Power distribution cabinet structure stiffness health monitoring system based on stress detection

Abstract

This invention relates to the field of power distribution cabinet monitoring technology, specifically to a power distribution cabinet structural stiffness health monitoring system based on stress detection. It includes a stress sensing unit to acquire raw stress data under mechanical and temperature loads; a load separation unit to sequentially separate thermal stress components and dynamic stress components using a thermoelastic mechanics model and an electrodynamic load model; a stiffness inversion unit to perform static inversion and dynamic identification using a beam-plate hybrid structural mechanics model to obtain the equivalent section moment of inertia and dynamic equivalent stiffness; and a health assessment unit to determine the risk of local instability by comparing with benchmark design values ​​and combining a dual-threshold method, outputting an overall structural stiffness health index. This system eliminates interference from temperature fields and electrodynamic forces by using a thermoelastic mechanics model and an electrodynamic load model, solving the problem that traditional monitoring systems struggle to accurately capture effective information on structural stiffness degradation.

Description

Technical Field

[0001] This invention relates to the field of power distribution cabinet monitoring technology, and more specifically, to a power distribution cabinet structural stiffness health monitoring system based on stress detection. Background Technology

[0002] The distribution cabinet structural stiffness health monitoring system is a power equipment protection system that integrates stress detection technology and structural health assessment logic. It is mainly used during the operation of distribution cabinets to monitor stiffness degradation in real time by detecting changes in structural stress, thus ensuring stable operation of the power equipment. However, existing distribution cabinet monitoring systems that rely on conventional stress detection equipment have two main problems: first, load interference, which fails to effectively separate the macroscopic strain response caused by dynamically changing electrodynamic loads from the subtle strain changes caused by structural stiffness degradation; second, the influence of the thermal environment, where uneven temperature distribution and cyclical changes generate thermal stress that interfere with the true stress signal caused by mechanical damage, making it difficult to accurately capture effective information on structural stiffness degradation. Summary of the Invention

[0003] To address the problems mentioned in the background art, this application provides a stress detection-based electrical distribution cabinet structural stiffness health monitoring system, which includes: a stress sensing unit, a load separation unit, a stiffness inversion unit, and a health assessment unit.

[0004] The system comprises the following components: a stress sensing unit, a load separation unit, and a health assessment unit. The stress sensing unit acquires raw stress data of the main load-bearing frame, thin plate structure, and key connection nodes of the distribution cabinet under mechanical and temperature loads. The load separation unit collects temperature field distribution parameters and bus current parameters of the cabinet and separates the thermal stress components and dynamic stress components in the raw stress data using a load decoupling model to obtain pure mechanical stress components. The load decoupling model is constructed from a thermoelastic mechanics model and an electrodynamic load model. The stiffness inversion unit performs static inversion and dynamic identification based on the pure mechanical stress components using a beam-plate hybrid structural mechanics model to obtain the equivalent section moment of inertia and dynamic equivalent stiffness. The health assessment unit compares the equivalent section moment of inertia and dynamic equivalent stiffness with the benchmark design values, calculates the stiffness loss factor, and uses a dual threshold method of strain gradient and stress amplitude to judge the risk of local instability, ultimately outputting the overall structural stiffness health index.

[0005] Furthermore, the original stress data includes: multiaxial strain data reflecting the stress distribution state of the main load-bearing frame, which includes axial strain along the main load-bearing direction, transverse strain perpendicular to the main load-bearing direction, and strain components in the shear strain sensitive direction; in-plane stress data reflecting the surface deformation and stress distribution state of the thin plate structure, which includes transverse and longitudinal strain components, in-plane shear strain components, and equivalent strain and equivalent stress; and stress concentration data reflecting the stress distribution state at key connection nodes.

[0006] Furthermore, the load separation unit includes a thermo-mechanical decoupling module, which is used to perform the following operations: acquire the temperature field distribution parameters of the cabinet and construct a three-dimensional temperature field; calculate the thermally induced strain components using the finite element interpolation method; based on the thermally induced strain components, introduce the material's linear expansion coefficient, elastic modulus, and material Poisson's ratio, and construct a thermoelastic mechanical model using the generalized Hooke's law to calculate the thermally induced stress components; and subtract the thermally induced stress components point by point from the original stress data in the time domain to obtain the preliminary mechanical stress.

[0007] Furthermore, the load separation unit also includes an electric decoupling module, which performs the following operations: acquiring bus current parameters, discretizing the bus into current elements, calculating the magnetic induction intensity generated by the current elements based on the Biot-Savart law, and constructing an electrodynamic load model in conjunction with the Ampere force formula to calculate the electrodynamic force on the bus; treating the electrodynamic force as an external load, obtaining the displacement vector by solving the structural dynamic equations containing the mass matrix, damping matrix, and reference stiffness matrix, and then calculating the dynamic stress components caused by the electrodynamic force through the linear elastic constitutive equations; and subtracting the preliminary mechanical stress from the dynamic stress components point by point in the time domain to obtain the pure mechanical stress components characterizing the quasi-static bearing state of the structure.

