CN106570289B - Method for measuring temperature rise of contact under high current of low-voltage apparatus based on finite element analysis - Google Patents
Method for measuring temperature rise of contact under high current of low-voltage apparatus based on finite element analysis Download PDFInfo
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- CN106570289B CN106570289B CN201610989987.3A CN201610989987A CN106570289B CN 106570289 B CN106570289 B CN 106570289B CN 201610989987 A CN201610989987 A CN 201610989987A CN 106570289 B CN106570289 B CN 106570289B
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
- G06F30/23—Design optimisation, verification or simulation using finite element methods [FEM] or finite difference methods [FDM]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/327—Testing of circuit interrupters, switches or circuit-breakers
- G01R31/3277—Testing of circuit interrupters, switches or circuit-breakers of low voltage devices, e.g. domestic or industrial devices, such as motor protections, relays, rotation switches
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
- G06F2119/08—Thermal analysis or thermal optimisation
Abstract
The invention discloses a method for measuring temperature rise of a contact under high current of a low-voltage apparatus based on finite element analysis, which comprises the steps of measuring voltage, current data and waveforms at two ends of the contact and arcing time of an electric arc of the low-voltage apparatus in a breaking process under overload and short-circuit high-current working environments through an industrial personal computer, virtual instrument LabVIEW software and a hardware circuit; calculating to obtain the overall temperature field distribution cloud chart of the contact system under different large currents by using ANSYS finite element software, and obtaining the change curve of the highest temperature of the contact along with time; establishing a mathematical relation between the highest temperature value of the contact and the current value of the low-voltage apparatus, and drawing a fitting curve; and measuring the current value flowing through the low-voltage apparatus, and calculating the highest temperature of the contact of the low-voltage apparatus by calling the mathematical relationship between the highest temperature value of the contact under the high current and the current value of the low-voltage apparatus by the computer. The temperature measuring device has the advantages that the temperature rise of the contact under the large current of the low-voltage apparatus can be measured, the detection time is effectively shortened, and the detection efficiency is improved.
Description
Technical Field
The invention relates to the technical field of circuit detection, in particular to a finite element analysis-based method for measuring temperature rise of a contact of a low-voltage apparatus under high current.
Background
When overload or short circuit occurs, a large current which is several times or even tens of times of the rated current flows in the system, and the low-voltage electric appliance can automatically break the circuit in order to protect other electric equipment in the system from the influence of the overload or the short circuit. However, when the low-voltage electrical appliance is subjected to current breaking, high-temperature electric arcs can be generated, the heat of the electric arcs can enable the temperature of the contact to rise rapidly within a short time and even exceed the temperature-resistant range of the contact material, and the generation of the electric arcs can also cause ablation of the contact material, which can reduce the mechanical strength and the insulating strength of the contact, cause the contact material to deform, accelerate the insulating aging, shorten the service life of the electrical appliance, further cause the low-voltage electrical appliance to lose efficacy, and cause the system to have potential safety hazards. Therefore, it is necessary to monitor the temperature rise of the contact of the low-voltage electric device in real time under a large current.
In the prior art, a probe of an optical fiber temperature sensor is tightly attached to the surface of a measured component, a temperature signal is converted into an optical signal and sent to a signal demodulator through the optical fiber temperature sensor, the temperature of the measured component is obtained after demodulation, and an industrial personal computer is connected with the signal demodulator and receives a temperature measurement signal. Obviously, due to the ablative nature of the arc, the fiber optic probe cannot be brought into close proximity with the contact surface where the high temperature arc is present. The principle of the infrared temperature measurement method is that infrared radiation energy emitted by a measured object is converted into an electric signal on a detector through an optical system of a temperature measuring instrument, and the surface temperature of the measured object is displayed through a display part of the infrared temperature measuring instrument. Although the infrared thermometer has the advantages of non-contact measurement, wide temperature measurement range, high response speed, high sensitivity and the like, the infrared thermometer is only used for measuring the surface temperature of a measured object due to the influence of the emissivity of the measured object, and the real temperature of the measured object can hardly be measured. Thus, both of these methods have their own limitations and are not suitable for measuring the temperature rise of the contacts in the presence of high temperature arcs.
Disclosure of Invention
The invention aims to solve the problems and designs a method for measuring the temperature rise of a contact of a low-voltage apparatus under high current based on finite element analysis.
