阅读说明：本技术 超声合成孔径聚焦的变压器套管内引线检测方法及系统 (Method and system for detecting inner lead of transformer bushing focused by ultrasonic synthetic aperture ) 是由 张继国 郝成钢 孙沃野 李凯 孙刚 李爽 于 2021-08-02 设计创作，主要内容包括：本发明公开了一种超声合成孔径聚焦的变压器套管内引线检测方法,包括如下步骤：S1：通过单个探头向待测变压器套管内引线进行弧形扫描,发送超声信号并接收回波信号。S2：基于回波信号获取相对应的弧形扫描数据。S3：沿待测变压器套管周向方向移动探头,并重复步骤S1和S2。S4：将探头各个位置所对应的弧形扫描数据进行数据处理,获得图像数据值。S5：对图像数据值的进行叠加得到若干聚焦点P,并基于若干聚焦点P形成扫描图像,根据扫描图像判断待测变压器套管内引线是否正常。本发明可以实现在线、定量地检测,以高成像分辨率获取变形情况,减少了计算量,更加方便与快捷。(The invention discloses a method for detecting an inner lead of a transformer bushing focused by ultrasonic synthetic aperture, which comprises the following steps: s1: and carrying out arc scanning on the inner lead of the transformer bushing to be tested through a single probe, sending an ultrasonic signal and receiving an echo signal. S2: and acquiring corresponding arc scanning data based on the echo signals. S3: and moving the probe along the circumferential direction of the transformer bushing to be tested, and repeating the steps S1 and S2. S4: and carrying out data processing on the arc scanning data corresponding to each position of the probe to obtain an image data value. S5: and superposing the image data values to obtain a plurality of focusing points P, forming a scanning image based on the plurality of focusing points P, and judging whether the inner lead of the transformer bushing to be detected is normal or not according to the scanning image. The invention can realize on-line and quantitative detection, obtain the deformation condition with high imaging resolution, reduce the calculated amount and is more convenient and rapid.)

1. A method for detecting an inner lead of a transformer bushing with focused ultrasonic synthetic aperture is characterized by comprising the following steps:

s1: performing arc scanning on the inner lead of the transformer bushing to be tested through a single probe, sending an ultrasonic signal and receiving an echo signal;

s2: acquiring corresponding arc scanning data based on the echo signals;

s3: moving the probe along the circumferential direction of the transformer bushing to be tested, and repeating the steps S1 and S2;

s4: carrying out data processing on the arc scanning data corresponding to each position of the probe to obtain an image data value;

s5: and superposing the image data values to obtain a plurality of focusing points P, forming a scanning image based on the plurality of focusing points P, and judging whether the inner lead of the transformer bushing to be tested is normal or not according to the scanning image.

2. The method for detecting transformer bushing inner lead wire with ultrasonic synthetic aperture focusing as claimed in claim 1, wherein the formula for obtaining the image data value in step S4 is

S(arc(s_i,t_i))＝ω_is_i(t_i)/r_i

Wherein, ω is_iReceived for the ith probe positionOf the echo signal s_iThe arc scan data, t, of the echo signal_iFor a delay time, r_iIs the distance from the ith probe position to the arc scan.

3. The method for detecting the transformer bushing inner lead wire with the ultrasonic synthetic aperture focus according to claim 2, wherein in the step S1, the arc scanning is performed along a direction in which the probe points to the transformer bushing inner lead wire to be detected, the probe obtains a plurality of scanning layers at each scanning position, the plurality of scanning layers are all arc-shaped, and the center of the circle is the probe.

4. The method for detecting transformer bushing inner lead wire with ultrasonic synthetic aperture focusing according to claim 3, wherein the image data of each point on the same scanning layer is the same and can be obtained by the image data value formula of the step S4.

5. The method for detecting transformer bushing lead wire with ultrasonic synthetic aperture focusing according to claim 1, further comprising filtering the arc scan data between the steps S3 and S4, wherein the arc scan data smaller than a threshold is defined as zero.

6. The method for detecting the transformer bushing inner lead wire of the ultrasonic synthetic aperture focusing according to claim 3, wherein in the step S5,

and superposing the image data values at the same positions of a plurality of scanning layers to obtain a focus point P on each scanning layer, wherein the focus point P is larger than the superposed image data values of all other points on the corresponding scanning layer.

