Source linear scanning local CT imaging method, storage medium and computer equipment for high-voltage cable water-blocking buffer layer defect detection

Abstract

The present invention relates to the field of scanning detection and analysis, and in particular to a source linear scanning local CT imaging method for defect detection of a water-blocking buffer layer of a high-voltage cable; based on an X-ray source, a unilateral scan is performed on the cable in a radial direction perpendicular to the cable to obtain projection data after scanning; the projection data is reconstructed using an image reconstruction algorithm to obtain projection information of the complete tested area to check for defects inside the cable. Furthermore, the center of the cable portion to be inspected is placed at the intersection point M of the cross-connecting lines of the two ends of the X-ray source scanning path and the two ends of the flat-panel detector, so that the projection coverage angle of the X-ray source scanning the cable portion to be inspected is maximized; the imaging method of the present invention has a simple motion mode and a fast imaging speed, and the local scanning and reconstruction of the water-blocking buffer layer of the high-voltage cable can realize online monitoring of hidden defects, and the collection of projection data can be realized even in a small space, providing a new idea for internal defect detection of high-voltage cables.

Description

Technical Field

[0001] The present invention relates to the field of scanning detection and analysis, and in particular to a source linear scanning local CT imaging method, a computer-readable storage medium and a computer device for detecting defects in a high-voltage cable water-blocking buffer layer. Background Art

[0002] Cross-linked polyethylene (XLPE) high-voltage cable plays an important role in urban power transmission due to its excellent mechanical properties, good heat resistance, and easy installation and maintenance. The cable consists of a conductor, a conductor shield, an XLPE insulation layer, an insulation shield, a semi-conducting water-blocking buffer layer, an aluminum sheath, and an outer sheath. Figure 1 As shown in the figure, when cables are operated with power for long periods of time, the underground working environment is humid, and some cable trenches or tunnels are severely flooded. The water-blocking buffer layer at the bottom of the high-voltage cable is easily affected by moisture, precipitating white powder, which increases the contact resistance between the insulating shield and the aluminum sheath, thereby generating a certain voltage difference in the radial direction. When the voltage difference exceeds a certain value, it will cause the air gap to break down, causing discharge between the aluminum sheath and the buffer layer. Over time, the buffer layer will be burned, posing a major safety hazard.

[0003] Currently, digital X-ray radiography (DR) technology is one of the primary methods for nondestructive detection of defects in in-service cables. DR images, using varying grayscale values, reveal the differences in X-ray absorption by various cable components. This allows for intuitive detection of the location and size of cable defects while the cable is energized. However, because DR presents a superimposed image of all structural features in a single direction and is obscured by irregular shadows created by gaps between the cable's corrugated aluminum sheath and outer sheath, DR can only detect areas with obvious defects within the cable, failing to distinguish hidden defects from the superimposed information. Computed tomography (CT) technology, by acquiring projection information from various angles, can clearly visualize the object's three-dimensional internal structure and determine the spatial location, shape, and size of defects. Circular scanning is a common scanning method in CT imaging. The X-ray source and detector rotate in a circular motion relative to the object, collecting complete projection data and enabling accurate reconstruction of the object. However, due to the limited space available at underground tunnel cable inspection sites, where cables are often arranged in a straight or triangular pattern, traditional circular CT scanning is challenging for inspecting in-service cables. Therefore, research on new CT imaging methods to detect in-service cables has important practical application value;

[0004] A review of numerous existing inspection reports reveals that defects in the water-blocking buffer layer of XLPE high-voltage cables often occur at the base of the cable connector, with the defects distributed tangentially along the cable's circumference. When examining defects in the water-blocking buffer layer of high-voltage cables, the density of the defects is similar to that of the buffer layer, resulting in low contrast on CT images. Therefore, lower-energy X-rays are required to improve image contrast. However, the cable core is dense, preventing low-energy rays from penetrating. Therefore, the primary objective is to detect tangential defects at the base of the cable's water-blocking buffer layer, with CT scanning performed only on the localized cable base. Furthermore, to meet the requirements of in-service inspection, the corresponding CT scanning imaging equipment should possess a simple structure, simple scanning motion, and be portable and removable. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a source linear scanning local CT imaging method (referred to as L-STCT imaging method) for defect detection of the water-blocking buffer layer of high-voltage cables. The bottom of the water-blocking buffer layer of in-service high-voltage cables is scanned and detected, and the bottom of the water-blocking buffer layer of the high-voltage cables is reconstructed using an iterative reconstruction algorithm. The feasibility of the L-STCT imaging method is verified through simulation experiments and actual experiments.

[0006] A first aspect of an embodiment of the present invention provides a source linear scanning local CT imaging method for detecting defects in a water-blocking buffer layer of a high-voltage cable, comprising the following steps:

[0007] Based on the X-ray source, the cable is scanned unilaterally along the radial direction perpendicular to the cable to obtain the projection data after scanning;

[0008] The projection data is reconstructed using an image reconstruction algorithm to obtain complete projection information of the tested area to check for defects inside the cable.

[0009] Furthermore, the center of the cable to be inspected part is placed at the intersection M of the two ends of the X-ray source scanning path and the two ends of the flat panel detector, so that the projection coverage angle of the X-ray source scanning the cable to be inspected part is maximized.

[0010] Furthermore, the specific method is:

[0011] Cut the radial scanning section of the cable, and construct a coordinate system with the center of the imaging area of the cable to be inspected in the radial scanning section as the origin o;

[0012] In the coordinate system, the two ends of the X-ray source scanning path are crossed with the two ends of the flat panel detector to obtain the intersection point M. The origin o is aligned with point M. At this time, the coordinate system is divided into four areas centered at point M.

[0013] Calculate the maximum projection coverage angle of each data point in the four regions of the coordinate system It is concluded that at point M Get the maximum value, the maximum projection coverage angle of point M Place the center of the cable's inspected portion at point M for scanning and imaging.

