Method and system for calculating ampacity and assessing health status of high voltage direct current cable

Abstract

This invention discloses a method and system for calculating the current-carrying capacity and assessing the health status of high-voltage direct current (HVDC) cables. The method includes dividing the cable into a first conventional heat dissipation section, a high-resistance section, and a second conventional heat dissipation section based on the identification results of high-resistance sections; constructing a first heat conduction equation for the first and second conventional heat dissipation sections; constructing a second heat conduction equation for the high-resistance section; solving the first and second heat conduction equations using boundary coupling conditions of continuous temperature and continuous heat flux density at the junction of adjacent sections as constraints to obtain the axial temperature distribution of the cable; based on the axial temperature distribution, using the highest allowable temperature of the conductor as a constraint, using a temperature-resistance coupled double-layer iterative method to deduce the maximum allowable current-carrying capacity of the cable; and calculating the temperature consistency between the measured temperature and the axial temperature distribution to perform cable health classification and defect location. This invention can effectively improve the accuracy of current-carrying capacity calculation and achieve quantitative assessment of cable aging status and accurate location of potential defects.

Description

Technical Field

[0001] This invention belongs to the field of high-voltage power cable operation and testing technology, specifically relating to a method and system for calculating the current carrying capacity and assessing the health status of high-voltage DC cables. Background Technology

[0002] High-voltage direct current (HVDC) cables often need to pass through areas with significantly higher thermal resistance than normal environments, such as walls and insulation layers, in urban power distribution networks, industrial facilities, building power supply, and cross-river and cross-sea projects (hereinafter referred to as "high-resistance zones"). The high thermal resistance in these areas hinders cable heat dissipation, creating localized hotspots and severely impacting cable current carrying capacity and operational safety. Especially with the widespread application of DC transmission technology and the increasing number of DC cable projects in cross-river tunnels, DC cables are more sensitive to temperature. Furthermore, DC transmission has the characteristics of large capacity and high utilization hours. Once a localized hotspot forms when crossing a high-resistance zone, it will accelerate the aging of insulation materials, posing a serious threat to the safe and stable operation of the transmission system.

[0003] However, existing technologies have the following key drawbacks:

[0004] 1. Traditional current carrying capacity calculation methods all assume that the cable is in a uniform heat dissipation environment throughout its length, without distinguishing the difference in heat conduction between high-resistance areas and conventional heat dissipation areas, resulting in a temperature prediction error of 15% to 20% in high-resistance areas.

[0005] 2. The lack of a refined heat conduction model for high-resistivity sections makes it impossible to accurately describe the coupled heat transfer characteristics of axial and radial directions, and the location error of hot spots can reach 3~5m.

[0006] 3. Existing technologies only determine the safety status of cables based on conductor temperature thresholds, without establishing a correlation mechanism between "temperature distribution deviation and aging degree," thus failing to identify potential risks such as early insulation aging and local defects.

[0007] 4. Ignoring the thermal boundary coupling effect between high-resistivity and non-high-resistivity regions leads to discontinuities in temperature distribution calculations, reducing the reliability of current-carrying capacity calculations.

[0008] 5. It is only applicable to a single uniform environment and cannot meet the dynamic calculation needs of complex high-resistivity scenarios such as wall penetration, pipe penetration, river crossing pipe gallery, and underground burial. Summary of the Invention

[0009] To address the aforementioned issues, this invention proposes a method and system for calculating the current carrying capacity and assessing the health status of high-voltage DC cables. This method can effectively improve the accuracy of current carrying capacity calculation, achieve quantitative assessment of cable aging status and precise location of potential defects, and is applicable to online monitoring and maintenance assessment scenarios for various types of DC high-voltage DC cables.

[0010] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0011] In a first aspect, the present invention provides a method for calculating the current carrying capacity and assessing the health status of high-voltage DC cables, including:

[0012] Obtain the predetermined parameters of the high-voltage DC cable, the characteristic parameters of the high-resistance section, and the field environmental parameters;

[0013] Based on the characteristic parameters and thermal resistance threshold of the high-resistivity section, the high-resistivity section is identified. According to the identification results, the high-voltage DC cable is divided into the first conventional heat dissipation section, the high-resistivity section and the second conventional heat dissipation section arranged in sequence, and the boundary coupling conditions of continuous temperature and continuous heat flux density at the junction of adjacent sections are defined.

