Surface flashover experiment electrode device with strong interface and adjustable vertical electric field

Abstract

The invention discloses a surface flashover experiment electrode device with an adjustable interface strong vertical electric field, and the device is characterized in that the device comprises a high-voltage electrode, a backboard electrode, a ground electrode, an epoxy pressing plate, a first fixing part and a second fixing part, the device is used for connecting and fixing the ground electrode and the backboard electrode through the first fixing part, and the epoxy pressing plate is used for connecting and fixing the ground electrode and the backboard electrode through the second fixing part. According to the device, the epoxy pressing plate is used for guaranteeing that no air gap exists among the high-voltage electrode, the sample and the backboard electrode, and the epoxy pressing plate is fixed through the second fixing part. According to the device, strong vertical electric field components with different sizes are adjusted by changing the sizes of the sample and the backboard electrode. The surface flashover experiment electrode with the adjustable interface strong vertical electric field has the advantages of being clear in structure, easy to install, adjustable in electric field and the like, and can be used in a flashover characteristic experiment or an equivalent insulation test of a converter valve side glue impregnated paper sleeve with a strong vertical electric field working condition.

Description

Technical Field

[0001] The invention relates to the technical field of insulation performance testing and converter valve side bushings, in particular to a surface flashover experimental electrode device with adjustable interface strong vertical electric field. Background Art

[0002] Ultra-high voltage direct current transmission (UHVDC) is suitable for long-distance transmission, has a large transmission capacity, and is easy to control and adjust. It is an inevitable choice for solving the problem of uneven energy distribution in my country. As an irreplaceable key part of the project, the safety and reliability of the converter valve side bushing are increasingly valued. Currently, the most widely used is the rubber-impregnated paper valve side bushing. In recent years, there have been several surface flashover failures of rubber-impregnated paper bushings, and relevant experiments are urgently needed to support the understanding of their flashover characteristics and mechanisms. The most prominent feature of the bushing is the extremely non-uniform field with a strong vertical component electric field. Current research shows that the vertical electric field component affects the discharge form and flashover voltage, posing a threat to surface insulation. Therefore, the design of an equivalent strong vertical electric field surface flashover experimental device is of great significance for the surface flashover experiment of the converter valve side bushing. Summary of the Invention

[0003] The main technical problem solved by the present invention is to provide a surface flashover experimental electrode device with adjustable strong vertical electric field at the interface. Finger-shaped electrodes are used as high-voltage electrodes to increase the flashover probability and facilitate the observation of sound, light and electricity. A strong vertical component is provided by the back plate electrode. The ground electrode and the back plate electrode are connected and fixed by fixing screws. The sample is clamped by the tension of the screws. An epoxy pressing plate is used to ensure that there is no air gap between the high-voltage electrode, the sample and the back plate electrode. The pressing plate is fixed by fixing screws. By changing the size of the sample and the back plate electrode, different sizes of strong vertical electric field components are adjusted, thereby realizing a surface flashover experimental electrode with adjustable strong vertical component at the interface. The surface flashover experimental electrode with adjustable strong vertical electric field at the interface provided by the present invention has the advantages of clear structure, simple installation, and adjustable electric field. It can be used in the flashover characteristic experiment or equivalent insulation test of the glue-impregnated paper bushing on the side of the converter valve under the condition of strong vertical electric field.

[0004] In order to achieve the above-mentioned purpose and features, the present invention adopts the following technical solution: a surface flashover experimental electrode device with adjustable strong vertical electric field at the interface, comprising: High voltage electrode, back plate electrode, ground electrode, epoxy pressing plate, first fixing part and second fixing part, wherein, The device connects and fixes the ground electrode and the back plate electrode through the first fixing part, and clamps the sample through the first fixing part. The device uses the epoxy pressing plate to ensure that there is no air gap between the high voltage electrode, the sample, and the back plate electrode. The device fixes the epoxy pressing plate through the second fixing part.

[0005] Preferably, the sample is a sheet sample.