[0014] Furthermore, the specific method of constructing the coordinate system is:

[0015] With the center of the imaging area of the cable to be inspected as the origin o, the vertical direction as the x-axis, the horizontal direction as the y-axis, and the axial direction of the cable as the z-axis, an o-xyz coordinate system is constructed, and the vertical upward direction is defined as the positive direction of the x-axis;

[0016] In the o-xyz coordinate system, the horizontal plane of the cone beam center is intercepted along the emission direction of the X-ray source to obtain the radial scanning section of the cable, that is, the xoy coordinate plane; in the xoy coordinate plane, the two end values s1 and s n The two-terminal values d1 and d m Cross-connect to obtain the intersection point M; record point M as the center point of the system, and make the origin o in the xoy coordinate plane coincide with point M.

[0017] Furthermore, the maximum projection coverage angle of each data point in the four regions is calculated The specific method is:

[0018] The horizontal width of the flat panel detector is d, the distance between the cable to be inspected and the X-ray source movement trajectory is h, and the distance between the cable to be inspected and the flat panel detector is l; suppose that any ray u emitted by the X-ray source ij The angle with the x-axis is The angle between the line connecting the focus of the X-ray source and point o and the positive x-axis is β, and the angle between point o and ray u is calculated. ij The distance r; according to the angle between each ray and the x-axis And the distance r from the origin o to the ray, make a Radon space distribution map of the projection data in the system; according to the Radon space distribution map, get the maximum projection coverage angle at point o

[0019] Determine the X-ray source scanning trajectory s, the horizontal width d of the flat panel detector, and the distance l+h between the X-ray source and the flat panel detector; set the two end values s1 and s n The horizontal width of the flat panel detector is d1 and d m Cross-connection, divide the xoy coordinate plane into four regions centered on point M, and calculate the maximum projection coverage angle of each data point in the four regions It is concluded that at the center point M of the system Obtain the maximum value; place the center of the cable to be inspected at point M for scanning imaging.

[0020] Furthermore, the angle The calculation formula is:

[0021]

[0022] In formula (1): l is the distance between the cable to be inspected and the flat panel detector;

[0023] h is the distance between the cable to be inspected and the X-ray source motion trajectory;

[0024] x D ——In the xoy coordinate plane, ray u ij The horizontal coordinate of the intersection point with the flat panel detector, x D ∈[-d / 2,d / 2];

[0025] x S ——In the xoy coordinate plane, ray u ij The horizontal coordinate of the intersection point with the X-ray source scanning trajectory, x S ∈[-s / 2,s / 2];

[0026] The calculation formula of distance r is:

[0027]

[0028] In formula (2): β is the angle between the line connecting the X-ray source to point M and the positive x-axis, β = arctan (-h / x S ), β∈(0,180°); projection coverage angle range The calculation formula is:

[0029]

[0030] In formula (3): ——When the focus of the X-ray source is at s1 and the distance between the emitted ray and the origin o of the xoy coordinate plane is r, the angle between this ray and the x-axis;

[0031] - the angle between the ray received by detector unit d1 and the x-axis when the distance between this ray and the origin o of the xoy coordinate plane is r;

[0032] In formula (3), and The calculation formula is:

[0033]

[0034]

[0035] In formula (5), s is the scanning trajectory of the X-ray source; d is the horizontal width of the flat panel detector.

[0036] Furthermore, when the origin o of the coordinate system in the xoy coordinate plane is located at point M, the maximum The straight-line distance from point M to the scanning path of the X-ray source is Divide the xoy coordinate plane into four areas centered on point M, named Area1, Area2, Area3, and Area4 respectively;

[0037] In Area1, the maximum projection coverage angle of any data point P(x,y) is the angle between ray d1P and ray s1P; the angle between ray d1P and x-axis is The angle between ray s1P and the x-axis is

[0038] In Area2, the maximum projection coverage angle of any data point P(x,y) For ray s n The angle between P and ray s1P; ray s n The angle between P and the x-axis is

[0039] In Area3, the maximum projection coverage angle of any data point P(x,y) For ray d1P and ray d m The angle of P; ray d m The angle between P and the x-axis is

[0040] In Area4, the maximum projection coverage angle of any data point P(x,y) For ray s n P and ray d m P; then the maximum projection coverage angle of the data points in each area The calculation formula is:

[0041]

[0042] In formula (6):

[0043] In the above formula: x – the horizontal coordinate of point P in the xoy coordinate plane;

[0044] y——the vertical coordinate of point P in the xoy coordinate plane.

[0045] Furthermore, the image reconstruction algorithm is an iterative reconstruction algorithm;

[0046] The mathematical model of the iterative reconstruction algorithm is:

[0047] Af=P, (7)

[0048] In formula (7): A=(a ij )∈R I×J ——system projection matrix;

[0049] I——number of projections;

[0050] J——the number of pixels of the reconstructed image;

[0051] P=[p1,p2,…,p I ] T ——projection vector;

[0052] When the system projection matrix A is large, the reconstructed image f cannot be obtained by direct inversion. j , so the SIRT algorithm is used to solve the reconstructed image f j , the formula is as follows:

[0053]

[0054] In formula (8): t is the number of SIRT current iterations;

[0055] λ——relaxation factor.

[0056] A second aspect of an embodiment of the present invention provides a computer-readable storage medium, which stores at least one instruction, and the at least one instruction is used to be executed by a processor to implement the source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of an in-service high-voltage cable as described in the first aspect of the present invention.

