High-voltage cable insulation defect positioning method, computer equipment and storage medium

Abstract

The invention provides a high-voltage cable insulation defect positioning method, computer equipment and a storage medium, and relates to the technical field of power transmission and transformation. The method comprises the steps that S101, the length L0 of a cable section is set, the high-voltage cable is divided into n cable sections, n = L / L0, and L is the length of the high-voltage cable; s102, calculating the wire core voltage and the sheath voltage of the insulation defect phase at the tail end of the ith cable section from the left end of the high-voltage cable; s103, calculating the wire core voltage and the sheath voltage of the insulation defect phase at the tail end of the # imgabs0 # cable section from the right end of the high-voltage cable; s104, calculating a voltage difference value of the tail end of the cable section; step S105, enabling i to be equal to i + 1, repeating the steps S102 to S104 until i is equal to n, and obtaining and storing the voltage difference values of the tail ends of the n cable sections; and S106, determining the cable section corresponding to the minimum value in the n voltage difference values as a defective cable section.

Description

Technical Field

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

[0002] In modern power systems, high-voltage cables are an important means of power transmission, and their safe and stable operation is of vital importance. Cable insulation defects are one of the main factors affecting the safe operation of cables. Once insulation defects occur, it will not only reduce the transmission efficiency of the cable, but may also cause serious power accidents. The cable insulation defect location methods currently widely used 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 time-frequency domain reflection method, by sending a specific test signal and analyzing its reflected signal in the cable, the location of the cable defect is determined; (3) Location method based on broadband impedance spectrum analysis: by injecting a sweep signal at the beginning and performing a windowed Fourier transform, the broadband impedance spectrum of the cable is analyzed, thereby achieving accurate location and identification of weak defects in the cable; (4) Based on oscillation wave voltage detection method, etc. It is suitable for evaluating the overall status of the cable and locating weak defects, which helps to discover potential insulation problems in advance.

[0003] However, the above-mentioned method for locating cable insulation defects has the following shortcomings: the signal energy is concentrated in the low-frequency segment, and the energy in the high-frequency segment is low, making it difficult to locate weak local defects in the cable; the detection results are affected by many factors, such as cable joints, metal pipes, etc., which will cause pulse wave reflections, and the inspection personnel need 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 consumed are high, and more professionals are required. The cable needs to be in an unpowered state during the inspection, which may cause inconvenience to the area. Summary of the Invention

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

[0005] In a first aspect, an embodiment of the present application provides a method for locating insulation defects in a high-voltage cable, the method comprising: Step S101, setting the cable segment length , divide the high voltage cable into n cable segments, n= , L is the length of the high-voltage cable; Step S102: From the left end of the high-voltage cable, the core voltage and sheath voltage of the insulation defect phase at the end of the i-th cable segment are theoretically derived and calculated based on the real-time sampled left-end cable core current and core voltage, and the sheath current and sheath voltage of the metal sheath, where i = 1, 2, 3, ..., n. Step S103, from the right end of the high-voltage cable, according to the real-time sampling of the right end cable core current and core voltage, the sheath current and sheath voltage of the metal sheath, theoretically derive and calculate the first The core voltage and sheath voltage of the insulation defect phase at the end of each cable segment; Step S104: Draw two cable insulation defect location curves according to step S102 and step S103, and calculate the voltage difference at the end of the cable segment based on the two curves. The voltage difference = , is the difference between the core voltage and the sheath voltage at the end of the i-th cable segment, 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 the voltage differences at the ends of n cable segments; Step S106: Determine the cable segment corresponding to the minimum value among the n voltage differences as a defective cable segment having insulation defects.

[0006] The above method according to the embodiment of the present application may also have the following additional technical features: In the above technical solution, optionally, the method of determining the insulation defect phase includes: At both ends of the high-voltage cable, measuring the phase of the current and voltage of each of the three phases; The phase differences of the phases are compared, and the phase corresponding to the maximum value of the phase difference is taken as the insulation defect phase.

[0007] In any of the above technical solutions, optionally, after step S101, the method further includes: For each cable segment, a double-π type equivalent circuit is used for equivalent performance. The equivalent parameters include: the corresponding impedance of the three-phase cable core of the cable segment, the corresponding 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 earth 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.

