A combined optical fiber EFPI broadband PD ultrasonic detection system

Abstract

The present invention relates to a combined optical fiber EFPI broadband PD ultrasonic detection system, which comprises a light source, an optical fiber 1 / 2 optical splitter, an optical fiber, an optical fiber coupler, a first optical cable head, a first 16-core optical cable, a second optical cable head, an optical fiber EFPI sensor combined probe, a third optical cable head, a second 16-core optical cable, a fourth optical cable head, a multi-channel photoelectric detector, a first coaxial cable, a broadband signal superposition amplification device, a second coaxial cable, and a high-speed data acquisition device. Compared with the prior art, the present invention has the following advantages: it solves the problem that the current EFPI sensor under the resonant frequency operation can only be used for narrow-band measurement of ultrasonic signals, and meets the frequency band requirement of 20kHz to 500kHz for partial discharge ultrasonic signals.

Description

Technical Field

[0001] The invention relates to the field of broadband PD ultrasonic detection, and in particular to a combined optical fiber EFPI broadband PD ultrasonic detection system. Background Art

[0002] The extrinsic Fabry-Perot Interferometer (EFPI) fiber optic sensor is a high-performance ultrasonic wave detection system that uses a sensitive diaphragm structure to convert ultrasonic waves into mechanical vibrations, and then uses Fabry-Perot interferometry to convert mechanical vibrations into optical parameter changes, which are finally converted, collected, and demodulated by related instruments such as photoelectric detectors. It has been used to detect ultrasonic signals of partial discharge (PD) generated by internal insulation defects in large power equipment. Figure 1 As shown, the sensor Fabry-Perot cavity probe is generally composed of a core containing optical fiber, a circular sleeve and a sensitive diaphragm (ultrasonic coupling vibration element); the main working parameters are: the thickness of the vibrating diaphragm is h, the effective diameter of the vibrating diaphragm is 2a, the length of the Fabry-Perot cavity is l, and the reflectivity of the two reflection end faces of the Fabry-Perot cavity is R1 and R2. According to the principle of elastic mechanics, the first-order natural frequency f (resonant frequency) of the circular diaphragm that is completely constrained on all sides and the displacement of the diaphragm at its center under the pressure P generated by the ultrasonic signal, that is, the sensitivity y (S), are as follows:

[0003]

[0004]

[0005] In the formula: C is a constant; a is the effective length (radius) of the sensitive diaphragm; D is the bending stiffness; g is the acceleration of gravity; h is the thickness of the sensitive diaphragm; ρ is the density of the diaphragm material; E is the elastic modulus of the diaphragm material; μ is the Poisson's ratio of the diaphragm material.

[0006] According to equations (1) to (2), it can be concluded that after material selection, the main parameters f and y(S)y(s) of the working performance of the optical fiber EFPI sensor are determined by the thickness h of the sensitive diaphragm and the effective length (radius) a. The natural frequency f of the sensitive diaphragm is proportional to its thickness h, and inversely proportional to the square of the effective length (radius) a of the diaphragm; when the natural frequency f of the diaphragm is kept constant, the thinner the thickness h of the vibrating diaphragm, the greater the sensitivity y(S) of the diaphragm. Therefore, under the premise of ensuring that the optical fiber EFPI sensor has a certain sensitivity y(S), the frequency response curve of the developed sensor is usually as follows: Figure 2 As shown, the resonant frequency f is used as the central response frequency of the sensor, which is used for narrow-band measurement of ultrasonic signals.

[0007] Since the frequency of ultrasonic signals of PD generated by insulation defects inside power equipment is tens to hundreds of kHz, in order to avoid interference such as equipment vibration and take into account the frequency characteristics of PD ultrasonic signals generated by different defects, the power industry standard DL / T1416-2015 General Technical Conditions for Ultrasonic Partial Discharge Testers recommends that the sensor operating frequency measurement range should be 20kHz to 500kHz. This makes the existing ultrasonic detection methods and systems based on single optical fiber EFPI sensors have the problem of missed detection in practical applications, and are insensitive to ultrasonic signals generated by certain insulation defects, which can easily result in the detection results being unable to determine whether there are insulation defects, resulting in insulation breakdown accidents caused by untimely maintenance. Summary of the invention

[0008] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a combined optical fiber EFPI broadband PD ultrasonic detection system and method.

