A multi-parameter optical fiber sensing on-line monitoring system and method for gas insulated equipment

Abstract

The application provides a multi-parameter optical fiber sensing on-line monitoring system and method for gas insulated equipment. The sensing system comprises a near-infrared broadband light source, a fiber splitter, a fiber tunable filter, a fiber coupler, a four-core optical cable, a fiber multi-parameter sensing probe, a signal processing circuit board, an arrayed waveguide grating, a fiber array and a photodiode array. Three Fabry-Perot interferometers are integrated in a micro fiber multi-parameter sensing probe to realize high sensitivity sensing of multi-parameters such as decomposition products, partial discharge ultrasonic waves and air pressure in a sulfur hexafluoride gas insulated equipment. By sharing and multiplexing the near-infrared broadband light source and the spectral detection part, the system structure is greatly simplified and the system cost is reduced. The excitation light and the detection light in the system are transmitted by optical fibers, and the sensing probe does not contain electrical elements, so it has anti-electromagnetic interference and long-distance sensing capability. The application provides a highly competitive technical solution for multi-parameter on-line monitoring of gas insulated equipment.

Description

Technical Field

[0001] This invention belongs to the field of online monitoring technology for high-voltage electrical equipment, and relates to a multi-parameter fiber optic sensing online monitoring system and method for gas-insulated equipment. Background Technology

[0002] Sulfur hexafluoride (SF6) gas-insulated electrical equipment employs a fully enclosed gas chamber structure to achieve insulation and arc extinguishing functions, making it an important substation and switchgear in high-voltage power grids. A single gas-insulated device typically consists of about 10 gas chambers. The fully enclosed structure and the large number of chambers present significant challenges to fault early warning for SF6 gas-insulated equipment. When a partial discharge fault occurs inside the gas-insulated equipment, ultrasonic waves are generated. Simultaneously, the released heat causes the temperature of the discharge site to become too high, leading to the decomposition of SF6 gas into characteristic products such as H2S and SO2. Among these, H2S gas is a representative gas for monitoring discharge faults. Therefore, real-time monitoring of the ultrasonic signal and H2S gas concentration within the equipment can provide effective early warning for discharge faults. The literature *Multi-pass Differential Photoacoustic Sensor for Real-Time Measurement of SF6 Decomposition Component H2S at the ppb Level*, 2023, 95(21): 8214–8222 reports a method for detecting H2S, a decomposition product of SF6, using photoacoustic spectroscopy, achieving high detection sensitivity. The ultrasonic frequencies generated by partial discharge are typically around 50kHz. Currently used piezoelectric ultrasonic sensors have low sensitivity and struggle to detect weak partial discharge ultrasonic signals. Furthermore, during long-term operation, minute leaks of sulfur hexafluoride (SF6) gas may occur inside the equipment. Accumulated gas leaks can seriously threaten the equipment's insulation performance, necessitating real-time monitoring of the internal gas pressure. Therefore, designing a low-cost, high-sensitivity, multi-parameter online monitoring system is of significant application value for detecting discharge faults and gas leaks in SF6 gas-insulated equipment. Summary of the Invention

[0003] The purpose of this invention is to propose a multi-parameter fiber optic sensing online monitoring system and method for gas-insulated equipment. It aims to use a single light source to simultaneously monitor discharge faults and gas leaks during equipment operation, improve the monitoring system's anti-electromagnetic interference capability, and reduce system costs, thereby expanding the application space of fiber optic sensing technology in fields such as electrical equipment condition monitoring.

[0004] The technical solution of the present invention:

