so that the serious waste of cable resources and channel resources is caused, the rapid calculation of the transient temperature rise of the calandria cable group is based on the rapid calculation of the transient temperature rise of the single cable in the calandria, and the development of the lean operation of the cable is supported by the lack of an effective method for the rapid lean calculation of the transient temperature rise of the single cable, which is suitable for the laying of the calandria and takes the nonlinear action of air convection into consideration.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for acquiring the transient temperature rise of a single cable in a calandria by considering the nonlinear action of air convection.
The purpose of the invention can be realized by the following technical scheme:
a duct bank single cable transient state temperature rise obtaining method considering air convection nonlinear effect comprises the following steps:
1) Constructing a temporary temperature rise lumped parameter model of the row pipe wall and a cable core temporary temperature rise lumped parameter model with the reference point being the wall temperature, and determining model parameters in the models;
2) Setting an initial variable thermal resistance value at an initial time, setting the temperature of an initial cable core to be equal to the ambient temperature, calculating according to the temperature of the initial cable core to obtain initial loss, namely initial cable heat flow, obtaining the temperature of an initial calandria wall according to a transient temperature rise lumped parameter model of the calandria wall, obtaining the heat flow of a branch where the variable thermal resistance is located according to the transient temperature rise lumped parameter model of the cable core, calculating and updating the temperature of the cable core at the next time, and updating the cable heat flow and the variable thermal resistance value at the next time according to the temperature of the cable core at the next time;
3) Obtaining the heat flow of the branch where the variable thermal resistance is located at the moment according to the cable heat flow and the variable thermal resistance value at the next moment, obtaining the tube wall temperature at the moment according to the cable heat flow and the environment temperature at the next moment, and updating the cable heat flow and the variable thermal resistance value according to the updating method in the step 2);
4) And repeating the step 3) until the calculation time length is finished, and finally obtaining the transient temperature rise of the single cable.
The expression of the calandria wall transient temperature rise lumped parameter model is as follows:
I1＝I C1 +I R1 +I R2
wherein, I1 is cable heat flow, C1 is the comprehensive self heat capacity of the cable and the calandria, C2 is equivalent heat capacity of the external section of the calandria, R1 is the equilibrium thermal resistance of the equivalent heat capacity of the external section of the calandria, R2 is the equivalent thermal resistance of the calandria to the external environment, L1 is the equilibrium thermal inductance of the equivalent thermal resistance of the external section of the calandria, I1 C1 、I R1 、I R2 Respectively the heat flow of the branch in which C1, R1 and R2 are located, t C2 The equivalent heat capacity of the external section of the calandria corresponds to the temperature, t1 is the temperature of the calandria wall, and t is the time.
The expression of the cable core transient temperature rise lumped parameter model is as follows:
I1＝I C3 +I R3 +I R4
wherein, I1 is cable heat flow, C3 is comprehensive self heat capacity between the cable and the calandria, C4 is equivalent heat capacity between the cable and the calandria, R3 is balance heat resistance of equivalent heat capacity between the cable and the calandria, R4 is equivalent heat resistance between the cable and the calandria considering air convection nonlinear action, namely variable heat resistance, I C3 、I R3 、I R4 Respectively the heat flow of the branch in which C3, R3 and R4 are located, T C4 The temperature corresponding to the equivalent heat capacity between the cable and the calandria, and t is time.
In the step 2), the temperature of the cable core at the next moment is updated according to the following formula, and the following steps are performed:
wherein r1, p1 and p2 are fitting parameters and are determined by the specific calandria aperture and the cable outer diameter, I R4 And t2 is the temperature of the cable core and t1 is the temperature of the pipe wall of the pipe for the heat flow of the branch where the R4 is located.
In step 2), the variable thermal resistance value at the next moment is updated according to the following formula, and the following formula is included:
wherein, R4 is a variable thermal resistance value, and I4 is a heat flow of a branch where the variable thermal resistance is located.
