A method for identifying cracks in a cable and its insulation layer

Abstract

The present invention relates to the field of cable detection, and specifically to a method for identifying cracks in a cable and its insulation layer. A transient simulation model is set and verified with actual samples, and the components of a first comprehensive magnetic field in the X-axis and Y-axis directions are evaluated, and the changes of the two at different speeds are comprehensively considered to obtain a standard speed for better detecting cracks in the cable. Subsequently, a second cable sample is used to obtain the position of a wave crest in an eddy current to set the relative position of an excitation coil and a probe module in an eddy current probe, so that cracks can be detected more clearly. Finally, a third sample is set to obtain two standard crack intervals for detecting cracks in the cable, so that the position of the crack in the cable can be quickly detected when detecting cracks in batches of cables, which is convenient for employees to evaluate and repair. The problem that the crack detection error is larger when the cable speed is larger due to the influence of eddy current and comprehensive magnetic field traction is solved.

Description

Technical Field

[0001] The invention relates to the field of cable detection, in particular to a method for identifying cracks in a cable and its insulation layer. Background Art

[0002] The general process flow of cable production is conductor - conductor twisting or bundled wire - insulation injection molding - combined sheath injection molding - inspection and packaging. During the processing or transportation process, there are factors that may cause cracks in the cables and wires. When inspecting the finished product at the end, it is necessary to check whether there are cracks on the wires and insulation layer inside the cable to reduce the probability of risks in the future use of the cable.

[0003] There are many methods for inspecting cables in the prior art. A commonly used method is the eddy current-based detection method. However, since the eddy currents and magnetic fields on the cable surface will cause dragging when the cable moves, and the degree of dragging increases with the increase of the cable movement speed, therefore when judging whether there is a crack on the cable by detecting the comprehensive magnetic field, when the cable speed is high, the crack detection error will be greater. Therefore, the current eddy current-based cable crack detection method is difficult to meet the current speed requirements for cable winding, affecting production efficiency. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for identifying cracks in cables and their insulation layers, which solves the problem that the crack detection error becomes larger when the cable speed is higher due to the influence of eddy current and comprehensive magnetic field traction phenomenon.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for identifying cracks in a cable insulation layer, the method comprising the following steps:

[0007] S1. Pull the cable in a straight line and set a number of eddy current probes with the same distribution radius around the cable, with the central axis as the center. The eddy current probes are sequentially distributed in the moving direction of the cable and are used to generate a constant magnetic field and obtain a comprehensive magnetic field on the cable;

[0008] S2, setting a transient simulation model of the cable to obtain a first moving speed when the components of the first comprehensive magnetic field in the X-axis and Y-axis directions are equal, and obtaining a standard speed according to the first moving speed;

[0009] S3, setting a plurality of second cable samples that move at a standard speed and contain cracks, and obtaining a second comprehensive magnetic field of each second cable sample in real time, and calculating a standard position of a probe module in an eddy current probe according to a peak position in each second comprehensive magnetic field;

[0010] S4, setting a plurality of third cable samples containing cracks, and passing the third cable samples under the eddy current probe of the probe module at a standard position at a standard speed to obtain a third comprehensive magnetic field, and setting a standard crack interval of the comprehensive magnetic field according to the third comprehensive magnetic field;

[0011] S5. Obtain the integrated magnetic field at various locations on the cable to be detected in real time, and mark the location corresponding to the integrated magnetic field in the crack interval as a crack area.

[0012] Preferably, in step S2, the following steps are specifically included:

[0013] S21, constructing a transient simulation model of the cable, and meshing the simulation model to obtain motional eddy currents;

[0014] S22, setting the cable in the transient simulation model to move at a plurality of different speeds, and obtaining in real time a first comprehensive magnetic field at a position on the cable corresponding to the eddy current probe;

[0015] S23, obtaining the components of the first comprehensive magnetic field in the X-axis and Y-axis directions respectively;

[0016] S24, constructing a first relationship diagram between the components of the first comprehensive magnetic field in the X-axis and Y-axis directions and the velocity;

[0017] S25, obtaining the movement speed corresponding to the position where the components of the first comprehensive magnetic field in the X-axis direction and the Y-axis direction are equal, which is the first movement speed;

[0018] S26, setting a first moving speed interval with the first moving speed as the center, and selecting a plurality of evenly distributed second moving speeds from the first moving speed interval;

[0019] S27, setting a first cable sample, and moving the first cable sample at a second moving speed to obtain a real-time first comprehensive magnetic field, and obtaining a second moving speed when the components of the first comprehensive magnetic field in the X-axis and Y-axis directions are equal, to obtain a standard speed.

