Ultrasonic end corner reflection wave detection and positioning method for internal crack of supporting insulator ceramic piece

Abstract

The invention discloses a support insulator ceramic member internal crack ultrasonic end corner reflection wave detection positioning method comprising the following steps: S1, using an ultrasonic flaw detector, using an ultrasonic emission probe to obliquely emit an incident longitudinal wave to the ceramic member arc surface, and generating an inclined refraction transverse wave in a ceramic test piece, receiving an end corner reflection echo reflected by the internal crack of the ceramic piece by an ultrasonic transmitting probe so as to measure the sound path distance of the crack defect in the ceramic test piece; and S2, calculating to obtain the depth from the surface and the distance in the circumferential direction by using the inclined incidence angle of the refracted transverse wave, the sound path distance and the structural size of the ceramic piece, and carrying out crack defect positioning. According to the method, low-speed propagation of transverse waves is utilized, a small-size ultrasonic transceiving wafer with the size smaller than 4 mm is preferably selected, a near-field blind area is controlled within 5 mm, and high signal-to-noise ratio detection is achieved. Meanwhile, the intensity of ultrasonic signals reaching the crack end angle surface is enhanced by utilizing a large refraction angle, so that the intensity of reflection echoes is enhanced, and the detection sensitivity is improved.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic flaw detection technology for ceramic insulators in power systems, specifically, to a method for detecting and locating internal cracks in ceramic supporting insulators using ultrasonic end-angle reflection waves. Background Technology

[0002] Capacitor bank support insulators are crucial components in substation reactive power compensation devices. They stably fix the high-voltage busbars to the cabinet or support structure and isolate the high-voltage ends to prevent leakage, effectively ensuring the reliability of the compensation device's operation. Porcelain insulators are made of ceramic fired at high temperatures. Their biggest drawback is their brittleness and poor toughness; once cracked, the cracks propagate rapidly, potentially causing the insulator to break completely. In recent years, power grids have experienced numerous faults involving cracked or even broken capacitor bank support insulators, resulting in the capacitor busbars losing support and posing a risk of discharge to the structure. Furthermore, once one support insulator breaks, the load on other support insulators on that busbar increases, triggering a chain reaction that can cause adjacent insulators to continue breaking. Therefore, conducting defect detection of capacitor bank support insulators is imperative.

[0003] Ultrasonic testing is an important method for detecting early defects in post porcelain insulators and bushings. When ultrasonic waves travel from one medium to another, refraction, reflection, and waveform conversion occur at the interface between the two media. Defects inside the insulator are detected by receiving the reflected echoes. Based on the intensity of the received defect echoes and their position on the time axis, the length and depth of the internal defects can be determined. This method is mainly used for detecting surface and internal defects such as pores, cracks, and inclusions in post insulators.

[0004] According to the power industry standard DL / T 303-2014 "Ultrasonic Testing of In-Service Porcelain Insulators and Bushings for Power Grids," a comprehensive testing process combining creeping wave testing, small-angle longitudinal wave testing, and dual-crystal transverse wave testing is used to detect minor defects and cracks caused by long-term operation expansion of internal minor defects and damage in in-service porcelain insulators and bushings for power grids, as well as cracks caused by excessive cement expansion stress on the surface and near-surface of the porcelain body inside cast iron flanges due to improper adhesive bonding processes. The standard specifies that the upper and lower ends of the tested porcelain components are relatively large, facilitating the installation of ultrasonic probes; the ultrasonic probe crystal size is greater than 6mm × 10mm, and the distance between the probe and the defect is between 10mm and 60mm.

[0005] However, the capacitor bank's supporting insulators are primarily made of ceramic components with hemispherical cast iron inserts at both ends, resulting in relatively small insulator dimensions. Operational failure cases indicate that the upper and lower ends of the ceramic components are the starting points for fracture failures. Strengthening the detection of cracks at these ends is crucial for timely defect detection and prevention. However, existing ceramic component flaw detection techniques cannot effectively detect cracks in this area. This is mainly because in the near-field blind zone near the ultrasonic probe, incident and reflected waves overlap, making it impossible to distinguish between them and thus hindering detection.

