A device and method for detecting the charge of gas-liquid two-phase flow

Abstract

This invention belongs to the field of transformer technology, and specifically relates to a device and method for detecting the charge carried by a gas-liquid two-phase flow. The device for detecting the charge carried by a gas-liquid two-phase flow is characterized by comprising a two-phase flow charge and detection housing (3) and a current testing device (5). The two-phase flow charge and detection housing (3) includes a phase change medium inlet (31), a metal box (34), insulating material (32), several layers of metal mesh, and a phase change medium outlet (35). The current testing device (5) includes several oscilloscopes (52) and several sampling resistors (51). This device for detecting the charge carried by a gas-liquid two-phase flow enables the detection of the total charge carried by the gas-liquid two-phase flow, improves the accuracy of charge collection from the oil flow, and enables a preliminary assessment of the charge carried by bubbles of different sizes.

Description

Technical Field

[0001] This invention belongs to the field of transformer technology, and specifically relates to a device and method for detecting the charge carried by a gas-liquid two-phase flow. Background Technology

[0002] Two-phase flow is widely used in thermal power engineering, nuclear power engineering, cryogenic engineering, aerospace, and transformer technology. Broadly speaking, two-phase flow refers to the rolling of one or two substances in different states; when gas and liquid roll together, it is called gas-liquid two-phase flow. In large power transformers with forced oil circulation, the insulating oil undergoes cyclic cooling, generating positive and negative charges through friction with the transformer's solid insulation materials such as insulating paper and laminates. Simultaneously, during the boiling motion of the liquid, the interface between the bubbles and the liquid (i.e., the bubble surface) also carries a charge. This phenomenon is prevalent inside transformers, typically occurring between the transformer oil and the insulating paper, and is called oil flow charging. Electrostatic discharge caused by oil flow charging is a significant factor threatening the safe operation of large transformers in China. To accurately obtain the charge on the oil flow, a specialized detection system needs to be designed to control the oil flow rate, temperature, and voltage, and accurately measure the charge under these conditions. Therefore, accurate measurement of the charge is a crucial aspect of the detection system. Currently, domestic researchers use methods such as the circulating injection method, the flow-through method, and the filtration method to measure the tendency of oil flow to become charged.

[0003] For the two-phase flow charging problem that occurs after the phase change medium becomes charged through friction with the insulating medium in its gas-liquid two-phase state after boiling, directly using these three detection methods has the following problems: 1. The cyclic injection method can only obtain the charge generated by the friction between the two-phase flow and the insulating material, but cannot obtain the charge on the surface of the bubble; 2. Although the downflow method can collect all the charge, the device is small in size and is not suitable for two-phase flows that require a large liquid volume to reach a boiling state. 3. The filtration method directly uses insulating paper as filter paper, which is very suitable for detecting the charge of oil flow, realizing the combination of charge and measurement. However, the insulating material for two-phase flow charge is FR4 material used in printed circuit boards or epoxy, ceramic and other materials used in insulators, which cannot be processed into filter paper.

[0004] To address the above problems, this invention designs a gas-liquid two-phase flow charge detection device and method. On one hand, it measures the leakage current of insulating materials, and on the other hand, it designs a multi-layer metal mesh for charge collection to achieve accurate measurement of the charge on the oil flow. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method for detecting the charge carried by a gas-liquid two-phase flow, overcoming the shortcomings of the inapplicability of high-voltage transformer insulation materials and the low accuracy of measuring the charge carried by oil flow.

[0006] To achieve the above objectives, the present invention provides a gas-liquid two-phase flow charge detection device, comprising a two-phase flow charge and detection chamber and a current testing device. The two-phase flow charge and detection chamber includes a phase change medium inlet, a metal box, an insulating material, several layers of metal mesh, and a phase change medium outlet. The phase change medium inlet is located at the bottom of the metal box, and the phase change medium outlet is located at the top of the metal box. The several layers of metal mesh are stacked and distributed inside the metal box, with a certain distance between the layers and the mesh openings of adjacent metal meshes are staggered. The insulating material is located at the bottom of the metal box, below the bottommost metal mesh. The first and second layers of metal mesh are arranged from bottom to top with the same aperture size. The aperture size of the second layer of metal mesh is larger than that of the third layer of metal mesh. The aperture size of the third and fourth layers of metal mesh is the same. The remaining layers are arranged in the same manner. The current testing device includes several oscilloscopes and several sampling resistors. The sampling resistors are connected to the insulating material and each layer of metal mesh through grounding wires. The several oscilloscopes and the several sampling resistors are connected in parallel to measure the voltage across the sampling resistors. Furthermore, the sampling resistors are 0.1 ohms.

