Optical high-voltage sensor based on two-stage lever amplification mechanism

Abstract

The invention belongs to the technical field of optical high-voltage sensors, and discloses an optical high-voltage sensor based on a two-stage lever amplification mechanism, which comprises a piezoelectric crystal, an electrode plate, the two-stage lever amplification mechanism, a fiber bragg grating, a fiber bragg grating demodulator and a data acquisition and processing module. The working process is as follows: when voltage acts on the electrode plate connected with the piezoelectric crystal, the inverse piezoelectric effect can cause the piezoelectric crystal to generate strain, the secondary lever amplification mechanism amplifies the strain and outputs the strain in an amplification area, and after the grating part of the fiber grating is subjected to external stress, the periodic distribution of the grating can be changed, so that the Bragg reflection wavelength is changed; and the central wavelength change of the reflected light can be detected by the grating fiber demodulator and is transmitted to the data acquisition and processing module to obtain the voltage on the electrode plate. The sensor provided by the invention has more than 10 times of strain amplification capability, and has excellent linear performance, wider dynamic range, lighter weight, smaller volume and higher safety.

Description

Technical Field

[0001] The invention belongs to the technical field of optical high-pressure sensors, and in particular relates to an optical high-pressure sensor based on a secondary lever amplification mechanism. Background Art

[0002] Instrument transformers are widely used in high-voltage equipment in substations, including voltage transformers (PT) and current transformers (CT). They provide accurate signals for protection, control and metering systems. This places strict requirements on the accuracy and reliability of instrument transformers. Since their introduction, instrument transformers have performed reliably in overvoltage and overcurrent protection. However, since existing instrument transformer equipment is made of materials such as copper, ceramics and iron, and is filled with oil, it is not only bulky, but also may explode, causing nearby equipment to be damaged by ceramic fragments, and even endangering the safety of substation workers.

[0003] The Faraday effect (magneto-optical effect) and the Poeckel effect (electro-birefringence effect) were proposed in 1845 and 1893, respectively. Since the 1990s, optical voltage and current sensing systems based on the above two effects have been widely used in high-voltage substations as candidate technologies to replace traditional CT and PT. Optical voltage sensors have many advantages over traditional inductive and capacitive PTs, including excellent linear performance, wider dynamic range, lighter weight, smaller size and higher safety. However, the system components of the Faraday effect and the Poeckel effect are unstable under temperature and stress changes, and complex compensation techniques or special optical fibers are required to ensure their reliability. In addition, Poeckel effect sensors usually use bulk crystals such as lithium niobate, which requires an open optical system including lenses and polarization filters, resulting in unstable and difficult to align systems. More importantly, this emerging technology is expensive to purchase and requires professional skills for maintenance.

[0004] In recent years, the voltage transformer technology based on fiber Bragg grating (FBG) has been fully studied and developed. Researchers convert voltage signals into strain signals based on the inverse piezoelectric effect of piezoelectric crystals such as lead zirconate titanate, and use FBG to sense the strain signals. Piezoelectric ceramics have the characteristics of high linearity and fast response speed. However, the elongation of piezoelectric ceramics greatly restricts the minimum detection limit. CN110780104A improves the output linearity of the inverse piezoelectric optical voltage sensor by optimizing the grating parameters, but does not amplify the original strain signal. However, with the diversification and complexity of application requirements, this type of sensor faces the challenge of further optimization: sensitivity limitation: the mechanical response ability of piezoelectric materials is limited. When the voltage signal is small, its deformation is difficult to significantly modulate the optical grating characteristics, thereby limiting the sensitivity of the sensor. Constraints on the detection limit: In micro-voltage or low-voltage signal detection scenarios, grating modulation signals may be difficult to be effectively captured. Insufficient adaptability: In the face of special application scenarios (such as low-noise measurement requirements in high-voltage transmission systems), existing designs are difficult to balance high sensitivity and compactness. Therefore, designing a strain amplification mechanism provides an effective way to improve the performance of the sensor. Summary of the invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, an object of the present invention is to provide an optical high-pressure sensor based on a two-stage lever amplification structure.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] An optical high-voltage sensor based on a two-stage lever amplification mechanism comprises a piezoelectric crystal (1), an electrode plate (2) (with leads), a two-stage lever amplification mechanism (3), a fiber Bragg grating (4), a fiber Bragg grating demodulator (5), and a data acquisition and processing module (6);

[0008] A specific area of ​​the piezoelectric crystal (1) is connected to the electrode plate (2) and abuts against the inside of the secondary lever amplification mechanism (3), and both ends of the grating part of the fiber grating (4) are fixed to the amplification area of ​​the secondary lever amplification mechanism (3);

[0009] The fiber Bragg grating (4) is connected to a fiber Bragg grating demodulator (5), and the fiber Bragg grating demodulator (5) is connected to a data acquisition and processing module (6);

[0010] The optical signal emitted by the fiber Bragg grating demodulator (5) is transmitted to the grating area through the optical fiber part of the fiber Bragg grating (4). The grating reflects light of a specific wavelength according to the Bragg condition, while allowing light of other wavelengths to pass through. The reflected optical signal is transmitted to the fiber Bragg grating demodulator (5) through the original optical fiber path, and finally reaches the data acquisition and processing module (6).

