CN110320274B - A Reconstruction Method of Internal Defects in Three-pillar Insulator Based on Ultrasonic Scanning Principle - Google Patents

Abstract

The invention discloses a method for reconstructing internal defects of a three-pillar insulator based on an ultrasonic scanning principle, comprising the steps of: S1, building an ultrasonic inspection system; S2, the ultrasonic inspection system detects the same position of the three-pillar insulator, and records the position of each inspection position. Ultrasonic reflection echo information; S3. Use the analogy method to judge the ultrasonic reflection echo information of each detection position to determine the defect position; S4. The ultrasonic inspection system performs ultrasonic scanning near the defect position, and records the ultrasonic reflection of each detection position Echo information; S5 , constructing a corresponding relationship between ultrasonic reflected echo information, defect depth and defect size, and obtaining a schematic diagram of defect reconstruction based on the detection results of each scanning position. The invention can identify, locate and quantify the internal defects of the three-pillar insulator efficiently, accurately and intuitively.

Description

A Reconstruction Method of Internal Defects in Three-pillar Insulator Based on Ultrasonic Scanning Principle

technical field

The invention relates to the field of power transmission and transformation insulation equipment, in particular to a method for reconstructing internal defects of a three-pillar insulator based on the principle of ultrasonic scanning.

Background technique

Three-pillar insulators are key electrical components in gas-insulated metal-enclosed transmission lines (GILs), serving as electrical insulation and mechanical support. The three-pillar insulator is made by mixing epoxy resin, curing agent (usually acid anhydride) and filler (alumina powder) into a mold with aluminum alloy inserts and curing at high temperature. If the quality control of the curing process is not good, the three-pillar insulator is The epoxy material of the insulator and the aluminum alloy will have defects such as shelling, interlayer, and loose bonding (these defects are collectively referred to as internal defects), especially the solid epoxy material and the grounding insert at the mold joint of the three-pillar insulator column foot binding site. In the actual application process, internal defects will cause uneven distribution of the electric field inside the insulator, resulting in partial discharge of the insulator, abnormal heating of the insulator, etc., which will accelerate the aging of the insulator, reduce the performance of the insulator, and directly threaten the normal operation of the GIL. Therefore, early confirmation of whether the three-pillar insulator has internal defects is of great significance to ensure the safe operation of the power system.

At present, the defect detection of three-pillar insulators is generally in the factory test stage, and two detection methods are commonly used: one is the direct method, that is, the industrial digital X-ray imaging technology is used, and the insulator is judged by comparing the brightness of the X-ray penetrating wave on the display panel. Whether there are internal defects such as air gaps, cracks, interlayers, etc., the advantages are defect visualization and high detection efficiency, but the detection sensitivity of crack defects with small widths is not high, and the X-ray radiation is harmful to the human body. X-ray imaging machine Expensive, bulky, unable to detect insulators in the process of assembly and maintenance; the other is the indirect method that uses power frequency partial discharge detection methods, including pulse current method, UHF method, acoustic detection method, optical detection method The most widely used method is the pulse current method, but it is difficult to accurately identify the defect location and defect shape of the insulator.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art, and to provide a method for reconstructing internal defects of a three-pillar insulator based on the principle of ultrasonic scanning. The invention has low detection cost, high detection accuracy, convenient portability, no radiation harm to human body, and can efficiently, accurately and intuitively identify, locate and quantify the internal defects of the GIL three-pillar insulator.

The object of the present invention can be realized through the following technical solutions:

A method for reconstructing internal defects of a three-pillar insulator based on the principle of ultrasonic scanning, comprising the steps of:

S1. Build an ultrasonic testing system;

S2. Use the ultrasonic testing system to detect the same position of the three-pillar insulator, and record the ultrasonic reflection echo information of each detection position;

S3. Use the analogy method to judge the ultrasonic reflection echo information of each detection position, and determine the defect position;

S4. Use the ultrasonic inspection system to perform ultrasonic scanning near the defect position, and record the ultrasonic reflection echo information of each inspection position;

S5 , constructing the correspondence between the ultrasonic reflected echo information and the defect shape and size, and obtaining a schematic diagram of defect reconstruction based on the detection results of each scanning position, so as to quantify the size of the defect and identify the shape of the defect.

