A partial discharge positioning system and positioning method based on fluorescent optical fiber

Abstract

The present invention discloses a local discharge positioning method based on fluorescent optical fiber, which obtains local discharge signals through fluorescent optical fiber, respectively obtains excitation light signals output from both ends of the fluorescent optical fiber, and calculates the local discharge position according to the excitation light signals obtained from both ends of the fluorescent optical fiber. The local discharge positioning method based on fluorescent optical fiber with the above-mentioned optimized design senses the local discharge signal of the conductor through the fluorescent optical fiber, and uses the attenuation principle of the excitation light emitted from both ends of the fluorescent optical fiber to locate the excitation light generation position corresponding to the local discharge position, thereby realizing accurate and reliable positioning of the local discharge position. The present invention also discloses a local discharge positioning system based on fluorescent optical fiber.

Description

Technical Field

[0001] The invention relates to the field of partial discharge detection, and in particular to a partial discharge positioning system and positioning method based on fluorescent optical fiber. Background Art

[0002] Electrical equipment such as gas insulated switchgear (GIS), transformers, and ring main units play a very important role in high-voltage power transmission and transformation systems. Any device failure may cause great economic losses. An important cause of these device failures is partial discharge (PD) caused by insulation degradation inside the device.

[0003] Partial discharge is a manifestation of insulation degradation, and it will further expand insulation defects and deepen the degree of degradation. Therefore, in the power system, it is necessary to monitor partial discharge online in real time and accurately locate partial discharge, so as to take protective measures in advance. Partial discharge detection methods are all based on physical or chemical phenomena occurring during partial discharge. Existing detection methods include pulse current method, ultra-high frequency method (UHF), ultrasonic method, chemical analysis method, optical measurement method, etc. The pulse current method is the only detection method with international standards. It has the advantages of simple equipment and high sensitivity, but this method has poor anti-interference ability; the ultra-high frequency method can improve its own anti-interference ability when using built-in sensors, but it cannot locate partial discharge; the ultrasonic method is easily disturbed by vibration and sound; the chemical analysis method requires long-term accumulation of data and is not suitable for real-time monitoring. The optical measurement method uses fluorescent optical fiber as a sensing element, which is not interfered with inside the electrical equipment, and its detection accuracy is extremely high when a suitable photoelectric detector is used. At present, many domestic teams have conducted in-depth research on the optical measurement method, including Tsinghua University, Xi'an Jiaotong University, Chongqing University, etc., but they are unable to locate partial discharge in real time. Summary of the invention

[0004] In order to solve the technical problems existing in the background technology, the present invention proposes a partial discharge positioning system and positioning method based on fluorescent optical fiber.

[0005] The present invention proposes a partial discharge locating method based on fluorescent optical fiber, comprising the following steps:

[0006] A local discharge signal is obtained through the fluorescent optical fiber, and excitation light signals output from both ends of the fluorescent optical fiber are respectively obtained, and the local discharge position is calculated according to the excitation light signals obtained from both ends of the fluorescent optical fiber.

[0007] Preferably, the partial discharge position is calculated based on the excitation light signal obtained at both ends of the fluorescent optical fiber, specifically: the fluorescent optical fiber excitation light generation position is calculated based on the light power intensity of the excitation light obtained at both ends of the fluorescent optical fiber, wherein the distance X from the excitation light generation position to the first end of the fluorescent optical fiber is It is a linear relationship, and P1 and P2 are the light power intensities output from the first end and the second end of the fluorescent optical fiber respectively.

[0008] Preferably, Wherein, L is the length of the fluorescent optical fiber, and α is the transmission attenuation coefficient of the fluorescent optical fiber.

[0009] Preferably, the step of respectively acquiring the fluorescent output light signals at both ends of the fluorescent optical fiber comprises: determining the fluorescent output light signals at both ends of the fluorescent optical fiber by respectively acquiring the optical power intensities at the outlets of the first transmission optical fiber and the second transmission optical fiber at both ends of the fluorescent optical fiber;

[0010] Calculate the distance X from the excitation light position to the first end of the fluorescent fiber according to the following formula:

[0011]

[0012] Wherein, D1 and D2 are the lengths of the first transmission optical fiber and the second transmission optical fiber respectively, β1 and β2 are the transmission attenuation coefficients of the first transmission optical fiber and the second transmission optical fiber respectively, and P1′ and P2′ are the optical power intensities obtained at the outlets of the first transmission optical fiber and the second transmission optical fiber respectively.

