A GIS metal particle defect distributed detection system and method based on a multi-probe pulse type phi-OTDR

Abstract

The present application relates to metal defect detection technical field, especially in kind of GIS metal particle defect distributed detection system based on multiple detection pulse type phi-OTDR, including: narrow linewidth laser, first coupler, first acoustooptic modulator, first erbium-doped fiber amplifier, cyclic frequency shift loop, circulator, third coupler, balanced photodetector and oscilloscope;Cyclic frequency shift loop is used for frequency shifting to the pulse light amplified by first erbium-doped fiber amplifier and dividing into n mutually different frequency detection light pulse, and detection light pulse is uniformly distributed between 2 times pulse light output by first erbium-doped fiber amplifier.The GIS metal particle defect distributed detection system based on multiple detection pulse type phi-OTDR provided by the present application expands the original one pulse light into multiple frequency different detection light pulse through cyclic frequency shift loop, without considering Rayleigh scattering light aliasing problem, solves the contradiction that optical pulse frequency and sensing fiber length are incompatible, and improves detection precision.

Description

Technical Field

[0001] This invention relates to the field of metal defect detection technology, and in particular to a GIS-based distributed detection system and method for metal particle defects based on a multi-probe pulsed φ-OTDR. Background Technology

[0002] Gas-insulated circuit breakers (GIS) are critical equipment in power systems, and their operational reliability directly affects the safety and stability of the power grid. Latent insulation defects within GIS, such as free metal particles, spikes, and floating electrodes, can trigger partial discharges. If not detected promptly, these can easily escalate into serious accidents like breakdown or flashover. Therefore, effective monitoring of partial discharges in GIS is a vital means of achieving early warning of equipment status and ensuring the stable operation of the power system.

[0003] Metal particles within GIS (Gas Insulated Switchgear) exhibit phenomena such as jumping and partial discharge under operating voltage. Therefore, partial discharge detection methods such as pulsed current and ultra-high frequency methods can be used to detect metal particle defects. However, due to the highly random and intermittent nature of partial discharge characteristics within GIS metal particles and their susceptibility to electromagnetic interference, electrical detection methods often struggle to accurately capture effective information in short-term experiments. Among numerous partial discharge detection methods, acoustic emission (AE) is favored in field applications due to its strong resistance to electromagnetic interference, fast response speed, and flexible deployment. Traditional AE detection primarily employs piezoelectric ceramic (PZT) sensors, diagnosing internal discharges by sensing ultrasonic signals on the GIS shell surface. However, PZT sensor technology has seen limited performance improvements over decades, and its inherent poor multiplexing capabilities make it difficult to construct economical and efficient multi-point synchronous detection networks, failing to meet the comprehensive monitoring needs of large-scale equipment such as ultra-high voltage and ultra-high voltage GIS.

[0004] In recent years, fiber optic acoustic emission sensing technology has rapidly developed as a potential alternative to PZT (polyether ionization). Among them, interferometric fiber optic sensors (such as Michelson and Mach-Zehnder structures) have demonstrated higher sensitivity in external GIS (Gas Insulator System) inspections, and related research has confirmed their application potential. However, this technology is essentially a discrete sensing method, meaning one sensor corresponds to one detection point. Due to the significant attenuation of acoustic signals by structures such as basin insulators and flanges in GIS equipment, a large number of sensors need to be deployed in each chamber to achieve coverage in actual operation and maintenance (especially in withstand voltage tests with a detection time window of only one minute). The inability to reuse discrete fiber optic sensors leads to high system costs and complex deployment, severely hindering its large-scale application.

[0005] To address the challenges of distributed detection, the research community has begun exploring technologies based on phase-sensitive optical time-domain reflectometers (φ-OTDR). φ-OTDR utilizes the backscattering Rayleigh effect of the sensing fiber itself to achieve true distributed acoustic measurements, transforming the entire fiber into countless continuously distributed sensors, fundamentally solving the problems of sensor reuse and large-scale deployment. Existing research has applied it to the distributed detection of partial discharge in cable joints. However, these exploratory works have revealed a core deficiency in traditional φ-OTDR systems: insufficient sensitivity. Their minimum measurable discharge quantity is only in the nC range (1000pC–3500pC), about two orders of magnitude lower than discrete fiber optic interferometers (typically reaching the hundreds of pC level), making it difficult to meet the detection requirements of weak discharge signals in GIS systems.