[0020] Preferably, in step S21, the following steps are specifically included:

[0021] S211, constructing a transient simulation model of the cable, and meshing the simulation model;

[0022] S212, marking the area where the cable is located as a dynamic area, marking the remaining areas as static areas, and setting a fixed time step to periodically update the grid in the dynamic area;

[0023] S213, constructing the control equation of the magnetic vector potential in the transient simulation model; the expression of the control equation of the magnetic vector potential is:

[0024] ;

[0025] In the above formula, A represents vector potential, t represents time, is the magnetic permeability of the material in the cable, v represents the moving speed of the cable, Excitation current, is the conductivity of the material in the cable, represents the scalar electric potential, represents the coercive force;

[0026] S214, constructing a nonlinear equation group for solving the control equation of the magnetic vector potential to output the motional eddy current through the transient simulation model; the expression of the nonlinear equation group is:

[0027] ;

[0028] In the above formula, is the approximate solution to the unknown magnetic vector potential, is a known vector, for The matrix is The nonlinear function of .

[0029] Preferably, in step S3, the following steps are specifically included:

[0030] S31, setting a plurality of second cable samples containing cracks, and moving each second cable sample in turn at a standard speed;

[0031] S32, setting the eddy current probe at any position above the second cable sample, and obtaining in real time a second comprehensive magnetic field on any straight line parallel to the central axis of the second cable sample;

[0032] S33, obtaining the position of each second cable when the second comprehensive magnetic field peak is the largest during the movement process;

[0033] S34, calculating the average value of the positions of the second integrated magnetic field peaks at the maximum value as the standard position of the probe module.

[0034] Preferably, in step S4, the following steps are specifically included:

[0035] S41, setting a plurality of third cable samples with different crack sizes, depths and positions, and making the third cable samples pass under the eddy current probe of the probe module located at a standard position at a standard speed to obtain a third comprehensive magnetic field;

[0036] S42, setting a basic interval;

[0037] S43, establishing a magnetic field interval based on the central value of any data in the third comprehensive magnetic field data as a basic interval, and calculating the data density of each magnetic field interval;

[0038] S44, setting a density threshold, and marking the third comprehensive magnetic field with data density less than the density threshold as segmented magnetic field data, and marking the remaining third comprehensive magnetic field data as concentrated magnetic field data;

[0039] S45, determining in sequence whether any two magnetic field intervals of segmented magnetic field data have an intersection;

[0040] S46, determining whether the number of the second segmented magnetic field groups is 3;

[0041] If yes, proceed to step S47;

[0042] If not, the size of the basic interval is adjusted according to the number of segmented magnetic fields, and then the process goes to step S43;

[0043] S47, respectively establishing concentrated magnetic field groups using the third integrated magnetic fields corresponding to the minimum spacing between any two adjacent second segmented magnetic field groups;

[0044] S48, respectively calculating the average value of the concentrated magnetic field data in each magnetic field group as the symmetry center;

[0045] S49. Establish a standard crack interval containing several concentrated magnetic field data in the concentrated magnetic field group with the symmetry center as the median.

[0046] Preferably, in step S43, the following steps are specifically included:

[0047] S431, establishing a magnetic field interval based on the center value of any third comprehensive magnetic field data as a basic interval; the expression of the magnetic field interval is: ,in, represents the third integrated magnetic field data of the ith time, represents the basic interval;

[0048] S432, calculating the data density of each magnetic field interval; the calculation formula of the data density is:

[0049] ;

[0050] in,

[0051] ;

[0052] In the above formula, represents the data density of the ith magnetic field interval, and Respectively represent the third integrated magnetic field data at the i-th and j-th time, represents half of the base interval, is a sign function, and A represents the total number of the third comprehensive magnetic field data.

[0053] Preferably, in step S45, the following steps are specifically included:

[0054] S451, determining in sequence whether the magnetic field intervals of any two segmented magnetic field data have an intersection or whether there is no third comprehensive magnetic field data between the two;

[0055] If yes, the two segmented magnetic fields are marked as the same first segmented magnetic field group;

[0056] If not, the two segmented magnetic fields are marked as different first segmented magnetic field groups;

[0057] S452, sequentially determining whether there is third comprehensive magnetic field data between any two first segmented magnetic field groups;

[0058] If yes, the two first segmented magnetic field groups are marked as different second segmented magnetic fields;

[0059] If not, the two first segmentation magnetic field groups are marked as the same second segmentation magnetic field.

[0060] Preferably, in step S46, the following steps are specifically included:

[0061] S461, obtaining the current number of iterations, and determining whether the number of the second segmented magnetic field groups is 3;

[0062] If yes, proceed to step S467;

[0063] If not, proceed to step S462;

[0064] S462, determining whether the number of the second segmented magnetic field groups is 2;

[0065] If yes, proceed to step S463;

[0066] If not, proceed to step S465;

[0067] S463, determining whether the current number of iterations is 1;

[0068] If yes, the current basic interval is reduced to obtain an updated basic interval, and the process proceeds to step S43; the calculation formula of the updated basic interval is:

[0069] ;

[0070] If not, proceed to step S464;

[0071] S464, determining whether the size of the current basic interval is smaller than the size of the basic interval in the previous iteration;

[0072] If yes, the current basic interval is reduced to obtain an updated basic interval, and the process goes to step S43;

[0073] If not, then select an interval whose size is between the current basic interval and the basic interval in the previous iteration as the updated basic interval, and then proceed to step S43;

[0074] S465, determining whether the current number of iterations is 1;

[0075] If yes, the current basic interval is increased to obtain an updated basic interval, and the process proceeds to step S43; the calculation formula of the updated basic interval is:

[0076] ;

[0077] If not, proceed to step S466;

[0078] S466, determining whether the size of the current basic interval is greater than the size of the basic interval in the previous iteration;

[0079] If yes, the current basic interval is increased to obtain an updated basic interval, and the process goes to step S43;

[0080] If not, then select an interval whose size is between the current basic interval and the basic interval in the previous iteration as the updated basic interval, and then proceed to step S43;

[0081] S467, reducing the current basic interval to obtain the minimum basic interval when the number of the second divided magnetic field groups is 3, and then entering step S47.

