FBG-based transformer oil temperature and low oil speed non-electric quantity composite self-checking operation and maintenance method

Abstract

The invention discloses an FBG-based transformer oil temperature and low oil speed non-electric quantity composite self-detection operation and maintenance method, and relates to the technical field of electrical detection, and the method comprises the steps: S1, building a non-electric quantity parameter-based transformer oil temperature and low oil speed composite calculation model; s2, the composite self-checking device and the closed pipeline are fixed; s3, the signal processing unit collects the central wavelength drift distance of each FBG sensor in real time; s4, the signal processing unit monitors and analyzes the oil temperature and oil speed data in real time, on-line monitoring of key parameters of the operation state of the transformer in a power grid system is achieved through the mapping rule of wavelength drift of the fiber bragg grating and oil flow speed and temperature change of the transformer, potential fault signs are recognized in time, transformer test and maintenance cost and risks are reduced, and the system reliability is improved. The asset utilization rate is improved, timely early warning is performed, power grid emergencies are handled, the overall safe operation level of the transformer substation is improved, risks of power grid stability, power supply load loss and the like caused by equipment faults are prevented, and the power supply reliability is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of electrical detection technology, and in particular to a transformer oil temperature and low oil speed non-electric quantity composite self-detection operation and maintenance method based on FBG. Background Art

[0002] With the continuous and rapid development of my country's economy, electricity consumption has increased rapidly, the peak load of the power grid has continued to rise, and the social and economic operation has become more and more dependent on the power system. The safety of the power grid has become more and more important in national security and social stability. With the continuous and rapid development of my country's power system, in order to improve the reliability of power grid operation and reduce the accident rate, the non-electric signal parameters of the transformer can be monitored online through the fault warning threshold, the abnormal situation of the transformer can be discovered in time, and corresponding measures can be taken to prevent potential faults from occurring, ensuring the safe operation of power equipment, which is of great significance to ensuring the quality of life of the people and the stable and rapid development of the economy.

[0003] From the perspective of the overall development of my country's power industry, it is crucial to ensure the reliability of the power grid. Strengthening the quality assurance and management of transformer manufacturing, and strengthening the inspection, maintenance and preventive monitoring of transformers are key factors in maintaining the stable operation of the power grid. At present, my country still has deficiencies in the online monitoring and fault warning technology of transformer operation status. The traditional transformer online monitoring and fault warning system has defects such as low monitoring accuracy and insufficient fault warning performance. Since the 1970s, fiber grating sensing technology has developed rapidly. It has the advantages of strong anti-electromagnetic interference ability, small size, light weight, corrosion resistance, etc., and it has passive characteristics, which can be applied to the detection of transformer non-electrical signal. In view of the problem of low temperature detection accuracy of transformers in power grid systems, the existing transformer temperature detection technology based on optical fiber sensors builds an online monitoring system for the internal temperature of transformers, realizing the online monitoring of transformer oil temperature, core temperature, and winding temperature. However, the system has a single monitoring parameter, and only uses the transformer temperature parameter for fault warning. When a fault occurs, other non-electrical parameters in the transformer are unknown. The non-electrical signal data before and after the fault period is not stored and analyzed, and there are fault warning defects.

[0004] Therefore, it is necessary to design a FBG-based transformer oil temperature and low oil speed non-electrical composite self-inspection operation and maintenance method to solve the above technical problems. Summary of the invention

[0005] In response to the above problems, the present application provides a FBG-based transformer oil temperature and low oil speed non-electrical composite self-inspection and operation and maintenance method. Through the mapping law of fiber grating wavelength drift and transformer oil flow velocity temperature change, online monitoring of key parameters of transformer operating status in the power grid system is realized, potential fault signs are identified in time, and the cost and risk of transformer testing and maintenance are reduced, the service life is extended, the asset utilization rate is improved, and timely warning and response to power grid emergencies are provided, the overall safe operation level of the substation is improved, and the risks of power grid stability and power supply load loss caused by equipment failure are prevented, which greatly improves the power supply reliability, and also brings important economic and safety benefits to the society.