[0006] To improve sensitivity, existing technologies employ a method of concentrating long segments of sensing fiber around the object under test, thereby enhancing the signal through accumulated phase changes. While this method can improve detection sensitivity to the order of hundreds of pC, it introduces a new fatal flaw: the effective sampling frequency of the system decreases sharply with the increase in the length of the sensing unit fiber. In existing reports, the sampling frequency of such improved systems can only reach 5kHz to 10kHz, far below the core frequency band (20kHz to 80kHz) of GIS partial discharge acoustic signals, resulting in the inability to accurately capture and reconstruct the discharge acoustic signal.

[0007] Therefore, existing distributed detection schemes based on φ-OTDR have an irreconcilable contradiction between "high sensitivity" and "high sampling frequency," making them unsuitable for GIS partial discharge detection scenarios that demand stringent requirements in both areas. Further improvements to the φ-OTDR distributed detection scheme are needed to meet the detection requirements of GIS partial discharge detection. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a distributed detection system and method for metal particle defects in GIS based on multi-probe pulsed φ-OTDR, so as to solve the problem that the existing φ-OTDR distributed detection scheme is difficult to adapt to the needs of GIS partial discharge detection.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a distributed detection system for GIS metal particle defects based on multi-probe pulsed φ-OTDR, used to detect acoustic vibration signals in GIS chambers, comprising:

[0010] Narrow linewidth lasers are used to emit narrow linewidth laser light.

[0011] The first coupler is connected to the output of the narrow linewidth laser and is used to divide the narrow linewidth laser into intrinsic light and signal light.

[0012] The first acoustic-optic modulator is used to receive the signal light transmitted from the first coupler and to frequency-shift and modulate the signal light to a frequency of [frequency value missing]. f pulse Pulsed light;

[0013] The first erbium-doped fiber amplifier is connected to the output of the first acousto-optic modulator and is used to amplify the pulsed light;

[0014] The cyclic frequency shifting loop is connected to the output of the first erbium-doped fiber amplifier and is used to shift the frequency of the pulse light amplified by the first erbium-doped fiber amplifier and divide it into n probe light pulses of different frequencies. The probe light pulses are evenly distributed between the two pulse lights output by the first erbium-doped fiber amplifier.

[0015] The circulator has a first end connected to the cyclic frequency shifting loop, a second end connected to the sensing fiber, and a third end connected to the third coupler. The probe light pulse forms Rayleigh scattered light under the action of the acoustic vibration signal inside the sensing fiber.

[0016] The third coupler simultaneously receives the intrinsic light from the first coupler and the Rayleigh scattered light from the circulator, causing the intrinsic light and the Rayleigh scattered light to interfere within the third coupler before being output.

[0017] A balanced photodetector is connected to the output of a third coupler to perform photoelectric conversion on the optical signal output by the third coupler.

[0018] An oscilloscope is connected to the output of a balanced photodetector to detect and store the electrical signals transmitted from the balanced photodetector.

[0019] Preferably, an isolator is provided between the narrow linewidth laser and the first coupler.

[0020] In one embodiment, the cyclic frequency shifting loop includes a second coupler, a second acousto-optic modulator, a second erbium-doped fiber amplifier, and a delay fiber. The second coupler is connected to the first erbium-doped fiber amplifier, and the pulse light from the first erbium-doped fiber amplifier is evenly split and sent to either the circulator or the second acousto-optic modulator. The output of the second acousto-optic modulator is connected to the second erbium-doped fiber amplifier, the output of the second erbium-doped fiber amplifier is connected to the delay fiber, and the delay fiber is connected to the input of the second coupler. The pulse light input to the second acousto-optic modulator is frequency-shifted by the second acousto-optic modulator, amplified by the second erbium-doped fiber amplifier, and its time-domain distribution is adjusted by the delay fiber before re-entering the second coupler for cyclic operation.

[0021] In one embodiment, a first filter is provided between the second erbium-doped fiber amplifier and the delay fiber, and a second filter is provided between the second coupler and the circulator.

[0022] In one embodiment, the frequency shift of the first acousto-optic modulator is Δf 1. The frequency shift of the second acousto-optic modulator is Δ f 2, where Δ f 1 and Δ f The ratio of 2 to 3 is 1.

[0023] In one embodiment, the overall sampling frequency f of the sensing fiber is always 750–800 kHz, and, f 总 =n f pulse , 5≤n≤8.

[0024] In one embodiment, a plurality of sensing units are connected in series on the sensing optical fiber, and the sensing unit includes a mandrel and a single-mode optical fiber wound on the mandrel.

[0025] In one embodiment, the total length of the sensing fiber and the wound single-mode fiber is L, and the length of the delay fiber is La, wherein, .

[0026] In one embodiment, the length of the wound single-mode fiber is 70% to 95% of the saturated signal-to-noise ratio, corresponding to the length of the optical pulse width covered in the fiber.