[0006] Therefore, there is an urgent need for a method to detect and locate internal cracks in ceramic components of supporting insulators using ultrasonic end-angle reflection waves, in order to solve the problem of near-field detection blind spots in ultrasonic testing technology. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide an ultrasonic end-angle reflection wave detection and positioning method for internal cracks in ceramic supporting insulators, which can be applied to the ultrasonic detection of early internal crack defects at both ends of small-sized capacitor bank supporting insulators, and solves the near-field detection blind zone problem of ultrasonic detection technology.

[0008] This invention provides a method for detecting and locating internal cracks in ceramic supporting insulators using ultrasonic end-corner reflection waves, comprising the following steps: S1. Detection of internal crack defects in ceramic parts: Using an ultrasonic flaw detector, an incident longitudinal wave is emitted at an angle from the ultrasonic transmitting probe toward the curved surface of the ceramic part, generating an inclined refracted transverse wave inside the ceramic specimen. The ultrasonic transmitting probe then receives the end-angle reflected echo from the internal crack of the ceramic part, thereby measuring the acoustic path of the crack defect in the ceramic specimen. S2. Locating internal cracks in ceramic parts: Using the angle of incidence of the refracted transverse wave, the sound path, and the structural dimensions of the ceramic part, the depth from the surface and the circumferential distance are calculated to locate the cracks.

[0009] Preferably, the method for calculating the distance to the surface depth is as follows: First, decompose the total sound path measured by the ultrasonic flaw detector into the round-trip path length s corresponding to "probe → crack → probe" into one-way sound paths, and then subtract the length of the probe leading edge. Ultimately, through the transverse wave refraction angle The cosine value converts the oblique sound path into the vertical depth of the crack to the outer surface. The sound path d of the ultrasonic wave propagating in the ceramic is: According to the law of cosines, the distance D from the crack to the center of the circle is: D The vertical depth H of the crack to the outer surface is: D Where: H - vertical depth of the crack from the outer surface of the ceramic; s - total ultrasonic path to and from the crack; - Length of the ultrasonic probe's leading edge; -Angle of transverse wave refraction; - The propagation speed of transverse waves in ceramics; - The total time for ultrasound to travel to and from the destination.

[0010] Preferably, the method for calculating the circumferential distance is as follows: The circumferential distance from the point of incidence to the point where the crack projects onto the circumference is L, and the corresponding central angle is θ. This can be calculated using the law of sines. The circumferential distance L is calculated using the following arc formula, conforming to the spatial measurement specifications for porcelain insulator defect location: Where: L - circumferential distance between the crack projection point and the reference point; R - outer radius of the ceramic end; - The central angle of the crack projection point.

[0011] Preferably, the ultrasonic flaw detector uses an acoustic emission crystal with a size of 4mm x 4mm and an operating frequency of 5MHz.

[0012] Preferably, the transverse wave refraction angle Not less than 45°.

[0013] The beneficial effects of this invention are as follows: The ultrasonic end-angle reflection wave detection and positioning method for internal cracks in ceramic supporting insulators of this invention utilizes an ultrasonic flaw detector. An incident longitudinal wave is emitted obliquely towards the arc-shaped surface of the ceramic component by an ultrasonic transmitting probe. This generates an obliquely refracted transverse wave within the ceramic specimen. The ultrasonic transmitting probe then receives the end-angle reflection echo from the internal crack in the ceramic component, thereby measuring the acoustic path of the crack defect in the ceramic specimen. After measuring the acoustic path of the reflected echo, the circumferential position and radial depth of the crack defect are obtained through geometric calculations, combined with the annular structural dimensions of the ceramic component at the end of the supporting insulator and the emission angle. This achieves accurate visualization of the location of internal crack defects in the ceramic component. This method uses a small-sized ultrasonic probe to emit longitudinal waves, ensuring that the longitudinal waves are obliquely incident on the surface of the ceramic component. By setting the incidence angle, only transverse waves propagate inside the ceramic component, and the refraction angle of the transverse waves is not less than 45°. When the transverse waves reach the crack in the ceramic component, end-angle reflection waves are generated. Crack defect detection is achieved by receiving these reflection waves. Furthermore, by utilizing the low-speed propagation of shear waves and selecting small-sized ultrasonic transceiver chips (less than 4 mm), the near-field blind zone is controlled within 5 mm, achieving high signal-to-noise ratio detection. Simultaneously, by employing a larger refraction angle, the intensity of the ultrasonic signal reaching the crack tip is enhanced, thereby increasing the intensity of the reflected echo and improving detection sensitivity. Attached Figure Description