7. An ultrasonic synthetic aperture focused transformer bushing inner lead detection system applying the ultrasonic synthetic aperture focused transformer bushing inner lead detection method as claimed in any one of claims 1 to 6, characterized by comprising an FPGA chip, a power amplification circuit, a signal conditioning circuit, a data acquisition circuit and a transducer;

the FPGA chip is controlled by an external upper computer to output a low pulse signal to the power amplifier circuit;

the power amplification circuit is used for receiving the low pulse signal, amplifying the power and outputting a high pulse signal to the energy converter;

the transducer is used for receiving the high pulse signal, outputting the high pulse signal to an inner lead of a transformer bushing to be tested, and receiving an echo signal;

the signal conditioning circuit is used for receiving the echo signal and processing the signal;

the data acquisition circuit is used for receiving the echo signal after signal processing and acquiring to obtain an acquired signal;

the FPGA chip is also used for receiving the acquisition signal, obtaining a scanning image based on the ultrasonic synthetic aperture focused transformer bushing inner lead detection method, and uploading the scanning image to an external upper computer for displaying.

8. The system of claim 7, wherein the transducer has a 400kHz central frequency transceiver transducer with a half power beam angle of 5.0 °, a limit voltage of 700V, and a diameter of 43 mm.

9. The system of claim 7,

the signal conditioning circuit is used for sequentially carrying out convolution filtering, envelope signal extraction through Hilbert transform and logarithmic amplification on the echo signals.

10. The system of claim 7, further comprising a power module that provides electrical support for the transformer bushing inner lead detection system.

Technical Field

The invention belongs to the field of electrical equipment detection, and particularly relates to a method and a system for detecting an inner lead of a transformer bushing with focused ultrasonic synthetic aperture.

Background

In recent years, the rapid increase of national economy is accompanied by the increasing demand of people, enterprises and countries for electric power. In order to guarantee that electric power can be transmitted to users in a guaranteed manner, the safety and reliability of electric power equipment are very important to the electric power system, and the reliability of the electric power equipment directly determines the reliability of the electric power system. The transformer is one of the most important power devices in the power system, is a junction of a power transmission line, and bears the responsibility of power transmission and distribution, when the transformer breaks down, the safety and stability of the whole power system are threatened, and a large-range power failure accident can happen in serious conditions. According to statistics, the fault of the transformer is caused by the insulation damage of the transformer, and the fault rate is increased year by year.

The inner lead of the transformer bushing is one of the most important components in the transformer, the transformer is connected with the outside through the inner lead of the bushing, electric energy is input or output through the lead, and the transformer bushing forms the main part of the main insulation of the transformer. In recent years, there are many transformer accidents caused by insulation damage of transformer bushings. The state of the inner lead of the transformer bushing directly influences the electric field distribution in the bushing, if the state of the inner lead of the transformer bushing is changed, the electric field intensity distribution in transformer oil in the bushing is uneven, a spark discharge phenomenon can occur in the severe case, and finally the whole bushing is subjected to insulation breakdown, so that the real-time detection of the state of the inner lead of the transformer bushing has great practical significance.

The existing detection technology for the inner lead of the transformer bushing mainly comprises the following steps: periodic preventative testing, infrared imaging, ultrasound, oil chromatography, and the like.

The regular preventive test is the earliest method applied to actual engineering, the transformer is overhauled in a large scale integrally by stopping the transformer at regular time, and partial devices are disassembled to directly maintain the transformer when necessary. The periodic preventive test has the defects of outage, high labor cost, long overhaul period, high requirement on professional ability of an overhaul worker due to the fact that detection results are judged by the experience of the professional, and the need for an electrified detection method is met.

The infrared imaging method can complete the task of live detection, and infrared imaging test is carried out through remote contactless, can detect the condition of generating heat of transformer bushing inner lead, discovers local overheat phenomenon sleeve pipe lead in advance and breaks down. Although the infrared imaging method can achieve the purpose of charged detection, the infrared imaging can not judge the specific position of the fault due to the fact that the infrared imaging carries out temperature imaging on the whole lead; in addition, the transformer has a large temperature variation range in the operation process, and the infrared imaging method may misjudge the detection result, so a more accurate detection method is needed.

The oil chromatographic analysis method is a chemical method, has high detection precision and can accurately judge whether latent faults occur in the transformer bushing and the lead, but the oil chromatographic analysis method borrows the transformer oil in the transformer bushing, so that the transformer oil in the transformer bushing can not be extracted in a large amount under normal conditions, the lead is exposed in the air, and the insulating capability is weakened, so that the detection method based on physical information is needed.

