A method, system, electronic device and storage medium for online monitoring of cable insulation dielectric loss factor

Abstract

The present invention discloses a method, system, electronic device and storage medium for online monitoring of the dielectric loss factor of cable insulation, which can obtain the range of the dielectric loss factor of cables with normal insulation performance; obtain the range of the dielectric loss factor of cables with different degrees of degradation; and perform online monitoring of the dielectric loss factor of cable insulation based on the range of the dielectric loss factor of cables with normal insulation performance and the range of the dielectric loss factor of cables with different degrees of degradation to obtain the insulation performance of the online cable. The present invention provides a method, system, electronic device and storage medium for online monitoring of the dielectric loss factor of cable insulation, which can be used to monitor the dielectric loss factor of cable insulation online, and provides the necessary theoretical support for online monitoring of the dielectric loss factor of cable insulation. An online monitoring scheme for the dielectric loss factor of cable insulation is proposed, which can be applied in engineering applications.

Description

Technical Field

[0001] The present invention relates to an online monitoring method, system, electronic equipment and storage medium for cable insulation dielectric loss factor, and belongs to the technical field of cable online detection. Background Art

[0002] With the ongoing urbanization process, cables are gradually replacing overhead wires, with some cities even achieving a 100% cable coverage rate. As one of the primary transmission lines, cables play a crucial role in the entire power grid. However, with increasing service life, under the long-term effects of electrical and thermal fields, cable insulation experiences polymer cracking, defects, and aging, with some even exhibiting more severe aging phenomena such as electrical treeing. Furthermore, some cables lack radial water-blocking structures and, due to prolonged exposure to humid environments, can form water trees under electric fields. These conditions can lead to cable insulation degradation, which in turn increases the dielectric loss factor.

[0003] In China, relatively mature methods for online monitoring of cable insulation performance primarily include partial discharge, ground loop current, and temperature testing. However, there has been relatively little research into the practical application of dielectric loss factor, a key performance indicator for cable insulation degradation. This is primarily due to the following: First, while there have been exploratory studies on online monitoring technology for cable insulation dielectric loss factor, most of these studies have focused on the feasibility of the methods and have not proposed specific theoretical expressions. Second, no specific and feasible online monitoring process has been proposed, let alone specific recommendations for determining cable insulation degradation criteria.

[0004] Therefore, it is necessary to propose corresponding expressions for the insulation dielectric loss factor based on the relevant parameters of the engineering site, summarize specific degradation criteria, and establish a specific and operational online monitoring process. Summary of the Invention

[0005] Objective: To overcome the shortcomings of existing technologies, this invention proposes a method, system, electronic device, and storage medium for online monitoring of cable insulation loss factor. Based on engineering parameters, a theoretical expression for the cable insulation loss factor is developed for online monitoring. Criteria for cable insulation degradation are also proposed, and an online monitoring scheme for the insulation loss factor is established.

[0006] The present invention provides a method and system for online monitoring the loss factor of cable insulation dielectric, an electronic device and a storage medium.

[0007] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is:

[0008] In a first aspect, a method for online monitoring of cable insulation dielectric loss factor comprises the following steps:

[0009] Step 1: Obtain the range of dielectric loss factor of cables with normal insulation performance.

[0010] Step 2: Obtain the range of dielectric loss factors of cables with different degrees of degradation.

[0011] Step 3: Based on the range of dielectric loss factor of cables with normal insulation performance and the range of dielectric loss factor of cables with different degrees of degradation, perform online monitoring of the dielectric loss factor of the cable insulation to obtain the insulation performance of the online cable.

[0012] Furthermore, the step 1 includes:

[0013] Step 1.1. Select a certain number of cables with normal insulation performance.

[0014] Step 1.2: Measure the phase difference θ between the currents at the beginning and end of all cables.

[0015] Step 1.3: Substitute the θ data corresponding to all cables into the dielectric loss factor formula to obtain the range of dielectric loss factor tanδ for normal cable insulation performance.

[0016] Furthermore, the step 2 includes:

[0017] Step 2.1. Select cables with different insulation degradation degrees and classify the cables into several insulation degradation degrees.

