Measurement system and method for surface conductance of anisotropic material at different micro-water content

Abstract

The application discloses a kind of anisotropic material surface conductance measuring system and method under different micro water content, belong to conductivity measurement technical field;The system includes signal acquisition control unit and three electrode cavity;Three electrode cavity is electrically connected with signal acquisition control unit;Three electrode cavity includes chamber and the cover plate connected at chamber top;Chamber side is provided with gas inlet and outlet, gas inlet and outlet are connected with trace liquid water injection device, SF6 gas cylinder, vacuum pump and micro water detector respectively by gas control loop;Heater, pedestal and guard electrode are sequentially arranged from bottom to top in chamber;Epoxy glue immersion paper sample is placed on guard electrode, and fixing part is arranged on epoxy glue immersion paper sample;Measuring electrode and high voltage electrode are arranged in parallel in fixing part;The high voltage electrode is at least provided with two, and is located at the two sides of measuring electrode respectively.The application can effectively separate and accurately measure the anisotropic surface conductivity of sample along epoxy-paper interface and through epoxy-paper interface.

Description

Technical Field

[0001] This invention belongs to the field of electrical conductivity measurement technology, and relates to a measurement system and method for the surface electrical conductivity of anisotropic materials under different micro-water contents. Background Technology

[0002] With the rapid development of ultra-high voltage direct current (UHVDC) transmission technology, the DC bushings on the valve side of converter transformers, as key insulation equipment in the system, face severe challenges to their long-term operational reliability. Epoxy-impregnated paper (RIP) material, due to its excellent electrical and mechanical properties, has become the dominant material for modern HVDC bushing cores. This material is formed by fully impregnating and curing epoxy resin after winding multiple layers of corrugated insulating paper around the central conductor, creating a layered structure where epoxy resin and insulating paper alternate along the radial direction, resulting in significant anisotropy in its electrical properties. When this structure extends to the surface of the epoxy-impregnated paper core, the carrier migration paths and interfacial resistances differ along different directions (e.g., along the direction of the insulating paper layers and perpendicular to the direction through the insulating paper layers) within the thin layer of the material surface, leading to anisotropic differences in the surface conductivity characteristics of the material.

[0003] Surface conductivity is a key parameter for evaluating the surface flashover performance, charge accumulation and dissipation behavior of insulating materials, directly affecting the insulation stability of bushings under extreme electric fields and complex environments (such as high temperature and moisture adhesion). Notably, the surface conductivity of epoxy-impregnated paper materials is extremely sensitive to the trace moisture content in their surrounding gas environment. The adsorption of even trace amounts of moisture significantly alters the charge transport characteristics of the material surface, thus affecting the overall electric field distribution and long-term insulation performance of the bushing. Therefore, accurately and in-situ measuring the anisotropic surface conductivity of epoxy-impregnated paper materials under simulated actual operating conditions (different moisture contents, different temperatures, and DC high voltage) is of paramount importance for material development, insulation design optimization, and equipment operation status assessment.

[0004] Currently, standard methods for measuring the surface and volume resistivity of solid insulating materials, such as the ring-shaped three-electrode system specified in the national standard GB / T 31838.2-2019 "Dielectric and resistive properties of solid insulating materials - Part 2: Resistive properties (DC method) - Volume resistivity and volume resistivity," are generally applicable to homogeneous materials. However, for anisotropic materials with significant layered structures, such as epoxy-impregnated paper, the standard ring electrode forms a 360° circumferential conductive channel between the measuring electrode and the high-voltage electrode when measuring surface conductivity. Within this channel, the current path structure differs at different angular positions: at some positions, the current primarily migrates along the epoxy-paper interface; while at others, the current needs to pass through the epoxy-paper interface. Therefore, the traditional method yields an indistinguishable average conductivity value that mixes the two different conductivity mechanisms of "along the interface" and "through the interface," failing to effectively separate and accurately characterize the complex anisotropic surface conductivity caused by the material's intrinsic layered structure. Furthermore, existing technologies typically conduct measurements in atmospheric or simple gas environments, lacking an integrated device and method for systematically testing the surface conductivity of anisotropic insulating materials such as epoxy-impregnated paper under controlled temperature and precisely controllable gas moisture content conditions. This makes it difficult to simulate the actual operating conditions of SF6 gas moisture content changes inside high-voltage DC bushings during long-term operation under laboratory measurement conditions, creating a data gap between material evaluation and engineering applications. Designers lack crucial data to accurately simulate the charge accumulation characteristics at the bushing's gas-solid interface and assess its operational risks.

[0005] In summary, there is an urgent need to develop a dedicated measurement system for anisotropic surfaces to achieve accurate, reliable, and repeatable measurements of the anisotropic surface conductivity of epoxy-impregnated paper materials used in UHV valve-side DC bushings under different temperatures and gas moisture content conditions. This would provide technical support and data for material development, bushing insulation design, and condition assessment. Summary of the Invention

[0006] The purpose of this invention is to provide a measurement system and method for the surface conductivity of anisotropic materials with different micro-water contents, so as to solve the technical problem that the measurement results of the prior art contain two current components, one along the epoxy-paper interface and the other through the epoxy-paper interface, which are difficult to distinguish effectively.

