Damage Detection Method for Overhead Transmission Lines Based on Electromagnetic Ultrasound

Abstract

A damage detection method for overhead transmission lines based on electromagnetic ultrasound includes the following steps: attenuation and dispersion compensation of the electromagnetic ultrasonic signal based on its attenuation and dispersion characteristics within the transmission line; determination of the transmission line damage location based on the wave velocity of the electromagnetic ultrasonic guided wave and its propagation time within the overhead transmission line; acquisition of the correlation between the amplitude of the electromagnetic ultrasonic echo signal and the depth of the transmission line damage, as well as the correlation between the energy of the electromagnetic ultrasonic echo signal and the lateral length of the transmission line damage, based on the correlation between the electromagnetic ultrasonic echo signal and the transmission line damage; and calculation of the percentage of the transmission line damage section corresponding to the electromagnetic ultrasonic echo signal, thus completing the detection of the degree of transmission line damage. This method can accurately detect the location, depth, and lateral length of transmission line damage; it allows for manual identification and monitoring of the degree of transmission line damage, facilitating early diagnosis of transmission lines before faults occur, and has the advantage of low cost.

Description

Technical Field

[0001] This invention belongs to the field of power transmission line defect detection technology, specifically relating to a damage detection method for overhead power transmission lines based on electromagnetic ultrasound. Background Technology

[0002] As a crucial component of the power system, overhead transmission lines span long distances, responsible for transmitting electrical energy within the system. Throughout their entire service life, overhead transmission lines are exposed to various factors, such as operational factors (applied tensile and voltage stresses) and environmental factors (wind-induced vibration, icing, and lightning strikes). These external factors, and even structural defects inherent in the manufacturing process of the overhead transmission lines themselves, can lead to mechanical failures (torsion / cracks / breakage) and corrosion, resulting in significant economic losses. Therefore, the health of overhead lines is directly related to the reliability of electricity supply for countless households.

[0003] Inspecting and monitoring the integrity of overhead transmission lines is a crucial aspect of facility maintenance and helps predict their lifespan. The traditional method for detecting defects in transmission lines is visual inspection. While simple and easy to implement, this method only observes external damage and cannot detect early-stage defects, resulting in low accuracy. Furthermore, the long inspection distances can cause eye fatigue, leading to significant workload for inspectors.

[0004] In addition, there are optical methods, infrared detection methods, X-ray detection methods, and radio wave detection methods. Optical methods, which use optical cameras and manual identification to identify defects in transmission lines, still have limitations in accuracy. Infrared detection methods are highly sensitive to ambient temperature, making them unsuitable for inspection in autumn and winter, and they are insensitive to micro-defects. X-ray detection methods can distinguish the internal structure, assembly condition, presence, nature, and size of defects in the inspected cross-section based on the grayscale of the image, but miniaturization of the detection equipment used is difficult, posing challenges to the storage and transmission of detection data. Eddy current detection methods determine damage and defects based on the direction of the receiving electromagnetic wave antenna and the intensity of the electromagnetic waves, but they have poor anti-interference capabilities, low sensitivity, and require on-site, point-by-point inspection of the transmission line.

[0005] For the reasons mentioned above, there are still significant technical and economic challenges in using effective diagnostic equipment and solutions to assess the integrity of power transmission lines. Summary of the Invention

[0006] To address the shortcomings of existing methods for inspecting and testing power transmission lines, such as poor anti-interference capabilities, high costs, and difficulty in achieving accurate measurements, this invention provides a damage detection method for overhead power transmission lines based on electromagnetic ultrasound. This method can accurately detect the location, depth, and lateral length of damage to power transmission lines, and allows for manual identification and monitoring of the extent of damage. It facilitates early diagnosis of power transmission lines before faults occur and has the advantage of low cost.

[0007] The technical solution adopted in this invention is as follows:

[0008] The damage detection method for overhead transmission lines based on electromagnetic ultrasound includes the following steps:

[0009] Step 1: Based on the attenuation and dispersion characteristics of electromagnetic ultrasonic signals in transmission lines, attenuation and dispersion compensation are performed on the electromagnetic ultrasonic signals to increase the detection distance of the electromagnetic ultrasonic signals.