[0057] A third aspect of an embodiment of the present invention provides a computer device, comprising a processor and a memory; the memory stores at least one instruction, and the at least one instruction is used to be executed by the processor to implement the source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of in-service high-voltage cables as described in the first aspect of the present invention.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] The L-STCT scanning imaging method has a simple motion mode and a fast imaging speed. The local scanning and reconstruction of the water-blocking buffer layer of the high-voltage cable can realize the online monitoring of hidden defects. Even when the detection site is crowded and the cable spacing is small, the projection data can be collected, which provides a new idea and solution for the internal defect detection of high-voltage cables. By establishing a geometric model, the maximum projection coverage angle of each data point in the imaging system is And scanning parameters were analyzed and it was found that at point M As s and d increase, the corresponding sub-area data points in Area1-4 As the distance h from the cable under test to the X-ray source increases, the collected projection information increases; the increase in the straight-line distance h from the measured cable to the X-ray source movement trajectory will also increase the number of data points in the corresponding sub-area within the scanning system. Increase; use SIRT image reconstruction algorithm for reconstruction. The simulation and actual experimental results show that when the estimated defect position is placed in a rectangular area centered on point M, the defect structure in the imaging area is well reconstructed, and the defect detection in the circumferential tangential direction of the water-blocking buffer layer of the high-voltage cable can be realized; the reconstructed image quality can be improved by increasing d, increasing s or decreasing h.

[0060] The present invention applies CT technology to in-service cable defect detection, solving the problem that conventional portable DR technology and other traditional methods cannot meet the needs of in-service detection. The L-STCT imaging method does not image the cable core conductor, has low requirements for X-ray source power, and has simple scanning motion. It achieves in-service detection of defects and hidden dangers through local scanning and reconstruction of the high-voltage cable water-blocking buffer layer. Even in crowded inspection sites and when cable spacing is small, it can accurately detect defects and hidden dangers, providing a new solution for internal defect detection in high-voltage cables. In addition, this method can be extended to in-service CT inspection of similar pipelines or cables, enriching the application field of CT. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a structural diagram of a high-voltage cable;

[0062] Figure 2 Schematic diagram of the o-xyz coordinate system geometric model of the L-STCT scanning system in the present invention:

[0063] Figure 3 Schematic diagram of the geometric model of the xoy coordinate plane in the present invention;

[0064] Figure 4 : This is the projection data distribution diagram of the L-STCT single-segment scan in Radon space in the present invention;

[0065] Figure 5 Schematic diagram of dividing the xoy coordinate plane into four regions centered at point M in the present invention;

[0066] Figure 6 Schematic diagram of solving the maximum projection coverage angle of each data point in Area 1-4 in the present invention;

[0067] Figure 7 The maximum projection coverage angle distribution diagram of each data point in the L-STCT scanning system of the present invention;

[0068] Figure 8 for Figure 7 Horizontal and vertical profiles passing through point M;

[0069] Figure 9 Schematic diagram of the structure of the simulation model in the simulation experiment of the embodiment of the present invention;

[0070] Figure 10 Schematic diagram of image reconstruction results when changing the X-ray source scanning trajectory s and the horizontal width d of the flat panel detector in a simulation experiment according to an embodiment of the present invention;

[0071] Figure 11 for Figure 10 ROI magnification;

[0072] Figure 12 Schematic diagram of image reconstruction results when the distance h between the X-ray source and the cable to be tested is changed in a simulation experiment according to an embodiment of the present invention;

[0073] Figure 13 for Figure 12 ROI magnification;

[0074] Figure 14 Schematic diagram of the structure of the L-STCT experimental system in the actual experiment of the embodiment of the present invention;

[0075] Figure 15 Schematic diagram of image reconstruction results of changing the X-ray source scanning trajectory s and changing the cable immersion condition in actual experiments of an embodiment of the present invention ((a) s = 120 mm; (b) s = 250 mm; (c) not immersed in water; (d) immersed in water);

[0076] Figure 17 Schematic diagram of the scanning mode of the STCT scanning system;

[0077] Figure 18 Schematic diagram of the scanning mode of the L-STCT scanning system;

[0078] Figure 19 Schematic diagram of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0079] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0080] Example 1:

[0081] A source linear scanning local CT imaging method for detecting defects in a high-voltage cable water-blocking buffer layer includes the following steps:

[0082] S1: Set up the L-STCT scanning imaging system: set up the X-ray source and flat panel detector at intervals. The X-ray source and flat panel detector are placed on both sides of the cable to be tested. The flat panel detector is close to the cable to be tested, and the center of the flat panel detector is aligned with the bottom of the cable.

[0083] S2: With the center of the imaging area of the cable to be inspected as the origin o, the vertical direction as the x-axis, the horizontal direction as the y-axis, and the axial direction of the cable as the z-axis, an o-xyz coordinate system is constructed, and the vertical upward direction is defined as the positive direction of the x-axis; the flat-panel detector and the cable to be tested remain stationary, and the X-ray source is translated equidistantly along the x-axis to scan the cable to be inspected;

[0084] S3: In the o-xyz coordinate system, intercept the horizontal plane of the cone beam center along the emission direction of the X-ray source to obtain the radial scanning section of the cable, that is, the xoy coordinate plane; in the xoy coordinate plane, the two end values s1 and s n The two-terminal values d1 and d m Cross-connect to obtain the intersection point M; record point M as the center point of the system, and make the origin o in the xoy coordinate plane coincide with point M;

[0085] S4: The horizontal width of the flat panel detector is d, the distance between the cable to be inspected and the X-ray source trajectory is h, and the distance between the cable to be inspected and the flat panel detector is l; let any ray u emitted by the X-ray source be ij The angle with the x-axis is The angle between the line connecting the focus of the X-ray source and point o and the positive x-axis is β, and the angle between point o and ray u is calculated. ij The distance r; for a cable with a radius of R, its projection covers an angle range is defined as the angle between the ray passing through d1 and tangent to the cable and the ray passing through s1 and tangent to the cable; And the distance r from the origin o to the ray can be used to obtain the Radon space distribution diagram of the projection data collected in the L-STCT scanning imaging system; according to the Radon space distribution diagram, it can be obtained that at point o, Has the maximum value, recorded as the maximum projection coverage angle

[0086] S5: To prove the properties of point M, determine the X-ray source scanning trajectory s, the horizontal width d of the flat panel detector, and the distance l+h between the X-ray source and the flat panel detector. At this time, a unique point M can be obtained. The two end values s1 and s n The horizontal width of the flat panel detector is d1 and d mCross-connection, divide the xoy coordinate plane into four regions centered on point M, and calculate the maximum projection coverage angle of each data point in the four regions It is concluded that at the center point M of the system Get the maximum value; at this time, define the system imaging area FOV as a rectangular area centered on point M; place the center of the cable's to-be-tested part at point M for scanning and imaging;

[0087] S6: Reconstruct the projection data of the cable to be inspected portion scanned by the X-ray source through an iterative reconstruction algorithm.

