Laser ultrasonic non-contact detection method for transverse crack of high-voltage insulator

Abstract

The invention relates to the technical field of high-voltage insulator detection, and provides a high-voltage insulator transverse crack laser ultrasonic non-contact detection method which comprises the following steps: step 1, building a detection system which comprises an industrial personal computer, a pulse laser, a light path system, an ultrasonic receiving system and a scanning system, the pulse laser and the ultrasonic receiving system are in two-way communication with the industrial personal computer through optical fibers, the optical path system is fixed to the scanning system, and the scanning system receives control signals of the industrial personal computer through an industrial bus. And 2, outputting a synchronous trigger signal by the industrial personal computer, and controlling the pulse laser to emit nanosecond laser with the wavelength of 1064nm. Live detection is realized through a non-contact design, and a blind area of a compact insulator is eliminated; the efficiency is improved by means of collaborative scanning, and batch standardized detection is met; the multi-modal fusion and standardization algorithm improves the recognition precision and realizes quantitative detection, the method can also adapt to the outdoor environment to reduce the misjudgment rate, and an efficient, accurate and reliable detection scheme is provided for power grid operation and maintenance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage insulator detection, in particular to a high-voltage insulator transverse crack laser ultrasonic non-contact detection method. BACKGROUND

[0002] High-voltage insulators are core components of high-voltage power transmission systems, bearing both mechanical support and electrical insulation functions, and their operating state directly determines the safety of the power grid. According to power grid operation and maintenance data, outdoor insulators are prone to transverse cracks after 3-5 years of service due to factors such as wind and rain erosion, sudden temperature changes, and icing flashover. These cracks, initially only 0.1-0.5mm wide, can gradually expand to cause insulation breakdown, leading to accidents such as line tripping and equipment burning, accounting for 12%-18% of total power grid equipment failures. Therefore, accurate detection of transverse cracks is crucial for power grid operation and maintenance.

[0003] Traditional contact ultrasonic detection requires power outage and the probe needs to be attached to the surface of the insulator. For compact insulators with a ratio of umbrella spacing S to umbrella overhang P ≤ 0.3, the probe cannot be inserted into the gap, resulting in a detection coverage rate of less than 60%. Machine vision-based technology is affected by the high reflectivity of ceramic materials, leading to large image segmentation errors and an accurate crack recognition rate of only 75%-80%. Moreover, it cannot quantitatively detect crack angles and lengths. Early laser ultrasonic technology relies on manual scanning, which takes ≥40 minutes to complete full-surface detection of a 1.5m high insulator, resulting in extremely low efficiency. Additionally, it lacks standardized B-scan imaging algorithms, with a crack angle calculation error exceeding 5°, making it unable to meet quantitative operational and maintenance requirements. Furthermore, none of the three technologies considers outdoor environmental interference, resulting in a high outdoor detection misjudgment rate of 22%-28%, making them unsuitable for actual operational and maintenance scenarios. SUMMARY

[0004] To address the shortcomings of existing technologies, the present application provides a high-voltage insulator transverse crack laser ultrasonic non-contact detection method, which solves the problems of existing high-voltage insulator transverse crack detection technologies, such as the need for power outage for contact detection and the existence of detection blind spots for compact insulators; the low recognition accuracy and inability to quantitatively detect cracks due to the influence of high reflectivity for machine vision technology; the low efficiency and lack of standardized imaging algorithms for early laser ultrasonic technology; and the susceptibility to outdoor environmental interference leading to misjudgment for all types of technology, making it difficult to meet actual operational and maintenance requirements.

