A method and device for dynamic evaluation of direct current cable ampacity

Abstract

The application provides a direct current cable current-carrying capacity dynamic evaluation method and device, and belongs to the field of cable operation detection. The method comprises the following steps: obtaining direct current cable structure parameters, electrical parameters, dynamic environment parameters and cable laying azimuth; based on the relative relationship among the solar elevation angle, the solar azimuth and the cable laying azimuth, calculating the sunlight radiation effective projection area and the absorbed heat flow density; selecting a correlation formula of forced convection heat transfer to calculate the forced convection heat transfer coefficient; using a segmented smooth transition function to calculate the actual convection heat transfer coefficient in the low wind speed interval; establishing a direct current cable heat balance equation, solving the direct current cable heat balance equation through the relaxation iteration method to obtain the maximum allowable current-carrying capacity; dynamically evaluating the ratio of the maximum allowable current-carrying capacity to the real-time load current, and outputting the dynamic evaluation result and the corresponding early warning information. Through the method, the application realizes dynamic evaluation of the current-carrying capacity, and fills the technical gap of the wind-sun coupling effect in the field of direct current cable dynamic capacity increase.

Description

Technical Field

[0001] This application relates to the field of cable operation and testing technology, and in particular to a method and apparatus for dynamic evaluation of the current carrying capacity of DC cables. Background Technology

[0002] With the rapid development of High Voltage Direct Current (HVDC) transmission technology and the large-scale grid connection of new energy sources, DC cables are increasingly widely used in power grids. Compared with AC cables, DC cables exhibit a more significant temperature gradient effect in their insulation layer, typically limiting their permissible operating temperature to 70℃, and making them more sensitive to heat accumulation. In actual outdoor operation, the cable surface is constantly exposed to sunlight, with external surface temperatures reaching 60-70℃. Furthermore, the outdoor cable terminals are significantly affected by wind speed and direction, severely restricting the actual current-carrying capacity of DC cables. Therefore, accurately assessing the current-carrying capacity of DC cables under dynamic conditions has become crucial for ensuring the safe, economical, and reliable operation of DC transmission systems.

[0003] Existing DC cable current carrying capacity assessment technologies have the following main drawbacks:

[0004] (1) The IEC 60287 standard and conventional DC cable standards only convert solar radiation into a fixed ratio as a correction of external thermal resistance, completely ignoring the relative geometric relationship between solar altitude angle, azimuth angle and cable laying azimuth angle, resulting in a daytime current carrying capacity assessment deviation of more than 20%.

[0005] (2) Traditional methods for calculating convective heat transfer are mostly based on the assumption of transverse flow or cylindrical flow, without distinguishing the heat transfer differences between longitudinal flow or parallel wind and transverse flow. In actual cable laying, the heat transfer coefficient difference caused by different wind speed and direction combinations can reach more than 30%, which directly leads to inaccurate current carrying capacity assessment.

[0006] (3) Existing technology treats solar radiation heat and wind cooling effect as independent linear superposition terms, and fails to reveal the nonlinear competitive relationship between solar heat accumulation and forced convection at low wind speeds. This leads to the physical inversion phenomenon that the evaluation results show "the wind load is lower than the no wind" under common working conditions such as light wind.

[0007] For the reasons mentioned above, there is an urgent need for a DC cable current carrying capacity assessment method and monitoring system that can solve the problem of wind-solar coupling, accurately characterize the difference between sunlight directionality and wind direction, and have dynamic response capabilities. Summary of the Invention

[0008] This application provides a method and apparatus for dynamic evaluation of the current carrying capacity of DC cables, so as to achieve dynamic and accurate evaluation of the current carrying capacity and fill the technical gap in the field of dynamic capacity expansion of DC cables due to wind-solar coupling effect.

[0009] Firstly, this application provides a method for dynamically evaluating the current-carrying capacity of a DC cable, which is executed by a computing device. The computing device can be understood as a computer or similar device, and is not limited thereto in this application. The method includes:

[0010] The system acquires the structural parameters, electrical parameters, dynamic environmental parameters, and cable laying azimuth of the DC cable. The dynamic environmental parameters include ambient temperature, wind speed, wind direction, and solar radiation intensity. Based on the relative relationship between the solar altitude angle, solar azimuth angle, and cable laying azimuth angle, the effective projected area of ​​solar radiation is calculated, and the absorbed heat flux density is calculated based on the effective projected area. A forced convection heat transfer correlation is selected based on the angle between the real-time wind speed and the cable axis from the dynamic environmental parameters, and the forced convection heat transfer coefficient is calculated based on this correlation. Based on the forced convection heat transfer coefficient, a piecewise smooth transition function is used to calculate the actual convection heat transfer coefficient in the low wind speed range. A DC cable heat balance equation is established based on the actual convection heat transfer coefficient and the absorbed heat flux density. The DC cable heat balance equation is solved using the relaxation iteration method to obtain the maximum allowable current carrying capacity. The ratio of the maximum allowable current carrying capacity to the real-time load current is used for dynamic state evaluation, and the dynamic evaluation results and corresponding early warning information are output.