[0006] Preferably, the high voltage electrode is a finger-type electrode.

[0007] Preferably, the first fixing part is a fixing screw, and the second fixing part is an insulating screw.

[0008] Preferably, the finger-shaped electrode has a length of 25-35 mm and a front finger radius of 5-15 mm.

[0009] Preferably, the back plate electrode is grounded and has a stepped shape, wherein the upper step is shorter and the lower step is longer, and the upper step is shorter than the lower step.

[0010] Preferably, the upper step is used to match the size of the sample.

[0011] Preferably, the thickness of the upper step electrode is kept at 2.5 mm, and the distance between the high-voltage electrode and the upper step electrode remains unchanged at 10 mm. When the sample thickness is about 5 mm, the ratio of the vertical electric field component to the parallel electric field component is about 3:1, and when the sample thickness is about 10 mm, the ratio of the vertical electric field component to the parallel electric field component is about 2:1.

[0012] Preferably, the back plate electrode and the ground electrode jointly clamp the sample.

[0013] Preferably, the ground electrode is grounded, and to ensure that the front end of the ground electrode is in close contact with the sample, a 1 mm protrusion is left at the rear end of the ground electrode.

[0014] Preferably, a potential difference is formed between the back plate electrode and the high voltage electrode.

[0015] Preferably, there are at least two epoxy pressing plates, namely an upper epoxy pressing plate located at the upper end and a lower epoxy pressing plate located at the lower end, which are used to clamp the high-voltage electrode, sample and backplate electrode from top to bottom.

[0016] Preferably, the fixing screw is a metal screw, and the insulating screw is an epoxy screw.

[0017] Preferably, the backplate electrode is used to provide a strong vertical electric field component, and the strong vertical electric field components of different sizes can be adjusted by changing the sizes of the sheet sample and the backplate electrode.

[0018] Preferably, the metal screws are used to connect and fix the ground electrode and the back plate electrode, and the epoxy screw rods are used to fix the epoxy pressing plate.

[0019] Preferably, the epoxy screw includes at least two parallel epoxy screws.

[0020] Preferably, each epoxy screw is a cylindrical rod having a base, wherein the diameter of the base is larger than the diameter of the cylindrical rod.

[0021] Preferably, each epoxy screw passes through the upper epoxy pressing plate, the high voltage electrode, the sample, and the lower epoxy pressing plate in sequence from top to bottom, wherein the base of the epoxy screw is located at the lower surface of the lower epoxy pressing plate.

[0022] Preferably, each epoxy screw passes through the upper epoxy pressing plate, the sample and the lower epoxy pressing plate respectively.

[0023] Preferably, when each epoxy screw passes through the sample and the lower epoxy pressing plate, the sample and the lower epoxy pressing plate clamp the portion of the back plate electrode extending between the sample and the lower epoxy pressing plate.

