GIS basin-type insulator fault detection method based on FMC strategy and Lamb wave

Abstract

The invention discloses a GIS basin-type insulator fault detection method based on an FMC strategy and Lamb waves, belongs to the technical field of intelligent recognition and processing of electrical equipment images, and solves the problem of how to realize high-precision and rapid positioning and visual recognition of GIS basin-type insulator defects. According to the method, a one-dimensional linear phased array ultrasonic probe is tightly attached along the flange edge of the GIS basin-type insulator, and the center of the probe is aligned with the geometric center of the insulator; selecting a beam control mode according to the defect depth, and performing front-end processing and ADC synchronous sampling on echo data; a three-dimensional FMC matrix is constructed, frequency dispersion compensation is carried out through inverse frequency dispersion transformation, and a delay superposition wave beam is formed; the propagation time and the pixel intensity are calculated and synthesized through a full-focus algorithm, and the geometric position of the defect is positioned and displayed; the three-dimensional FMC matrix is transmitted through DMA, and a defect imaging picture is output; the method can effectively meet the engineering requirements of defect detection and image reconstruction precision.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power equipment image intelligent recognition and processing, and relates to a GIS basin-type insulator fault detection method based on an FMC strategy and Lamb waves. BACKGROUND

[0002] With the in-depth promotion of smart grid construction, gas insulated switchgear (GIS) has become a core device of the power system due to its high reliability. GIS has a compact structure, a small footprint, is not easily affected by the external environment, has high operation reliability, and has a long maintenance period, and is widely used in power grids. However, the key component of the basin-type insulator is prone to hidden defects such as micro-cracks, air gaps, and metal impurities due to manufacturing process defects and long-term electrical-thermal-mechanical stress, which seriously threatens the safe operation of the power grid.

[0003] The basin-type insulator plays an important role in GIS, such as electrical insulation, support and fixation of conductors, ensuring air tightness, and connecting multiple functional units, and is a core part of GIS devices. If it fails, a large amount of manpower and material resources need to be invested for power outage maintenance, and the long power outage time often brings a large economic loss to the power supply company. Therefore, it is necessary to timely grasp the insulation state of GIS before it fails and to timely locate it.

[0004] The traditional detection method is based on a single probe or fixed multi-probe, detects defects through pulse-echo mode (i.e., B-scan), and relies on mechanical scanning to cover the detection area. Ultrasonic waves are emitted by a single point, and then the probe moves along the surface of the insulator, and the defect depth is converted through the echo time. The traditional detection method has the following defects:

[0005] 1) Low rate: the probe needs to move point by point along the surface, and the scanning speed is slow; 2) insufficient resolution: single-point emission results in limited sound field coverage, making it difficult to identify small defects (such as cracks and debonding); 3) high risk of missed detection: mechanical scanning cannot achieve full coverage of complex curved surfaces (such as flange edges); 4) sparse data: the amount of data from a single emission-reception channel is insufficient, the signal-to-noise ratio of the image is low, and the defect depth needs to be indirectly converted.

[0006] Therefore, there is an urgent need for a high-efficiency and high-precision non-destructive detection method to realize rapid positioning and visual identification of GIS basin-type insulator defects. SUMMARY

[0007] The technical solution of the application is used to solve the problem of how to realize high-precision, rapid positioning, and visual identification of GIS basin-type insulator defects.

[0008] The application solves the above technical problems through the following technical solutions:

[0009] The application provides a GIS pot-type insulator fault detection method based on an FMC strategy and Lamb waves, and comprises the following steps:

[0010] S1: a one-dimensional linear phased array ultrasonic probe is closely attached to a GIS pot-type insulator flange edge, and the probe center is aligned with the geometric center of the insulator;

[0011] S2: a beam control mode is selected according to a defect depth:

[0012] 1) a general deflection mode is used for far field detection, and a control method of the general deflection mode is that delay times of each array element in the phased array ultrasonic probe form an arithmetic sequence, each array element of the phased array ultrasonic probe is sequentially excited, a propagation direction of a synthesized wave front forms an included angle with an axis of the linear array probe, and thus deflection control of a wave beam is realized;

[0013] 2) a focused deflection mode is used for near field focusing, and a control method of the focused deflection mode is that delay times of each array element are directly calculated according to geometric path difference between the array elements, and thus deflection control of the wave beam is realized;