[0082] Preferably, in step S49, the following steps are specifically included:

[0083] S491, setting a ratio threshold;

[0084] S492, taking the symmetry center as the median, sequentially using each concentrated magnetic field data and its symmetric data points about the symmetry center to establish the first crack interval; the expression of the first crack interval is: or ,and ,in, and Respectively represent the concentrated magnetic field data and its symmetrical data points about the symmetry center, Indicates the center of symmetry;

[0085] S493, respectively calculating the ratio of the number of concentrated magnetic field data in each first crack interval to the total number of concentrated magnetic field data to obtain an interval probability;

[0086] ;

[0087] In the above formula, represents the interval probability of the i-th first crack interval, and represent the number of concentrated magnetic field data and the total number of concentrated magnetic field data in the first crack interval respectively;

[0088] S494, determining whether there is a first crack interval with any interval probability equal to the ratio threshold;

[0089] If yes, then output the first crack interval as the standard crack interval;

[0090] If not, proceed to step S495;

[0091] S495, obtaining two first crack intervals whose interval probabilities are respectively greater than and less than the ratio threshold and whose difference with the ratio threshold is the smallest, and marking them as second crack intervals;

[0092] S496. Calculate a standard crack interval according to the interval probability and the ratio threshold of the second crack interval; the expression of the standard crack interval is:

[0093] or ,in, For data points Symmetrical data points about the symmetry center, and are the maximum and minimum values ​​of the intervals of the two second crack intervals that are greater than and less than the ratio threshold, respectively. is the ratio threshold, and are the maximum and minimum values ​​of the interval probabilities of the two second crack intervals that are greater than and less than the ratio threshold, respectively.

[0094] The present invention also provides a cable, including a protective layer, a plurality of conductors arranged in the protective layer, an insulating layer arranged outside the conductor, a partition body arranged in the protective layer for dividing its cross section into a plurality of chambers, the plurality of insulating layers and conductors are arranged in different chambers in sequence, the inner wall of the protective layer and the surface of the partition body are provided with a plurality of elastic protrusions located in the chamber and in a compressed state, and the chamber is filled with granular matter.

[0095] Compared with the prior art, the present invention provides a method for identifying cracks in a cable and its insulation layer, which has the following beneficial effects:

[0096] 1. By setting up a transient simulation model and verifying it with actual samples, a standard speed that can better detect cracks in the cable is obtained. Then, through the second cable sample, the position of the wave crest in the eddy current is obtained to set the relative position of the excitation coil and the probe module in the eddy current probe, so that the cracks can be detected more clearly. Finally, by setting the third sample, two standard crack intervals for detecting cracks in the cable are obtained, so that the position of the cracks in the cable can be quickly detected when detecting cracks in batches of cables, which is convenient for employees to evaluate and repair.

[0097] 2. The present invention evaluates the components of the first comprehensive magnetic field in the X-axis and Y-axis directions respectively, comprehensively considers the changes of the two at different speeds, and takes the speed when the data of the two can be accurately obtained as the standard speed, thereby ensuring the accuracy of crack detection.

[0098] 3. The present invention sets a second cable sample and passes it under the eddy current probe at a standard speed. According to the distribution of the second comprehensive magnetic field, the relative position of the probe module and the excitation coil in the eddy current probe is set at the position when the wave peak is at the maximum position, thereby ensuring that the size of the second comprehensive magnetic field can be detected more accurately, so as to obtain a more accurate comprehensive magnetic field in the subsequent cable detection, thereby ensuring the accuracy of the crack position judgment.

[0099] 4. The present invention divides the third comprehensive magnetic field data by calculating the data density of each third comprehensive magnetic field data, and finally obtains 3 second divided magnetic field groups and 2 concentrated magnetic field groups, thereby obtaining 2 crack intervals according to the concentrated magnetic field groups. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] 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:

[0101] Figure 1 A flow chart of a method for identifying cracks in a cable insulation layer of the present invention;

[0102] Figure 2 is a graph showing the relationship between the components of the first comprehensive magnetic field in the X-axis and Y-axis directions and the velocity of the present invention;

[0103] Figure 3 It is a schematic diagram of eddy current on the surface of the cable conductor when it is stationary according to the present invention;

[0104] Figure 4 It is a schematic diagram of eddy currents on the cable surface when the present invention moves;

[0105] Figure 5 It is a schematic diagram of the comprehensive magnetic field peaks at different moving speeds of the present invention;