[0011] Through the above methods, this application introduces a solar radiation directional projection model to accurately quantify the geometric relationship between the solar altitude angle, azimuth angle and cable laying azimuth angle, avoiding the traditional method of simply equating solar radiation to a fixed heat flux density, thus reducing the deviation in current carrying capacity assessment. In the low wind speed range, the nonlinear fusion of natural convection and forced convection is adopted to solve the problem of "the current carrying capacity with wind is lower than that without wind" under light wind conditions, making the assessment results more consistent with the actual physical process.

[0012] The aforementioned dynamic assessment method for DC cable current carrying capacity also includes: classifying operating conditions according to solar radiation intensity and wind speed to achieve different processing strategies for different operating conditions; the classification results include at least one of wind-solar balanced type, solar-thermal dominant type, wind-cooled dominant type and natural foundation type; calculating the wind-solar coupling coefficient based on heat flux density, and calculating the wind-cooling enhancement coefficient based on actual convective heat transfer coefficient.

[0013] Through the above methods, this application classifies operating conditions and adopts different solutions for each type, thereby improving the accuracy of the assessment and its practicality in engineering. Simultaneously, it dynamically calculates the wind-solar coupling coefficient to quantify the proportion of solar thermal energy in the total heat output; it also dynamically calculates the wind-cooling enhancement coefficient to quantify the enhancement factor of forced convection relative to natural convection; and it achieves minute-level response and closed-loop control for status early warning and dynamic capacity expansion.

[0014] In the aforementioned dynamic assessment method for the current carrying capacity of DC cables, the effective projected area of ​​solar radiation is calculated based on the relative relationship between the solar altitude angle, solar azimuth angle, and cable laying azimuth angle. The absorbed heat flux density is then calculated based on this effective projected area, including: calculating the minimum angle between the solar azimuth angle and the cable laying azimuth angle.

[0015] ;

[0016] like Then let ;in, The azimuth of the sun. Determine the azimuth angle for cable laying; calculate the effective radiation factor. :

[0017] ;

[0018] Will Constrained to [0,1], where, Given the solar altitude angle; calculate the effective projected area of ​​solar radiation. With the absorbed heat flux density :

[0019] ;

[0020] ;

[0021] in, The outer diameter of the cable. The surface absorption coefficient, This is for the actual measurement of solar radiation intensity.

[0022] By using the above method, this application accurately quantifies the geometric relationship between the solar altitude angle, azimuth angle and cable laying azimuth angle, avoiding the traditional method of simply equating solar radiation to a fixed heat flux density, and reducing the deviation in current carrying capacity assessment.

[0023] In the aforementioned dynamic assessment method for the current carrying capacity of DC cables, the correlation formula for forced convection heat transfer is selected based on the angle between the real-time wind speed and the cable axis in the dynamic environmental parameters, including:

[0024] When the angle between the real-time wind speed and the cable axis At that time, the Linhart formula based on the flat plate boundary layer correction is used as the correlation for forced convection heat transfer:

[0025] ;

[0026] in, For the longitudinal flow Nusselt number, For Reynolds number, The value is the Prandtl number; when the real-time wind speed is at an angle to the cable axis. At that time, the Churchill-Bernstein cylinder flow formula was used as the correlation for forced convection heat transfer:

[0027] ;

[0028] in, For the transverse flow Nusselt number; when In this case, angle-weighted linear interpolation needs to be performed on the longitudinal and transverse Nusselt numbers to calculate the equivalent Nusselt number for the oblique flow:

[0029] ;

[0030] in, Let be the equivalent Nusselt number for oblique flow; under static or extremely low wind speed conditions, let Rayleigh number for natural convection. For Prandtl number, the Churchill-Zhu large-space natural convection correlation is used as the correlation for forced convection heat transfer:

[0031] ;

[0032] in, The Nusselt number is the stationary wind number.

[0033] By using the above method, this application selects different forced convection heat transfer correlations based on the angle between different wind speeds and the cable axis, thereby achieving dynamic and accurate assessment of the current carrying capacity and avoiding differences in heat transfer coefficients and inaccurate assessment of current carrying capacity caused by different combinations of wind speeds and directions.

[0034] In the aforementioned dynamic evaluation method for the current carrying capacity of DC cables, the forced convection heat transfer coefficient is calculated based on the correlation formula of forced convection heat transfer, including: Forced convection heat transfer coefficient:

[0035] ;

[0036] in, For Nusselt numbers; The thermal conductivity of air is calculated in real time based on the qualitative temperature. This refers to the outer diameter of the cable.

[0037] By using the above method, this application calculates the forced convection heat transfer coefficient based on the correlation formula of forced convection heat transfer, ensuring that the calculation result of the forced convection heat transfer coefficient is more accurate, thereby ensuring higher system reliability.

[0038] The aforementioned dynamic evaluation method for the current carrying capacity of DC cables calculates the wind-solar coupling coefficient based on heat flux density and the air-cooling enhancement coefficient based on the actual convective heat transfer coefficient, including:

[0039] The wind-solar coupling coefficient is expressed as:

[0040] ;

[0041] in, Indicates external thermal resistance. Indicates DC resistance. Indicates the internal temperature of the cable;

[0042] The air-cooling enhancement coefficient is expressed as:

[0043] ;

[0044] in, It represents purely natural convection.