[0013] Preferably, the calculated partial discharge position is corrected;

[0014] The correction value is obtained by the following equation:

[0015]

[0016] Where k is the intrinsic constant of the fluorescent fiber.

[0017] In the present invention, the proposed local discharge positioning method based on fluorescent optical fiber obtains local discharge signals through fluorescent optical fiber, respectively obtains excitation light signals output from both ends of the fluorescent optical fiber, and calculates the local discharge position according to the excitation light signals obtained from both ends of the fluorescent optical fiber. The above-mentioned optimized local discharge positioning method based on fluorescent optical fiber senses the local discharge signal of the conductor through fluorescent optical fiber, and uses the attenuation principle of the excitation light emitted from both ends of the fluorescent optical fiber to locate the excitation light generation position corresponding to the local discharge position, thereby achieving accurate and reliable positioning of the local discharge position.

[0018] The present invention also discloses a positioning system for realizing the above-mentioned partial discharge positioning method based on fluorescent optical fiber, characterized in that it comprises: a fluorescent optical fiber, a first photoelectric detection module, a second photoelectric detection module, and a signal processing module;

[0019] The signal input ends of the first photoelectric detection module and the second photoelectric detection module are respectively connected to the two ends of the fluorescent optical fiber, and the signal output ends of the first photoelectric detection module and the second photoelectric detection module are connected to the signal processing module, and the signal processing module calculates the excitation light position corresponding to the partial discharge according to the detection signals of the first photoelectric detection module and the second photoelectric detection module;

[0020] Preferably, the signal processing module calculates the excitation light position according to the fluorescence emission light power intensity obtained by the first photoelectric detection module and the second photoelectric detection module, wherein the distance X from the excitation light position to the first end of the fluorescent optical fiber is It is a linear relationship, P1 and P2 are the output optical power intensities at the first and second ends of the fluorescent optical fiber, respectively;

[0021] More preferably, Wherein, L is the length of the fluorescent optical fiber, and α is the transmission attenuation coefficient of the fluorescent optical fiber.

[0022] Preferably, it also includes a first transmission optical fiber and a second transmission optical fiber, the two ends of the first transmission optical fiber are respectively connected to the first end of the fluorescent optical fiber and the first photoelectric detection module, the two ends of the second transmission optical fiber are respectively connected to the second end of the fluorescent optical fiber and the second photoelectric detection module, and the signal processing module calculates the distance X from the excitation light position corresponding to the discharge position to the first end of the fluorescent optical fiber according to the following formula:

[0023]

[0024] Wherein, D1 and D2 are the lengths of the first transmission optical fiber and the second transmission optical fiber, respectively, β1 and β2 are the transmission attenuation coefficients of the first transmission optical fiber and the second transmission optical fiber, respectively, and P1′ and P2′ are the optical power intensities obtained at the outlets of the first transmission optical fiber 21 and the second transmission optical fiber 22, respectively;

[0025] Preferably, it also includes a first non-metallic fiber optic connector and a second non-metallic fiber optic connector, the first transmission fiber optic is connected to the first end of the fluorescent fiber optic via the first non-metallic fiber optic connector, and the second transmission fiber optic is connected to the second end of the fluorescent fiber optic via the second non-metallic fiber optic connector.

[0026] Preferably, the signal processing module corrects the calculated excitation light position by the following formula:

[0027]

[0028] Where k is the intrinsic constant of the fluorescent fiber.

[0029] Preferably, it comprises a plurality of fluorescent optical fibers, which are arranged in parallel and together enclose a detection space.

[0030] Preferably, the incident end of the first photoelectric detection module and / or the second photoelectric detection module is provided with a narrow-band filter;

[0031] Preferably, the first photoelectric detection module includes a first optical fiber coupler and a first photoelectric detector, and the second photoelectric detection module includes a second optical fiber coupler and a second photoelectric detector;

[0032] More preferably, it further comprises an isolation shell, on which a line inlet, a line outlet, a first optical fiber connection port, and a second optical fiber connection port are provided, and the fluorescent optical fiber is located in the isolation shell and has two ends connected to the first optical fiber connection port and the second optical fiber connection port respectively;

[0033] Further preferably, the fluorescent optical fiber extends from the line inlet to the line outlet.