[0005] To achieve the above purpose, the present application is implemented through the following technical solution: a high-voltage insulator transverse crack laser ultrasonic non-contact detection method, comprising the following steps: Step one, build a detection system, the detection system includes industrial computer, pulse laser, optical system, ultrasonic receiving system and scanning system, the pulse laser, ultrasonic receiving system and industrial computer communicate bidirectionally through optical fiber, the optical system is fixed on the scanning system, and the scanning system receives the control signal of the industrial computer through the industrial bus. Step two, the industrial computer outputs a synchronous trigger signal to control the pulse laser to emit nanosecond laser with a wavelength of 1064 nm, and the laser is adjusted by an optical system to be a linear light spot to be incident on the circumference of the shaft body of the high-voltage insulator to be measured to excite a surface ultrasonic signal; Step three, the ultrasonic receiving system synchronously collects the ultrasonic signal, stores it through a data acquisition card, and then transmits it to the industrial computer; Step four, the industrial computer controls the scanning system to perform multi-dimensional scanning on the insulator to be measured, filters and A-scan imaging processes the received signal, generates a B-scan image after completing the fixed-height circumferential scanning, and outputs a detection result containing the defect level. Step five, the industrial computer locates the crack position according to the surface wave loss feature in the B-scan image, obtains the crack distribution range through a crack angle calculation formula, and outputs a detection result containing the defect level.

[0006] Preferably, the optical system comprises a first mirror, a second mirror and a cylindrical mirror connected in sequence, the first mirror and the second mirror have a reflectivity of ≥98%, and can withstand a maximum laser power density of ≥1.2 kW / cm 2 ; the cylindrical mirror has a focal length of 100±5 mm, focuses the circular laser into a linear light spot with a length of 20±2 mm and a width of 0.8±0.1 mm, and the laser energy density is ≤0.5 kJ / cm 2 , so as to avoid damaging the surface of the insulator.

[0007] Preferably, the scanning system comprises a rotating platform and a two-dimensional moving platform, the rotating platform is used to coaxially fix the insulator, has a radius of 750±10 mm, a minimum rotation angle of 1°, and an angular velocity that can be adjusted in a range of 0.5-2° / s; the two-dimensional moving platform has a moving step of Δz=0.025±0.005 mm along the z-axis of the insulator and a moving step of Δy=0.1±0.01 mm along the y-axis, and the two are cooperatively moved through a PID algorithm of the industrial computer, and the scanning path satisfies that the single moving distance of the z-axis is 1 / 2 of the umbrella interval S of the insulator, and the moving distance of the y-axis is the difference between the lengths of the adjacent umbrella.

[0008] Preferably, the ultrasonic receiving system comprises a laser interferometer and an NI-PCI5114 data acquisition card, the laser interferometer has a wavelength of 532±5 nm, an output power of 1.5±0.2 W, and a focal length of 200±10 mm, and is used to receive the surface vibration signal of the alternating umbrella of the insulator; the data acquisition card has a sampling frequency =250±10 MHz and a time step =4±0.5 ns, and the collected signal is stored after being filtered by an 8-order Butterworth low-pass filter.

[0009] Preferably, in step four, the A-scan imaging determines the effectiveness of the signal through a peak signal-to-noise ratio, and the calculation formula is: wherein n=16,​ is signal noise standard deviation; when PSNR is greater than or equal to 35dB, the signal is determined to be valid, otherwise the industrial computer automatically adjusts the focal length of the laser interferometer until the signal meets the standard.

[0010] Preferably, the crack distribution circumferential angle in the fifth step is 5°-15°. The formula is as follows: wherein , are the starting and ending angles of the surface wave missing area respectively, is the calibration error; the crack length estimation formula is as follows: R is the radius of the insulator shaft body.

[0011] Preferably, the infrared signal of the insulator surface is synchronously collected in the second step, and the industrial computer adopts a multi-modal fusion algorithm to optimize the determination result. wherein is the ultrasonic signal crack confidence, is the infrared signal temperature anomaly confidence; when C is greater than or equal to 0.9, it is determined that there is a crack, otherwise it is determined to be normal.

[0012] Preferably, the industrial computer realizes energy consumption optimization through dynamic parameter adjustment: the pulse laser repetition frequency is reduced from 50Hz to 30Hz in the defect-free area, and the sampling frequency of the data acquisition card is reduced from 250MHz to 100MHz.

[0013] Preferably, the detection result in the fifth step includes: crack z-axis coordinate, circumferential angle, length estimation value and defect grade; the result is transmitted to the power grid operation and maintenance platform in real time, and the sound-light warning is triggered when the defect grade is greater than or equal to grade II, and the warning response time is less than or equal to 1s.