The ultrasonic method is realized based on a distance measurement principle, and the transmission time of an ultrasonic signal is calculated according to an autocorrelation algorithm, so that the distance between a casing lead and a casing shell is converted according to a distance conversion algorithm, and the real-time state of the casing lead is judged. However, although the existing ultrasonic method can preliminarily perform online detection on the state of the lead wire in the casing, the existing ultrasonic method has the defects of low detection efficiency, low speed and poor detection effect.

Disclosure of Invention

The invention aims to provide a method and a system for detecting an inner lead of a transformer bushing by ultrasonic synthetic aperture focusing, which aim to solve the technical problems of low detection efficiency, low speed and low precision.

In order to solve the problems, the technical scheme of the invention is as follows:

a method for detecting an inner lead of a transformer bushing with focused ultrasonic synthetic aperture comprises the following steps:

s1: and carrying out arc scanning on the inner lead of the transformer bushing to be tested through a single probe, sending an ultrasonic signal and receiving an echo signal.

S2: and acquiring corresponding arc scanning data based on the echo signals.

S3: and moving the probe along the circumferential direction of the transformer bushing to be tested, and repeating the steps S1 and S2.

S4: and carrying out data processing on the arc scanning data corresponding to each position of the probe to obtain an image data value.

S5: and superposing the image data values to obtain a plurality of focusing points P, forming a scanning image based on the plurality of focusing points P, and judging whether the inner lead of the transformer bushing to be detected is normal or not according to the scanning image.

Wherein the formula for obtaining the image data value in step S4 is

S(arc(s_i,t_i))＝ω_is_i(t_i)/r_i

Wherein, ω is_iIs an apodization function, s, of the echo signal received at the ith probe position_iData of arc scans for echo signals, t_iFor a delay time, r_iThe distance from the ith probe position to the arc scan.

In step S1, the arc scanning is performed along a direction in which the probe points to the inner lead of the transformer bushing to be tested, the probe obtains a plurality of scanning layers at each scanning position, the scanning layers are arc-shaped, and the center of the circle is the probe.

The image data of each point on the same scanning layer is the same and can be obtained through the image data value formula of step S4.

Preferably, a filtering process is further included between the steps S3 and S4, and the arc scan data smaller than the threshold is defined as zero.

In step S5, image data values at the same positions of several scanning layers are superimposed, and a focusing point P is obtained on each scanning layer, where the focusing point P is greater than the superimposed image data values of all other points on the corresponding scanning layer.

The transformer bushing inner lead detection system adopting ultrasonic synthetic aperture focusing is characterized by comprising an FPGA chip, a power amplification circuit, a signal conditioning circuit, a data acquisition circuit and a transducer.

The FPGA chip is controlled by an external upper computer to output a low pulse signal to the power amplifier circuit.

The power amplification circuit is used for receiving the low pulse signal, amplifying the power and outputting a high pulse signal to the energy converter.

The transducer is used for receiving the high pulse signal and outputting the high pulse signal to the inner lead of the transformer bushing to be tested, and receiving the echo signal.

The signal conditioning circuit is used for receiving the echo signal and processing the signal.

The data acquisition circuit is used for receiving the echo signals after the signal processing and acquiring to obtain acquired signals.

The FPGA chip is also used for receiving the acquired signals, obtaining a scanning image based on the transformer bushing inner lead detection method of ultrasonic synthetic aperture focusing, and uploading the scanning image to an external upper computer for displaying.

The central frequency of the transducer is 400kHz, the half-power beam angle of the transducer is 5.0 degrees, the limit voltage is 700V, and the diameter of the transducer is 43 mm.

The signal conditioning circuit is used for carrying out convolution filtering, envelope signal extraction through Hilbert transform and logarithmic amplification on the echo signals in sequence.

Further preferably, the transformer bushing inner lead detection system further comprises a power supply module, and the power supply module provides power support for the transformer bushing inner lead detection system.

Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects:

the invention provides a method for imaging and analyzing the real-time state of the lead in the transformer bushing by using an ultrasonic synthetic aperture focusing technology, which can realize online and quantitative detection, solve the defects of the traditional ultrasonic method, detect the deformation condition of the transformer winding in a high-imaging resolution mode, and ensure that the detection precision reaches the level of 0.1mm, and the detection time of the system is only that of the traditional ultrasonic detection method. In addition, the single probe is used for arc scanning, a focus point does not need to be acquired in advance, the calculation amount of the method is reduced, and the method is more convenient and quicker.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.

