A method, medium and system for testing heat generation of capacitor

Abstract

The present invention discloses a method, medium and system for testing the heat generation of a capacitor. The method comprises: dividing a first grid on each surface of the shell of the capacitor; setting an envelope surface that envelops the capacitor on the periphery of the shell of the capacitor; dividing a second grid on the envelope surface; when the capacitor is in a thermal equilibrium state, collecting the first temperature of each node of the first grid and the second temperature of each node of the second grid; calculating the average heat generation temperature of each first grid according to the first temperature of each node of each first grid; calculating the average heat generation temperature of the envelope surface according to each second temperature; calculating the heat generation of the capacitor according to the average heat generation temperature of each first grid and the average heat generation temperature of the envelope surface. The present invention can realize the loss measurement of power capacitors under high-voltage harmonic loads, and the measurement results are reliable and accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of capacitors, and in particular to a method, a medium and a system for testing the heat generation of a capacitor. Background Art

[0002] High-voltage oil-immersed capacitors are the main reactive power compensation equipment in the power system, and their loss is of great significance to the performance, life, and safe operation of the equipment. Since the impedance of the capacitor decreases with the increase of frequency, and the impedance of the test circuit increases with the increase of frequency, the test circuit will have a great impact on the loss test at high frequencies, resulting in unreliable test results. Summary of the invention

[0003] The embodiments of the present invention provide a method, a medium and a system for testing the heat generation of a capacitor, so as to solve the problem that the test results of the heat generation of a capacitor under high frequency in the prior art are unreliable.

[0004] In a first aspect, a method for testing heat generation of a capacitor is provided, comprising:

[0005] Divide a first grid on each surface of the capacitor housing;

[0006] An envelope surface enveloping the capacitor is arranged at the periphery of the shell of the capacitor, wherein the distance between the envelope surface and the corresponding surface of the shell of the capacitor is a first preset distance;

[0007] Dividing a second grid on the envelope surface;

[0008] When the capacitor is in a thermal equilibrium state, collecting a first temperature of each node of the first grid and a second temperature of each node of the second grid;

[0009] Calculate the average heating temperature of each of the first grids according to the first temperature of each node of each of the first grids;

[0010] Calculate the average heating temperature of the envelope surface according to each of the second temperatures;

[0011] The heat generated by the capacitor is calculated according to the average heat generation temperature of each of the first grids and the average heat generation temperature of the envelope surface.

[0012] In a second aspect, a computer-readable storage medium is provided, on which computer program instructions are stored; when the computer program instructions are executed by a processor, the method for testing the heat generation of a capacitor as described in the embodiment of the first aspect above is implemented.

[0013] In a third aspect, a capacitor heat generation testing system is provided, comprising: a computer-readable storage medium as described in the above-mentioned second aspect embodiment.

[0014] In this way, the embodiment of the present invention can realize the loss measurement of the power capacitor under the high voltage harmonic load, and the measurement result is reliable and accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0016] Figure 1 is a flow chart of a method for testing the heat generation of a capacitor according to an embodiment of the present invention;

[0017] Figure 2 2. It is a schematic diagram of the principle of testing the heat generation of a capacitor by enveloping a closed curve according to an embodiment of the present invention;

[0018] Figure 3 1 is a schematic diagram of the division of the first grid of a certain type of capacitor in an embodiment of the present invention, wherein (a) corresponds to the discharge resistor, (b) corresponds to the first connection row, and (c) corresponds to the second connection row;

[0019] Figure 4 is a schematic diagram of a first grid according to an embodiment of the present invention;

[0020] Figure 5 It is a schematic diagram of the curve of the integral area correction factor changing with the capacitor unit height. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] The embodiment of the present invention discloses a method for testing the heat generation of a capacitor, which is particularly suitable for testing the heat generation of a filter capacitor under high voltage harmonic load.

