Cable temperature rise calculation method based on dynamic resistance and environment temperature change

Abstract

The embodiment of the invention relates to a cable temperature rise calculation method based on dynamic resistance and environment temperature change, and the method comprises the steps: building a cable simulation model according to cable structure parameters, and the cable simulation model comprises a conductor layer and an insulating layer wrapping the conductor layer; setting a current constraint condition and a cable burial depth, and establishing a dynamic temperature boundary condition; calculating the real-time calorific value of the cable by taking the conductor layer as a heat source; and calculating the temperature rise by adopting a finite element method according to the cable heat conduction equation and the real-time heat productivity of the cable in combination with the dynamic resistance of the conductor layer and the dynamic heat conductivity coefficient of the insulating layer. According to the embodiment of the invention, during temperature rise calculation, the real-time change of the external environment temperature is considered, the change of the resistance of the cable conductor layer along with the temperature change and the influence of the dynamic heat conductivity coefficient of the insulating layer on the heat conduction between the adjacent material layers are also considered, and the accuracy of temperature rise calculation is improved.

Description

Technical Field

[0001] The present disclosure relates to the field of cable technology, and in particular to a method for calculating cable temperature rise based on dynamic resistance and ambient temperature changes. Background Art

[0002] As an important part of the power system, power cables use cable temperature to determine whether the current carrying capacity of the cables is reasonable, which is of great significance to ensure the safe operation of the power system and avoid thermal failures. However, as the operating conditions of power cables become increasingly variable and the laying environment becomes more complex, more and more factors need to be considered in estimating the temperature rise of cables.

[0003] The cable temperature rise calculation method in the prior art ignores the real-time change of the external environment temperature in actual situations and the factor that the resistance of the cable conductor changes with the temperature, resulting in inaccurate calculation results of the cable temperature rise.

[0004] Therefore, it is necessary to provide a new technical solution to improve one or more problems existing in the above solutions.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] The purpose of the embodiments of the present disclosure is to provide a cable temperature rise calculation method based on dynamic resistance and ambient temperature changes, so as to improve the accuracy of temperature rise calculation.

[0007] According to an embodiment of the present disclosure, a method for calculating cable temperature rise based on dynamic resistance and ambient temperature changes is provided, comprising:

[0008] Establishing a cable simulation model according to the cable structural parameters, wherein the cable simulation model includes a conductor layer and an insulating layer wrapping the conductor layer;

[0009] Set current constraints and cable burial depth, and establish dynamic temperature boundary conditions;

[0010] Taking the conductor layer as a heat source, calculating the real-time heating value of the cable;

[0011] The temperature rise is calculated using the finite element method according to the cable heat conduction equation and the real-time heat generation of the cable, combined with the dynamic resistance of the conductor layer and the dynamic thermal conductivity of the insulation layer.

[0012] In an exemplary embodiment of the present disclosure, the dynamic resistance of the conductor layer is determined by formula (1):

[0013]

[0014] Among them, R represents the real-time resistance value of the conductor layer, ρ0 represents the resistivity at the starting temperature, α represents the resistivity temperature coefficient, and T c It represents the real-time temperature of the conductor layer, L represents the length of the conductor layer, and S represents the cross-sectional area of ​​the conductor layer.

[0015] In an exemplary embodiment of the present disclosure, the obtaining of the real-time heating value of the cable by using the conductor layer as a heat source comprises:

[0016] Obtain the real-time resistance value of the conductor layer;

[0017] According to the real-time resistance value, the real-time heating value of the cable is calculated by formula (2):

[0018]

[0019] Among them, Q represents the heat generated by the conductor layer, I represents the current of the conductor layer, R represents the real-time resistance value of the conductor layer, S represents the cross-sectional area of ​​the conductor layer, and L represents the length of the conductor layer.

[0020] In an exemplary embodiment of the present disclosure, the dynamic thermal conductivity of the insulating layer is determined by formula (3):

[0021] λ i =a i T c +λ0(3)

[0022] Among them, λ i represents the thermal conductivity of the insulation layer, a i Represents the temperature coefficient, T c represents the temperature of the conductor layer, and λ0 represents the initial value of thermal conductivity.

