Methods for locating insulation defects in high-voltage cables, computer equipment, and storage media.

Abstract

This application provides a method for locating insulation defects in high-voltage cables, a computer device, and a storage medium, relating to the field of power transmission and transformation technology. The method includes: step S101, setting the cable segment length. L 0, divide the high-voltage cable into n cable segments, n= L / L 0, L is the length of the high-voltage cable; Step S102, calculate the core voltage and sheath voltage of the insulation defect phase at the end of the i-th cable segment from the left end of the high-voltage cable; Step S103, calculate the core voltage and sheath voltage of the insulation defect phase at the end of the i-th cable segment from the right end of the high-voltage cable; Step S104, calculate the voltage difference at the end of the cable segment; Step S105, let i = i + 1, repeat steps S102 to S104 until i = n, obtain and store n-1 voltage differences at the ends of n cable segments; Step S106, determine the cable segment corresponding to the minimum value among the n-1 voltage differences as the defective cable segment.

Description

Technical Field

[0001] This application relates to the field of power transmission and transformation technology, and in particular to a method for locating insulation defects in high-voltage cables, a computer device, and a readable storage medium. Background Technology

[0002] In modern power systems, high-voltage cables are an important means of power transmission, and their safe and stable operation is crucial. Cable insulation defects are one of the main factors affecting the safe operation of cables. Once insulation defects occur, they will not only reduce the transmission efficiency of the cable, but may also lead to serious power accidents. Currently, widely used cable insulation defect location methods include: (1) Location method based on traveling wave ranging technology: using the traveling wave signal generated when the cable fault occurs, the location of the fault point is determined by measuring the propagation time of the traveling wave signal in the cable; (2) Location method based on time-frequency domain reflection method: using the time-frequency domain reflection method, the location of the cable defect is determined by sending a specific test signal and analyzing its reflection signal in the cable; (3) Location method based on broadband impedance spectrum analysis: by injecting a sweep frequency signal at the beginning and applying a windowed Fourier transform, the broadband impedance spectrum of the cable is analyzed, thereby realizing the accurate location and identification of weak cable defects; (4) Based on oscillating wave voltage detection method, etc. These methods are suitable for evaluating the overall condition of the cable and locating weak defects, and help to discover potential insulation problems in advance.

[0003] However, the above-mentioned methods for locating cable insulation defects have the following shortcomings: the signal energy is concentrated in the low-frequency range, while the energy in the high-frequency range is low, making it difficult to locate weak local defects in the cable; the detection results are affected by various factors, such as cable joints and metal pipes, which can cause pulse wave reflections, requiring inspectors to eliminate interference to determine the fault location, and long-term use has adverse effects on the cable; the investment cost is high, the manpower and material resources required are high, and it requires many professionals, and the cable must be in a de-energized state during the inspection, which may cause inconvenience to the area. Summary of the Invention

[0004] In view of this, this application provides a method for locating insulation defects in high-voltage cables, a computer device, and a readable storage medium.

[0005] In a first aspect, embodiments of this application provide a method for locating insulation defects in high-voltage cables, the method comprising:

[0006] Step S101: Set the cable segment length The high-voltage cable is divided into n cable segments, where n = L is the length of the high-voltage cable;

[0007] Step S102: Starting from the left end of the high-voltage cable, based on the real-time sampled core current and core voltage, and sheath current and sheath voltage of the metal sheath, theoretically derive and calculate the core voltage and sheath voltage of the insulation defect phase at the end of the i-th cable segment, i=1,2,3...n.

[0008] Step S103: Starting from the right end of the high-voltage cable, based on the real-time sampled core current and voltage, and sheath current and voltage of the metallic sheath, theoretically derive and calculate the... The conductor voltage and sheath voltage of the insulation defect phase at the end of each cable segment;

[0009] Step S104: Based on steps S102 and S103, draw two cable insulation defect location curves, and calculate the voltage difference at the end of the cable segment based on the two curves. The voltage difference = , Let be the difference between the core voltage and the sheath voltage at the end of the i-th cable segment. This is the difference between the core voltage and the sheath voltage at the end of the ni-th cable segment;

[0010] Step S105: Let i = i+1, repeat steps S102 to S104 until i = n, and obtain and store n-1 voltage differences at the ends of n cable segments.

[0011] Step S106: The cable segment corresponding to the minimum value among the n-1 voltage differences is identified as the defective cable segment with insulation defects.

[0012] The method described in the embodiments of this application may also have the following additional technical features:

[0013] Optionally, in the above technical solution, the method for determining the insulation defect phase includes:

[0014] At both ends of the high-voltage cable, the phase of the current and voltage in each of the three phases is measured;

[0015] The phase differences of each phase are compared, and the phase corresponding to the maximum value of the phase difference is taken as the insulation defect phase.

