Method for monitoring vibration state of dry-type air-core reactor based on phi-OTDR (Optical Time Domain Reflectometer)

Abstract

The invention discloses a dry-type air-core reactor vibration state monitoring method based on a phase-sensitive optical time domain reflectometer (phi-OTDR). The method comprises the following steps: firstly, modeling a dry-type air-core reactor by utilizing finite element simulation, analyzing vibration characteristics of the dry-type air-core reactor under normal and turn-to-turn short circuit faults, and researching the influence of electromagnetic force on winding vibration based on a Maxwell equation set and a finite element method; then, a magnetic field-circuit coupling simulation and phi-OTDR diagnosis method is provided, a dry reactor finite element model is established, and vibration characteristics and insulation risks under different working conditions are evaluated. And finally, designing and building a distributed optical fiber sensing experiment platform based on the phi-OTDR, and verifying the effectiveness of the system on dry reactor vibration state monitoring and fault positioning through knocking excitation simulation faults. According to the method, high-sensitivity vibration monitoring and fault positioning are realized, the blank of distributed optical fiber sensing in the field of dry reactor state monitoring is filled, and a new means is provided for online monitoring and early warning of power equipment.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber technology, in particular to a method for monitoring the vibration state of a dry-type air-core reactor based on Φ-OTDR. Background Art

[0002] Dry-type air-core reactors (hereinafter referred to as "dry reactors") operate outdoors for long periods of time in practical power grids. They are susceptible to climatic factors and material aging, leading to a significantly increased risk of failure. Their operational failures primarily manifest in two typical modes: interturn insulation breakdown and magnetic flux leakage. Interturn insulation breakdown is primarily caused by moisture, partial discharge, or insulation degradation due to overheating. Magnetic flux leakage can lead to abnormal losses and heating in adjacent metal structures, grounding grids, and high-voltage cabinet terminals. Therefore, it is necessary to develop an effective method for monitoring interturn faults in reactors.

[0003] In practical applications, turn-to-turn short-circuit monitoring for reactors primarily relies on temperature monitoring. However, vibration signals are a key characteristic of interturn faults and can reflect abnormal changes in the mechanical state of the reactor winding. However, research on vibration-based monitoring methods is limited. Distributed fiber optic sensing technology offers advantages such as immunity to electromagnetic interference, excellent insulation performance, high reliability, good environmental adaptability, and long monitoring distance. It is currently widely used to monitor the operating status of power equipment such as transformers, motors, switchgear, overhead transmission lines, and cables, and is a relatively mature technology. Rayleigh scattering-based phase-sensitive optical time domain reflectometry (Φ-OTDR) not only shares the advantages of general distributed fiber optic sensing technology but also offers high sensitivity and fast response speed, providing opportunities for fault monitoring in reactors. Since scattering occurs at every location along the fiber, each location can be considered an independent sensor. By laying optical fiber within the reactor winding and continuously monitoring the phase changes caused by vibration in the fiber, the vibration state of the reactor can be monitored. Distributed acoustic sensing (DAS) technology based on Φ-OTDR is extremely sensitive to vibration signals. When an optical fiber is disturbed, the change in optical path length at the disturbed location causes a change in the phase difference of the Rayleigh scattered light generated at both ends of the disturbed fiber segment. In theory, this phase difference is linearly related to the disturbance amplitude. DAS demodulates this phase difference to quantitatively measure the disturbance amplitude, providing an effective means for vibration monitoring of electrical equipment such as reactors. To date, there are few reports on the use of Φ-OTDR-based DAS for condition monitoring of electrical equipment such as reactors. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for monitoring the vibration status of a dry-type air-core reactor based on Φ-OTDR vibration measurement, so as to solve the problems that the prior art lacks systematic research on dry-type air-core reactor vibration status monitoring and quantitative fault early warning methods.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] Step 1: Simulate the vibration state of the solid mechanics field of the dry-type air-core reactor when it is operating under rated conditions. The step 1 includes the following specific steps: Step 1-1: Define the structural composition and key parameters of the dry-type air-core reactor and establish a geometric model of the multi-layer encapsulated and parallel coils. Simulations were performed based on the physical structure of a CKGKL-240 / 10-12% dry-type reactor. Its key electrical parameters and the winding parameters of each encapsulated winding are shown in Tables 1 and 2, respectively. Table 1 Electrical parameters of CKGKL-240 / 10-12% dry-type air-core reactor Table 2 CKGKL-240 / 10-12% dry insulation and winding parameters of each layer Step 1-2: Based on Maxwell's equations, the finite element method is used to theoretically analyze the electromagnetic field of the interference resistor and derive the calculation method of the electromagnetic force. Step 1-3: Analyze the mechanism of how electromagnetic force affects winding vibration based on the structural characteristics of the resistor.