[0024] The beneficial effects of the present invention are: 1) Since the device disclosed in the present invention connects and fixes the ground electrode and the back plate electrode via the first fixing portion, clamps the sample via the first fixing portion, and fixes the epoxy pressing plate via the second fixing portion, all fixing functions are achieved by only two fixing portions in the present invention, which makes the device have the advantages of clear structure and simple installation; 2) Because the device disclosed in the present invention uses the epoxy pressing plate to ensure that there is no air gap between the high-voltage electrode, the sample, and the backplate electrode, the adverse effect of the air gap on the surface flashover test is eliminated. This makes the device applicable to flashover characteristic tests or equivalent insulation tests of the rubber-impregnated paper bushing on the converter valve side in the presence of a strong vertical electric field. This has important application value for understanding the flashover characteristics and mechanism of the converter valve side bushing. 3) Since the device disclosed in the present invention uses finger-shaped electrodes as high-voltage electrodes, the device can increase the flashover probability and facilitate the observation of sound, light and electricity; 4) Since the device disclosed in the present invention provides a strong vertical electric field component through the backplate electrode, and the size of the strong vertical electric field component can be adjusted by changing the size of the backplate electrode and the sample, the device can realize a surface flashover experimental device with adjustable strong vertical electric field at the interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1( a ) is a schematic structural diagram of an electrode device for a surface flashover experiment with an adjustable strong vertical electric field at the interface according to an embodiment of the present invention; FIG1( b ) is a side view of an electrode device for a surface flashover experiment with an adjustable strong vertical electric field at the interface according to one embodiment of the present invention; FIG1( c ) is a front view of an electrode device for a surface flashover experiment with an adjustable strong vertical electric field at the interface according to one embodiment of the present invention; FIG1 (d) is a top view of an electrode device for a surface flashover experiment with an adjustable strong vertical electric field at the interface according to an embodiment of the present invention; FIG1(e) is a rear view of an electrode device for surface flashover experiment with adjustable strong vertical electric field at the interface according to one embodiment of the present invention; FIG1( f ) is a bottom view of an electrode device for a surface flashover experiment with an adjustable strong vertical electric field at the interface according to one embodiment of the present invention; Figure 2 A physical picture of an electrode device for surface flashover experiment with adjustable strong vertical electric field at the interface according to one embodiment of the present invention; FIG3 (a) is a cloud diagram of the electric field distribution along a surface in one embodiment of the present invention; FIG3( b ) is a graph showing the field intensity distribution at different positions along the surface of the epoxy sample between the high voltage terminal and the ground electrode in one embodiment of the present invention; FIG4 (a) is a cloud diagram of the electric field distribution of the ±800 kV valve-side bushing core in one embodiment of the present invention; FIG4( b ) is a graph showing the distribution of the electric field strength in the tangential, normal and synthetic directions along the surface of the valve-side casing core in one embodiment of the present invention; FIG5( a ) is a Weibull distribution diagram of flashover voltage under different voltage types and electric field components obtained by experimental measurement in one embodiment of the present invention; FIG5( b ) is a schematic diagram of flashover voltages under different voltage types and electric field components obtained by experimental measurement in one embodiment of the present invention; FIG6 (a) is a schematic diagram of the mechanism of the influence of the vertical component electric field on the surface flashover process under the conditions of the experimental process in one embodiment of the present invention; Figure 6 (b) is a schematic diagram of the mechanism of the influence of DC superimposed AC voltage conditions on the surface flashover process during the experiment of the present invention in one embodiment of the present invention; Figure numerals: 1-high voltage electrode, 2-back plate electrode, 3-ground electrode, 4-epoxy pressing plate, 5-fixing screw, 6-sample, 7-epoxy screw, 8-matching part of lower epoxy pressing plate, 41-upper epoxy pressing plate, 42-lower epoxy pressing plate. DETAILED DESCRIPTION

[0026] Specific embodiments of the present invention will be described in detail below with reference to Figures 1(a) to 6(b). Although specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments described herein. Rather, these embodiments are provided to facilitate a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0027] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the present invention shall be as defined in the attached claims.

[0028] To facilitate understanding of the embodiments of the present invention, further explanation will be given below using specific embodiments as examples in conjunction with the accompanying drawings, and the accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0029] In one embodiment, the present invention provides an electrode apparatus for surface flashover experiments with an adjustable strong vertical electric field at the interface. The apparatus comprises: a high-voltage electrode, a backplate electrode, a ground electrode, an epoxy pressure plate, a first fixing portion, a specimen, and a second fixing portion. The epoxy pressure plates include at least two: an upper epoxy pressure plate and a lower epoxy pressure plate. Exemplarily, the first fixing portion is a set screw, and the second fixing portion is an insulating screw. More preferably, the insulating screw is an epoxy screw.

