A cable temperature rise test method considering axial heat transfer of cable joints

Abstract

The present invention discloses a cable temperature rise test method considering axial heat transfer of cable joints, which relates to the technical field of research on heat transfer and temperature rise characteristics of high-voltage cable joints. A physical model including the cable joint and the cables connected to both ends thereof is established; under the set critical working conditions, a corresponding temperature distribution model under different current conditions is established by using the physical model to determine the axial heat transfer range of the cable joint and the cable, and accordingly determine the length of the cable to be tested; temperature sensors are arranged at equal intervals on the cable joint and the determined length of the cable, and a temperature compensation device is arranged at the end of the cable to measure the conductor temperatures on the cable joint and the cable. The present invention simultaneously considers the axial heat transfer problem of the cable joint and the cost problem of experimental equipment, and uses the cable line as short as possible to reduce the cost of the experimental platform while eliminating the influence of the axial heat transfer of the joint on the temperature rise of the cable body.

Description

Technical Field

[0001] The present invention relates to the technical field of research on heat transfer and temperature rise characteristics of high-voltage cable joints, and specifically designs a cable temperature rise test method considering axial heat transfer of cable joints. Background Art

[0002] With the continuous increase of the country's electricity demand, the operating load of cable lines is constantly increasing. Long-distance cable lines need to be connected by cable joints in the middle. In high-voltage cable lines, the insulation requirements are relatively high, which makes the volume of the joint insulation parts relatively large. Such a structural design will inevitably increase the heat transfer path of the cable joints in the middle, thereby increasing the conductor temperature and leading to overheating operation. In severe cases, it may cause accidents such as fires and explosions at the joints.

[0003] Analyzing the radial thermal resistance of the cable body and the cable joint, the radial thermal resistance is inversely proportional to the thermal conductivity of the material. Due to the different materials used for the cable body and the joint, there are differences in their radial thermal resistances. Specifically, the total radial thermal resistance of the cable joint is much larger than that of the cable body. Therefore, during operation, the conductor temperature of the cable joint is higher than that of the body. When there is a temperature difference between the cable body and the joint, heat will conduct from the joint with a higher temperature along the copper core to the body with a lower temperature, raising the conductor temperature of the adjacent body and lowering the conductor temperature of the joint. When conducting a temperature rise test, if the selected length of the cable body is short, it will lead to incomplete axial heat transfer of the cable, and the cable body temperature will be greater than the actual operating value, and the experimental results will not have reference value; if the selected length of the cable body is long, although the influence of axial heat transfer on the body temperature can be effectively eliminated, too long a cable will increase the test cost. A better method is needed to take into account both the axial heat transfer effect and economic benefits. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of inaccurate cable temperature rise experiment values and cost waste caused by axial heat transfer of cable joints in the prior art, and provide a cable temperature rise test method considering axial heat transfer of cable joints. This test method constructs a temperature field model of the cable joint and the body through finite element simulation to determine the length of the experimental cable body; then, based on the determined cable length, a large-current temperature rise test circuit is built, and temperature sensors are arranged at equal distances on the conductors of the cable joint and the body to monitor the conductor temperature of the cable joint in real time.

[0005] To achieve the above object, the following technical solutions can be adopted:

[0006] A cable temperature rise test method considering axial heat transfer of cable joints, which includes the following steps:

[0007] Establish a physical model including the cable joint and the cables connected to its two ends;

[0008] Under the set critical working conditions, use the physical model to establish a temperature distribution model corresponding to different current conditions, determine the axial heat transfer range of the cable joint and the cable, and accordingly determine the length of the cable to be tested;

[0009] Arrange temperature sensors at equal intervals on the cable joint and the cable of the determined length, and set a temperature compensation device at the end of the cable to measure the conductor temperature on the cable joint and the cable.

[0010] For the cable temperature rise test method considering the axial heat transfer of the cable joint as described above, further, establishing the physical model includes the steps of:

[0011] Establish a two-dimensional axisymmetric geometric model, and add material properties to each structure in the model. The material properties include density, thermal conductivity, and constant pressure heat capacity;

[0012] Apply a heat source, where the heat source is a volume heat source and the application position of the heat source is on the conductor of the cable joint and the cable;

[0013] Set boundary conditions. Among them, set the axial end face as an adiabatic boundary, set the interface between the surface of the cable joint and the cable and the air as a natural convection boundary, and set the convection coefficient and air temperature.

