CN102288533A - Device and method for detecting corrosion of conductor of grounding grid of power system based on SH0 (horizontal shear) wave - Google Patents
Device and method for detecting corrosion of conductor of grounding grid of power system based on SH0 (horizontal shear) wave Download PDFInfo
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Abstract
The invention discloses a device and a method for detecting the corrosion of a conductor of a grounding grid of a power system based on an SH0 (horizontal shear) wave, which belong to the technical field of nondestructive detection. A pulse function generating instrument passes through an impedance matching instrument at an exciting end, and then is connected with an SH0 wave electromagnetic acoustic excitation energy converter, so as to excite the SH0 wave without frequency dispersion and with single modality, good directionality and large energy; an SH0 wave electromagnetic acoustic excitation energy converter 3 and an SH0 wave electromagnetic acoustic receiving energy converter 4 are placed on a central axis in the length direction of the conductor of the grounding grid; an excitation frequency is a maximum frequency of the working energy of a sensor; and the nondestructive detection is carried out on the corrosion of the conductor of the grounding grid by utilizing the SH0 wave generated under a central frequency. By using the device and the method, the defects that the detection of the corrosion of the conductor of the grounding grid is incomplete, the implementation of detecting a metal constructional element by utilizing a Lamb wave is inconvenient, and the Lamb wave has multimodality, frequency dispersion and an obvious boundary effect, and easily generates modality conversion are overcome, and the nondestructive detection method can serve the nondestructive detection remotely, quickly and completely, and is further popularized to the nondestructive detection of the corrosion of narrow strip metal structures.
Description
Technical field
The invention belongs to supersonic guide-wave Non-Destructive Testing field, be specifically related to a kind of SH0 of utilization (horizontal shear) ripple and detect electric system grounded screen conductor corroding method.
Background technology
The ground connection of transformer station is the connection between electrical equipment and the earth, makes electrical equipment can remain on same current potential, is the important measures that guarantee the power system security reliability service.The general practice is to lay grounded screen.The long-time running of grounded screen conductor is corroded easily, causes power equipment to quit work, even causes the electric system paralysis.Therefore, research ground net corrosion situation has important social benefit and economic benefit.
Grounded screen conductor cross section commonly used be rectangle 6mm * 60mm and slightly with pure limit zinc-coated flat steel sheet or the round steel horizontal laying overlap joint of Φ 20mm form, be arranged in slotted hole type or square groove, imbed underground 0.5m～0.8m.But because grounded screen is embedded in undergroundly, material becomes fragile, aliquation, loose, even the many places fracture can occur, particularly is embedded in the grounding body in the strong soil of Acidity of Aikalinity, corrodes serious especially.The grounded screen conductor life-span was generally about 8～10 years, need in time diagnose out the breakpoint and the corrosion section of grounded screen and take reclamation activities.
Detect at grounded screen conductor corrosion, at present domesticly mainly contain three kinds of corrosion diagnostic methods: based on the method for Circuit theory with based on the method for electromagnetic field, electrochemical methods.Preceding two kinds of methods can not have a power failure and not under the situation to grounded screen large tracts of land excavation, and the breakpoint and the corrosion situation of earth mat detected.The article that scholars such as Zhang Xiaoling deliver at 2002 " Power System and its Automation journal " " electric system grounded screen fault diagnostic circuit method " is found the solution the resistance increment of each section conductor in the grounded screen by adopting simplicial method, but diagnostic result out of true very; The article that scholars such as Michaloudaki deliver at 2005 " Magnetics " " Diagnosis of breaks in substations grounding grid by using the electromagnetic method " has detected the fracture position of conductor by the method for electromagnetic field, but can not determine its extent of corrosion for the grounded screen that fracture does not take place; Grounded screen galvanochemistry anti-corrosion method is subjected to the restriction of the complicacy and the field conduct condition of grounded screen, and China does not have the commercial Application of mature technology at present as yet.