Specifically, in step S1, the ultrasonic detection system includes an ultrasonic pulse generator, an oscilloscope, a narrow-pulse ultrasonic straight probe, a probe adapter line and a high-impedance transmission line.

The ultrasonic pulse generator is a pulse generator with sharp pulse excitation, adjustable output pulse width and gain, and low noise. The sharp pulse excitation can optimize the broadband response and improve the detection near-surface resolution, which is more conducive to strong attenuation of the sound beam. material detection and measurement applications.

The oscilloscope is a four-channel high-performance digital storage oscilloscope with a maximum sampling frequency of 1GHz and a sampling bandwidth of 200MHz. The input channel of the oscilloscope and the signal output end of the ultrasonic pulse generator are connected to the potential through a high-impedance transmission line, so that the emission and signal output can be displayed on the oscilloscope in real time. received ultrasound signal.

The narrow-pulse ultrasonic straight probe belongs to a cylindrical longitudinal wave straight probe, which adopts a circular composite material piezoelectric wafer, and the bottom surface of the probe is circular. The contact effect with the measured position of the insulator improves the detection accuracy. The smaller the radius of the probe bottom surface, the better, but the smaller probe bottom surface requires the circular composite piezoelectric chip to be small, and the ultrasonic energy emitted by the probe is also small. Characteristics, detection efficiency and production cost, the design range of the probe bottom diameter (D) is 5-10mm, and the design range of the probe height (H) is 15-20mm.

Further, the narrow-pulse probe refers to a pulsed ultrasonic straight probe with better response characteristics. The higher the nominal frequency of the narrow-pulse ultrasonic straight probe, the greater the attenuation coefficient in the tested material, and the worse the effect of the sound beam propagation characteristics. , Combined with the actual measurement experience, the frequency design of the narrow pulse ultrasonic straight probe is not more than 5MHz.

The probe adapter line is a signal line that matches the ultrasonic pulse generator and the narrow-pulse ultrasonic straight probe. At the same time, it ensures that the ultrasonic signal received by the narrow-pulse ultrasonic straight probe is converted into an electrical signal and returned to the receiving end of the ultrasonic pulse generator with high quality.

The high-impedance transmission line is a transmission line with small stray inductance and small resistance, which shortens the phase delay of the high-frequency signal during the transmission process, and ensures that the electrical signal received by the oscilloscope and the electrical signal at the signal output end of the ultrasonic pulse generator have the same potential in real time. , in the same phase, which greatly reduces the detection error and ensures the detection accuracy.

The ultrasonic testing object is a three-pillar insulator, which is composed of a solid epoxy piece, a central conductor and a grounding insert. The solid epoxy piece includes three cylinders, and each column foot is combined with a grounding insert; engineering , Internal defects such as air gaps and shelling are most likely to occur at the junction of the grounding insert and the bottom of the column (column foot); the central conductor is a cylindrical structure made of aluminum, and the size of the three-pillar insulator changes with the GIL voltage level.

The construction method of the ultrasonic detection system is as follows: the narrow-pulse ultrasonic straight probe is connected to the signal output end of the ultrasonic pulse generator through the probe adapter line, and the signal synchronization end of the ultrasonic pulse generator is connected to the oscilloscope through a high-impedance transmission line.

The same position means that the material type, size, etc. of the detection position are completely consistent, such as any position on the same radius circle of the three-pillar insulator cylinder.

Specifically, in step S2, the ultrasonic detection system detects the same position of the three-pillar insulator: adjusting the ultrasonic pulse generator, placing the narrow-pulse ultrasonic straight probe coated with the water-based ultrasonic couplant on the same position of the three-pillar insulator for detection, Record the ultrasonic reflection echo information at each homogeneous position. The water-based ultrasonic couplant increases the contact between the probe and the surface to be measured.

Specifically, in step S3, the defect position of the three-pillar insulator is determined by the analogy method: in the absence of defects, all ultrasonic reflection echo waveform information (peak value, phase, etc.) obtained at the same detection position are consistent, when the same detection position When the waveform information is different, it means that there is a defect under the detection position where the ultrasonic reflection echo is different. In the inspection process, the influence of dimensional tolerance and surface roughness is ignored.