[0018] Step 2.2: Measure the phase difference θ between the currents at the beginning and end of all cables.

[0019] Step 2.3: Substitute the θ data corresponding to all cables into the dielectric loss factor formula to determine the range of dielectric loss factor tanδ corresponding to different insulation degradation levels.

[0020] Furthermore, the step 3 includes:

[0021] Step 3.1. Measure the phase difference θ between the current at the beginning and end of the running cable line, and obtain the running voltage U of the running cable, the amplitude I1 of the current at the beginning of the running cable, the length l of the running cable line, and the inner and outer radii r1 and r2 of the insulation of the running cable.

[0022] Step 3.2: Calculate the dielectric loss factor of the operating cable according to the dielectric loss factor formula.

[0023] Step 3.3: Compare the dielectric loss factor of the operating cable with the range of dielectric loss factor tanδ of the cable with normal insulation performance and the range of dielectric loss factor tanδ corresponding to different insulation degradation levels to determine whether the insulation performance of the operating cable is normal or belongs to a certain insulation degradation level.

[0024] Furthermore, the dielectric loss factor formula is calculated as follows:

[0025]

[0026] Where, δ is the complex effective value of the capacitive current of the cable and The phase difference, is the effective value of the capacitive current of the cable and resistive current complex effective value The sum of ω is the circular frequency, C is the cable capacitance per unit length, π is the circumference ratio, and ε is the cable insulation dielectric constant.

[0027] Furthermore, the method for obtaining the dielectric loss factor formula includes:

[0028] Get the effective value of the current at the beginning of the cable The terminal current is effectively The effective value of the capacitive current of the cable and resistive current complex effective value

[0029] Calculate the complex effective value of the capacitive current of the cable and resistive current complex effective value The sum of

[0030] Get and The phase difference θ, and Phase difference A, and Phase difference B, and Phase difference δ.

[0031] Restore the current to its effective value and The phase differences θ, A, B, and δ are plotted on a complex plane coordinate system with the x-axis as the real axis and the y-axis as the imaginary axis.

[0032] According to the law of sine, we can get formula (1), which is as follows:

[0033]

[0034] Will Substituting into formula (1), we get formula (2):

[0035]

[0036] Among them, I C The calculation formula is as follows:

[0037]

[0038] Where l, r2 and r1 are the cable length, cable insulation outer radius and inner radius respectively, ε is the cable insulation dielectric constant, U is the cable voltage, ω is the circular frequency, C is the cable capacitance per unit length, and π is the circumference of the cable.

[0039] Substituting formula (3) into formula (2), we get formula (4) as follows:

[0040]

[0041] According to formula (4), the expression of sinθ is as follows:

[0042]

[0043] It is common knowledge that the angle δ is the dielectric loss angle of the cable insulation. Converting formula (5) into the cable insulation dielectric loss tangent formula, the calculation formula is as follows:

[0044]

[0045] Simplifying formula (6) into the dielectric loss factor formula, the calculation formula is as follows:

[0046]

[0047] In a second aspect, a cable insulation dielectric loss factor online monitoring system includes the following modules:

[0048] Normal range acquisition module: used to determine the range of dielectric loss factor of cables with normal insulation performance.

[0049] Abnormal range acquisition module: used to analyze the range of dielectric loss factors of cables with different degrees of degradation.

[0050] Online cable judgment module: used for online monitoring of cable insulation dielectric loss factor to obtain the insulation performance of online cables.

[0051] In a third aspect, a computer-readable storage medium stores a computer program, which, when executed by a processor, implements an online monitoring method for cable insulation dielectric loss factor as described in any one of the first aspects.

[0052] According to a fourth aspect, a computer device includes:

[0053] Memory, used to store instructions.

[0054] The processor is configured to execute the instructions so that the computer device performs the operations of the online monitoring method for the cable insulation dielectric loss factor as described in any one of the first aspects.

