Dry-type reactor turn-to-turn fault monitoring method based on distributed optical fiber temperature change rate measurement

Abstract

A dry-type reactor turn-to-turn fault monitoring method based on a distributed optical fiber measurement temperature change rate is characterized in that a dry-type hollow series reactor finite element simulation model is built, and temperature distribution during normal operation and turn-to-turn short circuit faults of the dry-type hollow series reactor is acquired. Based on a distributed optical fiber sensing temperature measurement technology of Brillouin scattering, path temperature information in a reactor package is extracted, temperature data after normal operation and turn-to-turn short circuit are compared, and influences of different factors on fault temperature are explored. The early warning method for monitoring the turn-to-turn short circuit fault of the dry-type air-core reactor is provided by taking the temperature change rate as a criterion, and the influence of different factors on the effectiveness of the early warning method is verified. The result shows that the environment temperature, the wind speed and the running current basically have no influence on the method for monitoring the turn-to-turn short circuit of the dry-type air-core reactor by taking the temperature change rate as the criterion, different temperature change rate thresholds need to be set under different sampling intervals, and the smaller the sampling interval is, the larger the threshold is.

Description

Technical Field

[0001] This invention relates to a method for monitoring inter-turn faults in dry reactors based on distributed optical fiber measurement of temperature variation, belonging to the field of measurement technology. Background Technology

[0002] Dry-type air-core series reactors (DTACSRs) are key equipment for reactive power compensation and harmonic suppression in power systems, with long service lives and significant impacts on grid stability. Compared to traditional oil-immersed air-core reactors, DTACSRs possess several technical advantages: good linearity, strong adaptability, convenient and low-cost maintenance, ease of outdoor installation, ability to withstand harsh operating conditions, low operating noise, and high mechanical strength. Dry-type air-core reactors are widely used in various power systems, primarily serving functions such as filtering, limiting short-circuit current, and reactive power compensation. However, DTACSRs frequently experience insulation faults during operation, and even fires, rendering them unable to operate normally. One of the key factors affecting the stable operation of DTACSRs is temperature. Excessive operating temperature can affect the normal operation of the DTACSR or even cause it to burn out. Reactor fires not only result in significant economic losses but also seriously threaten the safety and stability of the power system. Inter-turn short circuits are one of the main causes of abnormal encapsulation heating. During long-term operation, the accumulation of heat causes the reactor temperature to rise, making the polyester film between windings prone to hydrolysis and reducing the inter-turn insulation capacity. Traditional monitoring methods, such as infrared thermography, are difficult to monitor the internal encapsulation temperature of dry-type reactors, making it difficult to achieve accurate early warning during the fault latency period. Magnetic field monitoring methods are also difficult to extract signals when magnetic field interference is severe. Existing patent application CN119619596A, "Fault Monitoring Method for Dry-Type Reactors Based on Interlayer Current Ratio," sets multiple current sensors at the base of the dry-type reactor to calculate the ratio of the current in each layer to the current in the innermost layer to determine the fault location. However, this method takes a long time to monitor faults and cannot provide early warning. Therefore, it is necessary to study an effective method for online monitoring and early warning of inter-turn short circuits in reactors.

[0003] Distributed fiber optic sensing technology based on Brillouin scattering can measure strain and temperature along the fiber optic cable. It offers significant advantages in long-distance operation, low electromagnetic disturbance, intrinsic insulation, strong environmental adaptability, high resolution, multi-parameter sensing, and adaptability to harsh environments, making it an irreplaceable monitoring method in many important engineering fields. It also shows great promise for monitoring DTACSR faults. However, research on using distributed fiber optic sensors with temperature change rate as a criterion for monitoring the operational status of DTACSRs is rarely reported. Summary of the Invention

[0004] The problem to be solved by the present invention is a method for monitoring inter-turn faults in dry reactors based on distributed optical fiber measurement of temperature variation rate.

[0005] To solve the above problems, the present invention adopts the following technical solution:

[0006] 1. A method for monitoring inter-turn faults in dry-type reactors based on distributed optical fiber measurement of temperature change rate. This method models the dry-type air core series reactor (DTACSR) using finite element simulation software, obtains the temperature distribution during normal operation and inter-turn short-circuit faults, extracts the fiber path temperature information within the reactor enclosure using distributed optical fiber temperature sensing technology based on Brillouin scattering, compares the temperature data of the DTACSR during normal operation and after an inter-turn short circuit, proposes an early warning method for monitoring inter-turn short-circuit faults in DTACSRs based on the temperature change rate, and verifies the effectiveness of different factors. The method includes the following steps:

[0007] Step 1: Establish magnetic field-circuit coupling models of DTACSR under normal operation and inter-turn short circuit fault, and obtain the coil current in DTACSR under the corresponding conditions to calculate the heat dissipation rate;

[0008] Step 2: Establish a solid-fluid heat transfer-turbulent field coupling model for DTACSR under normal operation and inter-turn short-circuit fault. Input the coil heat dissipation rate, calculate the temperature of DTACSR under normal operation and inter-turn short-circuit fault, and study the effects of fault location, ambient temperature, wind speed and operating current on the temperature distribution of DTACSR inter-turn short-circuit fault.