[0014] Figure 1 This invention provides a process for detecting and locating internal cracks in ceramic specimens supporting insulators using transverse oblique waves. Figure 2 An axial view of the capacitor bank support insulator; Figure 3 A transverse oblique wave detection method for internal crack defects in ceramic parts; Figure 4 A method for locating internal cracks and defects in ceramic parts; Figure 5 This is a schematic diagram of the tested support insulator and crack defects in Example 1; Figure 6 To support the ultrasonic testing photograph of the insulator, (a) the insulator and ultrasonic instrument are supported; (b) the probe is placed at a defect-free location; (c) the reflected echo is shown. Figure 7 for Figure 6 Detection and reflected echo of crack #1 in the middle section, (a) probe attached near crack #1; (b) reflected echo; Figure 8 for Figure 6 Detection and reflected echo of crack #2 in the middle section, (a) probe attached near crack #1; (b) reflected echo; Figure 9 for Figure 6 Detection and reflected echo of crack #3 in the middle, (a) probe attached near crack #1; (b) reflected echo.

[0015] In the diagram: 1. Hemispherical cast iron insert; 2. Cement bonding layer; 3. Ceramic flange; 4. Ceramic crack; 5. Ultrasonic probe; 6. Incident longitudinal wave; 7. Refracted transverse wave; 8. Corner reflected echo; 1# crack; 2# crack; 3# crack. Detailed Implementation

[0016] To make the technical solution of the present invention easier to understand, the technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings and specific embodiments.

[0017] Example 1: This embodiment selects a 10kV capacitor bank support insulator ceramic component as the object. The outer diameter of the ceramic component is 90mm, the inner diameter is 70mm, and the thickness is 10mm. The ultrasonic end-corner reflection wave detection and location method for internal cracks in the support insulator ceramic component is used to conduct the inspection, including the following steps: S1. Detection of internal crack defects in ceramic parts: Using an ultrasonic flaw detector, an incident longitudinal wave is emitted at an angle from the ultrasonic transmitting probe toward the curved surface of the ceramic part, generating an inclined refracted transverse wave inside the ceramic specimen. The ultrasonic transmitting probe then receives the end-angle reflected echo from the internal crack of the ceramic part, thereby measuring the acoustic path of the crack defect in the ceramic specimen. In the transverse wave method, an angled probe is used for ultrasonic emission. The angled probe utilizes a sound-transmitting plexiglass wedge to generate an obliquely incident longitudinal wave. This longitudinal wave is obliquely incident on the interface, where it is refracted in the specimen to produce an oblique refracted transverse wave. A 4mm x 4mm acoustic emission crystal is selected, with an operating frequency of 5MHz.

[0018] In this embodiment, the incident angle is calculated based on the transverse and longitudinal wave velocities in the plexiglass and ceramic component, thereby obtaining a reasonable transverse wave refraction angle. The longitudinal wave velocity in the plexiglass is 2.72 × 10⁻⁶. 3 m / s, the longitudinal wave velocity of the ceramic is 6.35×10 3 m / s, transverse wave speed of sound is 3.75×10 3 m / s, with an incident angle αl of 30.9°, the angle of refraction β t The angle is 45°. The ultrasonic transceiver used is the HS610e digital ultrasonic flaw detector.