[0106] Figure 6 It is a schematic diagram of the concentrated magnetic field group and the second divided magnetic field group of the present invention;

[0107] Figure 7 Schematic diagram of the cross section of the cable of the present invention. DETAILED DESCRIPTION

[0108] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods, so that the implementation process of how the present application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0109] Those skilled in the art can understand that all or part of the steps in the following embodiments can be completed by instructing the relevant hardware through a program, so the present application can be in the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application can be in the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0110] In order to solve the problem that the crack detection error becomes larger when the cable speed is higher due to the influence of eddy current and comprehensive magnetic field drag phenomenon, the present invention proposes a method for identifying cracks in the cable insulation layer, and obtains the optimal theoretical moving speed of the cable when the crack recognition rate is the highest through finite element analysis, and obtains the actual standard moving speed based on the theoretical moving speed and through experiments, and in order to reduce the influence of the drag phenomenon, by changing the position of the probe module in the eddy current probe, finally by setting a reasonable standard crack interval for identifying cracks in the cable to be detected, the method specifically includes the following steps:

[0111] S1. Pull the cable in a straight line, and set a number of eddy current probes with the same distribution radius around the cable with the central axis as the center. The eddy current probes are sequentially distributed in the moving direction of the cable and used to generate a constant magnetic field and obtain the comprehensive magnetic field on the cable; the eddy current probe is generally provided with a DC excitation coil for generating a constant magnetic field, and a probe module for obtaining the comprehensive magnetic field and eddy current data on the cable;

[0112] S2. Set up a transient simulation model of the cable to obtain the first moving speed when the components of the first comprehensive magnetic field in the X-axis and Y-axis directions are equal, and obtain the standard speed according to the first moving speed; the X-axis direction is the direction of movement along the cable, the Y-axis direction is perpendicular to the X-axis direction, the XY plane is perpendicular to the direction of the eddy current probe, and the components of the first comprehensive magnetic field in the X-axis and Y-axis directions are respectively and , as the first cable speed increases, The value of gradually increases, The value of gradually decreases, so in order to comprehensively ensure and The detectability ensures that when the traction phenomenon occurs, the size of the comprehensive magnetic field can still be detected more clearly. and The relationship between the value of and the cable moving speed is as follows Figure 2 As shown, in step S2, the following steps are specifically included:

[0113] S21, constructing a transient simulation model of the cable, and meshing the simulation model to obtain motional eddy currents; the transient simulation model is constructed based on finite element analysis. Since the area where the cable is located is in a moving state and the rest of the area is in a stationary state, it is necessary to define the control equation of the magnetic vector potential. In step S21, the following steps are specifically included:

[0114] S211, constructing a transient simulation model of the cable, and meshing the simulation model;

[0115] S212, marking the area where the cable is located as a dynamic area, marking the remaining areas as static areas, and setting a fixed time step to periodically update the grid in the dynamic area;

[0116] S213, constructing the control equation of the magnetic vector potential in the transient simulation model; the expression of the control equation of the magnetic vector potential is:

[0117] ;

[0118] In the above formula, A represents vector potential, t represents time, is the magnetic permeability of the material in the cable, v represents the moving speed of the cable, Excitation current, is the conductivity of the material in the cable, represents the scalar electric potential, represents the coercive force, represents the differential operator;

[0119] S214, constructing a nonlinear equation group for solving the control equation of the magnetic vector potential to output the motional eddy current through the transient simulation model; the expression of the nonlinear equation group is:

[0120] ;

[0121] In the above formula, is the approximate solution to the unknown magnetic vector potential, is a known vector, for The matrix is The nonlinear function of .

[0122] S22, setting the cable in the transient simulation model to move at several different speeds, and obtaining in real time a first comprehensive magnetic field at a position on the cable that corresponds to the eddy current probe; the first comprehensive magnetic field is obtained based on motional eddy current calculation and obtained through simulation software, which will not be described in detail here;

[0123] S23, obtaining the components of the first comprehensive magnetic field in the X-axis and Y-axis directions respectively;

[0124] S24, constructing a first relationship diagram between the components of the first comprehensive magnetic field in the X-axis and Y-axis directions and the velocity;

[0125] S25, obtaining the movement speed corresponding to the position where the components of the first comprehensive magnetic field in the X-axis direction and the Y-axis direction are equal, which is the first movement speed;

[0126] S26, setting a first moving speed interval with the first moving speed as the center, and selecting a plurality of evenly distributed second moving speeds from the first moving speed interval;

[0127] S27, setting a first cable sample, and moving the first cable sample at a second moving speed to obtain a real-time first comprehensive magnetic field, and obtaining a second moving speed when the components of the first comprehensive magnetic field in the X-axis and Y-axis directions are equal, to obtain a standard speed.