[0007] Furthermore, in the aforementioned gas-liquid two-phase flow charge detection device, the side length of the aperture of the first and second metal mesh layers is half the diameter of the largest bubble when the phase change medium boils, and the distance between the two layers is equal to the side length of the aperture of the first metal mesh layer; the side length of the aperture of the third and fourth metal mesh layers is one-quarter the diameter of the largest bubble when the phase change medium boils, and the distance between the two layers is equal to the side length of the aperture of the third metal mesh layer; the distance between the second and third metal mesh layers is equal to the side length of the aperture of the second metal mesh layer; the apertures of adjacent metal mesh layers are arranged alternately; the side length of the aperture of the remaining metal mesh layers decreases successively according to the principle of halving, and is arranged according to the above rules.

[0008] The metal mesh aperture is gradually halved and arranged in an alternating pattern to maximize the capture of air bubbles, thereby maximizing the capture of the charge in the air bubbles. The number of metal mesh layers is controlled by the detection results of the leakage current. That is, during the test, the leakage current of each layer of metal mesh is measured until the leakage current of the smallest mesh layer is less than 1 / 10 of the current measurement value of the first layer within 5 minutes.

[0009] Furthermore, in the above-mentioned gas-liquid two-phase flow charge detection device, the gas-liquid two-phase flow charge detection device also includes a liquid storage tank, a condenser, and a flow meter; the liquid storage tank is sequentially connected to the flow meter, the two-phase flow charge detection box, and the condenser, and the other end of the condenser is connected to the liquid storage tank to form a circulation system.

[0010] Furthermore, in the aforementioned gas-liquid two-phase flow charge detection device, a heater is provided at the bottom of the outer side of the metal box to heat the two-phase flow medium and cause it to boil.

[0011] Furthermore, in the aforementioned gas-liquid two-phase flow charge detection device, the insulating material is an epoxy resin sheet or ceramic.

[0012] Furthermore, in the aforementioned gas-liquid two-phase flow charge detection device, the plurality of metal mesh layers are formed by winding fine bare copper wires with a radius of 0.05 mm.

[0013] The present invention also provides a method for detecting the charge on a gas-liquid two-phase flow using the above-mentioned gas-liquid two-phase flow charge detection device, comprising the following steps: (1) Adjust the flow rate by the flow meter to allow the two-phase flow medium to enter the two-phase flow charged and detection box from the liquid storage tank. Turn on the heater at the bottom of the metal box to make the two-phase flow medium boil. After boiling, the two-phase flow medium is converted into a gaseous state and enters the condenser from the phase change medium outlet of the two-phase flow charged and detection box. After being condensed by the condenser, it is converted into a liquid and returns to the liquid storage tank to form a circulation injection system. (2) The charge on the insulating material and each layer of metal mesh is measured using a current testing device (oscilloscope and sampling resistor): When the two-phase flow medium boils, the friction between the two-phase flow medium and the insulating material causes the insulating material to carry a certain charge; after the two-phase flow medium boils, the bubbles generated rise continuously and pass through the metal mesh. The metal mesh captures the charge carried by the bubbles. Bubbles with larger diameters cannot pass through the first and second mesh holes and are captured by the first and second metal meshes. Bubbles with smaller diameters will pass through the mesh holes and move to the next layer. The staggered stacked metal mesh reduces the diameter of the bubbles that can pass through by half and captures smaller bubbles. The remaining bubbles move to the next layer. The metal mesh with a hole diameter side length of half that of the upper layer captures smaller bubbles. The metal meshes are stacked in sequence to reduce the hole diameter until all bubbles cannot pass through. At this time, each layer of metal mesh carries a certain charge because of the charge carried by the captured bubbles. The charge on the insulating material and the charge on each layer of metal mesh are measured using an oscilloscope and a sampling resistor. That is, the voltage across the sampling resistor is measured with an oscilloscope to obtain the voltage waveform u(t), and then divided by the resistance value to obtain the current waveform i(t).

[0014] (3) Calculate the charge on the insulating material and the charge on the entire metal mesh. The sum of the two charges is the total charge value of the two-phase current, i.e., the total charge value is... The integral is the integration of the current over time T, where T = 1 ms.