Parameter values in the calandria wall transient state temperature rise lumped parameter model are only related to thermal characteristics of materials around the outside of the calandria, and the parameter values comprise comprehensive self heat capacity C1 of the cable and the calandria, equivalent heat capacity C2 of the outer section of the calandria, balance heat resistance R1 of the equivalent heat capacity of the outer section of the calandria, equivalent heat resistance R2 of the calandria to the external environment, and balance heat inductance L1 of the equivalent heat resistance of the outer section of the calandria.
The parameters of the calandria wall transient temperature rise lumped parameter model are obtained by solving through a genetic algorithm according to the transient temperature rise process of the calandria wall under the step heat flow.
The parameter values in the cable core transient temperature rise lumped parameter model are obtained by solving through a genetic algorithm according to the process of the cable core transient temperature rise under the step heat flow, and the parameter values comprise comprehensive self heat capacity C3 between cables and the calandria, equivalent heat capacity C4 between the cables and the calandria and balance heat resistance R3 of the equivalent heat capacity between the cables and the calandria.
Compared with the prior art, the invention has the following advantages:
1) The calculation efficiency is high: after the finite calculation, the quantitative relation between the thermal characteristics of the cross section and the calandria, particularly between the heat flow, the wall temperature of the calandria and the temperature of the cable core can be comprehensively mastered, and the subsequent calculation can obtain a satisfactory result only by simple circuit calculation and loss iteration, so that the defects of poor timeliness and reliability of a real-time monitoring method of a numerical calculation method are overcome, and a direct basis is provided for the actual operation of cable equipment.
2) 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.
3) The calculation precision is high: compared with the direct calculation result, the maximum deviation of the transient temperature rise of the wire core in the calculation example is less than 1K in the range of the ring temperature of 0-60 ℃, so that the accuracy of the transient temperature rise calculation method of the calandria cable considering the nonlinear action of air convection is proved, and the method can completely meet the requirement of lean operation scheduling of the power department.
Drawings
Fig. 1 is a lumped parameter model of transient temperature rise of the tube wall.
Fig. 2 is a model of transient temperature rise lumped parameter of cable core with reference point of wall temperature.
Fig. 3 is a schematic cross-sectional view of a cable bank in a calandria.
Fig. 4 is a schematic cross-sectional view of a single cable.
FIG. 5 shows the temperature rise of the core and the temperature rise of the rack pipe wall after the step load.
FIG. 6 is a graph of the results of direct calculation of the ring temperature at 0 ℃ and the wall temperature rise of the method of the invention compared to CYMCAP.
FIG. 7 is a graph showing the results of direct calculation of the temperature rise of the core of the present invention and CYMCAP at 0 ℃ around the temperature.
FIG. 8 shows the direct deviation of the method of the present invention and CYMCAP, when the ring temperature is 0 deg.C and the core temperature rises.
FIG. 9 is a graph showing the results of direct calculation of the temperature rise of the wall at 20 ℃ in the method of the present invention compared to CYMCAP.
FIG. 10 is a comparison of the direct calculation results of the inventive method and CYMCAP at an ambient temperature of 20 deg.C.
FIG. 11 shows the direct calculated deviation of the core temperature increase of the present invention from CYMCAP at an ambient temperature of 20 ℃.
FIG. 12 is a graph of the direct calculation of the ring temperature at 40 ℃ and the wall temperature rise for the method of the invention compared to CYMCAP.
FIG. 13 shows the results of direct calculation of the temperature rise of the core of the inventive method and CYMCAP at an ambient temperature of 40 ℃.
FIG. 14 shows the direct deviation of the temperature rise of the core at 40 ℃ from CYMCAP according to the method of the present invention.
FIG. 15 is a graph showing the direct calculation of the wall temperature rise at 60 ℃ in the method of the present invention compared to CYMCAP.
FIG. 16 is a comparison of the direct calculation results of the inventive method and CYMCAP at a ring temperature of 60 deg.C.