[0023] In an exemplary embodiment of the present disclosure, the cable heat conduction equation is expressed as:

[0024]

[0025] Where ρ represents density, c p represents the specific heat capacity at constant pressure, T represents the temperature, t represents the time, represents the convection term, u represents the velocity vector, Represents the temperature difference, represents the heat conduction term, k represents the thermal conductivity, Q total Represents the total heat source term.

[0026] In an exemplary embodiment of the present disclosure, setting the current constraint condition and the cable burial depth includes:

[0027] Obtain the functional relationship between cable temperature and cable burial depth;

[0028] The cable burial depth is determined according to the functional relationship between the cable temperature and the cable burial depth.

[0029] In an exemplary embodiment of the present disclosure, the step of obtaining the functional relationship between the cable temperature and the cable burial depth includes:

[0030] Multiple groups of cables are placed at different burial depths;

[0031] Putting the plurality of groups of cables into operation and collecting the operating temperatures of the plurality of groups of cables when they have been operated for a rated working time;

[0032] With the burial depth as the horizontal coordinate and the temperature as the vertical coordinate, a curve of the corresponding relationship between the burial depth and the temperature is drawn;

[0033] The functional relationship between cable temperature and cable burial depth is obtained according to the corresponding relationship curve between burial depth and temperature.

[0034] In an exemplary embodiment of the present disclosure, the cable burial depth is set to 0.7m to 0.9m.

[0035] In an exemplary embodiment of the present disclosure, the establishing of dynamic temperature boundary conditions includes:

[0036] Collect real-time surface ambient temperature;

[0037] The collected real-time surface ambient temperature is fitted to obtain the temperature boundary condition.

[0038] In an exemplary embodiment of the present disclosure, the cable structural parameters include material parameters, size parameters and thermal parameters.

[0039] The technical solution provided by the present disclosure may have the following beneficial effects:

[0040] In the embodiments of the present disclosure, a cable simulation model is established according to the cable structural parameters. For the cable simulation model, current constraint conditions are set to constrain the current of the cable in the operating state, and the cable burial depth is set so that the cable is at an appropriate burial depth. By establishing dynamic temperature boundary conditions, the real-time changes of the external ambient temperature are taken into account in the subsequent temperature rise calculation, which is conducive to improving the accuracy of the temperature rise calculation; in addition, when the finite element method is used to calculate the temperature rise according to the cable heat conduction equation and the real-time heating value of the cable, the dynamic resistance change of the conductor layer and the dynamic thermal conductivity of the insulation layer are also considered. In this way, the factor that the resistance of the cable conductor layer changes with the temperature and the influence of the dynamic thermal conductivity of the insulation layer on the heat conduction between adjacent material layers are taken into account in the temperature rise calculation, which is conducive to further improving the accuracy of the temperature rise calculation.

[0041] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0043] Figure 1 A flowchart showing the steps of a cable temperature rise calculation method based on dynamic resistance and ambient temperature changes in an exemplary embodiment of the present disclosure;

[0044] Figure 2 A schematic diagram showing a curve of corresponding relationship between burial depth and temperature in an exemplary embodiment of the present disclosure;

[0045] Figure 3 A schematic diagram showing the real-time ambient temperature of the ground surface in an exemplary embodiment of the present disclosure;

[0046] Figure 4 A schematic diagram showing the result of fitting the collected real-time surface ambient temperature in an exemplary embodiment of the present disclosure is shown;

[0047] Figure 5 A schematic diagram of temperature simulation results when the cable simulation model in the exemplary embodiment of the present disclosure runs to the 21st hour is shown;

[0048] Figure 6 A schematic diagram of temperature simulation results when the cable simulation model in the exemplary embodiment of the present disclosure runs to the 50th hour is shown;

[0049] Figure 7 A schematic diagram of temperature simulation results when the cable simulation model in the exemplary embodiment of the present disclosure runs to the 54th hour is shown. DETAILED DESCRIPTION

[0050] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the disclosure will be more comprehensive and complete and to fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0051] In addition, the accompanying drawings are only schematic illustrations of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the figures represent the same or similar parts, and their repeated description will be omitted. Some of the block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software form, or implemented in one or more hardware modules or integrated circuits, or implemented in different networks and / or processor devices and / or microcontroller devices.

