A Method for Evaluating the Contact Resistance of the Plum Blossom Contact of Switchgear Based on Digital Twin

Abstract

The present invention discloses a method for evaluating the contact resistance of switchgear plum blossom contacts based on digital twins. The method constructs a coupling model between the switchgear plum blossom contact resistance and thermal field distribution based on real-time data acquired by temperature sensors within a high-current switchgear and a simulation model built on the COMSOL computing platform. By calibrating the coupling model, a switchgear thermal field self-calibration model based on an iterative update process is formed. Finally, based on the newly calibrated switchgear thermal field self-calibration model and the coupling model between the switchgear plum blossom contact resistance and thermal field distribution, the contact resistance value of the plum blossom contact can be output by inputting the temperature data monitored at each point in the switchgear, thereby achieving the purpose of evaluating the contact resistance of the plum blossom contact. This method realizes intelligent detection of the switchgear, provides a guarantee for the safe and stable operation of the switchgear, and greatly reduces the difficulty of manual maintenance.

Description

Technical Field

[0001] The present invention relates to a method for evaluating the contact resistance of a switch cabinet plum blossom contact, and in particular to a method for evaluating the contact resistance of a switch cabinet plum blossom contact based on digital twins. Background Art

[0002] Switchgear is a critical node in power transmission and distribution lines. Failures within it severely impact the stability of subsequent transmission lines. Switchgear is often centrally located. A failure in a single switchgear unit can trigger a chain reaction, damaging other switchgear units and other distribution equipment. This can not only cause regional power outages and widespread load shedding, endangering the healthy operation of the power grid, but can also threaten the lives of maintenance personnel and create negative social impacts. Switchgear failures can be categorized as thermal, mechanical, and insulation failures. Each type of failure can cause abnormal temperature rise in the switchgear, or even explosion. According to statistics, thermal failure is the leading cause of switchgear failures and the most damaging type of failure. The main causes of thermal failures include improper switchgear electrical connection workmanship, oxidation of the electrical connection surface during operation, and mechanical wear of the contacts caused by improper operation of the circuit breaker trolley. These factors increase the contact resistance of the electrical connection surface. This increased contact resistance causes the switchgear to operate abnormally. Increased or sudden load changes can cause abnormal temperature rise, significantly increasing the probability of thermal failure.

[0003] With the surge in power load, switchgear overheating has become increasingly prominent. Thermal failure prevention has become a top priority for switchgear failure prevention. The plum blossom contact is a key component in the switchgear that requires temperature rise monitoring. During operation, the plum blossom contact is most susceptible to wear and deformation, leading to contact abnormalities. Operating in this state presents certain thermal defects. Without effective temperature monitoring and timely warning, thermal defects will gradually develop into thermal failures. Currently, due to the structural characteristics of the plum blossom contact's location and the obstruction of sensor measurement signal transmission, the plum blossom contact surface temperature is not easily monitored directly.

[0004] In the 1990s, researchers applied the thermal network method to thermal analysis of medium- and high-voltage switchgear, primarily for product design and optimization. In the early 21st century, with the rapid development of China's power grid and the widespread deployment of switchgear, domestic researchers began studying the temperature rise characteristics of switchgear. In 2012, Ding Jian roughly calculated the temperature rise of contact points using an empirical formula for contact resistance and a formula for calculating contact temperature rise under short-circuit current. In 2013, Jia Wenzhuo et al. constructed a three-dimensional model of a 40.5 kV switchgear and used ANSYS simulation to study the temperature field distribution characteristics. In the simulation, they simulated the presence of contact resistance by increasing the resistivity of electrical connections. The results qualitatively demonstrated that contact resistance is a significant factor affecting switchgear temperature. In 2013, Cao Ping et al. used 6SigmaET simulation software to simulate the temperature field of a low-voltage distribution cabinet. The model considered the impact of the skin effect on busbar resistance and the contact resistance of various electrical connection surfaces, and also incorporated analysis of convection and radiation heat dissipation. In their contact resistance calculation, they used an estimated contact pressure.