[0009] Step 3: Process the obtained temperature data to obtain the temperature change after the inter-turn short circuit fault occurs and the temperature change. Select appropriate values ​​as the criteria for the occurrence of inter-turn short circuit faults, and study the effectiveness of this method for monitoring DTACSR inter-turn faults under the influence of different ambient temperatures, wind speeds, operating currents and sampling intervals.

[0010] 2. The method for monitoring inter-turn faults in dry reactors based on distributed optical fiber measurement of temperature variation is characterized in that:

[0011] Step 1 includes the following specific steps:

[0012] Step 1-1: Based on the electrical and geometric structure of the reactor with model number CKGKL-240 / 10-12%DTACSR, simplify the reactor structure, ignore the influence of the reactor star frame on the DTACSR magnetic field distribution, and build a geometric model using finite element simulation software;

[0013] Steps 1-2: Construct a magnetic field-circuit coupling model of the reactor during normal operation, analyze the magnetic field calculation principle of DTACSR during normal operation, and make reasonable simplifications based on the magnetic field calculation equations, taking into account the speed and accuracy of the calculation.

[0014] Steps 1-3: Set material property parameters, and couple the magnetic field and circuit according to the equivalent circuit of DTACSR rated operation and inter-turn short circuit fault. Input the number of turns, conductivity and cross-sectional area of ​​each winding of DTACSR in the magnetic field.

[0015] Steps 1-4: To balance computational efficiency and result accuracy, a physical field-controlled mesh is selected for mesh generation, with a standard cell size. The calculation results converge, and the coil current is obtained to calculate the resistance loss.

[0016] 3. The method for monitoring inter-turn faults in dry reactors based on distributed optical fiber measurement of temperature variation is characterized in that:

[0017] Step 2 includes the following specific steps:

[0018] Step 2-1: To improve computational efficiency, considering the symmetry of the three-dimensional reactor structure, a 1 / 12 symmetry model is established as the finite element calculation field. The heat dissipation rate of the 14 windings of the reactor during normal operation is input into the solid fluid heat transfer field. When a fault occurs, the heat dissipation rate of the short-circuit turns is additionally constructed and input. Its value is obtained by processing the calculation results of Step 2. An air domain is added outside the reactor, and the air domain outside the reactor is set as a turbulent field to represent flowing air.

[0019] Step 2-2: Set the inlet velocity and outlet pressure in the turbulent field. The convective heat transfer coefficient is automatically calculated by the simulation software. The ambient temperature during normal operation is 293.15K. Set the lower side of the air domain as the inlet and the upper and side sides as the outlet. The initial air velocity is 0.3m / s to simulate the natural convection heat dissipation process of the reactor.

[0020] Steps 2-3: The mesh generation method is selected using physics-controlled meshing, the cell size is standard, and the calculation results converge.

[0021] Steps 2-4: Change the fault location, ambient temperature, wind speed, and operating current to obtain temperature information of DTACSR inter-turn short circuit faults under the influence of different factors.

[0022] 4. The method for monitoring inter-turn faults in dry-type reactors based on distributed optical fiber measurement of temperature variability is characterized in that:

[0023] Step 3 includes the following specific steps:

[0024] Step 3-1: The temperature difference is obtained by subtracting the temperature of the hot spot at the same location after the fault occurs from the temperature at the same point during normal operation. The temperature difference is divided by time to obtain the temperature change rate, and then the temperature change rate at different times after a single-turn short circuit is obtained. The temperature change rate threshold is determined by the operating condition data with the least severe temperature change of the short-circuit turn after a single-turn short circuit fault.

[0025] Step 3-2: Based on the different temperature rise rates of inter-turn short circuit faults with different winding numbers and winding positions, considering the inconsistency between the fault occurrence time and the start measurement time, as well as the error of fiber optic temperature measurement, set an appropriate temperature change rate warning value, select a value slightly smaller than the slowest temperature rise, and determine whether there is an inter-turn short circuit fault in the winding.

[0026] Step 3-3: Investigate the effects of different ambient temperatures, wind speeds, operating currents, and sampling intervals on the effectiveness of using temperature change rate as a measure of fiber optic monitoring for interference faults. Attached Figure Description

[0027] Figure 1 Abstract and accompanying figures

[0028] Figure 2 Dry-type air-core series reactor physical body

[0029] Figure 3 equivalent circuit diagram of reactor

[0030] Figure 4 Two-dimensional magnetic field circuit model

[0031] Figure 5 Magnetic field distribution map

[0032] Figure 6(a) Simplified model of a 1 / 12 reactor, partially magnified

[0033] Figure 6(b) Simplified model of 1 / 12 reactor

[0034] Figure 7 Temperature distribution diagram of 1 / 12 reactor body

[0035] Figure 8 Fluid flow diagram of 1 / 12 reactor body

[0036] Figure 9 Temperature rise at different axial heights under normal conditions (Figure)

[0037] Figure 10(a) Temperature distribution of the reactor body after a single-turn short circuit at the top for 60 seconds.

[0038] Figure 10(b) shows the temperature distribution of the reactor body 60 seconds after a single-turn short circuit in the upper middle part.

