An online detection method for eddy current distribution based on switch cabinet temperature inversion

Abstract

The present application relates to an online detection method for eddy current distribution based on switch cabinet temperature inversion, comprising the following steps: for components with eddy current loss in the switch cabinet, simplified modeling is performed according to the actual size of the switch cabinet, and the distribution of eddy currents in the switch cabinet is calculated; a temperature rise calculation model of the switch cabinet is established based on eddy current loss, and the relationship between the temperature rise caused by eddy currents and eddy currents of the components with eddy current loss is obtained; the real-time temperature of the components with eddy current loss in the switch cabinet is collected, and the corresponding eddy current size is obtained by inversion according to the relationship between the temperature rise caused by eddy currents and eddy currents of the components with eddy current loss. Under the condition of ensuring the normal operation of the switch cabinet, the present application obtains the real-time monitoring of the eddy current distribution in the switch cabinet by processing and analyzing the overall temperature signal, which is conducive to timely discovering internal hot spots, taking corresponding cooling and protection measures, and thus ensuring the safe and stable operation of power equipment.

Description

Technical Field

[0001] The present application relates to the technical field of eddy current detection, and in particular to an online detection method for eddy current distribution based on switch cabinet temperature inversion. Background Art

[0002] Switchgear is an important equipment for power distribution in substations. In the busbar room of the switchgear, when current flows through the current-carrying busbar, an alternating magnetic field is generated, which generates an induced electromotive force in the panel and partition of the cabinet, and then generates a large number of stray eddy currents. The switchgear housing, metal fixing plate, partition, etc. are all made of non-current-carrying ferromagnetic materials with high magnetic permeability and large resistance. When the high-current switchgear is running, the eddy current phenomenon is very serious, and the temperature rise and vibration generated in the switchgear are serious. The consequences range from causing the user load to fail to reach the operating rated value to causing aging of the insulation components in the switchgear, reduced insulation performance, reduced life, and even burning of components, causing major safety accidents. Therefore, in order to ensure the safe operation of the equipment, increase the detection function of eddy current and material surface status in the intelligent operation and maintenance of the product, and enhance the competitiveness of the product, it is of great significance to carry out eddy current research and analysis of the switchgear and propose eddy current process monitoring, diagnosis, maintenance and management system solutions. Summary of the invention

[0003] In order to achieve real-time detection and monitoring of eddy currents in a switch cabinet, the present application provides an online detection method for eddy current distribution based on switch cabinet temperature inversion.

[0004] The present application provides an online detection method for eddy current distribution based on switch cabinet temperature inversion, which adopts the following technical solution:

[0005] An online detection method for eddy current distribution based on switch cabinet temperature inversion includes the following steps:

[0006] For components with eddy current loss in the switch cabinet, simplified modeling is performed according to the actual size of the switch cabinet to calculate the distribution of eddy current in the switch cabinet;

[0007] A temperature rise calculation model of the switch cabinet is established based on eddy current loss, and the relationship between the temperature rise of the component with eddy current loss caused by eddy current and the eddy current is obtained;

[0008] The real-time temperature of the components with eddy current loss in the switch cabinet is collected, and the corresponding eddy current size is obtained by inversion based on the relationship between the temperature rise caused by the eddy current of the components with eddy current loss and the eddy current.

[0009] By adopting the above technical solution, the relationship between the temperature rise caused by eddy current and the eddy current of the component with eddy current loss is obtained, that is, the eddy current distribution is obtained by temperature inversion calculation, so that under the condition of ensuring the normal operation of the switch cabinet, the eddy current distribution in the switch cabinet is obtained by processing and analyzing the overall temperature signal in real time, which provides guarantee for the safe and stable operation of the switch cabinet and equipment, is conducive to timely discovering the internal hot spots, taking corresponding cooling and protection measures, and then ensuring the safe and stable operation of the power equipment, and has good engineering practical value. However, the traditional eddy current detection is greatly affected by the magnetic field and cannot measure the switch cabinet.