[0023] In order to obtain the heat generated by the capacitor more accurately and reliably, the embodiment of the present invention performs test calculations based on Fourier's law of heat conduction. Specifically, the heat change inside a closed surface within the time dt is:

[0024]

[0025] in, represents the temperature gradient, k represents the equivalent heat conductivity coefficient of the air layer, The normal direction of the closed surface micro-area element is outward, that is, the total heat generation power within a closed surface is proportional to the temperature gradient on the closed surface. Therefore, the temperature gradient of the closed surface surrounding the capacitor can be integrated to obtain the total heat generation of the capacitor. Specifically, Figure 2 As shown, when the system is in thermal equilibrium, the integral of the product of the temperature gradient and the thermal conductivity on any closed surface containing the capacitor is equal to the heat generation power of the capacitor.

[0026] In actual situations, the heat generation power of the capacitor is unevenly distributed in space. At the same time, it is impossible to directly measure the temperature gradient on both sides of a continuous surface. Therefore, the following method can be used to achieve equivalent results:

[0027] Divide the grid on the shell of the capacitor and measure the temperature of the grid nodes. The differential form of the Fourier heat conduction formula is as follows:

[0028]

[0029] Among them, A is the cross-sectional area of ​​the path between the two points. Generally, the inside of the capacitor is filled with thermal oil, and the shell of the capacitor is made of stainless steel, and the thermal conductivity coefficient is very large. Therefore, when the capacitor is in thermal equilibrium, the temperature of each part of the shell of the capacitor remains unchanged, and the temperature gradient is small, so the average value method can be used to obtain the temperature distribution of the shell surface of the capacitor.

[0030] In order to calculate the temperature gradient at the curved surface of the capacitor shell, it is also necessary to obtain the temperature of another closed surface that does not intersect the shell. The air temperature can be measured at a certain distance from the surface of the capacitor shell to obtain the temperature of the other closed surface.

[0031] The temperature gradient distribution from the capacitor shell to another temperature measuring surface in space is calculated based on the temperature distribution of the two closed surfaces and the equivalent thermal conductivity coefficient of the air layer. The product of the temperature gradient near the capacitor shell and the equivalent thermal conductivity coefficient of the air layer at this location is integrated on the spatial envelope surface at the gradient calculation position to calculate the heating power of the capacitor, which is the loss of the capacitor.

[0032] During the actual test, the capacitor can be placed in the center of the test box. The size of the test box can be determined according to the size of the capacitor. For example, the size of the inner wall of the test box can be 2m×2m×3m~3m×3m×3.5m. The inside of the test box is a non-ventilated environment. After the capacitor is placed in the test, it can be left to stand for 24 hours before testing.

[0033] Based on the above principles, Figure 1 As shown, the method comprises the following steps:

[0034] Step S1: Divide a first grid on each surface of a capacitor housing.

[0035] The purpose of dividing the first grid is to set thermocouples at the nodes of the first grid to measure the temperature of each node. It should be understood that the sizes of the first grids on different surfaces of the capacitor housing can be different or the same. The shape of the first grid is not limited and can be a square, a rectangle, a quadrilateral, etc. A square grid is used for illustration in the embodiment of the present invention.

[0036] In order to reduce calculation errors, the temperature extreme point between the two nodes used for temperature measurement should be avoided as much as possible. Therefore, when dividing the first grid, the node position used for temperature measurement is determined according to the arrangement of the main heating components inside the capacitor. The main heating components inside the capacitor are the discharge resistor and the connection row. Therefore, when dividing the first grid, the surface of the capacitor shell corresponding to these heating components should be divided according to the position of these heating components. For example, in a specific embodiment, Figure 3 As shown, a certain type of capacitor is provided with a discharge resistor 1 on a wider surface of a core 4 of the capacitor, a first connection row 2 is provided on another wider surface, and a second connection row 3 is provided on a narrower surface.

[0037] Theoretically, the denser the nodes used for temperature measurement, the more accurate the measurement results, but the requirements for the measurement equipment are higher, which increases the test cost. The results of multiple experiments show that when the distance between adjacent nodes is not greater than the fifth preset distance, continuing to increase the density of nodes has little effect on the measurement results. Therefore, preferably, when dividing the first grid, the distance between adjacent nodes is set to be no greater than the fifth preset distance, whether it is the surface of the shell of the capacitor corresponding to the heating device or not corresponding to the heating device. For example, the fifth preset distance is 10cm.