FIG. 1 is a flow chart of a method for detecting the inner lead of a transformer bushing with ultrasonic synthetic aperture focusing according to the present invention;

FIG. 2 is a schematic diagram of the SAFT sense lead of the present invention;

FIG. 3 is a schematic diagram of the relationship between effective aperture length and half power angle of the present invention;

FIG. 4 is a schematic diagram of another effective aperture length versus half power angle of the present invention;

FIG. 5 is a schematic view of a single probe scanning area of the present invention;

FIG. 6 is a schematic diagram of an ultrasonic echo signal according to the present invention;

FIG. 7 is a schematic diagram of the structure of an ultrasonic synthetic aperture focused transformer bushing inner lead detection system of the present invention;

fig. 8 is a schematic diagram of a waveform transformation of the signal conditioning circuit of the present invention.

Detailed Description

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description will be made with reference to the accompanying drawings. It is obvious that the drawings in the following description are only some examples of the invention, and that for a person skilled in the art, other drawings and embodiments can be derived from them without inventive effort.

For the sake of simplicity, the drawings only schematically show the parts relevant to the present invention, and they do not represent the actual structure as a product. In addition, in order to make the drawings concise and understandable, components having the same structure or function in some of the drawings are only schematically illustrated or only labeled. In this document, "one" means not only "only one" but also a case of "more than one".

The method and system for detecting the inner lead of the transformer bushing with ultrasonic synthetic aperture focusing according to the present invention will be described in detail with reference to the accompanying drawings and specific embodiments. Advantages and features of the present invention will become apparent from the following description and from the claims.

Example 1

The embodiment provides a method for detecting an inner lead of a transformer bushing by ultrasonic synthetic aperture focusing.

First, referring to fig. 2, an ultrasonic synthetic aperture focusing technique is explained. The synthetic aperture technology is to overlap image data scanned by a single ultrasonic transducer at different positions, and simulate a larger aperture by using a transducer with a smaller aperture, so that the resolution of imaging is only related to the transducer and is not blurred as the detection depth is increased. Synthetic aperture imaging consists of two parts, acquisition of data and superposition of images.

The principle of the ultrasonic synthetic aperture focusing technology is shown in figure 1, u₀,u₁,…,u_L-1The number of each movement of the transducer, z the depth of transmission of the transducer, is counted and one scan of depth z is made towards the lead for each movement of the transducer along the casing. Let the coordinates of the imaging focal point P on the lead be (x, R), where R is the vertical depth of the focal point, numbered u_iIs at a distance r from the focal point_i。

Scanning position u_iTo the focal point of the transducer of r₁The calculation formula of (2) is as follows:

ultrasonic signal from scanning position u_iEmitted to the focus point and reflected back to u via the lead wire_iPropagation time t of a location_iComprises the following steps:

scanning position u_iThe delay time is as follows:

wherein, i in the above formula is 0,1, …, L-1, c is the propagation speed of the ultrasonic signal in the transformer oil. Suppose that at each scan position u_iThe ultrasonic echo signal received after transmission is s (u)_iT), overlapping the echo signals obtained by scanning each position according to time delay to obtain image data at a focus point

Wherein, δ (t- τ)_i) For scanning position u_iTime delay impulse function of, omega_nThe formula is an apodization function, and the formula is a mathematical model of the ultrasonic synthetic aperture focusing.

When the traditional ultrasonic synthetic aperture focusing technology is used for focusing imaging, the probe scans a focus point in multiple movements, so that the calculation amount is increased. The actual effective aperture length can be calculated in advance according to the half-power angle, and the placement of the probe is reduced, so that the signal acquisition times are reduced.

The relationship between the actual effective aperture length and the half-power angle is shown in FIG. 3. At the scanning position u₀At which the focus point P starts to enter the scanning area at the scanning position u_L-1At which the focal point P leaves the scanning region, outside the synthetic aperture L, the transducer does not scan to the focal point P. The length of the synthetic aperture L can be calculated by the following formula:

it will be appreciated that the length of the synthetic aperture L is related only to the transducer itself and the depth of transmission.

In the implementation, the detection of the inner lead of the transformer bushing specifically comprises the following steps

First, in step S1, a focus point P on the lead is selected₁(x, R), the focusing point P₁(x, R) are known amounts.

Next, in step S2, a synthetic aperture L is obtained by calculation based on the synthetic aperture L calculation formula.