Specifically, in step S4, the ultrasonic detection system ultrasonic scanning method in the vicinity of the defect position: the narrow pulse ultrasonic straight probe is detected according to the ultrasonic scanning path and position, and the ultrasonic reflection echo information of each scanning position is recorded. The ultrasonic scanning path and position is a collection of scanning points near the defect and covering the entire defect. The detection position is determined by setting different step lengths on each scanning path, and listing all the detection positions is the scanning lattice collection of the entire defect. The number of ultrasound scan paths and the number of positions are set on a case-by-case basis.

Specifically, in step S5, the method of constructing the correspondence between the ultrasonic reflection echo information and the defect shape and size: according to the principle of the ultrasonic pulse reflection method, the peak value of the ultrasonic initial wave corresponds to the time t0. When detecting a defect-free object, the oscilloscope will The bottom echo B appears, the peak corresponds to time t1, and the depth of the detection surface to the bottom is H. When detecting a defective object, a defect echo F will appear between the initial wave and the bottom, and the peak corresponds to time t2, and the depth of the detection surface to the bottom is d, that is, t0<t2<t1, and the speed of sound is the same in the same medium, then the relationship between d and H can be expressed as

(d_(m,-n)、d_(m,n)为无缺陷位置，理论上二者相等，为了消除测量偏差，取二者均值)，这样就把扫描路径m上所有检测位置结果进行了归一化，将归一化后的结果进行三次样条插值，即可得到扫描路径m上表征缺陷长度、缺陷深度的曲线；同理，依次将其他扫描路径按照以上方法处理，可以得到所有扫描路径表征长度、缺陷深度的曲线；将这些曲线按照最小二乘曲面拟合方法即可得到三支柱绝缘子内部缺陷重构示意图。Assume that the coordinates of 2n+1 scanning positions on any scanning path m in step S3 are L _(m,-n) , L _(m,-n+1) ...L _(m,0) ...L _(m,n ) _-1) , L _(m,n) , substitute the ultrasonic detection echo information of the above position into formula (1), and obtain the depth of the above position as d _(m,-n) , d _(m,-n+1) … d _(m,0) …d _(m,n-1) , d _(m,n) , then these depth values are divided by

(d _(m,-n) and d _(m,n) are the defect-free positions, they are theoretically equal, in order to eliminate the measurement deviation, take the average of the two), so the results of all detection positions on the scanning path m are calculated. Normalize, perform cubic spline interpolation on the normalized results to obtain the curve representing the defect length and defect depth on the scan path m; similarly, by processing other scan paths in turn according to the above method, all scan paths can be obtained. The path characterizes the curves of length and defect depth; by fitting these curves according to the least squares surface fitting method, a schematic diagram of the reconstruction of the internal defects of the three-pillar insulator can be obtained.

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

1. The present invention uses the ultrasonic inspection system to inspect the three-pillar insulator. First, the general position of the defect is determined by comparing the ultrasonic reflection echo information of the same inspection position, and then the scanning inspection is performed near the defect according to the variable-step scanning method, and each scan is recorded. The ultrasonic reflection echo information of different detection positions under the path is used to construct the corresponding relationship between the ultrasonic reflection echo information and the defect shape and size. Finally, the defect shape and size are identified according to the corresponding relationship. The invention has the advantages of low detection cost, high detection accuracy, easy portability, no radiation to human body, etc., and can identify, locate and quantify the internal defects of the three-pillar insulator efficiently, accurately and intuitively.