[0007] Step 2: Study the vibration distribution law of the dry-type winding after a turn-to-turn short-circuit fault occurs. The step 2 includes the following specific steps: Step 2-1: Based on the numerical simulation method, establish a finite element simulation model of interference resistance. Step 2-2: Study the vibration characteristics of each encapsulated winding under rated operating conditions, including radial and axial electromagnetic force distribution, strain distribution, etc. Step 2-3: Analyze the vibration characteristics of the inner windings of Envelope 1, Envelope 2, Envelope 3, and Envelope 4, namely, Winding 1, Winding 5, Winding 8, and Winding 11, after inter-turn faults occurred at different heights. Based on the above analysis results, the diagnosis basis of inter-turn short circuit of the Φ-OTDR system in the dry anti-vibration state is obtained.

[0008] Step 3: Establish a "magnetic field-circuit" coupled simulation model of the dry-type inter-turn short-circuit fault and propose a turn-to-turn short-circuit fault diagnosis method based on the Φ-OTDR system. The step 3 includes the following specific steps: Step 3-1: Establish a "magnetic field-circuit" coupled simulation model for dry-type short-circuit faults, and simulate short circuits at different encapsulation levels and heights. Step 3-2: Analyze the impact of the short-circuit fault on the current, electromagnetic force, strain and optical fiber vibration phase of each winding. Step 3-3: Propose a turn-to-turn short circuit fault diagnosis method based on the Φ-OTDR system and determine the phase criteria and thresholds of each winding.

[0009] Step 4: Design and build a DAS system experimental platform based on Φ-OTDR. Use knocking excitation to simulate faults to verify the feasibility of the Φ-OTDR system for dry anti-vibration status monitoring and fault location, providing a reference for engineering applications. The step 4 includes the following specific steps: Step 4-1: Design and build a DAS system experimental platform based on Φ-OTDR and configure fiber optic sensing parameters. Step 4-2: Simulate faults through tapping excitation, collect anti-vibration signals, and analyze experimental data. Step 4-3: Verify the feasibility of the Φ-OTDR system for anti-vibration status monitoring and fault location, providing a reference for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 4 is a system flow chart of a method for monitoring the vibration status of a dry-type air-core reactor based on Φ-OTDR in a specific embodiment.

[0011] Figure 2 a and Figure 2 b respectively show the dry-type air-core reactor structure and winding distribution in a specific embodiment.

[0012] Figure 3 a and Figure 3 b are schematic diagrams of the overall dry reactor model and a partial schematic diagram of the winding in a specific embodiment.

[0013] Figure 4 This figure shows the influence of the air domain on the calculation results in the anti-interference modeling in a specific embodiment.

[0014] Figure 5 1 is the equivalent circuit and node numbering of the dry reactor under normal operating conditions in a specific embodiment.

[0015] Figure 6 This is the mesh division effect of the anti-interference model in a specific embodiment.

[0016] Figure 7 1 is the magnetic field distribution of the interference detector under normal state in a specific embodiment.

[0017] Figure 8 a. Figure 8 b. Figure 8 c and Figure 8 d are the distribution of the radial electromagnetic force per unit volume along the impedance height for each layer of windings in each package in a specific embodiment.

[0018] Figure 9 : is the relationship between the axial electromagnetic force per unit volume of each layer of winding and the winding height in a specific embodiment.

[0019] Figure 10 a. Figure 10 b. Figure 10 c and Figure 10 d is the strain distribution inside each layer of winding in the dry reactor in a specific embodiment.