[0027] The present invention also provides a detection method using any of the above-described GIS distributed detection systems for metal particle defects, the steps of which are as follows:

[0028] S1. The narrow linewidth laser emits a narrow linewidth laser beam. After entering the first coupler, the narrow linewidth laser beam is split into two paths. The first path is the intrinsic light and is output to the third coupler; the second path is the signal and is output to the first acousto-optic modulator.

[0029] S2. After the signal light enters the first acousto-optic modulator, it undergoes frequency shifting and is modulated to a frequency of... f pulse The pulsed light enters the first erbium-doped fiber amplifier for amplification, and the amplified pulsed light is then sent to the cyclic frequency shifting loop.

[0030] S3. The pulsed light is divided into two paths in the cyclic frequency shifting loop. The first path is sent to the circulator, and the second path is cyclically shifted in the cyclic frequency shifting loop. The single pulsed light is divided into n probe light pulses of different frequencies, and the last probe light pulse generated by the single pulsed light is generated before the next pulse light sent from the first erbium-doped fiber amplifier.

[0031] S4. The probe light pulse is injected into the sensing fiber through the circulator and the corresponding Rayleigh scattered light is generated. The Rayleigh scattered light returns to the circulator and is sent to the third coupler.

[0032] S5. Inside the third coupler, the intrinsic light interferes with the Rayleigh scattered light and is then sent to the balanced photodetector. The balanced photodetector receives the optical signal and performs photoelectric conversion to generate an electrical signal. The electrical signal is then detected and stored by an oscilloscope.

[0033] In one embodiment, in step S1, the splitting ratio of the first light path to the second light path is 1:9; in step S3, the splitting ratio of the pulsed light in the cyclic frequency shifting loop is 1:1.

[0034] In one embodiment, in step S4, when the Rayleigh scattered light generated by the last probe light pulse of the previous pulse light returns to the circulator, the first probe light pulse generated by the next pulse light from the first erbium-doped fiber amplifier does not enter the circulator.

[0035] The beneficial effects of this invention are as follows:

[0036] In GIS, the frequencies of partial discharge acoustic emission signals are mainly concentrated below 80kHz. To reconstruct the partial discharge acoustic emission signal as accurately as possible, the sampling frequency should be 10 times the highest frequency of the acoustic emission signal under test, i.e., 800kHz. However, for conventional φ-OTDR systems, the optical pulse frequency... f pulse It should be set to 800kHz. However, such a high optical pulse frequency will result in an excessively short sensing fiber. An excessively short sensing fiber will lead to a significant decrease in detection sensitivity. The improvement method of increasing the length of the sensing unit fiber to increase sensitivity will sacrifice the system sampling frequency, causing it to be unable to cover the core frequency band (20kHz~80kHz) of the GIS partial discharge acoustic signal, resulting in signal distortion and inaccurate measurement and location of partial discharge. This makes the traditional φ-OTDR scheme have a contradiction between "sensitivity" and "sampling frequency".

[0037] The distributed detection system for GIS metal particle defects based on multi-probe pulse type φ-OTDR provided by the present invention introduces multiple sets of probe light pulses with different frequencies through a cyclic frequency shifting loop, which greatly improves the effective sampling frequency of the system. Without shortening the length of the sensing fiber, the overall sampling frequency is greatly expanded, so that the sampling frequency can fully cover the core frequency band (20kHz-80kHz) of GIS partial discharge acoustic signal, effectively avoiding signal distortion.

[0038] Furthermore, while taking into account the sampling frequency and the length of the sensing fiber, the detection sensitivity of the GIS metal particle defect distributed detection system with multi-probe pulse type φ-OTDR provided by this invention is improved from the nC level to the hundreds of pC level compared with the detection scheme of ordinary φ-OTDR, which is nearly two orders of magnitude, ensuring that this invention has good application value.

[0039] Meanwhile, the distributed detection system for GIS metal particle defects based on multi-detection pulse type φ-OTDR provided by this invention can achieve full-line synchronous monitoring of different locations in GIS chambers through a single sensing optical fiber. Compared with the currently used discrete sensor solution, it significantly reduces deployment complexity and operation and maintenance costs, and has good promotion value.