Description of drawings

1 is a schematic diagram of a system for detecting internal defects of a three-pillar insulator based on an ultrasonic scanning principle in the present embodiment;

Fig. 2 is the structural schematic diagram of the narrow-pulse ultrasonic straight probe in this embodiment: wherein, a) is the front view of the narrow-pulse ultrasonic straight probe, and b) is the bottom schematic diagram of the narrow-pulse ultrasonic straight probe;

3 is a schematic diagram of three similar positions of the three-pillar insulator in this embodiment;

4 is a schematic diagram of the operation steps of a method for reconstructing internal defects of a three-pillar insulator based on an ultrasonic scanning principle in this embodiment;

Fig. 5 is a schematic diagram of the position of the three-pillar insulator column foot detected by the ultrasonic detection system in this embodiment; wherein, a) is a sectional view of the column foot I detection process, b) is a top view of the column foot I detection process, and c) is the column foot II detection process Sectional view, d) is the top view of the column foot II detection process;

Fig. 6 is the ultrasonic detection waveform diagram of three-pillar insulator column foot position in the present embodiment; Wherein, a) are four position detection result diagram of column foot I, b) four position detection result diagram of column foot II;

7 is a schematic diagram of an ultrasonic scanning lattice set in this embodiment;

8 is a schematic diagram of reconstruction of internal defects in a three-pillar insulator in this embodiment; wherein a) is a defect characterization curve on each scanning path, and b) a schematic diagram of reconstruction of internal defects of a three-pillar insulator.

Detailed ways

The present invention will be described in further detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example

As shown in Figure 1, the ultrasonic testing system includes an ultrasonic pulse generator 1, an oscilloscope 2, a narrow-pulse ultrasonic straight probe 3, a probe adapter line 4 and a high-impedance transmission line 5.

The three-pillar insulator 6 is composed of a solid epoxy 61 , a center conductor 62 and a ground insert 63 . The solid epoxy part consists of three cylinders, each of which is combined with a grounding insert, and defects such as air gaps and shelling are most likely to occur at the joint of the grounding insert and the column foot. The center conductor is an annular structure made of aluminum. The size of the three-pillar insulator varies with the GIL voltage level.

Figure 2 is a schematic diagram of the structure of the narrow-pulse ultrasonic straight probe. The narrow-pulse ultrasonic straight probe adopts a circular composite piezoelectric wafer, and the bottom surface 32 of the probe is circular. Considering that the three-pillar insulator is a cylindrical structure, and the surface of the insulator is an arc surface, in order to increase the contact effect between the probe and the measured position of the insulator , improve the detection accuracy, the smaller the diameter D of the probe bottom surface, the better, but the smaller probe bottom surface requires the circular composite piezoelectric chip to be small, and the ultrasonic energy emitted by the probe is also small, considering the detection characteristics, detection efficiency and production cost. , in this embodiment, the diameter D of the bottom surface of the probe is 6mm, and the height H of the probe is 20mm.

The higher the frequency of the narrow-pulse ultrasonic straight probe, the greater the attenuation coefficient of the tested material and the worse the effect of the sound beam propagation characteristics. Combined with actual measurement experience, the frequency of the narrow-pulse ultrasonic straight probe in this embodiment is set to 5MHz.

Figure 3 shows a schematic diagram of the same position of the three-pillar insulator. The same position means that the material category and size of the detection position are exactly the same. The three-pillar insulator can be divided into three types of positions: the first type of position is at the bottom of the main body (at the foot of the column). ), which is composed of solid epoxy parts and grounding inserts. Any point on the circumference of the same body radius belongs to the first type of position, such as the positions w11, w12, w13, w14, w15, w16 with the same body radius in Figure 3 . The second type of position is in the middle of the main body, which only contains solid epoxy parts. Any point on the circumference of the same main body radius belongs to the second type of position, such as w21, w22, w23, w24, w25, w26. The third type of position is on the column base. This type of position consists of a solid epoxy and a central conductor. Any point with the same curvature on the column base belongs to the third type of position, such as the same curvature positions w31, w32, and w33 in Figure 3.

In terms of engineering, the first type of similar position (that is, the junction of the grounding insert and the column foot) is most likely to have internal defects such as air gaps and shelling. As shown in Figure 4 is a flow chart of specific steps, including steps:

S1. Build an ultrasonic testing system;

Specifically, the narrow-pulse ultrasonic straight probe is connected to the sending end of the ultrasonic pulse generator through a probe adapter line, and the oscilloscope is connected to the synchronization end of the ultrasonic pulse generator through a high-impedance transmission line.