Then, the focus point P is set in step S3₁Centering, determining the position u of the transducer within the synthetic aperture L₀,u₁,…,u_L-1。

Thereafter, in step S4, u is located for each transducer position_i(i-0, 1, …, L-1) calculating the respective distances r₁Propagation time t_iDelay time tau_iAnd the sampled data value s (u)_i,t_i)。

Then, the process proceeds to step S5, where each transducer position u is determined_iThe data values are superposed to obtain a focus point P₁The image data value of (1).

Finally, step S6 checks whether there is any residual focus point within the scannable range, and if so, repeats step S1 to S5, otherwise, ends the detection and outputs the result.

Example 2

Referring to fig. 1, the present embodiment provides an improved method for detecting the lead-in wire of the transformer bushing based on the ultrasonic synthetic aperture focusing method of embodiment 1. The ultrasonic synthetic aperture focusing algorithm is a convolution operation, so that the imaging time is long, the calculated amount is large, and the requirement on hardware is high. In addition, a prerequisite of the calculation process of embodiment 1 is that the position of the focus point is known, but the detection point in practice is unknown, and the data acquired by the ultrasonic transducer at each time not only acts on the focus point but also participates in the imaging calculation of other points, so that the flow of the ultrasonic synthetic aperture focusing algorithm is large in calculation amount and the practical operation is complex, so that the embodiment uses a single-probe arc scanning algorithm to reduce the calculation amount in terms of guaranteeing the lead imaging resolution.

Referring to fig. 1, the method specifically includes the following steps:

first, in step S1, an arc scan is performed on the inner lead of the transformer bushing to be tested by a single probe, an ultrasonic signal is transmitted, and an echo signal is received. In this embodiment, the probe is a transducer. The arc scanning is to scan along the direction that the probe points to the inner lead wire of the transformer bushing to be measured, a plurality of scanning layers can be obtained within the scanning range of the probe, the plurality of scanning layers are all arc-shaped, and the circle center is the position of the probe.

Referring to FIG. 4, three different transducer positions u₀,u₁,u_iData s acquired at a focus point P₀(t₀),s₁(t₁),s_i(t_i) Acting not only on the focal point P, but also on the arc(s)₀,t₀)，arc(s₁,t₁),arc(s_i,t_i) All points on the same arc, the points on the same arc being a distance r from the respective transducer location_iSame, propagation time t_iThe same applies.

Thus, a single probe arc scan can be understood as: at each probe position u_iAs a center, with a radius r_iConcentric arcs are drawn on the image in order from zero to larger. Thus, the effective length of the synthetic aperture does not need to be solved according to the unknown focus point, and the transducer at each position is directly subjected to an arc drawing operation to acquire data.

Referring to fig. 5, data is collected from the moment A when the arc is tangent to the lead wire in the transformer bushing, when the radius r_iGradually increasing and the arc line begins to face downwardsScanning, at position u_iThe transducer can scan to all points on the arc (lar) on the inner lead of the transformer bushing.

Next, in step S2, the received echo signals are processed to obtain corresponding arc scan data, i.e., the echo signals are converted into analog signals.

Then, the process proceeds to step S3, the probe is moved along the circumferential direction of the transformer bushing to be tested, and steps S1 and S2 are repeated to collect u₀,u₁,…,u_L-1The data is scanned in an arc shape at a plurality of positions until the scannable area is completely scanned, and then the process proceeds to step S4.

Referring to FIG. 6, preferably, the radius r is_iIn the process of increasing from zero, a lot of invalid data may appear, and fig. 6 is an ultrasonic echo waveform of 1000 sampling points, it can be seen that the invalid data in the echo signal accounts for 80%, and the invalid data does not participate in the calculation of the algorithm, so that the arc scan data needs to be filtered, and the arc scan data smaller than the threshold is defined as zero, so as to reduce the subsequent calculation amount and improve the calculation speed.

In step S4, the arc scan data corresponding to each position of the probe is subjected to data processing to obtain image data values. Wherein, the image data of each point on the same scanning layer is the same, and the image data value can be obtained by the following formula

S(arc(s_i,t_i))＝ω_is_i(t_i)/r_i

Wherein, ω is_iIs an apodization function, s, of the echo signal received at the ith probe position_iData of arc scans for echo signals, t_iFor a delay time, r_iThe distance from the ith probe position to the arc scan.