[0055] Beneficial Effects: The present invention provides a method, system, electronic device, and storage medium for online monitoring of the cable insulation loss factor, providing the necessary theoretical support for online monitoring of the cable insulation loss factor. It also proposes an online monitoring solution for the cable insulation loss factor, which can be implemented in engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 Schematic diagram of the complex effective values ​​of the current at the beginning and end of the cable and the resistance and capacitance currents.

[0057] Figure 2 Schematic diagram of the process of the online monitoring method of the present invention.

[0058] Figure 3 It is a structural diagram of the online monitoring system of the present invention. DETAILED DESCRIPTION

[0059] The following is a clear and complete description of the technical solutions in the examples of the present invention, in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0060] The present invention will be further described below with reference to specific embodiments.

[0061] like Figure 1 As shown, the effective value of the current at the beginning of the cable is The terminal current is effectively The effective value of the capacitive current of the cable and resistive current complex effective value The sum is and The phase difference is θ, and The phase difference is A, and The phase difference is B. and The phase difference is δ. and The corresponding amplitudes are expressed as I1, I2, I CR , I C and I R .

[0062] Since the line voltage complex effective value and The phase is the same; (j is the imaginary unit, ω is the circular frequency, C is the cable capacitance per unit length and l is the cable length), so Phase ratio Phase leading by 90°, also leading Phase 90°, that is and vertical. Similarly, the resistive current also with In phase, so Phase Lead Phase 90°, also with vertical.

[0063] Restore the current to its effective value and The phase differences θ, A, B, and δ are plotted on a complex plane coordinate system with the x-axis as the real axis and the y-axis as the imaginary axis.

[0064] According to the law of sine,

[0065]

[0066] Among them, Substituting into formula (1), we get formula (2):

[0067]

[0068] in,

[0069]

[0070] Where l, r2, and r1 are the cable length, cable insulation outer radius, and cable insulation inner radius, respectively; ε is the cable insulation dielectric constant; U is the cable voltage; ω is the circular frequency; C is the cable capacitance per unit length; and π is the circumference of the circle. Substituting formula (3) into formula (2), we obtain formula (4) as follows:

[0071]

[0072] According to formula (4), the expression of sinθ is as follows:

[0073]

[0074] From formula (5), we can see that the angle θ is directly proportional to the angle δ, the voltage U, and the cable length l, and is inversely proportional to the head-end current I1 and the ratio of the outer and inner radii of the cable insulation r2\r1.

[0075] It is common knowledge that the angle δ is the dielectric loss angle of the cable insulation. Converting formula (5) into the cable insulation dielectric loss tangent formula, that is, the dielectric loss factor formula, is as follows:

[0076]

[0077] For cable insulation, tanδ is generally 10 -3 And below, that is, δ tends to 0, we get B ≈ 90°. In addition, A + B + θ = 180°, θ also tends to 0, so A ≈ 90°, sin A ≈ 1. Therefore, Equation (6) can be simplified to:

[0078]

[0079] This means that when other parameters are constant, the angle θ can reflect the cable insulation dielectric loss (tanδ) condition.

[0080] like Figure 2 As shown, the first embodiment of the present invention is a method for online monitoring of the dielectric loss factor of cable insulation. This method mainly analyzes the dielectric loss factors of existing cables with normal and abnormal insulation performance to obtain a dielectric loss factor criterion for evaluating the insulation status of the cable, and applies it to online monitoring of cable lines. The method includes the following steps:

[0081] Step 1: Determine the range of dielectric loss factor of cables with normal insulation performance.

[0082] Step 1.1. Select a certain number of cables with normal insulation performance, including new cables that have not been put into operation or cables that are in normal operation. Their insulation performance must at least not contain defects such as water trees and electrical trees.

[0083] Step 1.2: Use a dual CT in the laboratory to measure the phase difference θ between the currents at the beginning and end of the cable. Alternatively, use a dual CT at the construction site to measure the phase difference θ of the operating cable.

[0084] Step 1.3: Substitute the θ data corresponding to all cables into formula (7) to obtain the range of dielectric loss factor tanδ for normal cable insulation performance.

[0085] Step 2: Analyze the range of dielectric loss factors of cables with different degrees of degradation.