[0039] Figure 10(c) Temperature distribution of the reactor body 60s after a single-turn short circuit in the middle section.

[0040] Figure 11 Fault temperature at the upper end of winding 9 of the encapsulated coil

[0041] Figure 12 Temperature rise of the hottest spot after a fault occurs in winding 9 under different ambient temperatures

[0042] Figure 13 Temperature rise of the hottest spot after a fault occurs in winding 9 at different wind speeds

[0043] Figure 14 Temperature rise of the hottest spot after a fault occurs in winding 9 under different operating currents

[0044] Figure 15 Temperature rise at fault point after single-turn short circuit in the upper part of each winding

[0045] Figure 16 The fault point of the second winding was located at the temperature difference between two consecutive measurements.

[0046] Figure 17 The maximum temperature difference between the two measurements of the second winding (second measurement - first measurement).

[0047] Figure 18 Temperature change rate at different temperature sampling intervals (1 second)

[0048] Figure 19 Temperature change rate at different temperature sampling intervals of 10 seconds

[0049] Figure 20 Temperature change rate at different wind speeds over 1 second interval

[0050] Figure 21 Temperature change rate at different wind speeds over 10-second intervals

[0051] Figure 22 Temperature change rate at 1-second sampling intervals for different currents

[0052] Figure 23 Temperature change rate at 10-second sampling intervals for different currents

[0053] Figure 24 Temperature change rate at different sampling intervals Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0055] The problem this invention aims to solve is temperature measurement based on Brillouin frequency shift technology using distributed optical fiber. Compared with current reactor inter-turn fault monitoring technologies based on temperature, vibration, electrical parameters, and magnetic field monitoring, this invention proposes an early dry reactor inter-turn fault monitoring method based on distributed optical fiber measurement of temperature variation rate, which has strong anti-electromagnetic interference, high sensitivity, and strong real-time performance.

[0056] To solve the above problems, the present invention adopts the following technical solution:

[0057] A method for monitoring inter-turn faults in dry-type reactors based on distributed optical fiber measurement of temperature change rate is proposed. This method models the DTACSR (Diverterless Transformer Array) using finite element simulation software to obtain the temperature distribution during normal operation and inter-turn short-circuit faults. Based on Brillouin scattering-based distributed optical fiber temperature sensing technology, the path temperature information within the reactor envelope is extracted. By comparing the temperature data of the DTACSR during normal operation and after an inter-turn short circuit, an early warning method for monitoring inter-turn short-circuit faults in the DTACSR using the temperature change rate as a criterion is proposed. The effectiveness of this method is verified by considering the influence of different factors. The method includes the following steps:

[0058] Step 1: Establish magnetic field-circuit coupling models of DTACSR under normal operation and inter-turn short circuit fault, and obtain the coil current in DTACSR under the corresponding conditions to calculate the heat dissipation rate;

[0059] Step 2: Establish a solid-fluid heat transfer-turbulent field coupling model for DTACSR under normal operation and inter-turn short-circuit fault. Input the coil heat dissipation rate, calculate the temperature of DTACSR under normal operation and inter-turn short-circuit fault, and study the effects of fault location, ambient temperature, wind speed and operating current on the temperature distribution of DTACSR inter-turn short-circuit fault.

[0060] Step 3: Process the obtained temperature data to obtain the temperature change after the inter-turn short circuit fault occurs and the temperature change. Select appropriate values ​​as the criteria for the occurrence of inter-turn short circuit faults, and study the effectiveness of this method for monitoring DTACSR inter-turn faults under the influence of different ambient temperatures, wind speeds, operating currents and sampling intervals.

[0061] Step 1 includes the following specific steps:

[0062] Step 1-1: Based on the electrical and geometric structure of the reactor with model number CKGKL-240 / 10-12%DTACSR, simplify the reactor structure, ignore the influence of the reactor star frame on the DTACSR magnetic field distribution, and build a geometric model using finite element simulation software;

[0063] Steps 1-2: Construct a magnetic field-circuit coupling model of the reactor during normal operation, analyze the magnetic field calculation principle of DTACSR during normal operation, and make reasonable simplifications based on the magnetic field calculation equations, taking into account the speed and accuracy of the calculation.

[0064] Steps 1-3: Set material property parameters, and couple the magnetic field and circuit according to the equivalent circuit of DTACSR rated operation and inter-turn short circuit fault. Input the number of turns, conductivity and cross-sectional area of ​​each winding of DTACSR in the magnetic field. The relevant simulation data are shown in Tables 1, 2 and 3. Table 1 is the electrical and structural parameters of the reactor, Table 2 is the size parameters of each package, and Table 3 is the material property parameters of the reactor.

[0065] Table 1 Electrical and Structural Parameters of Reactors

[0066]

[0067] Table 2 Dimensional parameters of each package

[0068]

[0069] Table 3 Material Properties

[0070]

[0071] The thermal conductivity, specific heat capacity, and density of air are functions of temperature and have been defined by the simulation software. The specific expressions can be found in the material functions in COMSOL 6.2, and will not be elaborated on here.