[0014] For the first and second conventional heat dissipation sections, a first heat conduction equation coupling axial heat conduction and radial heat dissipation is constructed; for the high-resistivity section, a second heat conduction equation purely axial heat conduction is constructed.

[0015] Using the piecewise function analytical method, combined with the predetermined parameters of the high-voltage DC cable and the field environmental parameters, and taking the boundary coupling condition of continuous temperature and continuous heat flux density at the junction of adjacent sections as the constraint condition, the first heat conduction equation and the second heat conduction equation are solved to obtain the full axial temperature distribution of the high-voltage DC cable.

[0016] Based on the axial temperature distribution, and using the highest allowable temperature of the conductor as a constraint, the maximum allowable current carrying capacity of the high voltage DC cable is derived by using a temperature-resistance coupling double-layer iterative method.

[0017] Based on the measured temperature and the temperature distribution along the entire axis, the temperature matching degree is calculated, and the cable health is classified and defects are located.

[0018] In a second aspect, the present invention provides a system for calculating the current carrying capacity and assessing the health status of high-voltage DC cables, including a storage medium and a processor;

[0019] The storage medium is used to store instructions;

[0020] The processor is configured to operate according to the instructions to perform the method according to any one of the first aspects.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention breaks through the limitations of traditional uniform heat conduction models by segmenting high-voltage DC cables based on thermal resistance characteristics. It constructs a "first heat conduction equation with axial-radial coupling" and a "second heat conduction equation with pure axial heat conduction" in the conventional heat dissipation section and the high-resistance section, respectively. By introducing dual continuity conditions of temperature and heat flux density at the boundaries of adjacent sections, it accurately characterizes the heat concentration effect in the high-resistance section and establishes a precise mapping of "temperature distribution-heating power-current carrying capacity," achieving dynamic optimization of current carrying capacity and solving for the physical continuity of temperature. It also enables cable health classification and defect location. This invention can be flexibly adapted to various complex scenarios such as walls, insulation layers, and cross-river pipe corridors, significantly improving engineering applicability. This invention effectively reduces the risk of faults caused by overheating in high-resistance areas, promoting the intelligent leap of cable monitoring from "passive monitoring" to "active diagnosis." Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0024] Figure 1 This is a schematic diagram of a high-voltage DC cable partition in one embodiment of the present invention;

[0025] Figure 2 This is a flowchart of a method for calculating the current carrying capacity and assessing the health status of a high-voltage DC cable in one embodiment of the present invention;

[0026] Figure 3 This is a temperature distribution diagram along the entire axis in one embodiment of the present invention;

[0027] Figure 4 This is an iterative convergence curve of the current carrying capacity in one embodiment of the present invention;

[0028] Figure 5 This is a hotspot temperature iterative convergence curve in one embodiment of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0031] Example 1

[0032] This invention provides a method for calculating the current carrying capacity and assessing the health status of high-voltage DC cables, comprising the following steps:

[0033] Obtain the predetermined parameters of the high-voltage DC cable, the characteristic parameters of the high-resistance section, and the field environmental parameters;

[0034] Based on the characteristic parameters and thermal resistance threshold of the high-resistivity section, the high-resistivity section is identified. According to the identification results, the high-voltage DC cable is divided into the first conventional heat dissipation section, the high-resistivity section and the second conventional heat dissipation section arranged in sequence, and the boundary coupling conditions of continuous temperature and continuous heat flux density at the junction of adjacent sections are defined.

[0035] For the first and second conventional heat dissipation sections, a first heat conduction equation coupling axial heat conduction and radial heat dissipation is constructed; for the high-resistivity section, a second heat conduction equation purely axial heat conduction is constructed.

[0036] Using the piecewise function analytical method, combined with the predetermined parameters of the high-voltage DC cable and the field environmental parameters, and taking the boundary coupling condition of continuous temperature and continuous heat flux density at the junction of adjacent sections as the constraint condition, the first heat conduction equation and the second heat conduction equation are solved to obtain the full axial temperature distribution of the high-voltage DC cable.

[0037] Based on the axial temperature distribution, and using the highest allowable temperature of the conductor as a constraint, the maximum allowable current carrying capacity of the high voltage DC cable is derived by using a temperature-resistance coupling double-layer iterative method.

[0038] Based on the measured temperature and the temperature distribution along the entire axis, the temperature matching degree is calculated, and the cable health is classified and defects are located.