[0007] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a measurement system for the surface conductivity of anisotropic materials under different trace moisture contents, comprising a signal acquisition and control unit and a three-electrode cavity; the three-electrode cavity is electrically connected to the signal acquisition and control unit; the three-electrode cavity includes a chamber and a cover plate connected to the top of the chamber; a gas inlet and outlet are provided on one side of the chamber, and the gas inlet and outlet are respectively connected to a trace liquid water injection device, an SF6 gas cylinder, a vacuum pump and a trace moisture detector through a gas control circuit; a heater, a base and a protective electrode are arranged sequentially from bottom to top in the chamber; an epoxy resin impregnated paper sample is placed on the protective electrode, and a fixing member is provided on the epoxy resin impregnated paper sample; a measuring electrode and a high-voltage electrode are arranged in parallel in the fixing member; at least two high-voltage electrodes are provided, respectively located on both sides of the measuring electrode.

[0008] Furthermore, the signal acquisition and control unit includes a computer, a picoammeter, a high-voltage DC power supply, and a temperature controller; the temperature controller is connected to the heater; the picoammeter and the high-voltage DC power supply are electrically connected to the cover plate; and the computer is electrically connected to the picoammeter.

[0009] Furthermore, the cover plate is equipped with a high-voltage inlet insulator, a multi-port line vacuum adapter, and a BNC single-port line vacuum adapter; the high-voltage inlet insulator is connected to a high-voltage DC power supply; the multi-port line vacuum adapter is used to connect a temperature controller and a heater; and the BNC single-port line vacuum adapter is connected to a picoammeter.

[0010] Furthermore, the bottom of the cover plate is connected to the base via several lifting rods; several temperature sensors are installed on the base, and the temperature sensors are electrically connected to a computer.

[0011] Furthermore, the micro-liquid water injection device is connected to the gas control circuit through a two-way valve chamber; the micro-liquid water injection device includes a micro-sampler, a three-way valve chamber, and a transparent glass tube; the lower port of the three-way valve chamber is connected to the glass tube; the micro-sampler can enter the glass tube from the upper port of the three-way valve chamber; the side port of the three-way valve chamber is connected to the two-way valve chamber.

[0012] Furthermore, a sealing ring is provided at the connection between the lower port of the three-way valve cavity and the glass tube; a nut cap is installed at the upper port of the three-way valve cavity, a through hole is opened in the middle of the nut cap, and a silicone rubber disc is provided between the nut cap and the upper port of the three-way valve cavity.

[0013] Furthermore, the two-way valve chamber is connected to the side port of the three-way valve chamber and the gas control circuit via PU gas pipes.

[0014] Furthermore, a pressure gauge and a cavity valve are installed at the gas inlet and outlet; a gas valve, a first valve, a second valve, a third valve, a fourth valve, and a fifth valve are also installed on the gas control circuit; the gas valve is located near the SF6 gas cylinder; the first valve is located on the connecting trunk line between the micro-liquid water injection device and the SF6 gas cylinder; the second valve is located near the vacuum pump; the third valve is located near the micro-water detector; the fourth valve is located near the pressure gauge; and the fifth valve is located near the micro-liquid water injection device.

[0015] Secondly, the present invention provides a method for measuring the surface conductivity of anisotropic materials under different micro-water contents, based on the above-mentioned system for measuring the surface conductivity of anisotropic materials under different micro-water contents, comprising the following steps: Place the epoxy resin impregnated paper sample in the three-electrode cavity, and adjust the orientation of the parallel conductive channels between the measuring electrode and the high voltage electrode so that they are at a predetermined angle to the layered structure on the surface of the epoxy resin impregnated paper sample. A vacuum pump is used to evacuate the three-electrode chamber and the gas control circuit, and then the gas is washed through an SF6 cylinder. A measured amount of deionized water is injected into the gas control circuit through a micro-liquid water injection device, causing the deionized water to evaporate into water vapor and diffuse into the three-electrode cavity; SF6 gas is introduced into the three-electrode cavity to a preset pressure; The sample was left to stand to allow water vapor and SF6 gas to mix thoroughly and be adsorbed onto the surface of the epoxy resin-impregnated paper sample. Then, a micro-moisture detector was used to detect and record the micro-moisture content of the gas in the chamber. The three-electrode cavity is heated by a signal acquisition and control unit, a preset voltage is applied, and a current signal is acquired. The conductivity is calculated based on the recorded current and voltage values.