[0014] Preferably, the defect grade is grade I: <5°, grade II: 5°≤ <15°, grade III: ≥15°.

[0015] The present application provides a high-voltage insulator transverse crack laser ultrasonic non-contact detection method. It has the following beneficial effects: 1. The present application solves the problems of "power-off dependence" and "compact insulator blind area" of traditional contact detection: through non-contact laser excitation and receiving design, live detection under voltage level ≤500kV is realized without the need of power-off; combined with cylindrical lens linear spot and two-dimensional moving platform, the detection coverage of compact insulators is effectively improved, thereby completely eliminating the detection blind area.

[0016] 2. This invention completes the full end face inspection of a 1.5m high insulator through PID coordinated control of a rotating platform and a two-dimensional moving platform, which is time-saving and efficient; at the same time, the scanning repeatability and positioning error is small, which meets the standardized inspection requirements of batch insulators.

[0017] 2. Based on the B-scan imaging algorithm with missing surface waves and the online calibration mechanism, this invention improves the crack angle detection error and, combined with the length estimation formula, achieves quantitative calculation of crack length using laser ultrasound technology for the first time, filling a gap in existing technology. Attached Figure Description

[0018] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example: Please see the appendix Figure 1 This invention provides a laser-ultrasonic non-contact detection method for transverse cracks in high-voltage insulators, comprising the following steps: Step 1: Set up the detection system. The detection system includes an industrial control computer, a pulsed laser, an optical path system, an ultrasonic receiving system, and a scanning system. The pulsed laser and ultrasonic receiving system communicate bidirectionally with the industrial control computer via optical fiber. The optical path system is fixed to the scanning system, and the scanning system receives control signals from the industrial control computer via an industrial bus. Step 2: The industrial control computer outputs a synchronous trigger signal to control the pulsed laser to emit a nanosecond-level laser with a wavelength of 1064nm. The laser is adjusted into a linear spot by the optical path system and incident on the circumference of the shaft of the high-voltage insulator under test, exciting the surface ultrasonic signal. Simultaneously, the infrared signal on the insulator surface is collected. The industrial control computer uses a multi-modal fusion algorithm to optimize the judgment result. ,in The confidence level of the ultrasonic signal for cracks. The confidence level for infrared signal temperature anomalies is: when C ≥ 0.9, a crack is considered to exist; otherwise, it is considered normal. Step 3: The ultrasonic receiving system synchronously acquires ultrasonic signals, stores them on the data acquisition card, and then transmits them to the industrial control computer. The industrial control computer optimizes energy consumption by dynamically adjusting parameters: in the defect-free area, the repetition frequency of the pulse laser is reduced from 50Hz to 30Hz, and the sampling frequency of the data acquisition card is reduced from 250MHz to 100MHz. Step four, the industrial computer controls the scanning system to scan the insulator in multiple dimensions, filters and A-scan imaging processes the received signal, generates a B-scan image after completing the fixed-height circumferential scanning, and the A-scan imaging determines the signal effectiveness through the peak signal-to-noise ratio (PSNR), and the calculation formula is: wherein n = 16, is the signal noise standard deviation; when PSNR ≥ 35 dB, the signal is determined to be effective, otherwise the industrial computer automatically adjusts the focal length of the laser interferometer until the signal meets the standard; Step five, the industrial computer locates the crack position according to the surface wave loss characteristics in the B-scan image, obtains the crack distribution range through the crack angle calculation formula, and outputs the detection results containing the defect level, wherein the crack distribution circumferential angle is calculated by the following formula: wherein , are the starting and ending angles of the surface wave loss area, respectively, is the calibration error; the crack length estimation formula is: R is the radius of the insulator shaft, and the detection results include: the z-axis coordinate of the crack, the circumferential angle, the length estimation value and the defect level; the results are transmitted to the power grid operation and maintenance platform in real time, the sound-light warning is triggered when the defect level is ≥ II level, the warning response time is ≤ 1 s, and the defect levels are respectively: <5°, secondary: 5°≤ <15°, and tertiary: ≥ 15°.

