A method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity.

Abstract

A method for evaluating the temperature stability of high-voltage direct current (HVDC) cables based on the conductivity of XLPE is proposed. This method involves measuring the DC current of the XLPE insulation material at different temperatures using resistivity testing; calculating the corresponding conductivity and temperature stability characterization index based on the DC current to assess the temperature stability of the XLPE insulation material in the HVDC cable; calculating the temperature distribution cross-section using a simulation model of the XLPE insulation material in the HVDC cable using finite element analysis software; and evaluating the thermal stability of the XLPE insulation material in practical engineering applications based on the temperature difference between the tested cable and the reference cable sheath after transient internal pressurization. This method is efficient and highly accurate.

Description

Technical Field

[0001] This invention relates to the field of cable temperature detection technology, and in particular to a method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity. Background Technology

[0002] Cross-linked polyethylene (XLPE) has been widely used in AC and DC power cables due to its excellent electrical, heat resistance, and mechanical properties. With economic and social development and increasing electricity demand, the voltage levels of XLPE insulated cables are also rising. To address the challenges of higher voltage levels, current cable structure designs often increase insulation thickness. However, this increased thickness makes it difficult for cross-linking byproducts to be expelled and also increases the temperature difference between the inner and outer insulation layers. Since the conductivity of XLPE material is sensitive to temperature, this exacerbates electric field distortion within the insulation, increasing the probability of insulation failure. Therefore, for XLPE insulation materials used in higher voltage levels, in addition to examining their electrical and mechanical properties, it is necessary to further investigate the temperature stability of the material's conductivity. However, a simple and efficient method for assessing the thermal stability of XLPE materials is currently lacking.

[0003] The information disclosed in the background section is only for enhancing the understanding of the background of this invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] This invention provides a method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity. To meet the operating temperature range of the cable insulation, the ratio of high-temperature conductivity to low-temperature conductivity is selected to evaluate the temperature stability of the high-voltage DC cable insulation material. The thermal stability evaluation index is calculated based on the conductivity measured at the set temperature. The temperature distribution cross-section diagram in the cable model is obtained by combining finite element simulation software. The temperature stability of the cross-linked polyethylene DC cable is further evaluated based on the temperature distribution cross-section diagram, which is a simple and efficient method for evaluating temperature stability.

[0005] A method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity includes:

[0006] S1. The DC current of XLPE insulation material at different temperatures was measured by resistivity testing;

[0007] S2. Calculate the corresponding conductivity and temperature stability characterization index based on the DC current to evaluate the temperature stability of the XLPE insulation material of the high-voltage DC cable. The temperature stability characterization index is determined by the following formula:

[0008] ,

[0009] In the formula: This is an indicator of temperature stability. The high-temperature conductivity represents the maximum permissible temperature of XLPE insulation or the maximum operating temperature of the high-voltage DC cable, respectively. Low-temperature conductivity, representing room temperature or the lowest temperature of the cable insulation;

[0010] S3. Using finite element analysis software, the temperature distribution cross-section is calculated from the simulation model of the XLPE insulation material of the high-voltage DC cable. Based on the temperature difference between the sheath of the tested cable and the reference cable after transient internal pressurization, the thermal stability of the XLPE insulation material of the high-voltage DC cable in actual engineering is evaluated.

[0011] In the method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, step S1 includes at least a DC high-voltage source, an electrode system, an ammeter, a data acquisition system, and a temperature control device. The data acquisition system is located between the high-voltage ammeter and the electrode system. Data acquisition is performed by a computer for measurement time control and range selection, and the DC current data is recorded in real time.

[0012] In the method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, a shielding system is installed outside the electrode system to prevent electromagnetic interference during the measurement process; a constant temperature chamber is installed outside the shielding system to achieve temperature control during the measurement.

[0013] In the aforementioned method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, the maximum allowable temperature of XLPE insulation or the maximum operating temperature of the high-voltage DC cable is 90℃ or 70℃, respectively, and the minimum temperature of room temperature or cable insulation is 30℃.

[0014] In the aforementioned method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, the corresponding conductivity is determined by the following formula:

[0015]

[0016] In the formula: I v Leakage current; d The thickness of the sample; U This is an externally applied DC voltage; S To measure the effective area of ​​the electrode.