[0005] With the optimization of finite element simulation software, research on the temperature-rise characteristics of switchgear is continuously improving. From two-dimensional to three-dimensional finite element simulation, from considering a single heat transfer model to the coupling of heat transfer, electromagnetics, and convection, from estimating the contact resistance of switchgear electrical connections using empirical formulas to experimentally measuring it, and from simulation research to combining simulation with temperature-rise experiments, these advances have made switchgear temperature field simulation results increasingly realistic. However, currently, due to the structural characteristics of the plum blossom contact's location and the obstruction of sensor measurement signal transmission, the contact resistance and surface temperature of the plum blossom contact are difficult to monitor directly, severely restricting the assessment of the switchgear's health status. Summary of the Invention

[0006] In response to the problems existing in the prior art, the purpose of the present invention is to propose a method for evaluating the contact resistance of the plum blossom contacts of a switch cabinet based on digital twins. This method constructs a digital twin model of the thermal field of the switch cabinet with self-correction function based on the real-time data obtained by the temperature sensor in the switch cabinet and the simulation model built on the computing platform, thereby achieving the purpose of evaluating the contact resistance of the plum blossom contacts.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for evaluating the contact resistance of a switch cabinet plum blossom contact based on digital twins includes the following steps:

[0009] A method for evaluating the contact resistance of plum blossom contacts of a switch cabinet based on digital twins includes the following steps:

[0010] Step 1: Determine the switchgear model and electrical parameters, and analyze the switchgear internal structure and flow path;

[0011] Step 2: Analyze the heat transfer mode inside the switch cabinet and determine whether to consider the heat transfer inside the switch cabinet from the three basic heat transfer modes: heat conduction, heat convection, and heat radiation;

[0012] Step 3: Based on the actual switchgear structure, design a scheme for simultaneously arranging two or more temperature sensors for monitoring; after installing the temperature sensors, compare the data obtained by monitoring different temperature sensors to verify the accuracy of the switchgear thermal field temperature monitoring;

[0013] Step 4: Calculate the contact resistance of the junction between the plum blossom contact and the static contact, the opening and closing contacts in the vacuum interrupter of the circuit breaker, and the connection between the current transformer and the busbar. The calculation formula is R = k j / (F) m ,

[0014] Where R represents the contact resistance, k j It represents the coefficient related to the contact material and surface condition, F represents the contact pressure, and m represents the index related to the contact form, pressure range and number of contact points;

[0015] Step 5: Remove, smooth, and simplify the components in the 3D model of the switch cabinet. Set the grille heat dissipation shape in the COMSOL software to simulate the heat dissipation holes, and set the materials and properties of each component in the 3D model of the switch cabinet.

[0016] Step 6: Set the electromagnetic-heat transfer-convection multi-physics field coupling form to simulate the temperature rise characteristics of the switch cabinet;

[0017] Step 7. Use the calculation formula in step 4 to evaluate the range of contact resistance of the plum blossom contacts in the switchgear. Taking into account the site ambient temperature, annual load current changes, and contact wear intensity, establish the following uncorrected digital twin model of the switchgear thermal field.

[0018] R T =f(I,T ext ,R C ,R B ,γ)

[0019] Where f represents the action function of the uncorrected digital twin model of the switchgear thermal field, R T represents the contact resistance at the plum blossom contact, I represents the load current, T ext Indicates the ambient temperature, R c Indicates the contact resistance of the connection between the current transformer and the busbar, R crepresents the contact resistance of the vacuum circuit breaker opening and closing contacts, and γ represents the influence coefficient of wear loss on the contact resistance;

[0020] Step 8: Divide the entire switch cabinet into the cabinet body, conductive busbars, contacts, and insulating components for meshing, and finally run the operation to obtain the uncorrected thermal field characteristics of the switch cabinet;

[0021] Step 9. Calculate the switchgear thermal field data using the COMSOL software to construct a coupling model between the switchgear plum blossom contact resistance and the thermal field distribution. Correct the coupling model by monitoring the temperature data using a temperature sensor to form a switchgear thermal field self-correction model based on an iterative update process. Finally, based on the latest corrected switchgear thermal field self-correction model and the coupling model between the switchgear plum blossom contact resistance and the thermal field distribution, input the temperature data monitored at each point in the switchgear to output the plum blossom contact resistance value, thereby evaluating the status of the plum blossom contact. The mathematical expression of the switchgear thermal field self-correction model is as follows:

[0022]

[0023] Where Δf k Represents the correction term after the kth correction, R Tn Indicates the contact resistance at the plum blossom contact after the nth correction.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] By constructing a switchgear thermal field self-correction model and a coupling model between the switchgear plum blossom contact resistance and the thermal field distribution, real-time assessment of the switchgear health status is achieved, which greatly reduces the difficulty of manual maintenance. At the same time, it provides a guarantee for the safe and stable operation of the switchgear, solves the problem of difficult assessment of the contact resistance of the switchgear plum blossom contact in actual projects, and has great engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below with reference to the accompanying drawings and examples.