[0030] In one embodiment, the specimen is a sheet-like specimen, as shown in Figures 1(a) to 1(f). The central portion of the device, from top to bottom, comprises an epoxy screw 7, an upper epoxy pressure plate 41, a high-voltage electrode 1, a specimen 6, a fitting 8 for the lower epoxy pressure plate, and a lower epoxy pressure plate 42. The high-voltage electrode 1 is positioned above and in close contact with the specimen 6; the backing electrode 2 and the ground electrode 3 clamp the left end of the specimen 6; and the epoxy screw 7 extends through the upper and lower epoxy pressure plates 42 and the specimen 6. A fixing screw 5 secures the components by tension and ensures a reliable mechanical connection. It should be noted that at least two epoxy screws are required.

[0031] As can be seen from Figure 1 (a) to Figure 1 (f), the high-voltage electrode 1 is finger-shaped and is clamped between the epoxy pressing plate 4 and the sample 6. The fingertip does not exceed one side of the epoxy pressing plate 4, and the finger base is longer than the epoxy pressing plate 4 and shorter than the sample 6.

[0032] One end of the sample 6 is clamped between the back plate electrode 2 and the ground electrode 3, and the other end protrudes. The high-voltage electrode 1 is located above the middle of the sample 6, and the mating part 8 of the lower epoxy pressure plate is located below. The sample 6 is clamped between the high-voltage electrode 1 and the lower epoxy pressure plate 42, and is penetrated by the epoxy screw 7.

[0033] The epoxy screw 7 is a cylindrical rod with a base. The base is slightly thicker than the rod, that is, the diameter of the base is slightly larger than the diameter of the cylindrical rod.

[0034] In another embodiment, the high-voltage electrode is a finger-shaped electrode. This finger-shaped electrode can increase the probability of flashover and facilitate detection by acoustic, optical, and other means. It is 30 mm long and has a 10 mm radius at the front end. Furthermore, the contact surface between the finger-shaped electrode and the sample has a chamfer (e.g., a 2 mm chamfer) to reduce experimental scatter.

[0035] In another embodiment, the backplate electrode is grounded and fixed to the ground electrode via screws. The backplate electrode is stepped, with the lower step being longer and clamping the sample together with the ground electrode. This creates a potential difference with the high-voltage electrode, thereby generating a strong vertical component. The upper step is used to match the size of the sample, and adjusting this size can adjust the magnitude of the vertical electric field component. For example, if the thickness of the upper step electrode is maintained at 2.5 mm and the distance between the high-voltage electrode and the upper step electrode remains unchanged at 10 mm, when the sample thickness is approximately 5 mm, the ratio of the vertical electric field component to the parallel electric field component is approximately 3:1, while when the sample thickness is approximately 10 mm, the ratio is approximately 2:1.

[0036] In another embodiment, the upper step electrode has a thickness of 2.5 mm, and the distance between the high-voltage electrode and the upper step electrode remains constant at 10 mm. When the sample thickness is approximately 5 mm, the electric field distribution of the present invention is simulated using COMSOL simulation software, resulting in an electric field distribution cloud map and electric field distribution curve as shown in Figures 3(a) and 3(b). Figure 3(a) is a surface electric field distribution cloud map of one embodiment of the present invention, showing the spatial distribution of the electric field along the surface of the device in one embodiment of the present invention. The area with the highest electric field intensity is mainly distributed near the contact point between the metal electrode and the epoxy sample plate. Figure 3(b) is a field intensity distribution curve at different locations along the surface of the epoxy sample between the high-voltage terminal and the ground electrode. In the high-field intensity region, the ratio of the perpendicular component to the parallel component is approximately 3:1. It can be considered that this experimental device has a strong perpendicular electric field component, and the ratio is similar to the normal shear ratio at the area with the highest surface field intensity in the actual working conditions mentioned above. Therefore, this electrode has a high similarity with the actual bushing and can be used to simulate the actual working conditions of the rubber-impregnated paper bushing.

[0037] Figure 4 (a) is a cloud diagram of the electric field distribution of the ±800kV valve-side bushing core in an embodiment of the present invention, which can help illustrate the equivalence between the electric field distribution of the experimental device and the electric field distribution of the actual valve-side bushing; Figure 4 (b) is a curve diagram of the tangential, normal and synthetic electric field intensity distribution of the valve-side bushing core in an embodiment of the present invention, which can help illustrate the equivalence between the electric field distribution of the experimental device and the electric field distribution of the actual valve-side bushing.