[0128] S3, set a number of second cable samples with cracks moving at a standard speed, and obtain the second comprehensive magnetic field of each second cable sample in real time, and calculate the standard position of the probe module in the eddy current probe according to the peak position in each second comprehensive magnetic field; during the movement of the cable, a traction phenomenon will occur, such as Figure 3 and Figure 4 The eddy currents on the cable conductors are shown when the cable speed is 0.1m / s and 10m / s. Here, only the cable conductor is used to illustrate the traction phenomenon. It can be seen that when the cable speed is 10m / s, obvious traction phenomenon occurs. In step S3, the following steps are specifically included:

[0129] S31, setting a plurality of second cable samples containing cracks, and moving each second cable sample in turn at a standard speed;

[0130] S32, setting the eddy current probe at any position above the second cable sample, and obtaining in real time a second comprehensive magnetic field on any straight line parallel to the central axis of the second cable sample;

[0131] S33, obtaining the position of each second cable when the second comprehensive magnetic field peak is the largest during the movement process;

[0132] S34, calculating the average value of the positions of the second integrated magnetic field peaks at the maximum value as the standard position of the probe module, such as Figure 4 As shown, when each second cable sample is moved at a standard speed in turn, its curve form is roughly as shown by the green line. Point P6 in the figure is the position of the probe module, and the gray dotted line is the position of the excitation coil, so as to obtain the relative position of the two. By setting the relative position of the two, the second comprehensive magnetic field peak can be detected more clearly, so as to detect the crack in the cable more sensitively;

[0133] S4, set a number of third cable samples containing cracks, and make the third cable samples pass under the eddy current probe of the probe module at the standard position at a standard speed to obtain a third comprehensive magnetic field, and set a standard crack interval of the comprehensive magnetic field according to the third comprehensive magnetic field; since the cable crack may be located on the cable conductor or on the insulation skin, when the cable crack is on the same cross-section of the cable, if the cable crack is located on the conductor and the insulation layer respectively, the impedance generated by the third comprehensive magnetic field is different, so the third comprehensive magnetic field data also presents a situation of concentration in two areas, so it is necessary to select the data intervals with the most concentrated two third comprehensive magnetic field data from a large amount of data as the crack interval for crack identification, in step S4, specifically including the following steps:

[0134] S41, setting a plurality of third cable samples with different crack sizes, depths and positions, and making the third cable samples pass under the eddy current probe of the probe module located at a standard position at a standard speed to obtain a third comprehensive magnetic field;

[0135] S42, setting a basic interval;

[0136] S43, establishing a magnetic field interval based on the central value of any data in the third comprehensive magnetic field data as the basic interval, and calculating the data density of each magnetic field interval; by calculating the data density of the magnetic field interval, it is reflected whether the corresponding third comprehensive magnetic field data is located in the data interval where the data to be extracted is most concentrated. In step S43, the following steps are specifically included:

[0137] S431, establishing a magnetic field interval based on the center value of any third comprehensive magnetic field data as a basic interval; the expression of the magnetic field interval is: ,in, represents the third integrated magnetic field data of the ith time, represents the basic interval;

[0138] S432, calculating the data density of each magnetic field interval; the calculation formula of the data density is:

[0139] ;

[0140] in,

[0141] ;

[0142] In the above formula, represents the data density of the ith magnetic field interval, and Respectively represent the third integrated magnetic field data at the i-th and j-th time, represents half of the base interval, is a sign function, and A represents the total number of the third comprehensive magnetic field data.

[0143] S44, setting a density threshold, and marking the third comprehensive magnetic field with data density less than the density threshold as segmented magnetic field data, and marking the remaining third comprehensive magnetic field data as concentrated magnetic field data;

[0144] S45, determining in sequence whether any two magnetic field intervals of segmented magnetic field data have an intersection;

[0145] If yes, the two segmented magnetic fields are marked as the same second segmented magnetic field group;

[0146] If not, the two segmented magnetic fields are marked as different second segmented magnetic field groups; if the magnetic field intervals have an intersection, it means that the two segmented magnetic field data are very close, and they are merged into the same second segmented magnetic field group. The method for generating the second segmented magnetic field group is further described in detail below. In step S45, the following steps are specifically included:

[0147] S451, determining in sequence whether the magnetic field intervals of any two segmented magnetic field data have an intersection or whether there is no third comprehensive magnetic field data between the two;

[0148] If yes, the two segmented magnetic fields are marked as the same first segmented magnetic field group;

[0149] If not, the two segmented magnetic fields are marked as different first segmented magnetic field groups;

[0150] S452, sequentially determining whether there is third comprehensive magnetic field data between any two first segmented magnetic field groups;

[0151] If yes, the two first segmented magnetic field groups are marked as different second segmented magnetic fields;

[0152] If not, the two first segmentation magnetic field groups are marked as the same second segmentation magnetic field.