[0088] In step S4, the angle The calculation formula is:

[0089]

[0090] In formula (1): l is the distance between the cable to be inspected and the flat panel detector;

[0091] h is the distance between the cable to be inspected and the X-ray source motion trajectory;

[0092] x D ——In the xoy coordinate plane, ray u ij The horizontal coordinate of the intersection point with the flat panel detector, x D ∈[-d / 2,d / 2];

[0093] x S ——In the xoy coordinate plane, ray u ij The horizontal coordinate of the intersection point with the X-ray source scanning trajectory, x S ∈[-s / 2,s / 2];

[0094] The calculation formula of distance r is:

[0095]

[0096] In formula (2): β is the angle between the line connecting the X-ray source to point M and the positive x-axis, β = arctan (-h / x S ), β∈(0,180°); projection coverage angle range The calculation formula is:

[0097]

[0098] In formula (3): ——When the focus of the X-ray source is at s1 and the distance between the emitted ray and the origin o of the xoy coordinate plane is r, the angle between this ray and the x-axis;

[0099] - the angle between the ray received by detector unit d1 and the x-axis when the distance between this ray and the origin o of the xoy coordinate plane is r;

[0100] In formula (3), and The calculation formula is:

[0101]

[0102]

[0103] In formula (5), s is the scanning trajectory of the X-ray source; d is the horizontal width of the flat panel detector.

[0104] Introducing The Radon transform space of the coordinate system is used to describe the projection data. Each point in the Radon space represents the projection data obtained by each ray at different projection angles and positions. The projection data distribution of the L-STCT single-segment scan in the Radon space can be obtained by equations (1) to (3), as follows: Figure 4 shown; in Figure 4 It can be obtained that when r = 0, that is, at point M (also the coordinate origin o), Get the maximum value and record it as the maximum projection coverage angle

[0105] In step S5, when the origin o of the coordinate system in the xoy coordinate plane is located at point M, the maximum At this time, the system parameters meet The straight-line distance from point M to the scanning path of the X-ray source is Divide the xoy coordinate plane into four areas centered on point M, named Area1, Area2, Area3, and Area4 respectively;

[0106] In Area1, the maximum projection coverage angle of any data point P(x,y) is the angle between ray d1P and ray s1P; the angle between ray d1P and x-axis is The angle between ray s1P and the x-axis is

[0107] In Area2, the maximum projection coverage angle of any data point P(x,y) For ray s n The angle between P and ray s1P; ray s n The angle between P and the x-axis is

[0108] In Area3, the maximum projection coverage angle of any data point P(x,y) For ray d1P and ray d m The angle of P; ray d m The angle between P and the x-axis is

[0109] In Area4, the maximum projection coverage angle of any data point P(x,y) For ray s n P and ray d m The angle of P; Figure 6 Shown: (a) Area1, (b) Area2, (c) Area3, (d) Area4;

[0110] The maximum projection coverage angle of the data points in each area is The calculation formula is:

[0111]

[0112] In formula (6):

[0113] In the above formula: x – the horizontal coordinate of point P in the xoy coordinate plane;

[0114] y——the vertical coordinate of point P in the xoy coordinate plane;

[0115] from Figure 6 It can be seen that when the other parameters remain unchanged, the maximum projection coverage angle of the data points in Area1, Area2 and Area4 is It will increase with the increase of X-ray source scanning track s; when a larger flat panel detector is selected, the maximum projection coverage angle of Area1, Area2, and Area4 When the distance l+h between the X-ray source and the flat panel detector is reduced, the maximum projection coverage angle of Area1, Area2, and Area4 It will also increase accordingly, and vice versa.

[0116] According to formula (6), the maximum projection coverage angle of each data point in Area1, Area2, Area3, and Area4 can be obtained: Distribution map, such as Figure 7 As shown, the horizontal and vertical coordinates determine the geometric position of the data point in the xoy coordinate plane, and the corresponding values represent the maximum projection coverage angle exist Figure 7 It can be seen that the maximum projection coverage angle at point M Maximum, proving the properties of point M. Now we can get:

[0117]

[0118] Figure 8 for Figure 7 Horizontal line profile through point M ( Figure 8 (a)) and vertical line profile ( Figure 8 (b));

[0119] like Figure 8 (a) shows: In the area around point M, namely Area 1 and Area 4, the maximum projection coverage angle Symmetrical distribution, gradually decreasing to the left and right sides of the y-axis of the xoy coordinate plane;

[0120] like Figure 8 (b) shows the maximum projection coverage angle in the upper and lower areas of point M, namely Area 2 and Area 3. It gradually decreases toward the upper and lower sides of the x-axis of the xoy coordinate plane, and decreases faster toward the direction of the ray source.

[0121] From the above analysis, it can be seen that due to the limitations of the scanning system and the spatial environment of the imaging object, the projection angle is limited, and the L-STCT scan cannot obtain the complete data required for image reconstruction. The maximum is less than 180°, and decreases towards the left and right sides of the y-axis and the left and right sides of the x-axis;

[0122] When reconstructing an image from limited-angle projection data, if the boundary of a feature of the detected object is tangent to a ray in the limited data set, then the boundary is easy to reconstruct from the limited data, otherwise it is difficult to reconstruct. For a single data point P(x,y), the projection covers an angle range of The larger the value, the better the reconstructed image result will be. In the L-STCT imaging system, when other parameters remain unchanged, the projection coverage angle range of the data points of Area1, Area3 and Area4 is It is positively correlated with the horizontal width d of the flat panel detector. The larger d is, The larger the size, the more projection data is collected; so in actual use, a larger flat panel detector can be selected as much as possible; the longer the X-ray source scanning track s is, the more data points in Area1, Area2 and Area4 are collected. The larger the value, the more rays at different angles there are. You can choose to increase s to improve the quality of the reconstructed image. In addition, reducing the distance h between the X-ray source trajectory and the object under test will also make the data points in Area1, Area2 and Area4 The value of increases.