[0005] A multi-parameter fiber optic sensing online monitoring system for gas-insulated equipment includes a near-infrared broadband light source 1, a fiber optic splitter 2, a fiber optic tunable filter 3, a fiber optic coupler 4, a four-core optical cable 5, a fiber optic multi-parameter sensing probe 6, a signal processing circuit board 7, an arrayed waveguide grating 8, a fiber optic array 9, and a photodiode array 10. The near-infrared broadband light source 1 is connected to the fiber optic splitter 2, which is connected to both the fiber optic tunable filter 3 and the fiber optic coupler 4. The broadband light emitted by the near-infrared broadband light source 1 is split into two beams by the fiber optic splitter 2, which are then incident on the fiber optic tunable filter 3 and the fiber optic coupler 4, respectively. Both the fiber optic tunable filter 3 and the fiber optic coupler 4 are connected to the four-core optical cable 5, which is connected to the fiber optic multi-parameter sensing probe 6. The emitted light from fiber optic coupler 3 and fiber optic coupler 4 is incident on fiber optic multi-parameter sensor probe 6 via four-core optical cable 5; signal processing circuit board 7 is connected to fiber optic tunable filter 3, and signal processing circuit board 7 controls fiber optic tunable filter 3, generating wavelength-modulated light as excitation light for detecting H2S gas; fiber optic coupler 4, arrayed waveguide grating 8 and fiber array 9 are connected in sequence, and the signal light reflected by fiber optic multi-parameter sensor probe 6 is incident on fiber optic coupler 4 via three optical fibers in four-core optical cable 5, and then coupled to fiber array 9 after being dispersed by arrayed waveguide grating 8; fiber array 9, photodiode array 10 and signal processing circuit board 7 are connected in sequence, photodiode array 10 receives signal light emitted by fiber array 9, and signal processing circuit board 7 collects and processes the photoelectric converted optical signal.

[0006] The fiber optic multi-parameter sensing probe 6 mainly consists of an excitation fiber 11, a gas detection fiber 12, an ultrasonic detection fiber 13, a pressure detection fiber 14, a vent 15, a miniature air cavity 16, a cantilever beam 17, an ultrasonic sensitive diaphragm 18, a pressure sensitive diaphragm 19, and a ceramic shell 20. Gas enters the miniature air cavity 16 through the vent 15. The excitation fiber 11 emits near-infrared excitation light into the miniature air cavity 16, generating a photoacoustic signal. The cantilever beam 17 and the gas detection fiber 12 form the first Fabry-Perot interferometer, used to sense the gas photoacoustic signal to measure the concentration of H2S gas. The ultrasonic sensitive diaphragm 18 and the ultrasonic detection fiber 13 form the second Fabry-Perot interferometer, forming a sealed structure, used to sense the ultrasonic waves generated by partial discharge. The pressure sensitive diaphragm 19 and the pressure detection fiber 14 form the third Fabry-Perot interferometer, forming a sealed structure, used to sense the pressure changes inside the gas-insulated equipment. The cavity lengths of the three Fabry-Perot interferometers differ by more than 100 μm.

[0007] The near-infrared broadband light source 1 is a high-power amplified spontaneous emission light source with a spectral width greater than 40nm, a wavelength coverage of 1574-1575nm, and a power higher than 100mW.

[0008] The splitting ratio of the optical fiber splitter 2 is 50:50.

[0009] The wavelength tuning range of the fiber optic tunable filter 3 covers 1574-1575nm, and the tuning speed is higher than 100Hz.

[0010] The fiber optic coupler 4 is a 2×3 fiber optic coupler with a coupling ratio of 33.3:33.3:33.3.

[0011] The signal sampling rate of the signal processing circuit board 7 is not less than 200kHz.

[0012] The arrayed waveguide grating 8 has no fewer than 64 channels.

[0013] The number of optical fibers in the optical fiber array 9 is equal to the number of channels in the arrayed waveguide grating 8.

[0014] The number of photodiodes in the photodiode array 10 is equal to the number of channels in the array waveguide grating 8, and the detection bandwidth is not less than 200kHz.

[0015] A multi-parameter fiber optic sensing online monitoring method for gas-insulated equipment enables simultaneous detection of multiple parameters, including decomposition products, partial discharge ultrasound, and gas pressure, in sulfur hexafluoride gas-insulated equipment. By sharing and reusing the near-infrared broadband light source and spectral detection components, the system structure is significantly simplified and the system cost is reduced. The specific steps are as follows:

