Method and apparatus for selecting return wires of single-ended grounded cables

Abstract

This application discloses a method and apparatus for selecting the return line of a single-ended grounding cable. The method includes: acquiring the laying environment of the single-ended grounding cable in the single-ended grounding system and determining at least one target material type matching the laying environment; determining the target cross-sectional area of ​​the return line corresponding to each target material type whose short-circuit current can meet thermal stability conditions when a short-circuit fault occurs in the single-ended grounding system; determining multiple models of return lines matching the target material type and target cross-sectional area as candidate return lines; acquiring the performance parameters and cost parameters of each candidate return line, and comprehensively scoring each candidate return line based on the performance and cost parameters; and determining the candidate return line with the highest comprehensive score as the target return line corresponding to the single-ended grounding cable. This application solves the technical problem that unreasonable selection of return lines for single-ended grounding cables in engineering projects can easily lead to cost waste or safety accidents.

Description

Technical Field

[0001] This application relates to the field of power system technology, and more specifically, to a method and apparatus for selecting the return line of a single-ended grounded cable. Background Technology

[0002] When a ground fault occurs in a cable line with a single-end grounded sheath, an extremely high overvoltage will be induced in the metal sheath. To ensure the safety of the power system, the national standard "Code for Design of Cables for Power Engineering" (GB50217) stipulates that when a single-core cable of 110kV and above in an AC system has a single end of its metal sheath directly grounded, a conductor properly grounded at both ends must be laid along the cable line, which is called a return conductor.

[0003] However, the relevant standards have relatively lenient requirements for the selection of return cables, emphasizing only the need to meet functional requirements without taking into account the economic aspects of the return cables. This lenient standard leads to the fact that in actual engineering projects, the selection of return cables often relies on experience with previous cable lines of the same voltage level. The various parameters of the return cables selected in actual projects have excessive margins, which not only increases costs but also lacks specificity and site-specific considerations.

[0004] There is currently no effective solution to the above problems. Summary of the Invention

[0005] This application provides a method and apparatus for selecting the return line of a single-ended grounding cable, which at least solves the technical problem that unreasonable selection of the return line of a single-ended grounding cable in engineering projects can easily lead to cost waste or safety accidents.

[0006] According to one aspect of the embodiments of this application, a method for selecting the return line of a single-ended grounding cable is provided, comprising: obtaining the laying environment of the single-ended grounding cable in the single-ended grounding system, and determining at least one target material type that matches the laying environment; determining the target cross-sectional area corresponding to the return line of each target material type whose short-circuit current can meet the thermal stability conditions when a short-circuit fault occurs in the single-ended grounding system; determining multiple models of return lines that match the target material type and the target cross-sectional area as candidate return lines; obtaining the performance parameters and cost parameters of each candidate return line, and comprehensively scoring each candidate return line based on the performance parameters and cost parameters; and determining the candidate return line with the highest comprehensive score as the target return line corresponding to the single-ended grounding cable.

[0007] Optionally, the target material type of the reflow line includes at least one of the following: an aluminum alloy reflow line with strong corrosion resistance but poor vibration resistance, a copper reflow line with strong electrical conductivity and strong oxidation resistance, a high-temperature resistant special reflow line, a vibration-resistant special reflow line, and a polymer composite material reflow line with strong corrosion resistance, strong vibration resistance, strong electrical conductivity, strong oxidation resistance and high temperature resistance.

[0008] Optionally, determine the target cross-sectional area of ​​the return line for each target material type where the short-circuit current flowing through it can satisfy the thermal stability conditions when a short-circuit fault occurs in a single-ended grounded system. This includes: for each target material type of return line, determining the short-circuit current flowing through it and the short-circuit duration when a short-circuit fault occurs in a single-ended grounded system, and calculating the short-circuit current thermal effect of the return line using the following formula: In the formula, Q ki I represents the thermal effect of short-circuit current. ki Represents the short-circuit current, t k Indicates the short-circuit duration; obtain the first current carrying capacity of the return line of the target material type at the maximum allowable operating temperature and the second current carrying capacity at the rated operating temperature, and calculate the first thermal stability coefficient corresponding to the target material type using the following formula: In the formula, C i A represents the first thermal stability coefficient. Ki Indicates the first carrying capacity, A Li This represents the second flow rate; the minimum value of the target cross-sectional area corresponding to the return line of the target material type is calculated using the following formula: In the formula, S imin This represents the minimum value of the target cross-sectional area.

[0009] Optionally, determining the short-circuit current flowing through the return line when a short-circuit fault occurs in a single-ended grounding system includes: when there is only one return line to be laid, determining that the short-circuit current flowing through the single-ended grounding cable is the short-circuit current flowing through the return line when a short-circuit fault occurs in the single-ended grounding system; when there are multiple return lines to be laid, determining that the short-circuit current flowing through the single-ended grounding cable, the resistance per unit length of each return line, the frequency of the single-ended grounding system, and the earth conductivity are obtained, and calculating the short-circuit current flowing through each return line using the following formula: In the formula, I ki I represents the short-circuit current flowing through the i-th return line. k k represents the short-circuit current flowing through a single-ended grounded cable. i Z1, Z2, ..., Zn represent the proportion of the short-circuit current flowing through the i-th return line in the short-circuit current flowing through the single-ended grounded cable, where n represents the number of return lines to be laid. n These represent the impedance per unit length of the 1st, 2nd, ..., nth return lines, respectively, Z1 / / Z2 / / ... / / Z n Z represents the total impedance per unit length after n return lines are connected in parallel. i Let Z represent the impedance per unit length of the i-th return line, and Z i =R i +X i , R i X represents the resistance per unit length of the i-th return line. i D represents the reactance per unit length of the i-th return line. e ρ represents the equivalent resistance of the earth, f represents the frequency of the single-ended grounding system, and ρ represents the conductivity of the earth.