[0008] Furthermore, the stiffness inversion unit includes a static stiffness inversion module, which is used to construct a beam-plate hybrid structural mechanical model. The main load-bearing frame of the distribution cabinet is used as the beam element and the thin plate structure is used as the plate element. Deformation coordination conditions are set so that the displacement and rotation of adjacent elements at the connection nodes remain consistent. The pure mechanical stress components are input as static loads into the beam-plate hybrid structural mechanical model to establish and solve the static equilibrium equations and obtain the overall nodal displacement vector.

[0009] Furthermore, the static stiffness inversion module employs the mechanics-geometric ratio method for stiffness inversion, specifically including: based on the global nodal displacement vector and combined with the displacement shape function, solving for the geometric curvature of the beam element at position x using a numerical differentiation method. Based on the purely mechanical stress components, the actual bending moment of the beam element at position x is calculated using the section integral method. According to the formula Calculate the equivalent cross-sectional moment of inertia at position x. ,in It is the elastic modulus.

[0010] Furthermore, the stiffness inversion unit includes a dynamic stiffness identification module, which performs the following operations: within the time window of detecting a transient event, extracts the attenuated dynamic stress response from the pure mechanical stress components and performs bandpass filtering on it; uses a frequency response function fitting method to perform exponential envelope fitting on the filtered attenuated dynamic stress response and iteratively solves the natural frequency of the structure; determines the reference value of the natural frequency of the structure in a healthy state through a beam-plate hybrid structural mechanical model, and calculates the dynamic equivalent stiffness based on the proportional relationship between the square of the natural frequency and the eigenvalue of the stiffness matrix.

[0011] Furthermore, the method by which the health assessment unit calculates the stiffness loss factor includes: comparing the equivalent section moment of inertia with the design section moment of inertia to calculate the local static stiffness loss factor; comparing the dynamic equivalent stiffness with the design equivalent stiffness to calculate the dynamic stiffness loss factor; and weighting and fusing the average value of the local static stiffness loss factor at all measurement locations with the dynamic stiffness loss factor according to preset static stiffness weighting coefficients and dynamic stiffness weighting coefficients, respectively, to obtain the stiffness health level. .

[0012] Furthermore, the health assessment unit is also used to determine the risk of local instability, specifically including: acquiring in-plane strain data of the thin plate structure surface and calculating the composite strain nonuniformity index. The composite strain nonuniformity index is formed by superimposing the strain space gradient term and the overall deformation degree term of the region; the stress amplitude of the same thin plate region is calculated from the pure mechanical stress components. When the composite strain nonuniformity index exceeds the nonuniformity threshold and the stress amplitude exceeds the stress amplitude threshold, it is determined that there is a risk of local instability in the region.

[0013] Furthermore, the health assessment unit generates the overall structural stiffness health index in the following manner. If it is determined that there is no risk of local instability, then Equal to the stiffness health degree If it is determined that there is a risk of local instability, then For the stiffness health degree Subtract the preset penalty value; if If the value is below the set threshold, the overall structural stiffness health index will be output.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In this system, by separately separating the thermal stress component and the dynamic stress component from the original stress data, compared with the shortcomings of traditional monitoring systems that cannot distinguish between load interference and thermal environment influence, the interference of temperature field changes and periodic electrodynamic forces is fully eliminated, solving the problem that traditional systems are unable to accurately capture effective information on the structural stiffness degradation.

[0015] 2. In this system, static inversion and dynamic identification are achieved through a beam-slab hybrid structural mechanical model. Health assessment is performed by combining the strain gradient and stress amplitude dual threshold method. Compared with traditional monitoring methods that rely on only a single parameter or manual inspection, this system does not require interruption of equipment operation and can comprehensively acquire equivalent cross-sectional moment of inertia and dynamic equivalent stiffness data. This enables real-time quantitative assessment of the overall stiffness health of the structure and graded early warning of local instability risks, improving the comprehensiveness of monitoring and the accuracy of early warning. Attached Figure Description