[0039] The above scheme breaks through the limitations of traditional uniform heat conduction models. Based on thermal resistance characteristics, the high-voltage DC cable is segmented, and a "first heat conduction equation with axial-radial coupling" and a "second heat conduction equation with pure axial heat conduction" are constructed in the conventional heat dissipation section and the high-resistance section, respectively. By introducing a dual continuity condition of temperature and heat flux density at the boundary of adjacent sections, the heat concentration effect in the high-resistance section is accurately characterized, and a precise mapping of "temperature distribution - heat generation power - current carrying capacity" is established. This achieves dynamic optimization of current carrying capacity and a solution for the physical continuity of temperature, enabling cable health grading and defect location.

[0040] Specifically, such as Figure 2 As shown in the figure, this embodiment of the invention provides a method for calculating the current carrying capacity and assessing the health status of high-voltage DC cables, including the following steps:

[0041] Step S1: Obtain the predetermined parameters of the high-voltage DC cable, the characteristic parameters of the high-resistance section, and the field environmental parameters.

[0042] The predetermined parameters of the high-voltage DC cable include: conductor thermal conductivity. conductor cross-sectional area Resistance per unit length at 20℃ Temperature resistivity Thermal resistance per unit length of conductor to air and the highest allowable temperature of the conductor ;

[0043] The characteristic parameters of the high-resistivity section include: the starting coordinates of the high-resistivity section. and endpoint coordinates , , , It is half the length of the high-resistivity section;

[0044] The on-site environmental parameters include: ambient reference temperature. .

[0045] In the specific implementation process, it is also necessary to perform unit unification and numerical calibration preprocessing on the predetermined parameters of the high-voltage DC cable, the characteristic parameters of the high-resistance section, and the field environmental parameters.

[0046] Step S2: Based on the characteristic parameters and thermal resistance threshold of the high-resistance section, identify the high-resistance section, dividing the high-voltage DC cable into a first conventional heat dissipation section, a high-resistance section, and a second conventional heat dissipation section arranged sequentially, and defining boundary coupling conditions for continuous temperature and continuous heat flux density at the junction of adjacent sections. Specifically, this includes the following steps:

[0047] (1) If the overall thermal resistance of the high resistance section is Much greater than the thermal resistance per unit length of a conductor to air If the condition is met, it is determined to be a high-resistivity section, and the relationship between the two satisfies the following condition. ,in, The preset experience threshold is typically set between 5 and 10, and can be fine-tuned and optimized according to the actual working conditions. This is the thermal resistance threshold. In the formula, To preset an empirical threshold, For cable insulation thermal resistance, For wall thermal resistance, The wall's thermal resistance to air; , , The calculations are all existing technologies, and will not be elaborated upon in this invention;

[0048] (2) Determine the starting coordinates of the high-resistivity section and endpoint coordinates ,in, , The length of the high-resistivity section was calculated to be ;

[0049] (3) Segmentation: Based on differences in spatial location and heat dissipation mechanism, the entire high-voltage DC cable is divided into three independent calculation regions to avoid calculation deviations caused by a single model adapting to all operating conditions. Specifically, the division is as follows:

[0050] First conventional heat dissipation section (i.e., the left conventional heat dissipation section): Radial heat dissipation is smooth and efficient;

[0051] High-resistivity section: Radial heat dissipation is hindered, and axial heat conduction becomes dominant;

[0052] Second conventional heat dissipation section (i.e., the conventional heat dissipation section on the right): It has smooth radial heat dissipation and high heat dissipation efficiency.

[0053] (4) To ensure the rationality of heat transfer between adjacent sections, at the junction of the high-resistivity section and the conventional heat dissipation section ( , It needs to satisfy the dual constraints of temperature continuity and heat flux density continuity, and the mathematical expression is as follows:

[0054]

[0055] In the formula, In the first conventional heat dissipation section Temperature value at that location, In the second conventional heat dissipation section Temperature value at that location, In the high-resistivity section Temperature value at that location, In the high-resistivity section Temperature value at that location, In the first conventional heat dissipation section Heat flux density at that point In the second conventional heat dissipation section Heat flux density at that point In the high-resistivity section Heat flux density at that point In the high-resistivity section Heat flux density at that point Indicates location.

[0056] Step S3: For the first and second conventional heat dissipation sections, construct a first heat conduction equation coupling axial and radial heat dissipation; for the high-resistivity section, construct a second heat conduction equation purely axial. Specifically, this includes:

[0057] To address the differences in heat dissipation characteristics between the first conventional heat dissipation section, the high-resistance section, and the second conventional heat dissipation section, a differentiated steady-state heat conduction differential equation is established, which closely reflects the actual heat transfer law and balances computational accuracy and solution efficiency.