FIG. 17 shows the direct deviation of the temperature rise of the core at 60 ℃ from CYMCAP.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
The invention provides a method for acquiring the lean transient temperature rise of a single cable in a calandria in consideration of the nonlinear action of air convection, which has the following specific principle:
for the cable group laid in the pipe arrangement, the line length of the power cable group is approximate to infinity relative to the cable section and the thermal diffusion section, so that the thermal field of the power cable laid in the pipe arrangement can be simplified into a two-dimensional thermal field model for analysis and calculation.
The transient temperature rise of the cable core is decomposed into two parts, namely the transient temperature rise of the pipe arrangement wall and the transient temperature rise between the cable core and the pipe arrangement wall by utilizing the principle that a thermal field can be superposed, wherein the heat diffusion of the cable core to the surrounding soil is mainly carried out in a heat conduction mode, a heat transfer medium is unchanged, and the specific heat capacity coefficient, the heat transfer coefficient and the like of the cable core are unchanged; the thermal resistance of the air part in the calandria changes along with the temperature change, the thermal resistance needs to be corrected during lean calculation, and the correction rule can be obtained by fitting the calculation result or the experimental result of simulation software.
(1) Obtaining transient temperature rise t1 of the calandria wall
The temperature rise of the calandria wall to the environment temperature mainly depends on the cable loss and the thermal characteristics of the external section of the calandria wall, and the cable loss, the operation current and the operation temperature have a definite corresponding relation and can be directly applied; the latter mainly depends on the geometrical parameters of the external section and the physical parameters of each part, and the physical parameters are considered to be kept unchanged in the operating temperature range, which provides a theoretical basis for establishing the model. According to the analysis, a transient model of the temperature rise of the exhaust pipe wall is established as shown in fig. 1.
The expression of the lumped parameter model of the transient temperature rise of the row pipe walls is as follows:
I1＝I C1 +I R1 +I R2
wherein, I1 is cable heat flow, C1 is the comprehensive self heat capacity of the cable and the calandria, and C2 is the outside of the calandriaSection equivalent heat capacity, R1 is the balance thermal resistance of the equivalent heat capacity of the external section of the calandria, R2 is the equivalent thermal resistance of the calandria to the external environment, L1 is the balance thermal inductance of the equivalent thermal resistance of the external section of the calandria, I C1 、I R1 、I R2 Respectively the heat flow of the branch in which C1, R1 and R2 are located, t C2 The temperature corresponding to the equivalent heat capacity of the external section of the calandria, t1 is the temperature of the calandria wall, and t is the time.
The determination of the model does not depend on the self heat productivity or the current magnitude of the cable, and is only related to the thermal characteristics of the materials around the outside of the calandria, but the characteristics can be considered to be basically unchanged in the general operating temperature range, so that the satisfactory transient temperature rise result of the calandria wall can be obtained by directly calculating through a circuit without repeating numerical calculation such as finite elements and the like when the current of the cable is changed.
(2) Obtaining the transient temperature rise t2 of the cable core
The model of the transient temperature rise lumped parameter of the cable core with the reference point of the wall temperature is shown in figure 2. The air density is much less than that of cable and calandria, so the change of air in calandria along with the temperature change is mainly reflected in the thermal resistance between cable and calandria. The characteristic can be quantitatively described by heat flow, the temperature of the tube wall and the temperature of the cable core, and is represented by variable thermal resistance R4 in a model shown in figure 2.
The expression of the cable core transient temperature rise lumped parameter model is as follows:
I1＝I C3 +I R3 +I R4
wherein I1 is cable heat flowC3 is the comprehensive self heat capacity between the cable and the calandria, C4 is the equivalent heat capacity between the cable and the calandria, R3 is the equilibrium thermal resistance of the equivalent heat capacity between the cable and the calandria, R4 is the equivalent thermal resistance between the cable and the calandria considering the nonlinear action of air convection, namely variable thermal resistance, I C3 、I R3 、I R4 Respectively the heat flow of the branch in which C3, R3 and R4 are located, T C4 The temperature corresponding to the equivalent heat capacity between the cable and the calandria, and t is time.