[0016] Optionally, in any of the above technical solutions, after step S101, the method further includes:

[0017] For each cable segment, a double π-type equivalent circuit is used for equivalence. The equivalent parameters include: the impedance of the three-phase cable cores of the cable segment, the impedance of the three-phase cable metal sheath of the cable segment, the mutual impedance between the layers of the cable segment, the equivalent capacitance between the core and the sheath of the cable segment, the equivalent capacitance between the sheath and the ground of the cable segment, the three-phase core voltage of the cable segment, the three-phase core current of the cable segment, the three-phase sheath voltage of the cable segment, and the three-phase sheath current of the cable segment.

[0018] Optionally, in any of the above technical solutions, the method further includes:

[0019] Electrical quantities are collected from the beginning and the end of the high-voltage cable. Both the beginning and end electrical quantities include conductor voltage, conductor current, sheath voltage, and sheath current. The beginning electrical quantities are used to calculate the conductor current and sheath current at the end of the i-th cable segment, and the end electrical quantities are used to calculate the... The conductor current and sheath current at the end of each cable segment;

[0020] The calculation of the core voltage and sheath voltage of the insulation defect phase at the end of the i-th cable segment includes:

[0021] Using Kirchhoff's voltage and current theorems, calculate the conductor current and sheath current at the end of the i-th cable segment, calculate the conductor voltage based on the conductor current at the end of the i-th cable segment, and calculate the sheath voltage based on the sheath current at the end of the i-th cable segment.

[0022] The calculation of the first The conductor voltage and sheath voltage of the insulation defect phase at the end of each cable segment include:

[0023] Using Kirchhoff's voltage and current theorems, calculate the first... The conductor current and sheath current at the end of each cable segment are based on the first... Calculate the core voltage based on the core current at the end of each cable segment, and based on the first... Calculate the sheath voltage based on the sheath current at the end of each cable segment.

[0024] Optionally, in any of the above technical solutions, the method further includes:

[0025] The sheath current is determined based on the grounding method of the cable's metal sheath.

[0026] Optionally, in any of the above technical solutions, the method further includes:

[0027] Determine whether the defect location accuracy meets the preset conditions;

[0028] If the defect location accuracy meets the preset conditions, then the output insulation defect location X = i × based on the defective cable segment. .

[0029] Optionally, in any of the above technical solutions, the method further includes:

[0030] If the defect location accuracy does not meet the preset conditions, then the cable segment length will be adjusted. Updated to The defective cable segment is divided into n' segments, where n' = , Given the length of the defective cable segment, and based on both sides of the defective cable segment, repeat steps S102 to S106.

[0031] Optionally, in any of the above technical solutions, the method further includes:

[0032] The factors affecting the location of insulation defects in high-voltage cables are analyzed, including at least one of the following: grounding method of the cable's metallic sheath, cable length, degree of defect, and load level.

[0033] In a second aspect, embodiments of this application provide a computer device including a processor and a memory, the memory storing programs or instructions that can run on the processor, the programs or instructions implementing the steps of the method as described in the first aspect when executed by the processor.

[0034] Thirdly, embodiments of this application provide a readable storage medium on which a program or instructions are stored, which, when executed by a processor, implement the steps of the method as described in the first aspect.

[0035] This application presents a method, computer device, and readable storage medium for locating high-voltage cable insulation defects. It proposes an insulation defect location scheme based on a double-π type equivalent circuit. Leveraging the continuity of voltage and combining it with the identified insulation defect phase, the method achieves accurate defect location determination through the measurement and calculation of voltage and current at both ends. This method does not require ensuring consistent energy of the injected signal at all frequencies, thus avoiding location difficulties caused by insufficient high-frequency signal energy. Even in cases of uneven signal energy distribution, algorithm optimization can improve location accuracy. Furthermore, since iterative calculations are performed only on the insulation defect phase, the computational load is significantly reduced, improving computational efficiency and reducing manpower consumption. The electrical quantities in this algorithm are readily available, resulting in low implementation costs.

[0036] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0037] 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:

[0038] Figure 1 A structural diagram of the cable equivalent model according to an embodiment of this application is shown;

[0039] Figure 2(a) shows a schematic diagram of the voltage error of phase A conductor in an embodiment of this application;

[0040] Figure 2(b) shows a schematic diagram of the voltage error of the A-phase sheath in an embodiment of this application;

[0041] Figure 2(c) shows a schematic diagram of the current error of phase A conductor in an embodiment of this application;

[0042] Figure 2(d) shows a schematic diagram of the current error of the A-phase sheath in an embodiment of this application;

[0043] Figure 3 A structural diagram of the equivalent model of cable insulation defects according to an embodiment of this application is shown;

[0044] Figure 4 A structural diagram of the cable insulation defect location model according to an embodiment of this application is shown;

[0045] Figure 5 A schematic diagram illustrating the location of cable insulation defects according to an embodiment of this application is shown;

[0046] Figure 6 A flowchart illustrating a method for locating insulation defects in high-voltage cables according to an embodiment of this application is shown.

[0047] Figure 7 An equivalent diagram of cable insulation degradation according to an embodiment of this application is shown;

[0048] Figure 8 A schematic diagram of the conductor current waveforms before and after an insulation defect occurs, according to an embodiment of this application, is shown.