[0058] (1) The heat conduction equations for the first and second conventional heat dissipation sections are constructed using the same method, both including:

[0059] Radial heat dissipation is unimpeded in conventional heat dissipation sections. However, the coupling effect of axial and radial heat dissipation needs to be considered, leading to the establishment of a first heat conduction equation. The expression for this first heat conduction equation is as follows:

[0060] ,

[0061] ,

[0062] In the formula, This refers to the heat output per unit length of a high-voltage DC cable. This refers to the operating current of the high-voltage DC cable. Resistance per unit length of conductor For position The temperature at that location.

[0063] Far-end boundary condition: The temperature at infinity of the high-voltage DC cable approaches the steady-state temperature of the environment, i.e. hour, .

[0064] (2) Construct the second heat conduction equation;

[0065] Radial heat dissipation is severely impeded in the high-resistance section, with radial thermal resistance much greater than axial thermal resistance. Ignoring radial heat loss, a second heat conduction equation is established based on pure axial heat conduction. The expression for the second heat conduction equation is:

[0066] ,

[0067] Special operating condition correction: If radial heat dissipation in the high-resistivity section cannot be ignored, a radial heat flow correction term is introduced based on the above equation to adapt to complex laying scenarios.

[0068] Step S4: Using the piecewise function analytical method, combined with the predetermined parameters of the high-voltage DC cable and the field environmental parameters, and taking the boundary coupling condition of continuous temperature and continuous heat flux density at the junction of adjacent sections as the constraint, solve the first heat conduction equation and the second heat conduction equation to obtain the full axial temperature distribution of the high-voltage DC cable. Specifically, this includes:

[0069] (1) Solve for the temperature distribution in the high-resistivity section;

[0070] The high-resistivity section has no radial heat dissipation; heat accumulates along the axial direction, resulting in a parabolic temperature distribution. The center point of the high-resistivity section is the point of highest temperature. The expression for the temperature distribution in the high-resistivity section is:

[0071] ,

[0072] In the formula, This indicates the temperature distribution in the high-resistivity section. This is the temperature value at the center point of the high-resistivity section.

[0073] (2) Solve for the temperature distribution of the first conventional heat dissipation section and the temperature distribution of the second conventional heat dissipation section;

[0074] In the normal heat dissipation section, heat dissipates rapidly radially, and the temperature exhibits an exponentially decreasing distribution. Further away from the high-resistivity section, the temperature tends to reach a steady state. The expressions for the temperature distribution in the first and second normal heat dissipation sections are the same:

[0075] ,

[0076] ,

[0077] In the formula, This indicates the temperature distribution of the first or second conventional heat dissipation section. This is the temperature decay coefficient, in units of... ; The integral constant is obtained by solving for the temperature continuity condition at the boundary between adjacent sections. , It is an exponential decay factor.

[0078] Step S5: Based on the axial temperature distribution and using the highest permissible temperature of the conductor as a constraint, the maximum permissible current carrying capacity of the high-voltage DC cable is derived using a temperature-resistance coupling two-layer iterative method. Specifically, this includes:

[0079] This step, based on the axial temperature distribution and using the highest permissible temperature of the conductor as a constraint, employs a temperature-resistance coupled two-layer iterative method to deduce the maximum permissible current carrying capacity of the high-voltage DC cable. It fully considers the influence of the conductor's temperature resistivity, eliminating errors introduced by traditional fixed-value resistance calculations. The iterative process is closed-loop controllable and converges quickly. The specific implementation process is as follows:

[0080] (1) Setting initial parameters for iteration.

[0081] Set the maximum allowable temperature of the conductor The value is determined according to the cable insulation type and standard specifications, such as XLPE insulated DC cable. Or, the threshold can be customized according to special insulation materials;

[0082] Set initial values ​​for iteration: Select the initial operating current of the high-voltage DC cable. Set the initial average temperature ;

[0083] Set a convergence accuracy threshold: inner iteration convergence accuracy External iteration convergence accuracy In the specific implementation process, 0.01℃ can be used; The temperature can be 0.1~0.5℃;

[0084] (2) Temperature-resistance coupling internal iteration

[0085] For a given operating current, iteratively solve for the resistance per unit length of conductor. By coupling temperature and resistance calculations with the corresponding temperature field, the specific steps are as follows:

[0086] Resistance per unit length of conductor Calculate the resistance per unit length of conductor based on the current operating current and current average temperature. , ;