[0016] Figure 1 This is an overall flowchart of the present invention; The meanings of the labels in the diagram are as follows: 1. Stress sensing unit; 2. Load separation unit; 21. Thermodynamic decoupling module; 22. Electrical decoupling module; 3. Stiffness inversion unit; 31. Static stiffness inversion module; 32. Dynamic stiffness identification module; 4. Health assessment unit. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example: Please refer to Figure 1 As shown, a preferred embodiment of the present invention provides a stress detection-based structural stiffness health monitoring system for power distribution cabinets, including a stress sensing unit 1. The stress sensing unit 1 synchronously acquires the original stress data of the main load-bearing frame, thin plate structure and key connection nodes of the power distribution cabinet under mechanical load and temperature load. In this embodiment, the original stress data includes multiaxial strain data, in-plane stress data, and stress concentration data; Multiaxial strain data reflects the stress distribution at the main load-bearing frame; the multiaxial strain data includes strain components in at least three directions, and the strain components in the three directions include: Axial strain along the main load-bearing direction (i.e., axial normal strain, which is the linear deformation rate along the length of the member, used to characterize the degree of tension or compression of columns or beams under gravity and vertical loads). Transverse strain perpendicular to the direction of the main load (i.e., transverse normal strain, which is the transverse linear deformation rate along the width or cross-section of the member, used to characterize the transverse deformation of the member due to the Poisson effect or the bending deformation caused by lateral force). The shear strain sensitive direction at a 45° angle to the above two directions (obtained by collecting oblique strain data at a 45° angle to the main load-bearing direction, used to characterize the degree of angular distortion and torsional state in the plane of the main load-bearing frame, i.e., shear strain components). In-plane strain and stress data are acquired through plane strain sensors, covering the main load-bearing areas of the thin plate structure. This data reflects the deformation and stress distribution on the surface of the thin plate structure, specifically including: transverse and longitudinal strain components (and their corresponding normal stress components): used to characterize the tensile and compressive states of the thin plate in the horizontal and vertical directions, respectively; in-plane shear strain components (and their corresponding shear stress components): characterizing the shear force on the thin plate, used to monitor the risk of skin wrinkling caused by overall cabinet torsion; equivalent strain and equivalent stress: comprehensive values ​​calculated based on the above components using the Von Mises formula, serving as the basic input for subsequent calculations of the composite strain nonuniformity index and stress amplitude. Stress concentration data is acquired using high-sensitivity micro-strain gauges, reflecting the stress distribution at key connection nodes; these key connection nodes include frame connection points, door frame hinge areas, and busbar support points. The stress concentration data includes: Local peak stress: The maximum stress point measured at a point of geometric change (such as the edge of a bolt hole or the toe of a weld); Local plastic strain: If the stress concentration point cannot return to zero after an overload (such as a short-circuit electrodynamic impact), the resulting residual stress / strain is crucial for assessing whether irreversible damage has occurred at the connection joint. Contact compressive stress: (specifically refers to the compressive stress in the normal direction of the contact surface at the busbar support point and hinge) is used to monitor whether the support insulator is at risk of crushing due to excessive force.

[0019] The stress detection-based distribution cabinet structural stiffness health monitoring system also includes a load separation unit 2. The load separation unit 2 collects the cabinet temperature field distribution parameters and bus current parameters, and separates the thermal stress components and dynamic stress components in the original stress data through a load decoupling model to obtain the pure mechanical stress components. The load decoupling model is constructed from a thermoelastic mechanical model and an electrodynamic load model. In this embodiment, the cabinet temperature field distribution parameters are collected in real time by multiple digital temperature sensors (such as DS18B20 and PT100) distributed in key structural locations of the distribution cabinet (such as the inner wall of the main frame, the partition of the busbar compartment, and near the ventilation openings), which are used to construct a three-dimensional temperature field that reflects the temperature differences and changes in the cabinet space. The bus current parameters are acquired in real time by current transformers (CTs) or Rogowski coils installed on the main incoming or outgoing busbars of the distribution cabinet. The sampling frequency must meet the system analysis requirements in order to accurately capture the power frequency current and its harmonic components. In this embodiment, the load separation unit 2 includes a thermal decoupling module 21 and an electrical decoupling module 22; Among them, the thermal decoupling module 21, based on the temperature field distribution parameters of the cabinet, calculates and removes the thermal stress component from the original stress data by using a thermoelastic mechanical model constructed with the generalized Hooke's law to obtain the preliminary mechanical stress. Specifically, the temperature field distribution parameters of the cabinet are obtained, and a three-dimensional temperature field is constructed. ;in, Indicates the spatial coordinates inside the power distribution cabinet structure. Represents a time variable; Among them, the temperature field distribution parameters are the temperature values ​​collected by several temperature sensors arranged in the distribution cabinet; Based on a three-dimensional temperature field, the linear expansion coefficient of the material is introduced, and the discrete temperature values ​​are interpolated into a continuous field using the finite element method. The thermal strain components corresponding to each measurement point are then calculated. ; ; in, The thermal strain component of the distribution cabinet structural material caused by temperature change is dimensionless. The coefficient of linear expansion of a material (such as steel). ); The current temperature relative to the reference temperature (e.g., a temperature difference of 20°C) The finite element interpolation method discretizes the structure into a finite number of grids. Using the known physical quantities (such as displacement and temperature) of the grid nodes, it performs continuous and smooth interpolation within the grid through a preset shape function, thereby obtaining the physical field distribution at any location in the entire domain. Based on thermo-strain components By introducing the elastic modulus and the material Poisson's ratio, and using the generalized Hooke's law to construct a thermoelastic mechanical model, thermal stress components are calculated. Thermoelastic mechanical model: ; Among them, subscript , , This represents the tensor components, all of which take values ​​of 1, 2, and 3. A value of 1 corresponds to the x-axis in a three-dimensional Cartesian coordinate system, a value of 2 corresponds to the y-axis, and a value of 3 corresponds to the z-axis. The direction of the normal to the surface is The direction of stress is The thermal stress component, when hour, For normal stress components, when hour, This refers to the shear stress component; The direction of the normal to the surface is The direction of deformation is Thermo-induced strain components; The trace of the thermally induced strain tensor reflects the rate of volume change of the micro-element of the distribution cabinet structure due to thermal expansion and contraction. Poisson's ratio of the material (for steel) ); The Kronecker notation is used to filter the normal stress components corresponding to volumetric strain. The elastic modulus of the distribution cabinet structural material (such as the steel commonly used for the cabinet body). ); The generalized Hooke's law is a constitutive equation that describes the linear relationship between stress and strain within the linear elastic range of a material. Its complete form includes the material's elastic modulus and Poisson's ratio, and can be used to solve for the material response under complex three-dimensional stress states. Subtracting the thermal stress component from the original stress data yields the preliminary mechanical stress. ; ; in, For the original stress data, For thermally induced stress components (i.e., all) ); To remove the initial mechanical stress after removing the thermally induced stress component, the stripping operation is performed point-by-point in the time domain to ensure synchronization with the temperature field changes and avoid errors caused by thermal hysteresis.