[0006] To achieve the above object, the present invention provides the following technical solution: a transformer oil temperature and low oil speed non-electrical quantity composite self-inspection operation and maintenance method based on FBG, which comprises the following steps:

[0007] S1. Establish a transformer oil temperature and low oil speed composite calculation model based on non-electrical parameters, wherein the transformer oil temperature and low oil speed composite calculation model includes an oil temperature calculation sub-model and an oil speed calculation sub-model, wherein the oil temperature calculation sub-model calculates the oil temperature of the closed pipe in the transformer according to the sum of the center wavelength drift of the first FBG sensor and the second FBG sensor, and the oil speed calculation sub-model calculates the oil flow velocity of the closed pipe in the transformer according to the difference between the center wavelength drift of the first FBG sensor and the second FBG sensor;

[0008] S2, fixing the composite self-test device to the closed pipe, and installing the first FBG sensor in a square tube close to the frontal surface of the closed pipe, and installing the second FBG sensor in the square tube close to the rear surface of the closed pipe, and using a signal processing unit to collect the center wavelength drift of the first FBG sensor and the second FBG sensor respectively;

[0009] S3, inputting the real-time collected central wavelength drift into the transformer oil temperature and low oil speed composite calculation model to obtain the current oil temperature and oil speed of the transformer;

[0010] S4. The signal processing unit monitors and analyzes the oil temperature and oil speed data in real time. When the oil temperature or oil speed exceeds the preset threshold, an alarm signal is triggered and corresponding operation and maintenance measures are executed.

[0011] Further, as a preference, the oil temperature calculation sub-model calculates the transformer oil temperature by the following steps:

[0012] S1. According to the fiber coupling mode theory and the incident light emitted by the broadband light source, the incident light passes through the first FBG sensor and the second FBG sensor and satisfies the Bragg reflection condition, and a mathematical relationship between the center wavelength of the first FBG sensor and the second FBG sensor and the effective refractive index and the grating period is established;

[0013] S2. Based on the probe mechanism of the square tube, the differential structure method of the first FBG sensor and the second FBG sensor, and the temperature detection principle, a mathematical relationship between the center wavelength drift of the first FBG sensor and the second FBG sensor and the temperature change is established on the basis of S1 to solve the current transformer oil temperature.

[0014] Further, as a preference, the oil speed calculation sub-model calculates the transformer oil flow speed by the following steps:

[0015] S1. According to the fiber coupling mode theory and the incident light emitted by the broadband light source, the incident light passes through the first FBG sensor and the second FBG sensor and satisfies the Bragg reflection condition, and a mathematical relationship between the center wavelength of the first FBG sensor and the second FBG sensor and the effective refractive index and the grating period is established;

[0016] S2. Based on the probe-type mechanism based on the square tube, the differential structure method of the first FBG sensor and the second FBG sensor, and the strain detection principle, a mathematical relationship between the center wavelength drift of the first FBG sensor and the second FBG sensor and the flow velocity strain change is established on the basis of S1 to solve the current transformer oil flow rate.

[0017] Further, preferably, a threaded interface is provided at the upper end of the closed pipe, and the closed pipe and the composite self-test device are fixed to each other through the threaded interface, and the composite self-test device is respectively connected to a broadband light source and a signal processing unit, and the signal processing unit is used to receive and process the detected center wavelength drift of each of the first FBG sensor and the second FBG sensor.

[0018] Further, preferably, the composite self-test device comprises:

[0019] A square tube is configured as a square structure, an annular sheet is fixedly arranged on the upper end thereof, and the square tube is slidably arranged in a second-order stud, and the lower end thread of the second-order stud is threadedly connected with the threaded interface;

[0020] a cap nut, which can be connected to the square tube by threads, and the upper end of the square tube is limitedly disposed in the cap nut by the annular sheet; and

[0021] The reducing nut is threadedly connected with the upper thread of the second-stage stud, and sealing washers are sleeved on the square tube located between the reducing nut and the closed pipe, and between the cap nut and the annular sheet.