[0014] 3) different Lamb wave modes are selected according to different defect types, displacement equations of the different Lamb wave modes are substituted into a three-dimensional elastic wave equation of the Lamb wave for Lamb wave matching, and thus a frequency dispersion characteristic equation of the Lamb wave is obtained;

[0015] S3: echo data is subjected to low-noise amplification, Butterworth band-pass filtering and ADC synchronous sampling; a three-dimensional FMC matrix is constructed, dispersion compensation is performed through inverse dispersion transformation, a delay stack beam is formed; and the propagation time and pixel intensity are calculated and synthesized through a full focusing algorithm, and a geometric position of a defect is directly located and displayed;

[0016] S4: the three-dimensional FMC matrix is transmitted through DMA, and a defect imaging graph is visualized and output.

[0017] Further, a calculation formula of the delay time of the nth array element of the deflection control in the step S2 is as follows:

[0018]

[0019] Wherein, θ is an included angle formed by a propagation direction of a synthesized wave front and an axis of a linear array probe, τn is a delay value of the nth array element, c is an ultrasonic speed in a medium, and d is a spacing between the array elements. n

[0020] Further, a method of directly calculating the delay time of each array element according to the geometric path difference between the array elements in the step S2 is as follows:

[0021] The path difference of the nth array element satisfies:​

[0022]

[0023] Solving the equation gives:

[0024]

[0025] The delay time of the nth array element is:

[0026]

[0027] Where F is the focal length from the origin, the coordinates of the focus P are (Fsinθ, Fcosθ), τ0 is a constant added to avoid negative delay values, and N is the total number of array elements.

[0028] Further, the method of selecting different Lamb wave modes according to different defect types in step S2 is as follows:

[0029] 1) When detecting delamination defects, the S0 mode of Lamb wave is selected, and the displacement equation of the S0 mode is:

[0030] 2) When detecting surface cracks, the A0 mode of Lamb wave is selected, and the displacement equation of the A0 mode is:

[0031] Where u x (x,z,t) is the displacement component in the x direction, u z (x,z,t) is the displacement component in the z direction, U(z) is the distribution of the x-direction displacement amplitude along the z axis, W(z) is the distribution of the z-direction displacement amplitude along the z axis, V(z) is the distribution of the x-direction displacement amplitude along the z axis, Z(z) is the distribution of the z-direction displacement amplitude along the z axis, k is the wave number, x is the horizontal coordinate of wave propagation direction, z is the vertical coordinate of the plate thickness direction, and w is the angular frequency.

[0032] Further, the three-dimensional elastic wave equation of Lamb wave in step S2 is:

[0033]

[0034] Where ρ and μ are the density and shear modulus of the plate, respectively, u i and f i are the displacement and body force in the x i direction, respectively, u i,jj represents the shear deformation acceleration, u j,ji indicates the volume deformation acceleration, ü i represents the acceleration of the mass point in the i direction, and ρ·ü iis the inertial force term, λ is the Lame constant, υ is the Poisson's ratio, and E is the Young's modulus.

[0035] Further, the dispersion characteristic equation of the Lamb wave in step S2 is:

[0036]

[0037] where and describe the phase change of the wave in the thickness direction of the plate, is the normal compression, q is the tangential shear, is the square of the longitudinal wave speed, is the square of the transverse wave speed, h is the thickness of the plate, and k is the wave number.

[0038] Further, the method for constructing the three-dimensional FMC matrix in step S3 is as follows:

[0039] 1) Starting from the first transmitting element, the synchronous triggering of the pulse triggers the sampling of all receiving channels, and all elements synchronously receive the echo signal;

[0040] 2) The data of all receiving channels at the i-th transmission is a two-dimensional matrix D i of size N*M, and the two-dimensional matrix D j is filled into the i-th layer of the three-dimensional matrix FMC i .

[0041] 3) Looping, each transmitting element is activated in turn, and finally a complete three-dimensional matrix FMC i is formed.

[0042] Further, the method for dispersion compensation by inverse dispersion transformation in step S3 is as follows:

[0043] Through the calculation of the dispersion curve of the Lamb wave, the short-time Fourier transform is performed on the received signal, and the phase delay is compensated by the inverse filter:

[0044]

[0045] where Δt(f) is the time delay caused by dispersion, f is the signal frequency, H comp (f) is the frequency response function of the dispersion compensation filter, and j0 is the imaginary factor.