[0020] Figure 11 a. Figure 11 b. Figure 11 c and 11d are the relationships between the average strain inside each layer of winding in the dry-resistance envelope and time in a specific embodiment.

[0021] Figure 12 a. Figure 12 b. Figure 12 c and Figure 12 d is the relationship between the vibration phase and time on the optical fiber path within the interference-resistant envelope in a specific embodiment.

[0022] Figure 13 a. Figure 13 b. Figure 13 c and Figure 13 d is the relationship between the vibration phase and time of the inner side of each layer of winding in the dry-anti-vibration envelope in a specific embodiment.

[0023] Figure 14 It is the geometric model of the dry-type anti-turn short-circuit fault in the specific embodiment.

[0024] Figure 15 1 is the equivalent circuit and node numbering after the dry reactor turns are short-circuited in a specific embodiment.

[0025] Figure 16 The figure is a comparison of the current distribution of each winding before and after the dry reactor inter-turn short circuit in a specific embodiment.

[0026] Figure 17 Schematic diagram of the distribution of fault points of the dry-type reactor winding in a specific embodiment.

[0027] Figure 18 The figure shows the comparison of short-circuit currents of the dry reactor winding after faults at different heights in a specific embodiment.

[0028] Figure 19 a. Figure 19 b. Figure 19 c and Figure 19 d is the strain distribution of all windings of the dry-type anti-fault enclosure 1 after a fault in a specific embodiment.

[0029] Figure 20 a. Figure 20 b. Figure 20 c and Figure 20 d is the optical fiber vibration distribution after all windings of the dry-type anti-vibration enclosure 1 fail in a specific embodiment.

[0030] Figure 21 1 is a comparison of electromagnetic forces before and after faults at different heights of the dry-type winding 1 in a specific embodiment.

[0031] Figure 22 1 is a strain comparison before and after faults at different heights of the dry-type winding 1 in a specific embodiment.

[0032] Figure 23 1 is a comparison of optical fiber vibration phases before and after faults at different heights of the dry-type anti-fault winding 1 in a specific embodiment.

[0033] Figure 24 1 is a comparison of optical fiber vibration phases before and after a fault at different heights of the dry-resistance winding 5 in a specific embodiment.

[0034] Figure 25 1 is a comparison of optical fiber vibration phases before and after a fault at different heights of the dry-type anti-friction winding 8 in a specific embodiment.

[0035] Figure 26 1 is a comparison of optical fiber vibration phases before and after a fault at different heights of the dry-resistance winding 11 in a specific embodiment.

[0036] Figure 27 This is the equipment and arrangement for the anti-vibration monitoring experiment in a specific embodiment.

[0037] Figure 28 It is the time domain response before and after tapping the impedance in a specific embodiment. DETAILED DESCRIPTION

[0038] The dry-type air-core reactor is mainly composed of the body and insulating support parts. Figure 2 As shown, the main body comprises a multi-layer, parallel, coaxial cylindrical encapsulated structure, each layer mechanically secured by epoxy resin lead rods and a star-shaped bracket. Each encapsulated layer is wound with multiple layers of parallel coils, using aluminum or copper conductors of varying strand counts and diameters. The layers and turns are insulated with fiberglass or polyester film. The upper and lower star-shaped brackets serve as current collectors, with the outgoing wires from each winding layer welded to the star-shaped brackets. Current flows from the upper star-shaped bracket into the winding layers, where it is collected by the lower star-shaped bracket for output.

[0039] To clarify the impact of electric-magnetic field coupling on interference, analyzing electromagnetic problems involves solving Maxwell's equations under given boundaries. The partial differential equations used in the electromagnetic finite element method are derived from Maxwell's equations.

[0040] Where H is the magnetic field intensity, J is the density of the conduction current, D is the electric displacement vector, E is the induced electric field intensity, B is the magnetic induction intensity, and ρ is the charge density. Their differential forms are expressed as:

[0041] Since the interference resistor operates at power frequency, the frequency of the time-varying magnetic field is relatively low, and the time-varying electromagnetic field can be simplified to a steady-state field. Therefore, formula (2) can be simplified to:

[0042] In addition, the various equations in Maxwell's equations are not independent but influence each other. Therefore, the constitutive relationship between the medium and the magnetic and electric fields is also the key to calculating the magnetic field.