These have been delivered or disclosed achievement in research does not well solve grounded screen conductor corrosion detection problem.And the ultrasound in nature of propagating in the plate structure has: Lamb wave, SH ripple, R wave etc.Utilize the corrosion of ultrasound examination metal construction to carry out extensive studies both at home and abroad, confirmed that ultrasound wave is used to corrode the feasibility and the development potentiality of detection.It is a kind of method of Non-Destructive Testing.Scholars such as ZQ Su 2006 deliver " Guided Lamb waves for identification of damage in composite structures " analyzed target body profile space shuttle hardware by the small echo fingerprint digital signal processing method of complexity corrosion ripple bag at " Journal of Sound and Vibration "; 2007, scholars such as N Terrien have delivered one piece " Optimization of hidden corrosion detection in aircraft structures using Lamb waves:numerical predictions and experimental results " at " AIP Conference Proceedings ", experiment produces Lamb wave with angle probe and detects the aeronautical material local corrosion, MODAL TRANSFORMATION OF A and mode stack can take place in Lamb wave and the corrosion place effect of discovering, need to use the problem of modal Separation and the stack of two-dimentional Short Time Fourier Transform processing mode, and the angle probe experiment need be carried out pre-service to the test specimen surface, contact with measured piece by couplant, troublesome poeration, detection efficiency is lower.
The grounded screen conductor structure is the fillet type, utilizes Lamb wave to detect easily to take place mode stack and MODAL TRANSFORMATION OF A, surface influenced by ground end corrosive liquid etc.Still nobody utilizes ultrasound wave that correlative study was carried out in grounded screen conductor corrosion detection both at home and abroad at present.A kind of novel electromagnetic acoustic detection technique that adopts among the present invention has noncontact, need not coupling and to advantages such as tested surface of the work are less demanding, and can overcome well that Lamb wave is multi-modal, shortcomings such as MODAL TRANSFORMATION OF A take place in frequency dispersion, border easily.(Electromagnetic Acoustic Transducer EMAT) is made of coil and magnet electromagnet ultrasonic changer, and the grounded screen conductor belongs to ferrimagnet again, and triplicity is easy to detect.And electromagnet ultrasonic changer can extremely be easy to generate the SH ripple, a kind of SH0 (horizontal shear) ripple that produces is that particle vibration (displacement and speed) is all at the ripple that is arranged in the plane that is parallel to aspect, frequency dispersion not has in the steel plate of different-thickness the velocity of wave characteristics that do not change substantially.The SH0 ripple can not be converted into the ripple of other types when being parallel to the surface reflection of polarization direction, and its transmission coefficient also is higher than other wave modes far away, a little less than the decay, therefore is beneficial to long distance detecting.The sound field that the SH0 sensor produces, the acoustic beam spread angle is little, and is easy to control, can be applied to the fillet structure detection of width greater than sensor, and testing result is not subjected to the influence of structure boundary.
Summary of the invention
The objective of the invention is for solve fast, comprehensively, in the problem of labour Non-Destructive Testing grounded screen conductor corrosion.For the breakpoint of in time diagnosing out grounded screen and corrosion section and take reclamation activities, the method that a kind of SH0 of utilization (horizontal shear) ripple detects electric system grounded screen conductor corrosion Non-Destructive Testing has been proposed.