[0019] In this embodiment, testing was conducted on a 10kV capacitor bank support insulator sample. The instrument parameters were set as follows: gain 43.2dB, suppression 0%. The sensitivity was adjusted using a JYZ-BX 1 calibration block, with the 80% wave height of a 20mm deep, 1mm diameter transverse through-hole used as the reference sensitivity.

[0020] Top view of the sample and location of defects, as shown Figure 5As shown. First, the surface to be tested is cleaned of oil and dust. Then, the test is carried out, and the test process is as follows: (1) Place the probe in a defect-free location, with the distance between this location and cracks #1 and #3 greater than 70mm. Figure 6 (b) indicates the probe installation location. Figure 6 (c) shows the reflected echo. It can be seen that there is no reflected echo in the range of 8.2mm to 35mm.

[0021] (2) Place the probe near crack #1. The probe image and the reflected echo are as follows: Figure 7 As shown in (a) and (b), the reflected wave indicates that the acoustic path of crack #1 is 24.1 mm. The defect equivalent is greater than the equivalent of the transverse through-hole #1. The probe was placed near crack #2, and the probe images and reflected echoes are shown below. Figure 8 As shown in (a) and (b), the reflected wave indicates that the acoustic path of crack #2 is 15.7 mm. The defect equivalent is approximately equal to the equivalent of a transverse through-hole of diameter ∅1. The probe was placed near crack #3; the probe images and reflected echoes are shown below. Figure 9 As shown in (a) and (b), the reflected wave indicates that the acoustic path of crack #3 is 24.6 mm. The defect equivalent is greater than the equivalent of a ∅1 mm transverse through hole.

[0022] S2. Locating internal cracks in ceramic parts: Using the angle of incidence of the refracted transverse wave, the sound path, and the structural dimensions of the ceramic part, the depth from the surface and the circumferential distance are calculated to locate the cracks.

[0023] The method for calculating the distance to the surface depth is as follows: First, the total sound path measured by the ultrasonic flaw detector is decomposed into the round-trip path length s corresponding to "probe → crack → probe" into one-way sound paths. Then, the length l0 of the ultrasonic probe's leading edge is subtracted, and finally, the sound path is obtained through the refraction angle β. t The cosine value converts the oblique sound path into the vertical depth of the crack to the outer surface. The sound path d of the ultrasonic wave propagating in the ceramic is: According to the law of cosines, the distance D from the crack to the center of the circle is: D The vertical depth H of the crack to the outer surface is: D Where: H - vertical depth of the crack from the outer surface of the ceramic; s - total ultrasonic path to and from the crack; - The length of the ultrasonic probe's leading edge, i.e., the length of the horizontal line segment from the probe's front end to the point of sound wave incidence; -Angle of transverse wave refraction; - The propagation speed of transverse waves in ceramics; - The total time for ultrasound to travel to and from the destination.

[0024] The method for calculating the circumferential distance is as follows: The circumferential distance from the point of incidence to the point where the crack projects onto the circumference is L, and the corresponding central angle is θ. This can be calculated using the law of sines. The circumferential distance L is calculated using the following arc formula, conforming to the spatial measurement specifications for porcelain insulator defect location: Where: L - circumferential distance between the crack projection point and the reference point; R - outer radius of the ceramic end; - The central angle of the crack projection point, that is, the central angle between the crack projection point and the incident point.

[0025] In this embodiment, based on the measured data of cracks #1, #2, and #3 obtained by ultrasonic testing (total sound path S is 24.1 mm, 15.7 mm, and 24.6 mm, respectively), combined with... Figure 2 The structural parameters of the ceramic component shown are as follows (outer radius R = 45 mm, transverse wave refraction angle). =45°, ultrasonic probe leading edge length =5mm), the positioning calculation is completed through geometric projection and the formula for the circumferential arc length, as follows: Crack depth calculation from the surface: Based on the symmetry of the reflection path at the transverse wave end angle, the total sound path is first decomposed into single-path sound paths. After subtracting the length of the ultrasonic probe's leading edge to eliminate equipment errors, the oblique sound path is converted into vertical depth using the cosine value of the refraction angle. Using the formula, the calculated depths are approximately 5.00 mm for crack #1, 2.02 mm for crack #2, and 5.15 mm for crack #3. All these results fall within the 0-10 mm thickness range at the ceramic end, consistent with the defect distribution pattern.