[0123] In traditional circular CT scanning, the beam must rotate at least 180° plus a fan angle around the object to obtain complete projection data for image reconstruction. Therefore, the area through which all rays pass at all angles is defined as the system's field of view (FOV). The FOV is a circular region whose radius is related to the distance from the ray source to the center of rotation, the distance from the center of rotation to the detector, and the effective width of the detector. Furthermore, every point within this region is passed by rays for at least 180°, enabling accurate reconstruction of every point within the region. When the ray angle is less than 180°, this becomes a limited-angle problem within the CT system.

[0124] The above analysis shows that the L-STCT scanning system is not sufficient to cover 180°, so it is impossible to use a complete circular area to describe the L-STCT imaging area. However, in the area where the ray passes, a part of the area has a relatively larger amount of data, which is mainly concentrated near point M. The maximum projection coverage angle of the data points in this area is A relatively large area will make the reconstructed image quality relatively better. Therefore, in order to improve the imaging quality, the present invention defines the L-STCT imaging area FOV as a rectangular area centered on point M. When detecting defects in the water-blocking buffer layer of a high-voltage cable, the estimated defect position (the bottom of the high-voltage cable buffer layer) is placed in the FOV. At this time, the maximum projection coverage angle of each data point in the rectangular area is the largest, and the image reconstruction result is the best. The size of the FOV area is determined according to the actual detection requirements;

[0125] The essence of L-STCT imaging is the limited angle problem in CT imaging. Through incomplete scanning of the object to be tested, tomographic detection of its internal structure and defects is achieved. During the scanning process, for each focal position of the X-ray source, projection data of one angle can be obtained. Due to the limited distance between the X-ray source and the flat-panel detector in actual cable detection, and the large volume of the cable, the rays emitted by the X-ray source can only irradiate a part of the cable. The projection data at each angle is truncation and only contains the projection of part of the cable. The use of traditional analytical reconstruction algorithms (such as FBP algorithms) will produce serious truncation artifacts. In order to obtain a higher quality reconstructed image, the present invention uses an iterative reconstruction algorithm to reconstruct the scanned image; compared with the analytical reconstruction algorithm, the iterative reconstruction algorithm has lower requirements on data consistency and stronger noise resistance;

[0126] The mathematical model of the iterative reconstruction algorithm is:

[0127] Af=P, (7)

[0128] In formula (7): A=(a ij )∈R I×J ——system projection matrix;

[0129] I——number of projections;

[0130] J——the number of pixels of the reconstructed image;

[0131] P=[p1,p2,…,p I ] T ——projection vector;

[0132] When the system projection matrix A is large, the reconstructed image f cannot be obtained by direct inversion. j Therefore, the SIRT algorithm (joint iterative reconstruction algorithm) is used to solve the reconstructed image f j , the formula is as follows:

[0133]

[0134] In formula (8): t is the number of SIRT current iterations;

[0135] λ is the relaxation factor. The relaxation factor λ affects the convergence speed during the iteration process. When the value of λ is too large, the algorithm converges quickly, but the noise components introduced into the reconstructed image increase. When the value of λ is too small, the reconstructed image becomes smooth, but the algorithm converges slowly.

[0136] Simulation experiment:

[0137] In order to verify the source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of a high-voltage cable provided in Example 1, Figure 9 The simulation model shown is subjected to simulation scanning and image reconstruction;

[0138] The simulation model simulates the structure of a high-voltage cable, which consists of a multi-layer concentric circle structure with a metal conductor in the middle. The water-blocking buffer layer material is spirally wrapped and overlapped on the outside of the XLPE insulation layer. During operation, the water-blocking buffer layer absorbs water and swells after being damp. Under the pressure of the aluminum protective sheath, a chemical reaction will occur to produce a large amount of white powder accumulated at the bottom of the cable, which will visually show that the water-blocking buffer layer has become thicker or overlapped. As the amount of white powder increases, the potential difference between the water-blocking tape and the aluminum protective sheath increases. When the potential difference exceeds a certain range, it will cause current breakdown, triggering ablation of the insulation shielding layer, ablation holes, and even penetration of the insulation shielding layer. Therefore, during the simulation experiment, the following is set at the bottom of the water-blocking buffer layer of the simulation model. Figure 10 The different simulated defects shown are circular and elliptical, simulating ablation defects caused by current breakdown, and strip-shaped, simulating cracks or other defects. The changes in the ring structure of the simulation model itself can be used to observe whether the cable is leaking water, resulting in the accumulation of white powder.

[0139] The simulation model was placed between the X-ray source and the flat-panel detector. The o-xyz coordinate system and the xoy coordinate plane were constructed as described above. Since point M coincided with the origin o of the xoy coordinate plane, the estimated defect location of the simulation model (i.e., the bottom of the model) was placed at the origin o of the xoy coordinate plane as described above. The simulation model, with various defects, was scanned and the imaging area FOV was reconstructed using the SIRT algorithm. The reconstructed image had a size of 308 × 128 pixels. The SIRT relaxation factor λ was set to 0.8, and the number of iterations was set to 500. The programming environment was Matlab R2017a, Windows 10 64-bit, 8.0GB of RAM, a 3.4GHz CPU, and an NVIDIA GeForce GT720. Specific scanning parameters are shown in Table 1.