[0008] In any of the above technical solutions, optionally, the method further includes: The starting electrical quantity is collected from the starting end of the high-voltage cable, and the terminal electrical quantity is collected from the terminal of the high-voltage cable. The starting electrical quantity and the terminal electrical quantity both include the core voltage, core current, sheath voltage and sheath current; the starting electrical quantity is used to calculate the core current and sheath current at the end of the i-th cable segment, and the terminal electrical quantity is used to calculate the i-th cable segment. The core 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 theorem, calculate the core current and sheath current at the end of the i-th cable segment, calculate the core voltage based on the core 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 The core voltage and sheath voltage of the insulation defect phase at the end of each cable segment, including: Using Kirchhoff's voltage and current theorem, calculate The core current and sheath current at the end of the first cable segment are based on the The core voltage is calculated based on the core current at the end of the first cable segment, and the The sheath voltage is calculated from the sheath current at the end of each cable segment.

[0009] In any of the above technical solutions, optionally, the method further includes: The sheath current is determined based on the grounding method of the cable metal sheath.

[0010] In any of the above technical solutions, optionally, the method further includes: Determine whether the defect positioning accuracy meets the preset conditions; If the defect location accuracy meets the preset conditions, the insulation defect position X=i× .

[0011] In any of the above technical solutions, optionally, the method further includes: If the defect location accuracy does not meet the preset conditions, the cable segment length Updated to , divide the defective cable segment into n' segments, n'= , is the length of the defective cable segment, and steps S102 to S106 are repeated based on both sides of the defective cable segment.

[0012] In any of the above technical solutions, optionally, the method further includes: Factors influencing the insulation defect location results of the high-voltage cable are analyzed, wherein the factors include at least one of the following: cable metal sheath grounding method, cable length, defect degree, and load level.

[0013] In a second aspect, an embodiment of the present application provides a computer device comprising a processor and a memory, wherein the memory stores programs or instructions that can be run on the processor, and when the programs or instructions are executed by the processor, the steps of the method of the first aspect are implemented.

[0014] In a third aspect, an embodiment of the present application provides a readable storage medium, which stores a program or instruction. When the program or instruction is executed by a processor, the steps of the method of the first aspect are implemented.

[0015] The method for locating insulation defects in high-voltage cables, computer equipment, and readable storage media of the embodiments of the present application propose an insulation defect locating scheme based on a double-π-type equivalent circuit. Based on the characteristic of voltage continuity, combined with the insulation defect phase identified by the insulation defect, the defect position is accurately determined by measuring and calculating the voltage and current at both ends. This method does not need to ensure that the energy of the injected signal at each frequency point is consistent, thereby avoiding the positioning difficulty caused by insufficient high-frequency signal energy. Even in the case of uneven signal energy distribution, the positioning accuracy can be improved through algorithm optimization. In addition, since only the insulation defect phase is iteratively calculated, the amount of calculation is greatly reduced, the efficiency of the calculation is improved, and the consumption of manpower is reduced. The electrical quantity of this algorithm is easy to obtain, and the implementation cost is low.

[0016] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 A structural diagram of a cable equivalent model according to an embodiment of the present application is shown; FIG2( a ) is a schematic diagram showing a voltage error of a phase A core line according to an embodiment of the present application; FIG2( b ) shows a schematic diagram of the voltage error of the A-phase sheath in an embodiment of the present application; FIG2( c ) shows a schematic diagram of the current error of the phase A core in an embodiment of the present application; FIG2( d ) shows a schematic diagram of the current error of the A-phase sheath in an embodiment of the present application; Figure 3 A structural diagram of a cable insulation defect equivalent model according to an embodiment of the present application is shown; Figure 4 A structural diagram of a cable insulation defect location model according to an embodiment of the present application is shown; Figure 5 A schematic diagram showing the location of cable insulation defects according to an embodiment of the present application is shown; Figure 6 A schematic diagram showing a flow chart of a method for locating insulation defects of a high-voltage cable according to an embodiment of the present application is shown; Figure 7 An equivalent diagram of cable insulation degradation according to an embodiment of the present application is shown; Figure 8 A schematic diagram showing the core current waveform before and after the insulation defect occurs in an embodiment of the present application; Figure 9 shows a dertai-distance iteration curve diagram of an embodiment of the present application; Figure 10 A schematic diagram showing positioning errors of different cable lengths according to an embodiment of the present application is shown; Figure 11 A schematic diagram showing positioning errors of different insulation defect degrees according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0018] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.

[0019] The terms "first," "second," and the like in the specification and claims of this application are used to distinguish similar objects, and are not used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of this application can be implemented in an order other than that illustrated or described herein, and that the objects distinguished by "first," "second," and the like are generally of the same type, and do not limit the number of objects; for example, the first object can be one or more. In addition, the term "and / or" in the specification and claims refers to at least one of the connected objects, and the character " / " generally indicates that the objects connected are in an "or" relationship.