[0014] For the cable temperature rise test method considering the axial heat transfer of the cable joint as described above, further, determining the length of the cable to be tested includes the steps of:

[0015] There are several temperature measurement points arranged at equal intervals in the extending directions from the cable joint to both ends. When the temperature difference between two adjacent temperature measurement points in any direction is less than the set threshold, it is determined as the target temperature measurement point in one direction, and the length of the cable is determined based on the point farther from the cable joint among the two target temperature measurement points.

[0016] For the cable temperature rise test method considering the axial heat transfer of the cable joint as described above, further, determine a temperature measurement point every 0.5 m on the cable. When the temperature difference between two adjacent temperature measurement points is less than 0.2 °C, it is determined that the axial heat transfer reaches stability.

[0017] For the cable temperature rise test method considering the axial heat transfer of the cable joint as described above, further, use an experimental platform to measure the conductor temperature on the cable joint and the cable. Among them,

[0018] The experimental platform includes a power supply, a host computer, a controller, a voltage regulator, a transformer, a compensation capacitor, a current transformer, temperature sensors, and a paperless recorder;

[0019] The power supply is connected to the input end of the voltage regulator, the output end of the voltage regulator is connected to the input end of the transformer, and the output end of the transformer is connected to the cable joint and the cable to be tested through a low-voltage cable connection line;

[0020] The compensating capacitor is connected to the output terminal of the transformer and is used for reactive power compensation on the power supply side;

[0021] The current transformer is installed on the cable and is used to convert the current signal into a voltage signal and feedback it to the controller. The controller adjusts the output voltage of the voltage regulator according to the feedback voltage signal to form a negative feedback and continuously adjusts the current to the set value;

[0022] The temperature sensors are arranged on the cable at equal intervals and according to the structural characteristics of the cable joint;

[0023] The paperless recorder is used to record the temperature data recorded by the temperature sensors;

[0024] The upper computer is connected to the controller through a control signal.

[0025] For the cable temperature rise test method considering axial heat transfer of the cable joint as described above, further, temperature sensors are arranged on the cable body at equal intervals of 1.5 m.

[0026] For the cable temperature rise test method considering axial heat transfer of the cable joint as described above, further, the temperature compensation device is a copper coil, and the temperature of the copper coil is changed by controlling the magnitude of the current in the copper coil.

[0027] For the cable temperature rise test method considering axial heat transfer of the cable joint as described above, further, temperature sensors are arranged at a position on the cable at a set distance from the end. By comparing the temperature data at the two positions, if the temperature at the end of the cable in any direction is lower, the temperature compensation device is started until the temperature difference between the two positions is within the defined range.

[0028] For the cable temperature rise test method considering axial heat transfer of the cable joint as described above, further, the temperature sensors are arranged at a position 0.2 m from the end of the cable, and the defined range is 0.2 °C.

[0029] For the cable temperature rise test method considering axial heat transfer of the cable joint as described above, further, the set critical condition means that the cable insulation operates at 90 °C.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention simultaneously considers the axial heat transfer problem of the cable joint and the cost problem of the experimental equipment. While eliminating the influence of the axial heat transfer of the joint on the temperature rise of the cable body, the cable line is used as short as possible to reduce the cost of the experimental platform. The present invention has a wide range of applications and is suitable for the study of cable temperature characteristics under different voltage levels. Description of the Drawings

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings required for the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0032] Figure 1 is a flowchart of the cable temperature rise test method considering axial heat transfer of cable joints in the present invention

[0033] Figure 2 is a flowchart of modeling using COMSOL finite element simulation software in the present invention;

[0034] Figure 3 is a cable temperature curve graph obtained by using COMSOL finite element simulation software in the present invention;