[0140] Table 1 Simulation experiment scanning parameters

[0141] Table 1 Scanning parameters of siMulation experiments

[0142]

[0143] Figure 10 (a) is the reconstruction result when the X-ray source scanning trajectory s is changed. From left to right, they are the reconstruction results when the X-ray source scanning trajectory s is 150mm, 250mm, and 350mm respectively, while other parameters remain unchanged. It can be seen that due to the incomplete projection data obtained by the L-STCT scan and the truncation of the projection data, some white strip artifacts pointed by arrow 1 appear in the reconstructed image. Since there are fewer rays tangent to the direction parallel to the x-axis, there are obvious artifacts in the upper and lower parts of the annular structure and the circular simulated defects, but the bottom structure of the cable is completely reconstructed, and the elliptical defects and strip defects are clearly visible and the structure is complete. As s increases, the scanning system area Area1, Area2 and Area4 of each data point becomes relatively larger, and the number of projection rays tangent to the cable increases, making the upper structure of the image reconstruction result more complete (such as Figure 10 (a) as shown by arrow 2); the stripe artifacts caused by the lack of projection information are reduced (e.g. Figure 10 As shown by arrow 1 in (a), the stripe artifacts on the annular structure and circular defect are reduced, the structure becomes complete, and the image details become clearer. The above features can also be observed from the ROI magnified detail image shown in Figure 11;

[0144] Figure 10(b) The scan image reconstruction results when the horizontal width d of the flat-panel detector is changed. d is equal to the product of the number of detector elements m and the detector element size. In the simulation experiment, the size of d is changed by changing m. Figure 10 In (b), each row is the reconstructed image of a different defect simulation model, and each column is the reconstructed image when the number of detectors M is 1536, 2536, and 3536. As d increases, the system scans each data point in Area1, Area3, and Area4. As the diameter of the cable increases, the effective projection data received by the flat-panel detector increases, and the number of rays tangent to the edge structure of the cable increases, so that the structure below the image reconstruction result becomes complete (as shown by arrow 3), the ring structure and the structure below the circular defect become clearer, and the reconstructed image quality improves;

[0145] In the actual detection process, it is very important to determine the distances (i.e., l and h) between the cable under test and the X-ray source motion trajectory and the flat panel detector. When the distance l between the cable under test and the flat panel detector remains unchanged, the smaller the straight-line distance h between the cable under test and the X-ray source motion trajectory, the more rays tangent to the upper structure of the FOV area under the same X-ray source scanning trajectory s, and the scanning system for each data point in Area 1, Area 2, and Area 4. Get bigger. Figure 12 The reconstructed images are shown when h is 70mm, 120mm, and 150mm respectively, with other parameters remaining unchanged. As h increases, as indicated by arrows 4 and 5, the upper structure of the FOV area becomes blurred, the stripe artifacts in the image become more numerous, and the reconstructed image quality deteriorates. Figure 13 This is the enlarged image of the reconstruction result ROI details;

[0146] In summary, the L-STCT scanning imaging system produces a good reconstructed image of the cable bottom, and defects in the cable's water-blocking buffer layer are clearly visible, demonstrating the effectiveness of the proposed method. Increasing s or decreasing h increases the maximum projection coverage angle within the corresponding subregion, increasing the number of visible structures above the FOV. Increasing d also increases the maximum projection coverage angle within the corresponding subregion, increasing the number of visible structures below the FOV.

[0147] Actual test:

[0148] In order to further verify the source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of a high-voltage cable provided in Example 1, actual experiments were used to verify it again.

[0149] In this experiment, a L-STCT scanning imaging system was built. Figure 14As shown in the figure, experiments were carried out. The system consists of an X-ray source, a flat-panel detector, two linear slides and a computer. The two linear slides are used to control the movement of the X-ray source and the flat-panel detector, as well as to change the translation distance of the X-ray source. The computer is used to coordinate the work between the subsystems.

[0150] Based on the above experimental system, L-STCT scanning of high-voltage cables is performed. The radius R of the cable to be tested is 50mm, and it consists of multiple ring structures. In this experimental system, the X-ray source moves in the horizontal direction, and the cable is placed in the vertical direction. The distance a from the center of the cable to the coordinate origin is 35mm, and local imaging is performed on its left side. The distance from the ray source to the detector is 150mm, the distance h between the X-ray source movement trajectory and the part of the cable to be inspected is 98mm, the distance l from the flat-panel detector to the part of the cable to be inspected is 52mm, and the X-ray source scanning trajectory s is 250mm. The system center point M is determined to coincide with the coordinate origin o. The FOV area is set to be 30×80mm with point M as the center at the bottom of the cable. 2 The other scanning parameters are as shown in Table 1 in the previous simulation experiment. The scanned image is reconstructed using the algorithms shown in Equations (7) and (8). The relaxation factor λ in Equation (8) is set to 0.8 and iterated 500 times.

[0151] Figure 15 Figures (a) and (b) show the slice reconstruction results of the 900th cable layer with X-ray source scanning trajectories s of 120 mm and 250 mm, respectively, while other parameters remain unchanged. Due to truncated and incomplete projection data, some stripe artifacts still exist in the reconstructed image, but the fine stripe structure within the water-blocking buffer layer is clearly visible. As s increases, the FOV area structure becomes more complete, stripe artifacts are reduced, image details become clearer, and the reconstructed image quality improves. The small bright spots in the figure are metal shavings (copper or aluminum) that fell into the cable segment during cutting. To simulate actual inspection conditions, the cable was scanned and reconstructed before and after immersion in water. Figure 15 (c) and (d) are the slice reconstruction results of the 900th layer of the cable before and after 10 hours of immersion. The line structure of the buffer layer before immersion is thin and neat, while the line structure of the buffer layer after immersion becomes thicker and is completely penetrated by water molecules, and the buffer layer structure undergoes a more obvious change. Figure 15 As shown, the annular structure of the cable has been completely restored, indicating that no serious current breakdown has occurred, resulting in the cable being burned and damaged.