[0027] Figure 1 A flow chart of a method for evaluating the contact resistance of plum blossom contacts of a switch cabinet based on digital twin is shown.

[0028] Figure 2 Shown is a schematic diagram of the structure of the KYN-28 switchgear.

[0029] Figure 2 Middle: 1-cabinet; 2-busbar; 3-contact box; 4-static contact; 5-partition; 6-circuit breaker trolley; 7-zinc oxide lightning arrester; 8-earthing switch; 9-current transformer; 10-busbar bushing; A-busbar room; B-high-voltage incoming line room; C-relay instrument room; D-circuit breaker trolley room.

[0030] Figure 3 A simplified cross-sectional view of a plum blossom contact is shown.

[0031] Figure 4 (a) and (b) show the front and side views of the simplified model of the switchgear.

[0032] Figure 5 (a), (b), (c), and (d) show the mesh division results of the switchgear cabinet, conductive busbar, contacts, and insulating components. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] like Figure 1 As shown, the present invention provides a method for evaluating the contact resistance of a switch cabinet plum blossom contact based on digital twin, comprising the following steps:

[0035] 1. Determine the switchgear model and electrical parameters, analyze the switchgear's internal structure and current flow path, and analyze the heat sources within the switchgear to determine that the heat primarily comes from Joule heating generated by the load current flowing through the conductive circuit. The primary heat sources are located between the stationary and plum blossom contacts, the vacuum circuit breaker's opening and closing contacts, and the connection between the current transformer and the busbar. Ignore other heat sources within the switchgear. The formula for calculating Joule losses is as follows:

[0036] P=K f1 K f2 I 2 R

[0037] Where P represents Joule loss, K f1 represents the proximity effect coefficient, K f2 represents the skin effect coefficient, I represents the load current, and R represents the loop resistance.

[0038] 2. Analyze the heat transfer mode inside the switch cabinet and determine whether to consider the heat transfer inside the switch cabinet from the three basic heat transfer modes: heat conduction, heat convection, and heat radiation. Heat conduction follows Fourier's law as shown below:

[0039]

[0040] Where J represents heat flux, λ represents thermal conductivity, T represents temperature, and n represents the unit normal vector.

[0041] In the switchgear model, the key thermal convection to consider occurs within the switchgear cabinet, as well as the convection between the cabinet air and the outside world through the cabinet's surface heat dissipation holes. All of these convections are considered natural convection. In the switchgear model, heat conduction occurs within the busbar, between the busbar and contacts, between contacts, and between conductors and insulators. Thermal convection follows Newton's law of cooling as follows:

[0042] J=-hΔT

[0043] Where J represents the heat flux density, h represents the material convection heat transfer coefficient, and ΔT represents the temperature difference.

[0044] In the vacuum interrupter where the circuit breaker's opening and closing contacts are located, there is no convection heat transfer from the air. Therefore, heat radiation and heat conduction are the main ways for heat transfer between the opening and closing contacts and the surrounding insulating materials. Heat radiation follows the following heat radiation law:

[0045]

[0046] Where q represents the total energy of thermal radiation, ε represents the emissivity, δ0 represents the Boltzmann constant, T1 represents the temperature of the outer surface of the cable, and T2 represents the temperature of the inner wall of the switch cabinet.

[0047] 3. Based on the actual switchgear structure, design a solution that simultaneously deploys two or more temperature sensors for monitoring. After installing the temperature sensors, compare the data obtained from different temperature sensors to verify the accuracy of the switchgear thermal field temperature monitoring.