[0010] Step 2: Determine the location of the damage to the transmission line based on the wave velocity of the electromagnetic ultrasonic guided wave and its propagation time within the overhead transmission line;

[0011] Step 3: Based on the electromagnetic ultrasonic echo signal, obtain the correlation between the amplitude of the electromagnetic ultrasonic echo signal and the depth of the transmission line damage; and the correlation between the energy of the electromagnetic ultrasonic echo signal and the lateral length of the transmission line damage.

[0012] Step 4: Based on the correlation between the electromagnetic ultrasonic echo signal and the transmission line damage in Step 3, calculate the percentage of the transmission line damaged section corresponding to the electromagnetic ultrasonic echo signal, and complete the detection of the degree of transmission line damage.

[0013] In step 1, the attenuation characteristics of the electromagnetic ultrasonic signal in the transmission line are expressed by the attenuation equation of the electromagnetic ultrasonic signal:

[0014] A(t)=g(t)e -αt (1);

[0015] In equation (1), A(t) is the electromagnetic ultrasonic signal in the transmission line at time t; g(t) is the electromagnetic ultrasonic signal propagating without attenuation at time t; α is the attenuation coefficient of the ultrasonic signal in the transmission line, α = α s +α α α s and α α These are the scattering attenuation coefficient and absorption attenuation coefficient of the ultrasonic signal in the transmission line, respectively, and both are constants.

[0016] The dispersion characteristics of electromagnetic ultrasonic signals in transmission lines are represented by their frequency domain equations:

[0017] G(ω)=H(ω)exp(-[α+jk(ω)]d)+E(ω)(2);

[0018] In equation (2), ω is the angular frequency; H(ω) is the Fourier transform of the electromagnetic ultrasonic excitation signal h(t); E(ω) is the noise; k is the wave number, which is the ratio of the angular frequency to the phase velocity of the electromagnetic ultrasonic guided wave. j represents the complex unit; k(ω) is the Fourier expression for the wave number. v 相 d is the phase velocity of the ultrasonic guided wave; d is the propagation distance of the ultrasonic guided wave, and d = vt, where v is the wave velocity and t is the propagation time.

[0019] In step 1, the electromagnetic ultrasonic signal is attenuated and its dispersion is compensated, specifically as follows:

[0020] For signals that attenuate in practice Sampling is performed, and attenuation compensation is applied using equation (3):

[0021]

[0022] In equation (3), exp(αt) is the compensation equation for the signal.

[0023] Therefore, for each wave mode, the electromagnetic ultrasonic signal with the i-th propagation time or distance is subjected to dispersion compensation in the frequency domain using equation (4):

[0024] Y(ω,t i )=G(ω)exp(j[k(ω)d(t i )-ωt i ]) (4);

[0025] In equation (4), Y(ω,t) i ) represents the electromagnetic ultrasonic signal after propagation time dispersion compensation for the i-th time; d(t) i ) represents the waveguide propagation distance at the i-th time; t i Let i be the i-th propagation time.

[0026] In step 2, the method for determining the location of the damage to the transmission line is shown in equation (5):

[0027]

[0028] In equation (5), T represents the propagation time of electromagnetic ultrasound in the transmission line as recorded in the experiment; v represents the propagation speed of electromagnetic ultrasound in the transmission line; and d represents the distance between the damaged location of the transmission line and the electromagnetic ultrasound receiver / transmitter.

[0029] In step 3, the correlation between the amplitude of the electromagnetic ultrasonic echo signal and the depth of damage to the transmission line is obtained. The specific method is as follows:

[0030] By measuring the electromagnetic ultrasonic amplitude in transmission lines with different damage depths, the relationship between the electromagnetic ultrasonic echo signal amplitude in the transmission line and the depth of the damage is fitted as follows:

[0031] I = -9.235e-5d 3 +0.004938d 2 +0.01098d-0.0141(6);

[0032] In equation (6), d represents the depth of the transmission line damage, and I represents the echo amplitude after the electromagnetic ultrasonic guided wave signal interacts with the corresponding transmission line damage.

[0033] The correlation between electromagnetic ultrasonic echo signal energy and the transverse length of transmission line damage was obtained using the following method:

[0034] By measuring the electromagnetic ultrasonic amplitude in transmission lines damaged to different lateral lengths, the relationship between the electromagnetic ultrasonic echo signal energy and the lateral length of the transmission line damage was fitted as follows:

[0035] E = 0.0006173l 2 +0.00213x 2 +0.000746(7);

[0036] In equation (7), l is the transverse length of the power transmission line damage; E is the energy of the electromagnetic ultrasonic echo signal.