[0020] The power decoupling module 22 calculates the inter-bus segment force based on the bus current parameters by using the electrodynamic load model constructed with the Biot-Savart law and the Ampere force formula, and separates the dynamic stress component caused by the periodic electrodynamic force from the preliminary mechanical stress, and finally outputs the pure mechanical stress component used to characterize the quasi-static bearing state of the structure. Specifically, the bus current parameters are obtained, and a spatial coordinate system for the bus section is established based on the actual layout of the bus in the distribution cabinet, and the bus is discretized into several current elements. Specifically, let the first The current in the busbar segment is Its spatial location is determined by the coordinates of the starting point. and endpoint coordinates By definition, the current data comes from the bus current waveform collected in real time by the current transformer installed in the cabinet. The sampling frequency should be no less than 10 times the power frequency of the power system in order to capture harmonic components. For any current element Obtain its value at time from the bus current parameters. The current value is calculated at any target point using magnetic field calculation methods. The magnetic induction intensity generated at that location; ; in, Indicates the number of units inside the distribution cabinet The current element of the busbar at time Target point The magnetic induction intensity generated at a point is a vector physical quantity, the direction of which is determined by the right-hand screw rule combined with the cross product rule, and the unit is T (Tesla). Vacuum permeability ( ); For the first busbar segment at time The current value, in A (ampere); For the first The current element vector of the busbar segment, with the direction consistent with the current flow direction, and the unit is m; The coordinates of the target point for calculating the magnetic field strength in space; For the first Busbar Current Element Location coordinates; Represents the vector cross product; Based on the magnetic induction intensity of the current element, the target point is obtained by numerically integrating the current in each busbar segment using the Biot-Savart law. Total magnetic flux density at the location Then calculate the first according to the Ampere force formula. The Lorentz force on the busbar in the magnetic field gives us the electromotive force it experiences. ; Electrodynamic load model (combining Biot-Savart law and Ampere force formula): ; in, For the first Busbar length, For the first Current element vector of busbar segment For the first busbar segment at time The current value; Indicates the target point The total magnetic flux density at a given location is obtained by superimposing the magnetic flux density generated by all bus current elements in the distribution cabinet, and the unit is T (Tesla). Indicates the first The busbar segment in the surrounding magnetic field The real-time electrodynamic force, measured in Newtons (N), changes in magnitude and direction with variations in current and magnetic field. It is the direct load causing dynamic stress in the distribution cabinet structure. This electrodynamic force is a time function, and its frequency components include the fundamental frequency, harmonics, and transient impact components (such as sudden current changes caused by the opening and closing of circuit breakers). electric power As the corresponding nodes (such as busbar support points, fixing clamps, etc.) of the distribution cabinet subjected to external loads, the displacement vector of the response is obtained by solving the structural dynamics equations. Then, the dynamic stress components caused by the electrodynamic force are calculated using the linear elastic constitutive equations. ; Structural dynamics equations: ; in, This is the mass matrix of the structure, reflecting the mass distribution characteristics of each node in the structure, with units of kg; The damping matrix of the structure reflects the energy dissipation characteristics during structural vibration, such as material damping and support damping, and is expressed in N·s / m. The design stiffness matrix is ​​used as a reference during the system initialization phase. In subsequent operation phases, the updated dynamic equivalent stiffness matrix from the previous monitoring cycle is used. This eliminates the impact of stiffness degradation on load decoupling accuracy through iterative approximation. Let be the displacement vector of the structural node of the distribution cabinet, which is the objective of solving the structural dynamics equations, and its unit is m; The velocity vector representing the structural node of the distribution cabinet is the first derivative of the node displacement with respect to time, and its unit is m / s; The acceleration vector represents the structural node of the distribution cabinet, which is the second derivative of the node displacement with respect to time, and its unit is m / s². 2 ; The load vector applied to the structural nodes of the distribution cabinet is determined by the electrodynamic force. Assembled; Linear elastic constitutive equation: ; in, For in position ,time The dynamic stress component at the location, in Pa; For the elastic modulus of the cabinet structure material, steel is typically taken as... ; For in position ,time The dynamic strain (dimensionless) at the point is the local micro-deformation of the structure caused by electrodynamic force; For in position ,time Displacement vector at (unit: m); For displacement along The rate of change of direction, i.e., normal strain, describes the tensile or compressive deformation of a micro-segment of a material; In the time domain, the initial mechanical stress and dynamic stress components are combined. By subtracting point by point, the pure mechanical stress components are obtained. ; ; in, For in position ,time The purely mechanical stress component at a given point characterizes the stress caused by static loads (such as gravity, installation prestress, and long-term mechanical loads). For in position ,time The initial mechanical stress at the point is calculated by the thermo-decoupling module 21.