The invention achieves the aim that the technical scheme is that the method for measuring the temperature rise of the contact of the low-voltage apparatus under the heavy current based on finite element analysis comprises the following steps:
the method comprises the following steps: measuring voltage, current data and waveforms at two ends of a contact and arcing time of an electric arc of the low-voltage apparatus in a breaking process under overload, short-circuit and large-current working environments through an industrial personal computer, virtual instrument LabVIEW software and a hardware circuit;
step two: according to the measured size of the low-voltage electrical appliance contact system, establishing a physical model of the contact system in three-dimensional finite element software ANSYS; establishing a finite element model of the low-voltage electrical appliance contact system by defining material properties, selecting unit types, selecting network division precision and dividing a network; setting a temperature boundary condition and a composite heat dissipation coefficient; calculating the real-time heat flow rate flowing into the contact according to the measured voltage and current data at the two ends of the contact, and applying the real-time heat flow rate to the corresponding surface of the contact in a surface load mode; setting a solving type, solving time and a load step length, and performing transient thermal simulation; calculating the overall temperature field distribution cloud chart of the contact system under different large currents, and the variation curve of the highest temperature of the contact along with time;
step three: extracting the final maximum temperature value of each contact under large current, establishing a mathematical relation between the maximum temperature value of the contact and the current value of the low-voltage apparatus through curve fitting of MATLAB software, and drawing a fitting curve;
step four: the current value of the low-voltage electric appliance is measured by using an oscilloscope, and the highest temperature of the low-voltage electric appliance contact is calculated by calling the mathematical relation between the highest temperature value of the contact under the high current and the current value of the low-voltage electric appliance by using a computer.
The method for measuring the temperature rise of the contact of the low-voltage electrical appliance under the large current based on the finite element analysis, which is manufactured by the technical scheme of the invention, breaks through the limitation that the probe of the existing optical fiber temperature measurement method cannot be close to the surface of the contact and the infrared method cannot measure the real temperature of the measured object, and can measure the temperature of the contact of the low-voltage electrical appliance in real time; through finite element simulation calculation analysis, the measurement time of the temperature rise of the low-voltage electrical appliance contact is effectively shortened, and the working efficiency is greatly improved; the maximum temperature value of the low-voltage apparatus contact can be displayed in real time, and the maximum temperature rise value of the low-voltage apparatus contact can be conveniently calculated.
Drawings
FIG. 1 is a schematic flow chart of a method for measuring temperature rise of a contact of a low-voltage apparatus under high current based on finite element analysis according to the present invention;
FIG. 2 shows the voltage and current waveforms of the contacts in the 12A breaking process of the present invention;
FIG. 3 is a finite element model of the contact system of the present invention;
FIG. 4 is a graph of the maximum temperature of the 12A current of the present invention as a function of time;
FIG. 5 is a fitted curve of maximum temperature values and low voltage device current values for the contact of the present invention.
Detailed Description
The embodiments of the present invention will be described in detail below with reference to the accompanying drawings:
example 1
As shown in fig. 1, the method comprises the steps of:
the method comprises the following steps: the voltage, current data and waveform of two ends of a contact in the breaking process of the low-voltage apparatus under the working environment of overload, short circuit and large current and the arc time of the electric arc are measured by an industrial personal computer, virtual instrument LabVIEW software and a hardware circuit, for example, as shown in figure 2, the average arc time is as follows: 15.26ms
Step two: according to the measured size of the low-voltage electrical appliance contact system, establishing a physical model of the contact system in three-dimensional finite element software ANSYS; establishing a finite element model of a low-voltage electrical appliance contact system by defining material properties such as heat conductivity coefficient, resistivity, specific heat capacity, density, enthalpy and the like of each element of the contact, selecting an SOLID70 unit, selecting a network division precision of 6 and freely dividing a network, as shown in FIG. 3;
setting a temperature boundary condition as an initial temperature of 20 ℃ and a composite heat dissipation coefficient comprising convection and radiation; calculating real-time heat flow rate flowing into the contact according to the measured data of the voltage and the current at the two ends of the contact, and applying the real-time heat flow rate to the corresponding surface of the contact in the form of surface load, wherein the calculation steps of the heat flow rate are as follows:
in the formula: u-real-time voltage values at two ends of the contact in the breaking process;
i-real-time current values at two ends of the contact in the breaking process;
aαarc root spot area.
aα＝1.67×10-9I
In the formula: i-effective value of arc current.
Setting the solving type as transient, the solving time as 15.26ms and the load step length as 0.134ms, and carrying out transient thermal simulation; calculating the overall temperature field distribution cloud chart of the contact system under the large current of 12A, wherein the curve of the change of the highest temperature of the contact along with the time is shown in figure 4;
and adjusting the current value, repeating the steps, and calculating to obtain the cloud images of the overall temperature field distribution of the contact system under different large currents, wherein the curve of the change of the highest temperature of the contact along with the time is obtained.
