CN113310610B - Ultrasonic detection method for peripheral epoxy stress of three-post insulator insert - Google Patents

Abstract

The invention discloses an ultrasonic detection method for peripheral epoxy stress of a three-post insulator insert. The method comprises the following steps: building an ultrasonic detection system; measuring the acoustic elastic coefficient of the parallel stress of the epoxy composite material standard sample for the three-post insulator to obtain an acoustic elastic equation of the parallel stress of the epoxy composite material; carrying out ultrasonic detection on the peripheral epoxy of the insert under the axial load of the three-post insulator, and recording the sound velocity in an ultrasonic sound path at a detection position; and substituting the obtained ultrasonic sound velocity into an acoustic elastic equation of the parallel stress of the epoxy composite material to obtain the peripheral epoxy stress of the insert under the axial load of the three-post insulator. The invention can efficiently, intuitively and nondestructively detect the peripheral epoxy stress of the insert under the axial load.

Description

An ultrasonic testing method for epoxy stress on the periphery of three-pillar insulator inserts

technical field

The invention relates to the field of power transmission and transformation insulation equipment, in particular to an ultrasonic detection method for epoxy stress on the periphery of a three-pillar insulator insert.

Background technique

The three-post insulator is a key electrical component in a gas-insulated metal-enclosed transmission line (GIL), which plays the role of electrical insulation and mechanical support. The mechanical stress of the GIL three-post insulator may be one of the causes of insulator failure, and its sources include the manufacturing process. The residual stress, the stress caused by external loads during transportation, installation and operation. GIL three-pillar insulators are made by mixing liquid epoxy resin, curing agent and inorganic powder filler, and pouring them together with inserts at high temperature to cure them. There is residual stress in the manufacturing process. During GIL transportation, insulators may have bumps, vibrations and mechanical friction. Currently, a three-dimensional vibration and impact acceleration detector is installed to detect the impact force on GIL during transportation. The reasons for the stress of the insulator during GIL installation may be that the installation of the conductive rod is inclined or the fastening force of the fixed plate is uneven, etc., the insulator bears the weight of itself and part of the conductor during operation, and the electromotive force of the shell and the conductor in the alternating electromagnetic field of the current, etc. Therefore, early confirmation of the stress state of the three-post insulator is of great significance to ensure the safe operation of the power system.

At present, the mechanical load test can only assess whether the three-post insulator passes a certain limit, or measure the mechanical failure load (see "550kV GIL three-post insulator design" by Wang Jiancheng, Xie Wengang, Gong Ruilei, etc.), and cannot measure and evaluate any Mechanical performance or stress under a load, there is no way to know the stress evolution process from the generation and expansion of micro-defects such as cracks to the mechanical failure or electrical breakdown of the insulator.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and provide an ultrasonic detection method for epoxy stress on the periphery of a three-pillar insulator insert.

The object of the present invention is achieved at least by one of the following technical solutions.

An ultrasonic detection method for epoxy stress on the periphery of a three-pillar insulator insert, comprising the following steps:

S1. Build an ultrasonic testing system;

S2. Measure the parallel stress acoustoelastic coefficient of the epoxy composite material standard sample for the three-pillar insulator, and obtain the acoustoelastic equation of the parallel stress of the epoxy composite material;

S3. Ultrasonic detection of the epoxy around the insert under the axial load of the three-pillar insulator, and record the sound velocity within the ultrasonic sound path at the detection position;

S4. Substituting the obtained ultrasonic sound velocity into the acoustoelastic equation of the parallel stress of the epoxy composite material in S2, to obtain the epoxy stress on the periphery of the insert under the axial load of the three-pillar insulator.

Further, in step S1, the ultrasonic testing system includes an ultrasonic pulse generator, an oscilloscope, an ultrasonic longitudinal wave straight probe, a probe adapter line and a high-impedance transmission line;

The ultrasonic longitudinal wave straight probe is connected to the signal output terminal T or the signal input terminal R of the ultrasonic pulse generator through the probe adapter line, and the signal synchronization terminal of the ultrasonic pulse generator is connected to the oscilloscope through a high-impedance transmission line.