[0015] Compared with existing technologies, the present invention has the following advantages: The gas-liquid two-phase flow charge detection device provided by this invention detects the charge on the insulating material and sets up multiple layers of metal mesh in the two-phase flow charge detection box. The metal mesh is stacked alternately and the mesh aperture is gradually halved until all air bubbles cannot pass through. This device can completely capture the charge on the gas-liquid two-phase cooling medium, realize the detection of the total charge of the gas-liquid two-phase flow, improve the accuracy of charge collection of oil flow charge, and provide accurate data for studying the suppression of oil flow charge phenomenon. This avoids the occurrence of amplified sudden accidents caused by electrostatic discharge inside the transformer due to oil flow charge.

[0016] The gas-liquid two-phase flow charge detection device provided by the present invention uses metal mesh of different layers to test leakage current and simultaneously realizes a preliminary assessment of the charge of bubbles of different sizes. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the gas-liquid two-phase flow charge detection device of the present invention.

[0018] Figure 2 This is a schematic diagram of the two-phase flow charging and detection box structure of the present invention.

[0019] Figure 3 This is a top view showing the arrangement of the metal mesh of the present invention.

[0020] Figure 4 This is a schematic diagram of the current testing device of the present invention.

[0021] Figure 5 The current waveform diagrams of the first metal mesh and the second metal mesh in this embodiment of the invention are shown below.

[0022] Explanation of main reference numerals: 1-Storage tank, 2-Flow meter, 3-Two-phase flow electrified and detection box, 4-Cryotherm, 5-Current measuring device; 31-Phase change medium inlet, 32-Insulating material, 331-First layer metal mesh, 332-Second layer metal mesh, 333-Third layer metal mesh, 334-Fourth layer metal mesh, 34-Metal box, 35-Phase change medium outlet; 51-Sampling resistor, 52-Oscilloscope. Implementation

[0023] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Example

[0024] The two-phase flow medium used in this embodiment is a fluorocarbon compound, namely "fluorinated oil". First, the maximum bubble diameter when the fluorinated oil boils is measured: the bubble diameter is obtained by taking pictures. In the two-phase flow, the bubbles move faster and have stronger fluctuations, which makes it difficult to clearly reflect the bubble flow in a single image. It is difficult to distinguish the influence of the electric field on the bubble flow from a single frame image. However, by stacking, the offset characteristics of the bubble flow path can be reflected more obviously. In this embodiment, a gray-scale method is used to stack bubbles from multiple images onto a single image, highlighting the geometric dimensions and flow path characteristics of the bubble flow. This determines that the maximum radius of the bubbles after the "fluorinated oil" boils is 4mm, and the side lengths of the mesh openings in each layer are 2mm, 1mm, 0.5mm, 0.25mm, and 0.125mm. Next, the number of layers is evaluated, and the leakage current of each layer of metal mesh is measured. It is found that the leakage current of the metal mesh with a side length of 0.5mm is lower than that of the metal mesh with a side length of 2mm. Therefore, the gas-liquid two-phase flow charge detection device provided in this embodiment only needs 6 layers of metal mesh.

[0025] This embodiment provides a device for detecting the charge on a gas-liquid two-phase flow, such as... Figure 1-4As shown, it includes a liquid storage tank 1, a flow meter 2, a two-phase flow electrified and detection box 3, a current testing device 5, and a condenser 4. The liquid storage tank 1 is sequentially connected to the flow meter 2, the two-phase flow charging and detection box 3, and the condenser 4. The other end of the condenser 4 is connected to the liquid storage tank 1 to form a circulation system. The two-phase flow charging and detection box 3 is used to capture the charge in the phase change medium and test the captured charge through the current testing device 5. The two-phase flow charging and detection box 3 includes a phase change medium inlet 31, a metal box 34, several layers of metal mesh, insulating material 32, and a phase change medium outlet 35. The phase change medium inlet 31 is located at the bottom of the metal box 34, and the phase change medium outlet 35 is located at the top of the metal box 34. The several layers of metal mesh are stacked and distributed inside the metal box 34, with a certain distance between the layers, and the mesh openings of adjacent metal meshes are staggered. The insulating material 32 is located at the bottom of the metal box 34, below the bottom layer of metal mesh, and the insulating material 32 is an epoxy resin sheet or a ceramic sheet. The side length of the aperture of the first layer of metal mesh 331 and the second layer of metal mesh 332 near the insulating material 32 is 2mm, and the distance between the two layers is... The third and fourth metal mesh layers 333 and 334 have a side length of 1 mm and a spacing of 1 mm between them; the second and third metal mesh layers 332 and 333 are spaced 2 mm apart; the fifth and sixth metal mesh layers have a side length of 0.5 mm and a spacing of 0.5 mm between them; the fourth and fifth metal mesh layers are spaced 1 mm apart; the current testing device 5 is used to measure the charge on the insulating material and each metal mesh layer. The current testing device 5 includes several 0.1 ohm sampling resistors 51 and several oscilloscopes 52. The sampling resistors 51 are connected to the insulating material 32 and each metal mesh layer respectively through grounding wires; the oscilloscopes 52 are connected in parallel with the sampling resistors 51 to measure the voltage across the sampling resistors; the flow meter 2 is used to regulate the flow rate of the two-phase flow medium; a heater is installed at the bottom of the metal box 34 to heat the two-phase flow medium to make it boil. After boiling, the two-phase flow medium is converted into a gaseous state and condensed by the condenser 4 to become a liquid and return to the storage tank 1.