[0021] The optical path system includes a first mirror, a second mirror and a cylindrical mirror connected in sequence, the reflectivity of the first mirror and the second mirror is ≥ 98%, and the maximum laser power density borne is ≥ 1.2 kW / cm 2 ; the focal length of the cylindrical mirror is 100±5 mm, the circular laser is focused into a linear spot with a length of 20±2 mm and a width of 0.8±0.1 mm, and the laser energy density is ≤ 0.5 kJ / cm 2 to avoid damaging the surface of the insulator.

[0022] The scanning system includes a rotating platform and a two-dimensional moving platform, the rotating platform is used for coaxially fixing the insulator, the radius is 750±10 mm, the minimum rotation angle is 1°, and the angular velocity can be adjusted in the range of 0.5-2° / s; the two-dimensional moving platform moves along the z-axis of the insulator with a step length Δz = 0.025±0.005 mm and along the y-axis with a step length Δy = 0.1±0.01 mm, and the two are cooperatively moved through the PID algorithm of the industrial computer, and the scanning path satisfies that the single moving distance of the z-axis is 1 / 2 of the umbrella spacing S of the insulator, and the moving distance of the y-axis is the difference between the adjacent umbrella extensions.

[0023] The ultrasonic receiving system includes a laser interferometer and a NI-PCI5114 data acquisition card, the laser interferometer has a wavelength of 532±5nm, an output power of 1.5±0.2W and a focal length of 200±10mm, and is used for receiving the alternating umbrella surface vibration signal of the insulator; the data acquisition card has a sampling frequency of 250±10MHz, a time step of 4±0.5ns, and the collected signal is stored after being filtered by an 8-order Butterworth low-pass filter; =250±10MHz, time step =4±0.5ns, and the collected signal is stored after being filtered by an 8-order Butterworth low-pass filter; The specific scheme is as follows: Step one: detection system building and debugging An integrated detection system including a control center, an excitation unit, an optical path adjustment unit, a signal receiving unit and a scanning execution unit is built. The industrial computer is selected to have a Core i7-12700K processor, 32GB DDR4 memory and 2TB SSD storage, and is pre-installed with LabVIEW control software and MATLAB signal analysis module, and is responsible for issuing instructions, data processing and result output as the core of the system. The pulse laser adopts a Nd:YAG nanosecond laser with a rated output wavelength of 1064nm, a single pulse energy of 50mJ and a repetition frequency of 50Hz, and communicates with the industrial computer through a single-mode optical fiber, and the delay of the laser in response to the synchronization trigger signal of the industrial computer is ≤10ns. The optical path system is fixed on the two-dimensional moving platform of the scanning system by a customized metal bracket to ensure the stability of the optical path. The laser interferometer and the data acquisition card of the ultrasonic receiving system are directly connected to the industrial computer through a USB3.0 interface, and the data transmission rate is ≥5Gbps. The rotating platform and the two-dimensional moving platform of the scanning system are both equipped with servo motors and grating encoders, and receive the control instructions of the industrial computer through the RS485 industrial bus. After the completion of the building, the system needs to be calibrated: the standard crack sample is fixed on the rotating platform, the industrial computer calibration program is started, the focal length of the optical path system and the moving parameters of the scanning system are adjusted, and the system is calibrated until the measured crack angle error is ≤0.5°, so as to ensure the working precision of each module.