[0020] Below, in conjunction with the accompanying drawings, the high-voltage cable insulation defect positioning method, computer equipment and readable storage medium provided in the embodiments of the present application are described in detail through specific embodiments and their application scenarios. Unless there is a conflict, the following embodiments and features in the embodiments can be combined with each other.

[0021] In one embodiment of the present application, a method for locating insulation defects of a high-voltage cable is provided, comprising the following steps: 1. Analysis of high-voltage cable insulation defect model and defect characteristics: Establish a mathematical model of high-voltage cables: The equivalent model of high-voltage cables in healthy conditions is as follows: Figure 1 The cable equivalent model is shown in Figure 4. Figure 1 The equivalent model of medium and high voltage cables divides the entire high voltage cable of length L into several sections of length Each cable segment is equivalent to a double π type equivalent circuit. 、 、 They represent the impedance corresponding to the core of the small three-phase cable. Indicates the first section of the high voltage cable, Indicates the second section of the high voltage cable, Represents the third section of the high voltage cable, 、 、 It specifically indicates the impedance of the metal sheath of this short section of three-phase cable. Indicates the first segment of the metal sheath, Represents the second segment of the metal sheath, Represents the third segment of the metal sheath. Indicates the mutual impedance between layers of the cable segment, Indicates the equivalent capacitance between the cable core and the sheath. Indicates the equivalent capacitance between the sheath of the cable segment and the earth. 、 、 Represent the three-phase core voltage of the i-th cable segment, 、 、 They represent the core current of the i-th cable segment, 、 、 They represent the sheath voltage of the i-th cable segment, 、 、 They represent the sheath current of the i-th cable segment respectively.

[0022] Collect the electrical quantities of the high-voltage cable at the beginning and end. The electrical quantities at the beginning and end include the core voltage, core current, sheath voltage and sheath current. Figure 1 As shown, using Kirchhoff's voltage and current theorem, the length is obtained by the electrical quantity at the starting end. The electrical quantities at the end of the first cable segment are as follows: (1) The core current at the end of the first cable segment (the first one from the left end) at the starting point ( , , )for: Formula (1) (2) Sheath current at the end of the first cable segment at the starting point ( , , )for: Formula (2) In formula (2), , , is the equivalent capacitive reactance between the core and the sheath, and is the equivalent capacitive reactance between the sheath and the earth, and j is an imaginary unit. Then calculate the core voltage and sheath voltage at the end of the first cable segment.

[0023] (3) The core voltage at the end of the first cable segment at the starting point ( , , ) is expressed as: Formula (3) (4) Sheath voltage at the end of the first cable segment at the starting point ( 、 、 ) is expressed as: Formula (4) The voltage and current of the core and sheath at the end of the first cable segment can be calculated, and these calculated electrical quantities are 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: (5) Core current at the end of the second cable segment at the starting point ( , , ): Formula (5) (6) Sheath current at the end of the second cable segment at the starting point ( , , ): Formula (6) (7) Then the terminal voltage of the i-th cable segment can be expressed as: Formula (7) (8) The core current and sheath current of the (i+1)th cable segment can be calculated from the core and sheath voltages at the end of the i-th cable segment: Formula (8) (9) Similarly, given the end electrical quantities, the core and sheath voltages of the i-th (i-th from the right) cable segment at the end are: Formula (9) (10) The core and sheath currents of the (i+1)th cable segment at the end are: Formula (10) At this point, the voltage and current of the core and sheath of the starting and ending cables can be used to calculate the voltage and current of the core and sheath at the end of any small cable segment.

[0024] This application can also perform equivalent model error analysis: A reasonable cable equivalent model is the basis for accurate positioning of insulation defects, so the error between the cable equivalent model in this paper and the actual situation is analyzed first. Figure 1 The cable equivalent model is calculated starting from 1 km from the power supply side. The core voltage, current, sheath voltage and current of the cable are calculated every 1 km. The calculation results and the simulation software calculation results are analyzed using formula (11) for error: Formula (11) Analysis shows that the electrical parameters of the three-phase cable are symmetrical when arranged in a herringbone 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) shows that the error between the equivalent model and the simulation model is positively correlated with cable length, with the sheath current error being slightly larger due to the significant influence of electromagnetic induction on the sheath current. 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 of which are less than 1%. The calculated model and the simulation model are approximately equivalent, and this model can be used to effectively locate insulation defects.