[0038] According to the arrangement of the main heating components inside the capacitor, this step includes the following three situations:

[0039] The first type: the surface of the capacitor shell corresponds to the surface of the capacitor core provided with the discharge resistor.

[0040] (1) If the surface of the capacitor shell corresponds to the surface of the capacitor core provided with the discharge resistor, a first position point on the surface of the capacitor shell corresponding to each discharge resistor and the midpoint of the distance between two adjacent discharge resistors is obtained.

[0041] (2) Dividing the surface of the capacitor shell into a first grid so that the first position point and the vertices of the surface of the capacitor shell are located on the nodes of the first grid.

[0042] For example, Figure 3 As shown in (a), a discharge resistor 1 is provided on a wider surface of the core 4 of a certain type of capacitor, and the first position point of the surface of the capacitor shell 5 corresponding to the discharge resistor 1 and the first position point corresponding to the midpoint of the distance between adjacent discharge resistors are used as nodes of the first grid, and thermocouples 6 are placed on these nodes for temperature measurement. In addition, thermocouples 6 are also placed at the four vertices of the surface of the capacitor shell 5 for temperature measurement. Preferably, the distance between adjacent nodes of the first grid is not greater than the aforementioned fifth preset distance.

[0043] The second type: the surface of the capacitor shell corresponds to the surface of the capacitor core provided with the connection row.

[0044] (1) If the surface of the capacitor shell corresponds to the surface of the capacitor core provided with the connection row, a reference point is determined on the connection row at every second preset distance.

[0045] (2) Obtain a second position point on the surface of the capacitor housing corresponding to each reference point.

[0046] (3) Dividing the surface of the capacitor shell into a first grid so that the second position point and the vertices of the surface of the capacitor shell are located on the nodes of the first grid.

[0047] For example, Figure 3 As shown in (b), a wider surface of the core 4 of a certain type of capacitor is provided with a first connection row 2, and a reference point is determined on the first connection row 2 at every second preset distance. Preferably, the second preset distance is not greater than the aforementioned fifth preset distance. The second position points of the corresponding reference points on the surface of the shell 5 of the capacitor corresponding to the wider surface are used as nodes of the first grid, and thermocouples 6 are placed on these nodes for temperature measurement. In addition, thermocouples 6 are also placed at the four vertices of the surface of the shell 5 of the capacitor for temperature measurement. Preferably, the distance between adjacent nodes of the first grid is not greater than the aforementioned fifth preset distance.

[0048] Similarly, if Figure 3 As shown in (c), a narrower surface of the core 4 of a certain type of capacitor is provided with a second connection row 3, and the first grid is also divided like the wider surface mentioned above.

[0049] The third type: the surface of the capacitor shell does not correspond to the surface of the capacitor core on which the discharge resistor and the connection row are arranged.

[0050] If the surface of the capacitor shell does not correspond to the surface of the capacitor core on which the discharge resistor and the connection row are provided, a first grid is divided on the surface of the capacitor shell so that the distance between adjacent nodes of the first grid is a third preset distance and the vertices of the surface of the capacitor shell are located on the nodes of the first grid.

[0051] In this case, that is, the surface of the capacitor core corresponding to the surface of the capacitor shell has no heating device, it is only necessary to ensure that the vertices of the surface of the capacitor shell are located on the nodes of the first grid. The third preset distance can be selected based on experience and is generally not greater than the fifth preset distance.

[0052] Step S2: setting an envelope surface of the capacitor on the periphery of the capacitor shell.

[0053] Generally, the envelope surface completely envelopes the entire capacitor. The distance between the envelope surface and the corresponding surface of the capacitor housing is a first preset distance.

[0054] The first preset distance can be determined according to actual conditions. Specifically, due to the diffusion effect of air, the greater the distance between the envelope surface and the corresponding surface of the capacitor shell, the smaller the temperature change on the envelope surface. After testing, when the distance between the envelope surface and the corresponding surface of the capacitor shell is 0.1m, the temperature change at each location of the envelope surface is less than 2K, and the influence of the temperature distribution error of the envelope surface obtained by measuring the temperature and linear difference on the final calculation result can be ignored. Therefore, the distance between the envelope surface and the corresponding surface of the capacitor shell is not less than 0.1m, but if the distance is too large, it will affect the measurement accuracy, so it is usually set to 0.1m, that is, the first preset distance is 0.1m.