[0035] Figure 4 is an enlarged temperature curve graph when determining the cable length in the present invention; where Figure 4 (a) Enlarged temperature curve graph at one end of the cable, Figure 4 (b) Enlarged temperature curve graph at the other end of the cable;

[0036] Figure 5 is a layout diagram of temperature sensors during the experiment in the present invention;

[0037] Figure 6 is a composition connection diagram of the high - current experimental platform in the present invention. Specific Embodiments

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of them. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0039] Embodiment:

[0040] It should be noted that the terms "first", "second", etc. in the description, claims and the above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" in the embodiments of the present invention and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily limit to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0041] In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined. In addition, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] Figure 1 is a flowchart of the cable temperature rise test method considering axial heat transfer of cable joints in the present invention Figure 2 is a flowchart of modeling using COMSOL finite element simulation software in the present invention; Figure 3 is the cable temperature curve diagram obtained by using COMSOL finite element simulation software in the present invention; Figure 4 is the enlarged temperature curve diagram when determining the cable length in the present invention; wherein, Figure 4 (a) Enlarged temperature curve diagram of one end of the cable, Figure 4 (b) Enlarged temperature curve diagram of the other end of the cable; Figure 5 is the layout diagram of temperature sensors during the experiment in the present invention; Figure 6 is the composition connection diagram of the high-current experiment platform in the present invention.

[0043] The purpose of the present invention is to solve the problems of inaccurate numerical values of cable temperature rise experiments and cost waste caused by axial heat transfer of cable joints in the prior art, and provide a cable temperature rise test method considering axial heat transfer of cable joints. This test method constructs a temperature field model of the cable joint and the body through finite element simulation to determine the length of the experimental cable body; then, a high-current temperature rise experimental circuit is built according to the determined cable length, and temperature sensors are arranged at equal distances on the conductors of the cable joint and the body to monitor the conductor temperature of the cable joint in real time.

[0044] In this embodiment, taking a high-voltage cable with a voltage level of 220 kV and a cross-sectional area of 2500 mm 2 as an example, a method for cable temperature rise experiment considering axial heat transfer of cable joints is disclosed.

[0045] See Figure 1 , a method for cable temperature rise test considering axial heat transfer of cable joints, which comprises the following steps:

[0046] Step 1: Establish a physical model including the cable joint and the cables connected to both ends thereof.

[0047] See Figure 2 , in this embodiment, according to the structural dimensions of the cable joint and the body, a two-dimensional axisymmetric geometric model is established in the finite element simulation software. The structure and each structural dimension are determined according to the cross-sectional view and description of the cable body and the cable joint. The main structures of the cable body include conductor, semiconductive shielding tape, conductor shielding layer, cross-linked polyethylene main insulation, insulation shielding layer, semiconductive water blocking layer, air gap layer, metal aluminum sheath and outer sheath; the main structures of the cable joint include compression joint, grading ring, silicone rubber main insulation, semiconductive shielding layer, metal protective shell and colloidal filling layer. Among them, the silicone rubber main insulation also includes a high-voltage shielding layer and a stress cone structure, which should be drawn separately during modeling. The cable body lengths at both ends of the joint are selected as 10 m each. Add material properties to each structure in the model, and the material properties include density, thermal conductivity, and constant pressure heat capacity.

[0048] The initial temperature is set to 293.15 K, the boundary conditions are set, the axial end faces are set as adiabatic boundaries, the interfaces between the surfaces of the cable joint and the body and the air are set as natural convection boundaries, the convection coefficient of the cable joint part is 19.375 W / (m 2 ·K), the convection coefficient of the cable body part is 9 W / (m 2 ·K), and the boundary of the conductor far from the joint is set as an axisymmetric surface. Apply heat sources, the heat sources are volume heat sources, and the application positions of the heat sources are on the conductors of the cable joint and the body. Heat source 1 is the conductor, and heat source 2 is the joint compression joint. The mesh is divided into a conventional size.

[0049] Calculate the temperature distribution of the entire model diagram. The obtained temperature distribution curve is shown in the appendix Figure 3 , where the 10 m position is the center position of the cable joint. Figure 4 It is the enlarged view of the temperature curve when determining the cable length in the present invention.