The present invention adopts following technical scheme, corrosion pick-up unit based on SH0 ripple electric system grounded screen conductor: comprising: impulse function generator 1, digital oscilloscope 6 and computing machine 7, SH0 ripple electromagnetic sound excitation transducer 3, SH0 ripple electromagnetic sound receiving transducer 4 is placed on the grounded screen conductor 8, SH0 ripple electromagnetic sound excitation transducer 3 is connected with excitation terminal impedance coupling instrument 2, excitation terminal impedance coupling instrument 2 is connected with impulse function generator 1, SH0 ripple electromagnetic sound receiving transducer 4 is connected with receiving-end impedance coupling instrument 5, receiving-end impedance coupling instrument 5 is connected with digital oscilloscope 6, and computing machine 7 is connected with digital oscilloscope 6;
Technical scheme of the present invention specifically may further comprise the steps:
Step 1): it is adjustable in 1～20 scope to produce one-period by impulse function generator 1, centre frequency adjustable square-wave signal in 0～1MHz scope, in 0～1MHz scope, change frequency, excitation makes SH0 ripple electromagnetic sound excitation transducer 3 produce the maximum of points of signal energy in this scope, and then Ci Shi frequency is impulse function generator frequency of operation;
Step 2): above-mentioned square-wave signal is after pulse function generator 1 enters excitation terminal impedance coupling instrument 2, import SH0 ripple electromagnetic sound excitation transducer 3 into, SH0 ripple electromagnetic sound receiving transducer 4 receives the signal of being propagated by SH0 ripple electromagnetic sound excitation transducer 3 in grounded screen conductor 8, show on oscillograph 6 through receiving-end impedance coupling instrument 5, and store in the computing machine 7, utilize the one dimension analysis method of wavelet packet that the time-domain signal that receives is carried out denoising Processing, confirm the direct wave bag, the end face echo, corrosion ripple bags etc. are according to the time t of direct wave bag arrival
1, the spacing d between SH0 ripple electromagnetic sound excitation transducer 3 and the SH0 ripple electromagnetic sound receiving transducer 4, the time t that the ripple of the group velocity v=d/t that propagates in grounded screen conductor 8 according to the SH0 ripple, and corrosion again bag arrives
2, can try to achieve corrosion position s=v * t
2
The present invention has the following advantages: 1) the present invention proposes a kind of by the ultrasound wave method that corrosion detects to the grounded screen conductor.It is a kind of method of Non-Destructive Testing, utilizes hyperacoustic technology not need structure is carried out any destruction, can realize detecting, and can carry out online detection, need not to make whole electric system power failure and grounded screen is carried out the large tracts of land excavation; 2) compare Lamb wave Ultrasonic Detection corroding method, the electromagnetic sound detection technique detects the corrosion of grounded screen conductor, and testing process need not couplant, and is easy to detect, and labour intensity is low, and testing result signal to noise ratio (S/N ratio) height can accurately be located corrosion; 3) the SH0 ripple that adopts detects grounded screen fillet structure, has avoided the appearance of border echo, MODAL TRANSFORMATION OF A can not take place, and the ripple bag is simple, a little less than the decay, detects distance.
Description of drawings
Fig. 1: grounded screen conductor corrosion pick-up unit synoptic diagram;
Fig. 2: grounded screen conductor angle probe pick-up unit synoptic diagram;
SH wave dispersion curve in the long grounded screen conductor of the thick 4m of Fig. 3: 5.8mm;
Lamb wave dispersion curve in the long grounded screen conductor of the thick 4m of Fig. 4 5.8mm;
S in the thick grounded screen conductor of Fig. 5: 5.8mm
0Modal displacement wave structure figure;
A in the thick grounded screen conductor of Fig. 6: 5.8mm
0Modal displacement wave structure figure;