[0043] Where ε is the dielectric constant of the medium, μ is the magnetic permeability of the medium, and σ is the electrical conductivity of the medium.

[0044] The finite element method for solving electromagnetic field problems is based on Maxwell's equations. The quantity to be solved is the vector magnetic potential A, and other unknown quantities are then solved as needed. It is assumed that the reactor's windings, surrounding air, and insulating material are all uniform, isotropic, and linear. The reactor is a typical axisymmetric structure. In a cylindrical coordinate system, the vector magnetic potential A has only an axial component and satisfies:

[0045] Under the excitation of the power frequency voltage source, the relationship between the internal and external magnetic fields of the interference reactance satisfies the Poisson equation:

[0046] Where A θ is the axial component of the vector magnetic potential A, μ is the magnetic permeability of the material, J is the current density, r, θ, and z represent the radius, angle, and height in the cylindrical coordinate system, respectively.

[0047] Since the current density in the insulation material between the windings and the surrounding air medium is zero, the magnetic field equation in the air domain and the insulation material inside the dry reactor is:

[0048] By combining equations (5), (6) and (7), we can obtain the magnetic induction intensity of the interference:

[0049] From formula (8), we can see that the magnetic induction intensity B consists of two components: axial and radial. From this, we can calculate the current distribution of each winding.

[0050] When an alternating current is applied to the reactor coil, the charged coil will vibrate under the electromagnetic force generated by the alternating magnetic field, resulting in displacement and deformation of the winding. When a current i is applied to a conductor in a magnetic field B, the electromotive force per unit length of the conductor is: dF=idl×B (9)

[0051] Where i is the current flowing through the conductor, B is the magnetic induction intensity vector at the conductor dl, and dl is the vector of unit length on the current-carrying conductor segment, with the same direction as the current.

[0052] By integrating each current-carrying infinitesimal element, the electromagnetic force on the three-dimensional volume of any unit cross section on the dry-resistance winding is: F v =∫ v (J×B)dv (10)

[0053] The magnetic induction intensity B and current density J in the formula can be calculated through the previous step. The winding produces forced vibration under the action of the alternating electromagnetic force, and its vibration frequency is closely related to the current frequency. According to Ampere's law, the electromagnetic force of the dry winding is proportional to the product of the magnetic induction intensity and the winding current, and is proportional to the square of the current: F∝B×I∝I 2 (11)

[0054] When the dry winding is excited by a single-frequency current i=Asin(2πft), the electromagnetic force F=ki 2 ,Right now: F=kA 2 p1-cos(2π×2ft)] / 2 (12)

[0055] At this time, the frequency of the electromagnetic force on the winding is twice the current frequency. When the dry-resistance winding is excited by a current containing two frequencies i=i1+i2, let i1=A1sin(2πf1t), i2=A2sin(2πf2t), then i 2 =i1 2 +i2 2 +2i1i2, the electromagnetic force generated is:

[0056] in:

[0057] From the above derivation, we can see that when the dry-resistance winding contains currents of two frequencies, the frequencies of the electromagnetic force acting on the winding include not only 2f1 and 2f2 generated by the independent action of i1 and i2, but also the sum frequency f1+f2 and difference frequency f1-f2 generated by the interaction of i1 and i2. Obviously, the more harmonic components that flow into the dry-resistance winding, the more different frequencies of electromagnetic force are generated. This increases the probability that the electromagnetic force frequency acting on the dry-resistance winding coincides with its natural frequency, making resonance more likely to occur.

[0058] When the sensing fiber is disturbed by external factors, the optical sensing properties of the fiber in the disturbed area, such as its length and refractive index, will change, causing the phase of the RBS light in the fiber to change. The phase difference between the two scattering centers on the fiber is expressed as:

[0059] Where λ n represents the wavelength of light propagating in an optical fiber with a refractive index of n, d ab represents the optical path difference between the two scattering centers a and b, x a and x b is the fiber length of the two scattering centers a and b, so d ab =2(x a -x b ).