[0152] Figure 16 The control experimental group is the image reconstruction result of another cable of the same size: s is 120mm, and other parameters remain unchanged. The cable, which has been immersed in water for 2 hours, is left to stand for 25 minutes ( Figure 16 (a)) and 4.5h( Figure 16(b)). After immersion in water, water molecules enter the buffer layer material, increasing the overall density of the buffer layer material. As the diffusion time of the water molecules increases, the cable aluminum sheath undergoes further chemical reactions, producing white powder that accumulates in the water-blocking buffer layer. The line structure of the buffer layer becomes thicker, and the structural change effect is enhanced, making it possible to clearly observe the scope of cable leakage and the actual situation.

[0153] In actual experiments, due to the limited CT projection angle and truncation of projection information, Figure 15 and Figure 16 There are obvious artifacts in the reconstruction results, but the structural changes caused by the leakage water are clearly visible, and the FOV area is completely reconstructed, verifying the effectiveness of this imaging method in high-voltage cable defect detection.

[0154] like Figure 17 、 Figure 18 As shown in the figure, L-STCT is similar to STCT in terms of scanning motion. The main difference is that in the STCT scanning system, the object to be measured is placed close to the X-ray source, and the complete projection data of the object is collected through multi-segment STCT (mSTCT) scanning; in the L-STCT scanning system, the object to be scanned is closer to the flat-panel detector, and the maximum projection coverage angle of each data point in the imaging area is calculated based on the maximum projection coverage angle of each data point in the imaging area. Distribution, so that the local imaging center of the object to be measured is close to point M, and CT imaging is performed on the local area;

[0155] The present invention proposes an L-STCT imaging method to meet the defect detection needs of the water-blocking buffer layer of in-service high-voltage cables. By establishing a geometric model, the maximum projection coverage angle of each data point in the imaging system is And scanning parameters were analyzed and it was found that at point M As s and d increase, the data points in the corresponding sub-areas of Area1-4 As the distance h from the cable to the X-ray source increases, the amount of projection information collected increases; as the distance h increases, the amount of data points in the corresponding sub-area of the scanning system Increase; use the SIRT image reconstruction algorithm for scanning and reconstruction. The simulation and actual experimental results show that when the estimated defect position is placed in a rectangular area centered on point M, the defect structure in the imaging area is well reconstructed, and the defect detection in the circumferential tangential direction of the water-blocking buffer layer of the high-voltage cable can be realized. The reconstructed image quality can be improved by increasing d, increasing s, or decreasing h.

[0156] Example 2:

[0157] A second embodiment of the present invention further provides a computer-readable storage medium storing a computer program. When executed by a processor, the computer program executes the source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of in-service high-voltage cables, as described in the above method embodiment. The storage medium may be a volatile or non-volatile computer-readable storage medium.

[0158] Example 3:

[0159] Based on the same technical concept, the present invention also provides a computer device in the third embodiment. Figure 19 8 is a schematic diagram of the structure of a computer device 800 according to an embodiment of the present invention, comprising a processor 801, a memory 802, and a bus 803. The memory 802 is used to store execution instructions and includes a memory 8021 and an external memory 8022. The memory 8021, also referred to as internal memory, is used to temporarily store computational data in the processor 801 and data exchanged with an external memory 8022, such as a hard disk. The processor 801 exchanges data with the external memory 8022 via the memory 8021.

[0160] In the third embodiment, the memory 802 is specifically used to store program logic code corresponding to the scanning control method and / or image reconstruction algorithm of the X-ray source in the first embodiment of the present invention, and is controlled and executed by the processor 801. That is, when the computer device 800 is running, the processor 801 communicates with the memory 802 via the bus 803, so that the processor 801 executes the application code stored in the memory 802, thereby controlling the scanning action of the X-ray source and / or the complete reconstruction of the scanned image in the first embodiment.

[0161] Processor 801 may be an integrated circuit chip with signal processing capabilities. The aforementioned processor may be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it may also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. It may implement or execute the various methods, steps, and logic block diagrams disclosed in the embodiments of the present invention. The general-purpose processor may be a microprocessor or any conventional processor.

[0162] Among them, the memory 802 can be, but is not limited to, random access memory (RAM), read only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), etc.

[0163] It is understandable that the third embodiment and Figure 19 The structure illustrated in the figure does not constitute a specific limitation on computer device 800. In actual use, computer device 800 may include more or fewer components than shown, or some components may be combined or separated, or the components may be arranged differently. The components shown in the figure may be implemented in hardware, software, or a combination of software and hardware.

[0164] In addition, the present invention also provides a computer program product, which carries a program code. The instructions included in the program code can be used to execute the source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of in-service high-voltage cables described in the above method embodiment. For details, please refer to the implementation method in Example 1, which will not be repeated here.

[0165] The computer program product may be implemented in hardware, software, or a combination thereof. In one embodiment, the computer program product is implemented as a computer storage medium. In another embodiment, the computer program product is implemented as a software product, such as a software development kit (SDK).

[0166] Finally, it should be understood that those skilled in the art will appreciate that the embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention may be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0167] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0168] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0169] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0170] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0171] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of high-voltage cables, characterized in that: The steps include: Based on the X-ray source, the cable is scanned unilaterally along the radial direction perpendicular to the cable to obtain the projection data after scanning; Use image reconstruction algorithms to reconstruct projection data to obtain complete projection information of the tested area to check for defects inside the cable; The image reconstruction algorithm is an iterative reconstruction algorithm; The mathematical model of the iterative reconstruction algorithm is: Af=P, (7) In formula (7): A=(a ij )∈R I×J ——system projection matrix; I——number of projections; J——the number of pixels of the reconstructed image; P=[p1,p2,…,p I ] T ——projection vector; When the system projection matrix A is large, the reconstructed image f cannot be obtained by direct inversion. j , so the SIRT algorithm is used to solve the reconstructed image f j , the formula is as follows: In formula (8): t is the number of SIRT current iterations; λ——relaxation factor.