[0052] This example implementation first provides a cable temperature rise calculation method based on dynamic resistance and ambient temperature changes, referring to Figure 1 As shown in , the method may include the following steps:

[0053] Step S101: establishing a cable simulation model according to cable structural parameters, wherein the cable simulation model includes a conductor layer and an insulating layer wrapping the conductor layer;

[0054] Step S102: setting current constraint conditions and cable burial depth, and establishing dynamic temperature boundary conditions;

[0055] Step S103: taking the conductor layer as a heat source, calculating the real-time heating value of the cable;

[0056] Step S104: Calculate the temperature rise using a finite element method according to the cable heat conduction equation and the real-time heat generation of the cable, combined with the dynamic resistance of the conductor layer and the dynamic thermal conductivity of the insulation layer.

[0057] In the embodiments of the present disclosure, a cable simulation model is established according to the cable structural parameters. For the cable simulation model, current constraint conditions are set to constrain the current of the cable in the operating state, and the cable burial depth is set so that the cable is at an appropriate burial depth. By establishing dynamic temperature boundary conditions, the real-time changes of the external ambient temperature are taken into account in the subsequent temperature rise calculation, which is conducive to improving the accuracy of the temperature rise calculation; in addition, when the finite element method is used to calculate the temperature rise according to the cable heat conduction equation and the real-time heating value of the cable, the dynamic resistance change of the conductor layer and the dynamic thermal conductivity of the insulation layer are also considered. In this way, the factor that the resistance of the cable conductor layer changes with the temperature and the influence of the dynamic thermal conductivity of the insulation layer on the heat conduction between adjacent material layers are taken into account in the temperature rise calculation, which is conducive to further improving the accuracy of the temperature rise calculation.

[0058] Below, each step of the above method in this example implementation will be described in more detail.

[0059] For example, in step S101, a cable simulation model is established according to cable structural parameters, wherein the cable structural parameters include material parameters, size parameters and thermal parameters, which is specifically implemented in the following manner:

[0060] Select ZC-YJLW02 190 / 330kV 1×2500mm 2 The single-core cross-linked polyethylene cable of this type is taken as the research object, wherein the single-core cross-linked polyethylene cable of this type includes a conductor layer, an insulating layer, an insulating shielding layer, a corrugated aluminum sheath and an outer sheath and other structures;

[0061] Determine the material, nominal thickness and outer diameter of the cable's conductor layer, insulation layer, insulation shielding layer, corrugated aluminum sheath and outer sheath, as shown in Table 1 below:

[0062] Table 1 Cable parameters

[0063] structure Material Nominal thickness / mm Outer diameter / mm conductor copper - 61.0±1.0 Insulation layer Cross-linked polyethylene 28.0 122.0 Insulation shield Semi-conductive shielding material 1.5 125.0±1.5 Corrugated aluminum sheath aluminum 3.3 153.0 Outer sheath Polyvinyl chloride 5.5 164.0

[0064] Determine the laying environment parameters and thermal parameters of the cable structural layer materials, as shown in Table 2 below:

[0065] Table 2 Laying environment parameters and thermal parameters of each structural layer material of the cable

[0066]

[0067] Based on the above parameters, a cable simulation model is established in the finite element software to facilitate subsequent temperature rise calculation using the finite element method.

[0068] For example, in step S102, a current constraint condition is set, and a suitable current value is selected according to the actual operating condition of the cable. The current value may be 1000A, but other current values ​​may also be selected, which is not limited in this embodiment.

[0069] It should be noted that the cable will generate heat during operation, and this heat needs to be dissipated through the surrounding medium (for example, soil). Therefore, the burial depth of the cable needs to consider not only safety but also heat dissipation. Since an excessively deep burial depth will increase the thermal resistance of the soil to the cable, it will be difficult for the heat generated by the cable to be effectively transferred to the surrounding environment, thereby causing the cable temperature to rise, which is not conducive to the operation of the cable. Therefore, before calculating the cable temperature rise, this embodiment selects a burial depth of 0.3m to 2m to simulate the cable temperature in order to set a more favorable cable burial depth.

[0070] For example, in step S102, the cable burial depth needs to be set, and the cable burial depth can be determined by the following method:

[0071] The cable temperature is simulated and calculated at a burial depth of 0.3m to 2m to obtain the functional relationship between the cable temperature and the cable burial depth.