[0086] Step 2.1: Based on the needs of online monitoring research, select cables with different degrees of insulation degradation and classify them into several insulation degradation levels. These cables can be from faulty cables at the project site or cables that have been degraded in the laboratory.

[0087] Step 2.2: Use dual CTs in the laboratory to measure the phase difference θ between the currents at the beginning and end of the cable.

[0088] Step 2.3: Substitute the θ data corresponding to all cables into formula (7) to determine the range of dielectric loss factor tanδ corresponding to different insulation degradation levels.

[0089] Step 3: Monitor the cable insulation dielectric loss factor online to obtain the insulation performance of the online cable.

[0090] Step 3.1: For online monitoring of the dielectric loss factor of the operating cable, use dual CTs to measure the phase difference θ between the current at the beginning and end of the operating cable line online, and obtain the operating voltage U of the operating cable, the amplitude I1 of the current at the beginning of the operating cable, the length l of the operating cable line, and the inner and outer radii r1 and r2 of the insulation of the operating cable.

[0091] Step 3.2: Calculate the dielectric loss factor of the operating cable according to formula (7).

[0092] Step 3.3: Compare the dielectric loss factor of the operating cable with the range of dielectric loss factor tanδ of the cable with normal insulation performance and the range of dielectric loss factor tanδ corresponding to different insulation degradation levels to determine whether the insulation performance of the operating cable is normal or belongs to a certain insulation degradation level.

[0093] Based on the degradation degree criterion obtained in the above two steps, online monitoring of cable insulation performance can be achieved.

[0094] like Figure 3 As shown, a second embodiment of the present invention is an online monitoring system for cable insulation dielectric loss factor, including the following modules:

[0095] Normal range acquisition module: used to determine the range of dielectric loss factor of cables with normal insulation performance.

[0096] Abnormal range acquisition module: used to analyze the range of dielectric loss factors of cables with different degrees of degradation.

[0097] Online cable judgment module: used for online monitoring of cable insulation dielectric loss factor to obtain the insulation performance of online cables.

[0098] The normal range acquisition module specifically includes:

[0099] Select a certain number of cables with normal insulation performance, including new cables that have not been put into operation or cables that are operating normally, and their insulation performance shall at least not contain defects such as water trees and electrical trees.

[0100] In the laboratory, dual CTs are used to measure the phase difference θ between the currents at the beginning and end of a cable. Dual CTs can also be used to measure the phase difference θ of a running cable at a construction site.

[0101] Substituting the θ data corresponding to all cables into formula (7), we can obtain the range of dielectric loss factor tanδ for normal cable insulation performance.

[0102] The abnormal range acquisition module specifically includes:

[0103] Based on the needs of online monitoring research, cables with different degrees of insulation degradation are selected and divided into several insulation degradation levels. These cables can be from faulty cables at the project site or cables that have been degraded in the laboratory.

[0104] In the laboratory, dual CTs are used to measure the phase difference θ between the currents at the beginning and end of the cable.

[0105] Substitute the θ data corresponding to all cables into formula (7) to determine the range of dielectric loss factor tanδ corresponding to different insulation degradation levels.

[0106] The online cable judgment module specifically includes:

[0107] For online monitoring of the dielectric loss factor of a running cable, a dual CT is used to measure the phase difference θ between the current at the beginning and end of the running cable line online, and obtain the running voltage U of the running cable, the amplitude I1 of the current at the beginning of the running cable, the length l of the running cable line, and the inner and outer radii r1 and r2 of the insulation of the running cable.

[0108] Calculate the dielectric loss factor of the running cable according to formula (7).

[0109] Compare the dielectric loss factor of the operating cable with the range of dielectric loss factor tanδ of the cable with normal insulation performance and the range of dielectric loss factor tanδ corresponding to different insulation degradation levels to determine whether the insulation performance of the operating cable is normal or belongs to a certain insulation degradation level.

[0110] A third embodiment provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for online monitoring of the cable insulation dielectric loss factor as described in any one of the first embodiments is implemented.

[0111] A fourth embodiment provides a computer device, comprising:

[0112] Memory, used to store instructions.