[0037] In equations (6) and (7) above, the relationships are curves fitted from multiple data points. The so-called curve fitting method is to establish data relationships from given discrete data points; the mathematical model calculates a series of tiny straight line segments and connects these interpolation points into a curve. As long as the interval between the interpolation points is chosen properly, a smooth curve can be formed. This can generally be accomplished using the Matlab toolbox.

[0038] In step 3, the formula for calculating the electromagnetic ultrasonic echo signal energy is as follows:

[0039]

[0040] In equation (8), t1 is the start time of detecting the transmission line defect echo signal; t2 is the end time of detecting the transmission line defect echo signal. is the normalized ultrasonic detection signal; E is the energy of the electromagnetic ultrasonic echo signal.

[0041] In step 4, the formula for calculating the percentage of damaged cross-section of the transmission line corresponding to the electromagnetic ultrasonic echo signal is as follows:

[0042]

[0043] In equation (9), β is the percentage of the damaged section of the transmission line, S is the cross-sectional area of ​​the transmission line, d is the depth of the damage to the transmission line, and l is the lateral length of the damage to the transmission line.

[0044] This invention provides a damage detection method for overhead transmission lines based on electromagnetic ultrasound, with the following advantages:

[0045] 1) The transmission line damage detection method of the present invention is applied to the detection of transmission line damage in the transmission line system. With the attenuation compensation and dispersion compensation of the ultrasonic guided wave signal, it can simultaneously detect the damage location and cross-sectional damage percentage of the transmission line, and the detection accuracy is high.

[0046] 2) This invention can determine the location of damage by the propagation speed of electromagnetic ultrasonic guided wave signals and their propagation time in the transmission line. At the same time, it can also fit the relationship curves between the amplitude of electromagnetic ultrasonic echo signals and the depth of damage in the transmission line and the relationship between the energy of electromagnetic ultrasonic echo signals and the transverse length of damage in the transmission line based on the correlation between the amplitude of electromagnetic ultrasonic echo signals and the depth of damage in the transmission line and the relationship curves between the energy of electromagnetic ultrasonic echo signals and the transverse length of damage in the transmission line, so as to accurately detect the location of damage and the percentage of damage in the cross section.

[0047] 3) The entire detection method of this invention is innovative and low in cost, eliminating the need for manual identification and monitoring of the degree of damage to corroded grounding electrodes. 4) This invention can determine the degree of local damage to grounding electrodes based on a fitting function, which facilitates timely understanding of the transmission line status and early diagnosis of transmission lines before faults occur. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the detection method of the present invention.

[0049] Figure 2 The signal diagram before compensation.

[0050] Figure 3 The signal diagram is after compensation.

[0051] Figure 4 The signal image received for detecting a defect 2.5m away from an electromagnetic ultrasonic signal transmitter (receiver).

[0052] Figure 5 This is a graph showing the relationship between the depth of damage to the transmission line and the amplitude of the electromagnetic ultrasonic echo.

[0053] Figure 6 This is a graph showing the relationship between the transverse length of power transmission line damage and the energy of electromagnetic ultrasonic echo signals.

[0054] Figure 7 This is a cross-sectional view of the damaged section of the power transmission line.

[0055] Figure 8(1) is a schematic diagram of the connection of the detection system of the present invention;

[0056] Figure 8(2) is a schematic diagram of the cross section at point A in Figure 8(1);

[0057] Figure 8(3) is a magnified view of part B in Figure 8(2);

[0058] Figure 8(4) is a schematic diagram of the arrangement of magnets and silicon steel plates.

[0059] Figure 9 This is a diagram showing the actual test results. Detailed Implementation

[0060] A method and system for detecting damage to overhead transmission lines (ACSR) based on electromagnetic ultrasound is proposed. This method achieves long-distance detection of electromagnetic ultrasound signals through attenuation and dispersion compensation. The location of corrosion damage is determined by combining the wave velocity of the electromagnetic ultrasound guided wave and its propagation time within the overhead transmission line. Furthermore, based on the correlation between the amplitude and depth of the electromagnetic ultrasound echo signal and the lateral length of the damage, and the correlation between the energy and lateral length of the electromagnetic ultrasound echo signal, formulas are fitted to derive these relationships. Finally, the depth and lateral length of the transmission line damage corresponding to the actual electromagnetic ultrasound detection signal are obtained through these formulas, and the percentage of the damaged cross-section of the transmission line is calculated accordingly, achieving precise location and accurate detection of the damage. Figure 1 As shown, the specific steps include:

[0061] Step (1): Based on the attenuation and dispersion characteristics of the electromagnetic ultrasonic signal in the transmission line, perform attenuation compensation and dispersion compensation on the signal;

[0062] In step (1), the specific operation method for attenuation compensation and dispersion compensation of the electromagnetic ultrasonic signal is as follows: reverse compensation is performed on the electromagnetic ultrasonic signal based on its attenuation characteristics and dispersion characteristics in the transmission line.