[0072] The cable burial depth is determined according to the functional relationship between the cable temperature and the cable burial depth.

[0073] The cable burial depth is determined according to the functional relationship between the cable temperature and the cable burial depth. When determining the cable burial depth, the influence of different cable burial depths on the cable temperature can be considered, so as to select a burial depth that is more conducive to the heat dissipation of the cable while considering safety.

[0074] Specifically, the above-mentioned selection of a burial depth of 0.3m to 2m to simulate and calculate the cable temperature to obtain a functional relationship between the cable temperature and the cable burial depth may include the following steps:

[0075] In the finite element software, multiple groups of cables are placed under different burial depth conditions;

[0076] Putting the plurality of groups of cables into operation and collecting the operating temperatures of the plurality of groups of cables when they have been operated for a rated working time;

[0077] With the burial depth as the horizontal coordinate and the temperature as the vertical coordinate, a curve of the corresponding relationship between the burial depth and the temperature is drawn;

[0078] The functional relationship between cable temperature and cable burial depth is obtained according to the corresponding relationship curve between burial depth and temperature.

[0079] The corresponding relationship curve between burial depth and temperature drawn through the above steps is as follows: Figure 2 As shown in , it can be seen that as the burial depth is set larger, the corresponding operating temperature of the cable is also correspondingly larger. Therefore, under the premise of meeting relevant standards and specifications, a shallower burial depth should be selected as much as possible to better dissipate heat and reduce cable temperature. Therefore, according to the standard for direct burial of cables, the distance between the cable and the ground cannot be less than 0.7m. Combined with the corresponding relationship curve between burial depth and temperature, the cable burial depth can be set to 0.7m~0.9m.

[0080] Optionally, in this embodiment, the cable burial depth is set to 0.7 m.

[0081] For example, in step S102, establishing a dynamic temperature boundary condition includes:

[0082] Collect the real-time ambient temperature of the ground surface, which can be collected over several consecutive days;

[0083] The collected real-time surface ambient temperature is fitted to obtain the temperature boundary condition.

[0084] Specifically, take the real-time surface ambient temperature of Xi'an, Shaanxi Province for several consecutive days in mid-May 2024 as an example. Figure 3 The figure shows the real-time surface ambient temperature collected over several consecutive days, where: Figure 3 The horizontal axis is the acquisition time in hours, and the vertical axis is the surface temperature in degrees Celsius. Figure 3 It can be seen that the large temperature difference between day and night on the ground surface will have a certain impact on the temperature of cables buried in the shallow surface layer.

[0085] refer to Figure 4 As shown in the figure, the temperature boundary conditions obtained by fitting the collected real-time surface ambient temperature are shown. The red curve is the temperature boundary condition represented by the function fitting curve. When the finite element method is used for temperature rise calculation, the function fitting curve representing the temperature boundary condition can be input into the corresponding calculation module in the finite element software. In this way, when the finite element method is used to calculate the temperature rise, the influence of the surface air temperature on the cable temperature will be taken into account, so that the calculated temperature rise will be more accurate.

[0086] For example, in step S103, considering that the conductor layer carries load current during the operation of the cable, the conductor layer of the cable is the source of cable heating and the reason for the temperature rise of the cable. Therefore, when calculating the temperature rise of the cable, the conductor layer needs to be used as the heat source to calculate the real-time heating value of the cable.

[0087] Furthermore, in step S104, the temperature rise is calculated using a finite element method according to the cable heat conduction equation and the real-time heating value of the cable, combined with the dynamic resistance of the conductor layer and the dynamic thermal conductivity of the insulation layer.

[0088] Specifically, the dynamic resistance of the conductor layer is determined by formula (1):

[0089]

[0090] Among them, R represents the real-time resistance value of the conductor layer, ρ0 represents the resistivity at the starting temperature, α represents the resistivity temperature coefficient, and T c It represents the real-time temperature of the conductor layer, L represents the length of the conductor layer, and S represents the cross-sectional area of ​​the conductor layer.

[0091] The resistivity ρ0 in the above formula (1) can be selected as the resistivity of copper at 18°C, specifically 1.724×10 -8 The resistivity temperature coefficient α can be selected from the resistivity temperature coefficient of copper, which is specifically 0.00389.