[0016] First, the broadband light emitted by the near-infrared broadband light source 1 is split into two beams by the fiber optic splitter 2, which are then incident on the fiber optic tunable filter 3 and the fiber optic coupler 4, respectively. The signal processing circuit board 7 controls the fiber optic tunable filter 3, and the narrow-linewidth wavelength modulated light generated is used as the excitation light for detecting H2S gas, which is incident on the fiber optic multi-parameter sensor probe 6. The gas in the gas insulation device diffuses through the vent of the fiber optic multi-parameter sensor probe 6 into the miniature gas chamber in the fiber optic multi-parameter sensor probe 6. After absorbing the excitation light, the H2S gas generates photoacoustic pressure waves, which drive the cantilever beam in the gas chamber to vibrate. The gas detection fiber in the fiber optic multi-parameter sensor probe 6 and the cantilever beam constitute a Fabry-Perot interferometer. The generated interference signal is incident on the fiber optic coupler 4 through the four-core optical cable 5, and then dispersed by the arrayed waveguide grating 8 and coupled to the fiber array 9. The optical signals in different fibers in the fiber array 9 represent interference spectral information of different wavelengths.

[0017] Subsequently, the emitted light from the other two output ports of the fiber coupler 4 is incident on the fiber multi-parameter sensor probe 6 via two optical fibers in the four-core optical cable 5, and is used to detect partial discharge ultrasound and air pressure, respectively. The ultrasound-sensitive diaphragm in the fiber multi-parameter sensor probe 6 and the ultrasound detection optical fiber constitute a second Fabry-Perot interferometer, and the cavity length of the interferometer changes accordingly under the action of partial discharge ultrasound. The air pressure-sensitive diaphragm in the fiber multi-parameter sensor probe 6 and the air pressure detection optical fiber constitute a third Fabry-Perot interferometer, and its cavity length changes in the opposite direction with the air pressure in the gas-insulated equipment. The interference light from the two Fabry-Perot interferometers is incident on the fiber coupler 4 via the four-core optical cable 5, and is then dispersed by the arrayed waveguide grating 8 and coupled to the fiber array 9.

[0018] Finally, the photodiode array 10 receives the signal light emitted by the fiber optic array 9, and the signal processing circuit board 7 collects the photoelectric converted optical signal, thus obtaining the superimposed signal of the interference spectra of the three Fabry-Perot interferometers in the fiber optic multi-parameter sensing probe 6; by analyzing the three main frequency components in the spectrum, the cavity lengths of the three Fabry-Perot interferometers are simultaneously demodulated; ultimately, the simultaneous detection of the three parameters of gas decomposition products, partial discharge ultrasound, and gas pressure is achieved.

[0019] The beneficial effects of this invention are as follows: It integrates three Fabry-Perot interferometers into a miniature fiber optic multi-parameter sensing probe, enabling highly sensitive sensing of multiple parameters, including decomposition products, partial discharge ultrasound, and gas pressure, in sulfur hexafluoride gas-insulated equipment. Simultaneous detection of these three key parameters is achieved using frequency division multiplexing-based spectral demodulation technology. High-power near-infrared broadband light sources and high-speed spectral detection modules are costly, and traditional solutions can only demodulate the cavity length of one Fabry-Perot interferometer. This invention significantly simplifies the system structure and reduces system cost by sharing and multiplexing the near-infrared broadband light source and spectral detection components. Both excitation and detection light in the system are transmitted via optical fiber, and the sensing probe contains no electrical components, possessing electromagnetic interference resistance and long-distance sensing capabilities. This invention provides a highly competitive technical solution for online multi-parameter monitoring of gas-insulated equipment. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the system structure of the present invention.

[0021] Figure 2 This is a schematic diagram of the structure of a fiber optic multi-parameter sensor probe.

[0022] In the diagram: 1 Near-infrared broadband light source; 2 Fiber optic splitter; 3 Fiber optic tunable filter; 4 Fiber optic coupler; 5 Four-core optical cable; 6 Fiber optic multi-parameter sensor probe; 7 Signal processing circuit board; 8 Arrayed waveguide grating; 9 Fiber optic array; 10 Photodiode array; 11 Excitation fiber; 12 Gas detection fiber.

[0023] 13 Ultrasonic detection fiber; 14 Pressure detection fiber; 15 Vent hole; 16 Miniature air cavity; 17 Cantilever beam; 18 Ultrasonic sensitive diaphragm; 19 Pressure sensitive diaphragm; 20 Ceramic shell. Detailed Implementation

[0024] The specific embodiments of the present invention will be described in detail below with reference to the technical solutions and accompanying drawings.