S2. The ultrasonic detection system detects the junction between the grounding insert of the three-pillar insulator and the column foot;

Specifically, as shown in Figure 5, the ultrasonic detection system detects the schematic diagram of two different column foot positions of the three-pillar insulator, wherein Figure 5a) is a sectional view of the column foot I detection process, Figure 5b) is a top view of the column foot I detection process, Figure 5c ) is the sectional view of the detection process of the column foot II, and Figure 5d) is the top view of the detection process of the column foot II; start the ultrasonic detection system, adjust the ultrasonic pulse generator, and place the narrow-pulse ultrasonic straight probe coated with the water-based ultrasonic couplant on three 8 different positions (w11, w12, w17, w18, w13, w14, w19, w20) of two different column feet (pillar foot I, column foot II) of the pillar insulator are tested, and the ultrasonic reflection at each position is recorded Echo information, the results are shown in Figure 6;

S3, use the analogy method to determine the ultrasonic reflection echo information of the defect-free position and the ultrasonic reflection echo information of the defective position, so as to determine the defect position;

Specifically, as shown in Figures 6(a) and 6(b), the ultrasonic detection waveforms of the positions of the legs of the three-pillar insulator in this embodiment show that the ultrasonic initial wave F is vertically incident inside the solid epoxy and reaches the solid ring. At the interface between the oxygen element and the grounding insert, the acoustic impedance of the materials on both sides of the interface is different. A part of the ultrasonic wave is reflected and reaches the probe along the original path, and is displayed as the first echo B1 after the original wave in the received waveform; another part of the ultrasonic wave is transmitted into the grounding insert. Inside the component, it is totally reflected when it reaches the interface between the grounding insert and the air. At this time, the reflected wave passes through the interface between the grounding insert and the epoxy and then transmits and reflects again. The transmitted wave returns to the probe and is displayed as the second wave after the initial wave in the received waveform. When the echo B2; B1 reaches the probe, it will be reflected again on the contact surface. Repeat the above steps, so that the received waveform will be a secondary reflected echo B3 at the interface between the epoxy and the grounding insert after B2.

The detected waveforms of the four positions w11, w12, w17, and w18 of the column foot I and the three positions of w14, w19, and w20 of the column foot II are basically the same in shape, peak value, phase, etc. In contrast, only the column foot The peak values of echoes B1, B2, and B3 at the position of II position w13 are relatively small, especially the peak value of the position B1 is much smaller than that of other positions, and the time span of the B1 wave is also larger. Therefore, the position state of position w13 of column foot II can be classified into one category, and the other seven positions can be classified into one category. According to the theory and experience of reverse inference, it can be preliminarily determined that there is a defect in the position of position w13 of column foot II.

S4. The ultrasonic inspection system performs ultrasonic scanning near the defect position, and records the ultrasonic reflection echo information of each inspection position;

Specifically, ultrasonic scanning detection is performed near the position w13 of the above-mentioned column foot II. The scanning path and scanning position are shown in Figure 7, wherein the small circle represents the ultrasonic scanning detection position, the origin represents the w13 position of the column foot II, and the x-axis represents Along the axial direction of the column foot II position w13, the y-axis represents the tangential direction along the column foot II position w13, there are 6 ultrasonic scanning paths, namely x=0, x=1, x=2, x=3, x =4 and x=5, there are 13 points on each path i.e. y=-8, y=-6, y=-4, y=-3, y=-2, y=-1, y=0 , y=1, y=2, y=3, y=4, y=6 and y=8; the ultrasound scan lattice sets are (0,-8), (0,-6), (0,-4 ), (0,-3), (0,-2), (0,-1), (0,0), (0,1), (0,2), (0,3), (0, 4), (0,6), (0,8), (1,-8), (1,-6), (1,-4), (1,-3), (1,-2), (1,-1), (1,0), (1,1), (1,2), (1,3), (1,4), (1,6), (1,8), ( 2,-8), (2,-6), (2,-4), (2,-3), (2,-2), (2,-1), (2,0), (2, 1), (2,2), (2,3), (2,4), (2,6), (2,8), (3,-8), (3,-6), (3, -4), (3,-3), (3,-2), (3,-1), (3,0), (3,1), (3,2), (3,3), ( 3,4), (3,6), (3,8), (4,-8), (4,-6), (4,-4), (4,-3), (4,-2 ), (4,-1), (4,0), (4,1), (4,2), (4,3), (4,4), (4,6), (4,8) , (5,-8), (5,-6), (5,-4), (5,-3), (5,-2), (5,-1), (5,0), ( 5,1), (5,2), (5,3), (5,4), (5,6), (5,8); start the ultrasonic inspection system, adjust the ultrasonic pulse generator, The center of the narrow-pulse ultrasonic straight probe of the basic ultrasonic couplant is placed on the above-mentioned ultrasonic scanning lattice set in turn, and the ultrasonic echo information B1 of each scanning point is recorded.