[0040] Other features and beneficial effects of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects of the invention and other beneficial effects may be realized and obtained by means of the structures and / or components pointed out in the description and claims. Attached Figure Description

[0041] Figure 1 This is a photoelectric topology diagram of an embodiment of the present invention;

[0042] Figure 2 This is a schematic diagram of the overall structure of the test platform according to Embodiment 1 of the present invention;

[0043] Figure 3 This is a signal diagram detected by a single-probe pulse type φ-OTDR detection system;

[0044] Figure 4 This is a signal diagram detected in Embodiment 1 of the present invention;

[0045] Figure 5 This is a waterfall diagram showing the location of the signal detected in Embodiment 1 of the present invention;

[0046] Figure 6 This is a time-domain signal diagram of Embodiment 1 of the present invention;

[0047] Figure 7 This is a diagram showing the relationship between optical pulse width and signal-to-noise ratio according to an embodiment of the present invention.

[0048] Label Explanation:

[0049] 11. Narrow linewidth laser; 111. Isolator; 12. First coupler; 13. First acousto-optic modulator; 14. First erbium-doped fiber amplifier; 15. Cyclic frequency shifter loop; 151. Second coupler; 152. Second acousto-optic modulator; 153. Second erbium-doped fiber amplifier; 154. Delay fiber; 155. First filter; 156. Second filter; 16. Circulator; 17. Sensing fiber; 18. Third coupler; 19. Balanced photodetector; 20. Oscilloscope; 21. Signal generator. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. The technical features designed in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] In the description of this invention, it should be noted that all terms used in this invention (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and should not be construed as limiting the invention; it should be further understood that the terms used in this invention should be understood to have the same meaning as those in the context of this specification and in the relevant field, and should not be understood in an idealized or overly formal sense, except as expressly defined in this invention.

[0052] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0053] Please refer to Figures 1 to 7 A distributed detection system for metal particle defects in GIS based on a multi-probe pulsed φ-OTDR is used to detect acoustic vibration signals in GIS chambers, comprising:

[0054] Narrow linewidth laser 11, used to emit narrow linewidth laser;

[0055] The first coupler 12 is connected to the output end of the narrow linewidth laser 11 and is used to divide the narrow linewidth laser into intrinsic light and signal light.

[0056] The first acoustic-optic modulator 13 is used to receive the signal light transmitted from the first coupler 12 and to frequency-shift and modulate the signal light to a frequency of [frequency value missing]. f pulse Pulsed light;

[0057] The first erbium-doped fiber amplifier 14 is connected to the output of the first acousto-optic modulator 13 and is used to amplify the pulsed light;

[0058] The cyclic frequency shifting loop 15 is connected to the output end of the first erbium-doped fiber amplifier 14 and is used to shift the frequency of the pulse light amplified by the first erbium-doped fiber amplifier 14 and divide it into n probe light pulses with different frequencies. The probe light pulses are evenly distributed between the two pulse lights output by the first erbium-doped fiber amplifier 14.

[0059] The circulator 16 has a first end connected to the cyclic frequency shifting loop 15, a second end connected to the sensing fiber 17, and a third end connected to the third coupler 18. The probe light pulse forms Rayleigh scattered light under the action of acoustic vibration signal in the sensing fiber 17.

[0060] The third coupler 18 simultaneously receives the intrinsic light from the first coupler 12 and the Rayleigh scattered light from the circulator 16, causing the intrinsic light and the Rayleigh scattered light to interfere within the third coupler 18 before being output.

[0061] The balanced photodetector 19 is connected to the output of the third coupler 18 and performs photoelectric conversion on the optical signal output by the third coupler 18.

[0062] The oscilloscope 20 is connected to the output terminal of the balanced photodetector 19 to detect and store the electrical signal transmitted from the balanced photodetector 19.

[0063] Preferably, an isolator 111 is provided between the narrow linewidth laser 11 and the first coupler 12.

[0064] Specifically, the narrow linewidth laser 11 emits laser light with a wavelength of 1550nm.

[0065] Specifically, the first acousto-optic modulator 13 is connected to the signal generator 21, and the signal generator 21 is connected to the oscilloscope 20.

[0066] In this embodiment, the cyclic frequency shifting loop 15 includes a second coupler 151, a second acousto-optic modulator 152, a second erbium-doped fiber amplifier 153, and a delay fiber 154. The second coupler 151 is connected to the first erbium-doped fiber amplifier 14, and the pulse light from the first erbium-doped fiber amplifier 14 is evenly distributed and sent to the circulator 16 or the second acousto-optic modulator 152 respectively. The output end of the second acousto-optic modulator 152 is connected to the second erbium-doped fiber amplifier 153, and the output end of the second erbium-doped fiber amplifier 153 is connected to the delay fiber 154. The delay fiber 154 is connected to the input end of the second coupler 151. The pulse light input to the second acousto-optic modulator 152 is frequency shifted by the second acousto-optic modulator 152, amplified by the second erbium-doped fiber amplifier 153, and its time domain distribution is adjusted by the delay fiber 154 before re-entering the second coupler 151 for circulation.

