CN114739955B - Optical fiber sensing system for dissolved gas in transformer bushing oil - Google Patents
Optical fiber sensing system for dissolved gas in transformer bushing oil Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
- G01N21/45—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods
- G01N2021/458—Refractivity; Phase-affecting properties, e.g. optical path length using interferometric methods; using Schlieren methods using interferential sensor, e.g. sensor fibre, possibly on optical waveguide
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
- G01N2201/08—Optical fibres; light guides
- G01N2201/088—Using a sensor fibre
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Abstract
The invention provides an optical fiber sensing system for dissolved gas in transformer bushing oil, which comprises a light source, a circulator, a 2X 2 coupler, an erbium-doped optical fiber amplifier, a first 1X 2 coupler, a delay optical fiber, a gas sensing module, a second 1X 2 coupler, an acoustic-optical modulator driver, a balance photoelectric detector, a data acquisition unit and an upper computer, wherein the light source is connected with the circulator through the data acquisition unit; the gas sensing module is composed of a ceramic membrane and a hollow photonic crystal fiber, the ceramic membrane coated with a high polymer material can realize high-efficiency oil-gas separation, and the hollow photonic crystal fiber can be used as a gas chamber for interaction of light and gas. The gas sensing module is arranged in the transformer bushing oil conservator, so that the time for the fault gas to diffuse to the gas sensing module in a convection manner is shortened. The invention improves the real-time performance of on-line monitoring, reduces the performance requirements on the light source and the balance photoelectric detector while ensuring higher sensitivity and lower detection limit, and reduces the cost.
Description
Technical Field
The invention belongs to the technical field of optical sensing systems, and particularly relates to an optical fiber sensing system for dissolved gas in transformer bushing oil.
Background
Analysis of dissolved gas in transformer bushing oil is an important means for judging the running state of the transformer bushing. The type and the severity of the fault of the transformer bushing can be diagnosed by monitoring the type and the content of the dissolved gas in the oil of the transformer bushing, and the early latent fault inside the oil-immersed transformer bushing can be predicted. The method provides higher requirements for real-time performance, accuracy and lower detection limit of the online monitoring device for the dissolved gas in the transformer bushing oil. The on-line monitoring technology for the dissolved gas in the transformer bushing oil mainly comprises an oil-gas separation technology and a multi-component gas detection technology.
Two main problems that restrict the real-time performance of online monitoring of dissolved gas in transformer bushing oil are respectively long time for fault gas to diffuse from a generation point to an oil taking port of the transformer bushing through dissolution and convection and low oil-gas separation efficiency. At present, a sensing device for directly detecting the content of dissolved gas in-situ transformer bushing oil is not available at home and abroad. Whether the device is an off-line detection device or an on-line monitoring device, the oil-gas separation is carried out after an oil sample is obtained from an oil taking port of a transformer bushing, and then the components and the solubility of fault gas are tested. The large transformer bushing is large in size and complex in structure, fault gas is mostly generated at a high-temperature and concentrated field intensity position, and the distance between the fault gas and an oil taking port at the bottom of the oil immersed bushing is long. The fault gas is dissolved in the transformer bushing oil and then flows and diffuses to the oil taking port, so that the time of days or even months is consumed, and even the fault gas generated in a 'dead oil zone' is difficult to reach the oil taking port. The concentration of the fault gas which is convectively diffused to the oil taking port is reduced greatly compared with the reduced concentration of the fault gas at the position where the fault gas is generated. These not only reduce the real-time of on-line monitoring device, also greatly improved the requirement to on-line monitoring device detection lower limit. If oil-gas separation device can directly place in transformer bushing oil conservator, will greatly shorten the time of trouble gas convection diffusion stage, improve on-line monitoring's real-time.