[0009] The purpose of the present invention can be achieved by the following technical solutions:

[0010] A combined optical fiber EFPI broadband PD ultrasonic detection system, the system comprising a light source, an optical fiber 1 / 2 splitter, an optical fiber, an optical fiber coupler, a first optical cable head, a first 16-core optical cable, a second optical cable head, an optical fiber EFPI sensor combination probe, a third optical cable head, a second 16-core optical cable, a fourth optical cable head, a multi-channel photoelectric detector, a first coaxial cable, a broadband signal superposition amplifier, a second coaxial cable, and a high-speed data acquisition device;

[0011] A single light source is connected to a fiber 1 / 2 splitter via an optical fiber, and after passing through the fiber 1 / 2 splitter four times, it is divided into 16 identical light source signals and sent to 16 fiber couplers. The 16 optical fibers output by the 16 fiber couplers are connected to the first 16-core optical cable through the first optical cable head to achieve 16 independent optical path connection. The fiber EFPI sensing combination probe is connected to the first 16-core optical cable through the second optical cable head to achieve 16 independent optical path connection. The 16 fiber couplers input the 16 optical signals fed back by the fiber EFPI sensing combination probe into a multi-channel photoelectric detector through the optical fiber, the third optical cable head, the second 16-core optical cable, and the fourth optical cable head in sequence. The multi-channel photoelectric detector sends 16 corresponding voltage signals to a wide-band signal superposition and amplification module through the first coaxial cable. After the voltage signal superposition is completed, it is connected to a high-speed data acquisition device through the second coaxial cable to complete the detection of ultrasonic signals.

[0012] Preferably, the light source is a DFB laser or an ASE light source or a light emitting diode LED or a super luminescent diode SLD.

[0013] Preferably, the optical fiber 1 / 2 splitter is an optical fiber device that splits the incident light from the light source into two equal paths.

[0014] Preferably, the optical fiber is a single-mode optical fiber with a core diameter of 8 μm to 10 μm and an operating wavelength λ region of 1300 nm to 1600 nm.

[0015] Preferably, the optical fiber coupler is a Y-shaped optical fiber coupler, the operating wavelength λ region is: 1300nm~1600nm, and various losses are greater than 50dB.

[0016] Preferably, the first optical cable head, the second optical cable head, the third optical cable head and the fourth optical cable head are formed by fixing 16 optical fibers in a 4×4 symmetrical arrangement using insulating tape to form an optical fiber connector with an adapter sleeve;

[0017] The first 16-core optical cable and the second 16-core optical cable are 16 independent working optical fibers matched with the first optical cable head, the second optical cable head, the third optical cable head and the fourth optical cable head.

[0018] Preferably, the optical fiber EFPI sensor assembly probe is a probe made by bonding and assembling 16 symmetrically distributed optical fiber EFPI probes with resonance frequencies of f1 to f16;

[0019] The sensitive membranes in the 16 optical fiber EFPI probes are in the same plane;

[0020] The optical fiber EFPI probe comprises a sealed circular sleeve type Fabry-Perot cavity probe and a 3D printed insulating member with a through hole, wherein the 3D printed insulating member with a through hole is used to protect and fix the sealed circular sleeve type Fabry-Perot cavity probe and facilitate overall bonding and assembly;

[0021] The resonance frequencies f1-f16 are selected according to the equally spaced resonance frequencies to achieve a wide-band response of 20kHz-500kHz.

[0022] Preferably, the multi-channel photoelectric detector is a photon detection type multi-channel conversion device, and the operating wavelength λ region is: 1300nm~1600nm;

[0023] The parameters of the high-speed data acquisition device are set as: 14-bit accuracy, 2MS / s sampling rate, and 1MHz analog bandwidth.

[0024] Preferably, the first coaxial cable and the second coaxial cable are broadband coaxial cables with a shielding layer, and the characteristic impedance is 75Ω.

[0025] Preferably, the circuit parameters of the broadband signal superposition amplification module include:

[0026] U - =U +=0 (1)

[0027] According to the virtual cutoff and Kirchhoff's law, through R1~R 16 The sum of the currents flowing through R b The current is:

[0028]

[0029] Substituting (1) into (2), we get:

[0030]

[0031] Take R1~R 16 and R b The resistance values ​​are equal, then:

[0032] U1+U2+…U 16 =U out (4)

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1. The present invention combines EFPI probes with different resonant frequency responses to form a wide-band detection device, which solves the problem that the current EFPI sensor working at the resonant frequency can only be used for narrow-band measurement of ultrasonic signals, meets the frequency band requirement of 20kHz to 500kHz for partial discharge ultrasonic signals, and eliminates the problem of missed detection in practical applications.