[0010] Optionally, the third current carrying capacity of the single-ended grounding cable at the maximum allowable operating temperature and the fourth current carrying capacity at the rated operating temperature are obtained, and the second thermal stability coefficient corresponding to the single-ended grounding cable is calculated using the following formula: In the formula, C s A represents the second thermal stability coefficient. Ks Indicates the third carrying capacity, A Ls This indicates the fourth current-carrying capacity; obtain the outer and inner radii of the sheath of the single-ended grounded cable, and calculate the maximum value of the target cross-sectional area using the following formula: In the formula, S imax r represents the maximum value of the target cross-sectional area. so The outer radius r of the sheath of a single-ended grounded cable. si This indicates the inner radius of the sheath of a single-ended grounded cable.

[0011] Optionally, the performance parameters may include at least one of the following: rated operating current of the alternative return line, and unit conductivity; the cost parameters may include at least one of the following: unit length price of the alternative return line, rated service life, annual depreciation rate, and annual maintenance cost.

[0012] Optionally, each candidate return line is comprehensively scored based on performance and cost parameters, including: obtaining the load level of the single-ended grounding system and determining the performance weight based on the load level; randomly selecting one candidate return line from multiple candidate return lines as a reference return line, and determining the comprehensive score of the reference return line as 1; for any candidate return line other than the reference return line from multiple candidate return lines, the comprehensive score of the candidate return line is calculated using the following formula: Among them, F i Let A represent the overall score of the i-th candidate return line, λ represent the performance weight, and A' ...",""'"'"'"]"]""]""]"]"]"] ref A represents the unit length price of the reference return line. i Let k represent the unit length price of the i-th alternative return line. ref Indicates the rated service life of the reference return line, k i M represents the rated service life of the i-th alternative return line. ref M represents the annual maintenance cost of the reference return line. i I represents the annual maintenance cost of the i-th alternative return line. i I represents the rated operating current of the i-th alternative return line.ref ρ represents the rated operating current of the reference return line. i ρ represents the unit conductivity of the i-th candidate return line. ref ε represents the unit conductivity of the reference return line. i ε represents the annual loss rate of the i-th alternative return line. ref This indicates the annual depreciation rate of the reference return line.

[0013] According to another aspect of the embodiments of this application, a return line selection device for a single-ended grounding cable is also provided, comprising: a material selection module, used to acquire the laying environment of the single-ended grounding cable in the single-ended grounding system and determine at least one target material type matching the laying environment; a cross-section selection module, used to determine the target cross-section range corresponding to each target material type of return line when a short-circuit fault occurs in the single-ended grounding system, wherein the short-circuit current flowing through it can meet the thermal stability conditions; a candidate line selection module, used to determine multiple models of return lines matching the target material type and the target cross-section range as candidate return lines; a comprehensive scoring module, used to acquire the performance parameters and cost parameters of each candidate return line, and to comprehensively score each candidate return line based on the performance parameters and cost parameters; and a return line selection module, used to determine the candidate return line with the highest comprehensive score as the target return line corresponding to the single-ended grounding cable.

[0014] According to another aspect of the embodiments of this application, a computer program product is also provided, the computer program product comprising: a computer program, wherein the computer program, when executed by a processor, implements the above-described method for selecting the return line of a single-ended grounding cable.

[0015] According to another aspect of the embodiments of this application, an electronic device is also provided, the electronic device including: a memory and a processor, wherein the memory stores a computer program, and the processor is configured to execute the above-described method for selecting the return line of a single-ended grounded cable through the computer program.

[0016] In this embodiment, the laying environment of the single-ended grounding cable in the single-ended grounding system is obtained, and at least one target material type matching the laying environment is determined; the target cross-sectional area of ​​the return line corresponding to each target material type is determined so that the short-circuit current flowing through it can meet the thermal stability conditions when a short-circuit fault occurs in the single-ended grounding system; multiple models of return lines matching the target material type and target cross-sectional area are determined as candidate return lines; the performance parameters and cost parameters of each candidate return line are obtained, and each candidate return line is comprehensively scored based on the performance parameters and cost parameters; the candidate return line with the highest comprehensive score is determined as the target return line corresponding to the single-ended grounding cable. In this way, one or more return line material types are determined based on the laying environment. The cross-sectional range of the return line is further determined based on thermal stability conditions to select suitable candidate return lines. Finally, the performance and cost of the candidate return lines are comprehensively analyzed to determine the final target return line. Through scientific calculation and analysis, the problem of excessive parameter margin during selection is avoided, ensuring that the selection of return lines can meet functional requirements and have good economic efficiency. This solves the technical problem that unreasonable selection of return lines for single-end grounded cables in engineering projects can easily lead to cost waste or safety accidents. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0018] Figure 1 This is a flowchart illustrating an optional method for selecting the return line of a single-ended grounding cable according to an embodiment of this application.

[0019] Figure 2 This is a schematic diagram of the structure of an optional single-ended grounding cable return line selection device according to an embodiment of this application;

[0020] Figure 3 This is a schematic diagram of the structure of an optional electronic device according to an embodiment of this application. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0022] It should be noted that the terms "first," "second," etc., used in the specification, claims, and drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0023] Example 1

[0024] According to an embodiment of this application, a method for selecting the return line of a single-ended grounded cable is provided. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0025] Figure 1 This is a flowchart illustrating a method for selecting the return line of a single-ended grounding cable according to an embodiment of this application. Figure 1 As shown, the method includes the following steps:

[0026] Step S102: Obtain the laying environment of the single-ended grounding cable in the single-ended grounding system, and determine at least one target material type that matches the laying environment;

[0027] Step S104: Determine the target cross-sectional area of ​​the return line for each target material type that can meet the thermal stability conditions when a short-circuit fault occurs in a single-ended grounding system.

[0028] Step S106: Determine multiple models of reflux lines that match the target material type and target cross-sectional range as candidate reflux lines;

[0029] Step S108: Obtain the performance parameters and cost parameters of each candidate return line, and give a comprehensive score to each candidate return line based on the performance parameters and cost parameters;

[0030] Step S110: Determine the candidate return line with the highest comprehensive score as the target return line corresponding to the single-ended grounded cable.