[0045] Using the above methods, this application dynamically calculates the wind-solar coupling coefficient to quantify the proportion of solar thermal energy in the total heat; and dynamically calculates the wind-cooling enhancement coefficient to quantify the enhancement factor of forced convection relative to natural convection.

[0046] Secondly, this application provides a method and apparatus for dynamic evaluation of the current carrying capacity of DC cables, including: a parameter acquisition module, a heat flux density calculation module, a correlation selection module, a heat transfer coefficient calculation module, a current carrying capacity calculation module, and a dynamic evaluation module;

[0047] The system includes the following modules: a parameter acquisition module for acquiring DC cable structural parameters, electrical parameters, dynamic environmental parameters, and cable laying azimuth; dynamic environmental parameters including ambient temperature, wind speed, wind direction, and solar radiation intensity; a heat flux density calculation module for calculating the effective projected area of ​​solar radiation based on the relative relationship between the solar altitude angle, solar azimuth angle, and cable laying azimuth angle, and calculating the absorbed heat flux density based on the effective projected area; a correlation selection module for selecting the correlation for forced convection heat transfer based on the angle between the real-time wind speed and the cable axis in the dynamic environmental parameters, and calculating the forced convection heat transfer coefficient based on the correlation; a heat transfer coefficient calculation module for calculating the actual convective heat transfer coefficient in the low wind speed range using a piecewise smooth transition function based on the forced convection heat transfer coefficient; a current carrying capacity calculation module for establishing the DC cable heat balance equation based on the actual convective heat transfer coefficient and absorbed heat flux density, solving the DC cable heat balance equation using a relaxation iteration method to obtain the maximum allowable current carrying capacity; and a dynamic evaluation module for dynamically evaluating the ratio of the maximum allowable current carrying capacity to the real-time load current, outputting the dynamic evaluation results and corresponding warning information.

[0048] Thirdly, this application also provides a computing device, comprising: a memory for storing program instructions; and a processor for calling the program instructions stored in the memory and executing the method described in the first aspect according to the obtained program instructions.

[0049] Fourthly, this application also provides a computer-readable storage medium storing computer-readable instructions, which, when read and executed by a computer, implement the method of the first aspect described above.

[0050] Fifthly, this application provides a computer program product including a computer program executable by a computer device, which, when run on the computer device, causes the computer device to perform the method described in the first aspect.

[0051] Beneficial effects: Through the above methods, this application introduces a solar radiation directional projection model to accurately quantify the geometric relationship between the solar altitude angle, azimuth angle and cable laying azimuth angle, avoiding the traditional method of simply equating solar radiation to a fixed heat flux density, thus reducing the deviation in current carrying capacity assessment; in the low wind speed range, the nonlinear fusion of natural convection and forced convection is adopted to solve the problem of "the current carrying capacity with wind is lower than that without wind" under light wind conditions, making the assessment results more consistent with the actual physical process. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0053] Figure 1 A flowchart illustrating a dynamic evaluation method for the current carrying capacity of a DC cable provided in this application embodiment;

[0054] Figure 2 A schematic diagram of the current carrying capacity variation curve under horizontal wind conditions for a dynamic evaluation method of DC cable current carrying capacity provided in this application embodiment;

[0055] Figure 3 A schematic diagram of the current carrying capacity variation curve under vertical wind conditions for a dynamic evaluation method of DC cable current carrying capacity provided in this application embodiment;

[0056] Figure 4 A schematic diagram of the static air current carrying capacity variation curve with solar radiation intensity for a dynamic evaluation method of DC cable current carrying capacity provided in this application embodiment;

[0057] Figure 5 A schematic diagram of the solar radiation intensity variation curves under 0.5 m / s wind conditions for a dynamic evaluation method of DC cable current carrying capacity provided in this application embodiment;

[0058] Figure 6 This is a schematic diagram of the structure of a DC cable current carrying capacity dynamic evaluation device provided in an embodiment of this application;

[0059] Figure 7 This is a schematic structural diagram of a computing device provided by an embodiment of the present application. Specific embodiments

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0061] In the following embodiments of the present application, "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone, where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the preceding and following associated objects. "At least one (item) below" or similar expressions refer to any combination of these items, including any combination of single (item) or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, a - b, a - c, b - c, or a - b - c, where a, b, and c can be single or multiple. The singular expression forms "a", "one kind", "", "the above", "this", and "this one" are also intended to include expressions such as "one or more" unless there is a clear opposite indication in the context. Also, unless otherwise stated, the ordinal numbers such as "first", "second", etc. mentioned in the embodiments of the present application are used to distinguish multiple objects and are not used to limit the order, timing, priority, or importance of multiple objects.

[0062] Referring to "one embodiment" or "some embodiments" described in the specification of the present application means that specific features, structures, or characteristics described in conjunction with that embodiment are included in one or more embodiments of the present application. Thus, statements such as "in one embodiment", "in some embodiments", "in other some embodiments", "in still other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments" unless otherwise specifically emphasized. The terms "comprising", "including", "having", and their variants all mean "including but not limited to" unless otherwise specifically emphasized.