[0113] The processor is configured to execute the instructions so that the computer device performs the operations of the online monitoring method for the cable insulation dielectric loss factor as described in any one of the first embodiments.

[0114] Example 1:

[0115] The 10kV cable is now monitored online, including:

[0116] For a 10kV cross-linked polyethylene (XLPE) insulated cable, its phase voltage U = 6kV and length l = 550m. The cable insulation inner radius r1 = 10mm and outer radius r2 = 14.5mm. Consider the XLPE relative dielectric constant ε r =2.3, then the dielectric constant ε=ε r ε0=2×10 -11 F / m.

[0117] (1) Obtain the dielectric loss factor range of cables with normal insulation performance.

[0118] First, 10 cables with normal insulation performance were selected, including new cables and cables that were operating normally, whose insulation did not contain water trees, electrical trees, defects, etc.

[0119] Then, the phase difference θ of the current at the beginning and end of the cable was measured in the laboratory using a dual CT, which was 0.10°, 0.10°, 0.11°, 0.10°, 0.10°, 0.10°, 0.11°, 0.10°, and 0.11°.

[0120] Finally, the θ data is substituted into formula (7) to obtain the dielectric loss factor range of the cable with normal insulation performance: tanδ≤5×10 -3 .

[0121] (2) Obtain the dielectric loss factor range of the insulation-degraded cable.

[0122] First, 10 cables with insulation deterioration were selected. Water trees, electrical trees, defects, etc. were present in the insulation, and the insulation resistance was smaller than that of normal cables.

[0123] Then, the phase difference of the current at the beginning and end of the cable was measured in the laboratory using dual CT, θ = 0.14°, 0.15°, 0.14°, 0.15°, 0.15°, 0.15°, 0.15°, 0.14°, 0.15°.

[0124] Finally, substituting the θ data into equation (7), we obtain the dielectric loss factor range of the insulation deteriorated cable: 8.0×10 -2 ≤tanδ.

[0125] (3) Application of online monitoring of cable insulation dielectric loss factor

[0126] From Section (1), we can see that after testing multiple cables, the insulation dielectric loss factor of cables with normal performance is in the range of tanδ≤5×10 -3 , while the national standard stipulates that tanδ≤8×10 -3Considering that there are certain errors in the measurement process, the range of the insulation dielectric loss factor of cables with normal performance can be appropriately expanded. The following is recommended:

[0127] tanδ≤8×10 -3 (8)

[0128] Similarly, based on the relevant measurement data in Section (2) and taking into account the error, the lower limit of the dielectric loss factor of the insulation deteriorated cable is set to 8.0×10 -2 Appropriately increase to 1.0×10 -1 , the suggestion is:

[0129] 1.0×10 -1 ≤tanδ (9)

[0130] Thus, during the online monitoring of the cable, the phase difference θ between the currents at the beginning and end of the cable, the operating voltage U and current I1, the line length l, the cable structural dimension parameters r1 and r2, and other related parameters are substituted into Equation (7) to obtain tanδ. By comparing the tanδ value with the judgment criteria (Equations (8) and (9)), the online monitoring of the cable insulation status can be completed.

[0131] Example 2:

[0132] The 220kV cables are now being monitored online, specifically including:

[0133] For a 220kV cross-linked polyethylene (XLPE) insulated cable, its phase voltage U = 127kV, the head-end current I1 = 1000A, and the length l = 5km. The cable insulation inner radius r1 = 20mm, and the outer radius r2 = 44mm. Consider the XLPE relative dielectric constant ε r =2.3, then the dielectric constant ε=ε r ε0=2×10 -11 F / m.

[0134] (1) Obtain the dielectric loss factor range of cables with normal insulation performance.

[0135] First, 10 cables with normal insulation performance were selected, including new cables and cables that were operating normally, whose insulation did not contain water trees, electrical trees, defects, etc.

[0136] Then, the phase difference of the current at the beginning and end of the cable was measured in the laboratory using dual CT, θ = 1.82°, 1.83°, 1.82°, 1.82°, 1.82°, 1.82°, 1.83°, 1.82°, 1.82°, 1.82°.