[0031] The following section explains the steps involved in selecting the return line for a single-ended grounding cable, using a specific implementation process as an example.

[0032] To address the technical problem of inappropriate selection of return conductors for single-ended grounding cables in engineering projects, which can easily lead to cost waste or safety accidents, this application proposes a method for selecting return conductors for single-ended grounding cables. The implementation process of this method is as follows:

[0033] When selecting materials for single-ended grounding cables and their return conductors, the laying environment should be considered first. Different environmental conditions (such as temperature, humidity, and chemical corrosivity) will affect the physical and chemical properties of the return conductor, thereby affecting its safety and reliability. For example, in a highly corrosive environment, if a material with poor corrosion resistance is selected, the return conductor may be damaged prematurely, causing safety hazards. Suitable materials can better resist the effects of environmental factors, thereby extending the service life of the grounding cable and reducing replacement frequency and maintenance costs. Taking all factors into consideration, this application embodiment first obtains the laying environment of the single-ended grounding cable in the single-ended grounding system when selecting the return conductor and determines at least one target material type that matches the laying environment.

[0034] The target material type of the reflow line can include at least one of the following: aluminum alloy reflow line with strong corrosion resistance but poor vibration resistance, copper reflow line with strong conductivity and strong oxidation resistance, high temperature resistant special reflow line, vibration resistant special reflow line, and polymer composite material reflow line with strong corrosion resistance, strong vibration resistance, strong conductivity, strong oxidation resistance and high temperature resistance. These types of reflow lines can be selected according to the environment.

[0035] For example, in corrosive environments, such as coastal areas or industrial zones, aluminum alloy return lines with strong corrosion resistance but poor vibration resistance should be selected; in environments requiring high conductivity and oxidation resistance, such as high-voltage power transmission systems, copper return lines with strong conductivity and oxidation resistance should be selected; in high-temperature environments, such as near heat sources, high-temperature resistant special return lines should be selected; in environments with frequent vibrations, such as near rail transit or industrial equipment, vibration-resistant special return lines should be selected; in complex and variable environments, such as places where corrosion, vibration, high temperature, and high conductivity are required simultaneously, polymer composite return lines with strong corrosion resistance, strong vibration resistance, strong conductivity, strong oxidation resistance, and high temperature resistance should be selected.

[0036] In a single-ended grounding system, once a short-circuit fault occurs, a very large short-circuit current will flow through the return line. If the cross-section of the return line is too small, it will not be able to withstand such a large current, which will cause the return line to overheat or even melt, thus causing a safety accident. Therefore, it is very important to select a return line cross-section range that meets the thermal stability requirements.

[0037] As an alternative implementation, the target cross-sectional area corresponding to the return line of each target material type for which the short-circuit current flowing through can satisfy the thermal stability conditions can be determined in the following manner:

[0038] For each type of target material return line, determine the short-circuit current flowing through the return line and the short-circuit duration when a short-circuit fault occurs in a single-ended grounded system.

[0039] The duration of the short circuit flowing through the return line can be determined in the following ways: simulate a short circuit fault under laboratory conditions and record the total time from the occurrence of the short circuit to the clearing of the fault; or conduct a test in an actual operating single-ended grounded system and record the duration of the short circuit; or use power system simulation software to obtain the duration of the short circuit current flowing through the return line.

[0040] To determine the short-circuit current flowing through the return line, the following steps can be used:

[0041] When there is only one return line to be laid, the short-circuit current flowing through the single-ended grounded cable is taken as the short-circuit current flowing through the return line.

[0042] When there are multiple return lines to be laid, first obtain the short-circuit current flowing through the single-ended grounded cable, the resistance per unit length of each return line, the frequency of the single-ended grounding system, and the earth conductivity.

[0043] Considering that the equivalent resistance of the earth is one of the key parameters for evaluating the performance of a grounding system, and its magnitude directly affects the safety and reliability of the system, when a short-circuit fault occurs, the short-circuit current returns to the power source through the earth. The equivalent resistance of the earth affects the distribution of the short-circuit current in the earth, and thus affects the current distribution in the return line. To accurately evaluate and design the grounding and return paths in a single-ended grounding system, the equivalent resistance of the earth can be calculated in the following way:

[0044]

[0045] In the formula, D e ρ represents the equivalent resistance of the earth, f represents the frequency of the single-ended grounding system, and ρ represents the conductivity of the earth.

[0046] Next, calculate the reactance per unit length of each return line:

[0047]

[0048] In the formula, X i R represents the reactance per unit length of the i-th return line. i Let represent the resistance per unit length of the i-th return line. The impedance per unit length of each return line is obtained using the following formula:

[0049] Z i =R i +X i

[0050] In the formula, Z iLet represent the impedance per unit length of the i-th return line, and calculate the short-circuit current flowing through each return line using the following formula:

[0051]

[0052] In the formula, I ki I represents the short-circuit current flowing through the i-th return line. k k represents the short-circuit current flowing through a single-ended grounded cable. i Z1, Z2, ..., Zn represent the proportion of the short-circuit current flowing through the i-th return line in the short-circuit current flowing through the single-ended grounded cable, where n represents the number of return lines to be laid. n These represent the impedance per unit length of the 1st, 2nd, ..., nth return lines, respectively, Z1 / / Z2 / / ... / / Z n This represents the total impedance per unit length after n return lines are connected in parallel.

[0053] After obtaining the short-circuit current of each return line, the short-circuit current thermal effect of the return line is calculated using the following formula:

[0054]

[0055] In the formula, Q ki I represents the short-circuit current thermal effect of the i-th return line. ki Let t represent the short-circuit current of the i-th return line. k Indicates the duration of the short circuit.