[0072] Steps 1-4: To balance computational efficiency and result accuracy, a physical field-controlled mesh is selected for mesh generation, with a standard cell size. The calculation results converge, and the coil current is obtained to calculate the resistance loss.

[0073] Step 2 includes the following specific steps:

[0074] Step 2-1: To improve computational efficiency, considering the symmetry of the three-dimensional reactor structure, a 1 / 12 symmetry model is established as the finite element calculation field. The heat dissipation rate of the 14 windings of the reactor during normal operation is input into the solid fluid heat transfer field. When a fault occurs, the heat dissipation rate of the short-circuit turns is additionally constructed and input. Its value is obtained by processing the calculation results of Step 2. An air domain is added outside the reactor, and the air domain outside the reactor is set as a turbulent field to represent flowing air.

[0075] Step 2-2: Set the inlet velocity and outlet pressure in the turbulent field. The convective heat transfer coefficient is automatically calculated by the simulation software. The ambient temperature during normal operation is 293.15K. Set the lower side of the air domain as the inlet and the upper and side sides as the outlet. The initial air velocity is 0.3m / s to simulate the natural convection heat dissipation process of the reactor.

[0076] Steps 2-3: The mesh generation method is selected using physics-controlled meshing, the cell size is standard, and the calculation results converge.

[0077] Steps 2-4: Change the fault location, ambient temperature, wind speed, and operating current to obtain temperature information of DTACSR inter-turn short circuit faults under the influence of different factors.

[0078] Step 3 includes the following specific steps:

[0079] Step 3-1: The temperature difference is obtained by subtracting the temperature of the hot spot at the same location after the fault occurs from the temperature at the same point during normal operation. The temperature difference is divided by time to obtain the temperature change rate, and then the temperature change rate at different times after a single-turn short circuit is obtained. The temperature change rate threshold is determined by the operating condition data with the least severe temperature change of the short-circuit turn after a single-turn short circuit fault.

[0080] Step 3-2: Based on the different temperature rise rates of inter-turn short circuit faults with different winding numbers and winding positions, considering the inconsistency between the fault occurrence time and the start measurement time, as well as the error of fiber optic temperature measurement, set an appropriate temperature change rate warning value, select a value slightly smaller than the slowest temperature rise, and determine whether there is an inter-turn short circuit fault in the winding.

[0081] Step 3-3: Investigate the effects of different ambient temperatures, wind speeds, operating currents, and sampling intervals on the effectiveness of using temperature change rate as a measure of fiber optic monitoring for interference faults.

[0082] The DTACSR is modeled using finite element simulation to obtain the temperature distribution under normal operation and inter-turn short-circuit fault conditions. Based on Brillouin scattering-based distributed fiber optic temperature sensing technology, the path temperature information within the reactor envelope is extracted. The temperature data under normal operation and after an inter-turn short circuit are compared. The rate of temperature change is used as the criterion for fault monitoring. A method for locating and warning of inter-turn short-circuit faults is proposed, and the effectiveness of this method is verified by considering different factors. The method includes the following steps:

[0083] DTACSR structure is shown below Figure 2The reactor windings use flat aluminum conductors, wound in single strands. The winding conductors are wrapped with polyester film for inter-turn insulation, and epoxy resin glass fibers are wound around the inner and outer surfaces of the windings and cured to form encapsulated insulation. The reactor has four enclosures, with the number of windings in each enclosure from the inside out being 4, 3, 3, and 4 respectively. These windings are named windings 1 through 14 in order from the inside out. Insulating supports connect the enclosures, providing a fixing function. These supports create heat dissipation channels between the enclosures. Ignoring the influence of the supporting supports and star-shaped frame on the magnetic field distribution, and considering the reactor's axisymmetric structure, the three-dimensional model can be simplified to two-dimensional. A magnetic field-circuit model is established based on the reactor's geometric and electrical parameters.

[0084] A reactor is composed of multiple layers of encapsulation, each encapsulation consisting of multiple layers of aluminum wire spirally wound into multiple windings, typically cylindrical in shape. Assuming the reactor has X encapsulations, each with Y winding layers, for a total of n layers, the reactor can be structurally viewed as n layers of parallel windings, and in circuit terms as n branches of inductors and resistors connected in parallel, such as... Figure 2 As shown. Figure 3 In the circuit, the reactor has n parallel branches, according to Figure 3 Establish the voltage equation set. The branch voltage equation set satisfied by the reactor is as follows:

[0085]

[0086] in, For the node voltages of each layer, I1-I n For the current of each layer of windings, R1-R n For the resistance of each layer of windings, L1-L n For the self-inductance of each layer of windings, M 1,i -M n,i ω represents the mutual inductance between the winding layers, and ω is the frequency.

[0087] An AC voltage is applied to both sides of each winding of the reactor. The field-circuit coupling analysis method follows Maxwell's equations to solve for the magnetic field inside and outside the domain.

[0088]

[0089] Where H is the magnetic field strength and J is the conduction current density. Let E be the displacement current density and E be the electric field strength. Let B be the rate of change of magnetic flux density over time, and ρ be the volume density of free charges.

