Method for monitoring aeolian vibration and arch swing of low-voltage power transmission line

Abstract

The invention discloses a low-voltage power transmission line aeolian vibration and arch swing monitoring method, and relates to the technical field of power detection. According to the invention, the FBG sensors are arranged on the power transmission line, the vibration strain signals of the line are collected in real time by using a double-grating demodulation method on the premise that the central wavelength of the grating pair is determined, the vibration frequency and amplitude are analyzed by combining a frequency domain signal analysis method, and aeolian vibration and arch swing of the power transmission line are effectively monitored. The method achieves the evaluation of the operation state of the power transmission line, avoids the use of an expensive demodulation instrument, and has the advantages of electromagnetic interference resistance, long-distance monitoring, high environmental adaptability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of power detection, and particularly to a method for monitoring the aeolian vibration and bowing swing of a low-voltage transmission line. Background Technique

[0002] Aeolian vibration is one of the key challenges faced by low-voltage transmission lines during long-term operation. When a stable, low-amplitude wind continuously acts on the surface of the wire, it will excite the wire to generate high-frequency, micro-amplitude self-excited vibrations within a specific wind speed range. This continuous vibration effect will cause fatigue damage to the wire and fittings, resulting in wire strand breaks, fitting loosening, and even tower structure failure, seriously threatening the safe and stable operation of the power grid. The line faults caused by aeolian vibration account for a relatively high proportion in the operation and maintenance accidents of transmission lines, and their hidden and cumulative damage characteristics make it difficult for traditional manual inspections and regular maintenance modes to achieve precise prevention and control.

[0003] In the prior art, monitoring schemes based on traditional sensors such as accelerometers and strain gauges have defects such as electromagnetic interference sensitivity, insufficient durability, and high layout costs, and it is difficult to meet the real-time monitoring requirements of long-distance and large-scale transmission corridors. Monitoring technologies based on the principle of fiber optic sensing exhibit advantages such as anti-electromagnetic interference and distributed measurement.

[0004] Therefore, using fiber Bragg grating sensing technology to develop a new type of aeolian vibration monitoring technology for transmission lines with high sensitivity, wide dynamic range, and environmental self-adaptability, and realizing high-fidelity acquisition and intelligent analysis of vibration signals, is of great significance for improving the active protection ability of power grid infrastructure and promoting the intelligent transformation of the operation and maintenance mode of transmission lines. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for monitoring the aeolian vibration and bowing swing of a low-voltage transmission line, which has the characteristics of non-source, strong anti-electromagnetic interference ability, simple operation, and obvious effect, so as to solve the technical problems proposed in the background technique.

[0006] To achieve the above purpose, the present invention provides the following technical solution: A method for monitoring the aeolian vibration and bowing swing of a low-voltage transmission line, at least including the following steps:

[0007] S1: Define two fiber Bragg gratings as FBG1 and FBG2 respectively, and firmly install FBG1 and FBG2 on the transmission line after being respectively matched with optical circulators OC1 and OC2;

[0008] S2: Use the optical circulator OC1 and FBG1 as the sensing part, where FBG1 is used as the measurement grating. Since FBG1 is closely attached to the transmission line, FBG1 can accurately detect the strain and deformation of the transmission line caused by wind loads. When the wind load causes the wire to vibrate, this wire vibration will synchronously cause FBG1 to expand and contract, generating a deformation amount, which in turn causes a corresponding change in the central wavelength of FBG1;

[0009] S3: Use the optical circulator OC2 and FBG2 as the reference part, and use FBG2 as the reference grating. FBG2 will not be subjected to wind loads because FBG2 is mainly set to compensate for temperature effects;

[0010] S4: Set the spectral shapes of FBG1 and FBG2 to satisfy the theoretical expression of the grating reflection spectrum. The central wavelength difference between FBG1 and FBG2 should make the spectra 1 and 2 have an overlapping part. The light entering the photodetector is the light in the overlapping area. Use the photodetector to convert the optical signal into an electrical signal. When the transmission line is periodically deformed by the excitation of the gentle breeze, the overlapping area of the reflection spectra of FBG1 and FBG2 will change with the central wavelength. The intensity signal of the light in this overlapping area is captured in real time by the photoelectric detection unit, and the mapping relationship between the vibration displacement and the light intensity modulation is established;

[0011] S5: Extract the vibration frequency spectrum characteristics through fast Fourier transform, verify by combining finite element simulation, and effectively monitor the aeolian vibration and bowing swing of the transmission line by identifying the vibration frequency domain characteristics.