[0087] Calculation of heat generation power per unit length of high-voltage DC cable: Based on Joule's law, calculate the heat generation power per unit length of high-voltage DC cable. , ;

[0088] Hotspot temperature calculation: Substitute the expression for the temperature distribution in the high-resistivity section to calculate the temperature at the center point of the high-resistivity section (also known as the hotspot). , ;

[0089] Temperature calculation at the boundary between adjacent sections: Calculate the temperature at the boundary between the high-resistivity section and the conventional heat dissipation section. , ,

[0090] Inner iteration convergence criterion: Let ,

[0091] like If the inner iteration is found to be converged, proceed to the outer iteration; otherwise, let... Return to the step of calculating the resistance per unit length of conductor and repeat the inner iteration.

[0092] (3) External iteration and current correction

[0093] Compare the temperature at the center point of the high-resistivity section under the current operating current. With the conductor's maximum allowable temperature Determine whether the convergence requirement is met: If If the current is adjusted according to the first or second adjustment strategy, the internal iteration of temperature-resistance coupling is returned to recalculate until the external iteration converges.

[0094] The current adjustment in the outer iteration adopts a strategy combining rapid initial value adjustment and Newton's iteration refinement, balancing convergence speed and computational accuracy. Specifically:

[0095] The first adjustment strategy is to use the initial value to quickly adjust the correction current based on the square root relationship of temperature. ;

[0096] The second adjustment strategy is: when rapid adjustment using the initial value fails to meet the accuracy of the calculated temperature, then the sensitivity coefficient of the current is used. To further refine the current correction ;

[0097] The first adjustment strategy is used only during the first external iteration, while the second adjustment strategy is used during the second and subsequent external iterations.

[0098] After the outer iteration meets the convergence accuracy, the final converged current value is output, which is the current value of the high-voltage DC cable crossing the high-resistance region. Maximum allowable flow rate.

[0099] Step S6: Based on the measured temperature and the temperature distribution along the entire axis, calculate the temperature compatibility and perform cable health classification and defect location.

[0100] By combining actual temperature data collected by the distributed fiber optic temperature measurement system (DTS) with theoretically calculated temperature distribution, the aging degree of cable insulation can be quantitatively assessed, potential defects can be located, and the operational status can be visualized and graded, providing data support for operation and maintenance.

[0101] Obtain the measured temperature at various axial positions of the high-voltage DC cable. ;

[0102] Calculate the temperature deviation at each location. and average temperature deviation ,in, , ;

[0103] Calculate temperature fit , ;

[0104] Based on temperature compatibility The mapping relationship between the cable health level and the health level is used to complete the cable health classification.

[0105] In the specific implementation process, based on temperature compatibility The health status of cables is divided into four levels, corresponding to differentiated operation and maintenance strategies:

[0106] This indicates that the cable's health status is at the healthy level: the measured temperature distribution closely matches the theoretical temperature distribution, the cable insulation performance is intact, and routine inspections are sufficient.

[0107] This indicates that the cable's health status is slightly aged: the temperature deviation is slightly exceeded, and the insulation shows slight aging. It is recommended to increase the frequency of online monitoring.

[0108] This indicates that the cable's health condition is at a significantly aged level: the temperature deviation is large, the insulation aging is accelerated, and the testing cycle needs to be shortened and potential hazards need to be fully investigated.

[0109] This indicates that the cable's health status is at the fault warning level: the temperature deviation is seriously excessive, there are local defects or serious aging, and the machine should be stopped immediately for maintenance.

[0110] If the maximum temperature deviation Greater than the set temperature threshold (e.g.) (Celsius), then determine the corresponding The location indicates a potential defect point in the high-voltage direct current (HVDC) cable. Common defect types include: insulation damage, localized crushing damage, space charge accumulation in the DC cable, poor joint contact, and moisture absorption of the insulation.

[0111] This embodiment uses a ±500kV urban distribution network DC cable as an example to describe in detail the method provided in this embodiment of the invention. The high-voltage DC cable uses a 2500mm² copper conductor and cross-linked polyethylene (XLPE) insulation. One high-voltage DC cable unit is 30m long and needs to pass through a 0.3m thick concrete wall. This wall has a significantly higher thermal resistance than the surrounding soil, forming a high-resistance zone, the center of which is located 50m along the cable axis. The purpose of this embodiment is to calculate the maximum allowable current carrying capacity of the cable after passing through the wall and to analyze its axial temperature distribution characteristics.