Further, the ultrasonic pulse generator is a pulse generator with short pulse excitation, adjustable output pulse width, high gain, and low noise. Short pulse excitation can optimize broadband response and improve detection near-surface resolution, which is more conducive to acoustic Detection and measurement applications of materials with strong beam attenuation;

The oscilloscope is a three-channel high-performance digital storage oscilloscope with a maximum sampling frequency of 2 GHz and a sampling bandwidth of 500 MHz. The input channel of the oscilloscope is connected to the signal output terminal of the ultrasonic pulse generator with the same potential through a high-impedance transmission line, so that the emission and output can be displayed in real time on the oscilloscope. Received ultrasonic signal;

The ultrasonic longitudinal wave straight probe belongs to the cylindrical longitudinal wave straight probe, which adopts a circular composite piezoelectric wafer, and the bottom surface of the probe is circular. Good, but the small probe bottom requires a small circular composite piezoelectric wafer, and the ultrasonic energy emitted by the probe is also very small. Considering the detection characteristics, detection efficiency and production cost, the design range of the probe bottom diameter (D) is 5- 10mm, the design range of probe height (H) is 15-20mm;

The ultrasonic longitudinal wave straight probe refers to a pulsed ultrasonic straight probe with better response characteristics. The higher the nominal frequency of the ultrasonic longitudinal wave straight probe, the greater the attenuation coefficient in the material to be tested, and the worse the effect of the sound beam propagation characteristics. Measurement experience, the frequency design of the ultrasonic longitudinal wave straight probe is not greater than 2.5MHz;

The probe adapter line is a signal line matching the ultrasonic pulse generator and the ultrasonic longitudinal wave straight probe. Receive, at the same time, ensure that the ultrasonic signal received by the ultrasonic longitudinal wave straight probe is converted into an electrical signal with high quality and returned to the receiving end of the ultrasonic pulse generator;

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

Further, step S2 is specifically as follows:

Adjust the ultrasonic pulse generator, place two ultrasonic longitudinal wave straight probes coated with oil-based ultrasonic coupling agent symmetrically and coaxially on the surface of the upper plate and the bottom plate of the universal testing machine, and place the epoxy composite standard sample on the upper plate and the bottom plate of the universal testing machine. In the middle of the bottom plate, the propagation time of the ultrasonic longitudinal wave in the standard sample is recorded, and then the parallel stress acoustoelastic coefficient is obtained, and finally the acoustoelastic equation of the parallel stress of the epoxy composite is obtained.

Further, the two ultrasonic longitudinal wave straight probes are respectively connected to the signal output terminal T and the signal input terminal R of the ultrasonic pulse generator through a probe adapter line;

The oil-based ultrasonic coupling agent is used to increase the contact effect between the ultrasonic longitudinal wave straight probe and the measured surface to ensure the stability of the ultrasonic waveform;

The epoxy composite material standard sample is a cuboid standard sample whose material and process are the same as those of the _three -pillar insulator, and whose size is length d1 _× height _d2 ×width d3;

The symmetrical coaxial placement means that two ultrasonic longitudinal wave straight probes are respectively placed on the surface of the upper plate and the bottom plate of the universal testing machine, and the centerlines of the two ultrasonic longitudinal wave straight probes are coaxial;

The upper plate of the universal testing machine is an inverted 'T'-shaped steel plate with a flat bottom, and the bottom plate is an 'I'-shaped steel plate with a flat bottom; the thickness of both the upper plate and the bottom plate is d ₀ .

Further, the propagation time of the ultrasonic longitudinal wave in the standard sample is that a straight ultrasonic longitudinal wave probe emits an ultrasonic initial wave F on one side of the epoxy composite standard sample, and the ultrasonic initial wave F is vertically incident on the epoxy composite standard sample. Inside the epoxy part of the sample, the penetrating wave I is received by another ultrasonic longitudinal wave straight probe at the corresponding position on the other side of the epoxy part of the standard sample of epoxy composite material. The vibration time difference is the propagation time of the ultrasonic longitudinal wave at the position to be measured;