Finally, in step S5, the image data values at the same position of each scanning layer are superimposed, that is, as shown in fig. 4, three arcs intersect at the focusing point P, so that a focusing point P is obtained on each scanning layer, and the focusing point P is much larger than the superimposition of the image data values of other unfocused points on the corresponding scanning layer. And judging whether the inner lead of the transformer bushing to be tested is normal or not according to the scanning image formed by the plurality of focusing points P.

Example 3

Referring to fig. 2, this embodiment provides an ultrasonic synthetic aperture focused transformer bushing inner lead detection system based on embodiments 1 and 2, which employs an ultrasonic synthetic aperture focused transformer bushing inner lead detection method as claimed in any one of embodiments 2.

Referring to fig. 7, the system specifically includes an FPGA chip, a power amplifying circuit, a signal conditioning circuit, a data collecting circuit, and a transducer.

The FPGA chip is controlled by an external upper computer to output a low pulse signal to the power amplifier circuit, and the external upper computer is connected with the FPGA chip through a USB, so that communication is achieved. In order to transmit the transformer bushing shell and compensate the attenuation of energy, the power amplifier circuit is used for receiving the low pulse signal output by the FPGA chip and amplifying the power to obtain a high pulse signal, and the power of the high pulse signal is about 200V. The transducer is used for receiving the high pulse signal and outputting the high pulse signal to the inner lead of the transformer bushing to be tested, and receiving the echo signal rebounded by the lead. The signal conditioning circuit is used for receiving the echo signal and processing the signal. Referring to fig. 8, the signal conditioning circuit performs convolution filtering on the echo signal, so that part of noise is filtered and the waveform becomes smoother; and then, extracting an envelope signal from the waveform signal by using Hilbert transform, reducing errors caused by delay and phase, enabling the amplitude of the signal to be changed into a positive value, preventing the positive and negative amplitudes of the signal from being superposed and offset, and finally carrying out logarithmic amplification. The data acquisition circuit is used for receiving the echo signals after signal processing and acquiring acquired signals, and the sampling frequency is f_cAbout 50 times the center frequency of the ultrasonic transducer at 20 MHz.

The FPGA chip is also used for receiving the acquired signals, an ultrasonic synthetic aperture focusing algorithm is written in the FPGA chip, the superposition of wave beams is realized, and the calculation result is led into an upper computer to be presented. Because the acquired data is huge, the data is read and written by means of the off-chip SDRAM cache of the FPGA.

Selection of transducers will now be described

Ultrasonic signal in penetrating transformer sleeveEnergy losses occur both in the tube housing and when propagating in the transformer oil. The scattering attenuation occurs when the tube penetrates the transformer casing, the acoustic impedance of the transformer casing is Z₁＝4.6×10⁷N·/m³Acoustic impedance of transformer oil is Z₂＝1.28×10⁶N·/m³Acoustic impedance of air being Z₃＝415N·/m³In order to ensure that the transducer can receive a complete echo waveform, an ultrasonic coupling agent needs to be coated between air and a transformer shell, and hardware is also needed to send out a higher-energy voltage signal to excite the transducer.

Absorption decay occurs when propagating in transformer oil, and the sound pressure decay exhibits an exponential decay with propagation distance:

P(x+dx)＝P(x)e^-αdx

where α is the attenuation coefficient and p (x) is the sound pressure at the propagation distance x. The attenuation coefficient is calculated as follows:

where f is the frequency of the transducer and η is the viscosity coefficient. It can be seen that the absorption decay is proportional to the square of the frequency of the transducer, with the higher the frequency of the transducer, the more rapidly the acoustic energy decays.

The lateral resolution is determined by the beam itself, the smaller the diameter of the transducer, the smaller the diameter of the beam produced, and the higher the lateral resolution. The longitudinal resolution is determined by the frequency of the transducer, and is typically:

where c is the speed of the ultrasonic beam propagating in the medium, tau_pIs the pulse time, B_ωThe width of the pulse band. In summary, in order to ensure that the transducer can successfully penetrate the transformer bushing casing, reduce the attenuation in the transformer oil as much as possible, and improve the imaging resolution, the post-detection sampling is comprehensively consideredA transmitting-receiving transducer with the center frequency of 400kHz is used, the half-power beam angle is 5.0 degrees, the limit voltage of the transducer is 700V, and the diameter of the transducer is 43 mm.

Preferably, the transformer bushing inner lead detection system further comprises a power supply module, and the power supply module provides power support for the transformer bushing inner lead detection system.

The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, it is still within the scope of the present invention if they fall within the scope of the claims of the present invention and their equivalents.