[0012] Further, the relationship expression between the deformation amount of FBG1 and the change in its central wavelength in S2 is as follows:

[0013]

[0014] where, λ C1 represents the central wavelength of FBG1, Δλ C1 represents the change in the central wavelength of FBG1, ΔL FBG1 represents the change in the length of FBG1, ρ e represents the elasto-optic coefficient, α represents the thermal expansion coefficient, and η represents the thermo-optic coefficient.

[0015] Further, the relationship expression between the central wavelength of FBG2 and the temperature change in S3 is as follows:

[0016]

[0017] where, λ C2 represents the central wavelength of FBG2, Δλ C2 represents the change in the central wavelength of FBG2, α represents the thermal expansion coefficient, and η represents the thermo-optic coefficient.

[0018] Furthermore, the magnitude of the area value of the overlapping region in S4 determines the magnitude of the output light intensity. Since FBG1 and FBG2 are in the same environment, the thermal expansion coefficient α and the thermo-optic coefficient η are the same. When the temperature changes, FBG1 and FBG2 are affected by the same temperature. The output light intensity depends on the overlapping region of the spectra of FBG1 and FBG2, and the overlapping region value is only related to the relative central wavelength positions of FBG1 and FBG2;

[0019] The central wavelengths of FBG1 and FBG2 are close, and the relative central wavelength positions of FBG1 and FBG2 are obtained by combining Equation (1) minus Equation (2):

[0020]

[0021] where ΔL FBG1 represents the change in the length of FBG1, and ρ e represents the elasto-optic coefficient.

[0022] Furthermore, the optical signal received by the photodetector in S4 is shown as follows:

[0023]

[0024] where S(λ B ) is the spectrum provided by the broadband laser source; FBG1(λ) and FBG2(λ) are the reflectivities of the measured FBG1 and the reference FBG2 respectively, and the upper and lower bounds of the integral are determined by the optical range provided by the broadband laser source.

[0025] Furthermore, both FBG1 and FBG2 are C-band reflective fiber Bragg gratings. Both FBG1 and FBG2 are tightly attached to the surface of the power transmission cable using tin foil tape, and an insulating tape is wrapped around the outer layer of the tin foil tape for sealing and protection. The metal ductility of the tin foil enables it to closely adhere to the cable surface, reducing the adhesive layer gap, ensuring that the vibration deformation is directly transmitted to the FBG grating area, improving the detection sensitivity. Moreover, the high thermal conductivity of the tin foil quickly balances the temperature difference between the FBG and the cable, reducing the measurement error caused by local heat accumulation. The insulating tape is used to isolate rainwater, salt spray, and ultraviolet rays, preventing the tin foil from oxidation and corrosion, and extending the outdoor service life. The double insulation design (the inner layer of tin foil is already insulated from the cable contact surface + the outer layer of tape) meets the safety specifications of the power transmission line.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] In the present invention, FBG sensors are arranged on a transmission line. On the premise that the central wavelengths of the grating pairs are determined, the vibration strain signals of the line are collected in real time by using a dual-grating demodulation method. By combining the frequency-domain signal analysis method, the vibration frequency and amplitude are analyzed, and the aeolian vibration and bow-shaped swing of the transmission line are effectively monitored, realizing the assessment of the operating state of the transmission line, avoiding the use of expensive demodulation instruments, and having advantages such as anti-electromagnetic interference, long-distance monitoring, and strong environmental adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0029] Figure 1 Schematic diagram of the method of the present invention;

[0030] Figure 2 Waveform diagram of the amplitude of the transmission line varying with time and amplitude-frequency schematic diagram under five wind speeds of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0032] Please refer to Figure 1 , the present invention is based on fiber Bragg grating (FBG), specifically a method for monitoring aeolian vibration and bow-shaped swing of a low-voltage transmission line based on fiber Bragg grating (FBG), at least including the following steps:

[0033] S1: Two fiber Bragg gratings are respectively defined as FBG1 and FBG2, and FBG1 and FBG2 are respectively cooperated with optical circulators OC1 and OC2 and firmly installed on the transmission line;

[0034] S2: The optical circulator OC1 and FBG1 are used as the sensing part, where FBG1 is used as the measuring grating. Since FBG1 is in close contact with the transmission line, FBG1 can accurately detect the strain and deformation of the transmission line caused by wind load. When the wind load causes the wire to vibrate, this wire vibration will synchronously cause FBG1 to expand and contract, generating a deformation amount, and then causing a corresponding change in the central wavelength of FBG1;

[0035] S3: Use the optical circulator OC2 and FBG2 as the reference part, and use FBG2 as the reference grating. FBG2 will not be subjected to wind loads because FBG2 is mainly set to compensate for temperature effects;