S5 , constructing the correspondence between the ultrasonic reflected echo information and the defect shape and size, and obtaining a schematic diagram of defect reconstruction based on the detection results of each scanning position, so as to quantify the size of the defect and identify the shape of the defect.

(d_(0,-8)、d_(0,8)为无缺陷位置，理论上二者相等，为了消除测量偏差，取二者均值)，这样就把x＝0扫描路径下所有检测位置结果进行了归一化，将归一化后的结果进行三次样条插值，即可得到x＝0扫描路径下表征缺陷长度、缺陷深度的曲线；同理，将剩下的扫描点按照以上理论，可以得到x＝1、x＝2、x＝3、x＝4和x＝5扫描路径下表征缺陷长度、缺陷深度的曲线；如图8a)所示。Specifically, the scanning positions (0,-8), (0,-6), (0,-4), (0,-3), (0,-2), (0,-1), (0,0), (0,1), (0,2), (0,3), (0,4), (0,6), and (0,8) The ultrasonic echo information is substituted into formula (1) to calculate the depth value of each scanning position, denoted as d _(0,-8) , d _(0,-6) , d _(0,-4) , d _{(0,- 3)} , d _(0,-2) , d _(0,-1) , d _(0,0) , d _(0,1) , d _(0,2) , d _(0,3) , d _{(0 ,4)} , d _(0,6) and d _(0,8) , then these depth values are divided by

(d _(0,-8) and d _(0,8) are defect-free positions, they are theoretically equal, in order to eliminate the measurement deviation, take the average of the two), so that the results of all detection positions under the x=0 scanning path After normalization, the normalized result is subjected to cubic spline interpolation, and then the curve representing the defect length and defect depth under the x=0 scanning path can be obtained; similarly, the remaining scanning points are based on the above theory, Curves representing defect length and defect depth under scanning paths of x=1, x=2, x=3, x=4 and x=5 can be obtained; as shown in Fig. 8a).

According to the least squares surface fitting method, the curve in Fig. 8a) can be used to obtain a schematic diagram of the reconstruction of the internal defects of the three-pillar insulator in this embodiment, as shown in Fig. 8(b), from which it can be seen that the closer to x=0 ( The larger the defect boundary range near the bottom of the column foot), the defect width at x=0 is about 6mm, the defect width decreases nonlinearly along the x-axis, and the defect width at x=4 is about 2mm; the total length of the defect is about 4mm, The defect has a wedge-shaped shape of "wide head and narrow tail" as a whole.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be equivalent replacement manners, which are all included in the protection scope of the present invention.

Claims (5)

1. a three-pillar insulator internal defect reconstruction method based on ultrasonic scanning principle, is characterized in that, comprises the steps: S1. Build an ultrasonic testing system; S2. Use the ultrasonic testing system to detect the same position of the three-pillar insulator, and record the ultrasonic reflection echo information of each detection position; The same position means that the material category and size of the detection position are completely consistent, including any position on the same radius circle of the three-pillar insulator cylinder; S3. Use the analogy method to judge the ultrasonic reflection echo information of each detection position, and determine the defect position; In step S3, the principle of using the analogy method to determine the defect position of the three-pillar insulator is as follows: in the absence of defects, all ultrasonic reflection echo waveform information obtained at the same detection position is consistent, when the waveform information of the same detection position is different. When the ultrasonic reflection echo is different, there is a defect under the inspection position; during the inspection process, the influence of dimensional tolerance and surface roughness is ignored; S4. Use the ultrasonic inspection system to perform ultrasonic scanning near the defect position, and record the ultrasonic reflection echo information of each inspection position; S5. Construct the correspondence between the ultrasonic reflected echo information and the defect shape and size, and obtain a schematic diagram of defect reconstruction based on the detection results of each scanning position, so as to quantify the size of the defect and identify the shape of the defect; In step S5, the method of constructing the correspondence between the ultrasonic reflection echo information and the defect shape and size: according to the principle of the ultrasonic pulse reflection method, the peak value of the ultrasonic initial wave corresponds to the time t0. Wave B, the peak corresponds to time t1, the depth of the detection surface to the bottom is H, when detecting a defective object, a defect echo F will appear between the initial wave and the back surface, the peak corresponds to time t2, and the depth of the detection surface to the bottom is d , that is, t0<t2<t1, in the same medium, the speed of sound is the same, then the relationship between d and H can be expressed as