[0022] Further, preferably, the first FBG sensor and the second FBG sensor have the same structure, and both include:

[0023] an optical fiber core, connected to the broadband light source and the signal processing unit respectively; and

[0024] The grating grid is formed by irradiating the optical fiber core with ultraviolet rays, and a cladding is fixedly arranged on the outer side of the grating grid and the optical fiber core, and a coating layer is arranged on the cladding.

[0025] Compared with the prior art, the present invention provides a transformer oil temperature and low oil speed non-electrical quantity composite self-inspection operation and maintenance method based on FBG, which has the following beneficial effects:

[0026] The present invention can realize online monitoring of key parameters of transformer operating status in power grid system through mapping law of fiber Bragg grating wavelength drift and transformer oil flow velocity and temperature change, timely identify potential fault signs, reduce transformer testing and maintenance costs and risks, extend service life, improve asset utilization, timely warn and respond to power grid emergencies, improve the overall safe operation level of substation, prevent risks such as power grid stability and power supply load loss caused by equipment failure, greatly improve power supply reliability, and also bring important economic and safety benefits to society. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation to the present application.

[0028] Figure 1 It is a schematic diagram of the overall device of the transformer oil temperature and low oil speed non-electric quantity composite self-inspection operation and maintenance method based on FBG;

[0029] Figure 2 It is a schematic diagram of the three-dimensional structure of the composite self-inspection device in the FBG-based transformer oil temperature and low oil speed non-electrical composite self-inspection operation and maintenance method;

[0030] Figure 3 It is a schematic diagram of the internal cross-section of the composite self-inspection device and the closed pipeline in the FBG-based transformer oil temperature and low oil speed non-electrical composite self-inspection operation and maintenance method;

[0031] Figure 4 It is a schematic diagram of the structure of the first FBG sensor and the second FBG sensor in the FBG-based transformer oil temperature and low oil speed non-electrical quantity composite self-inspection operation and maintenance method;

[0032] Figure 5 It is a schematic diagram of incident spectrum entering the first FBG sensor and the second FBG sensor in the FBG-based transformer oil temperature and low oil speed non-electric quantity composite self-inspection operation and maintenance method;

[0033] Figure 6 It is a schematic diagram of the reflection spectrum of the first FBG sensor and the second FBG sensor in the FBG-based transformer oil temperature and low oil speed non-electric quantity composite self-inspection operation and maintenance method;

[0034] Figure 7 It is a schematic diagram of the transmission spectrum of the first FBG sensor and the second FBG sensor in the FBG-based transformer oil temperature and low oil speed non-electric quantity composite self-inspection operation and maintenance method;

[0035] Figure 8 It is a schematic diagram of the internal reflected light and the transmitted light of the first FBG sensor and the second FBG sensor in the FBG-based transformer oil temperature and low oil speed non-electric quantity composite self-inspection operation and maintenance method;

[0036] Fig. 9 It is a schematic diagram of the center wavelength displacement drift of the first FBG sensor and the second FBG sensor in the FBG-based transformer oil temperature and low oil speed non-electrical quantity composite self-inspection operation and maintenance method;

[0037] Figure numerals: 1, closed pipe; 2, composite self-test device; 21, square tube; 22, cap nut; 23, sealing gasket; 24, reducing nut; 25, first FBG sensor; 26, second FBG sensor; 251, optical fiber core; 252, cladding; 253, coating layer; 254, grating grid. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0039] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of this application, unless otherwise specified, "plurality" means two or more.

[0040] See also Figure 1-Figure 9 The embodiment of the present invention provides a transformer oil temperature and low oil speed non-electric quantity composite self-inspection operation and maintenance method based on FBG, which includes the following steps:

[0041] S1. Establish a transformer oil temperature and low oil speed composite calculation model based on non-electrical parameters, wherein the transformer oil temperature and low oil speed composite calculation model includes an oil temperature calculation sub-model and an oil speed calculation sub-model, wherein the oil temperature calculation sub-model calculates the oil temperature of the closed pipe 1 in the transformer according to the sum of the central wavelength drifts of the first FBG sensor 25 and the second FBG sensor 26, and the oil speed calculation sub-model calculates the oil flow velocity of the closed pipe 1 in the transformer according to the difference between the central wavelength drifts of the first FBG sensor 25 and the second FBG sensor 26;