The main oil-gas separation methods at present are a vacuum degassing method, a headspace degassing method and a polymer membrane degassing method. Although the vacuum degassing method and the headspace degassing method can quickly realize oil-gas separation balance, the devices have complex structures and complicated operation, and currently, the devices do not have the possibility of being arranged in a transformer bushing oil conservator. The polymer film has the characteristics of simple structure, oil resistance and high temperature resistance, can continuously perform gas exchange with the transformer bushing oil after the oil-gas separation reaches dynamic balance, and has the potential of being arranged in the transformer bushing oil conservator to realize continuous monitoring of dissolved gas in oil. At present, the multi-component gas detection technology mainly comprises a gas chromatography method, a semiconductor sensor method and an optical sensing method. Gas chromatography requires a chromatographic column to separate gas, consumes carrier gas, and cannot achieve continuous measurement. Although the semiconductor sensor is low in cost, the performance of the semiconductor sensor is gradually changed in the long-term use process, the semiconductor sensor needs to be calibrated and replaced regularly, and cross sensitivity is easy to occur among gas components, so that the detection accuracy is reduced. The optical sensing method has high sensitivity and low detection lower limit, is not easy to be interfered by electromagnetic waves, has good insulativity of the optical fiber, and is increasingly applied to the online monitoring of the transformer bushing.
Disclosure of Invention
The invention provides an optical fiber sensing system for dissolved gas in transformer bushing oil, which comprises a light source, a circulator, a 2 x 2 coupler, an erbium-doped optical fiber amplifier, a first 1 x 2 coupler, a delay optical fiber, a gas sensing module, a second 1 x 2 coupler, an acoustic-optical modulator driver, a balanced photoelectric detector, a data acquisition unit and an upper computer.
The gas sensing module consists of a ceramic membrane, a hollow photonic crystal fiber and a ceramic ring side wall.
The gas sensing module is disc-shaped, two circular ceramic membranes and the side wall of a ceramic ring are bonded together by utilizing silica gel, the side wall of the ceramic ring is clamped between the two ceramic membranes, a gap of 1mm is reserved between the two ceramic membranes, and the hollow photonic crystal fiber is coiled in the gap; two through holes are formed in the side wall of the ceramic ring, and the through holes are sealed after two ends of the hollow photonic crystal fiber are led out from the two through holes.
The diameter of the ceramic membrane is 6.5cm, the thickness of the ceramic membrane is 0.5mm, pores with the pore diameter of 50nm are distributed on the ceramic membrane, the porosity is more than 35%, and a high polymer material is coated on the surface of the ceramic membrane to form an oil-gas separation layer with the thickness of 6 mu m for realizing high-efficiency oil-gas separation; the inner diameter of the side wall of the ceramic ring is 6cm, and the outer diameter of the side wall of the ceramic ring is 6.5 cm.
The optical fiber length of the hollow photonic crystal optical fiber is 0.8m, a coating layer with the diameter of 10 mu m is stripped on the hollow photonic crystal optical fiber, micropores with the aperture of 3 mu m are formed on the coating layer by adopting a focused ion beam technology, 4 micropores distributed along the axial direction are processed totally, each micropore is processed from the surface of the optical fiber to the hollow fiber core along the radial direction and stops, the distance between every two adjacent micropores is 15cm, leading-out ends on two sides of the hollow photonic crystal optical fiber are welded with the single-mode optical fiber, and the welding loss is less than 0.1 dB.
And the gas dissolved in the oil enters the gap of the gas sensing module after penetrating through the ceramic membrane and finally diffuses to the hollow fiber core of the hollow photonic crystal fiber through the micropores.
The materials of all parts of the gas sensing module have good insulating, oil-resistant, pressure-resistant and high-temperature-resistant performances, the high temperature resistance of all the materials is not lower than 150 ℃, and the phenomena of oil leakage, air leakage and fracture of the ceramic membrane do not occur within the pressure range of 0.1 MPa-1 MPa.
The first 1 x 2 coupler and the second 1 x 2 coupler have a light splitting ratio of 99:1 and are connected with the delay optical fiber, the erbium-doped optical fiber amplifier and the gas sensing module to form a ring-down cavity; the ring-down cavity length is 51m and the delay fiber length is 47.1 m.
The erbium-doped optical fiber amplifier can amplify in two directions, synchronously amplifies clockwise light and anticlockwise light, compensates inherent loss in a ring-down cavity, increases the number of ring-down signal peak values, and improves the gas concentration detection accuracy of the device.