[0137] Finally, the θ data is substituted into formula (7) to obtain the dielectric loss factor range of normal cable insulation performance tanδ≤8×10 -4 .

[0138] (2) Obtain the dielectric loss factor range of the insulation-degraded cable.

[0139] First, 10 cables with insulation degradation were selected. These cables had electrical trees, micropores, and defects in their insulation, and their insulation resistance was lower than that of normal cables.

[0140] Then, the phase difference of the current at the beginning and end of the cable was measured in the laboratory using dual CT, and the values ​​were θ = 1.86°, 1.86°, 1.87°, 1.86°, 1.86°, 1.86°, 1.86°, 1.87°, and 1.86°;

[0141] Finally, the θ data is substituted into Equation (7) to obtain the dielectric loss factor range of the insulation deteriorated cable: 1.0×10 -2 ≤tanδ.

[0142] (3) Application of online monitoring of cable insulation dielectric loss factor

[0143] From Section (1), we can see that after testing multiple cables, the insulation dielectric loss factor of cables with normal performance ranges from tanδ≤8×10 -4 , which is consistent with the national standard tanδ≤8×10 -4 Considering that there are certain errors in the measurement process, the range of the dielectric loss factor of the cable with normal performance can be appropriately expanded. The following is recommended:

[0144] tanδ≤1×10 -3 (10)

[0145] Similarly, based on the relevant measurement data in Section (2) and taking into account the error, the lower limit of the dielectric loss factor of the insulation deteriorated cable is set to 1.0×10 -2 Appropriately increase to 2.0×10 -2 , the suggestion is:

[0146] tanδ≥2.0×10 -2 (11)

[0147] Thus, during the online cable monitoring process, tanδ can be obtained by substituting relevant parameters such as the phase difference θ between the cable head and end currents, the operating voltage U and current I1, the line length l, and the cable structural dimension parameters r1 and r2 into Equation (7). By comparing the tanδ value with the judgment criteria (Equations (10) and (11)), the online monitoring of the cable insulation status can be completed.

[0148] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0149] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts 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, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0150] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0151] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0152] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for online monitoring of cable insulation dielectric loss factor, characterized by: The steps include: Step 1: Obtain the range of dielectric loss factor of cables with normal insulation performance; Step 2: Obtain the range of dielectric loss factors of cables with different degrees of degradation; Step 3: Based on the range of dielectric loss factor of cables with normal insulation performance and the range of dielectric loss factor of cables with different degrees of degradation, perform online monitoring of the dielectric loss factor of the cable insulation to obtain the insulation performance of the online cable; The step 1 comprises: Step 1.1, select a certain number of cables with normal insulation performance; Step 1.2: Measure the phase difference θ of the current at the beginning and end of all cables respectively; Step 1.3: Substitute the θ data corresponding to all cables into the dielectric loss factor formula to obtain the range of dielectric loss factor tanδ for normal cable insulation performance; The step 2 comprises: Step 2.1, select cables with different insulation degradation degrees and classify the cables into several insulation degradation degree grades; Step 2.2, measure the phase difference θ of the current at the beginning and end of all cables; Step 2.3: Substitute the θ data corresponding to all cables into the dielectric loss factor formula to determine the range of dielectric loss factor tanδ corresponding to different insulation degradation levels; The step 3 comprises: Step 3.1, measuring the phase difference θ between the current at the beginning and end of the running cable line, obtaining the running voltage U of the running cable, the amplitude I1 of the current at the beginning of the running cable, the length l of the running cable line, and the inner and outer radii r1 and r2 of the insulation of the running cable; Step 3.2: Calculate the dielectric loss factor of the operating cable according to the dielectric loss factor formula; Step 3.3: Compare the dielectric loss factor of the operating cable with the range of dielectric loss factor tanδ of the cable with normal insulation performance and the range of dielectric loss factor tanδ corresponding to different insulation degradation levels to determine whether the insulation performance of the operating cable is normal or belongs to a certain insulation degradation level; The dielectric loss factor formula is calculated as follows: Where, δ is the complex effective value of the capacitive current of the cable and The phase difference, is the effective value of the capacitive current of the cable and resistive current complex effective value The sum of ω is the circular frequency, C is the cable capacitance per unit length, π is the circumference ratio, and ε is the cable insulation dielectric constant.