[0042] S2, fixing the composite self-test device 2 to the closed pipe 1, and installing the first FBG sensor 25 in the square tube 21 close to the upstream surface of the closed pipe 1, and installing the second FBG sensor 26 in the square tube 21 close to the downstream surface of the closed pipe 1, and using the signal processing unit to collect the center wavelength drift of the first FBG sensor 25 and the second FBG sensor 26 respectively;

[0043] S3, inputting the real-time collected central wavelength drift into the transformer oil temperature and low oil speed composite calculation model to obtain the current oil temperature and oil speed of the transformer;

[0044] S4. The signal processing unit monitors and analyzes the oil temperature and oil speed data in real time. When the oil temperature or oil speed exceeds the preset threshold, an alarm signal is triggered and corresponding operation and maintenance measures are executed.

[0045] Based on the above technical scheme, on the basis of the transformer oil temperature and low oil speed composite calculation model of the transformer non-electrical parameters, the structure and packaging material fatigue analysis of the square tube 21 is carried out in combination with finite element simulation, the square tube 21 sensor packaging structure model is designed, the sensor device size, packaging materials, etc. are optimized, the optimal packaging positions of the first FBG sensor 25 and the second FBG sensor 26 are determined, and the polyimide packaging method is used for protection and sensitivity enhancement packaging.

[0046] On the basis of the above technical scheme, through the mapping law of the central wavelength drift of the FBG sensor and the temperature change of the transformer oil flow rate, the key parameters of the transformer operating status in the power grid system can be monitored online, potential fault signs can be identified in time, the cost and risk of transformer testing and maintenance can be reduced, the life of the transformer can be extended, the asset utilization rate can be improved, and timely warning and response to power grid emergencies can be achieved. The overall safe operation level of the substation can be improved, and the risks of power grid stability and power supply load loss caused by equipment failure can be prevented, which greatly improves the power supply reliability and also brings important economic and safety benefits to the society.

[0047] In a possible implementation, the oil temperature calculation submodel calculates the transformer oil temperature using the following steps:

[0048] S1. According to the fiber coupling mode theory and the incident light emitted by the broadband light source, the incident light passes through the first FBG sensor 25 and the second FBG sensor 26 and satisfies the Bragg reflection condition, and a mathematical relationship between the central wavelength of the first FBG sensor 25 and the second FBG sensor 26 and the effective refractive index and the grating period is established;

[0049] S2, based on the probe-type mechanism of the square tube 21, the differential structure method of the first FBG sensor 25 and the second FBG sensor 26, and the temperature detection principle, a mathematical relationship between the center wavelength drift of the first FBG sensor 25 and the second FBG sensor 26 and the temperature change is established on the basis of S1 to solve the current transformer oil temperature.

[0050] In a possible implementation, the oil velocity calculation submodel calculates the transformer oil flow velocity using the following steps:

[0051] S1. According to the fiber coupling mode theory and the incident light emitted by the broadband light source, the incident light passes through the first FBG sensor 25 and the second FBG sensor 26 and satisfies the Bragg reflection condition, and a mathematical relationship between the central wavelength of the first FBG sensor 25 and the second FBG sensor 26 and the effective refractive index and the grating period is established;

[0052] S2, based on the probe-type mechanism of the square tube 21, the differential structure method of the first FBG sensor 25 and the second FBG sensor 26, and the strain detection principle, a mathematical relationship between the center wavelength drift of the first FBG sensor 25 and the second FBG sensor 26 and the flow velocity strain change is established on the basis of S1 to solve the current transformer oil flow rate.

[0053] It should be noted that according to the fiber coupled mode theory, when the incident light emitted by the broadband light source passes through the FBG sensor and satisfies the fiber Bragg reflection condition, reflected light will be formed. Its mathematical expression is:

[0054] λ B =2n eff Λ

[0055] Among them, λ B is the central wavelength value of the FBG sensor; n eff is the effective refractive index; Λ is the grating period.

[0056] When the external environment strain and temperature change, it causes n eff and Λ change simultaneously, causing the central wavelength value of the grating to drift. Based on this principle, the detection of physical variables such as pressure, flow, acceleration and temperature can be achieved by designing different sensing structure units.