[0010] Preferably, a simplified model of the switch cabinet is established by the following method:

[0011] Determine the eddy current field solution area, including the eddy current area and the non-eddy current area;

[0012] Solve the inner interface between the eddy current zone and the non-eddy current zone and the outer boundary of the eddy current field solution area; wherein the inner interface between the eddy current zone and the non-eddy current zone and the outer boundary of the eddy current field solution area meet the following boundary conditions:

[0013]

[0014]

[0015]

[0016] In the formula, is the inner interface between the eddy zone and the non-eddy zone. 12 The unit external normal vector of , the direction is from solving the non-eddy region Ω1 to solving the eddy region Ω2; is the unit external normal vector of the outer boundary of the eddy current field solution area Ω, and its direction is outward along the solution area Ω. B is the magnetic flux density, H is the magnetic field intensity, B1 is the magnetic flux density in the non-eddy current area, B2 is the magnetic flux density in the eddy current area, H1 is the magnetic field intensity in the non-eddy current area, and H2 is the magnetic field intensity in the eddy current area.

[0017] Preferably, the temperature rise calculation model of the switch cabinet is established based on the eddy current loss to obtain the relationship between the temperature rise of the component with eddy current loss caused by the eddy current and the eddy current, specifically including:

[0018] Divide the switch cabinet into different partitions, each partition is equivalent to a point;

[0019] The temperature distribution of the components with eddy current loss in the switch cabinet under different working conditions is analyzed to obtain the temperature of each point; the temperature rise effects of thermal radiation, heat conduction and thermal convection of other conductors are subtracted from the temperature of each point to obtain the relationship between the temperature rise caused by eddy current and the eddy current of the components with eddy current loss.

[0020] By adopting the above technical solution, especially dividing the switch cabinet into different partitions, each partition is equivalent to a point; analyzing the temperature distribution of the parts with eddy current loss in the switch cabinet under different working conditions, and obtaining the temperature of each point, each partition can be equivalent to a uniform distribution of eddy current, which can enable faster calculation.

[0021] Preferably, the components with eddy current loss include a cabinet and / or a structural member, and the relationship between the temperature rise of the cabinet or the structural member caused by the eddy current and the eddy current is:

[0022] I w = kT;

[0023] In the formula, I w is the size of the eddy current on the switch cabinet body or structural parts, in A; T is the temperature of the switch cabinet body or structural parts, in °C; k is the fitting coefficient corresponding to the eddy current at different temperatures of the switch cabinet body or structural parts, and the size of k (not a constant) varies with temperature.

[0024] By adopting the above formula, the corresponding eddy current distribution can be quickly and accurately obtained according to the real-time monitored temperature.

[0025] In the aforementioned method, the method further comprises:

[0026] During simulation, the temperature rise of the cabinet or structural parts caused by eddy current and the corresponding detected eddy current size are recorded under certain voltage and current;

[0027] Fitting the temperature rise data and the eddy current data to obtain a corresponding fitting coefficient k value;

[0028] Record the fitting coefficient k value and the corresponding voltage, current and temperature rise data;

[0029] Change the voltage and current, repeat the above process to simulate, and record the corresponding fitting coefficient k value and the corresponding voltage and current values ​​and temperature rise data;

[0030] During online real-time detection, the corresponding voltage and current values ​​are determined by the detected temperature rise of the cabinet or structural parts, and then the corresponding fitting coefficient k is determined to obtain the corresponding eddy current size.

[0031] By adopting the above technical solution, especially adopting the interpolation method to obtain the corresponding fitting coefficient, the eddy current situation at that time can be obtained in real time and accurately.

[0032] Preferably, the average temperature of each partition is used as the approximate temperature of the corresponding point, so as to improve the accuracy of the eddy current finally calculated.