[0063] For signals that attenuate in practice Sampling is performed and attenuation compensation is applied to (1) using formula:

[0064]

[0065] Therefore, for each wave mode and the electromagnetic ultrasonic signal with the i-th propagation time (or distance), dispersion compensation is performed in the frequency domain using equation (4):

[0066] Y(ω,t i )=G(ω)exp(j[k(ω)d(t i )-ωt i ])(4);

[0067] Where d is the propagation distance of the electromagnetic ultrasonic signal.

[0068] like Figure 2 and Figure 3 As shown, Figure 2 The signal before compensation. Figure 3 The signal after compensation is significantly improved compared to the original signal. This ensures that electromagnetic ultrasonic signals can be detected over long distances in power transmission lines.

[0069] Step (2): The specific operation method for obtaining the correlation between the electromagnetic ultrasonic echo signal and the damage location of the transmission line based on the electromagnetic ultrasonic echo signal is as follows: the damage location of the transmission line is determined based on the wave speed of the electromagnetic ultrasonic signal and its propagation time in the transmission line.

[0070] The method for determining the location of damage to a power transmission line based on the wave velocity of the electromagnetic ultrasonic signal and its propagation time in the transmission line is as follows:

[0071]

[0072] Where T represents the propagation time of the electromagnetic ultrasound in the transmission line as recorded in the experiment, v represents the propagation speed of the electromagnetic ultrasound in the transmission line, and d represents the distance between the damaged location of the transmission line and the electromagnetic ultrasound receiver (transmitter).

[0073] The received signal is obtained when detecting a defect 2.5m away from the electromagnetic ultrasonic signal transmitter (receiver). Figure 4 As shown, through Figure 4 The propagation time of the pulse wave in the grounding electrode can be obtained as T = 0.097 ms, and the ultrasonic signal wave velocity is 5200 m / s; thus, the distance between the transmitter and the defect can be obtained as d = 2.522 m, with an error of only 0.87%.

[0074] Step (3): Based on the electromagnetic ultrasonic echo signal, obtain the correlation between the amplitude of the electromagnetic ultrasonic echo signal and the damage depth of the transmission line. Specifically, this is done by measuring the corresponding electromagnetic ultrasonic amplitude in transmission lines with different damage depths; for example... Figure 5 As shown, the relationship between the amplitude of the electromagnetic ultrasonic echo signal in the transmission line and the depth of the transmission line damage is fitted using Matlab:

[0075] I = -9.235e-5d 3 +0.004938d 2 +0.01098d-0.0141(6);

[0076] Where d represents the depth of the transmission line damage, and I represents the echo amplitude after the electromagnetic ultrasonic guided wave signal interacts with the corresponding transmission line damage.

[0077] Step (4): Based on the electromagnetic ultrasonic echo signal, obtain the correlation between the electromagnetic ultrasonic echo signal energy and the transverse length of the transmission line damage. The specific method is as follows:

[0078] By measuring the corresponding electromagnetic ultrasonic amplitudes in transmission lines damaged at different lateral lengths, such as... Figure 6 As shown, the relationship between the electromagnetic ultrasonic echo signal energy and the transverse length of the transmission line damage, fitted using Matlab, is as follows:

[0079] E = 0.0006173l 2 +0.00213x 2 +0.000746(7);

[0080] Where l is the transverse length of the power line damage, and E is the energy of the electromagnetic ultrasonic echo signal.

[0081] Specifically, the formula for calculating the energy of electromagnetic ultrasonic echo signals is as follows:

[0082]

[0083] Where t1 is the start time of detecting the echo signal of the transmission line defect, and t2 is the end time of detecting the echo signal of the transmission line defect. E represents the normalized ultrasonic detection signal, and E represents the energy of the electromagnetic ultrasonic echo signal.