[0063] Embodiment 1

[0064] Embodiment 1 of the present application provides a method for dynamically evaluating the current-carrying capacity of a DC cable. This method is executed by a computing device, which can be understood as a device such as a computer, and the present application does not limit this here. The process of this method is as follows Figure 1 As shown, it includes:

[0065] Step 101: Obtain the structural parameters, electrical parameters, dynamic environmental parameters, and cable laying azimuth of the DC cable; among which, the dynamic environmental parameters include ambient temperature, wind speed, wind direction, and solar radiation intensity.

[0066] Step 102: Based on the relative relationship between the solar altitude angle, solar azimuth angle and cable laying azimuth angle, calculate the effective projected area of ​​solar radiation, and calculate the absorbed heat flux density based on the effective projected area.

[0067] Specifically, calculate the minimum angle between the solar azimuth and the cable laying azimuth:

[0068] ;

[0069] like Then let ;in, The azimuth of the sun. Specify the azimuth angle for cable laying;

[0070] Calculate the effective exposure factor :

[0071] ;

[0072] Will Constrained to [0,1], where, The solar altitude angle;

[0073] Calculate the effective projected area of ​​solar radiation With the absorbed heat flux density :

[0074] ;

[0075] ;

[0076] in, The outer diameter of the cable. The surface absorption coefficient, This is for the actual measurement of solar radiation intensity.

[0077] Step 103: Select the correlation formula for forced convection heat transfer based on the angle between the real-time wind speed and the cable axis in the dynamic environmental parameters, and calculate the forced convection heat transfer coefficient based on the correlation formula.

[0078] Specifically, through differential wind-heat exchange, when the angle between the real-time wind speed and the cable axis... At that time, the wind direction was horizontal, as follows: Figure 2 The figure shows the flow rate variation curve under horizontal wind conditions; in this case, the Lienhard formula based on the flat plate boundary layer correction is used as the correlation for forced convection heat transfer:

[0079] ;

[0080] in, For the longitudinal flow Nusselt number, For Reynolds number, It is a Prandtl number;

[0081] When the angle between the real-time wind speed and the cable axis At that time, the wind direction was perpendicular, as follows: Figure 3 The figure shows the flow rate variation curve under vertical wind conditions; in this case, the Churchill-Bernstein cylinder flow formula is used as the correlation for forced convection heat transfer:

[0082] ;

[0083] in, For the transverse flow Nusselt number;

[0084] when In this case, angle-weighted linear interpolation needs to be performed on the longitudinal and transverse Nusselt numbers to calculate the equivalent Nusselt number for the oblique flow:

[0085] ;

[0086] in, The equivalent Nusselt number for oblique flow;

[0087] Under static or extremely low wind speed conditions, natural convection becomes the dominant heat dissipation mechanism; as follows: Figure 4 This is a graph showing the change in airflow rate with solar radiation intensity at rest; let... Rayleigh number for natural convection. For Prandtl number, the Churchill-Chu large-space natural convection correlation is used as the correlation for forced convection heat transfer:

[0088] ;

[0089] in, The Nusselt number is the stationary wind number.

[0090] In one possible implementation, the forced convection heat transfer coefficient is:

[0091] ;

[0092] in, For Nusselt numbers; The thermal conductivity of air is calculated in real time based on the qualitative temperature. This refers to the outer diameter of the cable.

[0093] Step 104: Based on the forced convection heat transfer coefficient, the actual convection heat transfer coefficient in the low wind speed range is calculated using a piecewise smooth transition function.

[0094] Specifically, as follows: Figure 5 The figure shows the variation curves of solar radiation intensity under different wind conditions of 0.5 m / s. To completely solve the physical inconsistency of "carrying capacity inversion" that occurs in traditional models in light wind areas, i.e., wind speeds of 0~0.5 m / s, a cubic Hermitian interpolation-type smooth transition function is adopted:

[0095] Define transition interval ,in , .

[0096] Based on the current wind speed Calculate the actual convective heat transfer coefficient :

[0097] when hour, ; This indicates purely natural convection;

[0098] when hour, ; This indicates that forced convection is dominant;

[0099] when When using a smooth transition:

[0100] ;

[0101] ;

[0102] ;

[0103] Set a monotonicity protection mechanism; if the current step calculates... Smaller than the previous step If the percentage drops by more than 0.1%, then a mandatory withdrawal will be implemented. ,make sure It remains strictly monotonous and does not decrease with wind speed.

[0104] In one possible implementation, the method further includes: classifying the operating condition type according to solar radiation intensity and wind speed, so as to adopt different processing strategies for different operating condition types; the classification results include at least one of wind-solar balanced type, solar-thermal dominant type, wind-cooled dominant type and natural basic type.