[0112] (1) According to step S1 of the present invention, the predetermined parameters of the high-voltage DC cable, the characteristic parameters of the high-resistance section, and the field environmental parameters are collected and organized, as shown in Table 1.

[0113] Table 1. Predetermined parameters of high-voltage DC cables, characteristic parameters of high-resistance sections, and field environmental parameters.

[0114]

[0115] (2) Identification and segmentation of high-resistivity sections.

[0116] like Figure 1 As shown, the start and end coordinates of the high-resistivity section are determined based on the wall thickness:

[0117] Starting point of the high-resistivity section: ,

[0118] End of high-resistivity zone: ,

[0119] Half thickness of the high-resistivity section: ,

[0120] Location of the center point of the high-resistivity section: ,

[0121] Based on this, the high-voltage DC cable is divided into three sections:

[0122] Left side conventional heat dissipation section: ,

[0123] High-resistivity section: ,

[0124] Right side conventional heat dissipation section: ,

[0125] (3) Calculation of key parameters.

[0126] First, calculate the key parameters related to heat conduction:

[0127] Temperature decay coefficient:

[0128]

[0129] Exponential decay factor:

[0130] ,

[0131] Heat transfer coefficient:

[0132]

[0133] (4) Accurate calculation of current carrying capacity.

[0134] A two-layer iterative method was adopted, considering the coupling effect of temperature on resistance. The iterative process and results are shown in Figure 2.

[0135] 1) Iterative process

[0136] The maximum allowable current carrying capacity is determined by a temperature-resistance coupled two-layer iterative method, considering the temperature resistivity coefficient α = 0.00393 / ℃.

[0137] Table 2 Iteration process and results

[0138]

[0139] 2) Convergence Results

[0140] like Figure 4 As shown, the maximum allowable current carrying capacity is: ,

[0141] like Figure 5 As shown, the temperature at the center point of the high-resistivity section (i.e., the hot spot temperature): ,

[0142] Average conductor temperature: ,

[0143] Resistance per unit length of conductor: μΩ / m (7.20 μΩ / m at 20℃, an increase of 17.9%)

[0144] (5) Calculation of temperature distribution along the entire axis

[0145] In carrying capacity The temperature distribution along the entire axis of the high-voltage DC cable is calculated.

[0146] Temperature calculation at the center point of the high-resistivity section:

[0147] Temperature calculation at the boundary: , ;

[0148] Temperature distribution function expression:

[0149] 1. High-resistivity section ( The temperature distribution follows a parabolic pattern.

[0150]

[0151] 2. Heat dissipation section ( Temperature exhibits an exponential decay distribution:

[0152]

[0153] where constant The temperature is determined by the continuity of the temperature at the boundary; see details below. Figure 3 .

[0154] The key temperature points are summarized in Table 3:

[0155] Table 3 Summary of Key Temperature Points

[0156]

[0157] (6) Health status assessment

[0158] The actual temperature data collected by the distributed fiber optic temperature measurement system (DTS) is compared with the theoretically calculated temperature distribution:

[0159] Temperature compatibility: ,

[0160] Average temperature deviation: ,

[0161] Maximum temperature deviation: ,

[0162] Health classification: The cable is classified as healthy, indicating that its insulation performance is intact, and routine inspections are sufficient.

[0163] Defect location: Maximum temperature deviation < Set threshold ( No obvious defects were detected.

[0164] (7) Engineering application recommendations

[0165] Based on the calculation results, the following operation and maintenance strategy can be formulated for the cable in this embodiment:

[0166] 1. Recommended operating load capacity

[0167] Maximum permissible current carrying capacity: 1931 A

[0168] 2. Temperature monitoring threshold setting

[0169] Normal operating range (≤67℃): Perform routine online monitoring.

[0170] Warning zone (67~70℃): Initiate health status assessment and increase monitoring frequency.

[0171] Alarm zone (>70℃): Immediately reduce load and arrange for shutdown and maintenance.