[0056] After obtaining the short-circuit current thermal effect of each return line, the first current carrying capacity of the return line of the target material type at the maximum allowable operating temperature and the second current carrying capacity at the rated operating temperature are used to calculate the first thermal stability coefficient corresponding to the target material type using the following formula:

[0057]

[0058] In the formula, C i A represents the first thermal stability coefficient. Ki Indicates the first carrying capacity, A Li This represents the second flow rate; finally, the minimum value of the target cross-sectional area corresponding to the return line of the target material type is calculated according to the following formula:

[0059]

[0060] In the formula, S imin This represents the minimum value of the target cross-sectional area of ​​the i-th reflux line. The minimum value of the target cross-sectional area of ​​reflux lines of the same material type is the same.

[0061] As an optional implementation, to ensure that the cross-section of the return line does not exceed the thermal stability capability of the single-ended grounding cable and to avoid damage due to overheating during short-circuit faults, the maximum value of the target cross-section range of the return line can be further determined. This process can be carried out according to the following steps:

[0062] First, obtain the third current carrying capacity of the single-ended grounding cable at the maximum allowable operating temperature and the fourth current carrying capacity at the rated operating temperature, and then calculate the second thermal stability coefficient of the single-ended grounding cable using the following formula:

[0063]

[0064] In the formula, C s A represents the second thermal stability coefficient. Ks The third current-carrying capacity refers to the maximum continuous current carrying capacity of a single-ended grounded cable under the highest permissible operating temperature, expressed in A. Ls The fourth current carrying capacity refers to the maximum continuous current carrying capacity of a single-ended grounded cable at its rated operating temperature.

[0065] Based on the outer and inner radii of the sheath of the single-ended grounding cable, the maximum value of the target cross-sectional area is calculated using the following formula:

[0066]

[0067] In the formula, S imax r represents the maximum value of the range of the i-th target cross section. so The outer radius r of the sheath of a single-ended grounded cable. si This indicates the inner radius of the sheath of a single-ended grounded cable. The maximum value of the target cross-sectional area of ​​the return line of the same material type is the same.

[0068] It should be noted that before performing these calculations, ensure that all units used are consistent. For example, if the current carrying capacity is in amperes and the radius is in meters, then the units should be kept consistent during the calculation process.

[0069] After obtaining the target cross-sectional range corresponding to the reflux line of the target material type mentioned above, determine a variety of reflux line models that match the target material type and target cross-sectional range as candidate reflux lines.

[0070] For each candidate return line, it is also necessary to screen it by comprehensively considering factors such as performance and cost. Specifically, the performance parameters and cost parameters of each candidate return line are obtained, and each candidate return line is comprehensively scored based on the performance parameters and cost parameters. The candidate return line with the highest comprehensive score is determined as the target return line corresponding to the single-ended grounding cable.

[0071] The performance parameters include at least one of the following: rated operating current and unit conductivity of the alternative return line; the cost parameters include at least one of the following: unit length price of the alternative return line, rated service life, annual depreciation rate, and annual maintenance cost.

[0072] The process of comprehensively evaluating each candidate return line based on performance and cost parameters can be carried out using the following steps:

[0073] S1, obtain the rated operating current and unit conductivity of the alternative return line; the cost parameters include at least one of the following: unit length price of the alternative return line, rated service life, annual depreciation rate, and annual maintenance cost.

[0074] S2, obtain the load level of the single-ended grounding system, and determine the performance weight based on the load level;

[0075] In a single-ended grounding system, the load level typically reflects the load characteristics and importance of the system. For example, load levels can be divided into primary loads (most important), secondary loads (relatively important), and tertiary loads (general). Load levels can be obtained through system design documents, operation records, or communication with system administrators.

[0076] Performance weights reflect the importance of different performance indicators in the evaluation. Different performance indicators can be assigned different weights based on the load level. A weighting table can be pre-defined to determine the weight of each performance indicator according to the load level. For example: Level 1 loads have a high safety weight and a low economic weight; Level 2 loads have a relatively high safety weight and a medium economic weight; Level 3 loads have a medium safety weight and a high economic weight.

[0077] S3, randomly select one alternative return line from multiple alternative return lines as the reference return line, and determine the overall score of the reference return line as 1;

[0078] S4. For any candidate return line other than the reference return line among multiple candidate return lines, calculate the comprehensive score of the candidate return line using the following formula:

[0079]

[0080] Among them, F i Let A represent the overall score of the i-th candidate return line, λ represent the performance weight, and A' ...",""'"'"'"]"]""]""]"]"]"] ref A represents the unit length price of the reference return line. i Let k represent the unit length price of the i-th alternative return line. ref Indicates the rated service life of the reference return line, k i M represents the rated service life of the i-th alternative return line. refM represents the annual maintenance cost of the reference return line. i I represents the annual maintenance cost of the i-th alternative return line. i I represents the rated operating current of the i-th alternative return line. ref ρ represents the rated operating current of the reference return line. i ρ represents the unit conductivity of the i-th candidate return line. ref ε represents the unit conductivity of the reference return line. i ε represents the annual loss rate of the i-th alternative return line. ref This indicates the annual depreciation rate of the reference return line.

[0081] After calculating and obtaining the comprehensive score of each candidate return line, the return line with the highest score is selected as the final target return line.

[0082] In this embodiment, the laying environment of the single-ended grounding cable in the single-ended grounding system is obtained, and at least one target material type matching the laying environment is determined; the target cross-sectional area of ​​the return line corresponding to each target material type is determined so that the short-circuit current flowing through it can meet the thermal stability conditions when a short-circuit fault occurs in the single-ended grounding system; multiple models of return lines matching the target material type and target cross-sectional area are determined as candidate return lines; the performance parameters and cost parameters of each candidate return line are obtained, and each candidate return line is comprehensively scored based on the performance parameters and cost parameters; the candidate return line with the highest comprehensive score is determined as the target return line corresponding to the single-ended grounding cable. In this way, one or more return line material types are determined based on the laying environment. The cross-sectional range of the return line is further determined based on thermal stability conditions to select suitable candidate return lines. Finally, the performance and cost of the candidate return lines are comprehensively analyzed to determine the final target return line. In this process, scientific calculation and analysis are used to avoid the problem of excessive parameter margin during selection, ensuring that the selection of return lines can meet functional requirements and have good economic efficiency. This solves the technical problem that unreasonable selection of return lines for single-end grounded cables in engineering projects can easily lead to cost waste or safety accidents.