[0105] As shown in Table 1 below, based on solar radiation intensity and wind speed The operating conditions are dynamically classified into four types:

[0106] Table 1. Illustrated Table of Operating Conditions and Their Strategies

[0107] According to Table 1 above, when the light conditions (solar radiation intensity Q > 600 W / m²) and wind speed v ≥ 0.5 m / s, the operating condition is classified as a wind-solar balance type. In this case, wind cooling partially offsets solar heat, and the wind-solar coupling model constructed in this application ("light geometric projection + wind direction differential convection + low wind speed smooth transition") is directly used for processing. When the light conditions Q > 600 W / m² and wind speed v < 0.5 m / s, the operating condition is classified as a solar heat-dominated type. In this case, solar heat accumulates, and heat dissipation is insufficient, so a low wind speed smooth transition is used for processing. When the light conditions Q ≤ 200 W / m² and wind speed v ≥ 0.5 m / s, the operating condition is classified as a wind-cooling-dominated type. In this case, forced convection is significantly enhanced, and wind direction differential heat exchange is used for processing. When the light conditions Q ≤ 200 W / m² and wind speed v < 0.5 m / s, the operating condition is classified as a wind-cooling-dominated type. In this case, forced convection is significantly enhanced, and wind direction differential heat exchange is used for processing. At m / s, the operating condition is classified as the natural basic type, where natural convection dominates, and the Churchill-Chu formula is used for processing. Through the above method, this application employs different processing methods for different operating conditions, making the evaluation results more consistent with actual physical processes. It should be noted that the specific classification method described above is only an example; other numerical or classification methods that better meet actual engineering requirements can also be used, and this application does not limit this approach.

[0108] The wind-solar coupling coefficient is calculated based on the heat flux density, and the wind-cooling enhancement coefficient is calculated based on the actual convective heat transfer coefficient.

[0109] Specifically, the wind-solar coupling coefficient is used to quantify the proportion of solar thermal energy in the total heat, and is expressed as:

[0110] ;

[0111] in, Indicates external thermal resistance. Indicates DC resistance. Indicates the internal temperature of the cable;

[0112] The air-cooling enhancement factor is used to quantify the enhancement factor of forced convection relative to natural convection, and is expressed as:

[0113] ;

[0114] in, It represents purely natural convection.

[0115] Step 105: Establish the thermal balance equation of the DC cable based on the actual convective heat transfer coefficient and the absorbed heat flux density, and solve the thermal balance equation of the DC cable by the relaxation iteration method to obtain the maximum allowable current carrying capacity.

[0116] Specifically, maximum allowable flow rate The following heat balance equation is solved iteratively:

[0117] ;

[0118] in, , representing external thermal resistance; , representing the radiative heat transfer coefficient;

[0119] Iterative solution using relaxation factors Update surface temperature:

[0120] ;

[0121] The convergence criterion is as follows:

[0122] ;

[0123] In a preferred embodiment, the maximum number of iterations is set to 50. It should be noted that this application does not limit the maximum number of iterations; other numbers can also be used.

[0124] Step 106: Perform dynamic status assessment on the ratio of maximum allowable current carrying capacity to real-time load current, and output the dynamic assessment results and corresponding early warning information.

[0125] Based on the capacity utilization rate The dynamic evaluation of wind-solar coupling capacity is shown in Table 2 below.

[0126] Table 2 Wind-Solar Coupling Load Assessment Table

[0127] According to Table 2 above, when η≤0.70, the wind-solar coupling current carrying capacity is considered to be in a safe state, and normal recording is performed without any warning action; when 0.70<η≤0.85, the wind-solar coupling current carrying capacity is considered to be in a normal state, and a warning action of appropriate capacity increase is issued; when 0.85<η≤0.95, the wind-solar coupling current carrying capacity is considered to be in a state of alert, and a yellow warning is issued, suggesting attention to weather changes; when 0.95<η≤1.00, the wind-solar coupling current carrying capacity is considered to be in a state of warning, and an orange warning is issued, suggesting load reduction or activation of auxiliary cooling; when η>1.00, the wind-solar coupling current carrying capacity is considered to be in a state of alarm, and a red alarm is issued, executing protective load reduction. It should be noted that the above alarm methods are only examples, and this application does not limit the specific alarm methods.

[0128] Example 2

[0129] This application provides a specific implementation method for a dynamic evaluation method of DC cable current carrying capacity based on embodiment 1. In this embodiment, the method is described in detail using a ±500kV DC cable line of a city distribution network as an example.

[0130] Step 1: Select the basic parameters of the cable.

[0131] The cable uses a 2500mm² copper conductor, cross-linked polyethylene (XLPE) insulation, and has an outer diameter of 160mm. It is laid outdoors overhead at an azimuth angle of 30° east of north. The cable surface absorption coefficient is 0.9, and the emissivity is 0.9. The conductor's allowable operating temperature is 70℃, and the ambient temperature is set at 40℃.

[0132] Step 2: Deploy the monitoring system.