The splitting ratio of the 2 x 2 coupler is 50: 50; and the acoustic optical modulator and the ring-down cavity form a Sagnac interference ring.
The light source is a Santec TSL-710 laser, works in a coherent control mode, the line width of output light is 40MHz, and the coherence length is 5 m.
The gas sensing module is arranged in the transformer bushing oil conservator, and the gas sensing module is connected with the part outside a transformer bushing in the transformer bushing oil dissolved gas optical fiber sensing system by using the sealing screw which is inserted with two single-mode optical fibers to seal the transformer bushing oil conservator. Through the arrangement mode, the time for convection diffusion of fault gas to the gas sensing module can be shortened, and the detection real-time performance of the device is improved.
The optical fiber sensing system adopts a frequency shift cavity ring-down technology to demodulate sensing signals. Firstly, carrying out fast Fourier transform on sensing signal data detected by a balanced photoelectric detector to obtain a ring-down signal with the amplitude gradually reduced along with the distance, carrying out peak seeking on the ring-down signal, carrying out exponential fitting after obtaining a peak point to obtain a signal ring-down distance, and thus, deriving the concentration of a target gas in a gas chamber.
The combination of the optical fiber frequency shift cavity ring-down technology and the gas sensing module based on the hollow photonic crystal fiber is utilized, the processing of time domain signals is converted into the processing of space domain signals, the performance requirements on a light source and the detection performance are lowered, the efficiency and the distance of interaction of light and gas are increased, and the sensitivity and the lower detection limit of the device are further improved.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) the gas sensing module can be used for oil-gas separation and can also be used as a gas chamber for interaction of light and gas. The gas sensing module has good insulation, oil resistance, pressure resistance and high temperature resistance while having good oil-gas separation performance, can be directly placed in the transformer bushing oil conservator, greatly shortens the time from generation to convection diffusion of fault gas to the sensing module, improves the real-time performance of the device, and is beneficial to more rapidly finding early latent faults of the transformer bushing.
(2) The invention adopts the hollow photonic crystal fiber as the gas chamber of the optical fiber gas sensor and is connected into the optical fiber ring-down cavity. The hollow photonic crystal fiber has smaller bending loss, can be coiled with smaller diameter, has more compact air chamber structure, and is beneficial to obtaining the gas sensing module with smaller volume so as to be conveniently arranged in the transformer bushing. Meanwhile, the use of the hollow photonic crystal fiber increases the efficiency and distance of the action of light and gas, and the hollow photonic crystal fiber is connected into the ring-down cavity to be used as a gas chamber, so that the improvement of the sensitivity and the detection lower limit of the device are facilitated.
(3) The invention combines frequency shift interference with the fiber cavity ring-down technology, converts time domain signal detection into space domain signal detection, greatly reduces the performance requirements on a light source and a detector while ensuring sensitivity and detection lower limit, and reduces the device cost.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention.
Fig. 1 is a schematic diagram of an optical fiber sensing system for dissolved gas in transformer bushing oil.
Fig. 2 is a schematic diagram of a gas sensing module.
FIG. 3 is a schematic view of a hollow core photonic crystal fiber.
Fig. 4 is a partial schematic view of a transformer bushing with a gas sensing module installed.
The device comprises a light source 1, a circulator 2, an erbium-doped fiber amplifier 3, a first 1X 2 coupler 5, a delay fiber 6, a gas sensing module 7, a second 1X 2 coupler 8, an acousto-optic modulator 9, an acousto-optic modulator driver 10, a balanced photoelectric detector 11, a data acquisition unit 12 and an upper computer 13, wherein the light source 1, the circulator 2, the data acquisition unit 12 and the upper computer 13 are connected in series.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, embodiments of the present invention are further described in detail with reference to the accompanying drawings.