[0026] This embodiment also provides a method for detecting the charge on a gas-liquid two-phase flow using the above-mentioned gas-liquid two-phase flow charge detection device, comprising the following steps: (1) The flow rate is adjusted by the flow meter to make the two-phase flow medium flow out of the storage tank and enter the two-phase flow charged and detection box through the phase change medium inlet. The heater at the bottom of the metal box is turned on to make the two-phase flow medium boil. After boiling, the two-phase flow medium is converted into a gaseous state and enters the condenser from the phase change medium outlet of the two-phase flow charged and detection box. After being condensed by the condenser, it is converted into a liquid and returns to the storage tank to form a circulation injection system. (2) Detection of charge on insulating material: When the two-phase flow medium boils, the friction between the two-phase flow medium and the insulating material causes the insulating material to carry a certain charge. This charge flows through the sampling resistor connected to the insulating material. The voltage across the sampling resistor is measured with an oscilloscope to obtain the voltage waveform u0(t). Then, the voltage waveform i0(t) is obtained by dividing the resistance value.

[0027] (3) Total charge of bubbles in two-phase flow: After the two-phase flow medium boils, the bubbles generated rise continuously and pass through the metal mesh. The metal mesh captures the charge carried by the bubbles. Bubbles with larger diameters cannot pass through the first and second meshes and are captured by the first and second metal meshes. Bubbles with smaller diameters will pass through the meshes and move to the next layer. The staggered stacked metal meshes reduce the diameter of the bubbles that can pass by by half and capture even smaller bubbles. The remaining bubbles then move to the next layer. The metal mesh with a side length of half that of the upper layer captures even smaller bubbles. The metal meshes are stacked in sequence, and the aperture is reduced until the sixth metal mesh. When all bubbles cannot pass through, each metal mesh captures the charge carried by the bubbles. The charge of each metal mesh flows through the sampling resistors connected to each metal mesh. The voltage across each sampling resistor is measured with an oscilloscope to obtain the corresponding voltage waveforms u1(t)~u6(t). Then, the voltage waveforms are divided by the resistance value to obtain the corresponding current waveforms i1(t)~i6(t).

[0028] (4) Calculate the charge on the insulating material and the total charge on the two-phase flow bubbles (the charge on the entire metal mesh). The sum of the two charges is the total charge on the two-phase flow, i.e., the total charge is _____. The integral is the integration of the current over time T, where T = 1 ms.

[0029] During measurement, a value is recorded every 1 millisecond. Generally, the value is considered stable when the deviation does not exceed 20% for three consecutive milliseconds. Then, the average of the three measurement results is taken. Through measurement, it can be seen that the oscilloscope can hardly display the voltage waveform of the sampling resistors of the insulating material and the third to sixth layers of metal mesh. This indicates that the charge on the insulating material and the charge on the third to sixth layers of metal mesh are very small, almost zero. Therefore, the charge on this part can be ignored. The sum of the charge on the first layer of metal mesh and the charge on the second layer of metal mesh is the total charge of the two-phase current.

[0030] Based on the voltage waveforms of the first and second metal mesh layers, the current waveforms of the first and second metal mesh layers are obtained as follows: Figure 5 .Depend on Figure 5 The total charge of the first and second metal mesh layers was calculated to be 2.06 μC. Therefore, the total charge of the two-phase flow was 2.06 μC, which means the charge within 1 ms was 2.06 μC.