[0153] S46, determining whether the number of the second segmented magnetic field groups is 3;

[0154] If yes, proceed to step S47;

[0155] If not, the size of the basic interval is adjusted according to the number of segmented magnetic fields, and then the process goes to step S43;

[0156] Theoretically, the number of the second segmented magnetic field groups should be 3 so that two concentrated magnetic field groups can be obtained later, which are the data concentration intervals of the third comprehensive magnetic field data when cracks appear on the cable conductor and the insulation skin, respectively. In step S46, the following steps are specifically included:

[0157] S461, obtaining the current number of iterations, and determining whether the number of the second segmented magnetic field groups is 3;

[0158] If yes, proceed to step S467;

[0159] If not, proceed to step S462;

[0160] S462, determining whether the number of the second segmented magnetic field groups is 2;

[0161] If yes, proceed to step S463;

[0162] If not, proceed to step S465;

[0163] S463, determining whether the current number of iterations is 1;

[0164] If yes, the current basic interval is reduced to obtain an updated basic interval, and the process proceeds to step S43; the calculation formula of the updated basic interval is:

[0165] ;

[0166] If not, proceed to step S464;

[0167] S464, determining whether the size of the current basic interval is smaller than the size of the basic interval in the previous iteration;

[0168] If yes, the current basic interval is reduced to obtain an updated basic interval, and the process goes to step S43;

[0169] If not, then select an interval whose size is between the current basic interval and the basic interval in the previous iteration as the updated basic interval, and then proceed to step S43;

[0170] S465, determining whether the current number of iterations is 1;

[0171] If yes, the current basic interval is increased to obtain an updated basic interval, and the process proceeds to step S43; the calculation formula of the updated basic interval is:

[0172] ;

[0173] If not, proceed to step S466;

[0174] S466, determining whether the size of the current basic interval is greater than the size of the basic interval in the previous iteration;

[0175] If yes, the current basic interval is increased to obtain an updated basic interval, and the process goes to step S43;

[0176] If not, an interval whose size is between the current basic interval and the basic interval in the previous iteration is selected as the updated basic interval, and then the process goes to step S43.

[0177] S467, reduce the current basic interval to obtain the minimum basic interval when the number of the second segmented magnetic field groups is 3, and then enter step S47; this can ensure that the data capacity of the subsequently obtained concentrated magnetic field group is the largest, such as Figure 5 As shown, it is a data curve composed of data points of the third comprehensive magnetic field, and also includes a schematic diagram of the entire concentrated magnetic field group and the second divided magnetic field group.

[0178] S47, respectively establishing concentrated magnetic field groups using the third integrated magnetic fields corresponding to the minimum spacing between any two adjacent second segmented magnetic field groups;

[0179] S48, respectively calculating the average value of the concentrated magnetic field data in each magnetic field group as the symmetry center;

[0180] S49, establishing a standard crack interval containing a number of concentrated magnetic field data in the concentrated magnetic field group with the symmetry center as the median; since data points in the concentrated magnetic field data that are far from the symmetry center may be abnormal points, they are removed to obtain the crack interval. In step S49, the following steps are specifically included:

[0181] S491, setting a ratio threshold; the ratio threshold is generally set to 95%;

[0182] S492, taking the symmetry center as the median, sequentially using each concentrated magnetic field data and its symmetric data points about the symmetry center to establish the first crack interval; the expression of the first crack interval is: or ,and ,in, and Respectively represent the concentrated magnetic field data and its symmetrical data points about the symmetry center, Indicates the center of symmetry;

[0183] S493, respectively calculating the ratio of the number of concentrated magnetic field data in each first crack interval to the total number of concentrated magnetic field data to obtain an interval probability;

[0184] ;

[0185] In the above formula, represents the interval probability of the i-th first crack interval, and represent the number of concentrated magnetic field data and the total number of concentrated magnetic field data in the first crack interval respectively;

[0186] S494, determining whether there is a first crack interval with any interval probability equal to the ratio threshold;

[0187] If yes, then output the first crack interval as the standard crack interval;

[0188] If not, proceed to step S495;

[0189] S495, obtaining two first crack intervals whose interval probabilities are respectively greater than and less than the ratio threshold and whose difference with the ratio threshold is the smallest, and marking them as second crack intervals;

[0190] S496. Calculate a standard crack interval according to the interval probability and the ratio threshold of the second crack interval; the expression of the standard crack interval is:

[0191] or ,in, For data points Symmetrical data points about the symmetry center, and are the maximum and minimum values ​​of the intervals of the two second crack intervals that are greater than and less than the ratio threshold, respectively. is the ratio threshold, and are the maximum and minimum values ​​of the interval probabilities of the two second crack intervals that are greater than and less than the ratio threshold, respectively.

[0192] S5. Obtain the integrated magnetic field at various locations on the cable to be detected in real time, and mark the location corresponding to the integrated magnetic field in the crack interval as a crack area.

[0193] During the implementation of the present invention, a standard speed capable of better detecting cracks in a cable is obtained by verifying based on a transient simulation model and actual samples. Subsequently, the position of the wave crest in the eddy current is obtained through a second cable sample to set the relative position of the excitation coil and the probe module in the eddy current probe, so that the cracks can be detected more clearly. Finally, two standard crack intervals for detecting cracks in the cable are obtained by setting a third sample, so that the position of the cracks in the cable can be quickly detected when detecting cracks in batches of cables, which is convenient for employees to evaluate and repair.