[0024] Step two: laser excitation and multi-signal synchronous acquisition The industrial computer generates a synchronization trigger signal through LabVIEW software, which is divided into two paths: one is transmitted to the pulse laser through an optical fiber to control the laser to emit nanosecond laser pulses with a wavelength of 1064nm. The laser is first reflected by the first reflector to change the direction of the optical path, and then reflected by the second reflector for the second time, and then vertically incident on the cylindrical lens. The cylindrical lens has a focal length of 100mm and an effective light aperture of 25mm. The parameters of the first reflector and the second reflector are the same, both with a reflectivity of 98.5% and a diameter of 50mm. The material is quartz. The cylindrical lens focuses the circular laser spot into a linear spot with a length of 20mm and a width of 0.8mm. The linear spot is incident on the circumferential surface of the high-voltage insulator shaft to be measured. The laser energy density is strictly controlled to be 0.45kJ / cm 2, which meets the demand of surface ultrasonic signal excitation and avoids damaging the ceramic surface of the insulator; another trigger signal is transmitted to the ultrasonic receiving system and the infrared detector, the infrared detector with a wavelength of 8-14 pm and a resolution of 640x512 synchronously collects the temperature field signal of the insulator surface, the laser interferometer with a wavelength of 532 nm, an output power of 1.5 W and a focal length of 200 mm irradiates continuous laser on the surface of the insulator with alternating umbrella extension, and receives the surface ultrasonic vibration signal generated by the laser excitation; after the vibration signal is converted into an electrical signal by the interferometer, the signal is transmitted to the NI-PCI5114 data acquisition card for analog-to-digital conversion and storage; at the same time, the industrial computer calls a multi-thread data acquisition program to realize the synchronization of laser excitation, ultrasonic receiving and infrared acquisition, and the time synchronization error is controlled within 5 ns.

[0025] Step three: ultrasonic signal preprocessing and energy consumption dynamic optimization The original signal collected by the ultrasonic receiving system contains environmental noise, such as outdoor wind speed interference and equipment electromagnetic noise, which needs to be preliminarily de-noised by the 8-order Butterworth low-pass filter built in the data acquisition card, and then transmitted to the industrial computer for deep processing: the industrial computer calls the wavelet threshold de-noising algorithm through MATLAB, selects db4 wavelet basis to decompose the signal for 5 layers, suppresses high-frequency noise through a soft threshold function, and retains the effective ultrasonic signal characteristics; at the same time, the industrial computer analyzes the collected ultrasonic signal and infrared signal in real time, if the multi-modal fusion confidence C of the continuous 3 scanning points is less than 0.6, the energy consumption optimization mechanism is automatically triggered: the pulse laser repetition frequency is reduced from 50 Hz to 30 Hz to reduce the invalid laser emission; the data acquisition card sampling frequency is reduced from 250 MHz to 100 MHz to reduce the data processing load - this dynamic adjustment is realized through real-time communication between the industrial computer and the equipment, which reduces the system operation energy consumption on the premise of ensuring the reliability of defect detection in the non-defect area, and when the subsequent scanning point detects suspected defect signal, the system can restore high-frequency sampling and high-repetition frequency mode within 0.5 s without affecting the detection accuracy.

[0026] Step four: multi-dimensional scanning and A / B scan imaging The industrial computer generates a scanning path through the PID control algorithm according to the three-dimensional model of the insulator to be tested and the preset umbrella interval S, umbrella extension / Firstly, the two-dimensional moving platform is controlled to move along the z-axis to the starting detection height, and the position information is fed back in real time through the grating encoder during the movement, and the step precision is controlled to be 0.025 mm; after reaching the target height, the rotating platform drives the insulator to rotate at a minimum rotation angle of 1° and an angular velocity of 1° / s, realizing fixed-height circumferential scanning, and the ultrasonic receiving system collects one group of ultrasonic signals every 1° rotation, and the industrial computer synchronously performs A scan imaging on the signals - during A scan imaging, the signal effectiveness is determined by the peak signal-to-noise ratio, and the calculation formula is where n = 16, The signal noise standard deviation is used to automatically send a command to adjust the focal length of the laser interferometer if the PSNR is less than 35 dB until the signal meets the standard. After completing the fixed-height circumferential scanning, the industrial computer sorts all A-scan signals at the height according to the scanning angle to generate a two-dimensional B-scan image. The x-axis of the B-scan image is the scanning angle, the y-axis is the signal sampling time, and the pixel value corresponds to the signal amplitude, which intuitively presents the ultrasonic signal distribution characteristics in the circumferential direction of the insulator.