[0090] For the coil winding portion of the dry-type air-core reactor, since the induced current generated by the mutual inductance between the coil layers of the dry-type air-core reactor needs to be considered, the vector magnetic potential A and the current I are used as degrees of freedom; other regions of the dry-type air-core reactor use the vector magnetic potential A as the degree of freedom. Therefore, it also satisfies the Poisson equation, as shown in equation (6).

[0091]

[0092] Among them: A θ θ represents the circumferential component of the vector magnetic potential A; θ, z, and r represent the angle, axial coordinate, and radius in cylindrical coordinates, respectively; μ1 represents the permeability of the aluminum conductor; and J represents the current density flowing through each layer of windings.

[0093] The circuit equation satisfied by the i-th layer winding is:

[0094]

[0095] Where: U is the external constraint voltage; R i ψ i N i I i S and S represent the resistance, flux linkage, number of turns, current, and cross-sectional area of ​​the i-th layer coil, respectively.

[0096] The established two-dimensional magnetic field circuit model is shown below. Figure 4 The outer side is encapsulated insulation, and the inner side consists of aluminum wire and epoxy resin polymer. All coils are considered as uniform multi-turn coils. The magnetic field distribution diagram obtained in the established two-dimensional electro-magnetic field model is shown below. Figure 5 The magnetic field is mainly distributed in the center of the reactor, and the magnetomotive force gradually decreases from the inner enclosure to the outer enclosure.

[0097] The current of the reactor during normal operation was calculated using a magnetic field-circuit model. Table 4 shows that the overall trend of the simulated current is consistent with the actual current, with a small deviation, indicating that the simulation model has good accuracy.

[0098] Table 4 Simulation current of each coil series air-core reactor

[0099]

[0100] This type of reactor has relatively low eddy current losses. Neglecting eddy current losses, the heat source of the reactor mainly comes from the resistance losses of each winding layer. The heat source is obtained from the current in the magnetic field-circuit coupling model. Dividing the heat source by the volume of the corresponding coil yields the unit heat source density, as shown in Table 5.

[0101] Table 5 Unit heat source density of each coil

[0102]

[0103]

[0104] By applying a unit heat source to the model and controlling the mesh size by the user, the dry-state steady-state temperature distribution under normal operation can be obtained.

[0105] Dry-type air-core reactors dissipate heat from the surrounding air through natural convection and thermal radiation, while the internal components of the reactor dissipate heat through thermal conduction. According to heat transfer theory, the heat transfer between the internal coil and the insulation layer can be expressed by formula (9):

[0106]

[0107] Where: x, y, z are coordinates in each direction, t is the encapsulation temperature, λ1 is the thermal conductivity of the coil, and Q is the heat generated per unit volume.

[0108] The air encapsulated on the surface of a dry-type air-core reactor is considered as a fluid, and its convective motion follows the mass continuity equation, momentum continuity equation, and energy continuity equation. The mass continuity equation is:

[0109]

[0110] The momentum continuity equation is:

[0111]

[0112] Where μ is the aerodynamic viscosity coefficient, ρ is the air pressure, and S u With S v The source term is denoted as . The energy conservation equation is:

[0113]

[0114] Among them, c p Let λ be the specific heat capacity of air, and λ be the thermal conductivity of air.

[0115] When the air around the reactor enters a turbulent state, the widely used standard k-ε (SKE) turbulence model is required in engineering. This model is more stable and accurate than other models, including sub-models for compressibility, buoyancy, and combustion. The expression for the turbulent viscosity coefficient in the model is as follows:

[0116]

[0117] Where, μ t C is the turbulent viscosity coefficient. μ Let k be the source term, k be the turbulent kinetic energy, and ε be the dissipation rate.

[0118] In establishing the three-dimensional fluid-temperature coupled calculation model of the reactor, the physical model and boundary conditions are set as follows:

[0119] 1) The Rayleigh number of the innermost winding of the reactor is defined as follows: Wherein, the minimum winding radius of the winding is taken as r = 0.502m, and v is the kinematic viscosity of air, v = 16.96 × 10⁻⁶. -6 m / s, therefore, Ra>1×10 9 Since the flow is vigorous turbulence, a turbulent flow model is selected.

[0120] 2) The heat source of the reactor is the resistance loss of each layer of windings, and the heat density per unit volume is used as the heat source parameter for the temperature field.

[0121] 3) Assume the ambient temperature is 20℃, which is 293.15K.

[0122] 4) The bottom fluid domain of the reactor is the inlet boundary, with an air velocity of 0.3 m / s and a radial velocity of zero; the top fluid domain is the pressure outlet boundary, with a relative pressure of zero, and the relative pressure of other boundaries is also zero.

[0123] To improve computational efficiency, considering the symmetry of the three-dimensional reactor, a 1 / 12 symmetry model was established as the finite element calculation field, as shown in Figure 6(a). The outer side is encapsulated insulation, and the inner side is aluminum wire and epoxy resin polymer, as shown in Figure 6(b).

[0124] The temperature distribution of the 1 / 12 reactor body is shown in the figure. Figure 7 Under normal operating conditions, the highest temperature occurs at the upper end of encapsulation 3, with a maximum hotspot temperature of 77.343℃. Encapsulations 2 and 3 have higher temperatures than encapsulations 1 and 4. The velocity distribution of the fluid around the dry-type reactor is shown in [Figure / Image]. Figure 8 The flow velocity ranges from 0.971 m / s to 2.13 m / s. High flow velocities are concentrated in the region near the center of the reactor, reaching 2.13 m / s.