[0092] When the finite element method is used for temperature rise calculation, the formula (1) representing the dynamic resistance of the conductor layer needs to be input into the corresponding parameter calculation module in the finite element software. In the process of calculating the temperature rise, the influence of temperature on the resistance of the conductor layer is taken into account, that is, the resistance of the conductor layer at each moment is determined based on the temperature of the conductor layer at the current moment, which helps to ensure that the calculated temperature rise is more accurate.

[0093] It should be explained that when the conductor layer of the cable passes the load current, the conductor layer of the cable will generate heat due to the thermal effect of the current. The magnitude of the load current will affect the heat generation.

[0094] Specifically, the step S103 of using the conductor layer as a heat source to obtain the real-time heating value of the cable may include:

[0095] Obtain the real-time resistance value of the conductor layer;

[0096] According to the real-time resistance value, the real-time heating value of the cable is calculated by formula (2):

[0097]

[0098] Where Q represents the heat generated by the conductor layer, in W / m 3 , I represents the current of the conductor layer, R represents the real-time resistance value of the conductor layer, S represents the cross-sectional area of ​​the conductor layer, and L represents the length of the conductor layer.

[0099] After determining the load current applied to the cable, the real-time heating value of the cable can be calculated according to the above formula (2); wherein, the resistance R in the above formula (2) can be obtained by formula (1). Then, when the finite element method is used for temperature rise calculation, the calculation of the real-time heating value of the cable also takes into account the dynamic resistance change of the conductor layer, which is conducive to more accurate calculation of the cable temperature rise.

[0100] It should be explained that, with the conductor layer of the cable as the heat source, the temperature of the cable will also change over time due to the continuous heat generated by the conductor layer. However, this embodiment takes into account that the dynamic change of the conductor layer resistance with temperature and the dynamic change of the thermal conductivity of the insulation layer with temperature will affect the temperature rise of the cable. Therefore, in order to accurately calculate the temperature rise of the cable, this embodiment also needs to consider the influence of the dynamic thermal conductivity of the insulation layer on the heat conduction between adjacent material layers.

[0101] Specifically, the dynamic thermal conductivity of the insulation layer is determined by formula (3):

[0102] λ i =a i T c +λ0(3)

[0103] Among them, λ i represents the thermal conductivity of the insulation layer, a i Represents the temperature coefficient, T c represents the temperature of the conductor layer, and λ0 represents the initial value of thermal conductivity.

[0104] The power frequency temperature coefficient of single-core cross-linked polyethylene cable is about 1.13. Therefore, when calculating the dynamic thermal conductivity of the insulation layer using the above formula (3), the temperature coefficient a is iCan be set to 1.13.

[0105] It needs to be explained that the dynamic changes in the resistance of the conductor layer and the dynamic changes in the thermal conductivity parameters of the insulation layer will affect the heat conduction process of the cable. The heat conduction process is a process of energy transfer and is a natural convection generated by the temperature gradient. Therefore, this embodiment uses the conductor layer as the heat source and calculates the temperature rise by combining the dynamic resistance change of the conductor layer and the dynamic thermal conductivity change of the insulation layer.

[0106] Specifically, the cable heat conduction equation is expressed as:

[0107]

[0108] Where ρ represents density in kg / m 3 , c p represents the specific heat capacity at constant pressure, in J / (kg·K), T represents the temperature, in °C, t represents the time, in seconds, represents the convection term, u represents the velocity vector, the unit is m / s, Indicates the temperature difference in °C. represents the heat conduction term, k represents the thermal conductivity, the unit is W / (m·K), Q total represents the total heat source term, the total heat source term Q total It includes the heat generated by the conductor layer Q, the heat source generated by flow (such as viscous dissipation) and other heat sources, and the unit is W / m 3 .

[0109] It should be explained that the influence of temperature on the conductor layer of the cable will make the total heat source term Q total The influence of temperature on the insulation layer will change the thermal conductivity parameters of the insulation layer, and these influences will change the temperature rise calculation results. Therefore, based on the above cable heat conduction equation, combined with the dynamic resistance change of the conductor layer and the dynamic thermal conductivity of the insulation layer, it is conducive to more accurate calculation of the cable temperature rise.