[0046] Further, the method for forming a delay-and-stack beam in step S3 is as follows:

[0047] By adjusting the phase delay of the multi-element signal, the signal in a specific direction is enhanced, and the interference in other directions is suppressed, delay-and-stack is performed, and the signal xi (t), focus to position (x p ,z p ) is the synthetic signal: Among them, d i→p is the distance from the array element to the target, and y(t) is the synthetic signal.

[0048] Furthermore, the method for calculating and synthesizing the propagation time and pixel intensity by the all-focusing algorithm in step S3 is as follows:

[0049] Extracting D from the FMC dataset ij (t) At time t = T i +T j The amplitude of the image is , let P be a pixel point in the imaging grid, with coordinates (x, y), and calculate the total time T for the ultrasound to travel from the transmitting array element i to the pixel point P and then back to the receiving array element j. ij (x,z), the formula is as follows:

[0050]

[0051] The pixel intensity synthesis formula at point P is as follows:

[0052]

[0053] Among them, I(x,z) is the composite pixel intensity of point P, x i is the coordinate of the transmitting array element, x j is the receiving element coordinate, x is the horizontal coordinate of the target point, z is the depth coordinate of the target point, T i (x,z) is the propagation time from the transmitting element to the target point, T j (x,z) is the propagation time from the target point to the receiving array element.

[0054] The beneficial effects of the present invention are as follows:

[0055] The method of the present invention achieves electronic scanning of the beam without mechanical motion by precisely controlling the emission timing of each array element in a one-dimensional linear phased array, thereby significantly improving detection speed and flexibility. The method combines full matrix capture (FMC) and total focusing method (TFM). The former completely records the original signals of all array element transmit-receive combinations, while the latter uses a synthetic aperture focusing algorithm to dynamically optimize the imaging resolution, overcoming the data sparsity problem of the traditional single-element emission mode. Three-dimensional spatial scanning is completed without moving the probe, making it particularly suitable for global defect detection of complex curved surface structures such as pot-type insulators. The method of the present invention can effectively meet the engineering requirements of defect detection and image reconstruction accuracy in terms of spatial resolution and directional coverage. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a flow chart of a GIS pot-type insulator fault detection method based on FMC strategy and Lamb wave;

[0057] Figures 2 to 4 is a thermal diagram corresponding to the deflection angle of 0°, 30° and 60° of the ultrasonic beam emitted by the one-dimensional linear phased array ultrasonic probe;

[0058] Figure 5 is a received signal diagram of the 57th array element (a total of 64 array elements) when the full matrix capture mode is adopted;

[0059] Figure 6 is a defect echo diagram corresponding to the echo time position of Figure 5 ;

[0060] Figure 7 is a detection image of a bubble defect;

[0061] Figure 8 is a detection image of a crack defect;

[0062] Figure 9 is a detection image of a delamination defect;

[0063] Figure 10 and Figure 11 are a traditional B-scan imaging and a full matrix capture TFM imaging diagram, respectively. DETAILED DESCRIPTION

[0064] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are some embodiments but not all embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0065] The technical solutions of the present application will be further described below in conjunction with the drawings in the specification and specific embodiments:

[0066] As shown in Figure 1 , the implementation steps of the GIS pot-type insulator fault detection method based on FMC strategy and Lamb wave of the embodiments of the present application are as follows:

[0067] Step 1, probe arrangement and focusing control are performed, and Lamb wave mode is matched according to defect type; based on FMC strategy, a one-dimensional linear phased array ultrasonic probe is used as an excitation and receiving device, the one-dimensional linear phased array ultrasonic probe is arranged closely along the flange edge of the pot-type insulator, the center of the probe is aligned with the geometric center of the insulator, dynamic focusing deflection control is adopted, and normal deflection or focusing deflection is selected according to the detection depth.

[0068] Step 1.1, when the far field detection is performed (depth > 40mm), the common deflection mode is adopted, the delay time of each array element in the phased array probe is arranged in an arithmetic sequence, each array element of the phased array probe is excited in turn, the propagation direction of the synthetic wave front and the axis of the linear array probe will form a certain angle, thereby realizing the deflection control of the beam, the calculation formula of the delay time of the nth array element of the deflection control is as follows:

[0069]

[0070] Wherein, θ is the angle formed by the propagation direction of the synthetic wave front and the axis of the linear array probe, τ n is the delay time value of the array element n, c is the ultrasonic speed in the medium, and d is the spacing between the array elements.