[0049] Figure 9 The dertai-distance iteration curve of an embodiment of this application is shown;

[0050] Figure 10 A schematic diagram illustrating positioning errors for different cable lengths in embodiments of this application is shown;

[0051] Figure 11 A schematic diagram illustrating the location error of different degrees of insulation defects in embodiments of this application is shown. Detailed Implementation

[0052] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0053] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0054] The following description, in conjunction with the accompanying drawings, details the high-voltage cable insulation defect location method, computer equipment, and readable storage medium provided in this application through specific embodiments and application scenarios. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0055] In one embodiment of this application, a method for locating insulation defects in high-voltage cables is provided, comprising the following steps:

[0056] 1. Analysis of high-voltage cable insulation defect model and defect characteristics:

[0057] Establish a mathematical model for high-voltage cables: The equivalent model of a high-voltage cable under healthy conditions is as follows... Figure 1 The equivalent model of the cable is shown. Figure 1 The equivalent model of medium and high voltage cables divides a long high voltage cable of length L into several segments of length L. For each short cable segment, a double π-type equivalent circuit is used. , , These represent the impedances of the three-phase cable cores in this short segment. This refers to the first cross-section of the high-voltage cable. This is represented as the second cross-section of the high-voltage cable. This represents the third cross-section of the high-voltage cable. , , This indicates the impedance corresponding to the metal sheath of that short section of the three-phase cable. This is represented as the first segment of the metallic protective layer. This is represented as the second segment of the metallic protective layer. This is represented as the third segment of the metallic protective layer. This indicates the mutual impedance between different layers of the cable segment. This represents the equivalent capacitance between the cable core and the sheath in a cable segment. This represents the equivalent capacitance between the cable sheath and the ground for that cable section. , , These represent the voltages of the three-phase conductors in the i-th cable segment, respectively. , , These represent the current in the core of the i-th cable segment, respectively. , , These represent the sheath voltage of the i-th cable segment, , , These represent the sheath current of the i-th cable segment, respectively.

[0058] The electrical quantities at the beginning and end of the high-voltage cable are collected. Both the beginning and end electrical quantities include core voltage, core current, sheath voltage, and sheath current. Once the electrical quantities at the beginning and end of the high-voltage cable are known, such as... Figure 1 As shown, the length is obtained by using Kirchhoff's voltage and current theorems through the initial electrical quantities. The electrical quantities at the end of the first cable segment are shown below:

[0059] (1) The current in the conductor at the end of the first (first from the left) cable segment at the beginning ( , , )for:

[0060] Formula (1)

[0061] (2) Sheath current at the end of the first cable segment ( , , )for:

[0062] Formula (2)

[0063] In formula (2), , , The equivalent capacitance between the conductor and the sheath, and Let j be the equivalent capacitive reactance between the sheath and ground, where j is the imaginary unit. Then, calculate the core voltage and sheath voltage at the end of the first cable segment.

[0064] (3) The voltage of the conductor at the end of the first cable segment at the beginning ( , , ) is represented as:

[0065] Formula (3)

[0066] (4) Sheath voltage at the end of the first cable segment ( , , ) is represented as:

[0067] Formula (4)

[0068] From this, the voltage and current of the conductor and sheath at the end of the first cable segment can be calculated. These calculated electrical quantities are then used as the electrical quantities at the beginning of the second cable segment. Similarly, the electrical quantities at the end of the second cable segment can be calculated as follows:

[0069] (5) The current in the conductor at the end of the second cable segment at the beginning ( , , ):

[0070] Formula (5)

[0071] (6) Sheath current at the end of the second cable segment at the beginning ( , , ):

[0072] Formula (6)

[0073] (7) Then the voltage at the end of the i-th cable segment can be expressed as:

[0074] Formula (7)

[0075] (8) The core current and sheath current of the (i+1)th cable segment can be calculated from the end core and sheath voltage of the i-th cable segment:

[0076] Formula (8)

[0077] (9) Similarly, given the electrical quantities at the end, the core and sheath voltages of the i-th (i-th from the right end) cable segment at the end are:

[0078] Formula (9)

[0079] (10) The current in the conductor and sheath of the (i+1)th cable segment at the end is:

[0080] Formula (10)

[0081] Therefore, the voltage and current of the core and sheath at the end of any short cable segment can be calculated from the voltage and current of the core and sheath at the beginning and end of the cable.

[0082] This application can also perform equivalent model error analysis:

[0083] A reasonable cable equivalent model is the foundation for accurate location of insulation defects; therefore, this paper first analyzes the error between the cable equivalent model and the actual situation. Figure 1 The equivalent model of the cable was used to calculate the core voltage, current, sheath voltage, and current of the cable starting from 1km away from the power source. The calculation results were compared with the simulation software results using formula (11) for error analysis.