[0110] For example, in step S104, the temperature rise is calculated using a finite element method, including:

[0111] The above-mentioned current constraint conditions, cable burial depth, dynamic temperature boundary conditions, real-time heating value of the cable, dynamic resistance of the conductor layer, dynamic thermal conductivity of the insulation layer and cable heat conduction equation are respectively input into the corresponding parameter module and calculation module in the finite element software, the cable simulation model is meshed, and the finite element software is run to solve the temperature rise.

[0112] It should be noted that when the finite element software is used to perform temperature rise simulation calculations, under the effect of heat conduction, the heat generated by the conductor layer is transferred through the insulation layer, insulation shielding layer, corrugated aluminum sheath, and outer sheath in sequence. After the cable runs at the set load current for the target time, the Figure 5 The temperature of each layer of the cable shown in Figure 5 It can be seen that the temperature of the conductor layer as the heat source is the highest, and the temperatures of the insulation layer, the insulation shielding layer, the corrugated aluminum sheath, and the outer sheath decrease in sequence. In this embodiment, the temperature of the cable with the highest temperature among the layers is selected to calculate the temperature rise of the cable, that is, the temperature of the selected conductor layer is subtracted from the initial temperature of the cable to obtain the temperature rise.

[0113] In the embodiment of the present application, in order to further verify the accuracy of the cable temperature rise calculation method proposed in the present application, a field test was conducted, and the simulation experiment was compared with the field test to illustrate the accuracy of the cable temperature rise calculation method proposed in the present application. Among them, the simulation experiment was directly performed in the finite element software, and the finite element calculation was performed according to the parameter settings in the above steps. The field test was realized by building a 330 kV cable high current temperature rise test system.

[0114] The specific settings of the field test are as follows:

[0115] A total of 6 330 kV cable test samples were laid at the test site. The length of the cable test samples was 20 meters and the cross-sectional area was 2500mm 2 . Six 330 kV cable test samples were operated continuously for 54 hours, wherein from the start time to the 21st hour, the cable test samples were operated at a load current of 1000A, from the 21st hour to the 50th hour, the cable test samples were operated at a load current of 1850A, and from the 50th hour to the 54th hour, the cable test samples were operated at a load current of 2050A. By collecting the temperature of the cable test samples in real time, the temperatures of the cable test samples at the 21st hour, the 50th hour, and the 54th hour were obtained, thereby obtaining the corresponding cable temperature rise at the above three moments.

[0116] Similarly, the simulation experiment also lasted for 54 hours, and from the starting time to the 21st hour, the cable simulation model operated at a load current of 1000A, from the 21st hour to the 50th hour, the cable simulation model operated at a load current of 1850A, and from the 50th hour to the 54th hour, the cable simulation model operated at a load current of 2050A, and the temperature rise calculation results at the 21st hour, 50th hour and 54th hour were calculated. Figures 5 to 7 The temperature rise calculation results of the simulation experiment are shown respectively, where Figure 5 This is a schematic diagram of the temperature simulation results when the cable simulation model runs to the 21st hour. Figure 6This is a schematic diagram of the temperature simulation results when the cable simulation model runs for 50 hours. Figure 5 This is a simulation diagram of the temperature results when the cable simulation model runs for 54 hours.

[0117] The comparison results between the simulation experiment and the field test are shown in Table 3:

[0118] Table 3 Comparison of temperature rise results between simulation experiment and field test

[0119]

[0120] In the above Table 3, the first stage is from the start time to the 21st hour, the load current is 1000A, wherein the start temperature corresponds to the cable temperature at the 0th hour, and the stable temperature corresponds to the cable temperature at the 21st hour; the second stage is from the 21st hour to the 50th hour, the load current is 1850A, wherein the start temperature corresponds to the cable temperature at the 21st hour, and the stable temperature corresponds to the cable temperature at the 50th hour; the third stage is from the 50th hour to the 54th hour, the load current is 2050A, wherein the start temperature corresponds to the cable temperature at the 50th hour, and the stable temperature corresponds to the cable temperature at the 54th hour. By comparing the temperature rise results of the simulation experiment with the temperature rise results of the field test, it can be found that the temperature rise results calculated by the cable temperature rise calculation method proposed in this application can achieve a higher calculation accuracy within a certain load current range.