[0017] In the aforementioned method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, a simulation model of the XLPE insulation material of the high-voltage DC cable is established using finite element simulation software. The component parameters, heat source, initial temperature value, and initial potential value of the simulation model are set. Combined with the transient simulation of the temperature change trend after the internal pressure of the cable, the reference cable sheath temperature and the tested cable sheath temperature are obtained from the temperature cross section diagram, and the thermal stability of the high-voltage DC current is evaluated based on the temperature difference between the two.

[0018] In the aforementioned method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, the simulation model consists of, from the inside out, a conductor, a conductor shielding layer, an XLPE insulation layer, an insulation shielding layer, a water-blocking layer, a metal sheath, and an outer sheath, with the center lines of each component coinciding.

[0019] The component parameters of the simulation model include density, heat capacity, thermal conductivity, electrical conductivity, and dielectric constant.

[0020] In the aforementioned method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, the heat sources in the simulation model are Joule heat generated by the conductor current and heat generated by the insulation leakage current. The Joule heat generated by the conductor current depends on the cable conductor loss, and the heat generated by the insulation leakage current has a unit volume heating power of [missing information]. γE 2 , g conductivity ， E For field strength.

[0021] The initial temperature of the simulation model is between the highest operating temperature of the power cable and room temperature, and the initial temperature of each layer is the same.

[0022] In the method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, the initial potential of the conductor shielding layer and insulation layer in the simulation model is 0; the heat transfer mode of the simulation model is solid heat transfer.

[0023] In the aforementioned method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, the sheath temperature is determined according to the outer temperature of the temperature distribution cross-section obtained from simulation; the reference cable sheath temperature is the sheath temperature when the conductor is not energized under full load; the tested cable sheath temperature is the temperature after the cable is fully loaded and stabilized with a voltage of 1.45°C applied to the conductor. U The sheath temperature at 0°C is simulated to obtain the temperature change of the tested cable sheath over at least 120 hours. If the temperature difference between the tested cable and the reference cable sheath is less than 4°C in the last 96 hours and less than 2°C in the last 72 hours, it indicates good thermal stability. If the above conditions are not met, the time is extended to 240 hours. If the temperature difference requirement still cannot be met, the tested cable is considered to be non-thermal stable.

[0024] Compared with the prior art, the present invention has the following advantages: The present invention evaluates the temperature stability of cable insulation materials by calculating the characterization index based on the conductivity measured at different temperatures, which significantly reduces the experimental cost of temperature stability evaluation of cable insulation materials and greatly improves the speed and efficiency of temperature stability evaluation of cross-linked polyethylene cable insulation. Combined with the cable model of finite element simulation software for thermal stability testing, it achieves efficient and accurate evaluation of the temperature stability of high voltage DC cables. Attached Figure Description

[0025] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0026] In the attached diagram:

[0027] Figure 1 This is a flowchart illustrating the method for evaluating the temperature stability of cross-linked polyethylene DC cables provided in this invention.

[0028] Figure 2 This is a schematic diagram of the resistivity and conductivity testing system of the present invention;

[0029] Figure 3 This is a schematic diagram of the dimensions of the resistivity system in this invention;

[0030] Figure 4 This is a schematic diagram of the DC cable simulation model in this invention;

[0031] Figure 5 This is a cross-sectional view of the temperature distribution calculated from the cable simulation model in this invention;

[0032] Figure 6 A schematic diagram showing the variation of XLPE current over time (30°C, 20 kV / mm) as an exemplary embodiment of the present invention;

[0033] Figure 7 This is a schematic diagram illustrating the change in the conductivity of XLPE with temperature, provided as an exemplary embodiment of the present invention.

[0034] Figure 8 A schematic diagram of the activation energy of XLPE provided in an exemplary embodiment of the present invention;

[0035] Figure 9This is a schematic diagram of the internal electric field distribution of a cable insulation provided as an exemplary embodiment of the present invention.