[0194] The present invention also provides a cable that is convenient for identifying cracks in the insulation layer of a cable through a cable insulation layer crack identification method, comprising a protective layer 1, a plurality of conductors 2 arranged in the protective layer 1, an insulating layer 3 arranged outside the conductor 2, a partition body 4 for dividing its cross section into a plurality of chambers arranged in the protective layer 1, the plurality of insulating layers 3 and the conductors 2 are sequentially arranged in different chambers, the inner wall of the protective layer 1 and the surface of the partition body 4 are both provided with a plurality of elastic protrusions 5 located in the chamber and in a compressed state, the chamber is filled with granular matter 6, when cracks appear on the surface of the insulation layer 3, under the action of the elastic force of the plurality of elastic protrusions 5, the granular matter 6 will be squeezed into the cracks on the surface of the insulation layer 3, so that more air enters the cracks, thereby further improving the magnetic resistance at the cracks, and more obvious mutations will occur in the process of detecting eddy currents and magnetic fields.

[0195] The above implementation methods have been described in detail. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for identifying cracks in cable insulation, characterized in that: The method comprises the following steps: S1. Pull the cable in a straight line and set a number of eddy current probes with the same distribution radius around the cable, with the central axis as the center. The eddy current probes are sequentially distributed in the moving direction of the cable and are used to generate a constant magnetic field and obtain a comprehensive magnetic field on the cable; S2, setting a transient simulation model of the cable to obtain a first moving speed when the components of the first comprehensive magnetic field in the X-axis and Y-axis directions are equal, and obtaining a standard speed according to the first moving speed; In step S2, the following steps are specifically included: S21, constructing a transient simulation model of the cable, and meshing the simulation model to obtain motional eddy currents; S22, setting the cable in the transient simulation model to move at a plurality of different speeds, and obtaining in real time a first comprehensive magnetic field at a position on the cable corresponding to the eddy current probe; S23, obtaining the components of the first comprehensive magnetic field in the X-axis and Y-axis directions respectively; S24, constructing a first relationship diagram between the components of the first comprehensive magnetic field in the X-axis and Y-axis directions and the velocity; S25, obtaining the movement speed corresponding to the position where the components of the first comprehensive magnetic field in the X-axis direction and the Y-axis direction are equal, which is the first movement speed; S26, setting a first moving speed interval with the first moving speed as the center, and selecting a plurality of evenly distributed second moving speeds from the first moving speed interval; S27, setting a first cable sample, and moving the first cable sample at a second moving speed to obtain a real-time first integrated magnetic field, and obtaining a second moving speed when the components of the first integrated magnetic field in the X-axis and Y-axis directions are equal, to obtain a standard speed; S3, setting a plurality of second cable samples that move at a standard speed and contain cracks, and obtaining a second comprehensive magnetic field of each second cable sample in real time, and calculating a standard position of a probe module in an eddy current probe according to a peak position in each second comprehensive magnetic field; In step S3, the following steps are specifically included: S31, setting a plurality of second cable samples containing cracks, and moving each second cable sample in turn at a standard speed; S32, setting the eddy current probe at any position above the second cable sample, and obtaining in real time a second comprehensive magnetic field on any straight line parallel to the central axis of the second cable sample; S33, obtaining the position of each second cable when the second comprehensive magnetic field peak is the largest during the movement process; S34, calculating the average value of the positions of the second integrated magnetic field peaks when they are maximum as the standard position of the probe module; S4, setting a plurality of third cable samples containing cracks, and passing the third cable samples under the eddy current probe of the probe module at a standard position at a standard speed to obtain a third comprehensive magnetic field, and setting a standard crack interval of the comprehensive magnetic field according to the third comprehensive magnetic field; In step S4, the following steps are specifically included: S41, setting a plurality of third cable samples with different crack sizes, depths and positions, and making the third cable samples pass under the eddy current probe of the probe module located at a standard position at a standard speed to obtain a third comprehensive magnetic field; S42, setting a basic interval; S43, establishing a magnetic field interval based on the central value of any data in the third comprehensive magnetic field data as a basic interval, and calculating the data density of each magnetic field interval; In step S43, the following steps are specifically included: S431, establishing a magnetic field interval based on the center value of any third comprehensive magnetic field data as a basic interval; the expression of the magnetic field interval is: ,in, represents the third integrated magnetic field data of the ith time, represents the basic interval; S432, calculating the data density of each magnetic field interval; the calculation formula of the data density is: ； in, ； In the above formula, represents the data density of the ith magnetic field interval, and Respectively represent the third integrated magnetic field data at the i-th and j-th time, represents half of the basic interval, is a sign function, A represents the total number of the third comprehensive magnetic field data; S44, setting a density threshold, and marking the third comprehensive magnetic field with data density less than the density threshold as segmented magnetic field data, and marking the remaining third comprehensive magnetic field data as concentrated magnetic field data; S45, determining in sequence whether any two magnetic field intervals of segmented magnetic field data have an intersection; S46, determining whether the number of the second segmented magnetic field groups is 3; If yes, proceed to step S47; If not, the size of the basic interval is adjusted according to the number of segmented magnetic fields, and then the process goes to step S43; In step S46, the following steps are specifically included: S461, obtaining the current number of iterations, and determining whether the number of the second segmented magnetic field groups is 3; If yes, proceed to step S467; If not, proceed to step S462; S462, determining whether the number of the second segmented magnetic field groups is 2; If yes, proceed to step S463; If not, proceed to step S465; S463, determining whether the current number of iterations is 1; If yes, the current basic interval is reduced to obtain an updated basic interval, and the process proceeds to step S43; the calculation formula of the updated basic interval is: ； If not, proceed to step S464; S464, determining whether the size of the current basic interval is smaller than the size of the basic interval in the previous iteration; If yes, the current basic interval is reduced to obtain an updated basic interval, and the process goes to step S43; If not, then select an interval whose size is between the current basic interval and the basic interval in the previous iteration as the updated basic interval, and then proceed to step S43; S465, determining whether the current number of iterations is 1; If yes, the current basic interval is increased to obtain an updated basic interval, and the process proceeds to step S43; the calculation formula of the updated basic interval is: ； If not, proceed to step S466; S466, determining whether the size of the current basic interval is greater than the size of the basic interval in the previous iteration; If yes, the current basic interval is increased to obtain an updated basic interval, and the process goes to step S43; If not, then select an interval whose size is between the current basic interval and the basic interval in the previous iteration as the updated basic interval, and then proceed to step S43; S467, reducing the current basic interval to obtain the minimum basic interval when the number of the second segmented magnetic field groups is 3, and then entering step S47; S47, respectively establishing concentrated magnetic field groups using the third integrated magnetic fields corresponding to the minimum spacing between any two adjacent second segmented magnetic field groups; S48, respectively calculating the average value of the concentrated magnetic field data in each magnetic field group as the symmetry center; S49, establishing a standard crack interval containing a number of concentrated magnetic field data in the concentrated magnetic field group with the symmetry center as the median; In step S49, the following steps are specifically included: S491, setting a ratio threshold; S492, taking the symmetry center as the median, sequentially using each concentrated magnetic field data and its symmetric data points about the symmetry center to establish the first crack interval; the expression of the first crack interval is: or ,and ,in, and Respectively represent the concentrated magnetic field data and its symmetrical data points about the symmetry center, Indicates the center of symmetry; S493, respectively calculating the ratio of the number of concentrated magnetic field data in each first crack interval to the total number of concentrated magnetic field data to obtain an interval probability; ； In the above formula, represents the interval probability of the i-th first crack interval, and represent the number of concentrated magnetic field data and the total number of concentrated magnetic field data in the first crack interval respectively; S494, determining whether there is a first crack interval with any interval probability equal to the ratio threshold; If yes, then output the first crack interval as the standard crack interval; If not, proceed to step S495; S495, obtaining two first crack intervals whose interval probabilities are respectively greater than and less than the ratio threshold and whose difference with the ratio threshold is the smallest, and marking them as second crack intervals; S496. Calculate a standard crack interval according to the interval probability and the ratio threshold of the second crack interval; the expression of the standard crack interval is: or ,in, For data points Symmetrical data points about the symmetry center, and are the maximum and minimum values ​​of the intervals of the two second crack intervals that are greater than and less than the ratio threshold, respectively. is the ratio threshold, and are the maximum and minimum values ​​of the interval probabilities of the two second crack intervals that are greater than and less than the ratio threshold, respectively; S5. Obtain the integrated magnetic field at various locations on the cable to be detected in real time, and mark the location corresponding to the integrated magnetic field in the crack interval as a crack area.