[0034] In the present invention, the proposed local discharge positioning system based on fluorescent optical fiber captures the local discharge of the conductor through the fluorescent optical fiber, has excellent anti-interference performance, and detects the signals at both ends of the fluorescent optical fiber, so as to locate the position of the excitation light corresponding to the local discharge on the fluorescent optical fiber, thereby realizing the precise positioning of the local discharge position of the conductor. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic structural diagram of an implementation of a partial discharge locating system based on fluorescent optical fiber proposed by the present invention.

[0036] Figure 2 This is a schematic structural diagram of another embodiment of a partial discharge locating system based on fluorescent optical fiber proposed by the present invention. DETAILED DESCRIPTION

[0037] like Figure 1 and 2 As shown, Figure 1 This is a schematic diagram of the structure of an implementation of a partial discharge locating system based on fluorescent optical fiber proposed by the present invention. Figure 2 This is a schematic structural diagram of another embodiment of a partial discharge locating system based on fluorescent optical fiber proposed by the present invention.

[0038] Reference Figure 1 The present invention proposes a local discharge locating method based on fluorescent optical fiber, comprising the following steps:

[0039] A local discharge signal is obtained through the fluorescent optical fiber 1 , and excitation light signals outputted from both ends of the fluorescent optical fiber 1 are respectively obtained. The local discharge position is calculated based on the excitation light signals obtained from both ends of the fluorescent optical fiber 1 .

[0040] In order to describe in detail the partial discharge locating method based on fluorescent optical fiber proposed in this embodiment, this embodiment also proposes a locating system for implementing the partial discharge locating method based on fluorescent optical fiber, comprising: a fluorescent optical fiber 1, a first photoelectric detection module, a second photoelectric detection module, and a signal processing module 7;

[0041] The signal input ends of the first photodetection module and the second photodetection module are respectively connected to the two ends of the fluorescent optical fiber 1, and the signal output ends of the first photodetection module and the second photodetection module are connected to the signal processing module 7. The signal processing module 7 calculates the excitation light position corresponding to the local discharge according to the detection signals of the first photodetection module and the second photodetection module.

[0042] In the specific working mode of the positioning system of this embodiment, refer to Figure 1 , a fluorescent optical fiber is pre-placed on one side of the conductor 100 to be detected and arranged along the extension direction of the conductor 100; when partial discharge occurs in the conductor 100, an excitation light signal is generated at a position on the fluorescent optical fiber corresponding to the partial discharge of the conductor, and the excitation light signal is transmitted toward both ends of the fluorescent optical fiber, and the output signals at both ends of the fluorescent optical fiber are obtained through the first photodetector 41 and the second photodetector 42. The signal processor derives the excitation light generation position of the fluorescent optical fiber based on the optical characteristic parameters in the output signals at both ends, thereby locating the partial discharge of the conductor.

[0043] In this embodiment, the proposed local discharge positioning method based on fluorescent optical fiber obtains local discharge signals through fluorescent optical fiber, respectively obtains excitation light signals output from both ends of the fluorescent optical fiber, and calculates the local discharge position according to the excitation light signals obtained from both ends of the fluorescent optical fiber. Through the above-mentioned optimized local discharge positioning method based on fluorescent optical fiber, the local discharge signal of the conductor is sensed by fluorescent optical fiber, and the excitation light attenuation obtained from both ends of the fluorescent optical fiber is used to locate the excitation light generation position corresponding to the local discharge position, thereby achieving accurate and reliable positioning of the local discharge position.

[0044] In the specific signal processing of the signal processor, different optical characteristic parameters can be selected to obtain the position where the excitation light of the fluorescent fiber is generated. For example, according to the classical optical transmission theory: L = CT, where C is the speed of the excitation light in the optical fiber, L is the distance the excitation light travels in the optical fiber, and T is the time from the position where the excitation light is generated to the photodetector. Based on this theory, the signal processor can obtain the position where the excitation light is generated by the time difference when the photodetectors at both ends receive the light.

[0045] However, due to the limitation of the length of the fluorescent optical fiber for detecting partial discharge, the time difference in detecting the light signal at both ends of the fluorescent optical fiber is small. Therefore, for conventional photoelectric detection equipment, the detection signal time difference of the photoelectric detectors at both ends of the fluorescent optical fiber is greatly affected by the detection accuracy, resulting in a large error in the position accuracy calculated by the signal time difference.