[0025] 2. Analysis of single-phase insulation defect characteristics of high-voltage cables: Primary insulation defects can be caused by both internal and external factors. Externally, the contributing factors can be broadly categorized as external damage and environmental factors. Severe external damage to the cable's outer sheath or harsh environments can lead to sheath corrosion, resulting in abnormal grounding of the cable's metallic sheath. This, in turn, can result in abnormally high sheath currents for extended periods, accelerating primary insulation aging and even directly damaging the insulation. Even worse, external influences can directly damage the cable's primary insulation. Internally, the contributing factors can be poor manufacturing processes and prolonged abnormal operation. During manufacturing, the surface of the conductor or insulation shield is rough, and the presence of impurities and bubbles in the insulation can cause localized field inhomogeneities, triggering partial discharge. Harsh environmental conditions can also lead to phenomena like water and electrical treeing. Long-term accumulation creates carbonized channels, severely impacting the cable's insulation performance. High-voltage cables often have high current carrying capacity, are highly airtight, and have relatively poor heat dissipation. When the current flowing through the core conductor remains at the critical current carrying capacity for extended periods, severe heat generation can damage the cable's primary insulation and reduce its current-carrying capacity. If not addressed promptly, this can trigger a vicious cycle.

[0026] At both ends of the cable, measure the current and voltage phases of each phase. Due to insulation defects, the current and voltage phase differences of the defective phase may vary. Compare the phase differences of each phase and identify the phase with the largest phase difference, which is the defective phase.

[0027] When a cable insulation defect occurs, the defective cable is equivalently treated by combining a π-type equivalent circuit. Taking a single-phase insulation defect as an example, assuming that the insulation of the p-th small section of cable deteriorates, the insulation defect phase cable equivalent model is Figure 3 The equivalent model of cable insulation defects is shown in Figure 4.

[0028] like Figure 3 As shown, I ap I is the current flowing into the insulation deterioration point of the cable when the insulation deterioration occurs in the pth cable segment; xa1p I is the fault current that flows through the insulation degradation point of the cable and the capacitance between the cable core and the metal sheath when the insulation degradation occurs in the pth cable segment; xas I is the current flowing into the earth through the ground capacitance in the metal sheath when the insulation of the pth cable segment deteriorates; f I is the fault current generated by the fault resistance between the cable core and the metal sheath when the insulation of the pth cable section deteriorates. s1p I is the current flowing into the insulation degradation point of the cable in the metal sheath when the insulation degradation occurs in the pth cable segment; s1（n-p） It is the current flowing out of the metal sheath at the point where the insulation of the pth cable section deteriorates.

[0029] Figure 3 middle and They represent the equivalent capacitance and equivalent resistance of the defect, respectively, and the main insulation material of the cable under normal working conditions. The relative dielectric constant is generally a reference value, such as cross-linked polyethylene The relative dielectric constant is about 2.3. When there is an insulation defect, as the degree of the defect deepens, the relative dielectric constant value increases nonlinearly to a certain saturation value. According to the capacitance calculation formula: Formula (12) In formula (12) is the cable core diameter, is the main insulation thickness, is the relative dielectric constant of insulation, is the vacuum dielectric constant, that is, the capacitance at the defect increases to a certain saturation value; under normal conditions It is considered infinite. When insulation defects are present, its value decreases nonlinearly as the degree of the insulation defect increases, decreasing to a finite value. In other words, due to the degradation of the insulation material, the dielectric constant of the insulation layer may increase, resulting in an increase in the equivalent capacitance; due to the degradation of the insulation material, the resistance of the insulation layer may decrease, resulting in a decrease in the equivalent resistance.

[0030] According to Kirchhoff's current theorem, as the insulation defect deepens, the current I flowing through the defect xa1p +I f Gradually increases, at the defect there are: Formula (13) Formula (14) Formula (15) In other words, insulation degradation has occurred at point p, causing changes in the equivalent capacitance and resistance there. This, in turn, results in inconsistencies in the core and sheath currents on the left and right sides of the defective point p. At the same time, due to line voltage continuity, the voltages on both sides of point p should be equal. Insulation defects cause changes in electrical quantities at both ends, and one set of data corresponds to a single defect. Based on this characteristic and the aforementioned method for calculating electrical quantities for any segment given the electrical quantities at both ends, a correct insulation defect segment can be uniquely identified.