[0071] Step 1.2, when the near field focusing is performed (depth < 40mm), the focusing deflection mode is adopted, a rectangular coordinate system is established with the center of the linear array probe as the origin, the N array elements from 1 to N are distributed on the x axis in turn, the coordinates of the nth array element are (x n ,0), then x n =(n-(N+1) / 2)d, F is the focal length from the origin, and the coordinates of the focal point P are (Fsinθ, Fcosθ). In order to facilitate implementation, the first array element of the linear array probe is uniformly taken as the reference array element in calculation, the delay time of each array element can be directly calculated according to the geometric path difference between the array elements, and the path difference of the nth array element satisfies the following formula:

[0072]

[0073] The equation is solved as follows:

[0074]

[0075] In the above formula, τ0is a constant added to avoid negative delay values. Taking the first array element as the delay reference delay zero point, the delay time of the nth array element is:

[0076]

[0077] When F tends to infinity, the limit of τ n is: When the focal point F tends to infinity, the delay time formula of the focusing deflection becomes the delay time formula of the deflection.

[0078] Step 1.3, different Lamb wave modes are selected according to different defect types:

[0079] 1) when detecting delamination defects, the S0 mode of Lamb wave is selected, and the excitation frequency of the S0 mode is: The displacement equation is:

[0080] 2) When detecting surface cracks, select the A0 mode of Lamb wave, the excitation frequency of the A0 mode is The displacement equation is:

[0081] Wherein, u x (x,z,t) is the displacement component in the x direction, u z (x,z,t) is the displacement component in the z direction, U(z) is the distribution of the x-direction displacement amplitude along the z-axis, W(z) is the distribution of the z-direction displacement amplitude along the z-axis, V(z) is the distribution of the x-direction displacement amplitude along the z-axis, Z(z) is the distribution of the z-direction displacement amplitude along the z-axis, k is the wave number, x is the horizontal coordinate of the wave propagation direction, z is the vertical coordinate of the plate thickness direction, and w is the angular frequency.

[0082] Match the Lamb wave mode, and the three-dimensional elastic wave equation of the Lamb wave inside the homogeneous object can be represented by the following formula:

[0083] μ·u i,jj +(λ+μ)·u j,ji +ρ·f i =ρ·ü i (i,j=1,2,3)

[0084] Wherein, ρ and μ are the density and shear modulus of the plate respectively, u i and f i are the displacement and volume force along the x i direction respectively, u i,jj represents the shear deformation acceleration, u j,ji refers to the volume deformation acceleration, ü i indicates the acceleration of the mass point in the i direction, and ρ·ü i is the inertial force term.

[0085]

[0086] Wherein, λ is the Lame constant, υ is the Poisson's ratio, and E is the Young's modulus.

[0087] The dispersion characteristic equation of the Lamb wave derived from the above three-dimensional equation is:

[0088]

[0089] Wherein, and describe the phase change of the wave in the plate thickness direction, is the normal compression, q is the tangential shear, is the square of the longitudinal wave velocity, is the square of the transverse wave velocity, h is the plate thickness, and k is the wave number.

[0090] Step two, full element acquisition and full focus imaging based on FMC strategy, multi-channel synchronous receiving echo data, receiving Lamb wave according to matched excitation frequency and mode of Lamb wave, signal acquisition and imaging processing.

[0091] Step 2.1, signal acquisition and front-end conditioning to the collected data

[0092] Step 2.1.1, low noise amplification:

[0093]

[0094] Usually select gain G = 20 ~ 60dB, noise figure NF <2db.

[0095] Step 2.1.2, Butterworth band-pass filter is adopted to retain the target frequency band of Lamb wave and filter out related noise:

[0096]

[0097] Step 2.1.3, ADC synchronous sampling, according to Nyquist sampling theorem, sampling rate fs≥100MHz, time window according to group velocity c g Dynamic adjustment:

[0098]

[0099] Step 2.2, data construction and signal optimization, first construct a three-dimensional FMC matrix, then perform dispersion compensation through inverse dispersion transform, and finally form a delay stack beam.

[0100] Step 2.2.1, from the first transmitting element, the synchronous trigger of pulse transmission activates all receiving channels sampling, and all elements synchronously receive echo signals.

[0101] Step 2.2.2, the data of all receiving channels at the i-th transmission is a two-dimensional matrix D i [j][k] = A j [k](1≤j≤N,1≤k≤M), fill the two-dimensional matrix D i [j][k] to the i-th layer of the three-dimensional matrix.