[0133] The wind-solar coupling current-carrying capacity online monitoring system of this invention is deployed at key locations along the cable line, comprising: a sensing layer: a small weather station (containing wind speed and direction sensors, a solar radiation meter, and temperature and humidity sensors) installed on the cable terminal tower; a surface temperature sensor attached to the cable joint; and a current transformer and distributed fiber optic temperature measurement equipment installed at the cable terminal. A transmission layer: data collected is uploaded to the regional monitoring center via 4G wireless communication and Modbus TCP protocol. A core computing layer: an edge computing gateway is deployed to implement the wind-solar coupling algorithm of this invention, dynamically calculating the maximum allowable current-carrying capacity at 1-minute intervals. An application and user layer: the dispatch center's large screen displays the dynamic curve of the current-carrying capacity, the wind-solar coupling coefficient, the current operating condition type, and the warning status in real time.

[0134] Step 3: Perform dynamic evaluation on typical days.

[0135] A typical sunny summer day was selected as the evaluation day, with the peak solar radiation intensity reaching 950 W / m², wind speed varying between 0 and 4 m / s, and wind direction mainly consisting of southerly winds (longitudinal flow) and westerly winds (lateral flow) from 00:00 to 24:00.

[0136] With solar radiation intensity of 950 W / m² and wind speed of 0.2 m / s (considered a light breeze), the system identifies it as "photothermal-dominated" and initiates a low-wind-speed smooth transition. The natural convection heat transfer coefficient is 6.2 W / (m²·K), the forced convection heat transfer coefficient is 8.5 W / (m²·K), and the actual convection heat transfer coefficient after three Hermitian interpolations is 7.8 W / (m²·K). The maximum allowable flow rate drops to 980A, the flow rate utilization rate is 0.91, the status is "Caution," and the system issues a yellow warning, recommending monitoring weather changes and appropriately reducing the load.

[0137] Step 4: Perform comparative verification.

[0138] A comparison was made between this method and the IEC 60287 standard method used in parallel operation on the same cable line. The results show:

[0139] Under conditions of strong daytime radiation and light wind, the IEC method assessed the current carrying capacity as 1120A, while this method assessed it as 980A, a difference of 12.5%. Subsequent actual operation showed that operating under load according to the IEC method would cause the cable surface temperature to exceed the limit, verifying that this method is safer.

[0140] Under wind speed of 0.2 m / s, the IEC method shows a lower flow rate than the no-wind condition (inverted). This method eliminates this phenomenon through a smooth transition model, and the evaluation results are in good agreement with the measured heat balance data.

[0141] Step 5: Implement dynamic capacity expansion.

[0142] Under clear, windy conditions in winter, the system automatically identifies itself as "wind-cooled dominant," increasing the dynamic current carrying capacity by approximately 18% compared to the rated value. The system generates capacity expansion suggestions through the dynamic capacity expansion module, allowing the dispatch center to increase transmission power while ensuring safety. This achieves short-term dynamic capacity expansion of the cable line and improves the economic efficiency of power transmission.

[0143] Example 3

[0144] Based on Embodiments 1 and 2, Embodiment 3 of this application provides a method and apparatus for dynamic evaluation of the current carrying capacity of DC cables. The apparatus is as follows: Figure 6 As shown, the apparatus for performing the methods provided in Embodiments 1 and 2 of this application includes: a parameter acquisition module, a heat flux density calculation module, a correlation selection module, a heat transfer coefficient calculation module, a flow rate calculation module, and a dynamic evaluation module.

[0145] The parameter acquisition module is used to acquire DC cable structural parameters, electrical parameters, dynamic environmental parameters, and cable laying azimuth angle; among which, dynamic environmental parameters include ambient temperature, wind speed, wind direction, and solar radiation intensity.

[0146] The heat flux density calculation module is used to calculate the effective projected area of ​​solar radiation based on the relative relationship between the solar altitude angle, solar azimuth angle and cable laying azimuth angle, and to calculate the absorbed heat flux density based on the effective projected area.

[0147] The correlation selection module is used to select the correlation for forced convection heat transfer based on the angle between the real-time wind speed and the cable axis in the dynamic environmental parameters, and to calculate the forced convection heat transfer coefficient based on the correlation for forced convection heat transfer.

[0148] The heat transfer coefficient calculation module is used to calculate the actual convective heat transfer coefficient in the low wind speed range based on the forced convection heat transfer coefficient using a piecewise smooth transition function.

[0149] The current carrying capacity calculation module is used to establish the thermal balance equation of the DC cable based on the actual convective heat transfer coefficient and the absorbed heat flux density. The maximum allowable current carrying capacity is obtained by solving the thermal balance equation of the DC cable through the relaxation iteration method.

[0150] The dynamic evaluation module is used to dynamically evaluate the ratio of the maximum allowable current carrying capacity to the real-time load current, and output the dynamic evaluation results and corresponding warning information.

[0151] Example 4

[0152] Having introduced the DC cable current carrying capacity dynamic evaluation device in an exemplary embodiment of this application, we will now introduce a computing device in another exemplary embodiment of this application.

[0153] Those skilled in the art will understand that various aspects of this application can be implemented as a system, method, or program product. Therefore, various aspects of this application can be specifically implemented in the following forms: a completely hardware implementation, a completely software implementation (including firmware, microcode, etc.), or a combination of hardware and software implementations, collectively referred to herein as a "circuit," "module," or "system."