[0057] The strain detection principle of the first FBG sensor 25 and the second FBG sensor 26 is as follows:

[0058] When the ambient temperature is kept constant and the FBG sensor is only subjected to strain, the expansion and contraction of the grating axis causes the period of the grating to change, and at the same time causes the elastic-optical effect to change the effective refractive index of the grating. Based on this, the wavelength drift of the FBG sensor grating caused by strain can be expressed as:

[0059] Δλ B =2Δn eff Λ+2n eff ΔΛ

[0060] Among them, Δλ B is the center wavelength drift of the FBG sensor, Δn eff Λ is the center wavelength drift caused by the effective refractive index of the grating under stress; Δn eff ΔΛ is the center wavelength drift caused by the change of grating period under stress.

[0061] Grating effective refractive index Δn under stress eff It can be expressed as:

[0062]

[0063] Among them, Δn eff is the effective refractive index of the grating under stress, ν is the Poisson's ratio; P 11 , P 12 is the component of the strain tensor on the optical fiber; ε is the axial strain of the grating.

[0064] The relationship between strain and grating period change can be expressed as:

[0065] ε=ΔΛ / Λ

[0066]

[0067] make:

[0068]

[0069] Pe is the effective elastic-optical coefficient, then:

[0070] Δλ B =(1-P e ) B ε

[0071] Let Kε=(1-Pe)λB, then:

[0072] Δλ B =K ε ε

[0073] Among them, Kε is the FBG strain sensitivity coefficient.

[0074] When only subjected to strain, the center wavelength drift of the FBG sensor changes linearly with the strain.

[0075] The temperature detection principle of the first FBG sensor 25 and the second FBG sensor 26 is as follows:

[0076] When other parameters remain unchanged and the grating is only affected by temperature variables, the thermal expansion of the optical fiber causes the FBG sensor to stretch or shorten axially, resulting in changes in the grating period spacing. The optical fiber thermo-optic effect changes the refractive index of the FBG sensor, and the elastic-optic effect causes the core diameter to change. The above temperature-induced changes in the central wavelength of the FBG sensor can be expressed by the formula:

[0077]

[0078] Among them, ΔT is the temperature change; ——Thermal expansion coefficient of optical fiber; ——Thermo-optic coefficient of optical fiber; (Δneff)ep——elastic-optic effect caused by thermal expansion; ——Waveguide effect caused by change in core diameter.

[0079] The center wavelength drift of the FBG sensor caused by the photoelastic effect and the waveguide effect is extremely small and can generally be ignored. Then:

[0080]

[0081] Let K T =(α F +ξ)λ B , then the FBG central wavelength drift can be expressed as:

[0082] Δλ Β =K T ΔT

[0083] Among them, K T is the temperature sensitivity coefficient of the FBG sensor.

[0084] When affected only by temperature, the center wavelength drift of the FBG sensor changes linearly with temperature.

[0085] It should be added that the strain temperature differential structure method of the first FBG sensor 25 and the second FBG sensor 26 is:

[0086] The differential structure method is to arrange the first FBG sensor 25 and the second FBG sensor 26 with the same initial central wavelength value on the symmetric plane of the stress on the elastic body, and the plane formed by the two FBG sensors is parallel to the direction of the stress. At this time, the elastic body generates strain after being stressed, the first FBG sensor 25 is subjected to positive strain, and the second FBG sensor 26 is subjected to negative strain. The strains are the same in magnitude but opposite in direction, so the central wavelength drifts of the two FBG sensors are equal in magnitude and opposite in direction, which can be expressed by the formula:

[0087] Δλ B1 =[(α+ξ)ΔT+(1-P e )ε]λ B1

[0088] Δλ B2 =[(α+ξ)ΔT-(1-P e )ε]λ B2

[0089] Since the initial center wavelengths of the first FBG sensor 25 and the second FBG sensor 26 are equal, there is λ B1 =λ B2 =λ B , the relationship between the center wavelength drift and strain of the differential structure method FBG sensor can be obtained:

[0090] Δλ Bε =Δλ B1 -Δλ B2 =2(1-P e ) B ε=2K ε ε

[0091] The relationship between the center wavelength drift of the differential structure FBG sensor and temperature is:

[0092] Δλ BT =Δλ B1 +Δλ B2 =2(α+ξ)λ B ΔT=2K T ΔT

[0093] Therefore, the strain sensitivity and temperature sensitivity of the FBG sensor can be improved by using the differential structure method, and compared with the reference grating structure, the detection sensitivity of the sensor is effectively improved.