[0025] A multi-parameter fiber optic sensing online monitoring system for gas-insulated equipment mainly includes a near-infrared broadband light source 1, a fiber optic splitter 2, a fiber optic tunable filter 3, a fiber optic coupler 4, a four-core optical cable 5, a fiber optic multi-parameter sensing probe 6, a signal processing circuit board 7, an arrayed waveguide grating 8, a fiber optic array 9, and a photodiode array 10. The broadband light emitted by the near-infrared broadband light source 1 is split into two beams by the fiber optic splitter 2, which are respectively incident on the fiber optic tunable filter 3 and the fiber optic coupler 4. The signal processing circuit board 7 controls the fiber optic tunable filter 3, and the narrow-linewidth wavelength modulated light generated is used as the excitation for detecting H2S gas. Light is incident on the fiber optic multi-parameter sensing probe 6; the gas in the gas-insulated device diffuses through the vent of the fiber optic multi-parameter sensing probe 6 into the miniature gas chamber in the fiber optic multi-parameter sensing probe 6. After the H2S gas absorbs the excitation light, it generates photoacoustic pressure waves, which drive the cantilever beam in the gas chamber to vibrate; the gas detection fiber in the fiber optic multi-parameter sensing probe 6 and the cantilever beam constitute a Fabry-Perot interferometer. The generated interference signal is incident on the fiber optic coupler 4 through the four-core optical cable 5, and then dispersed by the arrayed waveguide grating 8 and coupled to the fiber array 9. The optical signals in different fibers in the fiber array 9 represent interference spectral information of different wavelengths. The emitted light from the other two output ports of the fiber coupler 4 is incident on the fiber multi-parameter sensor probe 6 via two optical fibers in the four-core optical cable 5, and is used to detect partial discharge ultrasound and air pressure, respectively. The ultrasound-sensitive diaphragm and the ultrasound detection fiber in the fiber multi-parameter sensor probe 6 form a second Fabry-Perot interferometer, and the cavity length of the interferometer changes accordingly under the action of partial discharge ultrasound. The air pressure-sensitive diaphragm and the air pressure detection fiber in the fiber multi-parameter sensor probe 6 form a third Fabry-Perot interferometer, and its cavity length changes in the opposite direction with the air pressure in the gas-insulated equipment. The interference light from the two Fabry-Perot interferometers is incident on the fiber coupler 4 via the four-core optical cable 5, and is then dispersed by the arrayed waveguide grating 8 and coupled to the fiber array 9. The photodiode array 10 receives the signal light emitted by the fiber optic array 9, and the signal processing circuit board 7 collects the optical signal after photoelectric conversion, which is the superposition signal of the interference spectra of the three Fabry-Perot interferometers in the fiber optic multi-parameter sensing probe 6. By analyzing the three main frequency components in the spectrum, the cavity lengths of the three Fabry-Perot interferometers are simultaneously demodulated. Finally, the simultaneous detection of three parameters—gas decomposition products, partial discharge ultrasound, and gas pressure—is achieved.

[0026] Among them, the near-infrared broadband light source 1 is a high-power amplified spontaneous emission light source with a wavelength range of 1530-1580nm and an output power of 200mW. The fiber optic splitter 2 has a splitting ratio of 50:50. The fiber optic tunable filter 3 is a fiber optic Fabry-Perot filter based on piezoelectric ceramics, with a wavelength tuning range of 1510-1590nm and a maximum tuning speed of 1kHz. The fiber optic coupler 4 is a 2×3 fiber optic coupler with a coupling ratio of 33.3:33.3:33.3.

[0027] The fiber optic multi-parameter sensing probe 6 mainly consists of an excitation fiber 11, a gas detection fiber 12, an ultrasonic detection fiber 13, a pressure detection fiber 14, a vent 15, a miniature air cavity 16, a cantilever beam 17, an ultrasonic sensitive diaphragm 18, a pressure sensitive diaphragm 19, and a ceramic shell 20. The cantilever beam 17 and the gas detection fiber 12 form the first Fabry-Perot interferometer, with a cavity length of 100 μm, used to sense gas photoacoustic signals to measure the concentration of H2S gas. The ultrasonic sensitive diaphragm 18 and the ultrasonic detection fiber 13 form the second Fabry-Perot interferometer, with a cavity length of 250 μm, used to sense ultrasonic waves generated by partial discharge. The pressure sensitive diaphragm 19 and the pressure detection fiber 14 form the third Fabry-Perot interferometer, with a cavity length of 400 μm, used to sense pressure changes inside gas-insulated equipment.