[0035] 2. The high-speed data acquisition device 16 of the present invention has 14-bit accuracy, 2MS / s sampling rate, and 1MHz analog bandwidth, which meets the sampling requirements of 20kHz to 500kHz ultrasonic signals.

[0036] 3. In order to achieve a wide-band response of 20kHz to 500kHz, the thickness and effective length (radius) of the sensitive diaphragm are selected according to the equally spaced resonant frequencies f1 to f16. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is the principle diagram of the existing optical fiber EFPI ultrasonic sensor;

[0038] Figure 2 is the working frequency response diagram of the existing optical fiber EFPI ultrasonic sensor;

[0039] Figure 3 It is a schematic diagram of the structure of the combined optical fiber EFPI broadband PD ultrasonic detection system of the present invention;

[0040] Figure 4 It is a schematic diagram of the structure of the optical fiber EFPI sensor combination probe of the present invention;

[0041] Figure 5 for Figure 4 A partial enlarged schematic diagram of

[0042] Figure 6 A curve diagram for selecting the thickness and effective length (radius) of the sensitive diaphragm of the optical fiber EFPI sensing combination probe of the present invention;

[0043] Figure 7 The electrical diagram of the broadband signal superposition amplification module of the present invention;

[0044] Figure 8 It is a schematic diagram of the working frequency response of the broadband PD ultrasonic detection of the present invention.

[0045] Among them, 1 is a light source, 2 is a fiber 1 / 2 splitter, 3 is an optical fiber, 4 is a fiber coupler, 5 is a first optical cable head, 6 is a first 16-core optical cable, 7 is a second optical cable head, 8 is an optical fiber EFPI sensing combination probe, 9 is a third optical cable head, 10 is a second 16-core optical cable, 11 is a fourth optical cable head, 12 is a multi-channel photoelectric detector, 13 is a first coaxial cable, 14 is a wide-band signal superposition and amplification device, 15 is a second coaxial cable, 16 is a high-speed data acquisition device, 81 is an optical fiber EFPI probe, 811 is a sealed circular sleeve type Fabry-Perot cavity probe, and 812 is a 3D printed insulating part with a through hole. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0047] like Figure 3As shown, a combined optical fiber EFPI broadband PD ultrasonic detection system comprises a light source 1, an optical fiber 1 / 2 optical splitter 2, an optical fiber 3, an optical fiber coupler 4, a first optical cable head 5, a first 16-core optical cable 6, a second optical cable head 7, an optical fiber EFPI sensing combined probe 8, a third optical cable head 9, a second 16-core optical cable 10, a fourth optical cable head 11, a multi-channel photoelectric detector 12, a first coaxial cable 13, a broadband signal superposition amplification device 14, a second coaxial cable 15, and a high-speed data acquisition device 16. The single light source 1 is connected to the optical fiber 1 / 2 optical splitter 2 through the optical fiber 3, and after passing through the optical fiber 1 / 2 optical splitter 2 four times, it is divided into 16 identical light source signals and sent to 16 optical fiber couplers 4. The 16 optical fiber couplers 4 output 16 channels of the same light source signals. The optical fiber and the first 16-core optical cable 6 are connected to each other through the first optical cable head 5 to achieve 16 independent optical paths. The optical fiber EFPI sensing combination probe 8 is connected to the first 16-core optical cable 6 through the second optical cable head 7 to achieve 16 independent optical paths. The 16 optical fiber couplers 4 input the 16 optical signals fed back by the optical fiber EFPI sensing combination probe 8 into the multi-channel photoelectric detector 12 through the optical fiber 3, the third optical cable head 9, the second 16-core optical cable 10, and the fourth optical cable head 11 in sequence. The multi-channel photoelectric detector 12 sends 16 corresponding voltage signals to the wide-band signal superposition and amplification module 14 through the first coaxial cable 13. After the voltage signal superposition is completed, it is connected to the high-speed data acquisition device 16 through the second coaxial cable 15 to complete the detection of ultrasonic signals.

[0048] The light source 1 is a DFB (Distributed Feedback) laser or an ASE (Amplifiedspontaneous Emission) light source or a light emitting diode (LED) or a super luminescent diode (SLD).

[0049] The optical fiber 1 / 2 splitter 2 is an optical fiber device that divides the incident light from the light source into two equal paths.