The basic process of the invention is as follows:
(1) Aiming at a certain section, a cable steady-state and transient-state temperature rise calculation model is established (the existing commercial software is adopted in the example, and numerical calculation such as finite element and the like or other similar commercial software can also be adopted in practical application);
(2) Randomly selecting a plurality of groups of boundary temperatures and load currents, and calculating the temperature rise of the tube bank wall and the steady temperature rise of the cable core under the steady working condition;
(3) Calculating equivalent thermal resistance of the calandria to the external environment, namely thermal resistance R2 in figure 1, according to the heat flow obtained in the step (2) and the temperature of the calandria wall;
(4) Obtaining a quantitative relation among the heat flow obtained in the step (2), the temperature of the tube discharging wall and the temperature of the cable core by fitting, namely, a mathematical expression of the variable thermal resistance R4 in the figure 2;
(5) Setting a certain environment temperature, and acquiring the transient temperature rise process of the drain wall and the cable core by using software;
(6) Obtaining model parameters shown in figure 1 by using the transient temperature rise process of the calandria wall obtained in the step (5) through a genetic algorithm, wherein the model parameters comprise C1, C2, R1 and L1;
(7) Obtaining model parameters shown in the figure 2 by using the transient temperature rise process between the cable cores and the calandria wall obtained in the step (5) through a genetic algorithm, wherein the model parameters comprise C3, C4 and R3;
(8) The iterative solution is carried out on the working condition to be solved in the actual operation, and the iterative solution specifically comprises the following steps:
81 The wall transient temperature rise at the moment t is obtained by using the model shown in FIG. 1, the cable core-wall transient temperature rise at the moment is obtained by using the model shown in FIG. 2, and the two are added to form the transient temperature rise of the cable core at the moment to the ambient temperature;
82 Calculating the wall transient temperature rise and the cable core-wall transient temperature rise at the time of t + dt by substituting the transient temperature rise of each element in the elements in the figures 1 and 2 into the transient data of the elements at the time of t + dt, forming the transient temperature rise and the cable loss of the cable core to the environment temperature at the time of t + dt, and substituting the transient temperature rise and the cable loss into the time of t +2 × dt;
83 ) so on until the end of the calculated duration.
Examples
1. Description of the examples
The simulation calculation of the invention can select the existing commercial software or simulation software such as finite elements, boundary elements and the like, and the CYMCAP calculation software of Canada is selected in the example.
The calculation objects are single (return) cable groups in the calandria, the ambient temperature is 0-40 ℃, the calandria structure is 2 x 5 holes, the cross section is shown in figure 3, the height is 0.75 m, the width is 1.6 m, the top of the calandria is 4.65 m away from the ground, the thermal resistivity of the calandria is 1.2 K.m/W, the thermal resistivity of the soil is 0.6 K.m/W, the cable is a 15kV three-core cable, and the cross section structure is shown in figure 4.
2. Steady state simulation calculation results
Randomly selecting a plurality of groups of boundary temperatures and load currents, and calculating the temperature rise of the tube bank wall and the steady temperature rise of the cable core under the steady working condition, wherein the temperature results are shown in table 1.
TABLE 1 Cable 1 and calandria wall calculation results
3. The equivalent thermal resistance of the calandria to the external environment, namely the thermal resistance R2 in figure 1 is obtained through the heat flow and the calandria wall temperature.
According to the thermal resistance R2= (wall temperature-ring temperature)/loss, the thermal resistance and the average value of the thermal resistance in each operating condition in table 1 can be obtained, as shown in table 2, it should be noted that the reason why the relative deviation of R2 in each operating condition shown in table 2 is large mainly comes from the small effective digit of the software data used.
4. The quantitative relation among the heat flow, the temperature of the exhaust pipe wall and the temperature of the cable core is obtained through fitting, namely the variable thermal resistance R4 in the figure 2.