2. The identification method according to claim 1, characterized in that: In step S21, the following steps are specifically included: S211, constructing a transient simulation model of the cable, and meshing the simulation model; S212, marking the area where the cable is located as a dynamic area, marking the remaining areas as static areas, and setting a fixed time step to periodically update the grid in the dynamic area; S213, constructing the control equation of the magnetic vector potential in the transient simulation model; the expression of the control equation of the magnetic vector potential is: ； In the above formula, A represents vector potential, t represents time, is the magnetic permeability of the material in the cable, v represents the moving speed of the cable, Excitation current, is the conductivity of the material in the cable, represents the scalar electric potential, represents the coercive force, represents the differential operator; S214, constructing a nonlinear equation group for solving the control equation of the magnetic vector potential to output the motional eddy current through the transient simulation model; the expression of the nonlinear equation group is: ； In the above formula, is the approximate solution to the unknown magnetic vector potential, is a known vector, for The matrix is Non-linear function.

3. The identification method according to claim 1, characterized in that: In step S45, the following steps are specifically included: S451, determining in sequence whether the magnetic field intervals of any two segmented magnetic field data have an intersection or whether there is no third comprehensive magnetic field data between the two; If yes, the two segmented magnetic fields are marked as the same first segmented magnetic field group; If not, the two segmented magnetic fields are marked as different first segmented magnetic field groups; S452, sequentially determining whether there is third comprehensive magnetic field data between any two first segmented magnetic field groups; If yes, the two first segmented magnetic field groups are marked as different second segmented magnetic fields; If not, the two first segmentation magnetic field groups are marked as the same second segmentation magnetic field.

Images