[0067] In this embodiment, a first filter 155 is provided between the second erbium-doped fiber amplifier 153 and the delay fiber 154, and a second filter 156 is provided between the second coupler 151 and the circulator 16. Preferably, the first filter 155 and the second filter 156 are fiber Bragg gratings (FBGs) with a center wavelength of 1550 nm and a bandwidth of 0.2 nm.

[0068] In this embodiment, the frequency shift of the first acousto-optic modulator 13 is Δ f 1. The frequency shift of the second acousto-optic modulator 152 is Δ f 2, where Δ f 1 and Δ f The size ratio of 2 is 2 to 3:1. Preferably, Δ f 1 is 100MHz, Δ f 2 is 40MHz.

[0069] In this embodiment, the overall sampling frequency of the sensing fiber 17 f 总 The frequency is 750–800 kHz, and, f 总 =n f pulse 5 ≤ n ≤ 8. Specifically, since each loop in the cyclic frequency shifting loop 15 of the pulsed light generates a corresponding frequency shift, if optical path loss is not considered, n probe light pulses with different frequency shifts can be generated and injected into the sensing fiber 17. In the actual system, due to the limitation of detection bandwidth and the objective existence of optical path loss, the detectable frequency of interference light signals is limited. To ensure the accuracy of detection, 5 ≤ n ≤ 8 is adopted. Preferably, n = 6.

[0070] Specifically, when n is 6, the optical pulse frequency in the system is... f pulse The sampling frequency of the acoustic emission signal is 6 times the maximum frequency of the signal being measured. However, the frequencies of partial discharge acoustic emission signals in GIS are mainly concentrated below 80kHz. To reproduce the partial discharge acoustic emission signal as accurately as possible, the sampling frequency is set to 10 times the highest frequency of the acoustic emission signal being measured. f 总 It is 800kHz. Specifically, when n is 6, .

[0071] Specifically, the GIS metal particle defect distributed detection system with a cyclic frequency shifting loop 15 structure provided by the invention expands the original single pulse light into six probe light pulses. Since the six probe light pulses have different frequencies, there is no need to consider the Rayleigh scattering light aliasing problem, which significantly improves the contradiction between the light pulse frequency and the length of the sensing fiber 17, allowing "high sensitivity" and "high sampling frequency" to coexist.

[0072] In this embodiment, a plurality of sensing units are connected in series on the sensing fiber 17. The sensing unit includes a core and a single-mode fiber wound on the core.

[0073] In this embodiment, the total length of the sensing fiber 17 and the wound single-mode fiber is L, and the length of the delay fiber 154 is L. a ,in, Preferably, given a fixed optical pulse frequency, the length L of the sensing fiber 17 needs to be controlled to ensure that the Rayleigh scattered light generated by two consecutive pulses in the φ-OTDR system does not alias. Therefore, L must satisfy the following equation:

[0074]

[0075] Where c is the speed of light in a vacuum, c = 3 × 10 8 m / s; n f n is the refractive index of a single-mode fiber. f Let's take 1.5. Therefore, L is 750m. a It is 125m.

[0076] Specifically, the function of the delay fiber 154 is to uniformly distribute the probe light pulses of different frequencies extended from the cyclic frequency shifting loop 15 in the time domain, placing them between two pulses emitted by the cyclic frequency shifting loop 15. Furthermore, the natural perturbation of the delay fiber 154 causes the pulse light re-injected into the second coupler 151 to have a random polarization state, thereby achieving uniform sampling of the acoustic emission signal. Specifically, if all probe light pulses use the same polarization state, at certain specific locations, signals of all frequencies may simultaneously attenuate due to polarization mismatch, making the vibration signals at these locations undetectable. By introducing a random polarization state through the delay fiber 154, the responses of probe light pulses of different frequencies to the same acoustic vibration event do not simultaneously fail due to identical polarization states, ensuring the accuracy and reliability of the detection results.