Step three: extracting the final maximum temperature value of each contact under large current, establishing a mathematical relation between the maximum temperature value of the contact and the current value of the low-voltage apparatus through curve fitting of MATLAB software, and drawing a fitting curve, as shown in FIG. 5;
step four: the current value of the low-voltage electric appliance is measured by using an oscilloscope, and the highest temperature of the low-voltage electric appliance contact is calculated by calling the mathematical relation between the highest temperature value of the contact under the high current and the current value of the low-voltage electric appliance by using a computer.
The technical solutions described above only represent the preferred technical solutions of the present invention, and some possible modifications to some parts of the technical solutions by those skilled in the art all represent the principles of the present invention, and fall within the protection scope of the present invention.
Claims (1)
1. A method for measuring temperature rise of a contact under high current of a low-voltage apparatus based on finite element analysis is characterized by comprising the following steps:
the method comprises the following steps: measuring voltage, current data and waveforms at two ends of a contact and arcing time of an electric arc of the low-voltage apparatus in a breaking process under overload, short-circuit and large-current working environments through an industrial personal computer, virtual instrument LabVIEW software and a hardware circuit;
step two: according to the measured size of the low-voltage electrical appliance contact system, establishing a physical model of the contact system in three-dimensional finite element software ANSYS; establishing a finite element model of the low-voltage electrical appliance contact system by defining material properties, selecting unit types, selecting network division precision and dividing a network; setting a temperature boundary condition and a composite heat dissipation coefficient; calculating the real-time heat flow rate flowing into the contact according to the measured voltage and current data at the two ends of the contact, and applying the real-time heat flow rate to the corresponding surface of the contact in a surface load mode; setting a solving type, solving time and a load step length, and performing transient thermal simulation; calculating the overall temperature field distribution cloud chart of the contact system under different large currents, and the variation curve of the highest temperature of the contact along with time;
setting a temperature boundary condition as an initial temperature of 20 ℃ and a composite heat dissipation coefficient comprising convection and radiation; calculating real-time heat flow rate flowing into the contact according to the measured data of the voltage and the current at the two ends of the contact, and applying the real-time heat flow rate to the corresponding surface of the contact in the form of surface load, wherein the calculation steps of the heat flow rate are as follows:
in the formula: u-real-time voltage values at two ends of the contact in the breaking process;
i-real-time current values at two ends of the contact in the breaking process;
aαarc root spot area
aα＝1.67×10-9I
In the formula: i-effective value of arc current
Setting the solving type as transient, the solving time as 15.26ms and the load step length as 0.134ms, and carrying out transient thermal simulation; calculating the overall temperature field distribution cloud chart of the contact system under the 12A heavy current, and the variation curve of the highest temperature of the contact along with the time;
adjusting the current value, repeating the steps, and calculating to obtain the cloud pictures of the overall temperature field distribution of the contact system under different large currents and the change curve of the maximum temperature of the contact along with the time
Step three: extracting the final maximum temperature value of each contact under large current, establishing a mathematical relation between the maximum temperature value of the contact and the current value of the low-voltage apparatus through curve fitting of MATLAB software, and drawing a fitting curve;
step four: the current value of the low-voltage electric appliance is measured by using an oscilloscope, and the highest temperature of the low-voltage electric appliance contact is calculated by calling the mathematical relation between the highest temperature value of the contact under the high current and the current value of the low-voltage electric appliance by using a computer.
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| CN107729672A (en) * | 2017-10-30 | 2018-02-23 | 安徽电气工程职业技术学院 | The predictor method of time is born in a kind of silicon carbide MOSFET short circuit |
| CN108089121B (en) * | 2017-12-07 | 2020-04-24 | 温州大学苍南研究院 | Temperature equivalent test method for overload protection characteristic of miniature circuit breaker |
| CN108536906A (en) * | 2018-03-01 | 2018-09-14 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | A kind of bushing temperature field distribution method of the calculating containing connected structure |
| CN109711078B (en) * | 2018-12-29 | 2023-06-27 | 云南电网有限责任公司电力科学研究院 | Calculation method for thermal stability in short-time tolerance process of circuit breaker contact system |
| CN109901011A (en) * | 2019-02-19 | 2019-06-18 | 中国电力科学研究院有限公司 | A kind of determining fuse drop holds the method and system of coefficient |
| CN110135003A (en) * | 2019-04-16 | 2019-08-16 | 中国电力科学研究院有限公司 | A kind of method and system for assessing low-voltage breaker contact system reliability |
| CN112763903B (en) * | 2020-12-28 | 2022-03-25 | 温州大学 | Method for checking temperature rise of contact under current action |
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| 基于Ansys的不同表面形式触头的温度场仿真;刘帼巾等;《电器与能效管理技术》;20160430;第27-31页 * |
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