[0036] S4: Set the spectral shapes of both FBG1 and FBG2 to satisfy the theoretical expression of the grating reflection spectrum. The central wavelength difference between FBG1 and FBG2 should make the spectra 1 and 2 have an overlapping part. The light entering the photodetector is the light in the overlapping area. Use the photodetector to convert the optical signal into an electrical signal. When the transmission line is excited by a gentle breeze to generate periodic deformation, the overlapping area of the reflection spectra of FBG1 and FBG2 will change with the central wavelength. Capture the light intensity signal of this overlapping area in real time through the photoelectric detection unit, and establish the mapping relationship between vibration displacement and light intensity modulation;

[0037] S5: Extract the vibration spectrum characteristics through fast Fourier transform, and verify through finite element simulation. Effectively monitor the aeolian vibration and bowing swing of the transmission line by identifying the vibration frequency domain characteristics.

[0038] The relationship expression between the deformation amount of FBG1 in S2 and the change in its central wavelength is as follows:

[0039]

[0040] Among them, λ C1 represents the central wavelength of FBG1, Δλ C1 represents the change in the central wavelength of FBG1, ΔL FBG1 represents the change in the length of FBG1, ρ e represents the elasto-optic coefficient, α represents the thermal expansion coefficient, and η represents the thermo-optic coefficient.

[0041] The relationship expression between the central wavelength of FBG2 in S3 and the temperature change is as follows:

[0042]

[0043] Among them, λ C2 represents the central wavelength of FBG2, Δλ C2 represents the change in the central wavelength of FBG2, α represents the thermal expansion coefficient, and η represents the thermo-optic coefficient.

[0044] The size of the area value of the overlapping area in S4 will determine the size of the output light intensity. Since FBG1 and FBG2 are in the same environment, in this way, the thermal expansion coefficient α and the thermo-optic coefficient η are the same. When the temperature changes, FBG1 and FBG2 are affected by the same temperature. The output light intensity depends on the overlapping area of the spectra of FBG1 and FBG2. The overlapping area value is only related to the relative central wavelength positions of FBG1 and FBG2;

[0045] The central wavelengths of FBG1 and FBG2 are close, and the relative central wavelength positions of FBG1 and FBG2 are obtained by combining Equation (1) minus Equation (2):

[0046]

[0047] where ΔL FBG1 represents the change in the length of FBG1, and ρ e represents the elasto-optic coefficient.

[0048] The optical signal received by the photodetector in S4 is as shown in the following equation:

[0049]

[0050] where S(λ B ) is the spectrum provided by the broadband light source; FBG1(λ) and FBG2(λ) are the reflectivities of the measured FBG1 and the reference FBG2 respectively, and the upper and lower limits of the integral are determined by the optical range provided by the broadband light source.

[0051] FBG1 is placed along the transmission line. When the transmission line moves, FBG1 will also move simultaneously, and both have the same acceleration. Therefore, FBG1 can sense the movement of the transmission line, and then the relationship between the deformation of FBG1 and the vibration amplitude of the transmission line can be deduced.

[0052] The acceleration of the sensing optical fiber with mass M is the same as that of the entire transmission line. At the same time, assuming its elastic coefficient is K and the shape variable is ΔL, the force on the sensing optical fiber satisfies the following equation:

[0053] F = M·a = K·ΔL (5)

[0054] Obtained by transforming Equation (3):

[0055]

[0056] Substituting Equation (6) into Equation (5), Equation (7) can be obtained:

[0057]

[0058] where M is the mass of the sensing optical fiber and α is the acceleration of the sensing optical fiber. When the vibration displacement of the transmission line is S, the second derivative of the displacement is the acceleration, which is the same as the acceleration of the sensing FBG. From Equation (7), Equation (8) can be obtained:

[0059]

[0060] The vibration amplitude of the transmission line is proportional to the relative central wavelengths of FBG1 and 2, where is a constant term.

[0061] By substituting the relationship between ΔL in Equation (6) and the relative central wavelength into Equation (4), the relationship between the vibration amplitude and the output light intensity can be obtained, and the relationship between the vibration amplitude and the output light intensity can be described by Equation (9):

[0062]

[0063] Both FBG1 and FBG2 are C-band reflective fiber Bragg gratings. FBG1 and FBG2 are both tightly attached to the surface of the power transmission cable using tin foil tape. An insulating tape is wrapped around the outer layer of the tin foil tape for sealing and protection. The metal ductility of the tin foil enables it to closely adhere to the cable surface, reducing the adhesive layer gap, ensuring that the vibration deformation is directly transmitted to the FBG grating area, improving the detection sensitivity. Moreover, the high thermal conductivity of the tin foil quickly balances the temperature difference between the FBG and the cable, reducing the measurement error caused by local heat accumulation. The insulating tape is used to isolate rainwater, salt spray, and ultraviolet rays, preventing the tin foil from oxidation and corrosion, and extending the outdoor service life. The double-insulation design (the contact surface between the inner layer of tin foil and the cable is already insulated + the outer layer of tape) meets the safety specifications of the power transmission line.