[0021] The stress detection-based distribution cabinet structural stiffness health monitoring system also includes a stiffness inversion unit 3. The stiffness inversion unit 3, based on pure mechanical stress components, performs static inversion and dynamic identification through a beam-plate hybrid structural mechanical model to obtain the equivalent section moment of inertia and dynamic equivalent stiffness. In this embodiment, the stiffness inversion unit 3 includes a static stiffness inversion module 31 and a dynamic stiffness identification module 32; Among them, the static stiffness inversion module 31 constructs a beam-slab hybrid structural mechanical model, inputs pure mechanical stress components, and inverts the equivalent section moment of inertia that characterizes the local bending resistance of the structure by setting deformation compatibility conditions and solving static equilibrium equations. Specifically, the main load-bearing frame of the distribution cabinet is used as the beam element and the thin plate structure is used as the plate element. The finite element method is used to construct the mechanical model of the beam-plate hybrid structure and set the initial geometric and material parameters. In this model, beam elements are used to simulate linear load-bearing components (such as columns and beams), while plate elements are used to simulate planar load-bearing components (such as side plates and top plates). Beam and plate elements are connected rigidly or hingedly to form a complete structural system. The finite element method (FEM) is a numerical analysis technique that discretizes a continuous structure into a combination of finite elements. By establishing mathematical relationships between each element and solving the entire system, it simulates the mechanical behavior of complex structures. The model also includes the geometric dimensions and material properties (elastic modulus) of each beam and plate element in the beam-plate hybrid structural mechanical model. Poisson's ratio Initial parameters such as connection stiffness are derived from design drawings or measured data; Set deformation compatibility conditions that require adjacent elements (beam elements or plate elements) to maintain consistent displacement and rotation at the connection nodes: ; in, For beam-slab hybrid structures In the connection node Displacement components at that location, For beam-slab hybrid structures In the connection node Displacement components at the location; For unit In the connection node The corner component at the point, For unit In the connection node The angular component at the point; this deformation compatibility condition ensures that the structure remains as a whole after being subjected to force, avoiding non-physical separation or overlap; For those with For a power distribution cabinet structure with one degree of freedom, the purely mechanical stress components are input as static loads into the beam-slab hybrid structural mechanical model. The stresses are then distributed to the nodes of the corresponding beam and slab elements according to their location and direction. The specific steps are as follows: Stress field discretization and element association: Based on the sensor placement, the continuously distributed pure mechanical stress components are discretized. Discretized into local stress vectors associated with finite element mesh elements, each stress measurement point is mapped to the nearest beam or plate element via spatial coordinates; Interpolation and integration of element internal stress: For beam elements: based on the axial stress at the measurement point. Given the bending stress distribution (if known), the stress field of the entire element is obtained by interpolation along the element length using shape functions. Then, based on the cross-sectional geometric parameters (such as the cross-sectional area of ​​a beam element)... The equivalent nodal axial forces at both ends of the unit are calculated by integration. and bending moment : ; in, This represents the equivalent nodal axial force, expressed in N. To bypass The equivalent nodal bending moment of the shaft. To bypass The equivalent nodal bending moment of the shaft, in N·m; This represents the cross-sectional area of ​​the beam element, in m². This is the axial normal stress, measured in Pa, along the beam axis. For plate elements: based on the in-plane stress components at the measurement point. , , The stress field inside the element is obtained by interpolation using the element shape function, and then the nodal forces of the element are obtained by integration along the element thickness. ; in, For stress vectors, For along In-plane normal stress of plate element in the direction of the direction, For along In-plane normal stress of plate element in the direction of the direction, This represents the in-plane shear stress of a plate element, expressed in Pa. This is the strain-displacement matrix, in meters. -1 , used to convert nodal displacements into element strains; The volume of a plate element is expressed in meters (m). 3 ; This is the nodal force vector of the plate element, in units of N, containing the force components of each node; Nodal load assembly: based on equivalent nodal axial force and plate element nodal force vector The nodal forces calculated from each element are assembled into an overall nodal load vector according to the node number. , as the right-hand side term of the static equilibrium equation; Since the static load changes slowly, the average stress over a period of time can be taken as the quasi-static input to eliminate the influence of instantaneous fluctuations. Based on the principle of nodal force equilibrium (i.e., the resultant force and resultant moment of each node in the three directions are zero), the static equilibrium equations are established, consisting of the global stiffness matrix, the global nodal displacement vector, and the static load vector: ； in, for The overall structural stiffness matrix is ​​assembled from the local stiffness matrices of each beam element and plate element; for The overall nodal displacement vector; for The static load vector is obtained by converting the pure mechanical stress components; The overall nodal displacement vector is obtained by solving the static equilibrium equations. By combining the displacement shape function, the axial bending deformation of the beam element is calculated and then placed at the position. Deflection at the point And its position is solved by numerical differentiation method. Geometric curvature at : ; in, Let the deflection of the beam be... Let be the row vector corresponding to the bending degree of freedom in the displacement shape function matrix of the beam element. This is a sub-vector composed of the displacement components of the beam element nodes in the bending direction (e.g., perpendicular to the axis) (from the global nodal displacement vector). (obtained from) For in position The curvature of the beam indicates the degree of bending of the beam.