[0016] Furthermore, the step of heating the three-electrode cavity and applying a preset voltage through the signal acquisition and control unit to acquire the current signal specifically includes: The temperature controller heats the interior of the three-electrode cavity to a preset temperature and maintains it stable via a heater. A preset voltage is applied to the high-voltage electrode using a high-voltage DC power supply. At the same time, the leakage current collected by the measuring electrode is measured using a picoammeter, and the current value after stabilization is recorded.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a measurement system and method for the surface conductivity of anisotropic materials under different trace moisture contents. For layered samples such as epoxy-impregnated paper, a parallel three-electrode structure is employed. While maintaining the original three-electrode configuration to eliminate the influence of the sample bulk current, the anisotropic surface conductivity along and through the epoxy-paper interface can be effectively separated and accurately measured by adjusting the angle between the parallel conductive channels and the layered structure of the sample surface. Furthermore, in previous experiments measuring the surface conductivity of samples under SF6 gas conditions, high-purity SF6 gas was usually directly introduced from SF6 cylinders, resulting in low trace moisture content (around 20 ppm). However, in actual operating conditions, the SF6 gas content in the casing equipment is typically around 100 ppm, and can reach 200-300 ppm in some cases. Therefore, this invention designs a simple and efficient gas control loop and its operating steps. Combined with a trace liquid water injection device, a vacuum pump, and a trace moisture detector, it can effectively improve, control, and detect the trace moisture content in high-purity SF6 gas. Meanwhile, the internal space formed by the gas control loop and the three-electrode cavity can remain sealed from the outside world throughout the entire experimental process, fully simulating the actual working environment and reducing external interference to the experiment. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A top view of the surface conductivity measurement of a ring-shaped three-electrode structure in the prior art; Figure 2 This invention relates to a parallel three-electrode surface conductivity measurement structure; Figure 3 This is a schematic diagram of the measuring electrode and high-voltage electrode structure of the present invention; Figure 4 This is a side view of the parallel three-electrode surface conductivity measurement structure of the present invention; Figure 5 This is a top view of the parallel three-electrode surface conductivity measurement structure of the present invention; Figure 6 This is a schematic diagram of the structure of the three-electrode cavity of the present invention; Figure 7 This invention provides a circuit for measuring and controlling the surface conductivity of the sample. Figure 8 This is a schematic diagram of the micro-liquid water injection device of the present invention; Figure 9This is a schematic cross-sectional view of the micro-liquid water injection device of the present invention; Figure 10 This is a schematic diagram of the measurement system for the surface conductivity of anisotropic materials under different micro-water contents according to the present invention.

[0020] The components include: 1. Circular measuring electrode; 2. Ring-shaped high-voltage electrode; 3. Sample; 4. Measuring electrode; 5. High-voltage electrode; 6. Fixing component; 7. Epoxy-impregnated paper sample; 8. Protective electrode; 9. Base; 10. Temperature sensor; 11. Heater; 12. Lifting rod; 13. Chamber; 14. Gas inlet / outlet; 15. Cover plate; 16. High-voltage inlet insulator; 17. Multi-port line vacuum adapter; 18. BNC single-port line vacuum adapter; 19. Micro-sampler; 20. Three-way valve chamber; 21. Glass tube; 22. 23. PU tubing; 24. Two-way valve chamber; 25. Nut cap; 26. Silicone rubber disc; 27. Sealing ring; 28. Three-electrode chamber; 29. ​​Computer; 30. Picoammeter; 31. High-voltage DC power supply; 32. Temperature controller; 33. Pressure gauge; 34. Micro-liquid water injection device; 35. SF6 gas cylinder; 36. Vacuum pump; 37. Micro-water detector; 38. Chamber valve; 39. Gas valve; 40. First valve; 41. Second valve; 42. Third valve; 43. Fourth valve; 44. Fifth valve. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0024] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0025] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0026] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0027] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 10 This invention discloses a measurement system for the surface conductivity of anisotropic materials under different trace moisture contents. The system comprises a signal acquisition and control unit and a three-electrode cavity 27. The three-electrode cavity 27 is electrically connected to the signal acquisition and control unit. The three-electrode cavity 27 includes a chamber 13 and a cover plate 15 connected to the top of the chamber 13. A gas inlet and outlet 14 are provided on one side of the chamber 13, and the gas inlet and outlet 14 are connected to a trace liquid water injection device 33, an SF6 gas cylinder 34, a vacuum pump 35, and a trace moisture detector 36 respectively through a gas control circuit. A heater 11, a base 9, and a protective electrode 8 are arranged sequentially from bottom to top inside the chamber 13. An epoxy resin-impregnated paper sample 7 is placed on the protective electrode 8, and a fixing member 6 is provided on the epoxy resin-impregnated paper sample 7. A measuring electrode 4 and a high-voltage electrode 5 are arranged parallel to each other inside the fixing member 6. At least two high-voltage electrodes 5 are provided, located on both sides of the measuring electrode 4. By adjusting the angle between the parallel conductive channel between the measuring electrode 4 and the high-voltage electrode 5 and the layered structure on the surface of the epoxy-impregnated paper sample 7, the anisotropic surface conductivity of the sample along and through the epoxy-paper interface can be effectively separated and accurately measured.