[0028] The signal processing circuit board 7 generates one modulation signal to control the fiber optic tunable filter 3 at a modulation frequency of 1 kHz; the signal processing circuit board 7 has 64 analog-to-digital conversion channels and a signal sampling rate of 200 kHz. The arrayed waveguide grating 8 has 64 channels. The fiber optic array 9 consists of 64 optical fibers. The photodiode array 10 consists of 64 photodiodes.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-parameter fiber optic sensing online monitoring system for gas-insulated equipment, characterized in that, The multi-parameter fiber optic sensing online monitoring system includes a near-infrared broadband light source (1), a fiber optic splitter (2), a fiber optic tunable filter (3), a fiber optic coupler (4), a four-core optical cable (5), a fiber optic multi-parameter sensing probe (6), a signal processing circuit board (7), an arrayed waveguide grating (8), a fiber optic array (9), and a photodiode array (10). The near-infrared broadband light source (1) is connected to the fiber optic splitter (2), which is connected to the fiber optic tunable filter (3) and the fiber optic coupler (4) respectively. The broadband light emitted by the near-infrared broadband light source (1) is split into two beams after passing through the fiber optic splitter (2), and is incident on the fiber optic tunable filter (3) and the fiber optic coupler (4) respectively. The fiber optic tunable filter (3) and the fiber optic coupler (4) are both connected to the four-core optical cable (5), which is connected to the fiber optic multi-parameter sensing probe (6). The emitted light from the fiber coupler (4) is incident on the fiber multi-parameter sensor probe (6) via the four-core optical cable (5); the signal processing circuit board (7) is connected to the fiber optic tunable filter (3), and the signal processing circuit board (7) controls the fiber optic tunable filter (3), and the generated wavelength-modulated light is used as the excitation light for detecting H2S gas; the fiber coupler (4), the array waveguide grating (8) and the fiber array (9) are connected in sequence, and the signal light reflected by the fiber multi-parameter sensor probe (6) is incident on the fiber coupler (4) via three optical fibers in the four-core optical cable (5), and then coupled to the fiber array (9) after being dispersed by the array waveguide grating (8); the fiber array (9), the photodiode array (10) and the signal processing circuit board (7) are connected in sequence, and the photodiode array (10) receives the signal light emitted by the fiber array (9), and the signal processing circuit board (7) collects and processes the optical signal after photoelectric conversion; The fiber optic multi-parameter sensing probe (6) mainly consists of an excitation fiber (11), a gas detection fiber (12), an ultrasonic detection fiber (13), a pressure detection fiber (14), a vent (15), a miniature air cavity (16), a cantilever beam (17), an ultrasonic sensitive diaphragm (18), a pressure sensitive diaphragm (19), and a ceramic shell (20). Gas enters the miniature air cavity (16) through the vent (15). The excitation fiber (11) directs near-infrared excitation light into the miniature air cavity (16), generating a photoacoustic signal. The arm beam (17) and the gas detection fiber (12) therein constitute the first Fabry-Perot interferometer, which is used to sense the gas photoacoustic signal to realize the concentration measurement of H2S gas; the ultrasonic sensitive diaphragm (18) and the ultrasonic detection fiber (13) constitute the second Fabry-Perot interferometer, forming a sealed structure, which is used to sense the ultrasonic waves generated by partial discharge; the pressure sensitive diaphragm (19) and the pressure detection fiber (14) constitute the third Fabry-Perot interferometer, forming a sealed structure, which is used to sense the pressure change inside the gas insulation equipment.

2. The multi-parameter fiber optic sensing online monitoring system according to claim 1, characterized in that, The cavity lengths of the three Fabry-Perot interferometers differ by more than 100 μm.

3. The multi-parameter fiber optic sensing online monitoring system according to claim 1, characterized in that, The near-infrared broadband light source (1) is a high-power amplified spontaneous emission light source with a spectral width greater than 40 nm, a wavelength coverage of 1574-1575 nm, and a power greater than 100 mW.