[0077] In this embodiment, the length of the wound single-mode fiber corresponds to the length of the optical pulse width covered by the fiber when the saturation signal-to-noise ratio is 70% to 95%. Preferably, the length of the single-mode fiber in each sensing unit is 18m. Specifically, in a φ-OTDR system, a smaller optical pulse width is more conducive to obtaining high spatial resolution. However, a larger optical pulse width means that a longer sensing fiber 17 is simultaneously modulated by the acoustic emission signal, which can obtain a larger phase change. Since the acoustic emission signal generated by discharge is often very weak, a larger optical pulse width is usually set, and sensing fibers 17 with matching optical path lengths are grouped together as a single sensing unit to improve detection sensitivity. However, as the optical pulse width increases, the system noise level will also increase. Figure 7As shown, this invention uses fitting calculations based on the corresponding test results of optical pulse width and signal-to-noise ratio (SNR). It finds that the SNR of the φ-OTDR system increases with increasing optical pulse width and tends to saturate. Since a larger optical pulse width results in lower spatial resolution, based on marginal benefit considerations, the optical pulse width at 90% of the saturated SNR is taken as the preferred optical pulse width, w = 90 ns. This optical pulse width covers a length of approximately 18m in the sensing fiber 17. Therefore, the length of the single-mode fiber wound on each sensing unit is 18m, thereby ensuring spatial resolution while achieving high anti-interference capability.

[0078] The present invention also provides a detection method using any of the above-described GIS distributed detection systems for metal particle defects, the steps of which are as follows:

[0079] S1. Narrow linewidth laser 11 emits narrow linewidth laser light. After entering the first coupler 12, the narrow linewidth laser light is split into two paths. The first path is intrinsic light and is output to the third coupler 18; the second path is signal and is output to the first acousto-optic modulator 13.

[0080] S2. After the signal light enters the first acousto-optic modulator 13, it undergoes frequency shifting and is modulated to a frequency of... f pulse The pulsed light enters the first erbium-doped fiber amplifier 14 for amplification, and the amplified pulsed light is sent to the cyclic frequency shifting loop 15.

[0081] S3. The pulsed light is divided into two paths in the cyclic frequency shifting loop 15. The first path is sent to the circulator 16, and the second path is cyclically shifted in the cyclic frequency shifting loop 15. The single pulsed light is divided into n probe light pulses of different frequencies, and the last probe light pulse generated by the single pulsed light is generated before the next pulsed light sent from the first erbium-doped fiber amplifier 14.

[0082] S4. The probe light pulse is injected into the sensing fiber 17 through the circulator 16 and the corresponding Rayleigh scattered light is generated. The Rayleigh scattered light returns to the circulator 16 and is sent to the third coupler 18.

[0083] S5. In the third coupler 18, the intrinsic light interferes with the Rayleigh scattered light and is then sent to the balanced photodetector 19. The balanced photodetector 19 receives the optical signal and performs photoelectric conversion to generate an electrical signal. The electrical signal is then detected and stored by the oscilloscope 20.

[0084] In this embodiment, in step S1, the splitting ratio of the first light path to the second light path is 1:9; in step S3, the splitting ratio of the pulsed light in the cyclic frequency shifting loop 15 is 1:1.

[0085] In this embodiment, during S4, when the Rayleigh scattered light generated by the last probe light pulse of the previous pulse light returns to the circulator 16, the first probe light pulse generated by the next pulse light from the first erbium-doped fiber amplifier 14 does not enter the circulator 16.

[0086] Example 1

[0087] To test the performance of the GIS distributed detection system for metal particle defects based on multi-probe pulsed φ-OTDR provided by this invention, a system was built as follows: Figure 2 The test platform shown is a cylindrical steel block with a diameter of 400 mm and a height of 300 mm. During testing, one sensing unit is connected in series with the sensing fiber optic cable 17 of the system, resulting in a total length of 750 m for the sensing fiber optic cable 17. The starting end of the sensing unit is 380 m from the starting point of the sensing fiber optic cable 17. After applying acoustic coupling agent to the bottom of the sensing unit, it is placed on the surface of the steel block and fixed with a clamp. Another clamp is used to fix a piezoelectric ceramic resonator, which can be driven by an electrical signal from a signal generator 21 to generate a corresponding acoustic signal.

[0088] To test the response level of the GIS distributed detection system for metal particle defects based on a multi-probe pulsed φ-OTDR to high-frequency signals, this embodiment uses a signal generator 21 to drive a piezoelectric ceramic oscillator to generate an 80kHz sine wave signal. The signal is then detected using both a single-probe pulsed φ-OTDR detection system and the GIS distributed detection system for metal particle defects based on a multi-probe pulsed φ-OTDR provided in this invention. The detected signals are shown below. Figure 3 and Figure 4 As shown. Specifically, the GIS distributed detection system for metal particle defects based on multi-probe pulsed φ-OTDR provided by this invention... f pulse 133kHz, n = 6, Δ f 1 is 100MHz, Δ f 2 is 40MHz, the bandwidth of the balanced photodetector 19 is 350MHz, L is 750m, L a The length is 125m, and the sensing unit structure consists of an 18m long single-mode optical fiber wound on a silicone rubber mandrel with a height of 20mm and a diameter of 30mm. The difference between the single-probe pulse type φ-OTDR detection system and the GIS metal particle defect distributed detection system based on multi-probe pulse type φ-OTDR provided in this invention is that the single-probe pulse type φ-OTDR system does not have a cyclic frequency shifting loop 15.