Referring to fig. 1, the invention provides an optical fiber sensing system for dissolved gas in transformer bushing oil, which includes a light source 1, a circulator 2, a 2 × 2 coupler 3, an erbium-doped optical fiber amplifier 4, a first 1 × 2 coupler 5, a delay optical fiber 6, a gas sensing module 7, a second 1 × 2 coupler 8, an acousto-optic modulator 9, an acousto-optic modulator driver 10, a balanced photodetector 11, a data collector 12 and an upper computer 13. The first 1 x 2 coupler 5, the delay optical fiber 6, the gas sensing module 7, the second 1 x 2 coupler 8 and the erbium-doped optical fiber amplifier 4 form a ring-down cavity; the split ratio of the ports (ii) and (iii) of the first 1 × 2 coupler 5 is 99:1, the second 1 × 2 coupler 8 has a split ratio of ports (c) to (c) of 99: 1; leading-out ends of the ring-down cavity are respectively a port III of the first 1X 2 coupler 5 and a port III of the second 1X 2 coupler 8; the length of the ring-down cavity can be controlled by the delay optical fiber 6, and a better demodulation effect can be obtained when the length of the ring-down cavity is integral multiple of the minimum spatial resolution of the demodulation module; the length of the delay optical fiber is 47.1m, and the total length of the ring-down cavity is 51 m. The 2 multiplied by 2 coupler 3, the acousto-optic modulator 9 and the ring-down cavity form a Sagnac interference ring; two ports of the Sagnac interference ring are a port I and a port II of the 2 multiplied by 2 coupler 3; the upper computer 13 is connected with an acousto-optic modulator driver 10, the acousto-optic modulator driver 10 is connected with an acousto-optic modulator 9, and the upper computer 13 controls the sweep frequency range, the sweep frequency step length and the interval time of each step of the acousto-optic modulator 9 through software; the acousto-optic modulator driver 10 is connected with the data acquisition device 12, and a synchronous signal sent by the acousto-optic modulator driver 10 is used as a trigger signal of the data acquisition device 12; the data acquisition unit 12 is connected with the upper computer 13, and the data acquisition unit 12 acquires the output signal of the balanced photoelectric detector 11 and sends the output signal to the upper computer 13 for processing; continuous laser emitted by the light source 1 enters the Sagnac interference ring through a port I and a port II of the circulator 2, and is divided into two beams of light with equal light intensity which are transmitted along the clockwise direction and the anticlockwise direction at the 2 multiplied by 2 coupler 3. Light propagating clockwise enters the ring-down cavity from the port III of the first 1X 2 coupler 5, 99% of the light is left in the ring-down cavity for next circulation in each ring, and only 1% of the light leaks from the port III of the second 1X 2 coupler 8 and returns to the 2X 2 coupler 3 after passing through the acousto-optic modulator 9. After passing through the acousto-optic modulator 9, the light propagating counterclockwise enters the ring-down cavity from the port c of the second 1 × 2 coupler 8, 99% of the light is left in the ring-down cavity for the next cycle in each ring, and only 1% of the light leaks from the port c of the first 1 × 2 coupler 5 and returns to the 2 × 2 coupler 3. The acousto-optic modulator 9 is asymmetrically arranged in the Sagnac interferometric ring, so that two beams of light with opposite directions have different phase changes after passing through the acousto-optic modulator 9, and generate phase difference when returning to the 2 x 2 coupler 3, so as to generate interference. The interference signal is output from the port (r) and the port (r) of the 2 x 2 coupler 3, wherein the port (r) of the 2 x 2 coupler 3 is connected to the balanced photodetector 11 through the port (r) of the circulator 2. The length of the optical fiber of the 2 x 2 coupler 3, the port of which is connected to the balanced photoelectric detector 11, is equal to the length of the optical fiber of the 2 x 2 coupler 3, the port of which is connected to the balanced photoelectric detector 11 through the port of the circulator 2 and the port of which is connected to the balanced photoelectric detector 11, so that the phase difference of signals connected to the input port of the balanced photoelectric detector is kept at 180 degrees, and a good differential amplification effect of the balanced photoelectric detector is obtained. The light source selects a tunable laser with a Santec TSL-710 model, works in a coherent control mode, the output light line width is 40MHz, the coherent length is 5m, and the