Fig. 7: the SH0 ripple displacement wave structural drawing in the thick grounded screen conductor of Figure 75 .8mm;
Fig. 8: Fig. 8 SH0 wave sensor detects 4m band defective grounded screen conductor and receives waveform;
Fig. 9: waveform behind Fig. 9 SH0 wave sensor detection 4m band defective grounded screen conductor wavelet de-noising;
Figure 10: frequency is that 0.5MHz, spacing are the angle probe detection 4m grounded screen conductor received signal waveform of 0.3m;
Figure 11: frequency is that 0.5MHz, spacing are the angle probe detection 4m grounded screen conductor received signal waveform of 0.5m;
The group velocity curve of mode in the thick free aluminium sheet of Figure 12: 1mm;
The phase velocity curve of mode in the thick free aluminium sheet of Figure 13: 1mm;
Figure 14: the SH0 wave sensor detects the thick wide aluminium sheet received signal of 1mm;
Figure 15: signal behind the thick wide aluminium sheet wavelet de-noising of SH0 wave sensor detection 1mm;
Figure 16: the SH0 wave sensor detects 7cm aluminium fillet received signal;
Figure 17: signal behind the SH0 wave sensor detection 7cm aluminium fillet wavelet de-noising;
Figure 18: Figure 18 spacing is the 30cm angle probe motivates frequency 460kHz at the thick wide aluminium sheet of 1mm S
0The mode waveform;
Figure 19: spacing is the 50cm angle probe motivates frequency 460kHz at the thick wide aluminium sheet of 1mm S
0The mode waveform;
Figure 20: spacing is the 30cm angle probe motivates a plurality of frequency 500kHz at the thick 7cm width of 1mm aluminum strip S
0The mode waveform;
Figure 21: spacing is the 50cm angle probe motivates a plurality of frequency 500kHz at the thick 7cm width of 1mm aluminum strip S
0The mode waveform.
Among the figure, 1, the impulse function generator, 2, excitation terminal impedance coupling instrument, 3, SH0 ripple electromagnetic sound excitation transducer, 4, SH0 ripple electromagnetic sound receiving transducer, 5, receiving-end impedance coupling instrument 6, digital oscilloscope, 7, computing machine, 8, grounded screen conductor, 9, function generator, 10, power amplifier, 11, angle probe stimulus sensor, 12, angle probe receiving sensor, 13, the thick wide aluminium sheet of 1mm, 14, thick be the narrow aluminum strip of L=7cm for the 1mm width.
Fig. 5, Fig. 6 is among Fig. 7: x: plate thickness direction, z: plate length direction, y: vertical panel length direction (being tangential direction)
Embodiment
Content in conjunction with the inventive method provides embodiment 1, and eigen is: to liking the grounded screen conductor.Provide a kind of with SH0 ripple electromagnetic acoustic Non-Destructive Testing grounded screen conductor method:
Embodiment 1:
(1) as shown in Figure 1, place SH0 ripple electromagnetic sound excitation transducer 3 and SH0 ripple electromagnetic sound receiving transducer 4 on the grounded screen conductor 8 length direction central axis.SH0 ripple electromagnetic sound excitation transducer 3 is connected with excitation terminal impedance coupling instrument 2, excitation terminal impedance coupling instrument 2 is connected with impulse function generator 1, SH0 ripple electromagnetic sound receiving transducer 4 is connected with receiving-end impedance coupling instrument 5, receiving-end impedance coupling instrument 5 is connected with digital oscilloscope 6, and computing machine 7 is connected with digital oscilloscope 6.SH0 ripple electromagnetic sound excitation transducer 3 is positioned at plate high order end (half sensor is adsorbed on the grounded screen conductor), and SH0 ripple electromagnetic sound receiving transducer 4 is positioned at apart from plate left end 0.75m, and artificial defect simulation corrosion is positioned at the place apart from grounded screen conductor right-hand member 1m.Grounded screen conductor 5 in the present embodiment, total length 4m, the cross section is 6mm * 60mm rectangle, density is 7.9g/cm
3, Poisson ratio is 0.31.The thick 4m of 5.8mm that Fig. 3 has provided above-mentioned parameter grows SH wave dispersion curve in the grounded screen conductor, and the SH0 group velocity does not have frequency dispersion not with frequency change; Lamb wave mode complexity among Fig. 4,0～0.5MHz scope S