[0172] 3. Key monitoring locations

[0173] Location of the center point of the high-resistivity section: (Center of the wall)

[0174] border and ,

[0175] 4. Operation and maintenance strategy:

[0176] Perform routine inspections

[0177] (8) Verification of technical effects

[0178] Based on the above analysis, to address the uneven heat dissipation problem when high-voltage AC and DC cables pass through high thermal resistance regions, a mathematical model is established to describe the segmented heat conduction characteristics of high-resistance regions and conventional heat dissipation regions. This solves the technical problem of large temperature prediction errors in high-resistance regions caused by the traditional assumption of uniform heat dissipation. In this invention, by solving the expression for the axial temperature distribution, the axial temperature distribution of the cable and the precise location of hot spots are calculated, controlling the temperature prediction error to within 2% and improving the hot spot location accuracy to ±0.5m. Based on the constraint relationship between the conductor's maximum allowable temperature and the temperature at the center point (i.e., the hot spot) of the high-resistance section, a scientific method for calculating the maximum allowable current carrying capacity is established, adapting to the different operating characteristics of AC and DC cables and effectively improving current carrying capacity utilization.

[0179] Meanwhile, this invention establishes a quantitative correlation mechanism between temperature distribution deviation and aging degree when cables pass through high-resistance areas. By analyzing the consistency between actual and theoretical temperature distributions, it achieves quantitative assessment of cable health status and precise location of local defects, upgrading cable operation monitoring from a single "threshold alarm" to a comprehensive "status diagnosis." Through parametric modeling, it adapts to various complex high-resistance scenarios such as wall penetration and conduit penetration, meeting the dynamic calculation needs of different engineering environments. It eliminates the need to reconstruct models for specific scenarios or perform time-consuming finite element simulations, significantly improving the engineering applicability and promotional value of the method.

[0180] Example 2

[0181] This invention provides a system for calculating the current carrying capacity and assessing the health status of high-voltage DC cables, including a storage medium and a processor;

[0182] The storage medium is used to store instructions;

[0183] The processor is configured to operate according to the instructions to execute the method according to any one of Embodiment 1.

[0184] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0185] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0186] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0187] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0188] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

[0189] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for high voltage direct current cable ampacity calculation and health assessment, characterized in that, include: Obtain the predetermined parameters of the high-voltage DC cable, the characteristic parameters of the high-resistance section, and the field environmental parameters; Based on the characteristic parameters and thermal resistance threshold of the high-resistivity section, the high-resistivity section is identified. According to the identification results, the high-voltage DC cable is divided into the first conventional heat dissipation section, the high-resistivity section and the second conventional heat dissipation section arranged in sequence, and the boundary coupling conditions of continuous temperature and continuous heat flux density at the junction of adjacent sections are defined. For the first and second conventional heat dissipation sections, a first heat conduction equation coupling axial heat conduction and radial heat dissipation is constructed; for the high-resistivity section, a second heat conduction equation purely axial heat conduction is constructed. Using the piecewise function analytical method, combined with the predetermined parameters of the high-voltage DC cable and the field environmental parameters, and taking the boundary coupling condition of continuous temperature and continuous heat flux density at the junction of adjacent sections as the constraint condition, the first heat conduction equation and the second heat conduction equation are solved to obtain the full axial temperature distribution of the high-voltage DC cable. Based on the axial temperature distribution, and using the highest allowable temperature of the conductor as a constraint, the maximum allowable current carrying capacity of the high voltage DC cable is derived by using a temperature-resistance coupling double-layer iterative method. Based on the measured temperature and the temperature distribution along the entire axis, the temperature matching degree is calculated, and the cable health is classified and defects are located.

2. The method for calculating the current carrying capacity and assessing the health status of a high-voltage DC cable according to claim 1, characterized in that: the predetermined parameters of the high-voltage DC cable include: conductor thermal conductivity , conductor cross-sectional area , unit length resistance at 20°C , temperature resistance coefficient , conductor to air unit length thermal resistance , and the highest temperature allowed by the conductor ; the characteristic parameters of the high-resistance section include: the starting coordinates and end coordinates of the high-resistance section , , is half the length of the high-resistance section; the site environment parameters include the site environment reference temperature .

3. The method for calculating the current carrying capacity and assessing the health status of a high-voltage DC cable according to claim 2, characterized in that: Overall thermal resistance in the high-resistivity section satisfy , This is the thermal resistance threshold. In the formula, To preset an empirical threshold, For cable insulation thermal resistance, For wall thermal resistance, The wall's thermal resistance to air; The expression for the boundary coupling condition at the junction of adjacent sections, where temperature and heat flux density are continuous, is as follows: ， In the formula, In the first conventional heat dissipation section Temperature value at that location, In the second conventional heat dissipation section Temperature value at that location, In the high-resistivity section Temperature value at that location, In the high-resistivity section Temperature value at that location, In the first conventional heat dissipation section Heat flux density at that point In the second conventional heat dissipation section Heat flux density at that point In the high-resistivity section Heat flux density at that point In the high-resistivity section Heat flux density at that point Indicates location.