[0050] The optical fiber 3 is a single-mode optical fiber with a core diameter of 8 μm to 10 μm and an operating wavelength λ region of 1300 nm to 1600 nm. The optical fiber coupler 4 has a Y-shaped structure and an operating wavelength λ region of 1300 nm to 1600 nm, and all losses are greater than 50 dB.

[0051] The first optical cable head 5, the second optical cable head 7, the third optical cable head 9 and the fourth optical cable head 11 are formed by fixing 16 optical fibers in a 4×4 symmetrical arrangement using insulating tape to form an optical fiber connector with an adapter sleeve.

[0052] The first 16-core optical cable 6 and the second 16-core optical cable 10 are 16 independent working optical fibers matched with the first optical cable head 5 , the second optical cable head 7 , the third optical cable head 9 and the fourth optical cable head 11 .

[0053] like Figure 4 and Figure 5 As shown, the optical fiber EFPI sensing combined probe 8 is made by bonding and assembling 16 symmetrically distributed optical fiber EFPI probes 81 with resonance frequencies of f1 to f16.

[0054] The sensitive membranes in the 16 optical fiber EFPI probes 81 are in the same plane. The optical fiber EFPI probe 81 includes a sealed circular sleeve Fabry-Perot cavity probe 811 and a 3D printed insulating member 812 with a through hole. The 3D printed insulating member 812 with a through hole is used to protect and fix the sealed circular sleeve Fabry-Perot cavity probe 811 and facilitate overall bonding and assembly.

[0055] The resonance frequencies f1 to f16 are selected according to the equally spaced resonance frequencies to achieve a wide-band response of 20kHz to 500kHz. The thickness and effective length (radius) of the probe sensitive membrane are selected as follows: Figure 6 shown.

[0056] The multi-channel photoelectric detector 12 is a photon detection type multi-channel conversion device, and its working wavelength λ region is 1300nm~1600nm.

[0057] The first coaxial cable 13 and the second coaxial cable 15 are broadband coaxial cables with shielding layers, and the characteristic impedance is 75Ω.

[0058] like Figure 7 As shown, the circuit parameters of the broadband signal superposition and amplification module 14 include:

[0059] U - =U + =0

[0060] According to the virtual cutoff and Kirchhoff's law, through R1~R 16 The sum of the currents flowing through R b The current is:

[0061]

[0062] Substituting 1 into 2, we get:

[0063]

[0064] Take R1~R 16 and R b The resistance values ​​are equal, then:

[0065] U1+U2+…U 16 =U out

[0066] The parameters of the high-speed data acquisition device 16 are set as: 14-bit accuracy, 2MS / s sampling rate, and 1MHz analog bandwidth to meet the sampling requirements of 20kHz to 500kHz ultrasonic signals.

[0067] like Figure 8 As shown, the corresponding wide-band PD ultrasonic detection working frequency response of the combined optical fiber EFPI wide-band PD ultrasonic detection system of the present invention.

[0068] The current EFPI sensor operating at a resonant frequency can only be used to measure ultrasonic signals in a narrow band, and cannot meet the frequency band requirement of 20kHz to 500kHz for partial discharge ultrasonic signals. In actual applications, there is a problem of missed detection, and it is insensitive to ultrasonic signals generated by certain insulation defects. The present invention combines EFPI probes with different resonant frequency responses to form a wide-band detection device and method to solve the above-mentioned defects.

[0069] The current EFPI sensor operating at a resonant frequency can only be used to measure ultrasonic signals in a narrow band, and cannot meet the frequency band requirement of 20kHz to 500kHz for partial discharge ultrasonic signals. In actual applications, there is a problem of missed detection, and it is insensitive to ultrasonic signals generated by certain insulation defects. The present invention combines EFPI probes with different resonant frequency responses to form a wide-band detection device and method to solve the above-mentioned defects.