[0048] 4. Calculate the contact resistance of the junction between the plum blossom contact and the static contact, the opening and closing contacts in the vacuum interrupter of the circuit breaker, and the connection between the current transformer and the busbar. The calculation formula is R = k j / (F) m , where R represents the contact resistance, k j It represents the coefficient related to the contact material and surface condition, F represents the contact pressure, and m represents the index related to the contact form, pressure range and number of contact points;

[0049] 5. Simplify the 3D geometric model of the switch cabinet, such as Figure 4 As shown in (a) and (b), structures with little influence on heat transfer and heat dissipation, such as busbar bushings, grounding switches, and zinc oxide lightning arresters, are removed; cabinet structures that are not conducive to meshing, such as cabinet screw holes and small gaps, are removed; the raised textures of insulating components such as contact boxes are simplified and smoothed; the shape of the contact fingers of the plum blossom contacts is equivalently simplified, such as Figure 3 As shown, narrow air gaps are reduced; the busbar structure is simplified to remove small gaps. In the COMSOL computing platform, the grille heat dissipation shape is set to simulate the heat dissipation holes, and the materials and properties of each component in the 3D switchgear model are set.

[0050] 6. Set up an electromagnetic-heat transfer-convection multiphysics coupling to simulate the temperature rise characteristics of the switchgear. The electromagnetic module sets the current excitation and contact resistance; the heat transfer module sets the boundary temperature conditions, the cabinet surface heat transfer coefficient, and the surface emissivity of each material; and the convection module sets the heat dissipation vent outlet pressure and the air volume force inside the cabinet.

[0051] 7. Use the calculation formula in step 4 to evaluate the range of contact resistance of the plum blossom contacts in the switchgear. Taking into account factors such as site ambient temperature, annual load current variation, and contact wear intensity, the range of characteristic variables in the switchgear thermal field digital twin model is determined. The mathematical expression of the uncorrected digital twin model of the switchgear thermal field is as follows:

[0052] R T =f(I,T ext , R C , R B ,γ)

[0053] Where f represents the action function of the thermal field digital twin model, R T represents the contact resistance at the plum blossom contact, I represents the load current, T ext Indicates the ambient temperature, R c Indicates the contact resistance of the connection between the current transformer and the busbar, R c It represents the contact resistance of the opening and closing contacts of the vacuum circuit breaker, and γ represents the influence coefficient of wear loss on the contact resistance.

[0054] 8. Divide the entire switch cabinet into the cabinet body, conductive busbar, contacts and insulation components for grid division, such as Figure 5 As shown in (a), (b), (c), and (d), in order to improve the calculation convergence speed and accuracy, the finite element simulation model is finally run to obtain the uncorrected thermal field characteristics of the switchgear under different ambient temperatures, different load currents, and different contact resistance conditions.

[0055] 9. Based on the switchgear thermal field data calculated by the COMSOL computing platform, a coupling model between the switchgear plum blossom contact resistance and the thermal field distribution is constructed; each time the temperature sensor monitoring data is input, the coupling model is corrected to form a switchgear thermal field self-correction model based on an iterative update process. Finally, based on the latest calibrated switchgear thermal field self-correction model and the coupling model between the switchgear plum blossom contact resistance and the thermal field distribution, the temperature data monitored at each point in the switchgear is input to output the plum blossom contact contact resistance value, thereby evaluating the status of the plum blossom contact. The mathematical expression of the switchgear thermal field self-correction model is as follows:

[0056]

[0057] Where Δfk Represents the correction term after the kth correction, R Tn Indicates the contact resistance at the plum blossom contact after the nth correction.

[0058] Furthermore, the flow path in step 1 is Figure 2 It is manifested as follows: the current flows into the busbar bushing 10, flows through the current transformer 9, and then flows through the static contact 4 and the plum blossom contact below, enters the opening and closing contacts in the vacuum interrupter of the circuit breaker, and then flows out from the upper plum blossom contact and static contact to the busbar 2, and finally flows out from the busbar 2.

[0059] Furthermore, the physical field setting in step 6 is specifically as follows: the electromagnetic module is used to set the current excitation and contact resistance. According to the calculated contact resistance value, the "contact impedance" module is applied to each contact surface in the conductive circuit to set the surface resistance. The heat transfer module is used to set the boundary temperature conditions, the cabinet surface heat transfer coefficient and the surface emissivity of each material. The setting of the boundary temperature conditions is specifically described as follows: for the heat dissipation holes, it is set to the first type of boundary conditions, and the initial temperature value on the heat dissipation holes is specified to be room temperature. The cabinet surface is set to the third type of boundary conditions, and the surface heat transfer coefficient is specified to be 10W / (m 2 ·K), with the gas temperature at room temperature. The conductor surface emissivity is set to 0.5. The convection module is used to set the heat dissipation vent outlet pressure, the air volume force inside the cabinet, and other parameters. There is no forced convection inside the cabinet; the gas flows naturally after heating.