According to the knowledge of heat transfer science, the fitting relation among the heat flow, the temperature of the tube wall of the tube and the temperature of the core of the cable is provided as
t2＝Q*(r1+p1/(1+p2*(t1+t2)/2))+t1 (1)
Wherein t1 is the temperature of the tube wall at DEG C; t2 is the temperature of the core of the cable, DEG C; q is heat flow, W/m; r1, p1 and p2 are coefficients related to the specific calandria aperture and the cable outer diameter.
The data in table 1 were combined with equation (1) and solved by the least squares method to obtain the fitting results shown in table 3. The fitting effect shows that there is a quantitative rule between the heat flow, the temperature of the calandria wall and the temperature of the cable core, and the rule can be accurately expressed by formula (1), namely variable thermal resistance R4 in FIG. 2.
TABLE 3 fitting results and fitting effects of temperature rise of core of cable 1
| Parameter(s) | p1 | p2 | r1 |
| Results | 0.5547 | 0.0165 | 0.6949 |
| Serial number | Software results (K) | Fitting result (K) | Deviation (K) |
| 1 | 11.1 | 11.076 | 0.024 |
| 2 | 14.5 | 14.493 | 0.007 |
| 3 | 20.0 | 19.922 | 0.078 |
| 4 | 21.1 | 21.043 | 0.057 |
| 5 | 24.4 | 24.366 | 0.034 |
| 6 | 29.7 | 29.666 | 0.034 |
| 7 | 31.1 | 31.016 | 0.084 |
| 8 | 34.3 | 34.266 | 0.034 |
| 9 | 39.5 | 39.461 | 0.039 |
Through heat flow, the equivalent thermal resistance of the cable core to the calandria is obtained as the initial value of the thermal resistance R4 in FIG. 2, which is shown in Table 3.
As can be seen from Table 4, the R4 value varies greatly with different working conditions, which also indicates that the non-linear influence needs to be fully considered to realize the refinement of the calculation.
TABLE 3 equivalent thermal resistance calculation results of cable cores and tube bank walls
It should be noted that the above rules are not only applicable to the present example, but also applicable to the combination of calandria cables with the same pipe diameter and the same cable outer diameter.
5. And setting a certain ring temperature, and utilizing software to obtain the transient temperature rise process of the tube wall and the cable core.
Setting the rated current of the cable 1 as 600A, the ambient temperature as 40 ℃, the current jump from 0 to 600A at 24h, the duration as 144h, the calculation step as 0.1h, the calculation software as CYMCAP, and the calculation results of the transient temperature rise of the cable core and the transient temperature rise of the tube wall as shown in fig. 5.
6. By utilizing the transient temperature rise process of the calandria wall and through a genetic algorithm, the model parameters shown in the figure 1 are obtained, including C1, C2, R1 and L1, and specifically:
61 ) set parameter ranges
And C1 and C2 belong to the group (100 and 5000), R1 belongs to the group (0.001 and 10), binary coding is carried out, the number of initial populations is 1000, the maximum genetic algebra is 200, the cross probability is 0.75, and the mutation probability is 0.3.
62 Set fitness function
According to the transient temperature rise response mc (i) of the exhaust pipe wall of the model shown in fig. 1 and the transient temperature rise response Tc (i) of the exhaust pipe wall calculated in fig. 3, the deviation of two groups of curves is set as a fitness function, and the following are taken:
63 Set convergence criteria
When the maximum genetic algebra is reached, the fitness function is less than 1440 × 0.1=14.4, i.e., convergence is considered.
The calculation result is as follows: c1=682.25, C2=3424.62, R1=0.171, L1= R1R 2C 2.
7. By utilizing the transient temperature rise process between the cable core and the wall of the cable duct, the model parameters shown in the figure 2 are obtained through a genetic algorithm, including C3, C4 and R3, and the method specifically comprises the following steps:
71 ) setting parameter ranges
And C3 and C4 belonged to (0.1 and 50), R3 belonged to (0.01 and 10), binary coding, wherein the number of the initial population is 1000, the maximum genetic algebra is 200, the cross probability is 0.75, and the variation probability is 0.3.