[0036] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0037] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0038] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0039] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0040] like Figures 1 to 9 As shown, the method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity includes the following steps:

[0041] S1. The DC current of XLPE insulation material at different temperatures was measured by resistivity testing;

[0042] S2. Calculate the corresponding conductivity and temperature stability characterization index based on the DC current to evaluate the temperature stability of the XLPE insulation material of the high-voltage DC cable. The temperature stability characterization index is determined by the following formula:

[0043] ,

[0044] In the formula: This is an indicator of temperature stability. The high-temperature conductivity represents the maximum permissible temperature of XLPE insulation or the maximum operating temperature of the high-voltage DC cable, respectively. Low-temperature conductivity, representing room temperature or the lowest temperature of the cable insulation;

[0045] S3. Using finite element analysis software, the temperature distribution cross-section is calculated from the simulation model of the XLPE insulation material of the high-voltage DC cable. Based on the temperature difference between the sheath of the tested cable and the reference cable after transient internal pressurization, the thermal stability of the XLPE insulation material of the high-voltage DC cable in actual engineering is evaluated.

[0046] In a preferred embodiment of the method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, in step S1, the resistivity test includes at least a DC high-voltage source, an electrode system, an ammeter, a data acquisition system, and a temperature control device. The data acquisition system is located between the high-voltage ammeter and the electrode system, and uses a computer to acquire data for measurement time control and range selection, and records DC current data in real time.

[0047] In a preferred embodiment of the high-voltage DC cable temperature stability assessment method based on XLPE conductivity, a shielding system is provided outside the electrode system to prevent electromagnetic interference during the measurement process; a constant temperature chamber is provided outside the shielding system to achieve temperature control during the measurement.

[0048] In a preferred embodiment of the method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, the maximum allowable temperature of XLPE insulation or the maximum operating temperature of the high-voltage DC cable is 90°C or 70°C, respectively, and the room temperature or the minimum temperature of the cable insulation is 30°C.

[0049] In a preferred embodiment of the method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, the corresponding conductivity is determined by the following formula:

[0050]

[0051] In the formula: I v Leakage current; d The thickness of the sample; U This is an externally applied DC voltage; S To measure the effective area of ​​the electrode.

[0052] In a preferred embodiment of the method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, a simulation model of the XLPE insulation material of the high-voltage DC cable is established using finite element simulation software. The component parameters, heat source, initial temperature value, and initial potential value of the simulation model are set. Combined with the transient simulation of the temperature change trend after the internal pressure of the cable, the reference cable sheath temperature and the tested cable sheath temperature are obtained from the temperature cross section diagram, and the thermal stability of the high-voltage DC current is evaluated based on the temperature difference between the two.

[0053] In a preferred embodiment of the high voltage DC cable temperature stability assessment method based on XLPE conductivity, the simulation model consists of, from the inside out, a conductor, a conductor shielding layer, an XLPE insulation layer, an insulation shielding layer, a water-blocking layer, a metal sheath, and an outer sheath, with the center lines of each component coinciding.

[0054] The component parameters of the simulation model include density, heat capacity, thermal conductivity, electrical conductivity, and dielectric constant.

[0055] In a preferred embodiment of the high-voltage DC cable temperature stability assessment method based on XLPE conductivity, the heat sources in the simulation model are Joule heat generated by the conductor current and heat generated by the insulation leakage current. The Joule heat generated by the conductor current depends on the cable conductor loss, and the heat generated by the insulation leakage current has a unit volume heating power of [missing information]. γE 2 , g conductivity ，E For field strength.

[0056] The initial temperature of the simulation model is between the highest operating temperature of the power cable and room temperature, and the initial temperature of each layer is the same.

[0057] In a preferred embodiment of the high-voltage DC cable temperature stability assessment method based on XLPE conductivity, the initial potential of the conductor shielding layer and insulation layer of the simulation model is 0; the heat transfer mode of the simulation model is solid heat transfer.

[0058] In a preferred embodiment of the high-voltage DC cable temperature stability assessment method based on XLPE conductivity, the sheath temperature is determined according to the outer temperature of the temperature distribution cross-section obtained from simulation; the reference cable sheath temperature is the sheath temperature when the conductor is not energized under full load; the tested cable sheath temperature is the temperature after the cable is fully loaded and stabilized with a voltage of 1.45°C applied to the conductor. U The sheath temperature at 0°C is simulated to obtain the temperature change of the tested cable sheath over at least 120 hours. If the temperature difference between the tested cable and the reference cable sheath is less than 4°C in the last 96 hours and less than 2°C in the last 72 hours, it indicates good thermal stability. If the above conditions are not met, the time is extended to 240 hours. If the temperature difference requirement still cannot be met, the tested cable is considered to be non-thermal stable.