[0028] Figure 1 The diagram shows a schematic of the original annular three-electrode system for surface conductivity measurement. A 360° annular conductive channel is formed between the circular measuring electrode 1 and the annular high-voltage electrode 2, allowing for precise measurement of the surface conductivity of sample 3. When the tested sample 3 is an anisotropic epoxy-impregnated paper sample with a layered structure, charge carriers at the 0° and 180° positions migrate along the epoxy-paper interface, while those at the 90° and 270° positions pass through the epoxy-paper interface, making effective separation and accurate characterization of the anisotropic surface conductivity difficult. Based on this, see... Figure 2 , Figure 4 and Figure 5 This invention designs a parallel three-electrode system for measuring the surface conductivity of anisotropic epoxy-impregnated paper samples. Figure 2 The intermediate measuring electrode 4 and the high-voltage electrode 5 are smooth copper sheets, each 80mm long, 4mm wide, and 30mm high. The parallel measuring surface of the electrodes is 76mm long (with semicircles of 2mm radius on both sides). The upper end of the measuring electrode 4 extends 10mm on each side to fit into the slot for fixation. Figure 3 As shown. Two high-voltage electrodes 5 are placed on either side of the measuring electrode 4, with a gap width of 4mm between them, effectively shielding the measuring electrode from interference from the surrounding environment. The two high-voltage electrodes 5 are connected to two fixing parts 6 on the left and right by screws (the volume conductivity and surface conductivity of polytetrafluoroethylene (PTFE) material are extremely low, and its leakage current will not affect the measurement results). The fixing parts 6 are preferably made of PTFE, and the two fixing parts 6 are connected as one piece by side bolts. The PTFE fixing parts 6 do not contact the sample surface, are 1mm high, and gravity is applied to the high-voltage electrodes 5 to ensure close contact with the sample. The extended parts on both sides of the PTFE fixing parts 6 are to prevent the measuring device from tipping over. The measuring electrode 4 is not connected to the PTFE fixing parts 6, but is fixed in position by inserting into the groove formed by the two fixing parts 6, and contacts the sample by its own weight. By applying the same high voltage to both high-voltage electrodes 5, the protective electrode 8 is grounded, and the measuring electrode 4 collects the surface leakage current to measure the surface conductivity. The surface conductivity calculation formula is as follows:

[0029] In the formula: σ S represents the surface conductivity. I A Leakage current measurement, in A; d The distance between the high-voltage electrode and the measuring electrode is in meters (m). l The length of the parallel measuring surface is in meters (m). U 0 represents the application of a high voltage, V.

[0030] Based on the layered surface structure of the epoxy resin-impregnated paper sample 7, the orientation of the parallel conductive channels between the high-voltage electrode 5 and the measuring electrode 4 is adjusted. When the electrode is parallel to the measuring surface and parallel to the epoxy-paper interface, the conductive channel will pass through the epoxy-paper interface, and the measurement result is the conductivity through the epoxy-paper interface. When the electrode is parallel to the measuring surface and perpendicular to the epoxy-paper interface, the conductive channel will be along the epoxy-paper interface, and the measurement result is the conductivity along the epoxy-paper interface. The epoxy resin-impregnated paper sample 7 is placed on a grounded protective electrode 8, which has a diameter of 120 mm and a thickness of 10 mm. The grounding setting can divert the volume current inside the epoxy resin-impregnated paper sample 7, avoiding its interference with the surface conductivity measurement.

[0031] In one feasible embodiment of the present invention, the signal acquisition and control unit includes a computer 28, a picoammeter 29, a high-voltage DC power supply 30, and a temperature controller 31; the temperature controller 31 is connected to the heater 11; the picoammeter 29 and the high-voltage DC power supply 30 are electrically connected to the cover plate 15; the computer 28 is electrically connected to the picoammeter 29, and the picoammeter 29 is preferably a 6485 picoammeter. Further, see... Figure 6 The cover plate 15 is equipped with a high-voltage inlet insulator 16, a multi-port line vacuum adapter 17, and a BNC single-port line vacuum adapter 18. The high-voltage inlet insulator 16 is connected to a high-voltage DC power supply 30. The multi-port line vacuum adapter 17 is used to connect the temperature controller 31 and the heater 11. The BNC single-port line vacuum adapter 18 is connected to a picoammeter 29. The bottom of the cover plate 15 is connected to the base 9 via several lifting rods 12. Several temperature sensors 10 are installed on the base 9, and the temperature sensors 10 are electrically connected to a computer 28.