[0046] In this embodiment, according to the transmission characteristics of optical fiber proposed in "Principles and Applications of Fiber Optics (2012)":

[0047] P Z =P0*exp(-γZ); (1)

[0048] Where γ is the transmission attenuation coefficient, Z is the fiber length, P Z is the output optical signal strength, and P0 is the input optical signal strength.

[0049] The local discharge position is calculated based on the excitation light signal obtained at both ends of the fluorescent optical fiber 1, specifically: the excitation light generation position of the fluorescent optical fiber 1 is calculated based on the light power intensity of the excitation light obtained at both ends of the fluorescent optical fiber 1, wherein the distance X from the excitation light generation position to the first end of the fluorescent optical fiber 1 is It is a linear relationship, and P1 and P2 are the optical power intensities output from the first end and the second end of the fluorescent optical fiber 1 respectively.

[0050] Based on equation (1), it can be deduced that

[0051] P0=P z *exp(YZ); (2)

[0052] Then, when partial discharge occurs, according to formula (2), the optical power intensity output from the first end and the second end of the fluorescent optical fiber 1 can be obtained:

[0053] P1=P0′*exp(-αX) (3)

[0054] P2=P0′*exp[-α(LX)] (4)

[0055] Wherein, X is the distance from the position where the excitation light is generated to the first end of the fluorescent optical fiber 1, and P0′ is the optical power intensity of the initial excitation light of the fluorescent optical fiber;

[0056] Therefore, according to equations (3) and (4), we can obtain:

[0057]

[0058] Wherein, L is the length of the fluorescent optical fiber 1, and α is the transmission attenuation coefficient of the fluorescent optical fiber 1. Therefore, according to the optical power intensities P1 and P2 detected at both ends of the fluorescent optical fiber, the precise positioning of X can be obtained.

[0059] In a specific implementation, for example, in the partial discharge detection of GIS equipment, since the side wall opening of the equipment has strict requirements, when the fluorescent optical fiber is arranged, the optical signals at both ends of the fluorescent optical fiber can be output from the single-side signal outlet flange through the transmission optical fiber, thereby detecting the partial discharge without affecting the normal working environment of the GIS; therefore, the positioning system of this embodiment also includes a first transmission optical fiber 21 and a second transmission optical fiber 22, and the two ends of the first transmission optical fiber 21 are respectively connected to the first end of the fluorescent optical fiber 1 and the first photoelectric detection module, and the two ends of the second transmission optical fiber 22 are respectively connected to the second end of the fluorescent optical fiber 1 and the second photoelectric detection module; when there are certain limitations on the space for the arrangement environment, the two ends of the fluorescent optical fiber are connected to the photoelectric detector through the transmission optical fiber, which is convenient for the arrangement and connection of the fluorescent optical fiber.

[0060] At this time, when processing the signal, it is necessary to further consider the influence of the attenuation of the two transmission optical fibers on the detection results of the photoelectric detection module. According to equation (1), the optical signal intensities at the entrances of the transmission optical fibers at both ends are:

[0061] P1=P1′*exp(β1D1) (6)

[0062] P2=P2′*exp(β2D2) (7)

[0063] Where D1 and D2 are the lengths of the first transmission optical fiber 21 and the second transmission optical fiber 22, β1 and β2 are the transmission attenuation coefficients of the first transmission optical fiber 21 and the second transmission optical fiber 22, and P1′ and P2′ are the optical power intensities detected by the photoelectric detection modules at both ends, that is, the optical power intensities at the outlets of the first transmission optical fiber and the second transmission optical fiber. Therefore, combining equations (5), (6), and (7) can yield:

[0064]

[0065] According to equation (8), the value of X can be calculated based on the optical power intensity obtained by the optical detection module, thereby accurately locating the location where the partial discharge occurs.

[0066] In actual operation, due to the influence of the intrinsic parameters of the fluorescent fiber, the signal processing module 7 corrects the calculated excitation light position by the following formula:

[0067]

[0068] Wherein, k is the intrinsic constant of the fluorescent fiber 1.