[0033] In summary, the present application includes at least one of the following beneficial technical effects:

[0034] 1. The present application obtains the relationship between the temperature rise caused by eddy currents and the eddy currents of the components with eddy current losses, that is, the eddy current distribution is obtained by temperature inversion calculation, so that under the condition of ensuring the normal operation of the switch cabinet, the eddy current distribution in the switch cabinet is obtained by real-time monitoring through processing and analysis of the overall temperature signal, which provides guarantee for the safe and stable operation of the switch cabinet and equipment, is conducive to timely detection of internal hot spots, and taking corresponding cooling and protection measures, thereby ensuring the safe and stable operation of power equipment, and has good engineering practical value.

[0035] 2. This application obtains the corresponding fitting coefficients by using interpolation, so that the eddy current conditions at that time can be obtained in real time and accurately.

[0036] 3. The detection method of the present application can use a non-contact temperature measurement system of a thermal imager to measure temperature, which will not affect the insulation layout and measurement accuracy inside the switch cabinet. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a method flow chart of an embodiment of the present application.

[0038] Figure 2 It is a schematic diagram of eddy current field solution.

[0039] Figure 3 It is a cross-section view of the switch cabinet. DETAILED DESCRIPTION

[0040] The following is combined with Figure 1-Figure 3 This application is described in further detail.

[0041] The present application embodiment discloses an online detection method for eddy current distribution based on switch cabinet temperature inversion. Figure 1 , an online detection method for eddy current distribution based on switch cabinet temperature inversion, comprising the following steps:

[0042] S1, for the components with eddy current loss in the switch cabinet, simplified modeling is performed according to the actual size of the switch cabinet to calculate the distribution of eddy current in the switch cabinet;

[0043] Specifically, using voltage and current as excitation, the electromagnetic distribution is solved by Maxwell's equations, and then the eddy current is calculated.

[0044] Among them, the simplified model of the switch cabinet can be established by the following methods:

[0045] S11, such as Figure 2As shown, the eddy current field solution area Ω is determined, including the non-eddy current area Ω1 and the eddy current area Ω2; the eddy current area mainly considers the effects of the cabinet, busbar, circuit breaker, and supporting structure; the non-eddy current area mainly considers the effect of the insulating sleeve; only the conductor part can generate eddy current. For the non-eddy current area, i.e., the busbar and circuit breaker, the source current density on the conductor is J s ; For the eddy current area, that is, the cabinet, it is a conductor but has no current source; Г 12 It is the interface between the eddy current area and the non-eddy current area;

[0046] Assume that the outer boundary of the solution region Ω can be divided into Г H and G B Two parts, border Г H The normal component of the given magnetic induction intensity on the boundary Г B The above gives the tangential component of the magnetic induction intensity, that is:

[0047]

[0048]

[0049] In formulas (1) and (2), σ is the conductivity of the field medium; is the operator; is the magnetic field strength; is the electric field strength; In specific implementation, the above parameters can be obtained through the corresponding relationship between voltage and current excitation and electromagnetic field.

[0050] S12, solving the inner interface between the eddy current area and the non-eddy current area and the outer boundary of the eddy current field solution area; wherein the inner interface between the eddy current area and the non-eddy current area and the outer boundary of the eddy current field solution area satisfy the following boundary conditions:

[0051]

[0052]

[0053]

[0054] In the formula, is the inner interface between the eddy zone and the non-eddy zone. 12 The unit external normal vector of , the direction is from solving the non-eddy region Ω1 to solving the eddy region Ω2; is the unit external normal vector of the outer boundary of the eddy current field solution area Ω, and its direction is outward along the solution area Ω. B is the magnetic flux density, H is the magnetic field intensity, B1 is the magnetic flux density in the non-eddy current area, B2 is the magnetic flux density in the eddy current area, H1 is the magnetic field intensity in the non-eddy current area, and H2 is the magnetic field intensity in the eddy current area.

[0055] S2, establishing a temperature rise calculation model of the switch cabinet based on eddy current loss, and obtaining the relationship between the temperature rise of the component with eddy current loss caused by eddy current and the eddy current; specifically including:

[0056] S21, divide the switch cabinet into different partitions, each partition is equivalent to a point;

[0057] The switch cabinet is partitioned according to the size of the eddy current. The significance of partitioning is that for places with large eddy currents, the measurement points can be denser, and for places with small and uniform eddy currents, the measurement points can be sparser, so that the final fitting coefficient is more accurate.