[0083] Example 2

[0084] According to an embodiment of this application, a return line selection device for a single-ended grounding cable is also provided for implementing the return line selection method for the single-ended grounding cable in Embodiment 1, such as... Figure 2 As shown, the return line selection device for the single-ended grounding cable includes at least: a material selection module 21, a cross-section selection module 22, a candidate line selection module 23, a comprehensive scoring module 24, and a return line selection module 25, wherein:

[0085] The material selection module 21 is used to obtain the laying environment of the single-end grounding cable in the single-end grounding system and determine at least one target material type that matches the laying environment.

[0086] The cross-section selection module 22 is used to determine the target cross-section range of the return line for each target material type in which the short-circuit current flowing through can meet the thermal stability conditions when a short-circuit fault occurs in a single-ended grounded system.

[0087] The alternative line selection module 23 is used to determine a variety of reflow lines as alternative reflow lines that match the target material type and target cross-sectional range;

[0088] The comprehensive scoring module 24 is used to obtain the performance parameters and cost parameters of each candidate return line, and to give a comprehensive score to each candidate return line based on the performance parameters and cost parameters.

[0089] The return line selection module 25 is used to determine the candidate return line with the highest comprehensive score as the target return line corresponding to the single-ended grounded cable.

[0090] The following section explains the functions of each module in the single-ended grounding cable return line selection device, based on a specific implementation process.

[0091] To address the technical problem of inappropriate selection of return conductors for single-ended grounding cables in engineering projects, which can easily lead to cost waste or safety accidents, this application proposes a method for selecting return conductors for single-ended grounding cables. The implementation process of this method is as follows:

[0092] When selecting materials for single-ended grounding cables and their return conductors, the laying environment should be considered first. Different environmental conditions (such as temperature, humidity, and chemical corrosivity) will affect the physical and chemical properties of the return conductor, thereby affecting its safety and reliability. For example, in a highly corrosive environment, if a material with poor corrosion resistance is selected, the return conductor may be damaged prematurely, causing safety hazards. Suitable materials can better resist the effects of environmental factors, thereby extending the service life of the grounding cable and reducing replacement frequency and maintenance costs. Taking all factors into consideration, this application embodiment first obtains the laying environment of the single-ended grounding cable in the single-ended grounding system when selecting the return conductor and determines at least one target material type that matches the laying environment.

[0093] The target material type of the reflow line can include at least one of the following: aluminum alloy reflow line with strong corrosion resistance but poor vibration resistance, copper reflow line with strong conductivity and strong oxidation resistance, high temperature resistant special reflow line, vibration resistant special reflow line, and polymer composite material reflow line with strong corrosion resistance, strong vibration resistance, strong conductivity, strong oxidation resistance and high temperature resistance. These types of reflow lines can be selected according to the environment.

[0094] For example, in corrosive environments, such as coastal areas or industrial zones, aluminum alloy return lines with strong corrosion resistance but poor vibration resistance should be selected; in environments requiring high conductivity and oxidation resistance, such as high-voltage power transmission systems, copper return lines with both strong conductivity and oxidation resistance should be selected; in high-temperature environments, such as near heat sources, high-temperature resistant special return lines should be selected; in environments with frequent vibrations, such as near rail transit or industrial equipment, vibration-resistant special return lines should be selected; in complex and variable environments, such as where corrosion, vibration, high temperature, and high conductivity are required simultaneously, polymer composite return lines with strong corrosion resistance, vibration resistance, conductivity, oxidation resistance, and high temperature resistance should be selected.

[0095] In a single-ended grounding system, a very large short-circuit current will flow through the return conductor in the event of a short-circuit fault. If the cross-section of the return conductor is too small to withstand such a large current, it will cause the return conductor to overheat or even melt, thus leading to a safety accident. Therefore, it is very important to select a return conductor cross-section range that meets the thermal stability requirements.

[0096] As an alternative implementation, the target cross-sectional area corresponding to the return line of each target material type for which the short-circuit current flowing through can satisfy the thermal stability conditions can be determined in the following manner:

[0097] For each type of target material return line, determine the short-circuit current flowing through the return line and the short-circuit duration when a short-circuit fault occurs in a single-ended grounded system;

[0098] The duration of the short circuit flowing through the return line can be determined in the following ways: simulate a short circuit fault under laboratory conditions and record the total time from the occurrence of the short circuit to the clearing of the fault; or conduct a test in an actual operating single-ended grounding system and record the duration of the short circuit; or use simulation software for single-ended grounding systems to obtain the duration of the short circuit current flowing through the return line.

[0099] The short-circuit current flowing through the return line can be obtained in the following way:

[0100] When there is only one return line to be laid, the short-circuit current flowing through the single-ended grounded cable is taken as the short-circuit current flowing through the return line.

[0101] When there are multiple return lines to be laid, first obtain the short-circuit current flowing through the single-ended grounded cable, the resistance per unit length of each return line, the frequency of the single-ended grounding system, and the earth conductivity.

[0102] Considering that the equivalent resistance of the earth is one of the key parameters for evaluating the performance of a grounding system, its magnitude directly affects the safety and reliability of the system. When a short-circuit fault occurs, the short-circuit current returns to the power source through the earth. The equivalent resistance of the earth affects the distribution of the short-circuit current in the earth, and thus affects the current distribution in the return line. To accurately evaluate and design the grounding and return paths in a single-ended grounding system, the equivalent resistance of the earth can be calculated using the following methods:

[0103]

[0104] In the formula, D e ρ represents the equivalent resistance of the earth, f represents the frequency of the single-ended grounding system, and ρ represents the conductivity of the earth.