0The mode frequency dispersion is big, and Lamb wave is run into defective MODAL TRANSFORMATION OF A or mode stack are taken place usually.Frequency is 0.46MHz, S
0Velocity of wave is 1980m/s, and frequency is 0.5MHz, A
0Velocity of wave is 3202m/s, and the SH0 velocity of wave is 3260m/s, not with frequency change.Fig. 5 provides S under the 0.46MHz frequency
0Modal displacement wave structure figure, Fig. 6 are A under the 0.5MHz frequency
0Modal displacement wave structure figure, Fig. 7 are SH0 ripple displacement wave structural drawing under the 0.31MHz frequency.S
0, A
0(z direction) and plate thickness direction (x direction) displacement are all bigger along the plate direction of propagation at the lower surface place onboard, are held on soil environment, decay easily along the plate upper and lower surface during ultrasonic propagation.(z direction) and plate thickness direction (x direction) displacement all are 0 and the SH0 ripple is along the plate direction of propagation, only have the tangential displacement perpendicular to the plate direction of propagation (y direction), to sum up establish ultrasound examination and select the SH0 ripple to detect the corrosion of grounded screen conductor.In frequency 0～310kHz scope, only have SH0 ripple and SH1 ripple by Fig. 3, and both modal velocity gaps are very big, the ripple bag is easy to identification;
(2) it is adjustable in 1～20 scope to produce one-period by impulse function generator 1, centre frequency adjustable square-wave signal in 0～1MHz scope, in 0～1MHz scope, change frequency, excitation makes SH0 ripple electromagnetic sound excitation transducer 3 produce signal energies to be in maximal value in this scope, the frequency of corresponding this moment is 0.31MHz, then is chosen for impulse function generator frequency of operation.The intensity of square-wave signal and gain etc. all can exert an influence to supersonic guide-wave.In this enforcement, by impulse function generator produce power grade 15, gain 40db, frequency is the square-wave signal in 3 concussion cycles of 0.31MHz;
(3) pumping signal is by excitation terminal impedance coupling instrument 2 excitation SH0 ripple electromagnetic sound excitation transducers 3, excitation SH0 ripple in band corrosion default grounded screen conductor 8;
(4) Ji Li SH0 ripple signal is propagated in grounded screen conductor 8, and after defective and grounded screen end reflections, SH0 ripple electromagnetic sound receiving transducer 4 shows at digital oscilloscope 6, and stores computing machine 7 into by ethernet port by receiving impedance matching instrument 5;
(5) during frequency 0.31MHz, waveform such as Fig. 8 of in band corrosion default grounded screen conductor 8, receiving.Utilize the one dimension analysis method of wavelet packet to carry out denoising Processing to the received signal, obtain waveform such as Fig. 9 after the de-noising.The wavelet function of selecting is db40 (Daubechies) small echo, and this signal is carried out 6 layers of decomposition;
(6) by the time of the reflection echo arrival acceptance point in the signal after the analysis de-noising, determine to corrode the position in the grounded screen conductor 8.Telling first echo among Fig. 8 is direct wave, is 0.240ms by the time location of first echo, and the actual velocity of wave of SH0 is 3125m/s during estimation 0.31MHz, with the error of the SH0 velocity of wave of theory only be 4.14%.Therefore tell the 3rd echo for being grounded screen conductor right side echo, second echo is corrosion ripple bag, the second echo time position is 1.667ms, can determine the distance propagated according to the velocity of wave time of multiply by, the position that obtains defective as can be known during time 1.142ms is for apart from stimulus sensor 2.98m, with the physical location relative error of corrosion only be 0.773%; Utilize a little less than the SH0 wave reflection echo attenutation, can also differentiate corrosion size, shape according to the amplitude of corrosion ripple bag;
Use device such as Fig. 2 provide and utilize Lamb wave to detect grounded screen conductor corroding method and experimental result.