[0011] Preferably, the working process of the optical high-pressure sensor based on the secondary lever amplification mechanism is as follows:

[0012] When voltage is applied to an electrode plate (2) connected to a piezoelectric crystal (1), the inverse piezoelectric effect causes strain in the piezoelectric crystal (1), and a secondary lever amplification mechanism (3) amplifies the strain and outputs it in an amplified region. When the grating portion of the fiber grating (4) is subjected to external stress, the periodic distribution of the grating is changed, thereby changing the Bragg reflection wavelength. The change in the central wavelength of the reflected light is detected by a grating fiber demodulator (5) and transmitted to a data acquisition and processing module (6) to obtain the voltage on the electrode plate (2).

[0013] Preferably, the secondary lever amplification mechanism (3) is provided with a primary lever and a secondary lever, the lever arm of the primary lever is BC, the lever arm of the secondary lever is DE, the output of the primary lever is the input of the secondary lever, and the end of the secondary lever amplifies the strain and outputs it in the amplification area.

[0014] Preferably, the electrode plate (2) comprises electrode plates (2-1) and (2-2), which are coated or pasted on specific areas of the piezoelectric crystal (1) and connected with leads, and the specific areas are preferably the upper and lower surfaces of the piezoelectric crystal (1);

[0015] The primary lever abuts against the electrode plate (2-1), and the electrode plate (2-2) abuts against the secondary lever amplification mechanism (3).

[0016] Preferably, the piezoelectric crystal (1) is one of PZT series ceramics, perovskite series ceramics, and potassium sodium niobate-based ceramics.

[0017] Preferably, the PZT series ceramics include PZT-4, PZT-5a, PZT5b, PZT-5h, and PZT-6;

[0018] The perovskite series ceramics include BaTiO3 and SrTiO3;

[0019] The potassium sodium niobate-based ceramic includes KNN.

[0020] Preferably, the piezoelectric crystal (1) is a cylinder with a diameter of 6 to 40 mm and a height of 30 to 300 mm.

[0021] Preferably, the secondary lever amplification mechanism (3) is made of one of photosensitive resin, polylactic acid and nylon, and is prepared by photocuring 3D printing, and is more preferably made of acrylate.

[0022] The technical principle of voltage transformer based on PZT and FBG is as follows:

[0023] When PZT is subjected to an electric field, its dimensions change, and the amount of deformation is a function of the applied voltage, polarization direction / degree, and the crystal structure of the PZT ceramic. The electromechanical equation for the inverse piezoelectric effect of PZT is

[0024]

[0025] Where ΔX / X is the strain of the PZT material, E is the electric field applied to the PZT electrode, is the piezoelectric strain coefficient, i represents the crystal polarization direction, and j is the Cartesian coordinate. The polarization direction (axis 3) depends on the electrode to which the voltage is applied. In a cylindrical PZT with electrodes coated on the upper and lower surfaces, d33 represents the axial displacement, i.e., the growth of the cylinder.

[0026] In a fiber Bragg grating, light transmitted along the fiber core is slightly reflected by each grating layer due to the periodic variation of the refractive index. These light waves reflected from each grating layer interfere with each other in opposite directions. This interference can be constructive or destructive, depending on whether the wavelength of the incident light meets the Bragg condition, which can be expressed by the following formula:

[0027] λ B =2nΛ (2)

[0028] Where n is the average refractive index of the fiber core; Λ is the grating period, that is, the distance between consecutive grating planes. B is the Bragg wavelength, i.e. the wavelength of light reflected by the grating. Formula (2) also reveals the relationship between the Bragg wavelength and Λ and the average refractive index n. When the axial deformation caused by external force can change Λ and n, n changes through the photoelastic effect, while Λ changes due to the increase of the grating spacing.