[0032] The epoxy resin-impregnated paper core layer of the converter valve side bushing is in an SF6 gas environment. This embodiment designs a three-electrode chamber 27 with controllable temperature and a controllable gas environment for conductivity measurement. The measuring electrode 4, high-voltage electrode 5, fixing component 6, epoxy resin-impregnated paper sample 7, and protective electrode 8 are placed on a high-temperature resistant insulating base 9. An aluminum plate heater 11 is installed close to the bottom of the base 9 and contains a temperature sensor. By connecting to an external aluminum heating plate temperature controller 31, a constant temperature control within the range of 20℃-140℃ can be achieved. Simultaneously, two temperature sensors 10 are attached to the upper surface of the base 9 near the protective electrode 8 and connected to an external display to further monitor the temperature of the three-electrode measurement system. The base 9 can be connected and fixed to the metal cover plate 15 via four high-temperature resistant insulating lifting rods 12. When it is necessary to install a sample or debug the three-electrode system, the entire measuring platform can be removed from the metal chamber 13 by lifting the cover plate 15. When performing measurements, the entire measuring platform is installed by lifting the cover plate 15, and the entire measuring platform is fixed by bolts connecting the cover plate 15 to the metal chamber 13. Gas inlet and outlet 14 are installed on the bottom side of the metal chamber 13, which are connected to the pressure gauge 32 and the external gas control circuit through the chamber valve 37. Sealing rings are installed at all metal connections inside the three-electrode chamber 27 to achieve chamber sealing.

[0033] High-voltage insulator 16, multi-port vacuum adapter 17, and BNC single-port vacuum adapter 18 are mounted on cover plate 15 to facilitate the transfer of control and measurement circuits within the cavity. Specifically, high-voltage insulator 16 introduces DC high voltage; multi-port vacuum adapter 17 connects the internal grounding wire, aluminum plate heater power line, and temperature sensor connection line; and BNC single-port vacuum adapter 18 is primarily used for current extraction, employing BNC shielded wire to effectively shield the measurement results from external environmental interference. Furthermore, the measurement circuit requires protection circuitry and a measuring device to achieve effective current measurement, as described in this invention. Figure 7 The design illustrates a circuit for measuring and controlling the surface conductivity of the sample. A high-voltage DC power supply 30 is connected to the high-voltage electrode 5 in the three-electrode system via a current-limiting resistor. The measuring electrode 4 is connected to a 6485 picoammeter via overcurrent and overvoltage protection circuits. Measurement results are transmitted in real-time and stored in the computer 28. A temperature controller 31, along with a gas pressure and trace moisture content control system, enables environmental control of the three-electrode measurement system.

[0034] In one feasible embodiment of the present invention, see [link to relevant documentation]. Figure 8The micro-liquid water injection device 33 is connected to the gas control circuit via a two-way valve chamber 23. The micro-liquid water injection device 33 includes a micro-sampler 19, a three-way valve chamber 20, and a transparent glass tube 21. The lower port of the three-way valve chamber 20 is connected to the glass tube 21. The micro-sampler 19 can enter the glass tube 21 from the upper port of the three-way valve chamber 20. The side port of the three-way valve chamber 20 is connected to the two-way valve chamber 23. A sealing ring 26 is provided at the connection between the lower port of the three-way valve chamber 20 and the glass tube 21. A nut cap 24 is installed at the upper port of the three-way valve chamber 20, with a through hole in the center of the nut cap 24. A silicone rubber disc 25 is provided between the nut cap 24 and the upper port of the three-way valve chamber 20. Preferably, the two-way valve chamber 23 is connected to the side port of the three-way valve chamber 20 and the gas control circuit via a PU gas pipe 22.

[0035] SF6 cylinders supplied by existing manufacturers contain high-purity liquefied SF6. The SF6 gas released from these cylinders has a low water content (around 20 ppm). Therefore, a device is needed to inject a quantitative amount of water molecules to control the water content of the gas. A micro-liquid water injection device was designed to inject water, and its internal cross-sectional structure is shown below. Figure 9As shown. The main body of the micro-liquid water injection device 33 consists of a micro-sampler 19 and a three-way valve chamber 20, which is connected to a two-way valve chamber 23 and a gas control circuit via a PU gas tube 22. A top-opening nut cap 24 is threaded onto the upper end of the three-way valve chamber 20, and a 2mm thick silicone rubber disc 25 is tightly pressed between the nut cap 24 and the three-way valve chamber 20, ensuring a seal while providing an injection port for the micro-sampler. A transparent glass tube 21 is installed at the lower end of the three-way valve chamber 20, mainly for holding the injected micro-liquid water and providing an observation window; it is sealed to the three-way valve chamber 20 via a sealing ring 26. Before performing the micro-water injection operation, the internal space is evacuated and purged with SF6 gas more than 5 times to remove air. Then, the internal space of the three-way valve chamber 20 is filled with SF6 gas at 1 atmosphere, the two-way valve chamber 23 is closed, and the external gas control circuit is evacuated. The micro-sampler 19, used to extract a quantitative amount of deionized water, pierces the silicone rubber disc 25 through the central hole at the top of the nut cap 24, passes through the three-way valve chamber 20, and then injects a trace amount of liquid water into the glass tube 21. After injecting the trace amount of liquid water, the needle tip of the micro-sampler 19 is retracted to the upper channel of the three-way valve chamber 20, but not completely withdrawn from the interior of the three-way valve chamber 20. First, the upper passage of the three-way valve chamber 20 is closed (at this time, only the lower and right channels are connected), and then the micro-sampler 19 is withdrawn from the three-way valve chamber 20. The final step is the evaporation of the trace amount of liquid water. Before this, the external gas control circuit is kept connected to the three-electrode chamber 27 and is in a vacuum state. At this time, the two-way valve chamber 23 is opened. Due to the small internal space of the three-way valve chamber 20, the entire gas control circuit will be in a vacuum state. The boiling point of the liquid water will be significantly reduced, directly evaporating into water vapor and diffusing throughout the entire gas control circuit and even into the three-electrode chamber 27. Once the water molecules have completely diffused, the two-way valve chamber 23 can be closed to proceed with the subsequent SF6 gas filling operation.