(1) angle probe stimulus sensor 11, angle probe receiving sensor 12 are placed on the grounded screen conductor 8, form experimental provision Fig. 2;
(2) produce a centre frequency adjustable narrow-band impulse in 0～5MHz scope by function generator 9, the type of narrow-band impulse, frequency, intensity and recurrent interval etc. all can exert an influence to supersonic guide-wave.In this enforcement, produce 5 sinusoidal signals of shaking the cycles that peak-to-peak value is 250mV by function generator 2 through the Hanning window modulation, the frequency of selection is 0.5MHz.100ms is got in these narrow-band impulse excitations at interval;
(3) pumping signal is carried out power amplification through power amplifier 10, and peak-to-peak value reaches 250V; By 90 ° of voussoirs, angle probe stimulus sensor 11 motivates the Lamb wave that frequency is 0.5MHz in grounded screen conductor 8;
(4) Ji Li Lamb wave signal is propagated in grounded screen conductor 8, and received signal such as Figure 10 when propagation distance is 0.3m show at digital oscilloscope 6, and store computing machine 7 into by ethernet port; Same by 90 ° of voussoirs, received signal such as Figure 11 when the angle probe distance is 0.5m;
(5) Figure 10 as can be known first echo be direct wave A
0Mode, time location are 115 μ s, and first echo time of arrival of Figure 11 is 184 μ s.Calculate A
0The group velocity of mode is about 2899m/s, and with theoretical velocity 3193m/s, relative error is 9.2%, and the cladding of received signal ripple is assorted, and the stack of serious MODAL TRANSFORMATION OF A and mode takes place.
Therefore adopt the SH0 ripple to detect ground net corrosion, avoided Lamb wave to detect and be subjected to edge effect generation MODAL TRANSFORMATION OF A, the shortcoming of mode stack, the ripple bag is simple, a little less than the decay, detects distance.
Embodiment 2:
Content in conjunction with the inventive method provides embodiment 2, and effective object is the thick wide aluminium sheet of 1mm that is.Utilize Fig. 1 device among the embodiment 1 equally, grounded screen conductor 8 becomes wide aluminium sheet 13:
(1) places SH0 ripple electromagnetic sound excitation transducer 3 and SH0 ripple electromagnetic sound receiving transducer 4 on the wide aluminium sheet 13 length direction central axis.SH0 ripple EMAT stimulus sensor 3 is positioned at plate high order end (half sensor is shelved on the wide aluminium sheet 13).SH0 ripple electromagnetic sound receiving transducer 4 is shelved the place apart from stimulus sensor 0.5m.Aluminium sheet 13 in the present embodiment, total length 1m, the cross section is 1mm * 20cm rectangle, density is 2.7g/cm
3, Poisson ratio is 0.33.Figure 12 has provided the group velocity curve of mode in the thick free aluminium sheet of 1mm of above-mentioned parameter.Obtain S by disperse software
0Velocity of wave is 5376m/s, A
0Velocity of wave is 3131m/s, and the SH0 velocity of wave is 3130m/s.The SH0 group velocity does not have frequency dispersion not with frequency change among Figure 12;
(2) produce a centre frequency adjustable square-wave signal in 0～1MHz scope by impulse function generator 2, the frequency of square-wave signal, intensity and gain etc. all can exert an influence to supersonic guide-wave.In this enforcement, by impulse function generator produce power grade 15, gain 40db, frequency is the square-wave signal in 3 concussion cycles of 0.31MHz;
(3) pumping signal is through blasting terminal impedance analyser 2 excitation SH0 ripple electromagnetic sound excitation transducers 3, excitation SH0 ripple in wide aluminium sheet 13;
(4) Ji Li SH0 ripple signal is propagated in wide aluminium sheet 13, after wide aluminium sheet 13 end reflections, by SH0 ripple electromagnetic sound receiving transducer 4, shows at digital oscilloscope 6, and stores computing machine 7 into by ethernet port;
(5) during frequency 0.31MHz, original waveform such as Figure 14 of receiving in wide aluminium sheet 13 utilize waveform such as Figure 15 after the de-noising of one dimension analysis method of wavelet packet.The wavelet function of selecting is db40 (Daubechies) small echo, and this signal is carried out 6 layers of decomposition.