[0038] It can be seen from Figures 3(a), 3(b) and 4(a), 4(b) that in the high field strength area, the ratio of the vertical component to the parallel component is about 3:1. It can be considered that the device of the present invention has a strong vertical electric field component, and is similar to the French shear ratio at the place where the surface field strength is strong in the above-mentioned actual working conditions. Therefore, this electrode has a high similarity with the actual casing and can be used to simulate the actual working conditions of the rubber-impregnated paper casing.

[0039] In another embodiment, the ground electrode is grounded and serves as the ground electrode of the surface flashover experimental device. To ensure that the front end of the ground electrode is in close contact with the sample, a 1 mm protrusion is left at the rear end of the ground electrode. The ground electrode and the back plate electrode are fixed by screws. The sample is clamped together by the tension of the screws and the back plate electrode, and the contact surface with the sample is chamfered by 2 mm to reduce the dispersion of the experiment. Figure 2 As shown in .

[0040] In another embodiment, at least two epoxy pressure plates are used to clamp the high-voltage electrode, sample, and backing plate electrode. The upper and lower epoxy pressure plates are tightened and fixed by at least two epoxy screws to ensure that there are no air gaps between the parts, thereby preventing the impact of local discharge in the air gap on the experiment itself. Referring to Figure 1(a), the portion of the backing plate electrode 2 that extends into the sample and the lower epoxy pressure plate is located on one side of the epoxy screw, while the mating piece 8 of the lower epoxy pressure plate is located on the other side of the epoxy screw. This ensures that the backing plate electrode is always clamped between the sample and the lower epoxy pressure plate while maintaining the sample level, and ensures that the force on the lower epoxy pressure plate is balanced.

[0041] In another embodiment, the fixing screws fix the components through tension and ensure reliable mechanical connection. The fixing screws in this device include two parts. One part is used for the first fixing part to connect and fix the ground electrode and the back plate electrode, and a metal screw is selected to ensure their electrical connection; the other part is used for the second fixing part to fix the upper and lower epoxy pressure plates, and an insulating screw is selected in combination with an epoxy screw to avoid the metal floating potential affecting the experiment.

[0042] In another embodiment, the present device is particularly suitable for sheet samples because the size of the vertical electric field component can be easily controlled by changing the thickness of the sample. It can be understood that when the sample is not a sheet sample, it is necessary to adaptively change multiple dimensions of the sample to control the size of the vertical electric field component. For sheet samples, if it is necessary to simulate the more stringent electric field distribution conditions in the high-voltage bushing, the sample thickness can be appropriately increased to obtain a higher vertical electric field component; conversely, if it is necessary to simulate relatively loose electric field distribution conditions, the sample thickness can be appropriately reduced to obtain a smaller vertical electric field component. For the simulation of only the parallel component electric field, it is only necessary to remove the backplate electrode so that the high-voltage terminal electrode and the ground electrode are placed on the same horizontal plane (i.e., the sample surface), thereby eliminating the vertical electric field component.

[0043] In another embodiment, the present device is used to study the surface flashover characteristics under different AC / DC voltage ratios and DC voltages, and under perpendicular electric field components and parallel electric field components. The experimental results are shown in FIG5(a) and FIG5(b).

[0044] Figure 5(a) is a Weibull distribution diagram of the flashover voltage under different voltage types and electric field components obtained from experimental measurements in one embodiment of the present invention, where the different voltage types include DC, AC / DC superposition voltage with an AC / DC ratio of 1:3, and AC / DC superposition voltage with an AC / DC ratio of 1:7; the different electric field components include a strong perpendicular electric field component and only a parallel electric field component.