[0070] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A combined optical fiber EFPI broadband PD ultrasonic detection system, characterized in that: The system comprises a light source (1), an optical fiber 1 / 2 splitter (2), an optical fiber (3), an optical fiber coupler (4), a first optical cable head (5), a first 16-core optical cable (6), a second optical cable head (7), an optical fiber EFPI sensor assembly probe (8), a third optical cable head (9), a second 16-core optical cable (10), a fourth optical cable head (11), a multi-channel photoelectric detector (12), a first coaxial cable (13), a broadband signal superposition amplification module (14), a second coaxial cable (15), and a high-speed data acquisition device (16); The single light source (1) is connected to the optical fiber 1 / 2 splitter (2) via an optical fiber (3). After passing through the optical fiber 1 / 2 splitter (2) four times, the light source is divided into 16 identical light source signals and sent to 16 optical fiber couplers (4). The 16 optical fibers output by the 16 optical fiber couplers (4) are connected to the first 16-core optical cable (6) via a first optical cable head (5) to achieve 16 independent optical path connection. The optical fiber EFPI sensor combination probe (8) is connected to the first 16-core optical cable (6) via a second optical cable head (7). The 16 optical fiber couplers ( 4) 16 optical signals fed back by the optical fiber EFPI sensor combination probe (8) are sequentially input into a multi-channel photoelectric detector (12) through the optical fiber (3), the third optical cable head (9), the second 16-core optical cable (10), and the fourth optical cable head (11) through the optical fiber (3); the multi-channel photoelectric detector (12) sends 16 corresponding voltage signals to a wide-band signal superposition amplification module (14) through the first coaxial cable (13); after the voltage signals are superimposed, they are connected to a high-speed data acquisition device (16) through the second coaxial cable (15) to complete the detection of ultrasonic signals; The optical fiber EFPI sensing combined probe (8) is a probe made by bonding and assembling 16 optical fiber EFPI probes (81) with resonance frequencies of f1 to f16 and distributed in a symmetrical structure; The sensitive membranes in the 16 optical fiber EFPI probes (81) are located in the same plane; The optical fiber EFPI probe (81) comprises a sealed circular sleeve type Fabry-Perot cavity probe (811) and a 3D printed insulating part (812) with a through hole, wherein the 3D printed insulating part (812) with a through hole is used to protect and fix the sealed circular sleeve type Fabry-Perot cavity probe (811) and facilitate overall bonding and assembly; The resonance frequencies f1-f16 are selected according to the equally spaced resonance frequencies to achieve a wide-band response of 20kHz-500kHz.

2. A combined optical fiber EFPI broadband PD ultrasonic detection system according to claim 1, characterized in that: The light source (1) is a DFB laser or an ASE light source or a light emitting diode LED or a super luminescent diode SLD.

3. A combined optical fiber EFPI broadband PD ultrasonic detection system according to claim 1, characterized in that: The optical fiber 1 / 2 splitter (2) is an optical fiber device that divides the incident light from a light source into two equal paths.

4. A combined optical fiber EFPI broadband PD ultrasonic detection system according to claim 1, characterized in that: The optical fiber (3) is a single-mode optical fiber with a core diameter of 8 μm to 10 μm and an operating wavelength λ region of 1300 nm to 1600 nm.

5. A combined optical fiber EFPI broadband PD ultrasonic detection system according to claim 1, characterized in that: The optical fiber coupler (4) is a Y-shaped optical fiber coupler with an operating wavelength λ region of 1300nm to 1600nm and various losses greater than 50dB.

6. A combined optical fiber EFPI broadband PD ultrasonic detection system according to claim 1, characterized in that: The first optical cable head (5), the second optical cable head (7), the third optical cable head (9) and the fourth optical cable head (11) are formed by fixing 16 optical fibers in a 4×4 symmetrical arrangement using insulating tape to form an optical fiber connector with an adapter sleeve; The first 16-core optical cable (6) and the second 16-core optical cable (10) are 16 independent working optical fibers matched with the first optical cable head (5), the second optical cable head (7), the third optical cable head (9) and the fourth optical cable head (11).

7. A combined optical fiber EFPI broadband PD ultrasonic detection system according to claim 1, characterized in that: The multi-channel photoelectric detector (12) is a photon detection type multi-channel conversion device, and the working wavelength λ region is: 1300nm~1600nm; The parameters of the high-speed data acquisition device (16) are set as: 14-bit accuracy, 2MS / s sampling rate, and 1MHz analog bandwidth.

8. A combined optical fiber EFPI broadband PD ultrasonic detection system according to claim 1, characterized in that: The first coaxial cable (13) and the second coaxial cable (15) are broadband coaxial cables with shielding layers, and the characteristic impedance is 75Ω.

9. A combined optical fiber EFPI broadband PD ultrasonic detection system according to claim 1, characterized in that: The circuit parameters of the broadband signal superposition amplification module (14) include: IN - =U + =0 (1) According to the virtual cutoff and Kirchhoff's law, through R1~R 16 The sum of the currents flowing through R b The current is: Substituting (1) into (2), we get: Take R1~R 16 and R b The resistance values ​​are equal, then: U1+U2+ΛU 16 =U out (4).

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