[0059] In one embodiment, the method includes the following steps:

[0060] Step 1: Measure the DC current of XLPE insulation material at different temperatures using a resistivity and conductivity testing system;

[0061] Step 2: Based on the measured DC current, calculate the corresponding conductivity and temperature stability characterization index, which can be used to evaluate the temperature stability of the high voltage DC cable insulation material.

[0062] Step 3: Use finite element simulation software to simulate the DC cable model to obtain the temperature distribution cross-section diagram. Based on the temperature difference between the tested cable and the reference cable sheath after transient internal pressurization, evaluate the thermal stability of high voltage DC cables in actual engineering.

[0063] Step 1:

[0064] In one embodiment, the resistivity testing system described in step one is as follows: Figure 2 As shown, the system mainly includes a DC high-voltage source, a temperature control system, a three-electrode system, a protective resistor, a high-resistivity meter, and a computer. A DC high-voltage source is used, with an output voltage of 0~40 kV and a ripple factor of 0.1%. A current-limiting resistor of approximately 15MΩ is used. An electrometer is used, with a current measurement range of 1 nA~21mA. Data acquisition is achieved through a computer, used for measurement time control and range selection, and real-time recording of current data. Following the working principle of the resistivity testing system, the wiring is connected. During testing, the sample surface is wiped clean beforehand to ensure its cleanliness, and then the appropriate voltage is applied. The leakage current is recorded by the high-resistivity meter and the computer. Specific parameters of the resistivity system are as follows. Figure 3 As shown, the material's conductivity is calculated. A sheet sample with dimensions of 100 mm × 100 mm × 0.2 mm is selected. The polarization process affects the conduction current value, and it takes a certain amount of time for the current to reach a steady state.

[0065] In order to determine the test time, Figure 6 The variation trend of XLPE current over time is presented at 30℃ and 20 kV / mm (close to the internal electric field strength of high-voltage DC cable insulation). It can be clearly seen that the current does not change significantly after 1000 s. Therefore, in this embodiment, 1860 s is selected as the measurement time, and the current value of the last 60 s is used to calculate the resistivity of the sample. The experimental temperature is selected based on the actual temperature range of the cable insulation.

[0066] In one embodiment, based on the DC current measured in step one at different temperatures, specifically, the high-temperature conductivity test temperature is selected as 70°C, the test field strength is selected as 20 kV / mm, and the XLPE DC current at different temperatures is shown in Table 1.

[0067] Table 1. DC current of the two XLPE materials at 30℃ and 70℃

[0068]

[0069] Step Two:

[0070] In one embodiment, specifically, the effective area of ​​the measuring electrode is 0.000491 m². 2 The DC conductivity of XLPE was calculated using equation (1) and is shown in Table 2.

[0071] Table 2. Electrical conductivity of the two XLPE materials at different temperatures

[0072]

[0073] Based on the measured conductivity at different temperatures, the temperature stability characterization index G of XLPE was calculated using equation (2), as shown in Table 3.

[0074] Table 3. Temperature stability characterization index of XLPE (G)

[0075]

[0076] In this embodiment, the characterization parameters of XLPE1 are greater than those of XLPE2, indicating that the temperature stability of XLPE1 is better than that of XLPE2.

[0077] According to the conductivity mechanism, XLPE exhibits primarily electron hopping conductance under experimental conditions. In amorphous dielectrics, the density of local states is very high, and electrons are mostly located in these local states. Therefore, electron migration between local states is the dominant process; that is, electrons migrate from one local state to another by jumping over potential barriers. This process can be figuratively described as hopping migration. The probability of an electron jumping between two adjacent local states is related to the spatial distance between the two states. a and barriers u 0 is related to the setting of the electronic thermal vibration frequency as v At that time, the mobility can be obtained as:

[0078] (4)

[0079] Furthermore, considering the concentration of conductive carriers... n and the amount of charge it carries q From this, we can derive the conductivity formula for the electron hopping conductivity case:

[0080] (5)

[0081] Taking the logarithm of both sides of equation (5) yields:

[0082] (6)

[0083] Therefore, if we plot the logarithm of conductivity on the ordinate and the reciprocal of absolute temperature on the abscissa, we can obtain a straight line, and the activation energy can be calculated from the slope of this line.