[0027] Step five: crack positioning, quantification, and result output The industrial computer calls the image recognition algorithm to analyze the B-scan image. First, the surface wave propagation trajectory is extracted through the edge detection algorithm. If there is a missing area of surface wave signals, it is determined that there is a transverse crack in the corresponding position of the insulator. The starting angle and the ending angle of the missing area are recorded. Then, the crack angle calculation formula is used where , are the starting and ending angles of the surface wave missing area, respectively, is the calibration error, and the crack distribution circumferential angle is calculated. Combined with the insulator shaft radius R, the crack length is estimated by Subsequently, according to Δα, the defect grade is divided: First level: <5° Second level: 5°≤ <15° Third level: ≥15° Finally, a detection report containing "crack z-axis coordinates, length estimation, defect grade, and B-scan image" is generated. Through the 4G / 5G module, it is transmitted to the power grid operation platform in real time. If the defect grade is ≥Ⅱ level, the industrial computer controls the local sound-light alarm to trigger an early warning, and the early warning response time is ≤1s. At the same time, the three-dimensional coordinates of the defect position are marked in the detection report, which is convenient for operation personnel to accurately position and subsequent maintenance.

[0028] Key module parameters and collaborative mechanism Optical system: The first and second mirrors use a coating process to ensure a laser reflectivity of more than 98% and can withstand a maximum laser power density of 1.2kW / cm 2 , avoiding damage to the lens over a long period of use. The focal length error of the cylindrical lens is controlled within ±5mm, ensuring the size accuracy of the linear light spot. This optical design allows the laser to accurately enter the insulator shaft, generating uniform surface wave signal strength, providing a stable signal source for subsequent detection.

[0029] ​Scanning system: the rotating platform radius is 750 mm, the insulator is fixed coaxially by three-jaw chuck, the coaxial error is less than or equal to 0.1 mm; the moving step of z-axis and y-axis of the two-dimensional moving platform is 0.025 mm and 0.1 mm respectively, when the two axes move cooperatively, the single moving distance of z-axis is strictly 1 / 2 of the umbrella spacing S, and the moving distance of y-axis is the difference of adjacent umbrella extension , which ensures that the scanning covers all the alternate umbrella end faces of the insulator and there is no detection omission.

[0030] Ultrasonic receiving system: the focal length of the laser interferometer is controlled within 200±10 mm, which ensures that the received laser can be stably focused on the surface of the alternate umbrella of the insulator, and the signal-to-noise ratio of the collected vibration signal is greater than or equal to 40 dB; the time step of the NI-PCI5114 data acquisition card is 4 ns, which can completely capture the propagation details of the surface wave and provide high-resolution signal data for crack detection.

[0031] Although the embodiments of the present application have been shown and described, it can be understood by those skilled in the art that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A laser-ultrasonic non-contact method for detecting transverse cracks in high-voltage insulators, characterized in that, Includes the following steps: Step 1: Set up the detection system. The detection system includes an industrial control computer, a pulsed laser, an optical path system, an ultrasonic receiving system, and a scanning system. The pulsed laser and the ultrasonic receiving system communicate bidirectionally with the industrial control computer via optical fiber. The optical path system is fixed to the scanning system, and the scanning system receives control signals from the industrial control computer via an industrial bus. Step 2: The industrial control computer outputs a synchronous trigger signal to control the pulsed laser to emit a nanosecond-level laser with a wavelength of 1064nm. The laser is adjusted into a linear spot by the optical path system and incident on the circumference of the shaft of the high-voltage insulator under test to excite the ultrasonic signal on the surface. Step 3: The ultrasonic receiving system synchronously acquires the ultrasonic signals, stores them on the data acquisition card, and then transmits them to the industrial control computer; Step 4: The industrial control computer controls the scanning system to perform multi-dimensional scanning of the insulator under test, while filtering the received signal and performing A-scan imaging processing. After completing the fixed-height circular scanning, a B-scan image is generated. Step 5: The industrial control computer locates the crack position based on the surface wave missing features in the B-scan image, obtains the crack distribution range through the crack angle calculation formula, and outputs the detection results including the defect level.