4. The multi-parameter fiber optic sensing online monitoring system according to claim 1, characterized in that, The optical fiber splitter (2) has a splitting ratio of 50:

50.

5. The multi-parameter fiber optic sensing online monitoring system according to claim 1, characterized in that, The wavelength tuning range of the fiber optic tunable filter (3) covers 1574-1575 nm, and the tuning speed is higher than 100 Hz.

6. The multi-parameter fiber optic sensing online monitoring system according to claim 1, characterized in that, The fiber optic coupler (4) is a 2×3 fiber optic coupler with a coupling ratio of 33.3: 33.3: 33.

3.

7. The multi-parameter fiber optic sensing online monitoring system according to claim 1, characterized in that, The signal sampling rate of the signal processing circuit board (7) is not less than 200 kHz.

8. The multi-parameter fiber optic sensing online monitoring system according to claim 1, characterized in that, The arrayed waveguide grating (8) has no fewer than 64 channels; The number of optical fibers in the optical fiber array (9) is equal to the number of channels in the arrayed waveguide grating (8); The number of photodiodes in the photodiode array (10) is equal to the number of channels in the array waveguide grating (8), and the detection bandwidth is not less than 200 kHz.

9. A multi-parameter fiber optic sensing online monitoring method for gas-insulated equipment, characterized in that, Simultaneous detection of multiple parameters, including decomposition products, partial discharge ultrasound, and gas pressure, in sulfur hexafluoride gas-insulated equipment is achieved. This is accomplished by sharing and reusing the near-infrared broadband light source and spectral detection components, significantly simplifying the system structure and reducing system costs. The specific steps are as follows: First, the broadband light emitted by the near-infrared broadband light source (1) is split into two beams by the fiber optic splitter (2) and incident on the fiber optic tunable filter (3) and the fiber optic coupler (4) respectively. The signal processing circuit board (7) controls the fiber optic tunable filter (3), and the generated narrow linewidth wavelength modulation light is used as the excitation light for detecting H2S gas and is incident on the fiber optic multi-parameter sensor probe (6). The gas in the gas insulation device diffuses through the air vent of the fiber optic multi-parameter sensor probe (6) into the miniature gas chamber in the fiber optic multi-parameter sensor probe (6). After absorbing the excitation light, the H2S gas generates photoacoustic pressure waves, which drive the cantilever beam in the gas chamber to vibrate. The gas detection fiber in the fiber optic multi-parameter sensor probe (6) and the cantilever beam constitute a Fabry-Perot interferometer. The generated interference signal is incident on the fiber optic coupler (4) through the four-core optical cable (5), and then coupled to the fiber array (9) after being dispersed by the arrayed waveguide grating (8). The optical signals in different fibers in the fiber array (9) represent interference spectral information of different wavelengths. Subsequently, the emitted light from the other two output ports of the fiber coupler (4) is incident on the fiber multi-parameter sensor probe (6) through two optical fibers in the four-core optical cable (5), and is used to detect partial discharge ultrasound and air pressure, respectively; the ultrasound-sensitive diaphragm in the fiber multi-parameter sensor probe (6) and the ultrasound detection optical fiber constitute the second Fabry-Perot interferometer, and the cavity length of the interferometer changes accordingly under the action of partial discharge ultrasound; the air pressure-sensitive diaphragm in the fiber multi-parameter sensor probe (6) and the air pressure detection optical fiber constitute the third Fabry-Perot interferometer, and its cavity length changes in the opposite direction with the air pressure in the gas-insulated equipment; the interference light from the two Fabry-Perot interferometers is incident on the fiber coupler (4) through the four-core optical cable (5), and is then dispersed by the arrayed waveguide grating (8) and coupled to the fiber array (9); Finally, the photodiode array (10) receives the signal light emitted by the fiber array (9), and the signal processing circuit board (7) collects the light signal after photoelectric conversion, thus obtaining the superimposed signal of the interference spectra of the three Fabry-Perot interferometers in the fiber multi-parameter sensing probe (6); by analyzing the three main frequency components in the spectrum, the cavity lengths of the three Fabry-Perot interferometers are simultaneously demodulated; finally, the simultaneous detection of the three parameters of gas decomposition products, partial discharge ultrasound and gas pressure is realized.

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