[0089] Depend on Figure 3 and Figure 4As can be seen, compared with the single-probe pulse type φ-OTDR detection system, the GIS metal particle defect distributed detection system based on multi-probe pulse type φ-OTDR provided by the present invention can increase the sampling rate by six times, better restore high-frequency signals, and meet the measurement of high-frequency acoustic signals.

[0090] Furthermore, actual operation simulation tests were conducted. A 1cm long, 0.3mm diameter aluminum wire was placed in one chamber of the GIS to simulate metal particle defects within the GIS cavity. A sensing unit was connected in series at a distance of 380m from the starting point of the sensing fiber 17, and the sensing unit was fixed below the defective cavity. A high voltage was applied to the central conductor of the piezoelectric ceramic resonator using a step-up method (1kV increments) through a power frequency test transformer. When the test voltage increased to 65kV, the PZT in the piezoelectric ceramic resonator detected a discharge ultrasonic signal, triggering acquisition by the oscilloscope 20. The signal localization waterfall plot of the GIS metal particle defect distributed detection system based on multi-probe pulse-type φ-OTDR provided by this invention is shown below. Figure 5 As shown.

[0091] Depend on Figure 5 It can be seen that a pulse-shaped disturbance signal exists approximately 380m from the starting point of the sensing optical path, a distance corresponding to the spatial position of the sensing unit. It can be reasonably inferred that this is due to the acoustic vibration signal generated by the sensing unit detecting defects in the metal particles.

[0092] The time-domain signal corresponding to the sensing unit is as follows Figure 6 As shown in part (a) of the diagram, the signal measured by PZT is as follows: Figure 6 As shown in section (b), the signals detected by the distributed fiber optic sensing system and those measured by the PZT have a good correspondence on the time axis. This confirms that the phase disturbance at 380m is caused by the acoustic vibration signal diffracted by the discharge of metal particles.

[0093] In summary, the GIS-based distributed detection system for metal particle defects based on multi-probe pulsed φ-OTDR provided by this invention can accurately capture the acoustic and vibration signals generated by the jumping or discharge of metal particles, and has good accuracy and efficiency.

[0094] Furthermore, those skilled in the art should understand that although many problems exist in the prior art, each embodiment or technical solution of the present invention can be improved in only one or a few aspects, without necessarily solving all the technical problems listed in the prior art or background art simultaneously. Those skilled in the art should understand that any content not mentioned in a claim should not be construed as a limitation on that claim.

[0095] Although this document frequently uses terms such as narrow-linewidth laser and first coupler, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of the invention; interpreting them as any additional limitation would contradict the spirit of the invention. The terms "first," "second," etc. (if present) in the specification and claims of the embodiments of the invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A GIS metal particle defect distributed detection system based on multi-probe pulse type φ-OTDR for detecting acoustic vibration signals in a GIS chamber, characterized in that, The application relates to a narrow-linewidth laser detection device. The device comprises a narrow-linewidth laser (11) for emitting narrow-linewidth laser light; a first coupler (12) connected with the output end of the narrow-linewidth laser (11) for dividing the narrow-linewidth laser light into intrinsic light and signal light; a first erbium-doped fiber amplifier (14) in communication with the output end of the first acousto-optic modulator (13) for amplifying the pulse light; a cyclic frequency shift loop (15) in communication with the output end of the first erbium-doped fiber amplifier (14) for frequency-shifting the pulse light amplified by the first erbium-doped fiber amplifier (14) and dividing the pulse light into n detection light pulses with different frequencies, which are uniformly distributed between the 2 times of the pulse light output by the first erbium-doped fiber amplifier (14); a circulator (16) in communication with the cyclic frequency shift loop (15) at a first end, in communication with a sensing optical fiber (17) at a second end, and in communication with a third coupler (18) through a third end, wherein the detection light pulses form Rayleigh scattering light under the action of acoustic vibration signals in the sensing optical fiber (17); the third coupler (18) simultaneously receives the intrinsic light delivered by the first coupler (12) and the Rayleigh scattering light delivered by the circulator (16), so that the intrinsic light and the Rayleigh scattering light interfere in the third coupler (18) and are then output; a balanced photodetector (19) in communication with the output end of the third coupler (18) for photoelectric conversion of the optical signal output by the third coupler (18); and an oscilloscope (20) connected with the output end of the balanced photodetector (19) for detecting and storing the electrical signal delivered by the balanced photodetector (19). The cyclic frequency shift loop (15) comprises a second coupler (151), a second acousto-optic modulator (152), a second erbium-doped fiber amplifier (153), and a delay optical fiber (154). The second coupler (151) is in communication with the first erbium-doped fiber amplifier (14) and divides the pulse light delivered by the first erbium-doped fiber amplifier (14) into two parts, which are respectively delivered into the circulator (16) or the second acousto-optic modulator (152). The output end of the second acousto-optic modulator (152) is in communication with the second erbium-doped fiber amplifier (153), the output end of the second erbium-doped fiber amplifier (153) is in communication with the delay optical fiber (154), and the delay optical fiber (154) is in communication with the input end of the second coupler (151). The pulse light delivered into the second acousto-optic modulator (152) is frequency-shifted by the second acousto-optic modulator (152), amplified by the second erbium-doped fiber amplifier (153), and adjusted in time domain distribution by the delay optical fiber (154) before re-entering the second coupler (151) for circulation. a first acousto-optic modulator (13) for receiving the signal light transmitted by the first coupler (12) and frequency-shift modulating the signal light into pulsed light with a frequency of f pulse ​ A first filter (155) is arranged between the second erbium-doped fiber amplifier (153) and the delay optical fiber (154), and a second filter (156) is arranged between the second coupler (151) and the circulator (16). ​ ​ ​ ​ ​ ​ 2.The GIS metal particle defect distributed detection system based on multi-probe pulse type φ-OTDR according to claim 1, characterized in that: ​ 3.The GIS metal particle defect distributed detection system based on multi-probe pulse type φ-OTDR according to claim 1, characterized in that: The frequency shift of the first acousto-optic modulator (13) is Δ f 1, the frequency shift of the second acousto-optic modulator (152) is Δ f 2. f 1 and Δ f 2 is 2-3:

1.

4. The multi-probe pulse type φ-OTDR based GIS metal particle defect distributed detection system according to claim 1, characterized in that: the overall sampling frequency of the sensing fiber (17) f 总 is 750-800 kHz, and f 总 = n f puls 5≤ n≤ 8.

5. The multi-probe pulse type φ-OTDR based GIS metal particle defect distributed detection system according to claim 4, characterized in that: A plurality of sensing units are connected in series on the sensing fiber (17), and the sensing unit comprises a core shaft and a single-mode optical fiber wound on the core shaft.

6. The multi-probe pulse type φ-OTDR based GIS metal particle defect distributed detection system according to claim 5, characterized in that: The sensing fiber (17) has a total length L around the single mode fiber and the length of the delay fiber (154) is L a wherein .

7. A detection method using the multi-probe pulse type φ-OTDR based GIS metal particle defect distributed detection system according to any one of claims 1 to 6, characterized by, The steps are as follows: S1, the narrow linewidth laser (11) emits narrow linewidth laser, which is divided into two paths after entering the first coupler (12), the first path light is the intrinsic light to the third coupler (18); the second path light is the signal to the first acousto-optic modulator (13); S2, the signal light enters the first acousto-optic modulator (13) and is frequency-shifted to be modulated as pulse light with a frequency of f pulse The pulse light enters the first erbium-doped fiber amplifier (14) and is amplified, and the amplified pulse light is transmitted to the circulating frequency-shift loop (15). S3, the pulse light is divided into two paths in the circulating frequency shift loop (15), the first path is input to the circulator (16), and the second path is subjected to frequency shift circulation in the circulating frequency shift loop (15); a single pulse light is divided into n mutually different frequency probe light pulses, and the last probe light pulse generated by a single pulse light is generated before the next pulse light delivered by the first erbium-doped fiber amplifier (14); S4, the probe light pulse is injected into the sensing fiber (17) through the circulator (16) and generates corresponding Rayleigh scattering light, which returns to the circulator (16) and is input to the third coupler (18); S5, in the third coupler (18), the intrinsic light and the Rayleigh scattering light interfere and then are input to the balanced photodetector (19), the balanced photodetector (19) receives the optical signal and performs photoelectric conversion to generate an electrical signal, and the oscilloscope (20) detects and stores the electrical signal.

8. The detection method of claim 7, wherein: In step S1, the splitting ratio of the first path light and the second path light is 1:9; in step S3, the splitting ratio of the pulse light in the circulating frequency shift loop (15) is 1:

1.

9. The method of claim 7, wherein: In step S4, when the Rayleigh scattering light generated by the last probe light pulse of the previous pulse light returns to the circulator (16), the first probe light pulse generated by the next pulse light delivered by the first erbium-doped fiber amplifier (14) has not entered the circulator (16).

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