[0055] In actual testing, the capacitor is usually placed on the bottom of the test box, and the temperature at the bottom of the capacitor is not easy to measure. Therefore, the capacitor can be placed on an insulating foam board to prevent heat from diffusing from the bottom and reduce measurement errors. In this case, since the heat at the bottom is difficult to diffuse, the envelope surface can only envelop the other surfaces of the capacitor except the bottom surface, that is, the envelope surface is equivalent to a cover.

[0056] Step S3: Divide the second grid on the envelope surface.

[0057] The distance between adjacent nodes of the second grid is the fourth preset distance. As mentioned above, preferably, the fourth preset distance is not greater than the fifth preset distance. The nodes of the second grid are used to set the thermocouple to measure the temperature.

[0058] For each node of each second grid, the distance between the aforementioned envelope surface and the corresponding surface of the capacitor housing may be specifically the distance between each node of each second grid and the corresponding surface of the capacitor housing.

[0059] The shape of the second grid is not limited, and may be a square, a rectangle, a quadrilateral, etc. In the embodiment of the present invention, a square grid is used for illustration.

[0060] Step S4: When the capacitor is in a thermal equilibrium state, a first temperature of each node of the first grid and a second temperature of each node of the second grid are collected.

[0061] Specifically, during the test, the test voltage and the specified harmonic current are applied to the capacitor for testing. When the temperature change values ​​of the first temperature and the second temperature do not exceed the preset temperature within the preset time, the capacitor is in thermal equilibrium. The preset time and the preset temperature can be selected based on experience. For example, the preset time is 6h and the preset temperature is 1K. The first temperature and the second temperature are collected by thermocouples set at corresponding nodes.

[0062] Step S5: Calculate the average heating temperature of each first grid according to the first temperature of each node of each first grid.

[0063] Specifically, the calculation formula for the average heating temperature of the first grid is:

[0064]

[0065] Among them, T i represents the average heating temperature of the first grid i, T i1 ~T i4 Respectively represent the first temperatures of the four nodes of the first mesh i.

[0066] For example, Figure 4 As shown, the shell of the capacitor is divided into N first grids, with areas of S1 to S2 respectively. N , the average heating temperature of each first grid is the average temperature of the four nodes P(i,j) surrounding the part. For example, the average heating temperature of the first grid with area S1 in the figure is

[0067] Step S6: Calculate the average heating temperature of the envelope surface according to each second temperature.

[0068] Specifically, the calculation formula for the average heating temperature of the envelope surface is:

[0069]

[0070] in, Indicates the average heating temperature of the envelope surface, T 2j represents the second temperature of the node j of the second grid, and M represents the total number of nodes j of the second grid.

[0071] Step S7: Calculate the heat generated by the capacitor according to the average heat generation temperature of each first grid and the average heat generation temperature of the envelope surface.

[0072] Specifically, the calculation formula for the heat generated by the capacitor is:

[0073]

[0074] Among them, P represents the heat generated by the capacitor, k represents the equivalent thermal conductivity of the air layer, r represents the integral area correction factor, S i represents the area of ​​the first grid i, D represents the first preset distance, and N represents the number of the first grids.

[0075] The integral area correction coefficient r is related to the height H of the capacitor and the distance D (first preset distance) from the node of the second grid of the envelope surface to the corresponding surface of the capacitor shell. For example, when the distance D from the node of the second grid of the envelope surface to the corresponding surface of the capacitor shell is 0.1m and 0.2m, the integral area correction coefficient r changes with the capacitor unit height H as shown in the following curve: Figure 5 As shown. This change correspondence can be summarized as a data table. Therefore, in practical application, the integral area correction coefficient r can be obtained by looking up the table according to the height H of the capacitor and the distance D from the node of the second grid of the envelope surface to the corresponding surface of the capacitor shell.

[0076] The above method can more accurately obtain the heat generated by the capacitor.

[0077] The embodiment of the present invention further discloses a computer-readable storage medium, on which computer program instructions are stored; when the computer program instructions are executed by a processor, the method for testing the heat generation of a capacitor as described in the above embodiment is implemented.