[0058] When zoning is performed, the cabinet, busbar, circuit breaker itself and surrounding partitions are denser.

[0059] S22, analyzing the temperature distribution of the locations of the components with eddy current loss in the switch cabinet under different working conditions (including normal working conditions and overload), and obtaining the temperature of each point; specifically, the average temperature of each partition can be used as the approximate temperature of the corresponding point;

[0060] S23, subtracting the temperature rise effects of heat radiation, heat conduction and heat convection of other conductors from the temperature of each point to obtain the relationship between the temperature rise of the component with eddy current loss caused by eddy current and the eddy current;

[0061] The temperature rise calculation model of the switch cabinet is established based on eddy current loss, that is, the eddy current loss is integrated with time to obtain energy, and then the temperature rise curve can be calculated according to the material parameters.

[0062] During specific implementation, the focus can be on calculating the relationship between the temperature rise caused by eddy currents and the eddy currents in the cabinet and conductor support components (i.e., structural parts) close to the busbar and the current-conducting conductor; because the busbar and circuit breaker can withstand high temperatures, while the cabinet and conductor support components are relatively thin, the temperature rise and vibration caused by eddy currents during the operation of high-current switch cabinets will affect the life of the cabinet, causing the life of the cabinet to decrease.

[0063] Specifically, the heat sources of the switch cabinet mainly include Joule heat and induction heat. Joule heat is determined by the current flowing through the conductor and the resistance and contact resistance of the current-carrying conductor, that is:

[0064] P=I 2 R (6)

[0065] When an alternating current passes through a current-carrying conductor, due to the generation of alternating magnetic flux, eddy currents will be induced in the conductor according to Lenz's law, resulting in a loss W. c (W), that is:

[0066]

[0067] Where f is the current frequency, Hz; Bm is the magnetic induction intensity, T; R is the eddy current resistance, Ω.

[0068] Heat transfer (i.e., induction heat) is the transfer of energy based on the temperature difference between objects. The basic modes of heat transfer are generally divided into three types: heat conduction, heat convection, and heat radiation. The heat conduction equation can be calculated by assigning thermal conductivity to the material. For heat convection and heat radiation, the convection heat transfer coefficient and radiation emissivity can be assigned to the surface to equate the convection and radiation processes. The temperature field distribution can be calculated by the thermal conductivity of the material, the surface convection heat transfer coefficient, and the radiation emissivity. However, since there is no convection heat transfer in the vacuum interrupter, 10-12W / (m 2 ·K) of the convection heat transfer coefficient.

[0069] Specifically, the three-dimensional heat conduction equation of the medium-voltage switchgear in steady state is shown in equation (8):

[0070]

[0071] In formula (8), T is temperature, K; λ is thermal conductivity, W / (m·K); q is energy generated per unit volume, W·m -3 ; x, y, z are rectangular coordinates. In the above parameters, T is the quantity to be determined, and the others are known quantities.

[0072] The power dissipated by convection per unit volume of fluid medium is:

[0073]

[0074] In formula (9), c, γ, and υ represent the specific heat capacity, density, and velocity of the fluid, respectively. The above parameters are the inherent properties of the material.

[0075] For a flat conductor placed in the air, the convection heat transfer coefficient can be calculated by the empirical formula (10):

[0076] K dl =2.55(θ-θ0) 0.25 (10)

[0077] Among them, θ and θ0 represent the temperature at different positions; in the calculation process, according to experience, the heat transfer coefficient K dl =6.

[0078] Thermal radiation is the energy transmitted by electromagnetic waves. The thermal radiation power of an object is proportional to the difference between the fourth power of the temperature of the heating body and the fourth power of the temperature of the absorbing body, which can be expressed by formula (11):

[0079]

[0080] In formula (11): bis the Boltzmann constant, W(m 2 ·K -4 );T2 is the surface temperature of the heating element, K;T1 is the temperature of the object receiving radiation, K;ε f is the emissivity. The above parameters are the intrinsic parameters of the material.