[0069] In one embodiment, due to the influence of the crystal structure of the uniform optical fiber material itself, there is a certain difference in the transmission power of the excitation light generated at a certain point of the fluorescent optical fiber to the two ends of the optical fiber. Therefore, in order to eliminate the influence of this difference on the calculation results, the corrected optical power intensity at the outlets of the two ends of the fluorescent optical fiber is respectively:

[0070] P 修1 =P 初1 ′*exp(-αX 修 ); (10)

[0071] P 修2 =P 初2 ′*exp[-α(LX 修 )]; (11)

[0072] Among them, P 初1 ′ is the initial optical power intensity of the excitation light toward the first end of the fluorescent optical fiber, P 初2 ' is the initial optical power intensity of the excitation light in the direction toward the second end of the fluorescent optical fiber;

[0073] Combining equations (10) and (11) to calculate:

[0074]

[0075] At this time, according to equations (9) and (12), we can obtain:

[0076]

[0077] In actual operation, for the fluorescent optical fiber of the existing positioning system, the occurrence of partial discharge can be simulated by a preset light source, so as to calculate the intrinsic constant k value of the fluorescent optical fiber in the system.

[0078] In a further specific implementation, since the internal conductor of the GIS equipment is a high-voltage conductor, a high-voltage electric field is generated around it. Therefore, a non-metallic fiber optic connector is selected when connecting the fluorescent fiber and the transmission fiber. The first transmission fiber 21 is connected to the first end of the fluorescent fiber 1 through a first non-metallic fiber optic connector 31, and the second transmission fiber 22 is connected to the second end of the fluorescent fiber 1 through a second non-metallic fiber optic connector 32. When detecting partial discharge, the non-metallic fiber optic connector will not affect the electric field around the conductor.

[0079] In order to improve the sensitivity of partial discharge detection, multiple fluorescent optical fibers 1 can be arranged around the conductor. The multiple fluorescent optical fibers 1 are arranged in parallel and together form a detection space. The multiple fluorescent optical fibers can capture the partial discharge excitation light in different directions around the conductor, thereby improving the detection accuracy.

[0080] In other specific embodiments, when partial discharge occurs, the fluorescent optical fiber is affected by the partial discharge and absorbs the light signal with a wavelength of λ1, and excites the light signal with a wavelength of λ2 and reaches both ends along the fluorescent optical fiber. The light signal with a wavelength of λ2 is acquired by the photodetector. Since λ2 is greater than λ1, in order to avoid the influence of λ1 on the final detection result, a narrow-band filter is set at the incident end of the first photodetection module and the second photodetection module to filter the light signal with a wavelength of λ1.

[0081] In a specific design of the photodetector, the first photodetection module includes a first optical fiber coupler 51 and a first photodetector 41 , and the second photodetection module includes a second optical fiber coupler 52 and a second photodetector 42 .

[0082] When detecting partial discharge of a conductor 200 in an open environment, refer to Figure 2 The positioning device of this embodiment also includes an isolation shell 6, which is provided with an input port, an output port, a first optical fiber connection port, and a second optical fiber connection port. The fluorescent optical fiber 1 is located in the isolation shell 6 and its two ends are respectively connected to the first optical fiber connection port and the second optical fiber connection port. During installation, the section of the conductor to be detected is isolated in the shell by the isolation shell, and the two ends of the conductor pass through the input port and the output port respectively. The fluorescent optical fiber is located on one side of the conductor and its two ends are respectively connected to the external photodetector through the optical fiber connection port, forming an isolated detection space outside the conductor to prevent external ambient light from interfering with the fluorescent optical fiber.

[0083] In the specific arrangement of the fluorescent optical fiber, the fluorescent optical fiber 1 extends from the line inlet to the line outlet.