[0031] 3. Analysis of high-voltage cable insulation defect location method: The equivalent model of high-voltage cable insulation defects is to divide the high-voltage cable into equal parts of length n= Each small section of cable is equivalent to a double π model. Determines the accuracy of defect location. Smaller values indicate higher accuracy, but a greater computational effort. Conversely, lower accuracy results in a smaller computational effort. Since insulation defect identification has already detected the defect phase, defect location only requires calculations for the insulation defect phase, significantly reducing the computational effort and increasing the speed of insulation defect location.

[0032] This method is explained by taking single-phase insulation defect as an example. Figure 4 The cable insulation defect location model is only a defect phase equivalent model. Assuming that the cable insulation at point p deteriorates, the defect is generated by and Insulation defects in parallel, Indicates the equivalent impedance of phase A load, and the corresponding 、 According to the KCL, when there is a defect, the current on both sides of the defect section is different, while the voltage is continuous and the same, to determine the insulation defect.

[0033] If the voltage and current values at the beginning or end of the cable are known, the voltage and current values at the end of any cable section can be calculated. Figure 4 The voltage and current values of the insulation defect section at point p of phase A cable are assumed to occur at the end of a small section of cable divided into equal lengths. Due to the differences in cable layout and the presence of metal sheaths, cables of each phase in the same circuit produce different degrees of coupling. Therefore, the cable layout and metal sheath structure need to be considered in the calculation. Cable layout methods include direct burial, cable trench, conduit, overhead, and tunnel. Metal sheath structures include single-layer metal sheath, double-layer metal sheath, metal wire braided sheath, and metal tape wrapped sheath.

[0034] Different cable metal sheath grounding methods require different electrical quantities in the iterative calculation, which will cause differences in the degree of contribution of the sheath current to the node in the KCL equation of the sheath at the end of each cable segment, resulting in different degrees of error in the calculation. Therefore, in the embodiment of the present application, the sheath current is determined based on the cable metal sheath grounding method. For example, under the single-end grounding method, no inductive current loop can be formed in the sheath, and only a capacitance current loop to the ground exists. The sheath current flowing into the node is smaller than that under the sheath two-end grounding and cross-interconnected grounding methods under the same conditions; in long-distance lines, the cross-interconnected grounding method can weaken the sheath current due to the sheath transposition, and the sheath current flowing into the node is smaller than that under the double-end grounding method under the same conditions. Here, the positioning results under different layout methods are compared. The total cable length is set to 4.5km, the arrangement method is a herringbone arrangement, the phase distance is 0.5m, the sheath grounding resistance is 1Ω, and there is an insulation defect of tanδ of 0.06217 (1m) in phase A. The iterative step size is 1m. Table 1 shows the insulation defect positioning result errors under different sheath grounding methods: Table 1 Defect location error

[0035] The layout method, under the premise of a constant laying method, mainly manifests itself in the difference in the grounding method of the metal sheath, the length of the grounding section, and the arrangement method. In actual calculation, the electrical values of the core and sheath should be obtained from the head end (substation) and then calculated according to the cable layout to the section where the defect exists. This method is based on the same layout method and metal sheath structure. Assuming that the cable is arranged horizontally and the metal sheath grounding method does not change, the left end is the starting end, and the core voltage calculated to the defect p is 、 、 , the sheath voltage is 、 、 , the core current is 、 、 , the sheath current is 、 、 This electrical quantity is deduced step by step from the electrical quantity at the head end (left end) by formula (1) to formula (8). Similarly, the electrical quantity at the end (right end) of the cable can be deduced to the defect by formula (9) and formula (10). The core voltage is 、 、 , the sheath voltage is 、 、 , the core current is 、 、 , the sheath current is 、 、 Due to the continuity of voltage, the electrical quantities at both ends should be equal to the cable core voltage at the defect p, that is: Formula (16) If the defect is not on the cable segment during the iterative calculation, the above formula does not hold. The above formula can be transformed into: Formula (17) Formula (18) Formula (19) because The division cannot always ensure that the insulation defect is at the end of each small cable segment. When the defect is in the middle of the small cable segment, Is a non-zero value, at this time the electrical quantities at both ends are calculated to the end of each small cable segment The small cable segment corresponding to the minimum value is the defective part. Figure 5 The cable insulation defect location diagram is a schematic diagram of the insulation defect location method. Figure 5 The two curves in the figure show the distribution curve of current and voltage calculated from left to right based on the electrical quantity at the left end of the high-voltage cable, and the other shows the distribution curve of current and voltage calculated from right to left based on the electrical quantity at the right end of the high-voltage cable. The figure shows the difference between the voltages at each point calculated by iteratively calculating the electrical quantities at both ends to the opposite side. The smallest point is where the defect is located.