[0022] The displacement shape function matrix of a beam element is an interpolation function matrix that is mathematically derived from the displacement mode of the beam (such as a cubic Hermite polynomial) in the local coordinate system of the element and assembled in sequence with the nodal degrees of freedom. It is used to establish a linear relationship between the displacement of any point in the element and the nodal displacement.

[0023] Based on the obtained geometric curvature (recorded as) The stiffness inversion is performed using the "mechanical-geometric ratio method". The specific steps are as follows: First, based on purely mechanical stress components The beam element position is calculated using the section integral method. Actual bending moment at the location : ; in, Let be the distance from the integral element to the neutral axis. The cross-sectional area of ​​the beam element; Based on the bending theory of beams Construct stiffness inversion equations and solve them directly or obtain the position through regression analysis. Equivalent cross section moment of inertia at the location : ； in, The mechanical bending moment is obtained from the stress integral. The geometric curvature is obtained from the displacement differential. This method utilizes the independence of mechanical equilibrium and geometric deformation to accurately invert the local bending stiffness characteristics of the structure through the ratio between the two. This avoids the parameter reduction problem in the single stress fitting process.

[0024] The dynamic stiffness identification module 32 is based on the beam-plate hybrid structural mechanical model. It extracts the attenuated dynamic stress response excited in the pure mechanical stress component by transient events (such as circuit breaker operation), and analyzes the changes in its natural frequency and damping ratio to identify the dynamic equivalent stiffness that characterizes the overall dynamic characteristics of the structure. Specifically, when a transient load caused by a transient event (such as circuit breaker operation, short-circuit fault, or bus inrush current) is detected, the time window of that event is marked. Within this time window, the decayed dynamic stress response of the pure mechanical stress component is extracted. The specific method is as follows: ; in, For position The steady state period before the event occurs The average static stress within the sample is used to strip the background static load component, and the unit is Pa. The point in time at which the transient event begins. The selected steady-state time window length (e.g., 5 seconds); For position ,time The damped dynamic stress response excited by a transient event, expressed in Pa. Bandpass filtering is applied to the attenuated dynamic stress response to preserve the main vibration frequency band of the distribution cabinet structure (typically 5Hz~200Hz). A frequency response function fitting method is then employed, using exponential envelope fitting and zero-point detection on the filtered attenuated dynamic stress response to iteratively solve for the structure's natural frequencies. With damping ratio ; Specifically, the frequency response function fitting method uses measured response data of a structure under transient events to fit the frequency response function, thereby identifying the modal parameters of the structure (such as natural frequencies, damping ratios, and mode shapes). Taking a single-degree-of-freedom system as an example, the time-domain expression of the decaying free response is: ; in, The amplitude of the attenuation dynamic stress response is positively correlated with the impact intensity of the transient event; For the first The undamped natural circular frequency of the first mode, in rad / s, is only related to the inherent properties of the structure (stiffness, mass); For the first The natural frequencies of the first mode, expressed in Hz; For the first The damped natural circular frequency of the first mode, in rad / s, is the actual vibration circular frequency of the structure under damping, and its value is slightly smaller than the undamped natural circular frequency. For the structure of the distribution cabinet The damping ratio of the first mode reflects the rate of energy dissipation of structural vibration; the larger the damping ratio, the faster the vibration decays. The initial phase of the attenuated dynamic stress response, in rad; Based on natural frequency By using a beam-slab hybrid structural mechanics model, the reference values ​​of the natural frequencies of each mode of the structure under healthy conditions are determined. Then, based on the relationship between the natural frequencies and the stiffness matrix, the dynamic equivalent stiffness of the structure is identified. ; Specifically, for multi-degree-of-freedom systems, the third degree of freedom is determined using a beam-plate hybrid structural mechanical model. Reference values ​​for the natural frequencies of the first mode: ; in, The overall stiffness matrix under healthy conditions is derived from initial experimental or simulation calibration. The mass matrix of the structure is considered to be invariant (the structure has no significant increase or decrease in mass). For the first The mode shape reference for the first mode; For the first The undamped natural circular frequency of the first mode, For the first time in a healthy state The reference value of the natural frequency of the first mode; The square of the natural frequency is proportional to the eigenvalues ​​of the stiffness matrix: ; Therefore, dynamic equivalent stiffness It can be estimated using the following formula: ; in, It is the dynamic equivalent stiffness, expressed in N / m, which reflects the actual stiffness state of the structure under dynamic loads.