[0081] In this embodiment, the components with eddy current loss include cabinets and / or structural parts. In order to eliminate the influence of busbar conductors and circuit breakers on the thermal radiation, thermal conduction and thermal convection of the cabinet and supporting conductor structural parts, the temperature rise when the eddy current of the cabinet and supporting conductor structural parts is not considered is calculated separately, and then the influence of the busbar on the thermal radiation, thermal conduction and thermal convection of the cabinet and supporting conductor structural parts can be obtained. Finally, the influence of busbar heating on the eddy current measurement of the cabinet or structural parts can be subtracted to obtain the relationship between the temperature rise of the cabinet or structural parts caused by eddy current and the eddy current.

[0082] The relationship between the temperature rise of the cabinet or structural parts caused by eddy current and the eddy current is:

[0083] I w = kT; (12)

[0084] In the formula, I w is the size of the eddy current on the switch cabinet body or structural parts, in A; T is the temperature of the switch cabinet body or structural parts (i.e., the temperature rise caused by the eddy current), in °C; k is the fitting coefficient corresponding to the eddy current at different temperatures of the switch cabinet body or structural parts, k is not a constant, and the size of k changes with temperature;

[0085] In specific implementation, the temperature rise of the cabinet or structural parts caused by eddy current and the corresponding detected eddy current size are recorded under certain voltage and current during simulation;

[0086] Fitting the temperature rise data and the eddy current data to obtain a corresponding fitting coefficient k value;

[0087] Record the fitting coefficient k value and the corresponding voltage, current and temperature rise data;

[0088] Change the voltage and current, repeat the above process to simulate, and record the corresponding fitting coefficient k value and the corresponding voltage and current values ​​and temperature rise data.

[0089] S3, collecting the real-time temperature of the components with eddy current loss in the switch cabinet, and inverting to obtain the corresponding eddy current size according to the relationship between the temperature rise of the components with eddy current loss caused by eddy current and the eddy current.

[0090] That is, during online real-time detection, the corresponding voltage and current values ​​are determined by the detected temperature rise of the cabinet or structural parts, and then the corresponding fitting coefficient k is determined, and the corresponding eddy current size is obtained by formula (12).

[0091] Among them, when collecting the real-time temperature of the components with eddy current loss in the switch cabinet, such as Figure 3 As shown in the cross-sectional view of the switch cabinet, multiple passive wireless temperature sensors can be installed on the support beams of the busbars of each phase in the switch cabinet and on the cabinet body close to the busbars. The passive sensors contain small-capacity batteries inside and can draw power from the magnetic field in the switch cabinet. The temperature sensors all comply with the IEC61850 wireless transmission protocol. Three passive wireless sleeve temperature sensors are added to the supporting steel members at the four busbar intervals of the three-phase incoming and outgoing lines and the neutral line (there are three intervals for the four busbars). Since there are low-voltage and high-voltage busbars, a total of six temperature sensors can be added between the busbars (i.e. three sensors for the incoming and outgoing lines). Five temperature sensors are evenly arranged on the three sides of the cabinet close to and passing through the busbar (one sensor for each of the three cabinets, and one sensor for each of the places closest to the incoming and outgoing lines). A passive wireless temperature sensor is placed at each contact of the circuit breaker, which can record the temperature distribution of the main eddy current area in the switch cabinet in real time. The point measured by the temperature sensor represents the average temperature of the measured area. The eddy current value of the point is directly output through the correspondence between the average temperature and the eddy current, and displayed on the computer or terminal interface.

[0092] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, all equivalent changes made according to the methods and principles of the present application should be included in the protection scope of the present application.