[0094] In a possible implementation, a threaded interface is provided at the upper end of the closed pipe 1, and the closed pipe 1 and the composite self-test device 2 are fixed to each other through the threaded interface, and the composite self-test device 2 is respectively connected to a broadband light source and a signal processing unit, and the signal processing unit is used to receive and process the detected center wavelength drift of each of the first FBG sensor 25 and the second FBG sensor 26.

[0095] Through the above technical solution, the probe structure is composed of a square tube 21, a first FBG sensor 25 and a second FBG sensor 26. The first FBG sensor 25 and the second FBG sensor 26 are symmetrically attached to the two sides of the inner wall of the square tube 21. The plane formed by the two FBG sensors is parallel to the fluid flow direction to form a differential structure. Under the impact of the fluid, the square tube 21 undergoes elastic deformation, and the deformation is transmitted from the outer surface of the square tube 21 to the FBG sensor inside the square tube 21. Among them, the first FBG sensor 25 is stretched on the frontal surface to generate positive strain, causing the central wavelength of the first FBG sensor 25 to drift positively, and the second FBG sensor 26 is compressed on the rear surface to generate negative strain, causing the central wavelength of the second FBG sensor 26 to drift negatively.

[0096] The square tube 21 is in the closed pipe 1 and is affected by the fluid impact stress and the fluid temperature, which causes the center wavelengths of the first FBG sensor 25 and the second FBG sensor 26 in the square tube 21 to drift. The drift of the center wavelength of the FBG sensor caused by the flow velocity and temperature can be expressed as:

[0097] Δλ B =K ε Δε+K T ΔT

[0098] Among them, the temperature sensitivity coefficient of the packaged FBG sensor can be expressed as:

[0099]

[0100] Among them, α S The thermal expansion coefficient of the sensing unit packaging substrate material.

[0101] Ideally, the first FBG sensor 25 and the second FBG sensor 26 have the same initial wavelength value. Under the same fluid temperature, the first FBG sensor 25 and the second FBG sensor 26 have the same temperature sensitivity. The strains generated by the fluid impact are of the same magnitude and opposite direction. The strain sensitivities of the first FBG sensor 25 and the second FBG sensor 26 are of the same magnitude and opposite direction, which can be expressed as:

[0102] λ B =λ B1 =λ B2

[0103] K T =K T1 =K T2

[0104] K ε =K ε1 =-K ε2

[0105] Then the corresponding relationship between the center wavelength drift of the first FBG sensor 25 and the second FBG sensor 26 and the strain and temperature is:

[0106]

[0107] The fluid state in the closed pipe 1 is turbulent. According to the turbulence theory and the velocity distribution in the closed pipe 1, the velocity at any position in the closed pipe 1 can be expressed as:

[0108]

[0109] Among them, y is the arbitrary length from the pipe wall to the radial direction of the pipe; Β is the loss coefficient along the way; k and B are constants; υ is the kinematic viscosity; and V is the average flow velocity in the pipe.

[0110] The square tube 21 installed in the closed pipe 1 is essentially a cantilever beam. According to the cantilever beam theory, combined with fluid mechanics and material mechanics, it can be known that under the impact of the fluid, the load, bending moment and axial strain at any length of the square tube 21 can be expressed as:

[0111]

[0112] Where, F(y) is the load on the square tube 21 at any length; C D is the resistance coefficient; ρ is the fluid density; M(y) is the bending moment at any length of the square tube 21; l is the length of the square tube 21; Iy is the centroid principal moment of inertia of the square tube 21; E is the elastic modulus of the material of the square tube 21; a1 is the outer width of the square tube 21; a0 is the inner width of the square tube 21.