[0036] After calculating the segment where the insulation defect point is located, if the accuracy does not meet the requirements, n can be further expanded, that is, reduced The relative error between the positioning result and the actual defect position requires the positioning accuracy to be within +1%. Figure 6 As shown, the insulation defect location method includes the following steps: Step S101, setting the cable segment length L0, dividing the high-voltage cable into n cable segments, n=L / L0, L is the length of the high-voltage cable; Step S102, calculating 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, where i=1, 2, 3...n; Step S103, calculating 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; Step S104, calculating the voltage difference at the end of the cable segment, the voltage difference = ΔV i -ΔV n-i , ΔV i is the difference between the core voltage and the sheath voltage at the end of the i-th cable segment, ΔV n-i 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 the voltage differences at the ends of n cable segments; Step S106: Determine the cable segment corresponding to the minimum value among the n voltage differences as a defective cable segment having insulation defects.

[0037] In one embodiment of the present application, after step S106, it is determined whether the defect location accuracy meets a preset condition; If the defect location accuracy meets the preset conditions, the insulation defect position X=i× ; If the defect location accuracy does not meet the preset conditions, the cable segment length Updated to , divide the defective cable segment into n' segments, n'= , is the length of the defective cable segment, and steps S102 to S106 are repeated based on both sides of the defective cable segment.

[0038] The embodiment of the present application proposes an insulation defect positioning scheme based on a double π-type equivalent circuit. Based on the characteristic of voltage continuity, combined with the insulation defect phase identified by the insulation defect, the defect position is accurately determined by measuring and calculating the voltage and current at both ends. This method does not need to ensure that the energy of the injected signal at each frequency point is consistent, thereby avoiding the positioning difficulty caused by insufficient high-frequency signal energy. Even in the case of uneven signal energy distribution, the positioning accuracy can be improved through algorithm optimization. In addition, since only the insulation defect phase is iteratively calculated, the amount of calculation is greatly reduced, the calculation efficiency is improved, and the consumption of manpower is reduced. The electrical quantity of this algorithm is easy to obtain, and the implementation cost is low.

[0039] A specific simulation case of this application includes: Cable arrangement as follows Figure 7 As shown in the equivalent diagram of cable insulation degradation, it is assumed that the insulation defect with a length of 10m occurs in phase A. The main insulation defect exists in the cross-connection section of the cable sheath, 1853m-1863m away from the right end, tanδ is 0.083, and the main insulation resistance 3MΩ, capacitance is 0.0128μF. When the defect exists, the current is as follows Figure 8 As shown in the waveform of the core current before and after the insulation defect occurs, the current amplitude has a slight change compared to the normal state after stabilization. At this time, the insulation degradation has caused the current of the core and sheath on both sides of the defect to be different, that is, the electrical quantities at both ends of the cable have changed compared to the normal state.

[0040] The insulation defect location method proposed in this application is used to locate the defect. First, the voltage and current values of the core and sheath at the beginning and end of the cable are obtained through ATP-EMTP, and the length of each small cable segment is set. The length of the cable is 50m, that is, it is calculated every 50m. The electrical quantity at the end of the first small section of the cable on the left is calculated from the left and right ends respectively by using formulas (1) to (4). Then the voltage difference derta between the core voltage and the sheath voltage is calculated and stored. The above process is repeated, and the calculation is iterated to the rightmost small section of the cable. The 196 derta values obtained are compared and plotted as shown below. Figure 9 The dertai-distance iteration curve can accurately measure the presence of derta in the 159th segment (7950m from the left and 1850m from the right). min , is the small section where the insulation defect is located. If you need to improve the positioning accuracy, shorten the search section length , update the starting and ending electrical quantities and repeat the above iterative process to further improve the insulation defect positioning accuracy.

[0041] In one embodiment of the present application, factors affecting the insulation defect location results of a high-voltage cable are analyzed, and the factors include at least one of the following: cable metal sheath grounding method, cable length, defect degree, and load level.