[0025] The stress detection-based distribution cabinet structural stiffness health monitoring system also includes a health assessment unit 4. The health assessment unit 4 compares the equivalent section moment of inertia and dynamic equivalent stiffness with the benchmark design value, calculates the stiffness loss factor, and combines the strain gradient and stress amplitude dual threshold method to judge the risk of local instability, and finally outputs the overall structural stiffness health index. In this embodiment, the equivalent cross-sectional moment of inertia is... Moment of inertia of the design section Compare and calculate the local static stiffness loss factor. ; ; in, is the local static stiffness loss factor of the beam element. It is a dimensionless percentage parameter used to quantify the degree of structural stiffness degradation. The larger the value, the more severe the structural stiffness loss. The design section moment of inertia of the beam element is expressed in meters (m). 4These data originate from structural design drawings or initial calibration data. Dynamic equivalent stiffness Equivalent stiffness to design Compare and calculate the dynamic stiffness loss factor. ; ; in, The dynamic stiffness loss factor is a dimensionless percentage parameter that reflects the degree of degradation of the overall vibration resistance of the structure. The equivalent stiffness is designed, with units of N / m, and is derived from the initial experimental modal analysis or calibration results under healthy conditions; Local static stiffness loss factor With dynamic stiffness loss factor The components are integrated to form the final stiffness and health rating. ; ; in, This is the average value of the local static stiffness loss factor at all measurement locations; This is the static stiffness weighting coefficient. For example, the dynamic stiffness weighting coefficient, This reflects the proportion of static and dynamic stiffness in the overall assessment; To find the function with the maximum value; The stiffness health score is the percentage that is closer to 100%, indicating a better structural stiffness health.

[0026] In this embodiment, in-plane strain data of the surface of a thin plate structure (such as a side plate or a top plate) is obtained. And calculate its composite strain nonuniformity index. ; ; in, For position ,time Measured in-plane strain at the location, This represents the maximum strain within the thin plate region. This represents the minimum strain within the thin plate region; The region's characteristic length, in meters, can be taken as the sensor spacing. The weighting coefficient (value 0~1) is used to balance the influence of local gradient and global deformation. The composite strain nonuniformity index is used for the thin plate region of the distribution cabinet. The first term represents the degree of local strain abrupt change, and the second term represents the severity of the overall deformation of the region. The two terms are superimposed to comprehensively reflect the nonuniform deformation state of the thin plate.

[0027] Extract the maximum and minimum stress values ​​of the same thin plate region from the purely mechanical stress components, and calculate the stress amplitude. ; ; in, This represents the stress amplitude in the thin plate region, used to assess whether the region is in a state of high stress alternation. The larger the value, the higher the degree of stress alternation, which is more likely to cause local instability. The pure mechanical stress components obtained for load separation unit 2; To find the minimum value function; Composite strain nonuniformity index Exceeding the set non-uniformity threshold and stress amplitude Exceeding the set stress amplitude threshold If so, it is determined that there is a risk of local instability in the area; The judgment logic is as follows: like and ; This indicates a risk of local instability in the region. in, The non-uniformity threshold, This is the stress amplitude threshold, and its value is based on the calibration data under the initial healthy state; Based on the number and location importance of areas with local instability risks, warning levels are divided. If a single area has local instability risks, a mild warning signal is issued; if two areas have local instability risks, a moderate warning signal is issued; if three or more areas or key areas (such as busbar support plates or door frame hinge areas) have local instability risks, a severe warning signal is issued. Among them, "region" refers to structural partitions, such as side panels, top panels, and support areas; When the warning signal is output, the coordinates of the trigger area and the current composite strain nonuniformity index are recorded simultaneously. With stress amplitude Duration and recommended remedial measures (such as checking whether the connecting bolts are loose, whether the plates are deformed, etc.); The results of the local instability risk assessment are combined with the stiffness health level. By integrating these components, an overall structural stiffness and health index can be formed. ; ; Among them, if If the value is below the set threshold, the overall structural stiffness health index will be output, indicating that a structural inspection or reinforcement is required.

[0028] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A stress detection based electrical switchgear structure stiffness health monitoring system, characterized in that, include: The stress sensing unit (1) is used to synchronously acquire the original stress data of the main load-bearing frame, thin plate structure and key connection nodes of the power distribution cabinet under mechanical load and temperature load. The load separation unit (2) is used to collect the cabinet temperature field distribution parameters and bus current parameters, and separate the thermal stress component and dynamic stress component in the original stress data through the load decoupling model to obtain the pure mechanical stress component. The load decoupling model is constructed from a thermoelastic mechanical model and an electrodynamic load model; The stiffness inversion unit (3) is used to perform static inversion and dynamic identification based on the pure mechanical stress components through the beam-plate hybrid structural mechanical model to obtain the equivalent section moment of inertia and dynamic equivalent stiffness. The health assessment unit (4) is used to compare the equivalent cross section moment of inertia and dynamic equivalent stiffness with the benchmark design value, calculate the stiffness loss factor, and combine the strain gradient and stress amplitude dual threshold method to judge the risk of local instability, and finally output the overall stiffness health index of the structure.

2. The stress-detection-based electrical cabinet structure stiffness health monitoring system according to claim 1, wherein, The original stress data includes: multiaxial strain data reflecting the stress distribution state of the main load-bearing frame, which includes axial strain along the main load-bearing direction, transverse strain perpendicular to the main load-bearing direction, and strain components in the shear strain sensitive direction; in-plane stress data reflecting the surface deformation and stress distribution state of the thin plate structure, which includes transverse and longitudinal strain components, in-plane shear strain components, and equivalent strain and equivalent stress; and stress concentration data reflecting the stress distribution state at key connection nodes.