2. The laser-ultrasonic non-contact detection method for transverse cracks in high-voltage insulators according to claim 1, characterized in that, The optical path system includes a first reflecting mirror, a second reflecting mirror, and a cylindrical mirror connected in sequence. The first and second reflecting mirrors have a reflectivity of ≥98% and can withstand a maximum laser power density of ≥1.2kW / cm². 2 The cylindrical mirror has a focal length of 100±5mm, which focuses the circular laser into a linear spot with a length of 20±2mm and a width of 0.8±0.1mm, and the laser energy density is ≤0.5kJ / cm². 2 To avoid damaging the surface of the insulator.

3. The laser-ultrasonic non-contact detection method for transverse cracks in high-voltage insulators according to claim 1, characterized in that, The scanning system includes a rotating platform and a two-dimensional moving platform. The rotating platform is used to coaxially fix the insulator, with a radius of 750±10mm, a minimum rotation angle of 1°, and an angular velocity adjustable within the range of 0.5~2° / s. The two-dimensional moving platform moves along the insulator's z-axis with a step size Δz=0.025±0.005mm and along the y-axis with a step size Δy=0.1±0.01mm. The two platforms move in tandem using a PID algorithm from an industrial control computer. The scanning path satisfies the following conditions: the single movement distance along the z-axis is half of the insulator umbrella spacing S, and the movement distance along the y-axis is the difference in extension between adjacent umbrellas. .

4. The laser-ultrasonic non-contact detection method for transverse cracks in high-voltage insulators according to claim 1, characterized in that, The ultrasonic receiving system includes a laser interferometer and an NI-PCI5114 data acquisition card. The laser interferometer has a wavelength of 532±5nm, an output power of 1.5±0.2W, and a focal length of 200±10mm, and is used to receive the vibration signal from the surface of the alternating insulator umbrellas. The data acquisition card has a sampling frequency... =250±10MHz, time step =4±0.5ns, the acquired signal is stored after being filtered by an 8th-order Butterworth low-pass filter.

5. The laser-ultrasonic non-contact detection method for transverse cracks in high-voltage insulators according to claim 1, characterized in that, In step four, the A-scan imaging determines the signal validity based on the peak signal-to-noise ratio (PSNR), calculated using the following formula: Where n=16, The signal noise standard deviation is used; when PSNR ≥ 35dB, the signal is considered valid; otherwise, the industrial control computer automatically adjusts the focal length of the laser interferometer until the signal meets the standard.

6. The laser-ultrasonic non-contact detection method for transverse cracks in high-voltage insulators according to claim 1, characterized in that, In step five, the crack distribution circumferential angle Calculated using the following formula: ,in , These represent the start and end angles of the surface wave missing region. To account for calibration error; the crack length estimation formula is: R is the radius of the insulator shaft.

7. The laser-ultrasonic non-contact detection method for transverse cracks in high-voltage insulators according to claim 1, characterized in that, In step two, infrared signals from the insulator surface are simultaneously acquired, and the industrial control computer uses a multi-modal fusion algorithm to optimize the judgment result. ,in The confidence level of the ultrasonic signal for cracks. The confidence level for infrared signal temperature anomalies is: when C≥0.9, a crack is considered to exist; otherwise, it is considered normal.

8. The laser-ultrasonic non-contact detection method for transverse cracks in high-voltage insulators according to claim 1, characterized in that, The industrial control computer optimizes energy consumption through dynamic parameter adjustment: in the defect-free area, the repetition frequency of the pulsed laser is reduced from 50Hz to 30Hz, and the sampling frequency of the data acquisition card is reduced from 250MHz to 100MHz.

9. The laser-ultrasonic non-contact detection method for transverse cracks in high-voltage insulators according to claim 1, characterized in that, The detection results in step five include: crack z-axis coordinates, circumferential angle, estimated length, and defect level; the results are transmitted to the power grid operation and maintenance platform in real time, and an audible and visual warning is triggered when the defect level is ≥ II, with a warning response time ≤ 1 second.

10. The laser-ultrasonic non-contact detection method for transverse cracks in high-voltage insulators according to claim 1, characterized in that, The defect levels are all Level 1: <5°, Level 2: 5°≤ <15°, Level 3: ≥15°.

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