The sound path of ultrasonic propagation in the epoxy composite standard sample is set as 2d ₀ +d ₁ and 2d ₀ +d ₂ in turn, and the ultrasonic propagation time t ₂ and t ₃ (unit μs) under the same stress are recorded respectively, and the sound velocity V ₁ ( unit m/s) is

The parallel stress acoustic elastic coefficient K is obtained as follows:

Among them, V ₀ is the sound velocity at zero stress σ ₀ , the unit is m/s, and the ultrasonic longitudinal wave sound velocity V ₀ of the standard sample of epoxy composite material under zero stress σ ₀ is 2 997.02m/s; σ ₀ , σ ₁ The unit is MPa, and the unit of K is /MPa; assuming that the external load F is evenly distributed on the stressed area, and the sound paths are 2d ₀ +d ₁ and 2d ₀ +d ₂ respectively, the relationship between stress σ ₁ and F is F= σ ₁ d ₂ d ₃ , F=σ ₁ d ₁ d ₃ , F unit is N; the test range of parallel stress is 0~50MPa, and the step size is 5MPa; parallel stress means that the direction of the internal stress of the standard sample is parallel to the direction of ultrasonic propagation.

Substituting the obtained parallel stress acoustoelastic coefficient K back into formula (2), the acoustoelastic equation of epoxy composite parallel stress can be obtained as formula (3):

That is, the stress σ can be obtained by measuring the sound velocity V.

Further, in step S3, the ultrasonic pulse generator is adjusted, and an ultrasonic longitudinal wave straight probe coated with an oil-based ultrasonic couplant is placed on the surface of the solid epoxy part on the periphery of the three-pillar insulator installed on the thruster, and the ultrasonic reflection method is used to Record the propagation time of the ultrasonic longitudinal wave in the epoxy around the insert, and then record the sound velocity in the ultrasonic sound path at the detection position.

Further, the three-post insulator includes a solid epoxy, a center conductor, and a grounding insert; the solid epoxy is made of epoxy composite material and includes three post legs, and the bottom of each post leg is combined with a grounding insert ;In engineering, stress concentration is most likely to occur at the joint between the grounding insert and the bottom of the column leg. Therefore, the detection position is the epoxy around the insert, and the epoxy around the insert refers to the solid epoxy around the grounding insert. ;The central conductor is a ring-shaped structure made of aluminum;

The installation on the thruster refers to fixing the leg of one of the three post insulators combined with the grounding insert on the thruster, and the thruster applies a load F to the center conductor, and the vertical distance between the load F and the fixing surface of the grounding insert is 330mm; at this time, the ultrasonic propagation direction is roughly parallel to the stress direction, and the sound propagation path is twice the thickness of the solid epoxy part;

Record the propagation time t of the ultrasonic longitudinal wave in the epoxy around the insert, as follows:

An ultrasonic longitudinal wave straight probe emits the initial ultrasonic wave F on the surface of the solid epoxy part on the periphery of the three-pillar insulator. Received by the ultrasonic longitudinal wave straight probe again, the difference between the start-up time of the ultrasonic initial wave F and the reflected wave B is the propagation time t in the epoxy surrounding the insert at the position to be measured;

The sound path of ultrasound on the periphery of the three-pillar insulator insert is set to D, and the ultrasonic propagation time t (unit μs) is recorded under the load F, then the sound velocity V (unit m/s) is:

Further, in step S4, the ultrasonic sound velocity V obtained in step S3 is substituted into the formula (3) to obtain the epoxy stress σ at the periphery of the insert under the axial load of the three-pillar insulator.

Beneficial effects of the present invention:

The present invention proposes an ultrasonic testing method for epoxy stress on the periphery of three-pillar insulator inserts, and builds an ultrasonic testing system; firstly, by measuring the parallel stress acoustic elastic coefficient of epoxy composite material standard samples for three-pillar insulators, the epoxy The acoustoelastic equation of the parallel stress of the composite material; then, ultrasonically detect the leg of the three-pillar insulator under the axial load, and record the sound velocity in the ultrasonic sound path at the detection position; finally, substitute the obtained ultrasonic sound velocity into the acoustoelastic equation, and calculate Epoxy stresses at the periphery of inserts of three-post insulators under axial load. This method has the advantages of low detection cost, high detection accuracy, portability, and no radiation to the human body. It can efficiently, intuitively, and non-destructively detect the epoxy stress on the periphery of the insert under the axial load of the three-pillar insulator.