[0036] In one feasible embodiment of the present invention, the gas control circuit is further equipped with a gas valve 38, a first valve 39, a second valve 40, a third valve 41, a fourth valve 42, and a fifth valve 43; the gas valve 38 is located near the SF6 gas cylinder 34; the first valve 39 is located on the connecting trunk line between the micro-liquid water injection device 33 and the SF6 gas cylinder 34; the second valve 40 is located near the vacuum pump 35; the third valve 41 is located near the micro-water detector 36; the fourth valve 42 is located near the pressure gauge 32; and the fifth valve 43 is located near the micro-liquid water injection device 33.

[0037] This embodiment discloses a method for measuring the surface conductivity of anisotropic materials under different micro-water contents, including the following steps: S1, Place the epoxy resin impregnated paper sample 7 in the three-electrode cavity 27, and adjust the orientation of the parallel conductive channel between the measuring electrode 4 and the high voltage electrode 5 so that it is at a predetermined angle to the layered structure on the surface of the epoxy resin impregnated paper sample 7. S2, vacuum pump 35 is used to evacuate the three-electrode cavity 27 and the gas control circuit, and then gas washing operation is performed through SF6 gas cylinder 34. S3, a certain amount of deionized water is injected into the gas control circuit through the micro-liquid water injection device 33, so that the deionized water evaporates into water vapor and diffuses into the three-electrode cavity 27; S4. Fill the three-electrode cavity 27 with SF6 gas to the preset pressure; S5, let stand, allowing water vapor and SF6 gas to mix fully and be adsorbed onto the surface of epoxy resin impregnated paper sample 7, and then use micro water detector 36 to detect and record the micro water content of the gas in chamber 13. S6, the three-electrode cavity 27 is heated by the signal acquisition and control unit, a preset voltage is applied, and the current signal is acquired; Temperature controller 31 heats the interior of the three-electrode cavity 27 to a preset temperature and maintains it stable through heater 11; A preset voltage is applied to the high-voltage electrode 5 by a high-voltage DC power supply 30, and the leakage current collected by the measuring electrode 4 is measured by a picoammeter 29, and the current value after stabilization is recorded.

[0038] S7, calculate the conductivity based on the recorded current and voltage values.

[0039] The working process / working principle of this invention is as follows: This invention combines a three-electrode cavity for measuring anisotropic surface conductivity in a controlled environment with a micro-liquid water quantitative injection device, ultimately designing an overall system for measuring the anisotropic surface conductivity of epoxy-impregnated paper under different micro-water contents, as follows: Figure 10 As shown, the system mainly consists of two parts: a current measurement circuit and a gas control circuit. Centered on the three-electrode cavity 27, a high-voltage DC power supply 30 and a picoammeter 29 are connected... Figure 7 The current measurement circuit is formed in the form of a three-electrode cavity 27. The temperature controller 31 realizes the temperature control inside the three-electrode cavity 27, and the computer 28 records the current measurement results in real time.

[0040] The gas control loop controls the gas environment inside the three-electrode chamber 27. A digital pressure gauge 32 provides real-time feedback on the internal gas pressure. A micro-liquid water injection device 33 increases the water content in the SF6 gas. An SF6 cylinder 34 provides high-purity SF6 gas. A vacuum pump 35 is used for vacuuming the gas control loop, and a micro-water detector 36 detects the water content in the SF6 gas. The entire gas control loop connects these devices via PU tubing and seven valves (37-43). The PU tubing uses quick-connect plugs, with Teflon tape wrapped around the threaded connections to the valves. Water-absorbing and curing silicone is applied to the connections to ensure a good seal between the entire gas control loop and the internal space of the three-electrode chamber 27. Relevant sealing tests have been conducted, as shown in Table 1 below, with significant results (gas pressure fluctuations in the table are mainly due to fluctuations in laboratory ambient temperature).

[0041] Table 1

[0042] After assembling the gas control circuit, the entire gas control circuit and the three-electrode chamber 27 are first evacuated and purged with SF6 more than five times using vacuum pump 35 and SF6 cylinder 34 to effectively ensure the removal of the original air from the internal space. During this process, the third valve 41 remains closed, while the chamber valve 37, the first valve 39, the fourth valve 42, and the fifth valve 43 remain open. The second valve 40 and the gas valve 38 are opened and closed sequentially according to the evacuation and purging operations.