[0125] To more intuitively analyze the axial temperature distribution of the reactor, the surface temperatures of windings 3, 6, 9, and 13 on the inner side of the 1st, 2nd, 3rd, and 4th enclosures were selected, and their variation curves with axial height were plotted. Figure 9 Since the end insulation has no internal heat source and has a low thermal conductivity, the axial temperature of the encapsulation rises and falls rapidly at the bottom and top end insulation. Overall, the temperature distribution is consistent with the actual situation, proving the effectiveness of the model.

[0126] Different short-circuit locations were set, and corresponding heat sources were added after the short circuit, while the heat sources of the other 14 windings remained unchanged for transient analysis. The temperature distribution of a single-turn short circuit occurring at the top, upper-middle, and middle sections at 60 seconds is shown in Figures 10(a), 10(b), and 10(c). At 60 seconds of fault, the highest temperature at the top of the casing 3 was 152℃, gradually decreasing axially to 28.8℃ at the bottom, with a maximum temperature rise of 74.657℃. The highest temperature at the upper-middle section was 130℃, while the normal temperature at this location was 74.055℃, resulting in a temperature rise of 55.945℃. The highest temperature at the middle section was 136℃, while the normal temperature at this location was 62.642℃, with a temperature rise of 73.358℃. It is evident that the reactor temperature rise is most severe when the short circuit is located at the top, followed by the middle section, and weakest at the upper-middle section. After 10 seconds, the outer insulation temperature was 90.236℃, and the winding temperature was 102.58℃, a difference of approximately 12.344℃. Placing the optical fiber inside the encapsulated winding allows for earlier fault detection. The upper fault has the most severe impact on the temperature of the hottest spot; therefore, unless the fault location is explicitly stated later, it will be assumed to be a single-turn short circuit in the upper part.

[0127] To more intuitively analyze the temperature changes after a fault, a graph showing the fault temperature at the upper end of winding 9 (enclosed by winding 3) is provided. Figure 11 In the early stages of a fault, the temperature rises rapidly. The initial short-circuit current changes rapidly, generating significant Joule heat and causing a rapid temperature increase. Later, the rate of temperature rise decreases, and the reactor temperature continues to rise until it reaches a steady state. Therefore, the rate of temperature change can be used to monitor faults.

[0128] To set different ambient temperatures, wind speeds, and operating currents, see [link / reference]. Figure 12 , Figure 13 and Figure 14 It can be seen that different factors affect the time when the temperature exceeds the insulation requirement after the fault, and have little effect on the rate of change of the temperature after the fault.

[0129] The temperature rise rate is relatively fast in the early stage of a fault and slows down in the later stage. Selecting the magnitude of the temperature rise rate can be used as a fault monitoring method. Setting an appropriate temperature rise threshold can determine whether there is an inter-turn short circuit fault in the winding. Figure 15 This describes the temperature rise at the fault point of each winding when a single turn is short-circuited in the upper part. The temperature rise of each winding is obtained by subtracting the temperature of the corresponding point of the winding under normal conditions from the temperature at the fault point.

[0130] from Figure 15It is known that the lowest temperature rise ΔT1 of the dry reactance 5 seconds after the fault occurred is 15.45℃. Setting the temperature rise threshold within 5 seconds to slightly less than 15.45℃, with a temperature rise rate of 3.09℃ / s, can effectively determine whether a single-turn short-circuit fault has occurred. For inter-turn short-circuit faults, which may occur between two measurements, the corresponding temperature rise between the two measurements will be less than the above-set threshold. Setting a threshold such that when this occurs, the temperature rise within the next 5 seconds must be greater than the threshold, can effectively determine an inter-turn short-circuit fault. Figure 15 Temperature rise data when a single-turn short circuit occurs in the second winding, and the temperature difference between two measurements at different fault times are shown below. Figure 16 As shown.

[0131] exist Figure 16 In the diagram, a fault occurs at point C at time 0. The temperature at the fault point measured 5 seconds ago is subtracted from the temperature at time 0, resulting in a value ΔT1 of 15.45℃. Therefore, the temperature rise at the fault point where an inter-turn short circuit occurs 0 seconds later from point A to point C will be less than ΔT1, causing this fault warning method to fail. Figure 16 The temperature rise data of a single-turn short circuit occurring in 3.4 seconds can be used as a fault early warning method to solve the failure problem of the above-mentioned fault early warning method.

[0132] Depend on Figure 16 The data shows that for single-turn short-circuit faults occurring at different times, the maximum temperature difference between two consecutive measurements of the second winding is as follows: Figure 17 As shown. Furthermore, considering the fiber optic temperature measurement error is approximately 2.4℃, the temperature difference threshold should be set to 5.79℃, i.e., 8.19-2.4℃. Therefore, when the temperature difference between two consecutive measurements exceeds 5.79℃, i.e., the temperature rise rate is 1.16℃ / s, it can be determined that an inter-turn short circuit has occurred at some point in the winding.