[0064] Refer to Figure 2 :

[0065] Under different wind speeds (2 m / s, 2.5 m / s, 3 m / s, 3.5 m / s, and 4 m / s) and different wind attack angles (30° and 90°), experimental tests were carried out on the monitoring method of the aeolian vibration and the galloping of the low-voltage power transmission line based on the fiber Bragg grating (FBG).

[0066] When the wind attack angle is 90°, the galloping waveforms of the power transmission line at five wind speeds are shown in Figure 2 (a), and the aeolian vibration waveforms are shown in Figure 2 (c). Figure 2 (b) and Figure 2 (d) are the amplitude-frequency diagrams after performing FFT analysis on the waveforms in Figure 2 (a) and Figure 2 (c) respectively. As shown in Figure 2 (b), when the wind speeds are 2 m / s, 2.5 m / s, and 3 m / s, when the power transmission line undergoes galloping, the oscillation frequency of the power transmission line is 1.56 Hz; when the wind speed increases to 3.5 m / s and 4 m / s, the oscillation frequency of the power transmission line is 1.78 Hz. At the same time, the amplitude of the galloping of the power transmission line also slightly increases with the slight increase of the wind speed. As shown in Figure 2 (d), at five wind speeds, when the power transmission line undergoes aeolian vibration, the vibration frequency of the power transmission line is 5.11 Hz, and the amplitude of the aeolian vibration of the power transmission line also slightly increases with the slight increase of the wind speed. When the wind attack angle is 30°, the galloping waveforms of the power transmission line at five wind speeds are shown in Figure 2 (e), and the aeolian vibration waveforms are shown inFigure 2 (g). Figure 2 (f) and Figure 2 (h) are respectively the amplitude-frequency diagrams after performing FFT analysis on the waveforms in Figure 2 (e) and Figure 2 (g). When the wind attack angle is 30°, the variation laws of the frequency and amplitude of the aeolian vibration and the bow-shaped oscillation of the transmission line are similar to those when the wind attack angle is 90°. However, at the same wind speed, the amplitudes of the bow-shaped oscillation and the aeolian vibration of the transmission line when the wind attack angle is 30° are smaller than those when the wind attack angle is 90°, which also indicates that when the angle between the wind direction and the transmission line is 90°, the aeolian vibration and the bow-shaped oscillation of the transmission line are more obvious.

[0067] The monitoring method for aeolian vibration and bow-shaped oscillation of low-voltage transmission lines based on fiber Bragg grating (FBG) can effectively monitor the motion state of the transmission line and does not require additional methods to compensate for temperature characteristics. For the fluctuations caused by temperature, they can be effectively eliminated by optimizing the sensor structure. The experimental results show that when the transmission line experiences bow-shaped oscillation, the oscillation frequency is concentrated around 1.56 Hz; if the transmission line is in the longitudinal aeolian vibration mode, its vibration frequency is approximately around 5.11 Hz. By monitoring the vibration of the transmission line, extracting the frequency-domain characteristics of these vibration signals for analysis, abnormal conditions of the transmission line can be detected in a timely manner. This method has obvious advantages in complex environments and does not require expensive demodulation equipment.

[0068] In summary:

[0069] The method proposed by the present invention based on the design of fiber Bragg grating (FBG) can effectively monitor the aeolian vibration and bow-shaped oscillation of low-voltage transmission lines, and the calculation process is simple and the practicability is strong. Through the overall method design, the reference grating effectively eliminates the influence of environmental temperature drift on the measurement accuracy; the double-grating spectral coupling mechanism is used for demodulation to realize the direct optical intensity modulation detection of the aeolian vibration signal of the low-voltage transmission line, avoiding the use of expensive demodulators.