[0105] Next, calculate the reactance per unit length of each return line:

[0106]

[0107] In the formula, X i R represents the reactance per unit length of the i-th return line. i Let represent the resistance per unit length of the i-th return line. The impedance per unit length of each return line is obtained using the following formula:

[0108] Z i =R i +X i

[0109] In the formula, Z i Let represent the impedance per unit length of the i-th return line, and calculate the short-circuit current flowing through each return line using the following formula:

[0110]

[0111] In the formula, I ki I represents the short-circuit current flowing through the i-th return line. k k represents the short-circuit current flowing through a single-ended grounded cable. i Z1, Z2, ..., Zn represent the proportion of the short-circuit current flowing through the i-th return line in the short-circuit current flowing through the single-ended grounded cable, where n represents the number of return lines to be laid. n These represent the impedance per unit length of the 1st, 2nd, ..., nth return lines, respectively, Z1 / / Z2 / / ... / / Z n This represents the total impedance per unit length after n return lines are connected in parallel.

[0112] After obtaining the short-circuit current of each return line, the short-circuit current thermal effect of the return line is calculated using the following formula:

[0113]

[0114] In the formula, Q ki I represents the short-circuit current thermal effect of the i-th return line. ki Let t represent the short-circuit current of the i-th return line. k Indicates the duration of the short circuit.

[0115] After obtaining the short-circuit current thermal effect of each return line, the first current carrying capacity of the return line of the target material type at the maximum allowable operating temperature and the second current carrying capacity at the rated operating temperature are used to calculate the first thermal stability coefficient corresponding to the target material type using the following formula:

[0116]

[0117] In the formula, C i A represents the first thermal stability coefficient. Ki Indicates the first carrying capacity, A Li This represents the second flow rate; the minimum value of the target cross-sectional area corresponding to the return line of the target material type is calculated using the following formula, and finally, the minimum value of the target cross-sectional area is obtained according to the following formula:

[0118]

[0119] In the formula, S imin This represents the minimum value of the target cross-sectional area.

[0120] As an alternative implementation, the maximum value of the target cross-sectional range can be determined, thereby more accurately selecting the most suitable return line. This can be done by following these steps:

[0121] Obtain the third current carrying capacity of the single-ended grounded cable at the maximum allowable operating temperature and the fourth current carrying capacity at the rated operating temperature, and calculate the second thermal stability coefficient corresponding to the single-ended grounded cable using the following formula:

[0122]

[0123] In the formula, C s A represents the second thermal stability coefficient. Ks The third current-carrying capacity refers to the maximum continuous current carrying capacity of a single-ended grounded cable under the highest permissible operating temperature, expressed in A. Ls The fourth current carrying capacity refers to the maximum continuous current carrying capacity of a single-ended grounded cable at its rated operating temperature.

[0124] Based on the outer and inner radii of the sheath of the single-ended grounding cable, the maximum value of the target cross-sectional area is calculated using the following formula:

[0125]

[0126] In the formula, Simax r represents the maximum value of the target cross-sectional area. so The outer radius r of the sheath of a single-ended grounded cable. si This indicates the inner radius of the sheath of a single-ended grounded cable.

[0127] It should be noted that before performing these calculations, ensure that all units used are consistent. For example, if the current carrying capacity is in amperes and the radius is in meters, then the units should be kept consistent during the calculation process.

[0128] After obtaining the above-mentioned cross-sectional range, several models of reflux lines that match the target material type and target cross-sectional range are identified as alternative reflux lines.

[0129] For each candidate return line, it is also necessary to screen it by comprehensively considering factors such as performance and cost. Specifically, the performance parameters and cost parameters of each candidate return line are obtained, and each candidate return line is comprehensively scored based on the performance parameters and cost parameters. The candidate return line with the highest comprehensive score is determined as the target return line corresponding to the single-ended grounding cable.

[0130] The performance parameters include at least one of the following: rated operating current and unit conductivity of the alternative return line; the cost parameters include at least one of the following: unit length price of the alternative return line, rated service life, annual depreciation rate, and annual maintenance cost.

[0131] The process of comprehensively evaluating each candidate return line based on performance and cost parameters can be carried out using the following steps:

[0132] S1, obtain the rated operating current and unit conductivity of the alternative return line; the cost parameters include at least one of the following: unit length price of the alternative return line, rated service life, annual depreciation rate, and annual maintenance cost.

[0133] S2, obtain the load level of the single-ended grounding system, and determine the performance weight based on the load level;

[0134] In a single-ended grounding system, the load level typically reflects the load characteristics and importance of the system. For example, load levels can be divided into primary loads (most important), secondary loads (relatively important), and tertiary loads (general). Load levels can be obtained through system design documents, operation records, or communication with system administrators.

[0135] Performance weights reflect the importance of different performance indicators in the evaluation. Different performance indicators can be assigned different weights based on the load level. A weighting table can be pre-defined to determine the weight of each performance indicator according to the load level. For example: Level 1 loads have a high safety weight and a low economic weight; Level 2 loads have a relatively high safety weight and a medium economic weight; Level 3 loads have a medium safety weight and a high economic weight.

[0136] S3, randomly select one alternative return line from multiple alternative return lines as the reference return line, and determine the overall score of the reference return line as 1;

[0137] S4. For any candidate return line other than the reference return line among multiple candidate return lines, calculate the comprehensive score of the candidate return line using the following formula:

[0138]

[0139] Among them, F i Let A represent the overall score of the i-th candidate return line, λ represent the performance weight, and A' ...",""'"'"'"]"]""]""]"]"]"] ref A represents the unit length price of the reference return line. i Let k represent the unit length price of the i-th alternative return line. ref Indicates the rated service life of the reference return line, k i M represents the rated service life of the i-th alternative return line. ref M represents the annual maintenance cost of the reference return line. i I represents the annual maintenance cost of the i-th alternative return line. i I represents the rated operating current of the i-th alternative return line. ref ρ represents the rated operating current of the reference return line. i ρ represents the unit conductivity of the i-th candidate return line. ref ε represents the unit conductivity of the reference return line. i ε represents the annual loss rate of the i-th alternative return line. ref This indicates the annual depreciation rate of the reference return line.