[0060] Without considering the influence of temperature and other factors on the optical fiber, when external force is applied to the optical fiber, the Poisson effect will cause the optical fiber to expand and contract in the radial, axial and tangential directions, and the resulting elastic-optic effect will cause the refractive index of the optical fiber to change. Ignoring the radial and tangential strains, the differential operation of Equation 17 yields:

[0061] At the same time, the relationship between strain, light refractive index and optical fiber axial expansion and contraction is: Δ(x a -x b )=(x a -x b )ε (20)

[0062] Where p is the photoelastic coefficient, p=[(1-μ)p 12 -μp 11 ], Poisson's ratio is μ = 0.17, strain-optical coefficient p 11 =0.121, p 12 =0.27; ε is the axial strain of the optical fiber. Substituting equations (19) and (20) into equation (18), we can obtain:

[0063] From Equation (21), we can see that the phase change of the scattered light is linearly related to the axial strain of the optical fiber. Therefore, in the absence of external disturbances, the phase difference between any two points in the optical fiber should remain unchanged. When disturbed, strain measurement can be achieved by measuring the phase difference change.

[0064] Based on the above theory, a geometric model for dry-type reactor turn-to-turn short-circuit faults was established. The CKGKL-240 / 10-12% single-phase outdoor dry-type air-core reactor was used for modeling and simulation. This reactor has a capacity of 240 kVar and a reactance ratio of 12%. It consists of four layers of aluminum rectangular conductors (the first and fourth layers consist of four layers, while the second and third layers consist of three layers), resulting in a total of 14 winding layers. The outer diameter of the envelope is 1247 mm, the inner diameter is 1004 mm, and the height is 719 mm. The air passages between the envelopes are 25 mm. The main electrical and winding parameters are shown in Tables 3 and 4. Table 3 Electrical parameters of CKGKL-240 / 10-12% dry-type air-core reactor Table 4 CKGKL-240 / 10-12% dry anti-encapsulation and winding parameters of each layer

[0065] Due to the geometric symmetry of the dry reactor structure, a two-dimensional axisymmetric coordinate system was used for modeling. The inter-turn insulation of the winding was ignored during modeling, and only the inter-layer and overall insulation of the package were considered. The star frame and the brace were omitted. According to the parameters in Table 4, a simplified geometric model of the CKGKL-240 / 10-12% single-phase outdoor dry-type air-core reactor was established. Figure 3 As shown in (a), the outermost layer is the air domain. Figure 3 The four rectangles in (b) represent the envelope, and the small rectangles within the envelope represent the windings. Insulation layers are provided between the winding layers and between the windings and the envelope. Key material properties for each region are shown in Table 5. Table 5 Model material property parameters

[0066] The air domain (magnetic field solution area) of the dry reactance is set to 5 times the maximum size of the dry reactance. The magnetic field calculation results are shown in Figure 4 . Circuit modules such as Figure 5The dry reactor has 4 layers of encapsulation and 14 layers of parallel windings, all of which are subjected to a DC voltage of 831.39V (corresponding to the power frequency terminal voltage). Each layer of winding is regarded as an independent branch, with a small resistor R in series, and the finite element domain coil is represented by an "external I VS.U" component. In the magnetic field module, the left boundary is axisymmetric and the other boundaries are magnetically insulated. The 14 "coil" interfaces are set as uniform multi-turn coils, and the parameters are shown in Table 2. The solid mechanics module sets the winding as a linear elastic material, with the upper and lower ends fixed, the initial displacement and velocity are 0, and the Lorentz force body load is applied. The grid is controlled by conventional physical fields, and after division, it contains 144,594 domain elements and 26,878 boundary elements (see Figure 6 ). Using the frequency domain solver, the frequency is 50Hz, and the magnetic field distribution is as follows Figure 7 .