[0102] Step 2.2.3, loop, activate each transmitting element in turn, and finally form a complete three-dimensional matrix FMC[i][j][k] = D i [j][k](1≤i,j≤N,1≤k≤M).

[0103] Step 2.2.4: The dispersion characteristics of Lamb waves cause the signal to broaden during propagation. The inverse dispersion transform is used to compress the signal energy and improve the signal-to-noise ratio. By calculating the dispersion curve of the Lamb wave, a short-time Fourier transform is performed on the received signal, and the phase delay is compensated using an inverse filter:

[0104]

[0105] Where Δt(f) is the time delay caused by dispersion, f is the signal frequency, H comp (f) is the frequency response function of the dispersion compensation filter, where j0 is the imaginary factor. The hyperbolic features of the bubble defect are made more focused by the inverse dispersion transform.

[0106] Step 2.2.5, delay superposition beamforming, by adjusting the phase delay of multi-element signals, enhance the signal in a specific direction, suppress interference in other directions, and perform delay superposition to the signal x of the i-th element. i (t), focus to position (x p ,z p ) is the synthetic signal:

[0107]

[0108] Among them, d i→p is the distance from the array element to the target.

[0109] Step 2.3: Perform full-focus imaging and defect location. Use the TFM imaging algorithm to calculate and synthesize the propagation time and pixel intensity to directly display the geometric position of the defect.

[0110] Step 2.3.1. Extract D from the FMC dataset ij (t) At time t = T i +T j The amplitude of the image is , let P be a pixel point in the imaging grid, with coordinates (x, y), and calculate the total time T for the ultrasound to travel from the transmitting array element i to the pixel point P and then back to the receiving array element j. ij (x,z), the formula is as follows:

[0111]

[0112] The pixel intensity synthesis formula at point P is as follows:

[0113]

[0114] Among them, I(x,z) is the composite pixel intensity of point P, x i is the coordinate of the transmitting array element, x j is the receiving element coordinate, x is the horizontal coordinate of the target point, z is the depth coordinate of the target point, T i(x,z) is the propagation time from the transmitting element to the target point, T j (x,z) is the propagation time from the target point to the receiving array element.

[0115] For each focus point P in the grid area, the full focusing algorithm will 2 The corresponding values ​​are taken out from the echo data of the transmitting and receiving array element pairs and superimposed. Since each pixel point P has N 2 The superposition of pixel-level signals is achieved through time difference, and dynamic focusing is achieved. If there is a defect at p, the signals of each channel will be aligned at t=T i +T j Coherence enhancement will occur at all times. It can effectively suppress the interference of random Gaussian white noise without affecting the accuracy of the detection results, and has a high fault tolerance for data.

[0116] Step 2.4: After front-end signal conditioning, the three-dimensional FMC matrix is ​​transmitted at high speed through DMA (Direct Memory Access) and visualized.

[0117] Experimental testing

[0118] like Figures 2 to 4 The figure shows a heat map of the ultrasonic beam deflection emitted by a one-dimensional linear phased array ultrasonic probe. The probe employs 64 array elements, with a spacing of 0.6 mm between each element. Based on the delay superposition principle, a time delay is applied to each element to achieve beam deflection. The deflection angles are 0°, 30°, and 60°, respectively. 0° represents vertical incidence, with the beam axis perpendicular to the array surface and concentrated energy propagating along the depth direction. 30° represents a medium angle, generating shear wave components in the pot insulator, improving the lateral resolution by 30% compared to 0°. 60° represents a large angle, generating surface waves near the second critical angle. The heat map represents the acoustic pressure field distribution, with white arrows indicating the direction of the beam's main lobe and white crosses marking the focal point of the acoustic energy.

[0119] Figure 5 and Figure 6 To adopt the full matrix capture mode (FMC), array elements 1 and 64 are arranged at the two ends, corresponding to -30° and +30°, and the middle array elements 32 / 33 correspond to the 0° normal direction. To simulate the structure-borne noise in the basin insulator, low-amplitude oscillations of 5-10μs are added. Each array element transmits in sequence, and all array elements receive simultaneously. The corresponding received signal when each array element transmits is Figure 5 The received signal of the 57th array element is selected. Figure 6 It can be clearly observed that the corresponding Figure 5 There is a peak at the echo time position, which is the defect echo.