[0113] The relationship between the center wavelength drift difference of the first FBG sensor 25 and the second FBG sensor 26 and the flow rate of the fluid in the pipeline can be expressed as:

[0114]

[0115] Similarly, the relationship between the center wavelength drift and value of the first FBG sensor 25 and the second FBG sensor 26 and the temperature of the fluid in the pipeline can be expressed as:

[0116] Δλ BT =Δλ B1 +ΔλB2 =2K T ΔT

[0117] It can be seen that the difference in the center wavelength drift of the square probe differential structure FBG sensor is quadratically related to the change in the fluid flow rate in the closed pipe 1, and the sum of the center wavelength drift of the FBG sensor is linearly related to the change in the fluid temperature in the probe type closed pipe 1. In theory, the use of a differential structure can effectively solve the nonlinear coupling problem of the FBG sensor sensing signal when the fluid flow rate and temperature act simultaneously, achieving the purpose of composite detection of fluid flow rate and temperature, and compared with the reference grating structure, it can significantly improve the flow sensitivity and temperature sensitivity.

[0118] In a possible implementation, the composite self-test device 2 includes:

[0119] The square tube 21 is configured as a square structure, and a ring sheet is fixedly provided on the upper end thereof, and the square tube 21 is slidably provided in the second-order stud, and the lower end thread of the second-order stud is threadedly connected with the threaded interface;

[0120] A cap nut 22, which can be connected to the square tube 21 by threads, and the upper end of the square tube 21 is limited and disposed in the inner cap nut 22 by the annular sheet; and

[0121] The reducing nut 24 is threadedly connected with the upper thread of the second-stage stud, and sealing washers 23 are sleeved on the square tube 21 located between the reducing nut 24 and the closed pipe 1, and between the cap nut 22 and the annular sheet.

[0122] By adopting the above technical solution, the sealing gasket 23 is first sleeved on the square tube 21, and then the square tube 21 is extended into the closed pipe 1 from the threaded interface, the second-stage stud is tightened with the threaded interface, and then the reducing nut 24 and the cap nut 22 are fastened to the square tube 21 to complete the installation of the composite self-inspection device 2 on the closed pipe 1.

[0123] In a possible implementation, the first FBG sensor 25 and the second FBG sensor 26 have the same structure and both include:

[0124] The optical fiber core 251 is connected to the broadband light source and the signal processing unit respectively; and

[0125] The grating grid 254 is formed by carving the optical fiber core 251 by irradiating ultraviolet rays. A cladding 252 is fixedly provided on the outer side of the grating grid 254 and the optical fiber core 251 , and a coating layer 253 is provided on the cladding 252 .

[0126] Through the above technical solution, the grating grid 254 is used to sense external strain and temperature changes, the optical fiber core 251 is used for sensing signal transmission, and the cladding 252 and the coating layer 253 are used to protect the optical fiber core 251 which is fragile and easy to break.

[0127] What is described above 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 transformer oil temperature and low oil speed non-electrical quantity composite self-inspection operation and maintenance method based on FBG, characterized in that: The following steps are involved: S1. Establishing a transformer oil temperature and low oil speed composite calculation model based on non-electrical parameters, the transformer oil temperature and low oil speed composite calculation model comprising an oil temperature calculation sub-model and an oil speed calculation sub-model, wherein the oil temperature calculation sub-model calculates the oil temperature of a closed pipe (1) in the transformer according to the sum of the central wavelength drifts of a first FBG sensor (25) and a second FBG sensor (26), and the oil speed calculation sub-model calculates the oil flow velocity of the closed pipe (1) in the transformer according to the difference between the central wavelength drifts of the first FBG sensor (25) and the second FBG sensor (26); S2, fixing the composite self-test device (2) to the closed pipe (1), and installing the first FBG sensor (25) in the square pipe (21) close to the frontal surface of the closed pipe (1), and installing the second FBG sensor (26) in the square pipe (21) close to the rear surface of the closed pipe (1), and using a signal processing unit to collect the central wavelength drift of each of the first FBG sensor (25) and the second FBG sensor (26); S3, inputting the real-time collected central wavelength drift into the transformer oil temperature and low oil speed composite calculation model to obtain the current oil temperature and oil speed of the transformer; S4. The signal processing unit monitors and analyzes the oil temperature and oil speed data in real time. When the oil temperature or oil speed exceeds the preset threshold, an alarm signal is triggered and corresponding operation and maintenance measures are executed.