[0067] The effective current values ​​of each layer of the "magnetic field-circuit" coupling model are obtained through simulation calculation (see Table 6). The simulation and rated current trends are consistent. Except for the first envelope, the errors between the simulation values ​​and the rated values ​​of the remaining envelopes are small, indicating that the model is basically reasonable. Table 6 Current distribution of each layer of coils calculated by magnetic field-circuit model

[0068] In order to analyze the vibration characteristics of the dry reactor under rated working conditions, the distribution of radial and axial electromagnetic forces along the height of each layer of winding per unit volume of each package was studied (see Figure 8 and Figure 9 The results show that radial electromagnetic forces dominate the center of the envelope, while axial electromagnetic forces dominate the top and bottom ends. This results in a large radial tensile force in the center of the envelope and axial compressive forces at the ends. Because the envelope is tightly wound with epoxy resin and glass yarn, the axial electromagnetic force is less restrained and is more susceptible to it at the top and bottom ends. Therefore, special attention should be paid to the insulation at these ends to prevent insulation cracking and inter-turn short circuits.

[0069] In addition, the vibration distribution characteristics of the Φ-OTDR-based interference impedance under rated working conditions were analyzed, and the strain and vibration phase variation laws on the optical fiber path within the envelope were studied. Figure 10 The peak longitudinal strain distribution of each encapsulated winding layer is shown. The strain distribution pattern of each winding layer is similar to the distribution pattern of the radial electromagnetic force. The winding strain in Encapsulation 1 is the largest, and the winding strain in Encapsulation 4 is the smallest. Due to the addition of fixed constraints at the upper and lower ends of the winding, the strain at these ends differs significantly from the strain at the center when subjected to the radial electromagnetic force. Table 7 shows the maximum strain of each winding layer. Table 7 Maximum strain values ​​of each layer of winding coil

[0070] Figure 11The time-varying law of the average strain of each layer of winding in the envelope is shown. The optical fiber vibration phase at the time of strain peak, the winding height and the average phase change with time are shown in Figure 12 and 13 When the dry-type reactor operates under rated conditions, the maximum phase differences caused by strain on the optical fiber path along the winding surface within the four-layer envelope are 2.99 rad, 1.61 rad, 1.00 rad, and 0.41 rad, respectively. The phases are greatest at the top and bottom ends of the winding, and near the center, the phase differences are approximately 2.24 rad, 1.25 rad, 0.66 rad, and 0.18 rad, respectively. The Φ-OTDR system is highly sensitive to vibration phase changes and can detect variations of the order of 0.1 rad, which is much smaller than the actual measured phase difference. Therefore, it can effectively monitor dry-type reactor vibration with minimal hardware and software requirements. A significant deviation from the normal phase of the optical fiber within the envelope indicates a turn-to-turn short circuit.

[0071] In order to analyze the vibration characteristics under fault conditions and verify the feasibility of using the Φ-OTDR system for online monitoring of dry-type reactor vibration, a "magnetic field-circuit" coupled turn-to-turn short-circuit model was established. Based on the rated working conditions, the situation after the dry-type reactor had a turn-to-turn short-circuit was simulated (see Figure 14 、 15 ). Taking the short circuit in the center of winding 1 as an example, the short circuit layer is divided into two series coils, and the new short circuit ring is electromagnetically coupled with the original branch, and is independently numbered in the circuit and magnetic field modules. The simulation results are shown in Figure 2. Figure 16 It shows that the inter-turn short circuit mainly affects the current of the fault layer, and the impact on other layers is relatively small. The short-circuit turn current is 958.34A, which is 49.86 times the rated current, which is consistent with existing research.

[0072] In order to systematically analyze the influence of inter-turn short circuit on vibration distribution, short circuits are set at different heights (0, h / 4, h / 2, 3h / 4, h) of windings 1, 5, 8, and 11 (see Figure 17 ), the current distribution when short circuit occurs at different locations is obtained by simulation ( Figure 18 The increase in short-circuit current will cause a significant increase in the electromagnetic force of the fault layer, causing violent vibrations, which the Φ-OTDR system can use to locate the fault. Simulation analysis shows that the strain distribution of all windings near the fault location is highly consistent ( Figure 19 ), the optical fiber vibration phase change law is basically the same ( Figure 20 ). Therefore, the subsequent analysis takes the inner windings of each package (windings 1, 5, 8, and 11) as representatives.