[0029] As a portable sensor, we ignore the effect of thermal expansion on the grating parameters. The relationship between the Bragg wavelength and strain satisfies

[0030] Δλ B / λ B =(1-ρ e )ε z (3)

[0031] ε z is the longitudinal strain, ρ e is the photoelastic coefficient. For silica fiber with a germanium-doped core, ρ e =0.22. At the center wavelength of 1550nm, the sensitivity of the grating to strain is

[0032]

[0033] pm is the relative change of Bragg wavelength Δλ Bis the unit symbol of displacement, μ∈ is the unit symbol of relative displacement change Δε (microstrain). Since Δε is very small, scientific notation is introduced10 -6 To represent microstrain, the symbol is μ∈.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] (1) The present invention breaks through the bottleneck of sensitivity. By introducing a secondary lever structure, the strain amplification mechanism effectively amplifies the mechanical deformation amplitude generated by the piezoelectric material, achieving an amplification of the displacement of the piezoelectric ceramic by more than 10 times, making the modulation characteristics of the optical grating more significant, greatly improving the sensor's response ability to voltage signals, and reducing the requirements for the inverse piezoelectric performance of the PZT material and the resolution of the grating demodulator.

[0036] (2) The present invention can achieve low-voltage and high-precision measurement. The two-stage lever mechanism greatly improves the detection capability of the sensor, especially in low-voltage signal scenarios, enabling the sensor to break through the existing detection limit, capture weak voltage fluctuations, and meet more precise application requirements.

[0037] (3) The sensor of the present invention also has the advantages of optical voltage sensors, including excellent linear performance, wider dynamic range, lighter weight, smaller size and higher safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a two-stage lever optical voltage sensor.

[0039] Figure 2 It is the deformation displacement distribution of the sensing structure when 400V voltage is applied.

[0040] Figure 3 The relationship between the deformation displacement and the applied DC voltage in the simulation (left), and the relationship between the central wavelength offset of the fiber Bragg grating reflected light and the applied voltage (right).

[0041] Figure 4 The relationship between the center wavelength offset of the fiber Bragg grating reflected light and the amplitude of the applied DC voltage in actual experiments.

[0042] Figure 5 (a) 1Hz sine wave (b) 10Hz sine wave (c) 1Hz ECG waveform voltage measurement results, amplitude 120V. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto. For process parameters not particularly noted, conventional techniques may be used.

[0044] A two-stage lever-type amplification mechanism is used to amplify the output displacement of the piezoelectric ceramic. The working principle is as follows: Figure 1 As shown. Point B is equivalent to the fulcrum of the first-stage lever, and the piezoelectric ceramic output force acts on point A, causing the end point C of the lever to produce a displacement after the first stage of amplification. In the second-stage lever deformation, point D is equivalent to the fulcrum, and the output point C of the first stage amplification serves as the input point of the second stage amplification, pushing the lever arm DE to deflect around point D, and producing the final output displacement (up to 10 times or more) at the end point E of the second stage amplification.

[0045] Example 1

[0046] The cylindrical piezoelectric sensing material PZT-5a is selected, with a diameter of 10mm and a height of 60mm. The overall height × length × width of the secondary lever is 80*40*10mm. The material is acrylic, and it is made by light-curing 3D printing. The printer parameters are: printing accuracy 0.1mm, layer thickness 0.05mm, and polyacrylate after molding. The length of the primary lever is 15mm, the magnification is 2, and the length of the secondary lever is 30mm, and the magnification is 5. The two ends of the grating are fixed at points E and F with glue. The basic performance parameters of different materials are shown in Table 1.

[0047] Table 1 Basic parameters of sensor materials

[0048]

[0049] In the simulation software, the G electrode is grounded and a DC voltage U (0-400V) is applied to the A electrode to obtain the overall deformation and stress distribution of the sensing structure, such as Figure 2 The figure shows the deformation displacement distribution cloud diagram when the applied voltage is 400 V. The displacement of point E is extracted to obtain the relationship between the displacement and the applied voltage. The relationship between the central wavelength offset of the fiber Bragg grating reflected light and the applied voltage is further transformed, as shown in Figure 3 The red curve shows

[0050] In the actual experiment, the G electrode of the sensor is grounded, and a DC voltage U (0-600V) is applied to the A electrode. The reflected light signal of the grating is collected by a grating demodulator to obtain the center wavelength offset Δλ. B The relationship with the applied voltage U is as follows: Figure 4 As shown by the red line, the linearity is excellent.

[0051] In the actual experiment, the G electrode of the sensor is grounded, and a 120V 1Hz sine wave, a 10Hz sine wave, and a 1Hz electrocardiogram waveform voltage are applied to the A electrode to obtain the central wavelength offset Δλ of the reflected light of the grating between EF B changes, such as Figure 5 As shown, it is confirmed that the structure has good frequency following ability.

[0052] Comparative Example 1

[0053] Choose cylindrical piezoelectric sensing material PZT-5a, with a diameter of 10mm and a height of 60mm. Use acrylic as the shell material, without using a lever structure, and fix the fiber Bragg grating directly on both ends of the cylindrical piezoelectric material. Figure 1 In the middle of the AG point.