[0084] Formula (11)

[0085] Analysis shows that the electrical parameters of the three-phase cable are symmetrical when arranged in a triangular pattern. Therefore, phase A is used as an example for analysis, and the error results are shown in Figures 2(a) to 2(d). Analysis of the data in Figures 2(a) to 2(d) reveals that the error between the equivalent model and the simulation model is positively correlated with the cable length. The sheath current error is slightly larger, which is because the sheath current is significantly affected by electromagnetic induction. Specifically, the core voltage error is less than 0.006%, the core current error is less than 0.05%, the sheath voltage error is less than 0.01%, and the sheath current error is less than 0.7%, all less than 1%. The calculated model and the simulation model are approximately equivalent, and this model can be used to effectively locate insulation defects.

[0086] 2. Characteristic analysis of single-phase insulation defects in high-voltage cables:

[0087] The causes of main insulation defects can be internal or external to the cable. External causes can be broadly categorized into external force damage and environmental factors. Severe external force damage to the cable sheath or harsh environments can lead to corrosion of the sheath, resulting in abnormal grounding of the metallic sheath. This causes the sheath circulating current to remain abnormally high for extended periods, accelerating the aging of the main insulation and even directly damaging its performance. In more severe cases, external forces can directly damage the cable's main insulation. Internal causes can be broadly categorized into poor cable manufacturing processes and prolonged abnormal operation. During manufacturing, uneven conductor or insulation shield surfaces, and the presence of impurities or bubbles in the insulation can cause uneven local electric field strength, leading to partial discharge. In harsh environmental conditions, this can also cause water trees and electrical trees, which, over time, accumulate and form carbonized channels, severely affecting the cable's insulation performance. High-voltage cables often have large current-carrying capacities, strong cable structures, and relatively weak heat dissipation. When the current flowing through the conductor remains at the critical current-carrying capacity for a prolonged period, severe heating can damage the main insulation, reducing the cable's current-carrying capacity. Failure to address this promptly can lead to a vicious cycle.

[0088] At both ends of the cable, the current and voltage phases of each phase are measured. Due to insulation defects, the phase difference between the current and voltage of the defective phase may change. By comparing the phase differences of each phase, the phase with the largest phase difference is identified as the defective phase.

[0089] When a cable insulation defect occurs, the defective cable is equivalently represented by a π-type equivalent circuit. Taking a single-phase insulation defect as an example, assuming that the insulation of the p-th segment of the cable deteriorates, the equivalent model of the cable with the defective insulation is as follows: Figure 3 The equivalent model of cable insulation defects is shown.

[0090] like Figure 3 As shown, I ap I is the current flowing into the point of insulation degradation when the p-th cable segment experiences insulation degradation; xa1p When the insulation of the p-th cable segment deteriorates, the fault current flowing through the deteriorated section of the cable insulation, passing through the capacitance between the cable core and the metallic sheath; I xas I represents the current flowing into the ground through the ground capacitance in the metallic sheath when the insulation of the p-th cable segment deteriorates; f When the insulation of the p-th cable segment deteriorates, the fault current flows through the deteriorated section of the cable insulation, generating the fault resistance between the cable core and the metallic sheath; I s1p I is the current flowing through the metallic sheath into the area of ​​insulation degradation when the p-th segment of the cable experiences insulation deterioration; s1（n-p） This is the current flowing out of the point of insulation degradation in the metal sheath when the insulation of the p-th segment of the cable deteriorates.

[0091] Figure 3 middle and These represent the equivalent capacitance and equivalent resistance at the defect location, respectively, and the main insulation material of the cable under normal operating conditions. The relative permittivity is generally a reference value, such as that of cross-linked polyethylene. The relative permittivity is approximately 2.3. When insulation defects exist, the relative permittivity increases non-linearly to a certain saturation value as the defect severity increases. According to the capacitance calculation formula:

[0092] Formula (12)

[0093] In formula (12) The diameter of the cable core. Main insulation thickness, The relative permittivity of the insulation, The vacuum permittivity is the capacitance at the defect point increasing to a certain saturation value; under normal conditions... If considered as infinite, its value decreases non-linearly with increasing degree of insulation defects, eventually dropping to a certain finite value. That is, due to the deterioration of the insulating material, the dielectric constant of the insulating layer may increase, leading to an increase in the equivalent capacitance; conversely, the resistance of the insulating layer may decrease, leading to a decrease in the equivalent resistance.

[0094] According to Kirchhoff's current theorem, as the insulation defect deepens, the current I flowing through the defect increases. xa1p +I f Gradually increasing in size, at the defect location:

[0095] Formula (13)

[0096] Formula (14)

[0097] Formula (15)

[0098] In other words, insulation degradation occurred at point p, causing changes in the equivalent capacitance and resistance at that point. This results in inconsistent currents in the conductors and sheathing on the left and right sides of the defect at point p. Simultaneously, due to the continuity of the line voltage, the voltages on the left and right sides of point p should be equal. Insulation defects cause changes in electrical quantities at both ends, and a set of data can correspond to a specific defect condition. Based on this characteristic and the method described above for calculating electrical quantities of any segment from known electrical quantities at both ends, a correct insulation defect segment can be uniquely identified.