[0084] In this embodiment, the electrical conductivity of two different XLPE materials at different temperatures is compared, such as... Figure 7 As shown, the activation energy was further calculated through fitting, as follows: Figure 8 As shown, XLPE1 has a relatively low activation energy, indicating that its conductivity changes little with temperature, meaning that the material has high temperature stability.

[0085] According to the electric field design of DC cables, the cable insulation layer exhibits a Laplace electric field (higher inside, lower outside) and a temperature difference (higher inside, lower outside). However, due to the influence of temperature and electric field on XLPE, the conductivity within the insulation layer shows a distribution that is higher inside and lower outside. Under a DC electric field, conductivity directly affects the distribution of the electric field in the insulation material. Due to the combined effect of these factors, the electric field is relatively smaller inside the insulation material and relatively larger outside, and in certain cases, even an "electric field reversal" phenomenon may occur. This causes a deviation between the actual electric field in the insulation material and the designed electric field, increasing the risk of cable failure. Figure 9 The paper presents the electric field distribution of cable insulation layers using the two types of XLPE as insulation. Although both exhibited the "electric field reversal" phenomenon, XLPE1, with its lower activation energy and better temperature stability, showed a smaller degree of "electric field reversal" and a lower maximum electric field strength. This demonstrates that activation energy can be used to measure the temperature stability of a material and guide its practical application.

[0086] Therefore, the temperature stability assessment method proposed in this invention can significantly reduce the experimental cost of assessing the temperature stability of cable insulation and greatly improve the speed and efficiency of assessing the temperature stability of cross-linked polyethylene cable insulation.

[0087] Step 3:

[0088] In this embodiment, a DC cable model is established in the simulation software based on the structure of a 500 kV DC cable model.

[0089] Furthermore, the density, heat capacity, and electrical conductivity can be obtained according to the specific type of each component. Density and heat capacity are usually obtained from the factory calibration values, the thermal conductivity of each component is measured by a thermal conductivity meter, and the relative permittivity is measured by broadband spectrum.

[0090] The reference cable conductor parameters are set as follows: thermal conductivity of 401 W / (m·K) and density of 8940 kg / m³. 3 Its heat capacity is 385 J / (kg·K), its electrical conductivity is 57142875 S / m, and its relative permittivity is 1;

[0091] The reference cable shielding layer parameters are set as follows: thermal conductivity of 0.28 W / (m·K) and density of 1120 kg / m³. 3Its heat capacity is 2700 J / (kg·K), its electrical conductivity is 0.1 S / m, and its relative permittivity is 100;

[0092] The parameters for the reference cable water-blocking layer are set as follows: thermal conductivity of 0.08 W / (m·K) and density of 200 kg / m³. 3 Its heat capacity is 60 J / (kg·K);

[0093] The reference cable metal sheath parameters are set as follows: thermal conductivity of 250 W / (m·K) and density of 8940 kg / m³. 3 Its heat capacity is 385 J / (kg·K);

[0094] The reference cable outer sheath parameters are set as follows: thermal conductivity of 0.29 W / (m·K) and density of 968 kg / m³. 3 Its heat capacity is 2532 J / (kg·K);

[0095] The reference cable XLPE insulation layer parameters are set as follows: thermal conductivity of 0.285 W / (m·K) and density of 980 kg / m³. 3 Its heat capacity is 2200 J / (kg·K), its relative permittivity is 2.2, and in particular, its conductivity satisfies equation (3). β For 1.0413, XLPE1 and XLPE2 γ 0 is set to 2.91 × 10 -29 S / m and 2.94×10 -31 S / m, α Set to 0.0608 and 0.0767 respectively, XLPE1 shows less temperature dependence than XLPE2. Equation (3) assumes the dielectric is uniform and considers the parameters... α and β A single value, but the parameter α and β It depends on temperature and electric field strength, respectively. During normal operation, α and β The value will vary throughout the insulation. Therefore, the effects of these stresses and temperatures must be taken into account. α and β The uncertainty in the calculation is approximately 3%.

[0096] In this embodiment, the parameter settings of each component of the cable under test are consistent with those of the standard cable.