2. The method for online monitoring of cable insulation dielectric loss factor according to claim 1, characterized in that: The method for obtaining the dielectric loss factor formula includes: Get the effective value of the current at the beginning of the cable The terminal current is effectively The effective value of the capacitive current of the cable and resistive current complex effective value Calculate the complex effective value of the capacitive current of the cable and resistive current complex effective value The sum of Get and The phase difference θ, and Phase difference A, and Phase difference B, and Phase difference δ; Restore the current to its effective value and The phase differences θ, A, B, and δ are marked on a complex plane coordinate system with the x-axis as the real axis and the y-axis as the imaginary axis; According to the sine theorem, we can get formula (1), which is as follows: Will Substituting into formula (1), we get formula (2): Among them, l C The calculation formula is as follows: Where l, r2 and r1 are the cable length, cable insulation outer radius and inner radius respectively, ε is the cable insulation dielectric constant, U is the cable voltage, ω is the circular frequency, C is the cable capacitance per unit length, and π is the circumference of the cable. Substituting formula (3) into formula (2), we get formula (4) as follows: According to formula (4), the expression of sinθ is as follows: It is known from common sense that the angle δ is the dielectric loss angle of the cable insulation. Converting formula (5) into the tangent formula of the cable insulation dielectric loss angle, the calculation formula is as follows: Simplifying formula (6) into the dielectric loss factor formula, the calculation formula is as follows:

3. An online monitoring system for cable insulation dielectric loss factor, characterized by: Includes the following modules: Normal range acquisition module: used to determine the range of dielectric loss factor of cables with normal insulation performance; Abnormal range acquisition module: used to analyze the range of dielectric loss factors of cables with different degrees of degradation; Online cable judgment module: used for online monitoring of cable insulation dielectric loss factor to obtain the insulation performance of online cables; The normal range acquisition module includes: Select a certain number of cables with normal insulation performance; Measure the phase difference θ of the current at the beginning and end of all cables respectively; Substitute the θ data corresponding to all cables into the dielectric loss factor formula to obtain the range of dielectric loss factor tanδ for normal cable insulation performance; The abnormal range acquisition module includes: Select cables with different insulation degradation degrees and classify the cables into several insulation degradation levels; Measure the phase difference θ of the current at the beginning and end of all cables; Substitute the θ data corresponding to all cables into the dielectric loss factor formula to determine the range of dielectric loss factor tanδ corresponding to different insulation degradation levels; The online cable judgment module includes: Measure the phase difference θ between the current at the beginning and end of the running cable line, and obtain the running voltage U of the running cable, the amplitude I1 of the current at the beginning of the running cable, the length l of the running cable line, and the inner and outer radii r1 and r2 of the insulation of the running cable; Calculate the dielectric loss factor of the running cable according to the dielectric loss factor formula; Compare the dielectric loss factor of the operating cable with the range of dielectric loss factor tanδ of the cable with normal insulation performance and the range of dielectric loss factor tanδ corresponding to different insulation degradation levels to determine whether the insulation performance of the operating cable is normal or belongs to a certain insulation degradation level; The dielectric loss factor formula is calculated as follows: Where, δ is the complex effective value of the capacitive current of the cable and The phase difference, is the effective value of the capacitive current of the cable and resistive current complex effective value The sum of ω is the circular frequency, C is the cable capacitance per unit length, π is the circumference ratio, and ε is the cable insulation dielectric constant.

4. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed by a processor, an online monitoring method for cable insulation dielectric loss factor as claimed in any one of claims 1 to 2 is implemented.

5. A computer device, characterized in that: include: a memory for storing instructions; The processor is configured to execute the instructions so that the computer device performs the operation of the online monitoring method for cable insulation dielectric loss factor as described in any one of claims 1-2.

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