Claims

1. An online detection method for eddy current distribution based on switch cabinet temperature inversion, characterized in that: The following steps are involved: For components with eddy current loss in the switch cabinet, simplified modeling is performed according to the actual size of the switch cabinet to calculate the distribution of eddy current in the switch cabinet; A temperature rise calculation model of the switch cabinet is established based on eddy current loss, and the relationship between the temperature rise of the component with eddy current loss caused by eddy current and the eddy current is obtained; The real-time temperature of the components with eddy current loss in the switch cabinet is collected, and the corresponding eddy current size is obtained by inversion based on the relationship between the temperature rise caused by the eddy current of the components with eddy current loss and the eddy current.

2. The online detection method based on switch cabinet temperature inversion eddy current distribution according to claim 1 is characterized in that: A simplified model of the switchgear is established by: Determine the eddy current field solution area, including the eddy current area and the non-eddy current area; Solve the inner interface between the eddy current zone and the non-eddy current zone and the outer boundary of the eddy current field solution area; wherein the inner interface between the eddy current zone and the non-eddy current zone and the outer boundary of the eddy current field solution area meet the following boundary conditions: In the formula, is the inner interface between the eddy zone and the non-eddy zone. 12 The unit external normal vector of , the direction is from solving the non-eddy region Ω1 to solving the eddy region Ω2; is the unit external normal vector of the outer boundary of the eddy current field solution area Ω, and its direction is outward along the solution area Ω, B is the magnetic flux density, H is the magnetic field intensity, B1 is the magnetic flux density in the non-eddy current area, B2 is the magnetic flux density in the eddy current area, H1 is the magnetic field intensity in the non-eddy current area, and H2 is the magnetic field intensity in the eddy current area; Γ B and Γ H Represents the outer boundary of the eddy current field solution area. The outer boundary of the eddy current field solution area is divided into Г H and G B Two parts, border Г H The normal component of the given magnetic induction intensity on the boundary Г B The tangential component of the given magnetic induction intensity.

3. The online detection method of eddy current distribution based on switch cabinet temperature inversion according to claim 1 is characterized in that: The temperature rise calculation model of the switch cabinet is established based on eddy current loss, and the relationship between the temperature rise of the component with eddy current loss caused by eddy current and the eddy current is obtained, which specifically includes: Divide the switch cabinet into different partitions, each partition is equivalent to a point; Analyze the temperature distribution of the components with eddy current loss in the switch cabinet under different working conditions and obtain the temperature of each point; By subtracting the temperature rise effects of heat radiation, heat conduction and heat convection of other conductors from the temperature of each point, the relationship between the temperature rise caused by the eddy current and the eddy current of the component with eddy current loss is obtained.

4. The online detection method based on switch cabinet temperature inversion eddy current distribution according to any one of claims 1 to 3, characterized in that: The components with eddy current loss include cabinets and / or structural parts. The relationship between the temperature rise of the cabinet or structural parts caused by eddy current and the eddy current is: I w =kT; In the formula, I w is the size of the eddy current on the switch cabinet body or structural parts, in A; T is the temperature of the switch cabinet body or structural parts, in °C; k is the fitting coefficient corresponding to the eddy current at different temperatures of the switch cabinet body or structural parts, and the size of k changes with temperature.

5. The online detection method based on switch cabinet box temperature inversion eddy current distribution according to claim 4 is characterized in that: The method further comprises: During simulation, the temperature rise of the cabinet or structural parts caused by eddy current and the corresponding detected eddy current size are recorded under certain voltage and current; Fitting the temperature rise data and the eddy current data to obtain a corresponding fitting coefficient k value; Record the fitting coefficient k value and the corresponding voltage, current and temperature rise data; Change the voltage and current, repeat the above process to simulate, and record the corresponding fitting coefficient k value and the corresponding voltage and current values ​​and temperature rise data; During online real-time detection, the corresponding voltage and current values ​​are determined by the detected temperature rise of the cabinet or structural parts, and then the corresponding fitting coefficient k is determined to obtain the corresponding eddy current size.

6. The online detection method of eddy current distribution based on switch cabinet box temperature inversion according to claim 3 is characterized in that: The average temperature of each partition is taken as the approximate temperature of the corresponding point.

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