[0084] Step (5): Based on the correlation between the electromagnetic ultrasonic signal in the transmission line and the depth of damage to the transmission line, and the correlation between the electromagnetic ultrasonic signal energy and the transverse length of the damage to the transmission line, the percentage of the damaged section of the transmission line corresponding to the actual detected electromagnetic ultrasonic echo signal is obtained, thus completing the detection of the degree of damage to the transmission line.

[0085] The specific method for calculating the percentage of damaged cross-section of transmission lines corresponding to actual detected electromagnetic ultrasonic echo signals is as follows:

[0086]

[0087] Where β is the percentage of the transmission line damaged cross section, S is the cross-sectional area of ​​the transmission line, d is the depth of the transmission line damage, and l is the lateral length of the transmission line damage.

[0088] Taking ACSR-720 / 50 as an example, such as Figure 4 The mid-echo signal amplitude is approximately 2V, and the calculated echo energy is 0.02. Based on... Figure 5 , Figure 6 The damage depth was found to be d = 27 mm, the transverse length of the damage was l = 2 mm, and the total damage area (S) was 775.41 mm. 2，The percentage of damaged cross section of the transmission line calculated by equation (9) is β = 6.964%.

[0089] Verification Example:

[0090] This example provides a transmission line damage detection system based on electromagnetic ultrasonic method, specifically applying the aforementioned transmission line damage detection method based on electromagnetic ultrasonic method to transmission line damage detection.

[0091] As shown in Figures 8(1), 8(2), and 8(3), the power transmission line damage detection system includes an AFG-2022B signal generator, a GA-2500A power amplifier, an impedance matching box, an ATA-5000 preamplifier, a TBS100C oscilloscope, and an electromagnetic ultrasonic transducer.

[0092] Figure 8(3) includes two N42 permanent magnets and a signal transmitting coil; the signal transmitting coil is a multi-turn wound coil.

[0093] Where: a is silicon steel plate, b is overhead transmission line, c is multi-turn wound coil, d is N42 permanent magnet, where: the blue part is the N pole of the magnet, the red part is the S pole of the magnet, as shown in Figure 8(4).

[0094] During installation, if Figure 8(2) and 8(3) As shown, a multi-turn wound coil c is wound on an overhead transmission line b; three I-shaped magnets (consisting of two N42 magnets d and a silicon steel plate a) are placed equidistantly (one every 120°) on the same section of the overhead transmission line b; during testing, an excitation power supply is provided to the multi-turn wound coil c.

[0095] A multi-turn wound coil c is connected to a preamplifier, and the preamplifier is connected to an oscilloscope.

[0096] A multi-turn wound coil is connected to an impedance matching box, which is then connected to a power amplifier, which in turn is connected to a signal generator.

[0097] The pulse echo signal generator emits a bipolar six-cycle square wave pulse with a peak value of 10 volts and a frequency of 200 kHz as the excitation signal to excite the electromagnetic ultrasonic transducer to generate ultrasonic guided waves in the transmission line. The ultrasonic guided waves are amplified and then drive the electromagnetic ultrasonic transducer to emit ultrasonic guided waves. The echo vibration signal is received by the ultrasonic transducer, filtered, and amplified, with a maximum gain of 80 dB. Finally, the data is recorded using an oscilloscope. The actual detection results are as follows: Figure 9 As shown. Figure 9 The detection effect is obvious, and clear defect echoes can be obtained, which facilitates the quantitative analysis of defects in the later stage.