[0154] In some possible implementations, the computing device according to this application may include at least one processor and at least one memory. The memory stores a computer program that, when executed by the processor, causes the processor to perform the steps of the cross-device assisted interaction method for off-site clearing according to various exemplary embodiments of this application described above.

[0155] The following reference Figure 7To describe a computing device 130 according to this embodiment of the present application. Figure 7 The computing device 130 shown is merely an example and should not be construed as limiting the functionality and scope of the embodiments of this application. Figure 7 As shown, the computing device 130 is presented in the form of a general-purpose smart terminal (or Bluetooth headset). The components of the computing device 130 may include, but are not limited to: at least one processor 131, at least one memory 132, and a bus 133 connecting different system components (including memory 132 and processor 131).

[0156] Bus 133 represents one or more of several bus architectures, including a memory bus or memory controller, peripheral bus, processor, or local bus using any of the various bus architectures. Memory 132 may include readable media in the form of volatile memory, such as random access memory (RAM) 1321 and / or cache memory 1322, and may further include read-only memory (ROM) 1323. Memory 132 may also include a program / utility 1325 having a set (at least one) of program modules 1324, including but not limited to: an operating system, one or more application programs, other program modules, and program data, each or some combination of these examples may include an implementation of a network environment.

[0157] The computing device 130 can also communicate with one or more external devices 134 (e.g., keyboard, pointing device, etc.), and / or with any device that enables the computing device 130 to communicate with one or more other smart terminals (e.g., router, modem, etc.). This communication can be performed via input / output (I / O) interface 135. Furthermore, the computing device 130 can also communicate with one or more networks (e.g., local area network (LAN), wide area network (WAN), and / or public networks, such as the Internet) via network adapter 136. As shown, network adapter 136 communicates with other modules used in the computing device 130 via bus 133. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with the computing device 130, including but not limited to: microcode, device drivers, redundant processors, external disk drive arrays, RAID systems, tape drives, and data backup storage systems.

[0158] In some possible implementations, various aspects of the dynamic evaluation method for DC cable current carrying capacity provided in this application can also be implemented in the form of a program product, which includes a computer program. When the program product is run on a computer device, the computer program is used to cause the computer device to perform the steps in the dynamic evaluation method for DC cable current carrying capacity according to the various exemplary embodiments of this application described above.

[0159] The program product may employ any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example—but not limited to—an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of readable storage media (a non-exhaustive list) include: an electrical connection having one or more wires, a portable disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof.

[0160] The program product for dynamic assessment of DC cable current carrying capacity according to the embodiments of this application can be a portable compact disc read-only memory (CD-ROM) and include a computer program, and can run on a smart terminal. However, the program product of this application is not limited to this. In this document, the readable storage medium can be any tangible medium that contains or stores a program that can be used by or in conjunction with an instruction execution system, apparatus, or device.

[0161] A readable signal medium may include a data signal propagated in baseband or as part of a carrier wave, carrying a readable computer program. Such propagated data signals may take various forms, including—but not limited to—electromagnetic signals, optical signals, or any suitable combination thereof. A readable signal medium may also be any readable medium other than a readable storage medium, capable of sending, propagating, or transmitting a program for use by or in conjunction with an instruction execution system, apparatus, or device.

[0162] It should be noted that although several units or sub-units of the device have been mentioned in the detailed description above, this division is merely exemplary and not mandatory. In fact, according to embodiments of this application, the features and functions of two or more units described above can be embodied in one unit. Conversely, the features and functions of one unit described above can be further divided and embodied by multiple units.

[0163] Furthermore, although the operations of the method of this application are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0164] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. 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 access frequency prediction device to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable access frequency prediction device, 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.

[0165] These computer program instructions may also be stored in a computer-readable storage medium capable of directing a computer or other programmable access predictive device to operate 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.

[0166] These computer program instructions can also be loaded onto a computer or other programmable access predictive device to cause a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable device 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.

[0167] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0168] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for dynamically evaluating the current carrying capacity of a DC cable, characterized in that, include: Obtain the structural parameters, electrical parameters, dynamic environmental parameters, and cable laying azimuth of the DC cable; wherein, the dynamic environmental parameters include ambient temperature, wind speed, wind direction, and solar radiation intensity; Based on the relative relationship between the solar altitude angle, solar azimuth angle and the cable laying azimuth angle, the effective projected area of ​​solar radiation is calculated, and the absorbed heat flux density is calculated based on the effective projected area. The forced convection heat transfer correlation is selected based on the angle between the real-time wind speed and the cable axis in the dynamic environmental parameters, and the forced convection heat transfer coefficient is calculated based on the forced convection heat transfer correlation. Based on the forced convection heat transfer coefficient, the actual convection heat transfer coefficient in the low wind speed range is calculated using a piecewise smooth transition function. A DC cable thermal balance equation is established based on the actual convective heat transfer coefficient and the absorbed heat flux density. The DC cable thermal balance equation is solved by the relaxation iteration method to obtain the maximum allowable current carrying capacity. The ratio of the maximum allowable current carrying capacity to the real-time load current is used for dynamic status evaluation, and the dynamic evaluation results and corresponding early warning information are output.