coherent length is far smaller than the length of the ring-down cavity 51m, so that interference can be generated only by clockwise light beams and anticlockwise light beams which pass through the ring-down cavity for the same times at the 2 x 2 coupler 3, and effective interference can not be generated between clockwise light and anticlockwise light which pass through the ring-down cavity for different times and between light itself which passes through two directions with different times of the ring-down cavity. The upper computer 13 is connected with an acousto-optic modulator driver and controls the acousto-optic modulator 9 to sweep frequency within the frequency range of 90-110 MHz in a step length of 0.01MHz and at a time interval of 1 ms. Acousto-optic modulator driver 10 sends a synchronization signal to data collector 12 each time a new sweep period begins. After receiving the synchronization signal, the data collector 12 collects the output signal of the light balance photodetector 11 at a sampling rate of 100 kHz. The data acquisition unit 12 outputs the acquired signals to the upper computer 13 for processing. Firstly, fast Fourier transform is carried out on signal data to obtain a ring-down signal with the amplitude gradually reduced along with the distance. And searching the peak of the ring-down signal, obtaining a peak point, then performing exponential fitting to obtain a signal ring-down distance, and deducing the concentration of the target gas in the gas chamber.
Referring to fig. 2, the gas sensing module is composed of a ceramic membrane, a hollow photonic crystal fiber and a ceramic ring side wall; the gas sensing module is disc-shaped, two circular ceramic membranes are bonded with the side wall of the ceramic ring by using silica gel, a gap of 1mm is reserved between the two ceramic membranes, and the hollow photonic crystal fiber is wound in the gap; two through holes are formed in the side wall of the ceramic ring, and the through holes are sealed after two ends of the hollow photonic crystal fiber are led out from the two through holes; the diameter of the ceramic membrane is 6.5cm, the thickness of the ceramic membrane is 0.5mm, pores with the pore diameter of 50nm are distributed on the ceramic membrane, the porosity is more than 35%, and a high polymer material is coated on the surface of the ceramic membrane to form an oil-gas separation layer with the thickness of 6 microns, so that efficient oil-gas separation is realized; the coating steps are as follows: soaking the ceramic membrane in an ethanol solution, and cleaning the surface; dissolving Teflon AF2400 resin in a perfluorinated solvent FC-770, and preparing a 1% Teflon AF2400 solution in mass fraction; soaking the surface of the ceramic membrane in the prepared solution for 10 s; taking out and placing in an oven, and drying for 24 hours at 60 ℃; finally, the temperature of the oven is adjusted to 120 ℃ for drying for 6 hours, so that the solvent is completely removed. In the process, the thickness of the formed polymer film can be controlled by controlling the times of soaking the surface of the ceramic film in the Teflon AF2400 solution; the inner diameter of the side wall of the ceramic ring is 6cm, and the outer diameter of the side wall of the ceramic ring is 6.5 cm.
Referring to fig. 3, the fiber length of the hollow photonic crystal fiber is 0.8m, a focused ion beam technology is adopted to strip a coating layer of 10 μm on the hollow photonic crystal fiber and form micropores with the aperture of 3 μm on the cladding, 4 micropores distributed along the axial direction are processed in total, each micropore is processed from the surface of the fiber to the hollow fiber core along the radial direction and stops, the distance between every two adjacent micropores is 15cm, and leading-out ends on two sides of the hollow photonic crystal fiber are welded with the single-mode fiber; the micropore processing steps are as follows: winding the optical fiber on the surface of a 3-inch silicon wafer stuck with conductive adhesive, determining the processing position of the micro-channel, and marking; taking down the optical fiber, placing the optical fiber in alcohol to be soaked for 1-2 hours, and stripping a coating layer of a marking area by using Miller pliers; winding the whole optical fiber on the silicon wafer again according to the marked position; fixing a silicon wafer on a sample table of a focused ion beam system, and carrying out gold spraying treatment through gold spraying equipment; and after the treatment is finished, placing the sample stage in a focused ion beam system, vacuumizing and carrying out focused ion beam processing.