(6) analyze the time that reflection echo in the signal after the de-noising arrives acceptance point: the time location of Figure 15 first echo is 0.168ms, during 0.31MHz in the aluminium sheet the actual velocity of wave of estimation SH0 be 2976m/s, with the error of the SH0 velocity of wave of theory only be 4.92%.Same analysis second echo is the right side echo.
Utilize experimental provision such as Fig. 2, provide method and the experimental result of utilizing Lamb wave to detect wide aluminium sheet.
(1) angle probe stimulus sensor 11, angle probe receiving sensor 12 are placed in the wide aluminium sheet 13;
(2) produce a centre frequency adjustable narrow-band impulse in 0～5MHz scope by function generator 9, the type of narrow-band impulse, frequency, intensity and recurrent interval etc. all can exert an influence to supersonic guide-wave.In this enforcement, produce 5 sinusoidal signals of shaking the cycles that peak-to-peak value is 250mV by function generator 9 through the Hanning window modulation, the frequency of selection has two kinds: 0.46MHz and 0.9MHz.100ms is got in these narrow-band impulse excitations at interval;
(3) pumping signal is carried out power amplification through power amplifier 3, and peak-to-peak value reaches 250V; By 30 ° of voussoirs, angle probe stimulus sensor 11 motivates the S that frequency is 0.46MHz in wide aluminium sheet 13
0Mode;
(4) Ji Li S
0The mode signal is propagated in wide aluminium sheet 13, and received signal such as Figure 18 when propagation distance is 30cm show at digital oscilloscope 6, and store computing machine 7 into by ethernet port; Same received signal such as Figure 19 when propagation distance is 50cm;
(5) comprehensive Figure 18, Figure 19 motivates S as can be known
0Mode.First echo is S in Figure 19
0The corresponding time location of mode is 103.9 μ s.Calculate S
0The group velocity of mode is about 5500m/s, with the theoretical velocity relative error only be 2.94%; Same by 90 ° of voussoirs, the A of excitation 0.9MHz in wide aluminium sheet 13
0The mode situation is similar.
Embodiment 3:
Effective object is the thick aluminium fillet of 7cm that is for 1mm is wide.
(1) same use device Fig. 1, object become the wide narrow aluminum strip 14 of L=7cm that is.SH0 ripple electromagnetic sound excitation transducer 3 is positioned over wide on the narrow aluminum strip 14 of L=7cm.SH0 ripple electromagnetic sound excitation transducer 3 is positioned at the place apart from aluminum strip left end 35cm, and SH0 ripple electromagnetic sound excitation transducer 3 and SH0 ripple electromagnetic sound receiving transducer 4 spacings keep 25cm.Wide is that the narrow aluminum strip 14 of L=7cm receives waveform such as Figure 16, and clutter is few, and echo is clear simple, MODAL TRANSFORMATION OF A can not take place, the signal to noise ratio (S/N ratio) height.Utilize waveform such as Figure 17 after the de-noising of one dimension analysis method of wavelet packet.Figure 16 among the comprehensive embodiment 2 among Figure 14 and the embodiment 3, Figure 14 is the same substantially with Figure 16 waveform; Direct wave, right side echo basically identical time of arrival, the amplitude influence belongs within the experimental error scope.
Utilize experimental provision 2, provide method and the experimental result of utilizing Lamb wave to detect wide aluminium sheet and aluminium fillet.