[0031] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A device for detecting the charge carried by a gas-liquid two-phase flow, characterized in that, It includes a two-phase flow charging and detection box (3) and a current testing device (5). The two-phase flow charging and detection box (3) includes a phase change medium inlet (31), a metal box (34), an insulating material (32), several layers of metal mesh, and a phase change medium outlet (35). A heater is provided at the bottom of the metal box (34). The phase change medium inlet (31) is located at the bottom of the metal box (34), the phase change medium outlet (35) is located at the top of the metal box (34), the several layers of metal mesh are stacked and distributed in the metal box (34) with a certain distance between the layers and the mesh holes of adjacent metal mesh are staggered; the insulating material (32) is located at the bottom of the metal box (34) and below the bottommost metal mesh. The first layer of metal mesh (331) and the second layer of metal mesh (332) are arranged from bottom to top with the same aperture. The aperture of the second layer of metal mesh (332) is larger than that of the third layer of metal mesh (333). The apertures of the third layer of metal mesh (333) and the fourth layer of metal mesh (334) are the same. The remaining layers are arranged in the same manner as described above. The current testing device (5) includes several oscilloscopes (52) and several sampling resistors (51). The several sampling resistors (51) are connected to the insulating material (32) and each layer of metal mesh through grounding wires respectively. The oscilloscopes (52) and the sampling resistors (51) are connected in parallel.

2. The gas-liquid two-phase flow charge detection device according to claim 1, characterized in that, The side length of the aperture of the first layer metal mesh (331) and the second layer metal mesh (332) is half the diameter of the maximum bubble when the phase change medium boils, and the distance between the two layers is equal to the side length of the aperture of the first layer metal mesh (331); the side length of the aperture of the third layer metal mesh (333) and the fourth layer metal mesh (334) is one-quarter the diameter of the maximum bubble when the phase change medium boils, and the distance between the two layers is equal to the side length of the aperture of the third layer metal mesh (333); the distance between the second layer metal mesh (332) and the third layer metal mesh (333) is equal to the side length of the aperture of the second layer metal mesh (332); the side length of the aperture of the remaining layers of metal mesh decreases by half each time, and is arranged according to the above rules.

3. The gas-liquid two-phase flow charge detection device according to claim 1, characterized in that, It also includes a liquid storage tank (1), a condenser (4), and a flow meter (2); the liquid storage tank (1), the flow meter (2), the two-phase flow electrified and detection box (3), and the condenser (4) are connected in sequence, and the other end of the condenser (4) is connected to the liquid storage tank (1) to form a circulation system.

4. The gas-liquid two-phase flow charge detection device according to claim 1, characterized in that, The insulating material (32) is an epoxy resin sheet or ceramic.

5. The gas-liquid two-phase flow charge detection device according to claim 1, characterized in that, The metal mesh is made of fine bare copper wire with a radius of 0.05 mm.

6. The gas-liquid two-phase flow charge detection device according to claim 1, characterized in that, The sampling resistor (51) is a 0.1 ohm sampling resistor.

7. A method for detecting the charge on a gas-liquid two-phase flow, characterized in that, The detection is performed using the gas-liquid two-phase flow charge detection device as described in any one of claims 1 to 6, comprising the following steps: (1) The two-phase flow medium enters the two-phase flow charging and detection box from the phase change medium inlet (31). The bottom heater of the metal box (34) is opened to make the two-phase flow medium boil. When the two-phase flow medium boils, the friction between the two-phase flow medium and the insulating material causes the insulating material to carry a certain charge. After the two-phase flow medium boils, the bubbles generated rise continuously and pass through the metal mesh. The metal mesh captures the charge carried by the bubbles layer by layer. (2) Use a current testing device to detect the charge on the insulating material and the charge on each layer of metal mesh; (3) The sum of the charge on the insulating material and the charge on the entire metal mesh is the total charge on the two-phase flow.

8. The method for detecting the charge on a gas-liquid two-phase flow according to claim 7, characterized in that, The two-phase flow medium enters the two-phase flow charged and detection box (3) from the storage tank (1) by adjusting the flow rate through the flow meter (2). After boiling, the two-phase flow medium is converted into a gaseous state and enters the condenser (4) from the phase change medium outlet (35). After being condensed by the condenser (4), it is converted into a liquid and returns to the storage tank (1), forming a circulating injection system.

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