Claims

1. A damage detection method for overhead transmission lines based on electromagnetic ultrasound, characterized in that... Includes the following steps: Step 1: Based on the attenuation and dispersion characteristics of electromagnetic ultrasonic signals in transmission lines, attenuation and dispersion compensation are performed on the electromagnetic ultrasonic signals. Step 2: Determine the location of the damage to the transmission line based on the wave velocity of the electromagnetic ultrasonic guided wave and its propagation time within the overhead transmission line; Step 3: Based on the electromagnetic ultrasonic echo signal, obtain the correlation between the amplitude of the electromagnetic ultrasonic echo signal and the depth of the transmission line damage; and the correlation between the energy of the electromagnetic ultrasonic echo signal and the lateral length of the transmission line damage. Step 4: Based on the correlation between the electromagnetic ultrasonic echo signal and the transmission line damage in Step 3, calculate the percentage of the transmission line damaged section corresponding to the electromagnetic ultrasonic echo signal, and complete the detection of the degree of transmission line damage. In step 3: the correlation between the amplitude of the electromagnetic ultrasonic echo signal and the depth of damage to the transmission line is obtained, and the specific method is as follows: By measuring the electromagnetic ultrasonic amplitude in transmission lines with different damage depths, the relationship between the electromagnetic ultrasonic echo signal amplitude in the transmission line and the depth of the damage is fitted as follows: （6）； In equation (6), d Indicates the depth of damage to the power transmission line. I This represents the echo amplitude after the electromagnetic ultrasonic guided wave signal interacts with the corresponding power transmission line damage. The correlation between electromagnetic ultrasonic echo signal energy and the transverse length of transmission line damage was obtained using the following method: By measuring the electromagnetic ultrasonic amplitude in transmission lines damaged to different lateral lengths, the relationship between the electromagnetic ultrasonic echo signal energy and the lateral length of the transmission line damage was fitted as follows: （7）； In equation (7), l The transverse length of the transmission line damage; E The energy of electromagnetic ultrasonic echo signals; In step 4, the formula for calculating the percentage of damaged cross-section of the transmission line corresponding to the electromagnetic ultrasonic echo signal is as follows: （9）； In equation (9), This represents the percentage of the transmission line's cross-sectional area damaged. S This refers to the cross-sectional area of ​​the transmission line. d The depth of damage to the transmission line. l This represents the lateral length of the damage to the power transmission line.

2. The damage detection method for overhead transmission lines based on electromagnetic ultrasound according to claim 1, characterized in that: In step 1, the attenuation characteristics of the electromagnetic ultrasonic signal in the transmission line are expressed by the attenuation equation of the electromagnetic ultrasonic signal: （1）； In equation (1), A ( t )for t Electromagnetic ultrasonic signals in the transmission line at all times; for t Electromagnetic ultrasonic signals that propagate without attenuation at all times; The attenuation coefficient of ultrasonic signals in the transmission line is denoted as . , and These are the scattering attenuation coefficient and absorption attenuation coefficient of the ultrasonic signal in the transmission line, respectively. The dispersion characteristics of electromagnetic ultrasonic signals in transmission lines are represented by their frequency domain equations: （2）； In equation (2), Angular frequency; It is the electromagnetic ultrasonic excitation signal h( t Fourier transform of ) For noise; k The wave number is the ratio of the angular frequency to the phase velocity of the electromagnetic ultrasonic guided wave. Indicates the complex unit; The Fourier expression for the wavenumber. , The phase velocity of the ultrasonic guided wave; Let be the propagation distance of the ultrasonic guided wave, and , v For wave speed, t For the duration of transmission.

3. The damage detection method for overhead transmission lines based on electromagnetic ultrasound according to claim 2, characterized in that: In step 1, the electromagnetic ultrasonic signal is attenuated and its dispersion is compensated, specifically as follows: For signals that attenuate in practice Sampling is performed, and attenuation compensation is applied using equation (3): （3）； In equation (3), This is a compensation formula for the signal; Therefore, for each wave mode, the first i Electromagnetic ultrasonic signals with a propagation time or distance are subjected to dispersion compensation in the frequency domain using equation (4): （4）； In equation (4), This represents the electromagnetic ultrasonic signal after propagation time dispersion compensation for the i-th time. This represents the propagation distance of the guided wave at the i-th time. Let i be the i-th propagation time.

4. The damage detection method for overhead transmission lines based on electromagnetic ultrasound according to claim 1, characterized in that: In step 2, the method for determining the location of the damage to the transmission line is shown in equation (5): （5）； In equation (5), T represents the propagation time of the electromagnetic ultrasonic wave in the transmission line as recorded in the experiment; v This indicates the propagation speed of electromagnetic ultrasonic waves in power transmission lines; d This indicates the distance between the location of the power line damage and the electromagnetic ultrasonic receiver / transmitter.

5. The damage detection method for overhead transmission lines based on electromagnetic ultrasound according to claim 1, characterized in that: In step 3, the formula for calculating the electromagnetic ultrasonic echo signal energy is as follows: （8）； In equation (8), t 1 represents the start time of detecting the echo signal of a defect in the transmission line; t 2 represents the end time of the detected transmission line defect echo signal; The normalized ultrasonic detection signal; E It represents the energy of the electromagnetic ultrasonic echo signal.

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