[0043] After vacuuming and purging the internal space, valves 38, 40, and 41 remain closed, while valves 37, 42, and 39 remain open. Figure 8 , Figure 9 The corresponding trace liquid water injection step injects the calculated water content into the gas control loop. After the water molecules have fully evaporated and diffused, the fifth valve 43 is closed, the gas valve 38 is opened, and the three-electrode chamber is filled with SF6 gas at the pressure value to be tested. Then, an additional 50 kPa of SF6 gas is added (the extra 50 kPa of gas is used for trace water content detection). Finally, the gas valve 38, the first valve 39, and the fourth valve 42 are closed to complete the gas filling operation.

[0044] The mixture is allowed to stand for a period of time to allow the water content to mix with the SF6 gas and adhere to the inner surface of the chamber and the sample surface. During the gas trace moisture content measurement phase, gas valve 38, first valve 39, and third valve 41 are first opened to continuously supply high-purity SF6 gas, reducing the trace moisture content inside the trace moisture detector 36 and maintaining the displayed value at a low, constant level. Then, fourth valve 42 is opened, first valve 39 and gas valve 38 are closed, and gas supply is switched to the three-electrode chamber 27. The trace moisture detector 36 displays the trace moisture content of the flowing gas in real time. After switching to the three-electrode chamber 27, the trace moisture content on its display gradually increases. A gas volume of 50 kPa is sufficient to detect the trace moisture content inside the gas, and the final result is recorded. After the trace moisture content measurement phase ends, all valves are closed, and the measurement of the anisotropic surface conductivity of the epoxy-impregnated paper sample begins.

[0045] This invention addresses the anisotropic surface orientation caused by the layered structure of epoxy-impregnated paper samples. A parallel three-electrode structure is designed to effectively separate and accurately measure the anisotropic surface conductivity along and through the epoxy-paper interface by adjusting the angle between the conductive channel and the anisotropic orientation of the sample surface. The designed gas control loop can simply and efficiently improve, control, and detect the trace moisture content in high-purity SF6 gas, effectively simulating the gas environment under different operating stages of the equipment and its impact on the gas-solid interface conductivity of the epoxy-impregnated paper material. Simultaneously, the system and device can control different gas pressures, ambient temperatures, and electric field strengths. Its sealed internal space further fully simulates actual complex operating conditions. The measurement results of the anisotropic surface conductivity of epoxy-impregnated paper samples under complex operating conditions effectively fill the gap in data on charge migration characteristics at different orientations under the layered structure of the epoxy-impregnated paper core gas-solid interface of the valve-side sleeve, providing data support for further analysis of charge accumulation at the gas-solid interface of the sleeve core under complex operating conditions.

[0046] The complete operation process of the measurement system for the surface conductivity of anisotropic materials under different micro-water contents according to the present invention is as follows: 1. First, assemble the three-electrode cavity 27 as required, connect the current measurement circuit and the gas control circuit, adjust the orientation of the electrode measurement surface according to the surface pattern of the sheet sample, and measure the surface conductivity along the epoxy-paper interface and through the interface respectively.

[0047] 2. Check and ensure the continuity of the current measurement circuit and the sealing of the gas control circuit.

[0048] 3. For the internal space formed by the three-electrode cavity 27 and the gas control circuit, perform the following operations in sequence: vacuuming and exhausting, injecting water content, filling with SF6 gas, waiting for mixing, and detecting the trace water content of SF6. Record the experimental conditions and close the cavity valve 37.

[0049] 4. Turn on the temperature controller 31, set the experimental temperature, and wait for the temperature to stabilize.

[0050] 5. Turn on the current measurement circuit equipment computer 28, 6485 picoammeter and high voltage DC power supply 30, apply the voltage to be measured, measure the current stability curve, and record the final stability result.

[0051] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A system for measuring the surface conductivity of anisotropic materials under different micro-water contents, characterized in that, The device includes a signal acquisition and control unit and a three-electrode cavity (27); the three-electrode cavity (27) is electrically connected to the signal acquisition and control unit; the three-electrode cavity (27) includes a chamber (13) and a cover plate (15) connected to the top of the chamber (13); a gas inlet and outlet (14) are provided on one side of the chamber (13), and the gas inlet and outlet (14) are connected to a micro-liquid water injection device (33), an SF6 gas cylinder (34), a vacuum pump (35) and a micro-water detector (36) respectively through a gas control circuit; a heater (11), a base (9) and a protective electrode (8) are arranged sequentially from bottom to top in the chamber (13); an epoxy resin impregnated paper sample (7) is placed on the protective electrode (8), and a fixing member (6) is provided on the epoxy resin impregnated paper sample (7); a measuring electrode (4) and a high-voltage electrode (5) are arranged in parallel in the fixing member (6); at least two high-voltage electrodes (5) are provided, located on both sides of the measuring electrode (4).

2. The measurement system for the surface conductivity of anisotropic materials under different micro-water contents according to claim 1, characterized in that, The signal acquisition and control unit includes a computer (28), a picoammeter (29), a high-voltage DC power supply (30), and a temperature controller (31); the temperature controller (31) is connected to the heater (11); the picoammeter (29) and the high-voltage DC power supply (30) are electrically connected to the cover plate (15); the computer (28) is electrically connected to the picoammeter (29).