2. The transformer oil temperature and low oil speed non-electrical quantity composite self-inspection operation and maintenance method based on FBG according to claim 1 is characterized in that: The oil temperature calculation sub-model uses the following steps to calculate the transformer oil temperature: S1. According to the fiber coupling mode theory and the incident light emitted by the broadband light source, the incident light passes through the first FBG sensor (25) and the second FBG sensor (26) and satisfies the Bragg reflection condition, and a mathematical relationship between the central wavelength of the first FBG sensor (25) and the second FBG sensor (26) and the effective refractive index and the grating period is established; S2, based on the probe-type mechanism of the square tube (21), the differential structure method of the first FBG sensor (25) and the second FBG sensor (26), and the temperature detection principle, a mathematical relationship between the center wavelength drift of the first FBG sensor (25) and the second FBG sensor (26) and the temperature change is established on the basis of S1 to solve the current transformer oil temperature.

3. The transformer oil temperature and low oil speed non-electrical quantity composite self-inspection operation and maintenance method based on FBG according to claim 1 is characterized in that: The oil velocity calculation sub-model uses the following steps to calculate the transformer oil flow velocity: S1. According to the fiber coupling mode theory and the incident light emitted by the broadband light source, the incident light passes through the first FBG sensor (25) and the second FBG sensor (26) and satisfies the Bragg reflection condition, and a mathematical relationship between the central wavelength of the first FBG sensor (25) and the second FBG sensor (26) and the effective refractive index and the grating period is established; S2, based on the probe-type mechanism based on the square tube (21), the differential structure method of the first FBG sensor (25) and the second FBG sensor (26), and the strain detection principle, a mathematical relationship between the center wavelength drift of the first FBG sensor (25) and the second FBG sensor (26) and the flow velocity strain change is established on the basis of S1 to solve the current transformer oil flow velocity.

4. The transformer oil temperature and low oil speed non-electrical quantity composite self-inspection operation and maintenance method based on FBG according to claim 1 is characterized in that: A threaded interface is provided at the upper end of the closed pipe (1), and the closed pipe (1) and the composite self-test device (2) are fixed to each other via the threaded interface. The composite self-test device (2) is respectively connected to a broadband light source and a signal processing unit, and the signal processing unit is used to receive and process the detected central wavelength drift of each of the first FBG sensor (25) and the second FBG sensor (26).

5. The transformer oil temperature and low oil speed non-electrical quantity composite self-inspection operation and maintenance method based on FBG according to claim 1 is characterized in that: The composite self-test device (2) comprises: A square tube (21) is configured as a square structure, an annular sheet is fixedly arranged on the upper end thereof, and the square tube (21) is slidably arranged in a second-order stud, and the lower end thread of the second-order stud is threadedly connected with the threaded interface; a cap nut (22) which can be connected to the square tube (21) by means of threads, and the upper end of the square tube (21) is limitedly disposed in the cap nut (22) by means of the annular sheet; and A reducing nut (24) is threadedly connected to the upper thread of the second-stage stud, and a sealing gasket (23) is sleeved on the square tube (21) between the reducing nut (24) and the closed pipe (1), and between the cap nut (22) and the annular sheet.

6. The transformer oil temperature and low oil speed non-electrical quantity composite self-inspection operation and maintenance method based on FBG according to claim 4 is characterized in that: The first FBG sensor (25) and the second FBG sensor (26) have the same structure, and both include: An optical fiber core (251) connected to the broadband light source and the signal processing unit respectively; and The grating grid (254) is formed by carving the optical fiber core (251) by irradiating ultraviolet rays, and a cladding (252) is fixedly arranged on the outer side of the grating grid (254) and the optical fiber core (251), and a coating layer (253) is arranged on the cladding (252).

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