[0078] The embodiment of the present invention further discloses a capacitor heat generation test system, comprising: a computer-readable storage medium as described in the above embodiment.

[0079] In summary, the embodiments of the present invention can achieve loss measurement of power capacitors under high voltage harmonic loads, and the measurement results are reliable and accurate.

[0080] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for testing the heat generation of a capacitor, characterized in that: include: Divide a first grid on each surface of the capacitor housing; An envelope surface enveloping the capacitor is arranged at the periphery of the shell of the capacitor, wherein the distance between the envelope surface and the corresponding surface of the shell of the capacitor is a first preset distance; Dividing a second grid on the envelope surface; When the capacitor is in a thermal equilibrium state, collecting a first temperature of each node of the first grid and a second temperature of each node of the second grid; Calculate the average heating temperature of each of the first grids according to the first temperature of each node of each of the first grids; Calculate the average heating temperature of the envelope surface according to each of the second temperatures; The heat generated by the capacitor is calculated according to the average heat generation temperature of each of the first grids and the average heat generation temperature of the envelope surface.

2. The method for testing the heat generation of a capacitor according to claim 1, characterized in that: The step of dividing the first grid on each surface of the capacitor housing comprises: If the surface of the shell of the capacitor corresponds to the surface of the core of the capacitor provided with the discharge resistor, then obtaining a first position point on the surface of the shell of the capacitor corresponding to each discharge resistor and a midpoint of a distance between two adjacent discharge resistors; A first grid is divided on the surface of the shell of the capacitor so that the first position point and the vertices of the surface of the shell of the capacitor are located on nodes of the first grid.

3. The method for testing the heat generation of a capacitor according to claim 1, characterized in that: The step of dividing the first grid on each surface of the capacitor housing comprises: If the surface of the shell of the capacitor corresponds to the surface of the core of the capacitor provided with the connection row, a reference point is determined on the connection row at every second preset distance; Acquire a second position point on the surface of the capacitor housing corresponding to each of the reference points; A first grid is divided on the surface of the shell of the capacitor so that the second position point and the vertices of the surface of the shell of the capacitor are located on the nodes of the first grid.

4. The method for testing the heat generation of a capacitor according to claim 1, characterized in that: The step of dividing the first grid on each surface of the capacitor housing comprises: If the surface of the shell of the capacitor does not correspond to the surface of the core of the capacitor on which the discharge resistor and the connection row are provided, a first grid is divided on the surface of the shell of the capacitor so that the distance between adjacent nodes of the first grid is a third preset distance and the vertices of the surface of the shell of the capacitor are located on the nodes of the first grid.

5. The method for testing the heat generation of a capacitor according to claim 1, characterized in that: The distance between adjacent nodes of the second grid is a fourth preset distance.

6. The method for testing the heat generation of a capacitor according to claim 1, characterized in that: When the temperature change values ​​of the first temperature and the second temperature do not exceed the preset temperature within the preset time, the capacitor is in a thermal equilibrium state.

7. The method for testing the heat generation of a capacitor according to claim 1, characterized in that: The calculation formula for the average heating temperature of the first grid is: Among them, T i represents the average heating temperature of the first grid i, T i1 ~T i4 Respectively represent the first temperatures of four nodes of the first grid i; The calculation formula for the average heating temperature of the envelope surface is: in, represents the average heating temperature of the envelope surface, T 2j represents the second temperature of the node j of the second grid, and M represents the total number of nodes j of the second grid.

8. The method for testing the heat generation of a capacitor according to claim 7, characterized in that: The calculation formula for the heat generation of the capacitor is: Wherein, P represents the heat generated by the capacitor, k represents the equivalent thermal conductivity of the air layer, r represents the integral area correction coefficient, S i represents the area of ​​the first grid i, D represents the first preset distance, and N represents the number of first grids.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer program instructions; when the computer program instructions are executed by a processor, the method for testing the heat generation of a capacitor according to any one of claims 1 to 8 is implemented.

10. A capacitor heat generation test system, characterized in that: include: The computer readable storage medium of claim 9.

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