[0133] With a spatial resolution positioning accuracy of 0.05m and an overall temperature difference of very small, the average value of the hottest point (approximately 98.7% of the overall height of the simulation model) after a period of time was taken as the temperature measured by the fiber. The rate of change of temperature over time, ΔT / Δt, was used as the standard for judging the fault. The influence of different factors on the monitoring method based on the rate of change of temperature was investigated.

[0134] Taking the 9th winding of package 3, which theoretically has the highest probability of failure, and changing the ambient temperature, wind speed, operating current, and sampling interval, we studied its feasibility for the above method.

[0135] When a single-turn short circuit occurs in the upper part, temperature changes are recorded. Sampling intervals of 1 second and 10 seconds are used, and the change in the average temperature is used as the basis for fault monitoring. Temperature measurements are conducted under seven ambient temperature conditions (-20℃, -10℃, 0℃, 10℃, 20℃, 30℃, and 40℃). When the ambient temperature changes, the rate of temperature change after the fault initially increases from the steady-state temperature, reaching its maximum value after a period of time. Starting from t=0s, all curves show a steep acceleration to the peak value, with the maximum temperature change rate appearing at... Figure 18 Approximately t=2s and Figure 19 At t=10s, after the peak, the rate of temperature change decreases following an exponential decay pattern. Shorter sampling intervals result in higher peak values ​​for the rate of temperature change. This analysis indicates that ambient temperature has virtually no effect on the rate of temperature change after a fault.

[0136] Different initial wind velocities were set (0.3 m / s, 0.4 m / s, 0.5 m / s, 0.6 m / s, 0.8 m / s, 1.0 m / s, 3.0 m / s), and the temperature change rate for each segment was calculated with sampling intervals of 1 s and 10 s. The results are as follows: Figure 20 and Figure 21 As shown, in the initial stage of the fault, significant abrupt changes in the rate of temperature rise were observed under all wind speed conditions, which then gradually decreased and tended to a steady state. At a 1-second interval, the peak temperature rise rate was approximately 4.5℃ / s, mainly concentrated within the first 5 seconds after the fault. Different wind speeds had no significant impact on the peak temperature rise rate. In contrast, the temperature change rate response at a 10-second interval was more gradual, with the peak value decreasing to approximately 1.2℃ / s. The analysis indicates that wind speed has virtually no effect on the rate of temperature change after the fault.

[0137] Five different operating current levels (0.90, 0.95, 1.00, 1.05, and 1.10 times the rated current) were set, and the temperature change rate over time was obtained based on BOTDR fiber optic temperature measurement technology. Figure 22 and Figure 23 .from Figure 21 As can be seen, the higher the operating current, the greater the peak temperature rise rate, and the overall temperature decay curve shifts upward accordingly, exhibiting good monotonicity. The temperature change rate varies under different operating currents. The higher the rated operating current, the higher the peak temperature change rate after a fault occurs. At 1.10 times the rated current, the peak temperature change rate can reach approximately 5.5℃ / s, which is much higher than approximately 3.6℃ / s at 0.90 times the rated current, indicating a significant temperature rise rate in the initial stage of the fault (0s–5s).

[0138] To more intuitively analyze the relationship between sampling interval and temperature change rate, the temperature change rate for different sampling intervals is plotted as follows: Figure 24Using three different sampling intervals of 1s, 4s, and 10s, it can be seen that the longer the sampling interval, the smaller the peak temperature change rate, and the time to reach the peak also varies, but eventually all tend towards a stable value of 0.3℃ / s. For the early stage of a fault, different temperature change rates should be set according to different sampling intervals as the criteria for determining whether the reactor has failed. This is related to various factors such as the importance of the selected monitoring equipment and the circuitry. Generally, under normal outdoor installation conditions, when the ambient temperature changes, such as from 20℃ to 10℃, it usually takes several hours, or at least 30 minutes. In this embodiment, 1 hour is used. Therefore, the temperature change rate can be roughly considered as 10 / 3600 = 0.002778 (℃ / s), and the stable value of 0.3℃ / s is much larger than the temperature change rate of 0.002778℃ / s over a period of time under steady-state normal conditions.

[0139] In summary, ambient temperature, wind speed, and operating current have virtually no impact on the DTACSR inter-turn short circuit monitoring method that uses temperature change rate as the criterion. By setting different temperature change rate thresholds for different fault locations, and setting different temperature change rate thresholds for different sampling intervals (the smaller the sampling interval, the larger the threshold), faults can be detected in the early stages of inter-turn short circuits.