Description of drawings

Fig. 1 is a schematic flow chart of an ultrasonic detection method applicable to the peripheral epoxy stress of a three-pillar insulator insert in an embodiment of the present invention;

Fig. 2 is a schematic diagram of an ultrasonic detection system applicable to the present invention in an embodiment of the present invention;

Fig. 3 is a schematic structural diagram of an ultrasonic longitudinal wave straight probe in an embodiment of the present invention: wherein, Fig. 3a is a front view of an ultrasonic longitudinal wave straight probe, and Fig. 3b is a schematic diagram of the bottom of an ultrasonic longitudinal wave straight probe;

4 is a schematic diagram of a parallel stress acoustoelastic coefficient test system for a standard sample of epoxy composite material for three-pillar insulators in an embodiment of the present invention;

Fig. 5 is a schematic structural diagram of a standard sample of an epoxy composite material for implementing three-pillar insulators in the present invention: wherein, Fig. 5a is a schematic diagram of a standard sample, Fig. 5b is a front view of a standard sample, and Fig. 5c is a side view of a standard sample;

Fig. 6 is a waveform diagram of ultrasonic longitudinal wave penetration method detection of standard sample of epoxy composite material for three-pillar insulators in the embodiment of the present invention, wherein Fig. 6a and Fig. 6b respectively show the different modes of propagation of ultrasonic waves in the standard sample of epoxy composite material Ultrasonic longitudinal wave penetration method detection waveform diagram of the sound path;

Fig. 7 is a schematic diagram of an ultrasonic testing system for the epoxy stress on the periphery of the insert under the axial load of the three-pillar insulator in the embodiment of the present invention;

Fig. 8 is a schematic diagram of the structure of a three-post insulator in an embodiment of the present invention: Fig. 8a is a front view of a three-post insulator, and Fig. 8b is a schematic diagram of epoxy detection positions around the insert of a three-post insulator.

detailed description

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

Example:

An ultrasonic testing method for epoxy stress on the periphery of a three-pillar insulator insert, as shown in Figure 1, includes the following steps:

S1. Build an ultrasonic testing system;

As shown in Figure 2, the ultrasonic longitudinal wave reflection detection system includes an ultrasonic pulse generator 1, an oscilloscope 2, an ultrasonic longitudinal wave straight probe 3, a probe adapter line 4 and a high-impedance transmission line 5;

Two ultrasonic longitudinal wave straight probes 3 are respectively connected to the output terminal T of the ultrasonic pulse generator 1 and the signal input terminal R through the probe adapter line 4, and the signal synchronization terminal of the ultrasonic pulse generator 1 is connected to the oscilloscope 2 through a high-impedance transmission line 5 .

The ultrasonic pulse generator 1 is a pulse generator with short pulse excitation, adjustable output pulse width, high gain, and low noise. Short pulse excitation can optimize broadband response and improve detection near-surface resolution, which is more conducive to sound beam attenuation Detection and measurement applications for highly resistant materials;

The oscilloscope 2 is a three-channel high-performance digital storage oscilloscope with a maximum sampling frequency of 2GHz and a sampling bandwidth of 500MHz. The input channel of the oscilloscope 2 is connected to the same potential as the signal synchronous end of the ultrasonic pulse generator 1 through a high-impedance transmission line 5, so that the oscilloscope 2 can be connected to the same potential. Real-time display of transmitted and received ultrasonic signals;

The probe adapter line 4 is a signal line matching the ultrasonic pulse generator 1 and the ultrasonic longitudinal wave straight probe 3, which has the characteristics of high impedance and strong anti-interference ability, and ensures that the output electrical signal of the ultrasonic pulse generator 1 can be detected with high quality. The ultrasonic longitudinal wave straight probe 3 receives, and at the same time, ensures that the ultrasonic longitudinal wave straight probe 3 receives the ultrasonic signal and converts it into an electrical signal with high quality and returns it to the receiving end of the ultrasonic pulse generator 1;

The high-impedance transmission line 5 is a transmission line with less stray inductance and less resistance, which shortens the phase delay of the high-frequency signal during transmission, and ensures that the electrical signal received by the oscilloscope 2 and the electrical signal at the synchronous end of the ultrasonic pulse generator 1 signal The real-time same potential and same phase greatly reduce the detection error and ensure the detection accuracy.