[0121] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any modification, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary techniques in the art that are not disclosed in the present disclosure. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present disclosure are indicated by the appended claims.

Claims

1. A method for calculating cable temperature rise based on dynamic resistance and ambient temperature changes, characterized in that: include: Establishing a cable simulation model according to the cable structural parameters, wherein the cable simulation model includes a conductor layer and an insulating layer wrapping the conductor layer; Set current constraints and cable burial depth, and establish dynamic temperature boundary conditions; Taking the conductor layer as a heat source, calculating the real-time heating value of the cable; The temperature rise is calculated using the finite element method according to the cable heat conduction equation and the real-time heat generation of the cable, combined with the dynamic resistance of the conductor layer and the dynamic thermal conductivity of the insulation layer.

2. The cable temperature rise calculation method based on dynamic resistance and ambient temperature change according to claim 1 is characterized in that: The dynamic resistance of the conductor layer is determined by formula (1): Among them, R represents the real-time resistance value of the conductor layer, ρ0 represents the resistivity at the starting temperature, α represents the resistivity temperature coefficient, and T c It represents the real-time temperature of the conductor layer, L represents the length of the conductor layer, and S represents the cross-sectional area of ​​the conductor layer.

3. The cable temperature rise calculation method based on dynamic resistance and ambient temperature change according to claim 2 is characterized in that: The method of using the conductor layer as a heat source to obtain the real-time heat generated by the cable includes: Obtain the real-time resistance value of the conductor layer; According to the real-time resistance value, the real-time heating value of the cable is calculated by formula (2): Among them, Q represents the heat generated by the conductor layer, I represents the current of the conductor layer, R represents the real-time resistance value of the conductor layer, S represents the cross-sectional area of ​​the conductor layer, and L represents the length of the conductor layer.

4. The cable temperature rise calculation method based on dynamic resistance and ambient temperature change according to claim 1 is characterized in that: The dynamic thermal conductivity of the insulating layer is determined by formula (3): λ i that i T c +λ0(3) Among them, λ i represents the thermal conductivity of the insulation layer, a i Represents the temperature coefficient, T c represents the temperature of the conductor layer, and λ0 represents the initial value of thermal conductivity.

5. The cable temperature rise calculation method based on dynamic resistance and ambient temperature change according to claim 1 is characterized in that: The cable heat conduction equation is expressed as: Where ρ represents density, c p represents the specific heat capacity at constant pressure, T represents the temperature, t represents the time, represents the convection term, u represents the velocity vector, Represents the temperature difference, represents the heat conduction term, k represents the thermal conductivity, Q total Represents the total heat source term.

6. The cable temperature rise calculation method based on dynamic resistance and ambient temperature change according to claim 1 is characterized in that: The setting of current constraint conditions and cable burial depth includes: Obtain the functional relationship between cable temperature and cable burial depth; The cable burial depth is determined according to the functional relationship between the cable temperature and the cable burial depth.

7. The cable temperature rise calculation method based on dynamic resistance and ambient temperature change according to claim 6 is characterized in that: The obtaining of the functional relationship between the cable temperature and the cable burial depth includes: Multiple groups of cables are placed at different burial depths; Putting the plurality of groups of cables into operation and collecting the operating temperatures of the plurality of groups of cables when they have been operated for a rated working time; With the burial depth as the horizontal coordinate and the temperature as the vertical coordinate, a curve of the corresponding relationship between the burial depth and the temperature is drawn; The functional relationship between cable temperature and cable burial depth is obtained according to the corresponding relationship curve between burial depth and temperature.

8. The cable temperature rise calculation method based on dynamic resistance and ambient temperature change according to any one of claims 1 to 7, characterized in that: The cable burial depth is set to 0.7m to 0.9m.

9. The cable temperature rise calculation method based on dynamic resistance and ambient temperature change according to any one of claims 1 to 7, characterized in that: The establishing of dynamic temperature boundary conditions comprises: Collect real-time surface ambient temperature; The collected real-time surface ambient temperature is fitted to obtain the temperature boundary condition.

10. The cable temperature rise calculation method based on dynamic resistance and ambient temperature change according to any one of claims 1 to 7, characterized in that: The cable structural parameters include material parameters, size parameters and thermal parameters.

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