In the experimental provision 2, grounded screen conductor 8 becomes the thick 1mm that is, wide is the narrow aluminum strip 14 of L=7cm:
(2) object is changed to widely on the narrow aluminum strip 14 of L=7cm in the use device 2, and the angle probe spacing keeps 30cm, the waveform of reception such as Figure 20.The first ripple bag is direct wave S among analysis Figure 20
0Mode, the second ripple bag, the 3rd ripple bag are edge reflection echo S
0Mode or MODAL TRANSFORMATION OF A are other mode, and clutter is many, poor signal to noise.Receive waveform such as Figure 21 during same angle probe spacing 50cm, ripple bag one, ripple bag two, ripple bag three are all S
0Mode, a lot of wavelet packets of following belong to S
0Mode is run into the border MODAL TRANSFORMATION OF A generation is taken place.Utilize Lamb wave test experience boundary effect obvious, MODAL TRANSFORMATION OF A takes place in the echo complexity, and poor signal to noise is unfavorable for that the fillet structure erosion detects.
Claims (2)
1. based on the corrosion pick-up unit of SH0 ripple electric system grounded screen conductor, it is characterized in that: comprising: impulse function generator 1, digital oscilloscope 6 and computing machine 7, SH0 ripple electromagnetic sound excitation transducer 3, SH0 ripple electromagnetic sound receiving transducer 4 is placed on the grounded screen conductor 8, SH0 ripple electromagnetic sound excitation transducer 3 is connected with excitation terminal impedance coupling instrument 2, excitation terminal impedance coupling instrument 2 is connected with impulse function generator 1, SH0 ripple electromagnetic sound receiving transducer 4 is connected with receiving-end impedance coupling instrument 5, receiving-end impedance coupling instrument 5 is connected with digital oscilloscope 6, and computing machine 7 is connected with digital oscilloscope 6;
2. the detection method of the corrosion pick-up unit based on SH0 ripple electric system grounded screen conductor according to claim 1 is characterized in that: may further comprise the steps:
Step 1): it is adjustable in 1～20 scope to produce one-period by impulse function generator 1, centre frequency adjustable square-wave signal in 0～1MHz scope, in 0～1MHz scope, change frequency, excitation makes SH0 ripple electromagnetic sound excitation transducer 3 produce the maximum of points of signal energy in this scope, and then Ci Shi frequency is impulse function generator frequency of operation;
Step 2): above-mentioned square-wave signal is after pulse function generator 1 enters excitation terminal impedance coupling instrument 2, import SH0 ripple electromagnetic sound excitation transducer 3 into, SH0 ripple electromagnetic sound receiving transducer 4 receives the signal of being propagated by SH0 ripple electromagnetic sound excitation transducer 3 in grounded screen conductor 8, show on oscillograph 6 through receiving-end impedance coupling instrument 5, and store in the computing machine 7, utilize the one dimension analysis method of wavelet packet that the time-domain signal that receives is carried out denoising Processing, confirm the direct wave bag, the end face echo, corrosion ripple bag etc., time t1 according to the arrival of direct wave bag, spacing d between SH0 ripple electromagnetic sound excitation transducer 3 and the SH0 ripple electromagnetic sound receiving transducer 4, the time t that the ripple of the group velocity v=d/t that propagates in grounded screen conductor 8 according to the SH0 ripple, and corrosion again bag arrives
2, can try to achieve corrosion position s=v * t
2
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| CN108801892B (en) * | 2018-06-19 | 2020-09-29 | 国家电网公司 | Transformer substation grounding grid corrosion diagnosis method and system |
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| CN114459648B (en) * | 2022-01-19 | 2022-08-02 | 哈尔滨工业大学 | Multi-mode Lamb wave data fusion-based baseline-free stress online monitoring method |
| CN115184252A (en) * | 2022-09-07 | 2022-10-14 | 国网湖北省电力有限公司超高压公司 | Pulse echo method-based vertical grounding electrode corrosion damage detection method and system |
| CN115184252B (en) * | 2022-09-07 | 2022-12-23 | 国网湖北省电力有限公司超高压公司 | Pulse echo method-based vertical grounding electrode corrosion damage detection method and system |
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