[0050] Step 2: Under the set critical working conditions, use the physical model to establish temperature distribution models corresponding to different current conditions, determine the axial heat transfer ranges of the cable joint and the cable, and accordingly determine the length of the cable to be tested.

[0051] In this embodiment, the axial heat transfer range between the cable joint and the cable body is determined according to the temperature distribution corresponding to different current conditions. A temperature measurement point is selected every 0.5 m on the cable body. When the temperature difference between two adjacent temperature measurement points is less than 0.2 °C, it can be considered that the axial heat transfer reaches stability, and the length of the cable body is determined based on the point farther from the joint among the two points. Analyzing the left end of the joint, it can be seen that the temperature difference is 0.1 °C from 7.5 m to 8 m. Therefore, 8 m is selected as the cable length, that is, the distance from the end of the cable body to the center of the joint is 2 m; analyzing the right end of the joint, it can be seen that the temperature difference is slightly greater than 0.2 °C from 12 m to 12.5 m, and the temperature difference is about 0.1 °C from 12.5 m to 13 m. Therefore, 13 m is selected as the cable length, that is, the distance from the end of the cable body to the center of the joint is 3 m. Based on this, the length of the experimental cable body is determined. It should be noted that the set critical condition means that the cable insulation operates at 90 °C.

[0052] Step 3: Arrange temperature sensors at equal intervals on the cable joint and the determined-length cable, and set up a temperature compensation device at the end of the cable to measure the conductor temperatures on the cable joint and the cable.

[0053] In this embodiment, according to the cable length described in the previous step, a large-current temperature rise experimental loop for the cable joint and the cable body is built. Temperature sensors are arranged at equal intervals on the conductors of the cable joint and the cable body to monitor the conductor temperature of the cable joint in real time.

[0054] See Figure 5 , the large-current temperature rise experimental platform for the cable joint and the cable body includes a power supply, a computer monitoring platform (host computer), a PLC control platform (controller), a voltage regulator, a transformer, a compensation capacitor, a current transformer, a temperature sensor, a paperless recorder, a cable body, and a cable joint;

[0055] The power supply is connected to the input end of the voltage regulator, the output end of the voltage regulator is connected to the transformer, and a shunt compensation capacitor performs reactive power compensation on the power supply side. The transformer is connected to the current boosting coil, and then through a low-voltage cable connection line, the output end of the transformer is connected to the experimental cable;

[0056] Secondly, install a current transformer on the cable to monitor the line current, convert the current signal into a voltage signal, and feedback it to the PLC control platform to adjust the output voltage of the voltage regulator, forming a negative feedback to continuously adjust the current to the set value.

[0057] See Figure 6, temperature sensors are arranged on the cable body at an equidistant interval of 1.5 m, and sensors are arranged on the cable joints according to their structural characteristics. The specific arrangement method can be seen in the attached drawings. The temperature sensors are connected to a paperless recorder. A temperature compensation device is installed at the end of the experimental cable. The temperature compensation device is a copper coil, and the temperature of the coil is changed by controlling the magnitude of the current in the coil. A temperature sensor is arranged at a position 0.2 m away from the end of the cable, and the temperature data at the two positions are compared. If the temperature at the end is lower, the temperature compensation device is activated until the temperature difference between the two is within the defined range. The defined range is 0.2 °C.

[0058] After the experimental platform is built, the current value is set to 2200 A and the working time is 96 h. The device is started for a temperature rise test. During the experiment, the temperature change is monitored through a paperless recorder, and it is determined whether the temperature reaches a steady state according to the temperature-time curve. After reaching the steady state, the experiment ends and the data is recorded.

[0059] In summary, this embodiment combines finite element simulation technology with a large current experimental platform, and proposes a method for cable temperature rise test considering axial heat transfer of cable joints, which solves the problems of inconsistent temperature measurement values with actual operating conditions and cost waste caused by axial heat transfer in cable temperature rise experiments. It is applicable to experiments on measuring cable temperature rise and heat transfer characteristics under different voltage levels.