[0026] Crack circumferential distance calculation: Taking the left edge of the first letter of the ceramic part's serial number as the 0° reference point, the corresponding central angle of the crack projection point is obtained by scanning with a probe (1# crack ≈ 30°, 2# ≈ 120°, 3# ≈ 35°). Combined with the outer radius, the circumferential distance of crack 1# is calculated according to the arc length formula, which gives crack 1# ≈ 23.56mm, crack 2# ≈ 94.25mm, and crack 3# ≈ 27.49mm, thus accurately locating the physical position of the crack on the circumference.

[0027] It should be noted that the embodiments described herein are only some embodiments of the present invention, and not all implementations of the present invention. These embodiments are merely illustrative and are intended only to provide a more intuitive and clear way to understand the content of the present invention, not to limit the technical solutions described herein. All other implementation methods that can be conceived by those skilled in the art without creative effort, as well as other simple substitutions and variations of the technical solutions of the present invention, without departing from the concept of the present invention, are within the protection scope of the present invention.

Claims

1. A method for detecting and locating internal cracks in a ceramic piece of a support insulator by ultrasonic end corner reflection, characterized in that, The method comprises the following steps: S1. Detection of internal crack defects of the ceramic piece: using an ultrasonic flaw detector, an incident longitudinal wave is emitted obliquely from an ultrasonic emission probe to the arc surface of the ceramic piece, an oblique refracted transverse wave is generated in the ceramic test piece, and then an end angle reflection echo reflected by the internal crack of the ceramic piece is received by the ultrasonic emission probe, so that the acoustic path of the crack defect in the ceramic test piece is measured; S2. Positioning of the internal crack defects of the ceramic piece: the distance from the surface depth and the circumferential direction distance are obtained by calculation through the oblique incidence angle, the acoustic path of the refracted transverse wave and the structural size of the ceramic piece, and the crack defect positioning is performed.

2. The method for detecting and locating internal cracks of a support insulator ceramic piece by ultrasonic end corner reflection wave according to claim 1, characterized in that, The calculation method of the distance from the surface depth is: First, the total sound path measured by the ultrasonic flaw detector is decomposed into single sound path corresponding to the round trip path length s of "probe-crack-probe", and then the probe front length is deducted Finally, the oblique sound path is converted into the vertical depth of the crack to the outer surface by the cosine value of the shear wave refraction angle The sound path d of the ultrasonic wave propagating in the ceramic is: According to the cosine theorem, the distance D from the crack to the center of the circle is: D The vertical depth H of the crack to the outer surface is: D where: H - vertical depth of the crack from the outer surface of the ceramic; s - total sound path of the ultrasound wave to and from the crack; - length of the front of the ultrasound probe; - refraction angle of the shear wave; - propagation speed of the shear wave in the ceramic; - total time of the ultrasound wave to and from the propagation.

3. The method for detecting and locating internal cracks in a ceramic piece of a support insulator according to claim 1, characterized in that, The calculation method of the circumferential direction distance is: The circumferential direction distance L from the incident point to the projection point of the crack on the circumference is, and the corresponding central angle is θ, which can be calculated through the sine theorem: The circumferential direction distance L is calculated through the following circular arc formula, which meets the space measurement specification for defect positioning of porcelain insulators: Where: L - the circumferential distance between the crack projection point and the reference point; R - the outer radius of the ceramic end portion; - the central angle of the circle of the crack projection point.

4. The method for detecting and locating internal cracks in a ceramic piece of a support insulator according to claim 1, characterized in that, The ultrasonic flaw detector uses a sound emission wafer with a size of 4mm╳4mm and a working frequency of 5MHz.

5. The method for detecting and locating internal cracks in a ceramic piece of a support insulator according to claim 2, characterized in that, The shear wave refraction angle Not less than 45°.

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