Claims

1. A method for evaluating the contact resistance of plum blossom contacts in switchgear based on digital twins, characterized by: The steps include: Step 1: Determine the model and electrical parameters of the switchgear, and analyze the internal structure and flow path of the switchgear; Step 2: Analyze the heat transfer mode inside the switch cabinet and determine whether to consider the heat transfer inside the switch cabinet from the three basic heat transfer modes: heat conduction, heat convection, and heat radiation; Step 3: Based on the actual switchgear structure, design a scheme for simultaneously arranging two or more temperature sensors for monitoring; after installing the temperature sensors, compare the data obtained by monitoring different temperature sensors to verify the accuracy of the switchgear thermal field temperature monitoring; Step 4: Calculate the contact resistance of the junction between the plum blossom contact and the static contact, the opening and closing contacts in the vacuum interrupter of the circuit breaker, and the connection between the current transformer and the busbar. The calculation formula is R = k j / (F) m , Where R represents the contact resistance, k j It represents the coefficient related to the contact material and surface condition, F represents the contact pressure, and m represents the index related to the contact form, pressure range and number of contact points; Step 5: Remove, smooth, and simplify the components in the 3D model of the switch cabinet. Set the grille heat dissipation shape in the COMSOL software to simulate the heat dissipation holes, and set the materials and properties of each component in the 3D model of the switch cabinet. Step 6: Set the electromagnetic-heat transfer-convection multi-physics field coupling form to simulate the temperature rise characteristics of the switch cabinet; Step 7. Use the calculation formula in step 4 to evaluate the range of contact resistance of the plum blossom contacts in the switchgear. Taking into account the site ambient temperature, annual load current changes, and contact wear intensity, establish the following uncorrected digital twin model of the switchgear thermal field. R T =f(I,T ext ,R c ,R B ,γ) Where f represents the action function of the uncorrected digital twin model of the switchgear thermal field, R T represents the contact resistance at the plum blossom contact, I represents the load current, T ext Indicates the ambient temperature, R c Indicates the contact resistance of the connection between the current transformer and the busbar, R c represents the contact resistance of the opening and closing contacts of the vacuum circuit breaker, and γ represents the influence coefficient of wear loss on the contact resistance; Step 8: Divide the entire switch cabinet into the cabinet body, conductive busbars, contacts, and insulating components for meshing, and finally run the operation to obtain the uncorrected thermal field characteristics of the switch cabinet; Step 9. Calculate the switchgear thermal field data using the COMSOL software to construct a coupling model between the switchgear plum blossom contact resistance and the thermal field distribution. Correct the coupling model by monitoring the temperature data using a temperature sensor to form a switchgear thermal field self-correction model based on an iterative update process. Finally, based on the latest corrected switchgear thermal field self-correction model and the coupling model between the switchgear plum blossom contact resistance and the thermal field distribution, input the temperature data monitored at each point in the switchgear to output the plum blossom contact resistance value, thereby evaluating the status of the plum blossom contact. The mathematical expression of the switchgear thermal field self-correction model is as follows: Where Δf k Represents the correction term after the kth correction, R Tn Indicates the contact resistance at the plum blossom contact after the nth correction.

2. A method for evaluating contact resistance of plum blossom contacts of a switch cabinet based on digital twinning according to claim 1, characterized in that: The temperature rise characteristics of the switch cabinet are simulated and calculated in the form of electromagnetic-heat transfer-convection multi-physics field coupling as described in step 6, wherein the electromagnetic module sets the current excitation and contact resistance; the heat transfer module sets the boundary temperature conditions, the cabinet surface heat transfer coefficient, and the surface emissivity of each material; and the convection module sets the heat dissipation hole outlet pressure and the air volume force inside the cabinet.

3. The method for evaluating contact resistance of plum blossom contacts of a switch cabinet based on digital twinning according to claim 1, characterized in that: As described in step 8, the entire switch cabinet is divided into a cabinet body, a conductive busbar, contacts and insulating components for meshing, and finally the uncorrected thermal field characteristics of the switch cabinet under different ambient temperatures, different load currents and different contact resistance conditions are obtained.

Images