[0060] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0061] The above embodiments are only used to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable ordinary technicians in the art to understand the content of the present invention and implement it accordingly, and cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the essence of the content of the present invention should be covered within the protection scope of the present invention.

Claims

1. A cable temperature rise test method considering axial heat transfer of cable joints, characterized in that, it includes the following steps: Establish a physical model including the cable joint and the cables connected to both ends thereof; wherein, establishing the physical model includes the steps of: establishing a two-dimensional axisymmetric geometric model, adding material properties to each structure in the model, and the material properties include density, thermal conductivity, and constant pressure heat capacity; applying a heat source, the heat source is a volume heat source and the application position of the heat source is on the conductor of the cable joint and the cable; setting boundary conditions, wherein, setting the axial end face as an adiabatic boundary, setting the interface between the surface of the cable joint and the cable and the air as a natural convection boundary, and setting the convection coefficient and the air temperature; Under the set critical working conditions, use the physical model to establish corresponding temperature distribution models under different current conditions, determine the axial heat transfer range of the cable joint and the cable by equidistantly arranging a number of temperature measurement points along the extending direction from the center of the cable joint to both ends, and determine the length of the cable to be tested accordingly; Equidistantly arrange temperature sensors on the cable joint and the cable with the determined length, and set a temperature compensation device at the end of the cable to measure the conductor temperature on the cable joint and the cable.

2. The cable temperature rise test method considering axial heat transfer of cable joints according to claim 1, characterized in that, determining the length of the cable to be tested includes the steps of: When the temperature difference between two adjacent temperature measurement points in any direction is less than the set threshold value, determine the target temperature measurement points in one direction, and determine the length of the cable based on the point farther from the cable joint among the two target temperature measurement points.

3. The cable temperature rise test method considering axial heat transfer of cable joints according to claim 2, characterized in that, Determine a temperature measurement point every 0.5 m on the cable. When the temperature difference between two adjacent temperature measurement points is less than 0.2 °C, it is determined that the axial heat transfer reaches stability.

4. The cable temperature rise test method considering axial heat transfer of cable joints according to claim 1, characterized in that, Use an experimental platform to measure the conductor temperature on the cable joint and the cable, wherein, the experimental platform includes a power supply, a host computer, a controller, a voltage regulator, a transformer, a compensation capacitor, a current transformer, a temperature sensor, and a paperless recorder; The power supply is connected to the input end of the voltage regulator, the output end of the voltage regulator is connected to the input end of the transformer, and the output end of the transformer is connected to the cable joint and the cable to be tested through a low-voltage cable connection line; The compensation capacitor is connected to the output end of the transformer for reactive power compensation on the power supply side; The current transformer is installed on the cable and the current transformer is used to convert the current signal into a voltage signal and feedback it to the controller, and the controller adjusts the output voltage of the voltage regulator according to the feedback voltage signal to form a negative feedback and continuously adjust the current to the set value; The temperature sensors are arranged equidistantly on the cable and arranged according to the structural characteristics of the cable joint; The paperless recorder is used to record the temperature data recorded by the temperature sensors; The host computer is connected to the controller for control signals.

5. The cable temperature rise test method considering axial heat transfer of cable joints according to claim 4, characterized in that, Temperature sensors are arranged at equal intervals of 1.5 m on the cable body.

6. The cable temperature rise test method considering axial heat transfer of cable joints according to claim 1, characterized in that the temperature compensation device is a copper coil, and the temperature of the copper coil is changed by controlling the magnitude of the current in the copper coil.

7. The cable temperature rise test method considering axial heat transfer of cable joints according to claim 6, characterized in that temperature sensors are arranged at a position on the cable at a set distance from the end, and the temperature data at the two positions are compared. If the temperature at the end of the cable in any direction is lower, the temperature compensation device is activated until the temperature difference between the two positions is within the defined range.

8. The cable temperature rise test method considering axial heat transfer of cable joints according to claim 7, characterized in that the temperature sensors are arranged at a position 0.2 m from the end of the cable, and the defined range is 0.2 °C.

9. The cable temperature rise test method considering axial heat transfer of cable joints according to claim 1, characterized in that the set critical condition means that the cable insulation operates at 90 °C.

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