72 Set fitness function
According to the transient temperature rise response ms (i) of the model shown in FIG. 1 and the transient temperature rise response Ts (i) calculated in FIG. 3, the deviation of the two sets of curves is set as a fitness function, and the deviation is taken
73 Set convergence criteria
The fitness function when the maximum number of genetic generations is reached is less than 1440 × 0.1=14.4, i.e. convergence is considered.
The calculation result is as follows: c3=3.591, C4=9.973, R3=0.546.
8. The specific iteration applies as follows:
a. an iterative calculation step:
1) Initially assuming that the temperature of a cable core = the ambient temperature, calculating the conductor loss and the dielectric loss of the cable at the time t0 to form loss P0, namely cable heat flow I1;
2) Calculating to obtain the temperature rise t1 of the tube wall at the time t0 according to the formula (1) according to the transient temperature rise lumped parameter model of the cable core;
3) According to a cable core transient temperature rise lumped parameter model (an average value in a table 3 is taken as an initial value of R4) and a cable heat flow I1, obtaining a branch heat flow where the R4 is located at the time of t0, obtaining a cable core-pipe arrangement wall transient temperature difference, and calculating according to the cable core-pipe arrangement wall transient temperature difference/the branch heat flow where the R4 is located to obtain an R4 value at the next time;
the update formula is specifically as follows:
4) Obtaining new cable heat flow by using the temperature of the cable core at the time t0, and substituting the new cable heat flow into the next time;
5) And repeating the steps 2) -4) until the calculation time length is finished.
b. Trial calculation case
The environmental temperatures are respectively set to be 0 ℃, 20 ℃, 40 ℃ and 60 ℃ (the environmental temperature in the example actually represents the temperature rise effect of other cables on the cable in operation, so that the extreme environmental temperature of 60 ℃ is selected), the current of the cable 1 is increased from 0 to 700A at the moment of 24h, the duration is 144h, and the calculation step length is 0.1 h.
The comparison shows that the maximum deviation of the direct calculation of the temperature rise of the wire core and the CYMCAP is less than 1K under different working conditions, particularly under the condition that the ring temperature is changed from 0 ℃ to 60 ℃, so that the accuracy of the method provided by the invention is proved, and the requirement of lean calculation of the transient temperature rise of the operating cable can be completely met.
Claims (8)
1. A method for acquiring transient temperature rise of a single cable in a row in consideration of nonlinear action of air convection is characterized by comprising the following steps:
1) Constructing a temporary temperature rise lumped parameter model of the row pipe wall and a cable core temporary temperature rise lumped parameter model with the reference point being the wall temperature, and determining model parameters in the models;
2) At an initial time, setting an initial variable thermal resistance value, setting the temperature of an initial cable core to be equal to the ambient temperature, calculating according to the temperature of the initial cable core to obtain initial loss, namely initial cable heat flow, obtaining the temperature of the initial pipe arranging wall according to a pipe arranging wall transient temperature rise lumped parameter model, obtaining the heat flow of a branch where the variable thermal resistance is located according to the cable core transient temperature rise lumped parameter model, calculating and updating the temperature of the cable core at the next time, and updating the cable heat flow and the variable thermal resistance value at the next time according to the temperature of the cable core at the next time;
3) Obtaining the heat flow of the branch where the variable thermal resistance is located at the moment according to the cable heat flow and the variable thermal resistance value at the next moment, obtaining the pipe wall temperature at the moment according to the cable heat flow and the environment temperature at the next moment, and updating the cable heat flow and the variable thermal resistance value according to the updating method in the step 2);
4) And repeating the step 3) until the calculation time length is finished, and finally obtaining the transient temperature rise of the single cable.