[0084] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A partial discharge locating method based on fluorescent optical fiber, characterized in that: The following steps are involved: Acquiring a local discharge signal through the fluorescent optical fiber (1), respectively acquiring excitation light signals output from both ends of the fluorescent optical fiber (1), and calculating the local discharge position based on the excitation light signals acquired from both ends of the fluorescent optical fiber (1); The step of respectively obtaining the fluorescent light signals emitted from the two ends of the fluorescent optical fiber (1) comprises: determining the fluorescent light signals emitted from the two ends of the fluorescent optical fiber (1) by respectively obtaining the light power intensities at the outlets of the first transmission optical fiber (21) and the second transmission optical fiber (22) at the two ends of the fluorescent optical fiber (1); The distance X from the excitation light position to the first end of the fluorescent optical fiber (1) is calculated according to the following formula: Wherein, D1 and D2 are respectively the lengths of the first transmission optical fiber (21) and the second transmission optical fiber (22), β1 and β2 are respectively the transmission attenuation coefficients of the first transmission optical fiber (21) and the second transmission optical fiber (22), P1′ and P2′ are respectively the optical power intensities obtained at the outlets of the first transmission optical fiber (21) and the second transmission optical fiber (22); L is the length of the fluorescent optical fiber (1), and α is the transmission attenuation coefficient of the fluorescent optical fiber (1); The calculated partial discharge position is corrected; the correction value is obtained by the following equation: Where k is the intrinsic constant of the fluorescent fiber (1), ,in, is the initial optical power intensity of the excitation light toward the first end of the fluorescent optical fiber, is the initial optical power intensity of the excitation light in the direction toward the second end of the fluorescent optical fiber.

2. A positioning system for implementing the partial discharge positioning method based on fluorescent optical fiber as claimed in claim 1, characterized in that: include: Fluorescent optical fiber (1), a first photoelectric detection module, a second photoelectric detection module, and a signal processing module (7); The signal input ends of the first photoelectric detection module and the second photoelectric detection module are respectively connected to two ends of the fluorescent optical fiber (1), and the signal output ends of the first photoelectric detection module and the second photoelectric detection module are connected to a signal processing module (7), and the signal processing module (7) calculates the excitation light position corresponding to the local discharge according to the detection signals of the first photoelectric detection module and the second photoelectric detection module; It also comprises a first transmission optical fiber (21) and a second transmission optical fiber (22), wherein two ends of the first transmission optical fiber (21) are respectively connected to the first end of the fluorescent optical fiber (1) and the first photoelectric detection module, and two ends of the second transmission optical fiber (22) are respectively connected to the second end of the fluorescent optical fiber (1) and the second photoelectric detection module, and the signal processing module (7) calculates the distance X from the excitation light position corresponding to the discharge position to the first end of the fluorescent optical fiber (1) according to the following formula: Wherein, D1 and D2 are respectively the lengths of the first transmission optical fiber (21) and the second transmission optical fiber (22), β1 and β2 are respectively the transmission attenuation coefficients of the first transmission optical fiber (21) and the second transmission optical fiber (22), P1′ and P2′ are respectively the light power intensity obtained by the first photoelectric detection module and the light power intensity obtained by the second photoelectric detection module, L is the length of the fluorescent optical fiber (1), and α is the transmission attenuation coefficient of the fluorescent optical fiber (1); It also includes a first non-metallic optical fiber connector (31) and a second non-metallic optical fiber connector (32), wherein the first transmission optical fiber (21) is connected to the first end of the fluorescent optical fiber (1) via the first non-metallic optical fiber connector (31), and the second transmission optical fiber (22) is connected to the second end of the fluorescent optical fiber (1) via the second non-metallic optical fiber connector (32); The signal processing module (7) corrects the calculated excitation light position using the following formula: Where k is the intrinsic constant of the fluorescent fiber (1), ,in, is the initial optical power intensity of the excitation light toward the first end of the fluorescent optical fiber, is the initial optical power intensity of the excitation light in the direction toward the second end of the fluorescent optical fiber.

3. The positioning system according to claim 2, characterized in that: It comprises a plurality of fluorescent optical fibers (1), which are arranged in parallel and together enclose a detection space.

4. The positioning system according to claim 2, characterized in that: The incident ends of the first photoelectric detection module and the second photoelectric detection module are both provided with narrow-band filters; The first photoelectric detection module comprises a first optical fiber coupler (51) and a first photoelectric detector (41), and the second photoelectric detection module comprises a second optical fiber coupler (52) and a second photoelectric detector (42); It also comprises an isolation shell (6), the isolation shell (6) being provided with a line inlet, a line outlet, a first optical fiber connection port, and a second optical fiber connection port, the fluorescent optical fiber (1) being located in the isolation shell (6) and having two ends respectively connected to the first optical fiber connection port and the second optical fiber connection port; The fluorescent optical fiber (1) extends from the line inlet to the line outlet.

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