[0140] After calculating and obtaining the comprehensive score for each return flow line, the return flow line with the highest score is selected as the final target return flow line.

[0141] It should be noted that each module in the single-ended grounding cable return line selection device in this application embodiment corresponds one-to-one with each implementation step of the single-ended grounding cable return line selection method in Embodiment 1. Since Embodiment 1 has been described in detail, some details not shown in this embodiment can be referred to Embodiment 1, and will not be elaborated further here.

[0142] Example 3

[0143] According to an embodiment of this application, a computer program product is also provided, which includes a computer program, wherein when the computer program is executed by a processor, it implements the return line selection method for a single-ended grounded cable in Embodiment 1.

[0144] According to an embodiment of this application, a non-volatile storage medium is also provided, which includes a stored computer program, wherein the device containing the non-volatile storage medium executes the return line selection method for a single-ended grounded cable in Embodiment 1 by running the computer program.

[0145] According to an embodiment of this application, a processor is also provided for running a computer program, wherein the computer program executes the return line selection method for a single-ended grounded cable in Embodiment 1.

[0146] According to an embodiment of this application, an electronic device is also provided, comprising: a memory and a processor, wherein the memory stores a computer program, and the processor is configured to execute the return line selection method for a single-ended grounded cable in Embodiment 1 via the computer program.

[0147] Specifically, the computer program executes the following steps during runtime: acquiring the laying environment of the single-ended grounding cable in the single-ended grounding system and determining at least one target material type matching the laying environment; determining the target cross-sectional area of ​​the return line corresponding to each target material type whose short-circuit current can meet the thermal stability conditions when a short-circuit fault occurs in the single-ended grounding system; determining multiple models of return lines matching the target material type and target cross-sectional area as candidate return lines; acquiring the performance and cost parameters of each candidate return line and comprehensively scoring each candidate return line based on the performance and cost parameters; and determining the candidate return line with the highest comprehensive score as the target return line corresponding to the single-ended grounding cable.

[0148] As an alternative implementation, the above-mentioned electronic device may exist in the form of a mobile terminal, a computer terminal, or a similar computing device. Figure 3 A hardware block diagram of an electronic device for implementing a return line selection method for single-ended grounded cables is shown. Figure 3As shown, the electronic device 30 may include one or more processors 302 (shown as 302a, 302b, ..., 302n in the figure) (processor 302 may include, but is not limited to, a microprocessor MCU or a programmable logic device FPGA, etc.), a memory 304 for storing data, and a transmission device 306 for communication functions. In addition, it may also include: a display, an input / output interface (I / O interface), a universal serial bus (USB) port (which may be included as one of the ports of a BUS bus), a network interface, a power supply, and / or a camera. Those skilled in the art will understand that... Figure 3 The structure shown is for illustrative purposes only and does not limit the structure of the electronic device described above. For example, electronic device 30 may also include... Figure 3 The more or fewer components shown, or having the same Figure 3 The different configurations shown.

[0149] It should be noted that the aforementioned one or more processors 302 and / or other data processing circuits are generally referred to herein as "data processing circuits". These data processing circuits may be embodied, in whole or in part, in software, hardware, firmware, or any other combination thereof. Furthermore, the data processing circuits may be a single, independent processing module, or may be integrated, in whole or in part, into any other element of the electronic device 30. As involved in the embodiments of this application, the data processing circuits serve as a processor control mechanism (e.g., selection of a variable resistor termination path connected to an interface).

[0150] The memory 304 can be used to store software programs and modules of application software, such as the program instruction / data storage device corresponding to the single-ended grounding cable return line selection method in this embodiment. The processor 302 executes various functional applications and data processing by running the software programs and modules stored in the memory 304, thereby implementing the above-mentioned application vulnerability detection method. The memory 304 may include high-speed random access memory, and may also include non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some instances, the memory 304 may further include memory remotely located relative to the processor 302, and these remote memories can be connected to the electronic device 30 via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0151] The transmission device 306 is used to receive or send data via a network. Specific examples of the network described above may include a wireless network provided by the communication provider of the electronic device 30. In one example, the transmission device 306 includes a Network Interface Controller (NIC), which can connect to other network devices via a base station to communicate with the Internet. In another example, the transmission device 306 may be a Radio Frequency (RF) module, used for wireless communication with the Internet.

[0152] The display may be, for example, a touchscreen liquid crystal display (LCD), which allows the user to interact with the user interface of the electronic device 30.

[0153] The sequence numbers of the above embodiments are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0154] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0155] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. The device embodiments described above are merely illustrative; for example, the division of units can be a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some interfaces; indirect couplings or communication connections between units or modules may be electrical or other forms.

[0156] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0157] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0158] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, read-only memory (ROM), random access memory (RAM), portable hard drive, magnetic disk, or optical disk.

[0159] The above are merely preferred embodiments of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for selecting the return line of a single-ended grounded cable, characterized in that, include: Obtain the laying environment of the single-ended grounding cable in the single-ended grounding system, and determine at least one target material type that matches the laying environment; When a short-circuit fault occurs in the single-ended grounding system, the short-circuit current flowing through it can satisfy the thermal stability conditions for the target cross-sectional area of ​​the return line corresponding to each of the target material types. Several models of reflux lines that match the target material type and the target cross-sectional range are identified as candidate reflux lines; Obtain the performance parameters and cost parameters of each of the candidate return lines, and give a comprehensive score to each of the candidate return lines based on the performance parameters and the cost parameters; The candidate return line with the highest comprehensive score is determined as the target return line corresponding to the single-ended grounding cable.

2. The method according to claim 1, characterized in that, The target material type of the reflow line includes at least one of the following: an aluminum alloy reflow line with strong corrosion resistance but poor vibration resistance, a copper reflow line with strong conductivity and strong oxidation resistance, a high-temperature resistant special reflow line, a vibration-resistant special reflow line, and a polymer composite material reflow line with strong corrosion resistance, strong vibration resistance, strong conductivity, strong oxidation resistance and high temperature resistance.