[0042] (1) Analyze the influence of cable metal sheath grounding method: The cable sheath grounding method is a crucial factor in selecting a cable layout. Different sheath grounding methods involve different electrical quantities in the iterative calculation, resulting in varying degrees of error in the sheath current contribution to the node in the KCL equation for the sheath at each end of the cable segment. For example, with single-ended grounding, no inductive current loop forms in the sheath, leaving only a capacitive current loop to ground. The sheath current flowing into the node is smaller than with two-end and cross-connected sheath grounding methods under the same conditions. In long-distance lines, cross-connected grounding can reduce the sheath current due to sheath transposition, resulting in a smaller sheath current flowing into the node than with two-end grounding methods under the same conditions. This comparison compares the location results for different sheath grounding methods, assuming a total cable length of 4.5 km, a herringbone arrangement, a phase-to-phase spacing of 0.5 m, a sheath grounding resistance of 1 Ω, an insulation defect with a tan delta of 0.06217 (1 m) in phase A, and an iterative step size of 1 m. Table 1 shows the insulation defect location errors for different sheath grounding methods.

[0043] Analysis of the data in Table 1 shows that this location method is applicable to various sheath grounding methods. Single-ended grounding offers the highest accuracy. While accurate positioning is possible, double-ended grounding is most affected by the sheath structure compared to other methods. Ignoring the sheath grounding method—that is, neglecting the sheath structure—incurs significant errors and makes it impossible to locate insulation defects. Therefore, the sheath grounding method must be considered when calculating insulation defect location.

[0044] (2) Analysis of the influence of cable length and defect location: Based on the analysis of the impact of the layout method, starting with an initial cable length of 2000m, the cable length is gradually increased, and the herringbone arrangement is used as the arrangement method. The phase distance is 0.5m, the sheath grounding resistance is 1Ω, and there is an insulation defect of tanδ of 0.06217 in phase A (1m). The defect is located at 500m, 1000m, and 1500m from the starting end, respectively. The iterative step size is 1m. The defect location error under different cable lengths is calculated. Analysis Figure 10 It can be seen from the positioning errors of different cable lengths that the percentage of insulation defect positioning error changes extremely slightly with the increase of cable length and can be approximately ignored. The positioning error in the middle of the cable is larger than that close to the two ends, and the error percentage is much less than 0.5%, which is at a low level. This method is not affected by cable length and defect position, and can accurately locate any defect position of any length cable.

[0045] (3) Impact of insulation defect degree: Different degrees of cable insulation defects have different effects on the electrical quantities at both ends. The total cable length is 5 km, the phase distance is 0.25 m, the sheath grounding resistance is 1 Ω, and when the sheath is grounded at both ends in a herringbone arrangement, the defect position of phase A is set every 1000 m at a distance of 500 m from the head end. The degree of insulation defect (1 m) is shown in Table 2: Table 2 Insulation defect degree

[0046] The electric charge at both ends of the above defects of different degrees was measured, and the iteration step was set to 1m. The positioning error caused by the change of insulation equivalent resistance R and capacitance C was calculated by the defect positioning method. Figure 11 It can be seen from the positioning error of different insulation defect degrees in that as tanδ increases, the positioning error is within 1%, and the accuracy increases slightly with the increase of degradation degree. This method is more adaptable to insulation defects of cables with a larger degree of degradation. For insulation defects in the early stage of degradation, since the changes in the electrical charge at both ends are not obvious, rough positioning can be performed by expanding the search segment length L0.

[0047] (4) Analyze the impact of load levels: Assuming the total cable length is 5 km, the arrangement is a herringbone arrangement, the phase distance is 0.25 m, the sheath grounding resistance is 1 Ω, the power phase angle differences are 15°, 30°, and 45°, and there is an insulation defect of tanδ of 0.06217 (1 m) in phase A. The iteration step size is 1 m. The positioning results under different load changes are calculated in Table 3: Table 3 Positioning results of different loads

[0048] Analysis of Table 3 shows that the positioning error increases slightly with the increase of load level, but is still at a low level. The error of defects farther away from the end is slightly larger than that of defects closer to the end. The error in the middle of the cable is less than 1%. Therefore, this positioning method is slightly affected by the load level and can accurately locate under both light and heavy loads.

[0049] The examples of this application analyze the effects of cable layout, cable length, defect degree and load level on positioning accuracy. The results show that this method is not affected by cable length or defect location. The maximum error does not exceed 1% under different layout methods, and it has good positioning accuracy, providing an important reference basis for practical applications.

[0050] An embodiment of the present application also provides a computer device, which includes a processor and a memory, wherein the memory stores programs or instructions that can be run on the processor. When the program or instructions are executed by the processor, the various steps of the above-mentioned embodiment of the method for locating insulation defects of high-voltage cables are implemented, and the same technical effect can be achieved. To avoid repetition, they will not be repeated here.