2. The source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of a high-voltage cable according to claim 1, characterized in that: The center of the cable to be inspected part is placed at the intersection point M of the lines connecting the two ends of the X-ray source scanning path and the two ends of the flat panel detector, so that the projection coverage angle of the X-ray source scanning the cable to be inspected part is maximized.

3. The source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of a high-voltage cable according to claim 2, characterized in that: The specific method is: Cut the radial scanning section of the cable, and construct a coordinate system with the center of the imaging area of the cable to be inspected in the radial scanning section as the origin o; In the coordinate system, the two ends of the X-ray source scanning path are crossed with the two ends of the flat panel detector to obtain the intersection point M. The origin o is aligned with point M. At this time, the coordinate system is divided into four areas centered at point M. Calculate the maximum projection coverage angle of each data point in the four regions of the coordinate system It is concluded that at point M Get the maximum value, the maximum projection coverage angle of point M Place the center of the cable's inspected portion at point M for scanning and imaging.

4. The source linear scanning local CT imaging method for detecting defects in a high-voltage cable water-blocking buffer layer according to claim 3, characterized in that: The specific method of constructing the coordinate system is: With the center of the imaging area of the cable to be inspected as the origin o, the vertical direction as the x-axis, the horizontal direction as the y-axis, and the axial direction of the cable as the z-axis, an o-xyz coordinate system is constructed, and the vertical upward direction is defined as the positive direction of the x-axis; In the o-xyz coordinate system, the horizontal plane of the cone beam center is intercepted along the emission direction of the X-ray source to obtain the radial scanning section of the cable, that is, the xoy coordinate plane; in the xoy coordinate plane, the two end values s1 and s n The two-terminal values d1 and d m Cross-connect to obtain the intersection point M; record point M as the center point of the system, and make the origin o in the xoy coordinate plane coincide with point M.

5. The source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of a high-voltage cable according to claim 4, characterized in that: Calculate the maximum projection coverage angle for each data point in the four regions The specific method is: The horizontal width of the flat panel detector is d, the distance between the cable to be inspected and the X-ray source movement trajectory is h, and the distance between the cable to be inspected and the flat panel detector is l; suppose that any ray u emitted by the X-ray source ij The angle with the x-axis is The angle between the line connecting the focus of the X-ray source and point o and the positive x-axis is β, and the angle between point o and ray u is calculated. ij The distance r; according to the angle between each ray and the x-axis And the distance r from the origin o to the ray, make a Radon space distribution map of the projection data in the system; according to the Radon space distribution map, get the maximum projection coverage angle at point o Determine the X-ray source scanning trajectory s, the horizontal width d of the flat panel detector, and the distance l+h between the X-ray source and the flat panel detector; set the two end values s1 and s n The horizontal width of the flat panel detector is d1 and d m Cross-connection, divide the xoy coordinate plane into four regions centered on point M, and calculate the maximum projection coverage angle of each data point in the four regions It is concluded that at the center point M of the system Obtain the maximum value; place the center of the cable to be inspected at point M for scanning imaging.

6. The source linear scanning local CT imaging method for detecting defects in a high-voltage cable water-blocking buffer layer according to claim 5, characterized in that: Angle The calculation formula is: In formula (1): l is the distance between the cable to be inspected and the flat panel detector; h is the distance between the cable to be inspected and the X-ray source motion trajectory; x D ——In the xoy coordinate plane, ray u ij The horizontal coordinate of the intersection point with the flat panel detector, x D ∈[-d / 2,d / 2]; x S ——In the xoy coordinate plane, ray u ij The horizontal coordinate of the intersection point with the X-ray source scanning trajectory, x S ∈[-s / 2,s / 2]; The calculation formula of distance r is: In formula (2): β is the angle between the line connecting the X-ray source to point M and the positive x-axis, β = arctan (-h / x S ), β∈(0,180°); Projection coverage angle range The calculation formula is: In formula (3): ——When the focus of the X-ray source is at s1 and the distance between the emitted ray and the origin o of the xoy coordinate plane is r, the angle between this ray and the x-axis; - the angle between the ray received by detector unit d1 and the x-axis when the distance between this ray and the origin o of the xoy coordinate plane is r; In formula (3), and The calculation formula is: In formula (5), s is the scanning trajectory of the X-ray source; d is the horizontal width of the flat panel detector.

7. The source linear scanning local CT imaging method for detecting defects in a high-voltage cable water-blocking buffer layer according to claim 6, characterized in that: When the origin o of the coordinate system in the xoy coordinate plane is located at point M, the maximum The straight-line distance from point M to the scanning path of the X-ray source is Divide the xoy coordinate plane into four areas centered on point M, named Area1, Area2, Area3, and Area4 respectively; In Area1, the maximum projection coverage angle of any data point P(x,y) is the angle between ray d1P and ray s1P; the angle between ray d1P and x-axis is The angle between ray s1P and the x-axis is In Area2, the maximum projection coverage angle of any data point P(x,y) For ray s n The angle between P and ray s1P; ray s n The angle between P and the x-axis is In Area3, the maximum projection coverage angle of any data point P(x,y) For ray d1P and ray d m The angle of P; ray d m The angle between P and the x-axis is In Area4, the maximum projection coverage angle of any data point P(x,y) For ray s n P and ray d m The angle of P; The maximum projection coverage angle of the data points in each area is The calculation formula is: In formula (6): In the above formula: x – the horizontal coordinate of point P in the xoy coordinate plane; y——the vertical coordinate of point P in the xoy coordinate plane.

8. A computer-readable storage medium, characterized in that The storage medium stores at least one instruction, and the at least one instruction is used to be executed by the processor to implement the source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of an in-service high-voltage cable as described in any one of claims 1-7.

9. A computer device comprising a processor and a memory; the memory storing at least one instruction, the at least one instruction being executed by the processor to implement the source linear scanning local CT imaging method for detecting defects in the water-blocking buffer layer of an in-service high-voltage cable as described in any one of claims 1 to 7.

Images