3. The method according to claim 1, characterized in that, When a short-circuit fault occurs in the single-ended grounding system, the target cross-sectional area of ​​the return line corresponding to each of the target material types that satisfies the thermal stability conditions is determined, including: For each type of target material return line, determine the short-circuit current flowing through the return line and the short-circuit duration when a short-circuit fault occurs in the single-ended grounding system, and calculate the short-circuit current thermal effect of the return line using the following formula: In the formula, Q ki I represents the short-circuit current thermal effect. ki The short-circuit current, t k Indicates the duration of the short circuit; Obtain the first flow rate of the reflux line of the target material type at the maximum allowable operating temperature and the second flow rate at the rated operating temperature, and calculate the first thermal stability coefficient corresponding to the target material type using the following formula: In the formula, C i A represents the first thermal stability coefficient. Ki A represents the first carrying capacity. Li This indicates the second current carrying capacity; The minimum value of the target cross-sectional range corresponding to the return line of the target material type is calculated using the following formula: In the formula, S imin This represents the minimum value of the target cross-sectional range.

4. The method according to claim 3, characterized in that, Determine the short-circuit current flowing through the return line when a short-circuit fault occurs in the single-ended grounding system, including: When there is only one return line to be laid, it is determined that when a short circuit fault occurs in the single-ended grounding system, the short circuit current flowing through the single-ended grounding cable will be used as the short circuit current flowing through the return line. When there are multiple return lines to be laid, to determine when a short-circuit fault occurs in the single-ended grounding system, obtain the short-circuit current flowing through the single-ended grounding cable, the resistance per unit length of each return line, the frequency of the single-ended grounding system, and the earth conductivity, and calculate the short-circuit current flowing through each return line using the following formula: In the formula, I ki I represents the short-circuit current flowing through the i-th return line. k k represents the short-circuit current flowing through the single-ended grounded cable. i Z1, Z2, ..., Zn represent the proportion of the short-circuit current flowing through the i-th return line in the short-circuit current flowing through the single-ended grounded cable, and n represents the number of return lines to be laid. n These represent the impedance per unit length of the 1st, 2nd, ..., nth return lines, respectively, Z1 / / Z2 / / ... / / Z n Z represents the total impedance per unit length after n return lines are connected in parallel. i Let Z represent the impedance per unit length of the i-th return line, and Z i =R i +X i , R i X represents the resistance per unit length of the i-th return line. i D represents the reactance per unit length of the i-th return line. e ρ represents the equivalent resistance of the earth, f represents the frequency of the single-ended grounding system, and ρ represents the conductivity of the earth.

5. The method according to claim 3, characterized in that, The method further includes: Obtain the third current carrying capacity of the single-ended grounding cable at the maximum allowable operating temperature and the fourth current carrying capacity at the rated operating temperature, and calculate the second thermal stability coefficient of the single-ended grounding cable using the following formula: In the formula, C s A represents the second thermal stability coefficient. Ks Indicates the third current carrying capacity, A Ls This indicates the fourth current carrying capacity; Obtain the outer and inner radii of the sheath of the single-ended grounding cable, and calculate the maximum value of the target cross-sectional area using the following formula: In the formula, S imax r represents the maximum value of the target cross-sectional range. so r represents the outer radius of the sheath of the single-ended grounded cable. si This indicates the inner radius of the sheath of the single-ended grounded cable.

6. The method according to claim 1, characterized in that, The type of the performance parameter includes at least one of the following: the rated operating current of the alternative return line, and the unit conductivity. The cost parameters include at least one of the following: unit length price of the alternative return line, rated service life, annual depreciation rate, and annual maintenance cost.

7. The method according to claim 6, characterized in that, Each of the candidate return lines is comprehensively evaluated based on the performance parameters and the cost parameters, including: Obtain the load level of the single-ended grounding system and determine the performance weight based on the load level; One alternative return line is randomly selected from the various alternative return lines as a reference return line, and the overall score of the reference return line is determined to be 1. For any candidate return line other than the reference return line among the various candidate return lines, the comprehensive score of the candidate return line is calculated using the following formula: Among them, F i Let A represent the overall score of the i-th candidate return line, λ represent the performance weight, and A ref A represents the unit length price of the reference return line. i Let k represent the unit length price of the i-th alternative return line. ref k represents the rated service life of the reference return line. i M represents the rated service life of the i-th alternative return line. ref M represents the annual maintenance cost of the reference return line. i I represents the annual maintenance cost of the i-th alternative return line. i I represents the rated operating current of the i-th alternative return line. ref ρ represents the rated operating current of the reference return line. i ρ represents the unit conductivity of the i-th candidate return line. ref ε represents the unit conductivity of the reference return line. i ε represents the annual loss rate of the i-th alternative return line. ref This represents the annual depreciation rate of the reference return line.

8. A return line selection device for a single-ended grounded cable, characterized in that, include: The material selection module is used to obtain the laying environment of the single-end grounding cable in the single-end grounding system and determine at least one target material type that matches the laying environment. A cross-section selection module is used to determine the target cross-section range corresponding to the return line of each of the target material types for which the short-circuit current flowing through the single-ended grounding system can meet the thermal stability conditions when a short-circuit fault occurs. The alternative line selection module is used to determine a variety of reflow lines that match the target material type and the target cross-sectional range as alternative reflow lines; The comprehensive scoring module is used to obtain the performance parameters and cost parameters of each of the candidate return lines, and to give a comprehensive score to each of the candidate return lines based on the performance parameters and the cost parameters; The return line selection module is used to determine the candidate return line with the highest comprehensive score as the target return line corresponding to the single-ended grounding cable.

9. A computer program product, characterized in that, include: A computer program, wherein when executed by a processor, the computer program implements the return line selection method for a single-ended grounded cable as described in any one of claims 1 to 7.

10. An electronic device, characterized in that, include: A memory and a processor, wherein the memory stores a computer program, and the processor is configured to execute, via the computer program, the method for selecting the return line of a single-ended grounded cable as described in any one of claims 1 to 7.

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