[0099] 3. Analysis of methods for locating insulation defects in high-voltage cables:

[0100] An equivalent model for insulation defects in high-voltage cables is used, dividing the high-voltage cable into sections of equal length. n= Each segment of cable is equivalent to a double-π model. The value determines the accuracy of defect location; the smaller the value, the higher the location accuracy but the greater the computational load, and vice versa. Since insulation defect identification has already detected the phase where the defect is located, only the phase with the insulation defect needs to be calculated during defect location, which greatly reduces the computational load and improves the speed of insulation defect location.

[0101] This method will be explained using a single-phase insulation defect as an example. Figure 4 The cable insulation defect location model is only an equivalent model of the defect phase. It assumes that the cable insulation deteriorates at point p, resulting in defects caused by… and Parallel insulation defects, This represents the equivalent impedance of phase A load, and there is also a corresponding... , The location of insulation defects can be determined based on the characteristic that when a defect exists in a KCL (Knowledge, Current, and Chance) segment, the currents on both sides of the defect segment are different, while the voltages are continuous and the same.

[0102] Given the voltage and current values ​​at the beginning or end of the cable, the voltage and current values ​​at the end of any cable segment can be calculated, and the following can be deduced. Figure 4 The voltage and current values ​​at point p of the insulation defect in phase A cable are given. It is assumed that the insulation defect occurs at the end of a cable segment of equal length. Due to differences in cable arrangement and the presence of the metal sheath, different phases of the same circuit are coupled to varying degrees. Therefore, the cable arrangement and metal sheath structure must be considered in the calculation. Cable arrangement methods include direct burial, cable trench laying, duct laying, overhead laying, tunnel laying, etc. Metal sheath structures include single-layer metal sheath, double-layer metal sheath, metal wire braided sheath, metal tape wrapped sheath, etc.

[0103] Different cable metal sheath grounding methods involve different electrical quantities in iterative calculations, which will cause differences in the contribution of sheath current to the node in the KCL equation of each cable end, resulting in different degrees of error in the calculation. Therefore, in this embodiment, the sheath current is determined based on the cable metal sheath grounding method. For example, under the single-end grounding method, no induced current loop can be formed in the sheath, only the ground capacitance current loop exists, and the sheath current flowing into the node is smaller than that under the same conditions for sheath-end grounding and cross-interconnection grounding methods; in long-distance lines, the cross-interconnection grounding method can weaken the magnitude of the sheath current due to sheath transposition, and the sheath current flowing into the node is smaller than that under the same conditions for double-end grounding. Here, the positioning results under different arrangement methods are compared. The total cable length is set to 4.5km, the arrangement is a triangular arrangement, the phase distance is 0.5m, the sheath grounding resistance is 1Ω, phase A has an insulation defect with tanδ of 0.06217 (1m), and the iteration step size is 1m. Table 1 shows the error of the insulation defect positioning results under different sheath grounding methods:

[0104] Table 1 Defect Location Error

[0105]

[0106] Under the premise that the laying method is constant, the main differences in cable arrangement lie in the grounding method of the metal sheath, the length of the grounding section, and the arrangement. In actual calculations, the electrical quantities of the conductor and sheath should be obtained from the starting point (substation) and then calculated up to the point where the defect exists based on the cable arrangement. This method is based on the assumption that the cable arrangement and metal sheath structure are the same, assuming the cable is horizontally arranged and the metal sheath grounding method remains unchanged. Then, according to the formula, the conductor voltage calculated from the left end to the defect p is... , , The sheath voltage is , , The current in the conductor is , , The sheath current is , , These electrical quantities are derived segment by segment from the electrical quantities at the beginning (left end) using formulas (1) to (8). Similarly, they can be derived from the electrical quantities at the end (right end) of the cable using formulas (9) and (10) to the defect location. The core voltage is , , The sheath voltage is , , The current in the conductor is , , The sheath current is , , Due to the continuity of voltage, the electrical quantities at both ends should be equal up to the cable core voltage at defect p, i.e.:

[0107] Formula (16)

[0108] If, during the iterative calculation, the defect is not on the cable segment being calculated, then the above equation does not hold. The above equation can be transformed to express:

[0109] Formula (17)

[0110] Formula (18)

[0111] Formula (19)

[0112] because The division of the cable segment does not always ensure that the insulation defect is at the end of each segment; it can also occur when the defect is in the middle of the segment. It is a non-zero value, at which point the electrical quantities at both ends are calculated up to the end of each small cable segment. The cable segment corresponding to the minimum value is the location of the defect. Figure 5 The schematic diagram of cable insulation defect location illustrates the method for locating insulation defects. Figure 5 The graph shows two curves: one representing the current and voltage distribution calculated from left to right based on the electrical quantities at the left end of the high-voltage cable, and the other representing the current and voltage distribution calculated from right to left based on the electrical quantities at the right end of the high-voltage cable. This graph illustrates the difference between the voltages at each point calculated iteratively from the electrical quantities at both ends to the opposite side. The smallest point is where the defect is located.