3. The stress-detection-based electrical cabinet structure stiffness health monitoring system according to claim 1, wherein, The load separation unit (2) includes a thermal decoupling module (21), which is used for: The cabinet temperature field distribution parameters are obtained and a three-dimensional temperature field is constructed. The thermal strain components are calculated using the finite element interpolation method. Based on the aforementioned thermally induced strain components, the material's linear expansion coefficient, elastic modulus, and Poisson's ratio are introduced. The generalized Hooke's law is used to construct the thermoelastic mechanical model and calculate the thermally induced stress components. The thermal stress component is subtracted point by point from the original stress data in the time domain to obtain the preliminary mechanical stress.

4. The stress-detection-based electrical cabinet structure stiffness health monitoring system according to claim 3, wherein, The load separation unit (2) further includes a power decoupling module (22), which is used for: Obtain the bus current parameters, discretize the bus into current elements, calculate the magnetic induction intensity generated by the current elements based on the Biot-Savart law, and construct the electrodynamic load model in combination with the Ampere force formula to calculate the electrodynamic force on the bus. The electrodynamic force is used as an external load. The displacement vector is obtained by solving the structural dynamics equations that include the mass matrix, damping matrix and reference stiffness matrix. Then, the dynamic stress components caused by the electrodynamic force are calculated by the linear elastic constitutive equation. In the time domain, the preliminary mechanical stress is subtracted from the dynamic stress component point by point to obtain the pure mechanical stress component that characterizes the quasi-static bearing state of the structure.

5. The stress-detection-based electrical cabinet structure stiffness health monitoring system according to claim 1, wherein, The stiffness inversion unit (3) includes a static stiffness inversion module (31). The static stiffness inversion module (31) is used to construct the mechanical model of the beam-plate hybrid structure, with the main load-bearing frame of the distribution cabinet as the beam unit and the thin plate structure as the plate unit. The deformation coordination condition is set so that the displacement and rotation angle of the adjacent units at the connection node remain consistent. The pure mechanical stress component is input as a static load into the mechanical model of the beam-plate hybrid structure, and the static equilibrium equation is established and solved to obtain the overall node displacement vector.

6. The stress-detection-based electrical cabinet structure stiffness health monitoring system according to claim 5, wherein, The static stiffness inversion module (31) uses the mechanical-geometric ratio method for stiffness inversion, specifically including: Based on the whole node displacement vector, combined with displacement shape function, the geometric curvature of beam element at position x is solved by numerical differentiation method ; Based on the pure mechanical stress component, the actual acting bending moment of the beam element at position x is calculated using the sectional area integral method ; According to the formula The equivalent cross-sectional moment of inertia at a position x is calculated where E is the modulus of elasticity.

7. The stress-detection-based electrical cabinet structure stiffness health monitoring system according to claim 1, wherein, The stiffness inversion unit (3) includes a dynamic stiffness identification module (32), which is used for: Within the time window of the transient event detection, the attenuated dynamic stress response is extracted from the pure mechanical stress component and bandpass filtered. The frequency response function fitting method is used to perform exponential envelope fitting on the filtered attenuated dynamic stress response, and the natural frequency of the structure is solved iteratively. The natural frequency reference value of the structure under healthy conditions is determined by the beam-slab hybrid structural mechanical model. Based on the proportional relationship between the square of the natural frequency and the eigenvalue of the stiffness matrix, the dynamic equivalent stiffness is calculated.

8. The stress-detection-based electrical cabinet structure stiffness health monitoring system according to claim 1, wherein, The health assessment unit (4) calculates the stiffness loss factor in the following ways: The equivalent cross-sectional moment of inertia is compared with the design cross-sectional moment of inertia to calculate the local static stiffness loss factor. The dynamic equivalent stiffness is compared with the design equivalent stiffness to calculate the dynamic stiffness loss factor; The average value of the local static stiffness loss factors of all the measurement positions is weighted and fused with the dynamic stiffness loss factor according to preset static stiffness weight coefficients and dynamic stiffness weight coefficients respectively to obtain a stiffness health degree .

9. The stress-detection-based electrical cabinet structure stiffness health monitoring system according to claim 8, wherein, The health assessment unit (4) is also used to perform the judgment of the local instability risk, and the specific steps include: Obtain in-plane strain data of the surface of the sheet structure, calculate the composite strain non-uniformity index , the composite strain non-uniformity index is superimposed by a strain space gradient term and a regional overall deformation degree term; Calculate the stress amplitude of the same thin plate region from the purely mechanical stress components. ; When the composite strain nonuniformity index exceeds the nonuniformity threshold and the stress amplitude exceeds the stress amplitude threshold, it is determined that there is a risk of local instability in the region.

10. The distribution cabinet structural stiffness health monitoring system based on stress detection according to claim 9, characterized in that, The health assessment unit (4) forms the overall structural stiffness health index in the following manner. If it is determined that there is no risk of local instability, then Equal to the stiffness health degree ; If it is determined that there is a risk of local instability, then For the stiffness health degree Subtract the preset penalty value; if If the value is below the set threshold, the overall structural stiffness health index will be output.

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