[0070] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to encompass all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

Claims

1. A monitoring method for aeolian vibration and bow-shaped swing of low-voltage transmission lines, characterized in that: It includes at least the following steps: S1: Two fiber Bragg gratings are respectively defined as FBG1 and FBG2. After FBG1 and FBG2 are respectively matched with optical circulators OC1 and OC2, they are firmly installed on the transmission line; S2: Optical circulator OC1 and FBG1 are used as the sensing part, where FBG1 is used as the measurement grating. Since FBG1 is in close contact with the transmission line, FBG1 can accurately detect the strain and deformation of the transmission line caused by wind load. When the wind load causes the conductor to vibrate, this conductor vibration will synchronously cause FBG1 to undergo telescopic deformation, generating a deformation amount, which in turn causes a corresponding change in the central wavelength of FBG1; S3: Optical circulator OC2 and FBG2 are used as the reference part, and FBG2 is used as the reference grating. FBG2 is not subjected to wind load because FBG2 is mainly set to compensate for temperature effects; S4: It is set that the spectral shapes of FBG1 and FBG2 satisfy the theoretical expression of the grating reflection spectrum. The central wavelength difference between FBG1 and FBG2 should make the spectra 1 and 2 have an overlapping part. The light entering the photodetector is the light in the overlapping area. The photodetector is used to convert the optical signal into an electrical signal. When the transmission line is periodically deformed by the excitation of gentle breeze, the overlapping area of the reflection spectra of FBG1 and FBG2 will change with the central wavelength. The intensity signal of the light in this overlapping area is captured in real time by the photodetection unit, and the mapping relationship between the vibration displacement and the light intensity modulation is established; S5: The vibration frequency spectrum characteristics are extracted by fast Fourier transform and verified by finite element simulation. The gentle breeze vibration and bow swing of the transmission line are effectively monitored by identifying the vibration frequency domain characteristics.

2. A method for monitoring the aeolian vibration and bowing swing of a low-voltage transmission line according to claim 1, characterized in that: The relationship expression between the deformation amount of FBG1 and the change in its central wavelength in S2 is as follows: Among them, λ C1 represents the central wavelength of FBG1, Δλ C1 represents the change in the central wavelength of FBG1, ΔL FBG1 represents the change in the length of FBG1, ρ e represents the elasto-optic coefficient, α represents the coefficient of thermal expansion, and η represents the thermo-optic coefficient.

3. A monitoring method for aeolian vibration and bow-shaped swing of a low-voltage transmission line according to claim 2, characterized in that: The relationship expression between the central wavelength of FBG2 and the temperature change in S3 is as follows: Among them, λ C2 represents the central wavelength of FBG2, Δλ C2 represents the change in the central wavelength of FBG2, α represents the coefficient of thermal expansion, and η represents the thermo-optic coefficient.

4. A method for monitoring the aeolian vibration and bow-shaped swing of a low-voltage transmission line according to claim 3, characterized in that: The size of the area value of the overlapping area in S4 will determine the size of the output light intensity. Since FBG1 and FBG2 are in the same environment, in this way, the thermal expansion coefficient α and the thermo-optic coefficient η are the same. When the temperature changes, FBG1 and FBG2 are affected by the same temperature. The output light intensity depends on the overlapping area of the spectra of FBG1 and FBG2. The overlapping area value is only related to the relative central wavelength positions of FBG1 and FBG2; The central wavelengths of FBG1 and FBG2 are close. The relative central wavelength positions of FBG1 and FBG2 are obtained by combining Equation (1) minus Equation (2): Among them, ΔL FBG1 represents the change in the length of FBG1, and ρ e represents the elasto-optic coefficient.

5. A method for monitoring the aeolian vibration and bowing swing of a low-voltage transmission line according to claim 4, characterized in that: The optical signal received by the photodetector in S4 is as shown in the following formula: where S(λ B ) is the spectrum provided by the broadband laser source; FBG1(λ) and FBG2(λ) are the reflectivities of the measurement FBG1 and the reference FBG2 respectively, and the upper and lower limits of the integral are determined by the optical range provided by the broadband laser source.

6. A method for monitoring the aeolian vibration and bow-shaped swing of a low-voltage transmission line according to claim 1, characterized in that: Both the FBG1 and FBG2 are C-band reflective fiber Bragg gratings. The FBG1 and FBG2 are both tightly attached to the surface of the power transmission cable using tin foil tape, and an insulating tape is wrapped around the outer layer of the tin foil tape for sealing and protection. The metal ductility of the tin foil enables it to closely adhere to the cable surface, reducing the adhesive layer gap, ensuring that vibration deformation is directly transmitted to the FBG grating area, improving the detection sensitivity. Moreover, the high thermal conductivity of the tin foil quickly balances the temperature difference between the FBG and the cable, reducing the measurement error caused by local heat accumulation. The insulating tape is used to isolate rainwater, salt spray, and ultraviolet rays, prevent the oxidation and corrosion of the tin foil, and extend the outdoor service life.

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