[0113] After calculating the segment where the insulation defect point is located, if the accuracy does not meet the requirements, n can be further increased, i.e., reduced. The relative error between the positioning result and the actual defect location must be within +1%. For example... Figure 6 As shown, the steps for implementing the insulation defect location method include:

[0114] Step S101: Set the cable segment length L0, and divide the high-voltage cable into n cable segments, n=L / L0, where L is the length of the high-voltage cable;

[0115] Step S102: Calculate the core voltage and sheath voltage of the insulation defect phase at the end of the i-th cable segment from the left end of the high-voltage cable, i=1,2,3...n;

[0116] Step S103: Calculate the core voltage and sheath voltage of the insulation defect phase at the end of the ni-th cable segment from the right end of the high-voltage cable.

[0117] Step S104: Calculate the voltage difference at the end of the cable segment, wherein the voltage difference = ΔV i -ΔV n-i ΔV i Let ΔV be the difference between the core voltage and the sheath voltage at the end of the i-th cable segment. n-i This is the difference between the core voltage and the sheath voltage at the end of the ni-th cable segment;

[0118] Step S105: Let i = i+1, repeat steps S102 to S104 until i = n, and obtain and store n-1 voltage differences at the ends of n cable segments.

[0119] Step S106: The cable segment corresponding to the minimum value among the n-1 voltage differences is identified as the defective cable segment with insulation defects.

[0120] In one embodiment of this application, after step S106, it is determined whether the defect positioning accuracy meets the preset conditions;

[0121] If the defect location accuracy meets the preset conditions, then based on the defective cable segment, the output insulation defect location X = i × ;

[0122] If the defect location accuracy does not meet the preset conditions, then the cable segment length will be adjusted. Updated to Divide the defective cable segment into n' segments, where n' = , Given the length of the defective cable segment, and based on both sides of the defective cable segment, repeat steps S102 to S106.

[0123] This application proposes an insulation defect location scheme based on a double-π type equivalent circuit. Leveraging the continuity of voltage and combining it with the identified insulation defect phase, the scheme achieves accurate defect location through measurement and calculation of the voltage and current at both ends. This method does not require ensuring consistent energy of the injected signal at all frequencies, thus avoiding location difficulties caused by insufficient high-frequency signal energy. Even in cases of uneven signal energy distribution, algorithm optimization can improve location accuracy. Furthermore, since iterative calculations are performed only on the insulation defect phase, the computational load is significantly reduced, improving computational efficiency and reducing manpower consumption. The electrical quantities in this algorithm are readily available, resulting in low implementation costs.

[0124] A specific simulation example of this application includes:

[0125] Cable layout method as follows Figure 7 The equivalent diagram of cable insulation degradation is shown. Assuming a 10m long insulation defect occurs in phase A, the main insulation defect exists on the cross-interconnection section of the cable sheath, at a distance of 1853m-1863m from the right end, with a tanδ of 0.083 and a main insulation resistance of... 3MΩ, capacitor The current is 0.0128 μF, and the current is as follows when the defect is present. Figure 8 The waveform diagram of the conductor current before and after the insulation defect is shown. After stabilization, the current amplitude has a slight change compared to the normal state. At this time, the insulation deterioration has caused the current of the conductor and sheath on both sides of the defect to be different, that is, the electrical quantity at both ends of the cable has changed compared to the normal state.

[0126] The insulation defect location method proposed in this application is used to locate the defect. First, the voltage and current values ​​of the conductor and sheath at the beginning and end of the cable are obtained through ATP-EMTP. The length of each small cable segment is then set. The calculation is performed every 50m. Using formulas (1) to (4), the electrical quantities at the end of the first small section of cable on the left are calculated from both the left and right ends. The voltage difference derta between the core voltage and the sheath voltage is then calculated and stored. This process is repeated iteratively until the rightmost small section of cable is reached. The 196 derta values ​​obtained are compared and plotted as shown below. Figure 9 The derta-distance iteration curve can accurately measure the existence of derta in the 159th segment (7950m from the left and 1850m from the right). min This is the small segment where the insulation defect is located. To improve the positioning accuracy, the search segment length should be reduced. By updating the electrical quantities at the beginning and end and repeating the above iteration process, the accuracy of insulation defect location can be further improved.

[0127] In one embodiment of this application, the factors affecting the location of insulation defects in high-voltage cables are analyzed. These factors include at least one of the following: the grounding method of the cable's metallic sheath, the cable length, the degree of defect, and the load level.

[0128] (1) Analyze the impact of the grounding method on the metal sheath of the cable:

[0129] The grounding method of the cable's metallic sheath is a crucial aspect in the selection of the layout. Different sheath grounding methods involve different electrical quantities in iterative calculations, leading to variations in the contribution of the sheath current to the node in the KCL equation for each cable segment, resulting in varying degrees of error in the calculations. For example, in a single-end grounding method, no induced current loop can be formed in the sheath, only a capacitance current loop to ground exists, and the sheath current flowing into the node is smaller compared to the sheath-end-grounding and cross-interconnected grounding methods under the same conditions. In long-distance lines, the cross-interconnected grounding method reduces the magnitude of the sheath current due to sheath transposition, resulting in a smaller sheath current flowing into the node compared to the double-end grounding method under the same conditions. This paper compares the location results under different layout methods, setting the total cable length to 4.5km, the arrangement to a triangular configuration, the phase-to-phase distance to 0.5m, the sheath grounding resistance to 1Ω, and the presence of an insulation defect (tanδ) of 0.06217 (1m) in phase A. The iteration step size is 1m. Table 1 shows the errors in the insulation defect location results under different sheath grounding methods.