2. The method according to claim 1, characterized in that, The method further includes: The operating conditions are classified according to the solar radiation intensity and the wind speed, so as to adopt different processing strategies for different operating conditions; the classification results include at least one of the following: wind-solar balanced type, solar-thermal dominant type, wind-cooled dominant type, and natural basic type. The wind-solar coupling coefficient is calculated based on the heat flux density, and the wind-cooling enhancement coefficient is calculated based on the actual convective heat transfer coefficient.

3. The method according to claim 1, characterized in that, The calculation of the effective projected area of ​​solar radiation based on the relative relationship between the solar altitude angle, solar azimuth angle, and the cable laying azimuth angle, and the calculation of the absorbed heat flux density based on the effective projected area, includes: Calculate the minimum angle between the solar azimuth and the cable laying azimuth: ； like Then let ;in, The azimuth of the sun. Specify the azimuth angle for cable laying; Calculate the effective exposure factor : ； The Constrained to [0,1], where, The solar altitude angle; Calculate the effective projected area of ​​solar radiation With the absorbed heat flux density : ； ； in, The outer diameter of the cable. The surface absorption coefficient, This is for the actual measurement of solar radiation intensity.

4. The method according to claim 1, characterized in that, The correlation formula for selecting forced convection heat transfer based on the angle between the real-time wind speed and the cable axis in the dynamic environmental parameters includes: When the angle between the real-time wind speed and the cable axis At that time, the Linhart formula based on the flat plate boundary layer correction is used as the correlation for forced convection heat transfer: ； in, For the longitudinal flow Nusselt number, For Reynolds number, It is a Prandtl number; When the angle between the real-time wind speed and the cable axis At that time, the Churchill-Bernstein cylinder flow formula was used as the correlation for forced convection heat transfer: ； in, For the transverse flow Nusselt number; when In this case, angle-weighted linear interpolation needs to be performed on the longitudinal and transverse Nusselt numbers to calculate the equivalent Nusselt number for the oblique flow: ； in, The equivalent Nusselt number for oblique flow; Under static or extremely low wind speed conditions, let For natural convection Rayleigh number, For Prandtl number, the Churchill-Zhu large-space natural convection correlation is used as the correlation for forced convection heat transfer: ； in, The Nusselt number is the stationary wind number.

5. The method according to claim 1, characterized in that, The calculation of the forced convection heat transfer coefficient based on the correlation of the forced convection heat transfer includes: Forced convection heat transfer coefficient: ； in, For Nusselt numbers; The thermal conductivity of air is calculated in real time based on the qualitative temperature. This refers to the outer diameter of the cable.

6. The method according to claim 2, characterized in that, The calculation of the wind-solar coupling coefficient based on the heat flux density and the calculation of the air-cooling enhancement coefficient based on the actual convective heat transfer coefficient include: The wind-solar coupling coefficient is expressed as: ； in, Indicates external thermal resistance. Indicates DC resistance. Indicates the internal temperature of the cable; The air-cooling enhancement coefficient is expressed as: ； in, It represents purely natural convection.

7. A method and apparatus for dynamic evaluation of the current carrying capacity of DC cables, characterized in that, include: The parameter acquisition module is used to acquire DC cable structural parameters, electrical parameters, dynamic environmental parameters, and cable laying azimuth angle; wherein, the dynamic environmental parameters include ambient temperature, wind speed, wind direction, and solar radiation intensity; The heat flux density calculation module is used to calculate the effective projected area of ​​solar radiation based on the relative relationship between the solar altitude angle, the solar azimuth angle and the cable laying azimuth angle, and to calculate the absorbed heat flux density based on the effective projected area. The correlation selection module is used to select the correlation of forced convection heat transfer based on the angle between the real-time wind speed and the cable axis in the dynamic environmental parameters, and to calculate the forced convection heat transfer coefficient based on the correlation of forced convection heat transfer. The heat transfer coefficient calculation module is used to calculate the actual convective heat transfer coefficient in the low wind speed range based on the forced convection heat transfer coefficient using a piecewise smooth transition function. The current carrying capacity calculation module is used to establish the DC cable thermal balance equation based on the actual convective heat transfer coefficient and the absorbed heat flux density, and solve the DC cable thermal balance equation by the relaxation iteration method to obtain the maximum allowable current carrying capacity. The dynamic evaluation module is used to dynamically evaluate the ratio of the maximum allowable current carrying capacity to the real-time load current, and output the dynamic evaluation results and corresponding early warning information.

8. A computing device, characterized in that, Its features include: Memory, used to store program instructions; A processor is configured to invoke program instructions stored in the memory and execute the method as described in any one of claims 1-6 according to the obtained program instructions.

9. A computer-readable storage medium, characterized in that, Includes computer-readable instructions that, when read and executed by a computer, cause the method as described in any one of claims 1 to 6 to be implemented.

10. A computer program product, characterized in that, It includes a computer program executable by a computer device, which, when run on the computer device, causes the computer device to perform the steps of the method according to any one of claims 1 to 6.

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