As shown in Figures 3a and 3b, the ultrasonic longitudinal wave straight probe 3 belongs to a cylindrical longitudinal wave straight probe, which adopts a circular composite material piezoelectric chip 31, and the bottom surface 32 of the probe is circular, in order to increase the contact between the probe and the measured position of the insulator To improve the detection accuracy, the smaller the radius of the probe bottom, the better, but the smaller probe bottom requires a small circular composite piezoelectric wafer, and the ultrasonic energy emitted by the probe is also small. Considering the detection characteristics, detection efficiency and production cost comprehensively , In this embodiment, the design range of the probe bottom diameter D is 8 mm, the design range of the probe height H is 18 mm, and the frequency of the ultrasonic longitudinal wave straight probe 3 is set to 2.5 MHz.

S2. Measure the parallel stress acoustoelastic coefficient of the epoxy composite material standard sample for the three-pillar insulator, and obtain the acoustoelastic equation of the parallel stress of the epoxy composite material, as follows:

In this embodiment, as shown in Figure 4, it is a schematic diagram of a parallel stress acoustoelastic coefficient test system for a standard sample of epoxy composite material for a 550kV three-pillar insulator; Schematic diagram of the composite material standard sample structure;

Adjust the ultrasonic pulse generator 1, place two ultrasonic longitudinal wave straight probes 3 coated with oil-based ultrasonic coupling agent symmetrically and coaxially on the surface of the upper plate 61 and the bottom plate 62 of the universal testing machine 6, and fix the epoxy composite material standard sample 7 Place it between the upper plate 61 and the bottom plate 62 of the universal testing machine 6, record the propagation time of the ultrasonic longitudinal wave in the standard sample, and then obtain the parallel stress acoustoelastic coefficient, and finally obtain the acoustoelastic equation of the parallel stress of the epoxy composite material.

Two ultrasonic longitudinal wave straight probes 3 are respectively connected to the signal output terminal T and the signal input terminal R of the ultrasonic pulse generator 1 through the probe adapter line 4;

The oil-based ultrasonic coupling agent is used to increase the contact effect between the ultrasonic longitudinal wave straight probe 3 and the measured surface, so as to ensure the stability of the ultrasonic waveform;

As shown in Figure 5a, Figure 5b, and Figure 5c, the epoxy composite material standard sample 7 is a cuboid standard with the same material and process as the three-pillar insulator, and the size is length d ₁ × height d ₂ × width d ₃ Sample; in this embodiment, the length, height and width are 70mm, 60mm, and 50mm, respectively.

The symmetrical coaxial placement means that two ultrasonic longitudinal wave straight probes 3 are respectively placed on the surface of the upper plate 61 and the bottom plate 62 of the universal testing machine 6, and the centerlines of the two ultrasonic longitudinal wave straight probes 3 are coaxial;

In this embodiment, the universal testing machine 6 is an automatic mechanical load loading device controlled by a microcomputer. In this embodiment, the model of the universal testing machine 6 is WAW-500C, the maximum mechanical load is 500kN, and the control accuracy is 1%;

The upper plate 61 of the universal testing machine 6 is an inverted 'T'-shaped steel plate with a flat bottom, and the bottom plate 62 is an "I"-shaped steel plate with a flat bottom; the thickness of the upper plate 61 and the bottom plate 62 are both d ₀ , in this embodiment Among them, d ₀ is 25mm, and the materials of the upper plate 61 and the bottom plate 62 are both No. 50 steel.