[0130] Analysis of the data in Table 1 shows that this positioning method is applicable to different sheath grounding methods. Single-end grounding has higher accuracy. Under the premise of accurate positioning, two-end grounding is most affected by the sheath than other methods. Ignoring the sheath grounding method (i.e., neglecting the sheath structure) results in a large error and makes it impossible to locate insulation defects. Therefore, the sheath grounding method must be considered when calculating insulation defect positioning.

[0131] (2) Analyze the influence of cable length and defect location:

[0132] Based on the analysis of the impact of the cable arrangement, starting with an initial cable length of 2000m, the cable length is increased sequentially, using a triangular arrangement as the arrangement method, with a phase-to-phase distance of 0.5m and a sheath grounding resistance of 1Ω. Phase A has an insulation defect with a tanδ of 0.06217 (1m) at locations 500m, 1000m, and 1500m from the initial point. The iteration step size is 1m. The defect location error is calculated for different cable lengths. Analysis Figure 10 As can be seen from the positioning errors of different cable lengths, the percentage of insulation defect positioning error changes very little with the increase of cable length and can be approximately ignored. The positioning error at the middle position of the cable is larger than that at the closer positions to the ends. The error percentages are all much less than 0.5%, which is at a low level. This method is not affected by the cable length and defect position and can accurately locate any defect position of any cable of any length.

[0133] (3) Influence of insulation defect degree:

[0134] Different degrees of cable insulation defects have varying effects on electrical quantities at both ends. The total cable length is 5km, the phase-to-phase distance is 0.25m, the sheath grounding resistance is 1Ω, and in a triangular arrangement, when the sheath is grounded at both ends, the defect location of phase A is set every 1000m, 500m from the beginning. The degree of insulation defect (1m) is shown in Table 2.

[0135] Table 2 Insulation Defect Level

[0136]

[0137] The electrical quantities at both ends of the device were measured under different degrees of defects. The iteration step size was set to 1m. The location error caused by the changes in the insulation equivalent resistance R and capacitance C was calculated using the defect location method. Figure 11 The positioning error for different degrees of insulation defects is shown to be within 1% as tanδ increases. The accuracy increases slightly with the degree of deterioration. This method is more adaptable to insulation defects in cables with a high degree of deterioration. For insulation defects in the early stage of deterioration, since the change in electrical charge at both ends is not obvious, the positioning can be roughly located by expanding the search segment length L0.

[0138] (4) Analyze the impact of load level:

[0139] The total cable length is set to 5km, the cable is arranged in a triangular pattern, the phase spacing is 0.25m, the sheath grounding resistance is 1Ω, the power supply phase angle differences are 15°, 30°, and 45°, phase A has an insulation defect with tanδ of 0.06217 (1m), and the iteration step size is 1m. The location results under different load changes are calculated and shown in Table 3.

[0140] Table 3 Location results under different loads

[0141]

[0142] As shown in Table 3, the positioning error increases slightly with the increase of load level, but it is still at a low level. The error is slightly larger for defects farther from the end than for defects closer to the end. The error at the middle of the cable is less than 1%. Therefore, the positioning method is only slightly affected by the load level and can accurately locate defects under both light and heavy loads.

[0143] This application analyzes the influence of cable arrangement, cable length, defect severity, and load level on positioning accuracy. The results show that the method is not affected by cable length or defect location, and the maximum error does not exceed 1% under different arrangement methods, demonstrating good positioning accuracy and providing important reference for practical applications.

[0144] This application also provides a computer device, which includes a processor and a memory. The memory stores a program or instructions that can be run on the processor. When the program or instructions are executed by the processor, they implement the various steps of the above-described method for locating insulation defects in high-voltage cables and achieve the same technical effect. To avoid repetition, they will not be described again here.

[0145] Memory can be used to store software programs and various data. Memory can primarily include a first storage area for storing programs or instructions and a second storage area for storing data. The first storage area can store the operating system, application programs or instructions required for at least one function (such as sound playback, image playback, etc.). Furthermore, memory can include volatile memory or non-volatile memory, or both. Non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. Volatile memory can be random access memory (RAM), static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDRSDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous linked dynamic random access memory (Synchlink DRAM, SLDRAM), and direct memory bus RAM (DRRAM). The memory in the embodiments of this application includes, but is not limited to, these and any other suitable types of memory.