[0120] Figure 7 The middle echo is symmetrical hyperbolic and omnidirectional, which is a bubble defect.Figure 8 For the low amplitude echo of multiple elements, it is a crack defect, Figure 9 The signal is strongest when transmitting / receiving on the same side, and the amplitude decays by more than 50% when transmitting / receiving on the opposite side, which is a delamination defect.

[0121] Figure 10 And Figure 11 Traditional B-scan imaging and full-matrix capture TFM imaging, respectively. Figure 10 Traditional imaging only uses the center element for transmission and all elements for reception, and the defect appears as a bright spot in the horizontal direction, which can indirectly reflect the depth. However, it cannot directly display the depth information of the defect, is limited by single element transmission, has low resolution and signal-to-noise ratio, and causes geometric distortion due to the arc array. Figure 11 Using the combined transmission-reception data of all elements, the spatial position of the defect is reconstructed by the delay-and-sum method, the geometric position of the defect is directly displayed without time conversion, has higher resolution and signal-to-noise ratio, and weak signals are highlighted by the db scale. The defect display appears as a bright color focal point, and the white x is the actual position, which is consistent with the actual position.

[0122] Embodiment two

[0123] An electronic device, comprising a memory and a processor, the memory being used to store a program supporting the processor to execute the GIS basin-type insulator fault detection method based on the FMC strategy and Lamb wave in embodiment one, and the processor being configured to execute the program stored in the memory.

[0124] Embodiment three

[0125] A storage medium, the storage medium storing a computer program, the computer program being executed by a processor to perform the steps of the GIS basin-type insulator fault detection method based on the FMC strategy and Lamb wave in embodiment one.

[0126] The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A GIS pot insulator fault detection method based on FMC strategy and Lamb wave, characterized in that: The following steps are involved: S1 puts the one-dimensional linear phased array ultrasonic probe tightly along the edge of the GIS pot insulator flange, and aligns the center of the probe with the geometric center of the insulator; S2 selects beam steering mode according to defect depth: 1) Far-field detection uses a common deflection mode. The control method for this common deflection mode is as follows: the delay time of each element in the phased array ultrasonic probe is controlled to form an arithmetic progression, and each element of the phased array ultrasonic probe is excited in sequence. The propagation direction of the synthesized wavefront forms an angle with the axis of the linear array probe, thereby achieving beam deflection control. 2) Near-field focusing uses a focus deflection mode, which is controlled by directly calculating the delay time of each array element based on the geometric acoustic path difference between the array elements, thereby achieving beam deflection control; 3) Select different Lamb wave modes according to different defect types, substitute the displacement equations of different Lamb wave modes into the three-dimensional elastic wave equation of Lamb wave to match the Lamb wave, and thus obtain the dispersion characteristic equation of Lamb wave; S3 performs low-noise amplification, Butterworth bandpass filtering and ADC synchronous sampling on the echo data; Construct a three-dimensional FMC matrix, perform dispersion compensation through inverse dispersion transformation, and form a delayed superposition beam; The propagation time and pixel intensity are calculated and synthesized by the full focusing algorithm to directly locate and display the geometric position of the defect; S4 transmits the 3D FMC matrix via DMA and outputs the defect imaging diagram visually.

2. The GIS pot insulator fault detection method based on FMC strategy and Lamb wave according to claim 1 is characterized in that: The calculation formula for the delay time of the nth array element in the deflection control in step S2 is as follows: Where θ is the angle between the propagation direction of the synthetic wavefront and the axis of the linear array probe, τ n is the delay value of array element n, c is the ultrasonic sound speed in the medium, and d is the spacing between array elements.

3. The GIS pot insulator fault detection method based on FMC strategy and Lamb wave according to claim 2 is characterized in that: The method for directly calculating the delay time of each array element according to the geometric acoustic path difference between array elements in step S2 is as follows: The acoustic path difference of the nth array element satisfies: Solving the equation yields: Taking the first array element as the delay reference delay zero point, the delay time of the nth array element is: Where F is the focal length from the origin, the coordinates of the focus P are (Fsinθ, Fcosθ), τ0 is a constant added to avoid negative delay values, and N is the total number of array elements.