[0051] Memory can be used to store software programs and various data. The memory may primarily include a first storage area for storing programs or instructions and a second storage area for storing data. The first storage area may store an operating system, applications or instructions required for at least one function (such as sound playback or image playback), and the like. Furthermore, the memory may include volatile memory or non-volatile memory, or both. Non-volatile memory may 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 link dynamic random access memory (SLDRAM), and direct RAM bus random access memory (DRRAM). The memory in the embodiments of the present application includes but is not limited to these and any other suitable types of memory.

[0052] The processor may include one or more processing units; optionally, the processor may integrate an application processor and a modem processor, wherein the application processor primarily handles operations related to the operating system, user interface, and application programs, and the modem processor primarily processes wireless communication signals, such as a baseband processor. It is understood that the modem processor may not be integrated into the processor.

[0053] An embodiment of the present application also provides a readable storage medium, on which a program or instruction is stored. When the program or instruction is executed by a processor, the various processes of the above-mentioned embodiment of the method for locating insulation defects of a high-voltage cable are implemented, and the same technical effect can be achieved. To avoid repetition, it will not be repeated here.

[0054] It should be noted that, in this article, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element. In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in the opposite order according to the functions involved. For example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0055] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of this application, ordinary technicians in this field can also make many forms without departing from the purpose of this application and the scope of protection of the claims, all of which are within the protection of this application.

Claims

1. A method for locating insulation defects of a high-voltage cable, characterized in that: The method comprises: Step S101, set the cable segment length , divide the high voltage cable into n cable segments, n= , L is the length of the high-voltage cable; Step S102: From the left end of the high-voltage cable, based on the real-time sampled left end cable core current value and 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, where i = 1, 2, 3...n; Step S103, from the right end of the high-voltage cable, according to the real-time sampling of the right end cable core current value, based on the cable equivalent model, theoretically derive and calculate the first The core voltage and sheath voltage of the insulation defect phase at the end of each cable segment; Step S104: Draw two cable insulation defect location curves according to step S102 and step S103, and calculate the voltage difference at the end of the cable segment based on the two curves. The voltage difference = , is the difference between the core voltage and the sheath voltage at the end of the i-th cable segment, 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 the voltage differences at the ends of n cable segments; Step S106, determining the cable segment corresponding to the minimum value among the n voltage differences as a defective cable segment having insulation defects; The method further comprises: Determine whether the defect positioning accuracy meets the preset conditions; If the defect location accuracy meets the preset conditions, the insulation defect position X=i× ; If the defect location accuracy does not meet the preset conditions, the cable segment length Updated to , divide the defective cable segment into n' segments, n'= , is the length of the defective cable segment, and steps S102 to S106 are repeated based on both sides of the defective cable segment.

2. The method according to claim 1, characterized in that The method of determining the insulation defect phase includes: At both ends of the high-voltage cable, measuring the phase of the current and voltage of each of the three phases; The phase differences of the phases 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 equivalent performance. The equivalent parameters include: the corresponding impedance of the three-phase cable core of the cable segment, the corresponding 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 earth 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 comprises: The starting electrical quantity is collected from the starting end of the high-voltage cable, and the terminal electrical quantity is collected from the terminal of the high-voltage cable. The starting electrical quantity and the terminal electrical quantity both include the core voltage, core current, sheath voltage and sheath current; the starting electrical quantity is used to calculate the core current and sheath current at the end of the i-th cable segment, and the terminal electrical quantity is used to calculate the i-th cable segment. The core 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 theorem, calculate the core current and sheath current at the end of the i-th cable segment, calculate the core voltage based on the core 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 The core voltage and sheath voltage of the insulation defect phase at the end of each cable segment, including: Using Kirchhoff's voltage and current theorem, calculate The core current and sheath current at the end of the first cable segment are based on the The core voltage is calculated based on the core current at the end of the first cable segment, and the The sheath voltage is calculated from the sheath current at the end of each cable segment.

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

6. The method according to claim 1, characterized in that The method further comprises: Factors influencing the insulation defect location results of the high-voltage cable are analyzed, wherein the factors include at least one of the following: cable metal sheath grounding method, cable length, defect degree, and load level.

7. A computer device, characterized in that: The method comprises a processor and a memory, wherein the memory stores a program or instruction running on the processor, and when the program or instruction is executed by the processor, the steps of the method for locating insulation defects of a high-voltage cable according to any one of claims 1 to 6 are implemented.

8. A readable storage medium having a program or instruction stored thereon, characterized in that: When the program or instruction is executed by a processor, the steps of the method for locating insulation defects of a high-voltage cable according to any one of claims 1 to 6 are implemented.

Images