[0146] The processor may include one or more processing units; optionally, the processor integrates an application processor and a modem processor, wherein the application processor mainly handles operations related to the operating system, user interface, and applications, while the modem processor mainly handles wireless communication signals, such as a baseband processor. It is understood that the aforementioned modem processor may also not be integrated into the processor.

[0147] This application also provides a readable storage medium storing a program or instructions. When the program or instructions are executed by a processor, they implement the various processes of the above-described high-voltage cable insulation defect location method embodiment and achieve the same technical effect. To avoid repetition, they will not be described again here.

[0148] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0149] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A method for locating insulation defects in high-voltage cables, characterized in that, The method includes: Step S101: Set the cable segment length The high-voltage cable is divided into n cable segments, where n = L is the length of the high-voltage cable; Step S102: Starting from the left end of the high-voltage cable, based on the real-time sampled core current value of the left end cable, and using the cable equivalent model, theoretically derive and calculate the core voltage and sheath voltage of the insulation defect phase at the end of the i-th cable segment, i=1,2,3...n. Step S103: Starting from the right end of the high-voltage cable, based on the real-time sampled current value of the right-end cable core, and using the cable equivalent model, theoretically derive and calculate the... The conductor voltage and sheath voltage of the insulation defect phase at the end of each cable segment; Step S104: Based on steps S102 and S103, draw two cable insulation defect location curves, and calculate the voltage difference at the end of the cable segment based on the two curves. The voltage difference = , Let be the difference between the core voltage and the sheath voltage at the end of the i-th cable segment. This is the difference between the core voltage and the sheath voltage at the end of the ni-th cable segment; Step S105: Let i = i+1, repeat steps S102 to S104 until i = n, and obtain and store n-1 voltage differences at the ends of n cable segments. Step S106: The cable segment corresponding to the minimum value among the n-1 voltage differences is identified as the defective cable segment with insulation defects; The method further includes: Determine whether the defect location accuracy meets the preset conditions; If the defect location accuracy meets the preset conditions, then the output insulation defect location X = i × based on the defective cable segment. ; If the defect location accuracy does not meet the preset conditions, then the cable segment length will be adjusted. Updated to The defective cable segment is divided into n' segments, where n' = , Given the length of the defective cable segment, and based on both sides of the defective cable segment, repeat steps S102 to S106.

2. The method according to claim 1, characterized in that, The methods for determining the insulation defect phase include: At both ends of the high-voltage cable, the phase of the current and voltage in each of the three phases is measured; The phase differences of each phase are compared, and the phase corresponding to the maximum value of the phase difference is taken as the insulation defect phase.

3. The method according to claim 1, characterized in that, After step S101, the method further includes: For each cable segment, a double π-type equivalent circuit is used for equivalence. The equivalent parameters include: the impedance of the three-phase cable cores of the cable segment, the impedance of the three-phase cable metal sheath of the cable segment, the mutual impedance between the layers of the cable segment, the equivalent capacitance between the core and the sheath of the cable segment, the equivalent capacitance between the sheath and the ground of the cable segment, the three-phase core voltage of the cable segment, the three-phase core current of the cable segment, the three-phase sheath voltage of the cable segment, and the three-phase sheath current of the cable segment.

4. The method according to claim 3, characterized in that, The method further includes: Electrical quantities are collected from the beginning and the end of the high-voltage cable. Both the beginning and end electrical quantities include conductor voltage, conductor current, sheath voltage, and sheath current. The beginning electrical quantities are used to calculate the conductor current and sheath current at the end of the i-th cable segment, and the end electrical quantities are used to calculate the... The conductor current and sheath current at the end of each cable segment; The calculation of the core voltage and sheath voltage of the insulation defect phase at the end of the i-th cable segment includes: Using Kirchhoff's voltage and current theorems, calculate the conductor current and sheath current at the end of the i-th cable segment, calculate the conductor voltage based on the conductor current at the end of the i-th cable segment, and calculate the sheath voltage based on the sheath current at the end of the i-th cable segment. The calculation of the first The conductor voltage and sheath voltage of the insulation defect phase at the end of each cable segment include: Using Kirchhoff's voltage and current theorems, calculate the first... The conductor current and sheath current at the end of each cable segment are based on the first... Calculate the core voltage based on the core current at the end of each cable segment, and based on the first... Calculate the sheath voltage based on the sheath current at the end of each cable segment.

5. The method according to claim 4, characterized in that, The method further includes: The sheath current is determined based on the grounding method of the cable's metal sheath.

6. The method according to claim 1, characterized in that, The method further includes: The factors affecting the location of insulation defects in high-voltage cables are analyzed, including at least one of the following: grounding method of the cable's metallic sheath, cable length, degree of defect, and load level.

7. A computer device, characterized in that, It includes a processor and a memory, the memory storing a program or instructions that run on the processor, the program or instructions being executed by the processor to implement the steps of the method for locating high-voltage cable insulation defects as described in any one of claims 1 to 6.

8. A readable storage medium having a program or instructions stored thereon, characterized in that, When the program or instructions are executed by the processor, they implement the steps of the method for locating high-voltage cable insulation defects as described in any one of claims 1 to 6.

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