[0097] Furthermore, the initial temperature of each part of the cable model was set to 303.15 K, and the heat sources in the cable model were set as Joule heating from the conductor current and heat generation from the insulation leakage current, with the former being 17300 W / m. 3 The latter has a heat output power per unit volume of γE 2 During thermal stability testing, a 1.45 ohm flux is applied to the outside of the conductor. U 0, i.e., 725 kV transient voltage, the simulation time is selected from 0 to 120 h, and the measurement interval is selected as 12 h. The temperature of the cable sheath in the last 96 h is determined according to the temperature cross section. The test results are shown in Table 4.

[0098] Table 4. Temperature and temperature difference of the reference cable and the cable under test.

[0099]

[0100] Continued from Table 4

[0101]

[0102] Based on Table 4, the temperature difference between XLPE1 and the reference cable sheath was less than 4℃ in the last 96 hours and less than 2℃ in the last 72 hours, as obtained from the temperature cross-section diagram, indicating good thermal stability. However, the temperature difference between XLPE2 and the reference cable sheath was greater than 2℃ in the last 72 hours, and even after extending to 240 hours, it still could not meet the temperature difference requirement. Therefore, it is considered that the tested cable XLPE2 does not meet the thermal stability standard, which is consistent with the evaluation results of the temperature stability characterization index.

[0103] In summary, this invention demonstrates that by using finite element simulation software to simulate a cable model and obtain a steady distribution cross-section diagram, the thermal stability of different high-voltage DC cables in actual engineering can be evaluated based on the temperature difference between the sheath of the tested cable and the reference cable after transient internal pressurization, thereby improving the accuracy of high-voltage DC cable temperature stability assessment.

[0104] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity, characterized in that, Includes the following steps: S1. The DC current of XLPE insulation material at different temperatures was measured by resistivity testing; S2. Calculate the corresponding conductivity and temperature stability characterization index based on the DC current to evaluate the temperature stability of the XLPE insulation material of the high-voltage DC cable. The temperature stability characterization index is determined by the following formula: ， In the formula: This is an indicator of temperature stability. The high-temperature conductivity represents the maximum permissible temperature of XLPE insulation or the maximum operating temperature of the high-voltage DC cable, respectively. Low-temperature conductivity, representing room temperature or the lowest temperature of the cable insulation; S3. Using finite element analysis software, the temperature distribution cross-section is calculated from the simulation model of the XLPE insulation material of the high-voltage DC cable. Based on the temperature difference between the sheath of the tested cable and the reference cable after transient internal pressurization, the thermal stability of the XLPE insulation material of the high-voltage DC cable in actual engineering is evaluated.

2. The method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity according to claim 1, characterized in that, In step S1, the resistivity test includes at least a DC high voltage source, an electrode system, an ammeter, a data acquisition system, and a temperature control device. The data acquisition system is located between the high voltage ammeter and the electrode system. Data acquisition is performed by a computer for measurement time control and range selection, and the DC current data is recorded in real time.

3. The method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity according to claim 2, characterized in that, A shielding system is installed outside the electrode system to prevent electromagnetic interference during the measurement process; a constant temperature chamber is installed outside the shielding system to achieve temperature control during the measurement.

4. The method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity according to claim 1, characterized in that, The maximum permissible temperature for XLPE insulation or the maximum operating temperature for high-voltage DC cables is 90℃ or 70℃, respectively, and the minimum temperature for room temperature or cable insulation is 30℃.

5. The method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity according to claim 1, characterized in that, The corresponding conductivity is determined by the following formula: ， In the formula: I v Leakage current; d The thickness of the sample; U This is an externally applied DC voltage; S To measure the effective area of ​​the electrode.

6. The method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity according to claim 1, characterized in that, A simulation model of XLPE insulation material for high-voltage DC cables was established using finite element simulation software, and the component parameters, heat source, initial temperature value, and initial potential value of the simulation model were set. By combining the transient simulation of the temperature change trend inside the cable after pressurization, the reference cable sheath temperature and the tested cable sheath temperature are obtained from the temperature cross section, and the thermal stability of the high voltage DC current is evaluated based on the temperature difference between the two.

7. The method for evaluating the temperature stability of high-voltage DC cables based on XLPE conductivity according to claim 6, characterized in that, The simulation model consists of, from the inside out, a conductor, a conductor shielding layer, an XLPE insulation layer, an insulation shielding layer, a water-blocking layer, a metal sheath, and an outer sheath, with the center lines of each component coinciding. The component parameters of the simulation model include density, heat capacity, thermal conductivity, electrical conductivity, and dielectric constant.

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