3. The measurement system for the surface conductivity of anisotropic materials under different micro-water contents according to claim 2, characterized in that, The cover plate (15) is provided with a high-voltage inlet insulator (16), a multi-port line vacuum adapter (17) and a BNC single-port line vacuum adapter (18); the high-voltage inlet insulator (16) is connected to a high-voltage DC power supply (30); the multi-port line vacuum adapter (17) is used to connect the temperature controller (31) and the heater (11); the BNC single-port line vacuum adapter (18) is connected to a picoammeter (29).

4. The measurement system for the surface conductivity of anisotropic materials under different micro-water contents according to claim 2, characterized in that, The bottom of the cover plate (15) is connected to the base (9) by several lifting rods (12); several temperature sensors (10) are provided on the base (9), and the temperature sensors (10) are electrically connected to the computer (28).

5. The measurement system for the surface conductivity of anisotropic materials under different micro-water contents according to claim 1, characterized in that, The micro-liquid water injection device (33) is connected to the gas control circuit through the two-way valve chamber (23); the micro-liquid water injection device (33) includes a micro-sampler (19), a three-way valve chamber (20) and a transparent glass tube (21); the lower port of the three-way valve chamber (20) is connected to the glass tube (21); the micro-sampler (19) can enter the glass tube (21) from the upper port of the three-way valve chamber (20); the side port of the three-way valve chamber (20) is connected to the two-way valve chamber (23).

6. The measurement system for the surface conductivity of anisotropic materials under different micro-water contents according to claim 5, characterized in that, A sealing ring (26) is provided at the connection between the lower port of the three-way valve chamber (20) and the glass tube (21); a nut cap (24) is installed at the upper port of the three-way valve chamber (20), a through hole is opened in the middle of the nut cap (24), and a silicone rubber disc (25) is provided between the nut cap (24) and the upper port of the three-way valve chamber (20).

7. The measurement system for the surface conductivity of anisotropic materials under different micro-water contents according to claim 5, characterized in that, The two-way valve chamber (23) is connected to the side port of the three-way valve chamber (20) and the gas control circuit through the PU gas pipe (22).

8. The measurement system for the surface conductivity of anisotropic materials under different micro-water contents according to claim 1, characterized in that, A pressure gauge (32) and a cavity valve (37) are installed at the gas inlet and outlet (14); a gas valve (38), a first valve (39), a second valve (40), a third valve (41), a fourth valve (42), and a fifth valve (43) are also installed on the gas control circuit; the gas valve (38) is located near the SF6 gas cylinder (34); the first valve (39) is located on the connecting trunk line between the micro-liquid water injection device (33) and the SF6 gas cylinder (34); the second valve (40) is located near the vacuum pump (35); the third valve (41) is located near the micro-water detector (36); the fourth valve (42) is located near the pressure gauge (32); and the fifth valve (43) is located near the micro-liquid water injection device (33).

9. A method for measuring the surface conductivity of anisotropic materials under different micro-water contents, characterized in that, A measurement system for the surface conductivity of anisotropic materials under different micro-water contents, based on any one of claims 1 to 8, includes the following steps: Place the epoxy resin impregnated paper sample (7) in the three-electrode cavity (27), and adjust the orientation of the parallel conductive channel between the measuring electrode (4) and the high voltage electrode (5) so that it is at a predetermined angle to the layered structure on the surface of the epoxy resin impregnated paper sample (7). A vacuum pump (35) is used to evacuate the three-electrode cavity (27) and the gas control circuit, and then the gas is washed through an SF6 gas cylinder (34). A measured amount of deionized water is injected into the gas control circuit through a micro-liquid water injection device (33), causing the deionized water to evaporate into water vapor and diffuse into the three-electrode cavity (27); SF6 gas is introduced into the three-electrode cavity (27) to a preset pressure; The sample was left to stand, allowing the water vapor and SF6 gas to mix thoroughly and be adsorbed onto the surface of the epoxy resin-impregnated paper sample (7). Then, the micro-water content of the gas in the chamber (13) was detected and recorded using a micro-water detector (36). The three-electrode cavity (27) is heated by the signal acquisition and control unit, and a preset voltage is applied to acquire the current signal; The conductivity is calculated based on the recorded current and voltage values.

10. The method for measuring the surface conductivity of anisotropic materials under different micro-water contents according to claim 9, characterized in that, The steps of heating the three-electrode cavity (27) and applying a preset voltage through the signal acquisition and control unit, and acquiring the current signal, specifically include: The temperature controller (31) heats the interior of the three-electrode cavity (27) to a preset temperature and maintains it stable through the heater (11); A preset voltage is applied to the high-voltage electrode (5) by a high-voltage DC power supply (30), and the leakage current collected by the measuring electrode (4) is measured by a picoammeter (29), and the current value after stabilization is recorded.

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