[0045] Figure 5(b) shows the flashover voltages under different voltage types and electric field components obtained by experimental measurement in one embodiment of the present invention. The different voltage types include DC, AC / DC superposition voltage with an AC / DC ratio of 1:3, and AC / DC superposition voltage with an AC / DC ratio of 1:7. The different electric field components include a strong perpendicular electric field component and only a parallel electric field component.

[0046] Under the same experimental conditions, the flashover probability increases with the increase in the flashover voltage peak. However, under different experimental conditions, the surface flashover voltage in the case of a perpendicular component electric field is lower than that in the case of a parallel component electric field. On the one hand, the presence of the backplate electrode provides a strong perpendicular component electric field on the surface, which increases the surface composite field strength and makes flashover more likely to occur. On the other hand, the strong perpendicular electric field component first intensifies the impact of charged particles in SF6 on the epoxy cylinder surface, resulting in more charge detrapping compared to the parallel electric field case. This leads to the release of a large number of electrons, photons, and depolarization energy, which disturbs the equilibrium state of space charge and causes surface flashover at a lower voltage. The mechanism diagram is shown in Figure 6(a).

[0047] In addition, the flashover voltage under DC superimposed on AC is lower than that under pure DC, and the flashover voltage gradually decreases as the AC voltage ratio increases. First, under AC voltage, the electric field distribution is negatively correlated with the dielectric constant of the material, while under DC voltage, it is related to the conductivity of the material. Therefore, the electric field under the two voltages is different. At the same time, SF6's own ionization and collision ionization with electrons will generate space charge. This part of the space charge is affected by the external DC electric field and moves, forming a reverse electric field that weakens its own electric field. This does not form under the AC voltage component. Moreover, with the introduction of the AC component, the rising and falling stages of the voltage lead to different degrees of trapping of electrons during migration, causing surface electric field distortion. For these reasons, the flashover voltage under DC superimposed on AC is lower than that under pure DC. The mechanism diagram is shown in Figure 6(b).

[0048] The above general description of the invention and the description of its specific embodiments involved in this application should not be construed as limiting the technical solutions of the invention. Based on the disclosure of this application, those skilled in the art may, without violating the constituent elements of the invention involved, add to, subtract from, or combine the disclosed technical features in the above general description and / or specific embodiments (including examples) to form other technical solutions within the scope of protection of this application.

Claims

1. A surface flashover experimental electrode device with adjustable strong vertical electric field at the interface, characterized in that: The device comprises: A high voltage electrode, a back plate electrode, a ground electrode, an epoxy pressing plate, a first fixing part and a second fixing part, wherein: The device connects and fixes the ground electrode and the back plate electrode through the first fixing part, and clamps the sample through the first fixing part. The device uses the epoxy pressing plate to ensure that there is no air gap between the high voltage electrode, the sample, and the back plate electrode. The device fixes the epoxy pressing plate through the second fixing part.

2. The device according to claim 1, characterized in that Preferably, the high voltage electrode is a finger-type electrode.

3. The device according to claim 1, characterized in that The first fixing part is a fixing screw, and the second fixing part is an insulating screw.

4. The device according to claim 2, characterized in that The length of the finger-shaped electrode is 25-35 mm, and the radius of the front finger-shaped electrode is 5-15 mm.

5. The device according to claim 1, characterized in that The back plate electrode is in a step shape, and the upper step is shorter than the lower step.

6. The device according to claim 1, characterized in that The back plate electrode and the ground electrode jointly clamp the sample.

7. The device according to claim 1, characterized in that A potential difference is formed between the back plate electrode and the high voltage electrode.

8. The device according to claim 1, characterized in that The back plate electrode is used to provide a strong vertical electric field component, and the strong vertical electric field components of different sizes can be adjusted by changing the sizes of the sheet sample and the back plate electrode.

9. The device according to claim 3, characterized in that The fixing screw is a metal screw, and the insulating screw is an epoxy screw.

10. The device according to claim 9, characterized in that The metal screws are used to connect and fix the ground electrode and the back plate electrode, and the epoxy screw rods are used to fix the epoxy pressing plate.

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