[0140] The DTACSR was modeled using finite element simulation software to obtain the temperature distribution under normal operation and inter-turn short-circuit fault conditions. Based on Brillouin scattering-based distributed fiber optic temperature sensing technology, the path temperature information within the reactor envelope was extracted. The temperature data of the DTACSR under normal operation and after inter-turn short circuit were compared to explore the influence of different factors on the temperature after the fault. A method for monitoring inter-turn short-circuit faults of the DTACSR based on the rate of temperature change was proposed. The feasibility of the method was demonstrated by verifying the influence of different factors on its effectiveness.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for monitoring inter-turn faults in dry-type reactors based on distributed optical fiber measurement of temperature change rate. This method models the dry-type air core series reactor (DTACSR) using finite element simulation software, obtains the temperature distribution during normal operation and inter-turn short-circuit faults, extracts the fiber path temperature information within the reactor enclosure using distributed optical fiber temperature sensing technology based on Brillouin scattering, compares the temperature data of the DTACSR during normal operation and after an inter-turn short circuit, proposes an early warning method for monitoring inter-turn short-circuit faults in DTACSRs based on the temperature change rate, and verifies the effectiveness of different factors. The method includes the following steps: Step 1: Establish magnetic field-circuit coupling models of DTACSR under normal operation and inter-turn short circuit fault, and obtain the coil current in DTACSR under the corresponding conditions to calculate the heat dissipation rate; Step 2: Establish a solid-fluid heat transfer-turbulent field coupling model for DTACSR under normal operation and inter-turn short-circuit fault. Input the coil heat dissipation rate, calculate the temperature of DTACSR under normal operation and inter-turn short-circuit fault, and study the effects of fault location, ambient temperature, wind speed and operating current on the temperature distribution of DTACSR inter-turn short-circuit fault. Step 3: Process the obtained temperature data to obtain the temperature change after the inter-turn short circuit fault occurs and the temperature change. Select appropriate values ​​as the criteria for the occurrence of inter-turn short circuit faults, and study the effectiveness of this method for monitoring DTACSR inter-turn faults under the influence of different ambient temperatures, wind speeds, operating currents and sampling intervals.

2. The method for monitoring inter-turn faults in dry reactors based on distributed optical fiber measurement of temperature variability as described in claim 1, characterized in that: Step 1 includes the following specific steps: Step 1-1: Based on the electrical and geometric structure of the reactor with model number CKGKL-240 / 10-12%DTACSR, simplify the reactor structure, ignore the influence of the reactor star frame on the DTACSR magnetic field distribution, and build a geometric model using finite element simulation software; Steps 1-2: Construct a magnetic field-circuit coupling model of the reactor during normal operation, analyze the magnetic field calculation principle of DTACSR during normal operation, and make reasonable simplifications based on the magnetic field calculation equations, taking into account the speed and accuracy of the calculation. Steps 1-3: Set material property parameters, and couple the magnetic field and circuit according to the equivalent circuit of DTACSR rated operation and inter-turn short circuit fault. Input the number of turns, conductivity and cross-sectional area of ​​each winding of DTACSR in the magnetic field. Steps 1-4: To balance computational efficiency and result accuracy, a physical field-controlled mesh is selected for mesh generation, with a standard cell size. The calculation results converge, and the coil current is obtained to calculate the resistance loss.

3. The method for monitoring inter-turn faults in dry reactors based on distributed optical fiber measurement of temperature variability as described in claim 1, characterized in that: Step 2 includes the following specific steps: Step 2-1: To improve computational efficiency, considering the symmetry of the three-dimensional reactor structure, a 1 / 12 symmetry model is established as the finite element calculation field. The heat dissipation rate of the 14 windings of the reactor during normal operation is input into the solid fluid heat transfer field. When a fault occurs, the heat dissipation rate of the short-circuit turns is additionally constructed and input. Its value is obtained by processing the calculation results of Step 2. An air domain is added outside the reactor, and the air domain outside the reactor is set as a turbulent field to represent flowing air. Step 2-2: Set the inlet velocity and outlet pressure in the turbulent field. The convective heat transfer coefficient is automatically calculated by the simulation software. The ambient temperature during normal operation is 293.15K. Set the lower side of the air domain as the inlet and the upper and side sides as the outlet. The initial air velocity is 0.3m / s to simulate the natural convection heat dissipation process of the reactor. Steps 2-3: The mesh generation method is selected using physics-controlled meshing, the cell size is standard, and the calculation results converge. Steps 2-4: Change the fault location, ambient temperature, wind speed, and operating current to obtain temperature information of DTACSR inter-turn short circuit faults under the influence of different factors.

4. The method for monitoring inter-turn faults in dry reactors based on distributed optical fiber measurement of temperature variability as described in claim 1, characterized in that: Step 3 includes the following specific steps: Step 3-1: The temperature difference is obtained by subtracting the temperature of the hot spot at the same location after the fault occurs from the temperature at the same point during normal operation. The temperature difference is divided by time to obtain the temperature change rate, and then the temperature change rate at different times after a single-turn short circuit is obtained. The temperature change rate threshold is determined by the operating condition data with the least severe temperature change of the short-circuit turn after a single-turn short circuit fault. Step 3-2: Based on the different temperature rise rates of inter-turn short circuit faults with different winding numbers and winding positions, considering the inconsistency between the fault occurrence time and the start measurement time, as well as the error of fiber optic temperature measurement, set an appropriate temperature change rate warning value, select a value slightly smaller than the slowest temperature rise, and determine whether there is an inter-turn short circuit fault in the winding. Step 3-3: Investigate the effects of different ambient temperatures, wind speeds, operating currents, and sampling intervals on the effectiveness of using temperature change rate as a measure of fiber optic monitoring for interference faults.

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