Fig. 6 is the waveform diagram of the ultrasonic longitudinal wave penetration detection of the standard sample of epoxy composite material used for three-pillar insulators in this embodiment, and the propagation time of the ultrasonic longitudinal wave in the standard sample is one ultrasonic longitudinal wave straight probe 3 in the epoxy composite material One side of the standard sample 7 emits the initial ultrasonic wave F, and the initial ultrasonic wave F is vertically incident into the epoxy part of the standard sample 7 of the epoxy composite material, and the penetrating wave I is in the epoxy part of the standard sample 7 of the epoxy composite material The corresponding position on the other side is received by another ultrasonic longitudinal wave straight probe 3, and the time difference between the initial ultrasonic wave F and the penetrating wave I is the propagation time of the ultrasonic longitudinal wave at the position to be measured;

As shown in Figure 6a and Figure 6b, the sound path of ultrasonic propagation in the epoxy composite standard sample 7 is set to 2d ₀ +d ₁ and 2d ₀ +d ₂ in sequence, and the ultrasonic propagation time t ₂ and t ₃ under the same stress are recorded respectively (unit μs), sound velocity V ₁ (unit m/s) is

The parallel stress acoustic elastic coefficient K is obtained as follows:

Among them, V ₀ is the sound velocity at zero stress σ ₀ , the unit is m/s, and the ultrasonic longitudinal wave sound velocity V ₀ of the standard sample of epoxy composite material under zero stress σ ₀ is 2 997.02m/s; σ ₀ , σ ₁ The unit is MPa, and the unit of K is /MPa; assuming that the external load F is evenly distributed on the stressed area, and the sound paths are 2d ₀ +d ₁ and 2d ₀ +d ₂ respectively, the relationship between stress σ ₁ and F is F= σ ₁ d ₂ d ₃ , F=σ ₁ d ₁ d ₃ , the unit of F is N; the test range of parallel stress is 0~50MPa, and the step size is 5MPa;

Substituting the obtained parallel stress acoustoelastic coefficient K back into formula (2), the acoustoelastic equation of epoxy composite parallel stress can be obtained as formula (3):

That is, the stress σ can be obtained by measuring the sound velocity V.

S3. Perform ultrasonic testing on the peripheral epoxy of the insert under the axial load of the three-pillar insulator, and record the sound velocity within the ultrasonic sound path at the testing position, as follows:

In this embodiment, as shown in Figure 7, it is a schematic diagram of an ultrasonic detection system for the epoxy stress on the periphery of the insert under the axial load of a 550kV three-pillar insulator in this embodiment;

Adjust the ultrasonic pulse generator 1, place an ultrasonic longitudinal wave straight probe 3 coated with an oil-based ultrasonic coupling agent on the surface of the peripheral solid epoxy part 91 of the three-pillar insulator 9 installed on the thruster 8, and record with the ultrasonic reflection method The propagation time of the ultrasonic longitudinal wave in the epoxy 931 on the periphery of the insert, and then record the sound velocity within the ultrasonic sound path at the detection position.

Fig. 8 is a schematic structural diagram of a 550kV three-post insulator in this embodiment. As shown in Fig. 8a and Fig. 8b, the three-post insulator 9 includes a solid epoxy part 91, a central conductor 92 and a grounding insert 93; the solid epoxy part 91 is made of epoxy composite material, including three column legs 911, and the bottom of each column leg 911 is combined with a grounding insert 93; in engineering, stress concentration is most likely to occur at the joint between the grounding insert 93 and the bottom of the column leg 911 , therefore, the detected position is the epoxy 931 on the periphery of the insert, and the epoxy on the periphery of the insert refers to the solid epoxy 91 on the periphery of the ground insert 93; the central conductor 92 is a ring-shaped structure made of aluminum;

The installation on the thruster refers to fixing the leg 911 of one of the three post insulators 9 combined with the grounding insert 93 on the thruster, the thruster applies a load F to the center conductor 92, and the load F is fixed to the grounding insert 93 The vertical distance of the surface is 330 mm; at this time, the ultrasonic propagation direction is roughly parallel to the stress direction, and the propagation sound path is twice the thickness of the solid epoxy part 91;

Record the propagation time t of the ultrasonic longitudinal wave in the epoxy 931 on the periphery of the insert, as follows:

An ultrasonic longitudinal wave straight probe emits an ultrasonic initial wave F on the surface of the solid epoxy part 91 on the periphery of the three-pillar insulator 9, and the ultrasonic initial wave F is vertically incident on the interior of the solid epoxy part 91, and when it reaches the interface between the solid epoxy part 91 and the grounding insert 93 Reflection, the reflected wave B is received by the ultrasonic longitudinal wave straight probe again, and the start-up time difference between the ultrasonic initial wave F and the reflected wave B is the propagation time t in the epoxy 931 on the periphery of the insert at the position to be measured;

The sound path of the ultrasonic wave in the epoxy 931 on the periphery of the three-pillar insulator 9 insert is set to D, and the ultrasonic propagation time t (unit μs) is recorded under the load F, then the sound velocity V (unit m/s) is:

S4. Substituting the obtained ultrasonic sound velocity V into the formula (3) to obtain the stress σ at this time, that is, to obtain the stress of the epoxy 931 on the periphery of the insert under the axial load of the three-pillar insulator 9 .

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (1)

1. An ultrasonic detection method for peripheral epoxy stress of a three-post insulator insert is characterized by comprising the following steps:

s1, building an ultrasonic detection system;

the ultrasonic detection system comprises an ultrasonic pulse generator, an oscilloscope, an ultrasonic longitudinal wave straight probe, a probe adapting wire and a high-impedance transmission line;

the ultrasonic longitudinal wave straight probe is connected with a signal output end T or a signal input end R of the ultrasonic pulse generator through a probe adaptive line, and a signal synchronization end of the ultrasonic pulse generator is connected with an oscilloscope through a high-impedance transmission line;

s2, measuring the acoustic elastic coefficient of the parallel stress of the epoxy composite material standard sample for the three-post insulator to obtain an acoustic elastic equation of the parallel stress of the epoxy composite material, which is as follows:

adjusting an ultrasonic pulse generator, symmetrically and coaxially placing two ultrasonic longitudinal wave straight probes coated with an oil-based ultrasonic coupling agent on the surfaces of an upper plate and a bottom plate of a universal testing machine, fixedly placing an epoxy composite material standard sample between the upper plate and the bottom plate of the universal testing machine, recording the propagation time of ultrasonic longitudinal waves in the standard sample, further obtaining the acoustic-elastic coefficient of parallel stress, and finally obtaining the acoustic-elastic equation of the parallel stress of the epoxy composite material;

an ultrasonic longitudinal wave straight probe sends out an ultrasonic initial wave F at one side of an epoxy composite material standard sample, the ultrasonic initial wave F vertically enters the epoxy part of the epoxy composite material standard sample, a penetrating wave I is received by another ultrasonic longitudinal wave straight probe at a corresponding position at the other side of the epoxy part of the epoxy composite material standard sample, and the starting oscillation time difference of the ultrasonic initial wave F and the penetrating wave I is the propagation time of the ultrasonic longitudinal wave at the position to be detected in the standard sample;

the sound path of the ultrasound transmitted in the standard sample of the epoxy composite material is set as 2d in sequence ₀ +d ₁ 、2d ₀ +d ₂ Respectively recording ultrasonic propagation time t under the same stress ₂ And t ₃ Velocity of sound V ₁ Is composed of

Obtaining a parallel stress acoustic elastic coefficient K, which is as follows:

wherein, V ₀ Is zero stress sigma ₀ Measuring the sound velocity of the standard sample of the epoxy composite material under zero stress sigma ₀ Lower ultrasonic longitudinal sound velocity V ₀ Is 2 997.02m/s; the external applied load F is uniformly distributed on the stressed area, and the sound paths are respectively 2d ₀ +d ₁ 、2d ₀ +d ₂ Stress of time σ ₁ The relationship with F is respectively F = sigma ₁ d ₂ d ₃ 、F＝σ ₁ d ₁ d ₃ (ii) a The test range of the parallel stress is 0-50 MPa, and the step length is 5MPa;

and (3) returning the obtained parallel stress acoustic-elastic coefficient K to substitute the formula (2) to obtain the acoustic-elastic equation of the parallel stress of the epoxy composite material, wherein the formula is as follows:

namely, the stress sigma can be obtained by measuring the sound velocity V;

s3, performing ultrasonic detection on the peripheral epoxy of the insert under the axial load of the three-post insulator, and recording the sound velocity in an ultrasonic sound path at a detection position;

s4, substituting the obtained ultrasonic sound velocity into the acoustoelastic equation of the parallel stress of the epoxy composite material in the S2 to obtain the peripheral epoxy stress of the insert under the axial load of the three-post insulator;

the ultrasonic longitudinal wave straight probe belongs to a cylindrical longitudinal wave straight probe, and adopts a circular composite material piezoelectric wafer, the bottom surface of the probe is circular, the design range of the diameter D of the bottom surface of the probe is 5-10mm, and the design range of the height H of the probe is 15-20mm; the frequency design of the ultrasonic longitudinal wave straight probe is not more than 2.5MHz;

the two ultrasonic longitudinal wave straight probes are respectively connected with a signal output end T and a signal input end R of the ultrasonic pulse generator through probe adaptive wires;

the oil-based ultrasonic coupling agent is used for increasing the contact effect of the ultrasonic longitudinal wave straight probe and the surface to be detected and ensuring the stability of ultrasonic waveforms;

the standard sample of the epoxy composite material is made of the same material and process as the three-post insulator, and has the size of length d ₁ X is high d ₂ X width d ₃ A rectangular parallelepiped standard sample of (1);

the symmetrical coaxial arrangement means that the two ultrasonic longitudinal wave straight probes are respectively arranged on the surfaces of an upper plate and a bottom plate of the universal testing machine, and the central lines of the two ultrasonic longitudinal wave straight probes are coaxial;

the upper plate of the universal testing machine is a reverse T-shaped steel plate with a flat bottom surface, and the bottom plate is an I-shaped steel plate with a flat bottom surface; the upper plate and the bottom plate are both d in thickness ₀ ；

Step S3, adjusting an ultrasonic pulse generator, placing an ultrasonic longitudinal wave straight probe coated with an oil-based ultrasonic coupling agent on the surface of a solid epoxy piece on the periphery of a three-post insulator installed on a thrust machine, and recording the propagation time of the ultrasonic longitudinal wave in the epoxy on the periphery of the insert by using an ultrasonic reflection method so as to record the sound velocity in an ultrasonic sound path at a detection position;

the three-post insulator comprises a solid epoxy piece, a central conductor and a grounding insert; the solid epoxy piece is made of epoxy composite materials and comprises three column legs, and the bottom of each column leg is combined with one grounding insert; the detection position is epoxy at the periphery of the insert, and the solid epoxy piece at the periphery of the insert is grounded; the central conductor is of an aluminum annular structure;

the installation on the thrust machine means that one of the three-pillar insulators and the pillar leg combined with the grounding insert are fixed on the thrust machine, the thrust machine applies a load F to the central conductor, and the vertical distance between the load F and the fixing surface of the grounding insert is 330mm; at the moment, the ultrasonic propagation direction is approximately parallel to the stress direction, and the propagation sound path is twice the thickness of the solid epoxy piece;

recording the propagation time t of the ultrasonic longitudinal wave in the peripheral epoxy of the insert, specifically as follows:

an ultrasonic longitudinal wave straight probe sends out an ultrasonic initial wave F on the surface of a solid epoxy piece on the periphery of the three-post insulator, the ultrasonic initial wave F vertically enters the solid epoxy piece and is reflected when reaching the interface of the solid epoxy piece and the grounding insert, a reflected wave B is received by the ultrasonic longitudinal wave straight probe, and the oscillation starting time difference between the ultrasonic initial wave F and the reflected wave B is the propagation time t in the peripheral epoxy of the insert at the position to be detected;

the sound path of the ultrasound on the periphery of the three-post insulator insert is set as D, the propagation time t of the ultrasound under the load F is recorded, and then the sound velocity V is as follows:

in the step S4, substituting the ultrasonic sound velocity V obtained in the step S3 into the formula (3) to obtain the peripheral epoxy stress sigma of the insert under the axial load of the three-post insulator.

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