[0073] Further analysis of the vibration characteristics after short circuit at different heights (h, 3h / 4, h / 2). Taking winding 1 as an example, the radial electromagnetic force is the largest when short circuit is at h / 2 ( Figure 21 ), the strain peak is the largest (4.23×10 -7), which is 1.79×10 -7 ; h and 3h / 4 are next ( Figure 22 The optical fiber vibration phase also increases significantly after the fault occurs ( Figure 23 ), see Table 8 for specific data.

[0074] Table 8 Strain and phase distribution of winding 1 before and after fault at different heights

[0075] The results show that the closer the fault location is to the winding center (at H / 2), the greater the increase in the fiber vibration phase, indicating that a central fault has the most significant impact on the phase. The phase change decreases as the fault point moves away from the center. Monitoring the phase change along the fiber path along the winding surface using a Φ-OTDR system effectively locates the fault. Similarly, the strain and phase distributions of windings 5, 8, and 11 before and after faults at different heights were obtained using the same method. Specific data are shown in Tables 9, 10, and 11.

[0076] Table 9 Strain and phase distribution of winding 5 before and after fault at different heights

[0077] Table 10 Strain and phase distribution of winding 8 before and after fault at different heights

[0078] Table 11 Strain and phase distribution of winding 11 before and after fault at different heights

[0079] The analysis shows that the strain and optical fiber vibration phase distribution of each winding in the same envelope are basically the same, so this chapter selects the innermost windings of each layer of envelope (windings 1, 5, 8, and 11) as the research objects. Figure 23 、 24 , 25 and 26, the inter-turn short circuit fault will cause the optical fiber vibration phase at the fault location to increase significantly. Based on this, a turn-to-turn short circuit fault diagnosis method for the Φ-OTDR system is proposed:

[0080] (1) Winding 1: The maximum vibration phase is 2.99 rad when normal, and 3.64 rad when faulty. The judgment threshold is set to 3.30 rad. A phase less than 3.30 rad is considered normal, and a phase greater than 3.30 rad is considered a fault.

[0081] (2) Winding 5: The maximum vibration phase is 1.64 rad when normal, and 2.52 rad when faulty. The judgment threshold is set to 2.00 rad. A phase less than 2.00 rad is considered normal, and a phase greater than 2.00 rad is considered a fault.

[0082] (3) Winding 8: The maximum vibration phase is 1.00 rad under normal conditions and 1.40 rad after a fault. The judgment threshold is set to 1.20 rad. A phase less than 1.20 rad is considered normal, and a phase greater than 1.20 rad is considered a fault.

[0083] Winding 11: The maximum vibration phase is 0.18 rad under normal conditions and 0.41 rad after a fault. The threshold is set to 0.30 rad. A phase less than 0.30 rad indicates normal operation, while a phase greater than 0.30 rad indicates a fault.

[0084] In order to verify the monitoring capability of Φ-OTDR DAS system to the interference and vibration signal, an experimental scheme was designed (see Figure 27 The experiment used a single-mode optical fiber with an FC / APC interface, a central wavelength of 1550.12 nm, a linewidth of 2.5 kHz, an AOM frequency shift of 80 MHz, and a pulse width of 80 ns as the sensing medium. The optical fiber was laid within the encapsulated insulation. A tapping excitation was applied to the sidewall near the center of the winding to simulate the vibration characteristics of a short-circuit fault. The DAS system settings were 50 m fiber length, 1000 Hz pulse repetition frequency, 15,000 acquisition cycles, and 15 s acquisition time.

[0085] Experimental results ( Figure 28 ) shows that the phase is stable at rest. After impact excitation, the phase amplitude increases from 0.11 rad to 7.98 rad, exhibiting a decaying oscillation. This experiment validates the feasibility of a DAS system for monitoring vibration signals in dry-type reactors, providing a reference and support for its application in online monitoring of power equipment and guiding the application of distributed fiber optic sensing technology in dry-type reactors.

[0086] The above is only one embodiment of the present invention, not all or the only embodiment. Any equivalent transformation of the technical solution of the present invention made by ordinary technicians in this field after reading the specification of the present invention is covered by the claims of the present invention.