2. The method for acquiring the transient temperature rise of the single calandria cable in consideration of the nonlinear effect of air convection according to claim 1, wherein the expression of the lumped parameter model of the transient temperature rise of the calandria wall is as follows:
I1＝I C1 +I R1 +I R2
wherein, I1 is cable heat flow, C1 is the comprehensive self heat capacity of the cable and the calandria, C2 is equivalent heat capacity of the external section of the calandria, R1 is the equilibrium thermal resistance of the equivalent heat capacity of the external section of the calandria, R2 is the equivalent thermal resistance of the calandria to the external environment, L1 is the equilibrium thermal inductance of the equivalent thermal resistance of the external section of the calandria, I1 C1 、I R1 、I R2 Respectively the heat flow of the branch in which C1, R1 and R2 are located, t C2 The equivalent heat capacity of the external section of the calandria corresponds to the temperature, t1 is the temperature of the calandria wall, and t is the time.
3. The method for acquiring the transient temperature rise of the calandria single cable in consideration of the nonlinear action of air convection according to claim 1, wherein the expression of the cable core transient temperature rise lumped parameter model is as follows:
I1＝I C3 +I R3 +I R4
wherein, I1 is cable heat flow, C3 is comprehensive self heat capacity between the cable and the calandria, C4 is equivalent heat capacity between the cable and the calandria, R3 is balance heat resistance of equivalent heat capacity between the cable and the calandria, R4 is equivalent heat resistance between the cable and the calandria considering air convection nonlinear action, namely variable heat resistance, I C3 、I R3 、I R4 Respectively the heat flow of the branch circuit where C3, R3 and variable thermal resistance R4 are positioned, T C4 The temperature corresponding to the equivalent heat capacity between the cable and the calandria, and t is time.
4. The method for obtaining the transient temperature rise of the calandria single cable in consideration of the nonlinear effect of air convection as claimed in claim 1, wherein in the step 2), the temperature of the cable core at the next moment is updated according to the following formula:
wherein r1, p1 and p2 are fitting parameters and are determined by the specific calandria aperture and the cable outer diameter, I R4 The heat flow of the branch where the variable thermal resistance R4 is located is shown as t2, the temperature of a cable core is shown as t1, and the temperature of a calandria wall is shown as t 1.
5. The method for obtaining transient temperature rise of single cable in calandria in consideration of air convection nonlinear effect as claimed in claim 1, wherein in said step 2), the variable thermal resistance value at the next moment is updated according to the following formula:
wherein, R4 is a variable thermal resistance value, and I4 is a heat flow of a branch where the variable thermal resistance is located.
6. The method for acquiring the transient state temperature rise of the single cable in the calandria in consideration of the nonlinear effect of air convection according to claim 2, wherein the parameter values in the transient state temperature rise lumped parameter model of the calandria wall are only related to the thermal characteristics of the surrounding materials outside the calandria, and the method comprises the comprehensive self heat capacity C1 of the cable and the calandria, the equivalent heat capacity C2 of the external section of the calandria, the balanced thermal resistance R1 of the equivalent heat capacity of the external section of the calandria, the equivalent thermal resistance R2 of the calandria to the external environment and the balanced thermal inductance L1 of the equivalent thermal resistance of the external section of the calandria.
7. The method for acquiring the transient temperature rise of the calandria single cable in consideration of the nonlinear effect of air convection according to claim 6, wherein the parameters of the calandria wall transient temperature rise lumped parameter model are obtained by solving through a genetic algorithm according to the process of the transient temperature rise of the calandria wall under the step heat flow.
8. The method for acquiring the transient temperature rise of the single calandria cable in consideration of the nonlinear effect of air convection according to claim 3, wherein the parameter values in the cable core transient temperature rise lumped parameter model are obtained by solving through a genetic algorithm according to the process of the transient temperature rise of the cable cores under the step heat flow, and the method comprises the steps of the comprehensive self heat capacity C3 between the cables and the calandria, the equivalent heat capacity C4 between the cables and the calandria and the balance heat resistance R3 of the equivalent heat capacity between the cables and the calandria.
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