Assume that the coordinates of 2n+1 scanning positions on any scanning path m in step S3 are L _(m,-n) , L _(m,-n+1) ...L _(m,0) ...L _(m,n ) _-1) , L _(m,n) , substitute the ultrasonic detection echo information of the above position into formula (1), and obtain the depth of the above position as d _(m,-n) , d _(m,-n+1) … d _(m,0) …d _(m,n-1) , d _(m,n) , then these depth values are divided by

In this way, the results of all detection positions on the scanning path m are normalized, and the normalized results are subjected to cubic spline interpolation to obtain the curves representing the defect length and defect depth on the scanning path m; The other scan paths are processed in turn according to the above method, and the curves representing the length and defect depth of all the scan paths are obtained; the obtained curves are obtained according to the least squares surface fitting method to obtain a schematic diagram of the reconstruction of the internal defects of the three-pillar insulator. 2. A method for reconstructing internal defects of three-pillar insulators based on ultrasonic scanning principle according to claim 1, wherein in step S1, the ultrasonic detection system comprises an ultrasonic pulse generator, an oscilloscope, a narrow-pulse ultrasonic direct Probes, probe adapter cables and high impedance transmission lines; The construction method of the ultrasonic testing system is as follows: the narrow-pulse ultrasonic straight probe is connected to the signal output end of the ultrasonic pulse generator through the probe adapter line, and the signal synchronization end of the ultrasonic pulse generator is connected to the oscilloscope through a high-impedance transmission line; The ultrasonic pulse generator is a pulse generator with sharp pulse excitation, adjustable output pulse width and gain, and low noise; The oscilloscope is a four-channel high-performance digital storage oscilloscope with a maximum sampling frequency of 1GHz and a sampling bandwidth of 200MHz; The narrow pulse ultrasonic straight probe is a cylindrical longitudinal wave straight probe, using a circular composite material piezoelectric wafer, the bottom surface of the probe is circular, the surface of the insulator is an arc surface, the diameter of the bottom surface of the probe is designed to be 5-10mm, and the height of the probe is designed The range is 15-20mm; the frequency design of the narrow pulse ultrasonic straight probe is not more than 5MHz. 3. A method for reconstructing internal defects of a three-pillar insulator based on the principle of ultrasonic scanning according to claim 1, wherein in step S2, the ultrasonic detection system detects the same position of the three-pillar insulator: adjusting the ultrasonic pulse generator , place the narrow-pulse ultrasonic straight probe coated with water-based ultrasonic couplant on the same position of the three-pillar insulator for testing, and record the ultrasonic reflection echo information at each similar position. 4. The method for reconstructing internal defects of a three-pillar insulator based on the principle of ultrasonic scanning according to claim 1, wherein in step S4, the ultrasonic scanning method of the ultrasonic inspection system in the vicinity of the defect position: the narrow-pulse ultrasonic straight probe Detection is performed according to the ultrasonic scanning path and position, and the ultrasonic reflection echo information of each scanning position is recorded. 5. A method for reconstructing internal defects of a three-pillar insulator based on the principle of ultrasonic scanning according to claim 4, wherein the ultrasonic scanning path and the position are a collection of scanning points whose area covers the entire defect, Set different step lengths to determine the detection position, and listing all the detection positions is the scanning lattice set of the entire defect.

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