4. The method for calculating the current carrying capacity and assessing the health status of a high-voltage DC cable according to claim 2, characterized in that, The expression for the first heat conduction equation is: ， ， The expression for the second heat conduction equation is: In the formula, This refers to the heat output per unit length of a high-voltage DC cable. This refers to the operating current of the high-voltage DC cable. Resistance per unit length of conductor For position The temperature at that location.

5. The method for calculating the current carrying capacity and assessing the health status of a high-voltage DC cable according to claim 4, characterized in that: The axial temperature distribution of the high-voltage DC cable includes the temperature distribution of the high-resistance section, the temperature distribution of the first conventional heat dissipation section, and the temperature distribution of the second conventional heat dissipation section. The expression for the temperature distribution in the high-resistivity section is: ， In the formula, This indicates the temperature distribution in the high-resistivity section; The expressions for the temperature distribution of the first conventional heat dissipation section and the temperature distribution of the second conventional heat dissipation section are the same, both being: ， ， In the formula, This indicates the temperature distribution of the first or second conventional heat dissipation section. This is the temperature value at the center point of the high-resistivity section; The integral constant is obtained by solving for the temperature continuity condition at the boundary between adjacent sections. ; The temperature decay coefficient is It is an exponential decay factor.

6. The method for calculating the current carrying capacity and assessing the health status of a high-voltage DC cable according to claim 5, characterized in that: The calculation method for the maximum allowable current carrying capacity of the high-voltage DC cable includes: Set the initial operating current of the high-voltage DC cable. Initial average temperature Inner iteration convergence threshold External iteration convergence threshold ; The inner iteration is continuously executed until it converges. The inner iteration includes the following steps: Calculate the resistance per unit length of conductor based on the current operating current and the current average temperature. and the heat output per unit length of high voltage DC cable ,in, , ; Heat output per unit length of high voltage DC cable will bring in and The temperature at the center point of the high-resistivity section was calculated. Boundary between adjacent sections and Temperature; Based on the temperature at the center point of the high-resistivity section Boundary between adjacent sections and The temperature was then used to calculate a new average temperature using a weighted average method. ; Calculate the new average temperature Compared with the current average temperature The difference is considered if it is greater than or equal to the inner iteration convergence threshold. Then, the calculated new average temperature is taken as the current average temperature. Return to calculate the resistance per unit length of conductor. Repeat the inner iteration; If the new average temperature Compared with the current average temperature The difference is less than the inner iteration convergence threshold. Then, perform the outer iteration until the outer iteration converges, and output the maximum allowable current carrying capacity. The outer iteration includes the following steps: Calculate the temperature at the center point of the high-resistivity section. With the conductor's maximum allowable temperature The difference is considered if it is greater than or equal to the outer iteration convergence threshold. The operating current is adjusted sequentially according to the first adjustment strategy or the second adjustment strategy, and the inner iteration is returned to recalculate until the outer iteration converges.

7. The method for calculating the current carrying capacity and assessing the health status of a high-voltage DC cable according to claim 6, characterized in that: The formula used in the first adjustment strategy is: , The formula used in the second adjustment strategy is as follows: ,in , The first adjustment strategy is used only during the first external iteration, while the second adjustment strategy is used during the second and subsequent external iterations.

8. The method for calculating the current carrying capacity and assessing the health status of a high-voltage DC cable according to claim 5, characterized in that: Cable health grading is achieved through the following steps: Obtain the measured temperature at various axial positions of the high-voltage DC cable. ; Calculate the temperature deviation at each location. and average temperature deviation ,in, , ; Calculate temperature fit , ; Based on temperature compatibility The mapping relationship between the cable health level and the health level is used to complete the cable health classification.

9. The method for calculating the current carrying capacity and assessing the health status of a high-voltage DC cable according to claim 5, characterized in that: Defect localization is achieved through the following steps: Obtain the measured temperature at various axial positions of the high-voltage DC cable. ; Calculate the temperature deviation at each location. and maximum temperature deviation , , ; If the maximum temperature deviation If the temperature exceeds the set threshold, then the corresponding... The location is a potential defect point in the high-voltage DC cable.

10. A system for calculating the current carrying capacity and assessing the health status of high-voltage DC cables, characterized in that, Including storage media and processor; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the method according to any one of claims 1-9.

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