Referring to fig. 4, the gas sensing module is arranged in the transformer bushing oil conservator, the transformer bushing oil conservator is sealed by using a sealing screw inserted with two single-mode fibers, and the gas sensing module is connected with the part outside a transformer bushing in the transformer bushing oil dissolved gas fiber sensing system, and the type and severity of the transformer bushing fault can be diagnosed by monitoring the type and content of the dissolved gas in the transformer bushing oil, so that the early latent fault inside the oil-immersed transformer bushing can be predicted.
Claims (1)
1. An optical fiber sensing system for dissolved gas in transformer bushing oil is characterized by comprising a light source (1), a circulator (2), a 2 x 2 coupler (3), an erbium-doped optical fiber amplifier (4), a first 1 x 2 coupler (5), a delay optical fiber (6), a gas sensing module (7), a second 1 x 2 coupler (8), an acousto-optic modulator (9), an acousto-optic modulator driver (10), a balanced photoelectric detector (11), a data collector (12) and an upper computer (13),
the split ratio of the ports II and III of the first 1X 2 coupler (5) is 99:1, the second 1 x 2 coupler (8) has a split ratio of ports (ii) to ports (iii) of 99: 1; a first 1 multiplied by 2 coupler (5), a delay optical fiber (6), a gas sensing module (7), a second 1 multiplied by 2 coupler (8) and an erbium-doped optical fiber amplifier (4) form a ring-down cavity; the length of the ring-down cavity is integral multiple of the minimum spatial resolution of the sensing system;
the length of the optical fiber of which the port II of the 2 multiplied by 2 coupler (3) is connected to the balanced photoelectric detector (11) is equal to the length of the optical fiber of which the port I of the 2 multiplied by 2 coupler (3) is connected to the balanced photoelectric detector (11) through the port II of the circulator (2) and the port III;
the light source (1) selects a tunable laser, works in a coherent control mode, the line width of output light is 40MHz, the coherence length is 5m, and the coherence length is far smaller than the length of a ring-down cavity;
the gas sensing module (7) consists of a ceramic membrane, a hollow photonic crystal fiber and a ceramic ring side wall;
the gas sensing module (7) is disc-shaped, two ceramic membranes in a circular shape are bonded with the side wall of a ceramic ring by using silica gel, the side wall of the ceramic ring is clamped between the two ceramic membranes, a gap of 1mm is formed between the two ceramic membranes, and the hollow photonic crystal fiber is coiled and placed in the gap; two through holes are formed in the side wall of the ceramic ring, and two ends of the hollow photonic crystal fiber are respectively led out from the two through holes; the diameter of the ceramic membrane is 6.5cm, the thickness of the ceramic membrane is 0.5mm, pores with the pore diameter of 50nm are distributed on the ceramic membrane, and the porosity of the ceramic membrane is more than 35%; coating a high polymer material Teflon AF2400 on the surface of the ceramic membrane to form an oil-gas separation layer with the thickness of 6 mu m; the inner diameter of the side wall of the ceramic ring is 6cm, and the outer diameter of the side wall of the ceramic ring is 6.5 cm; the optical fiber length of the hollow photonic crystal optical fiber is 0.8m, the side surface of the hollow photonic crystal optical fiber is provided with 4 micropores distributed along the axial direction in total, the distance between every two adjacent micropores is 15cm, and the diameter of each micropore is 3 mu m; each micropore is formed by adopting a focused ion beam technology after a coating layer with the length of 10 mu m is stripped on the hollow photonic crystal fiber; leading-out ends on two sides of the hollow photonic crystal fiber are welded with the single-mode fiber, and the welding loss is less than 0.1 dB.
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| CN104807805A (en) * | 2015-05-04 | 2015-07-29 | 华北电力大学 | Detection device for gas dissolved in transformer oil based on Raman spectrum |
| CN104807765B (en) * | 2015-05-04 | 2018-01-23 | 华北电力大学 | The Gas in Oil of Transformer detection means of high sensitivity spectral absorption damped oscillation chamber |
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