4. The GIS pot insulator fault detection method based on FMC strategy and Lamb wave according to claim 1 is characterized in that: The method for selecting different Lamb wave modes according to different defect types in step S2 is as follows: 1) When detecting delamination defects, the S0 mode of Lamb wave is selected. The displacement equation of the S0 mode is: 2) When detecting surface cracks, the A0 mode of Lamb wave is selected. The displacement equation of the A0 mode is: Among them, u x (x,z,t) is the displacement component in the x direction, u z (x,z,t) is the displacement component in the z direction, U(z) is the distribution of the x-direction displacement amplitude along the z axis, W(z) is the distribution of the z-direction displacement amplitude along the z axis, V(z) is the distribution of the x-direction displacement amplitude along the z axis, Z(z) is the distribution of the z-direction displacement amplitude along the z axis, k is the wave number, x is the horizontal coordinate in the wave propagation direction, z is the vertical coordinate in the thickness direction of the plate, and w is the angular frequency.

5. The GIS pot insulator fault detection method based on FMC strategy and Lamb wave according to claim 4 is characterized in that: The three-dimensional elastic wave equation of the Lamb wave in step S2 is: Where ρ and μ are the density and shear modulus of the plate, respectively, and u i and f i Along x i Displacement and body force in the direction, u i,jj represents the shear deformation acceleration, u j,ji Refers to the volume deformation acceleration, represents the acceleration of the particle in the i direction, is the inertial force term, λ is the Lame constant, v is the Poisson's ratio, and E is the Young's modulus.

6. The GIS pot insulator fault detection method based on FMC strategy and Lamb wave according to claim 5, characterized in that: The dispersion characteristic equation of the Lamb wave in step S2 is: Among them, and describe the phase change of the wave in the thickness direction, is the normal compression, q is the tangential shear, is the square of the longitudinal wave velocity, is the square of the shear wave velocity, h is the plate thickness, and k is the wave number.

7. The GIS pot insulator fault detection method based on FMC strategy and Lamb wave according to claim 1 is characterized in that: The method for constructing the three-dimensional FMC matrix in step S3 is as follows: 1) Starting from the first transmitting array element, the synchronous triggering of the transmitting pulse on all receiving channels causes all array elements to synchronously receive the echo signal; 2) The data of all receiving channels at the time of the i-th transmission is a two-dimensional matrix D with a size of N*M i [j][k]=A j [k](1≤j≤N,1≤k≤M), the two-dimensional matrix D i [j][k] fills the i-th layer of the three-dimensional matrix; 3) Repeat the process, activating each transmitting element in turn, and finally forming a complete three-dimensional matrix FMC[i][j][k]=D i [j][k](1≤i,j≤N,1≤k≤M).

8. The GIS pot insulator fault detection method based on FMC strategy and Lamb wave according to claim 1 is characterized in that: The method for performing dispersion compensation by inverse dispersion transformation in step S3 is as follows: By calculating the dispersion curve of the Lamb wave, the received signal is short-time Fourier transformed and the phase delay is compensated using an inverse filter: Where Δt(f) is the time delay caused by dispersion, f is the signal frequency, H comp (f) is the frequency response function of the dispersion compensation filter, and j0 is the imaginary factor.

9. The GIS pot insulator fault detection method based on FMC strategy and Lamb wave according to claim 1, characterized in that: The method for forming the delayed superposition beam in step S3 is as follows: By adjusting the phase delay of multi-element signals, the signal in a specific direction is enhanced, interference in other directions is suppressed, and delayed superposition is performed to obtain the signal x of the i-th element. i (t), focus to position (x p ,z p ) is the synthetic signal: Among them, d i→p is the distance from the array element to the target, and y(t) is the synthetic signal.

10. The GIS pot insulator fault detection method based on FMC strategy and Lamb wave according to claim 1, characterized in that: The method for calculating and synthesizing the propagation time and pixel intensity using the all-focusing algorithm in step S3 is as follows: Extracting D from the FMC dataset ij (t) At time t = T i +T j The amplitude of the image is , let P be a pixel point in the imaging grid, with coordinates (x, y), and calculate the total time T for the ultrasound to travel from the transmitting array element i to the pixel point P and then back to the receiving array element j. ij (x,z), the formula is as follows: The pixel intensity synthesis formula at point P is as follows: Among them, I(x,z) is the composite pixel intensity of point P, x i is the coordinate of the transmitting array element, x j is the receiving element coordinate, x is the horizontal coordinate of the target point, z is the depth coordinate of the target point, T i (x,z) is the propagation time from the transmitting element to the target point, T j (x,z) is the propagation time from the target point to the receiving array element.

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