[0054] In the simulation software, the G electrode is grounded and a DC voltage U (0-400V) is applied to the A electrode. The displacement of point A is extracted to obtain the relationship between the displacement and the applied voltage. The relationship between the central wavelength offset of the fiber Bragg grating reflected light and the applied voltage is further transformed, as shown in Figure 3 As shown in the blue curve, compared with Example 1, the signal is weaker, which proves that Example 1 has a strain amplification capability of >10 times.

[0055] In the actual experiment, the G electrode of the sensor is grounded, and a DC voltage U (0-600V) is applied to the A electrode. The reflected light signal of the grating is collected by a grating demodulator to obtain the center wavelength offset Δλ. B The relationship with the applied voltage U is as follows: Figure 4 As shown by the blue line, the signal is weak and the linearity is poor, which further proves that Example 1 has a strain amplification capability of >10 times.

[0056] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. An optical high-pressure sensor based on a two-stage lever amplification mechanism, characterized in that: It comprises a piezoelectric crystal (1), an electrode plate (2), a secondary lever amplification mechanism (3), a fiber Bragg grating (4), a fiber Bragg grating demodulator (5), and a data acquisition and processing module (6); A specific area of ​​the piezoelectric crystal (1) is connected to the electrode plate (2) and abuts against the inside of the secondary lever amplification mechanism (3), and both ends of the grating part of the fiber grating (4) are fixed to the amplification area of ​​the secondary lever amplification mechanism (3); The fiber Bragg grating (4) is connected to a fiber Bragg grating demodulator (5), and the fiber Bragg grating demodulator (5) is connected to a data acquisition and processing module (6); The optical signal emitted by the fiber Bragg grating demodulator (5) is transmitted to the grating area through the optical fiber part of the fiber Bragg grating (4). The grating reflects light of a specific wavelength according to the Bragg condition, while allowing light of other wavelengths to pass through. The reflected optical signal is transmitted to the fiber Bragg grating demodulator (5) through the original optical fiber path, and finally reaches the data acquisition and processing module (6).

2. The optical high-pressure sensor based on the secondary lever amplification mechanism according to claim 1, characterized in that: The working process of the optical high-pressure sensor based on the secondary lever amplification mechanism is as follows: When voltage is applied to an electrode plate (2) connected to a piezoelectric crystal (1), the inverse piezoelectric effect causes strain in the piezoelectric crystal (1), and a secondary lever amplification mechanism (3) amplifies the strain and outputs it in an amplified region. When the grating portion of the fiber grating (4) is subjected to external stress, the periodic distribution of the grating is changed, thereby changing the Bragg reflection wavelength. The change in the central wavelength of the reflected light is detected by a grating fiber demodulator (5) and transmitted to a data acquisition and processing module (6) to obtain the voltage on the electrode plate (2).

3. The optical high-pressure sensor based on the secondary lever amplification mechanism according to claim 2, characterized in that: The secondary lever amplification mechanism (3) is provided with a primary lever and a secondary lever, the force arm of the primary lever is BC, the force arm of the secondary lever is DE, the output of the primary lever is the input of the secondary lever, and the end of the secondary lever amplifies the strain and outputs it in the amplification area.

4. The optical high-pressure sensor based on the secondary lever amplification mechanism according to claim 3 is characterized in that: The electrode plate (2) includes electrode plates (2-1) and (2-2), which are coated or pasted on specific areas of the piezoelectric crystal (1) and connected with leads; The primary lever abuts against the electrode plate (2-1), and the electrode plate (2-2) abuts against the secondary lever amplification mechanism (3).

5. The optical high-pressure sensor based on the two-stage lever amplification mechanism according to claim 1, characterized in that: The piezoelectric crystal (1) is one of PZT series ceramics, perovskite series ceramics, and potassium sodium niobate-based ceramics.

6. The optical high-pressure sensor based on the two-stage lever amplification mechanism according to claim 5, characterized in that: The PZT series ceramics include PZT-4, PZT-5a, PZT5b, PZT-5h, and PZT-6; The perovskite series ceramics include BaTiO3 and SrTiO3; The potassium sodium niobate-based ceramic includes KNN.

7. The optical high-pressure sensor based on the two-stage lever amplification mechanism according to claim 5, characterized in that: The piezoelectric crystal (1) is a cylinder with a diameter of 6 to 40 mm and a height of 30 to 300 mm.

8. The optical high-pressure sensor based on the two-stage lever amplification mechanism according to claim 1, characterized in that: The secondary lever amplifying mechanism (3) is made of a material selected from the group consisting of photosensitive resin, polylactic acid and nylon, and is prepared by photocuring 3D printing.

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