Claims

1. A method for monitoring the vibration state of a dry-type air-core reactor based on vibration measurement using a phase-sensitive optical time domain reflectometer (hereinafter referred to as "Φ-OTDR"), characterized in that: A dry-type reactor (hereinafter referred to as "dry reactor") was modeled through finite element simulation. A dry reactor operating condition and turn-to-turn short-circuit model were determined. Vibration information inside the reactor was acquired using distributed fiber-optic sensing vibration measurement technology. Vibration comparisons were performed between normal dry reactor operation and after turn-to-turn faults. A method for early warning and locating turn-to-turn short-circuit faults was proposed. This method includes the following steps: Step 1: Simulate the vibration state of the solid mechanics field of the dry-type air-core reactor when it is operating under rated conditions. Step 2: Study the vibration distribution law of the dry-type winding after a turn-to-turn short-circuit fault occurs. Step 3: Establish a "magnetic field-circuit" coupled simulation model of the dry-type inter-turn short-circuit fault and propose a turn-to-turn short-circuit fault diagnosis method based on the Φ-OTDR system. Step 4: Design and build a distributed fiber optic sensing system experimental platform based on Φ-OTDR. Use knocking excitation to simulate faults to verify the feasibility of the Φ-OTDR system for anti-vibration status monitoring and fault location, providing a reference for engineering applications.

2. The method for monitoring the vibration state of a dry-type air-core reactor based on Φ-OTDR vibration measurement according to claim 1, wherein: The step 1 includes the following specific steps: Step 1-1: Define the structural composition and key parameters of the dry-type air-core reactor and establish a geometric model of the multi-layer encapsulated and parallel coils. Simulations were performed based on the physical structure of a CKGKL-240 / 10-12% dry-type reactor. Its key electrical parameters and the winding parameters of each encapsulated winding are shown in Tables 1 and 2, respectively. Table 1 Electrical parameters of CKGKL-240 / 10-12% dry-type air-core reactor Table 2 CKGKL-240 / 10-12% dry anti-encapsulation and winding parameters of each layer Step 1-2: Based on Maxwell's equations, the finite element method is used to theoretically analyze the electromagnetic field of the interference resistor and derive the calculation method of the electromagnetic force. Step 1-3: Analyze the mechanism of how electromagnetic force affects winding vibration based on the structural characteristics of the resistor.

3. The method for monitoring the vibration state of a dry-type air-core reactor based on Φ-OTDR vibration measurement according to claim 1, wherein: The step 2 includes the following specific steps: Step 2-1: Based on the numerical simulation method, establish a finite element simulation model of interference resistance. Step 2-2: Study the vibration characteristics of each encapsulated winding under rated operating conditions, including radial and axial electromagnetic force distribution, strain distribution, etc. Step 2-3: Analyze the vibration characteristics of the inner windings of Envelope 1, Envelope 2, Envelope 3, and Envelope 4, namely, Winding 1, Winding 5, Winding 8, and Winding 11, after inter-turn faults occurred at different heights. Based on the above analysis results, the diagnosis basis of inter-turn short circuit of the Φ-OTDR system in the dry anti-vibration state is obtained.

4. The method for monitoring the vibration state of a dry-type air-core reactor based on Φ-OTDR vibration measurement according to claim 1, wherein: The step 3 includes the following specific steps: Step 3-1: Establish a "magnetic field-circuit" coupled simulation model for dry-type short-circuit faults, simulating short circuits occurring at different packages and heights. Step 3-2: Analyze the impact of the short-circuit fault on the current, electromagnetic force, strain and optical fiber vibration phase of each winding. Step 3-3: Propose a turn-to-turn short circuit fault diagnosis method based on the Φ-OTDR system and determine the phase criteria and thresholds of each winding.

5. The method for monitoring the vibration state of a dry-type air-core reactor based on Φ-OTDR vibration measurement according to claim 1, wherein: The step 4 includes the following specific steps: Step 4-1: Design and build a distributed fiber optic sensing system experimental platform based on Φ-OTDR and configure fiber optic sensing parameters. Step 4-2: Simulate faults through tapping excitation, collect anti-vibration signals, and analyze experimental data. Step 4-3: Verify the feasibility of the Φ-OTDR system for anti-vibration status monitoring and fault location, providing a reference for engineering applications.

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