Gradient conductivity anti-corona insulator for extra-high voltage direct current transmission and preparation process thereof

Abstract

The application discloses a gradient conductivity anti-corona insulator for extra-high voltage direct current transmission and a preparation process thereof. The application relates to the technical field of insulator manufacturing, and the process comprises the following steps: injecting a composite slurry containing a dielectrophoretic active core-shell filler, a nonlinear conductivity response filler, a thermally induced self-adaptive filler and an epoxy resin matrix into a mold with an electrode; in the curing process, an alternating electric field is applied, the dielectrophoretic force is used to drive the filler to migrate along the direction of the electric field and form a gradient distribution of the filler density, wherein the frequency applied to the high filler density area is greater than that applied to the low filler density area; then, a multi-dimensional gradient network is constructed through mold turning and secondary induction of a low-frequency electric field, the gradient structure is locked through a high-frequency pulse voltage, and finally, a gradient curing treatment is performed. The application realizes active and controllable migration of the filler in situ and three-dimensional gradient network construction, so that the insulator has electric field-temperature double-parameter dynamic self-adaptive regulation and control capability, and the anti-corona performance and operation reliability are improved.

Description

Technical Field

[0001] This invention relates to the field of insulator manufacturing technology, and more specifically, to gradient conductivity anti-corona insulators for ultra-high voltage direct current transmission and their manufacturing process. Background Technology

[0002] In ultra-high voltage direct current (UHVDC) transmission systems, insulators, as key supporting and insulating components, are subjected to the combined effects of steady-state DC electric fields, polarity-reversal transient electric fields, and operational shock transient electric fields over long periods. Near the high-voltage electrodes and at the gas-solid interface, severe electric field distortion easily induces corona discharge, leading to insulator surface aging and a decrease in flashover voltage, seriously threatening the safety of the transmission system. To suppress corona, researchers have proposed constructing insulators with conductivity gradients to uniformly distribute the electric field: that is, ensuring the conductivity of the insulator decreases continuously or in a stepwise manner from the high-voltage side to the ground side, allowing accumulated charges to be orderly conducted and reducing local electric field peaks.

[0003] Existing technologies mainly revolve around the following approaches: First, the surface segmented coating gradient method, which achieves a surface gradient through multiple coating regions with different electrical conductivity, but the coating-substrate bonding is weak and the gradient is limited to a two-dimensional surface; second, the centrifugal casting continuous gradient method, which uses rotational speed gradient to control the radial distribution of filler, but the filler distribution fluctuates greatly due to the influence of hydrodynamics, and the gradient becomes fixed once solidified; third, the 3D printing multidimensional gradient method, which can achieve arbitrary gradient distribution in space, but the printing speed is slow, there are many interlayer interface defects, and the cost is high; fourth, the nonlinear conductive composite material method, which endows the material with adaptive field adjustment capabilities by doping with SiC, ZnO, etc., but lacks active gradient construction capabilities, and the nonlinear response threshold is difficult to control regionally when the filler is uniformly dispersed.

[0004] The common inherent drawback of the aforementioned existing technologies lies in the fact that the gradient structures are all pre-designed and locked once solidified, making dynamic adjustment impossible based on operating conditions (such as voltage polarity reversal, temperature fluctuations, and contamination accumulation). This leads to gradient failure and exacerbated corona discharge during long-term service. Furthermore, the fabrication processes are generally complex, gradient resolution is limited, and filler utilization is low. Therefore, there is an urgent need to develop a novel insulator technology that combines dynamic adaptive gradient control capabilities, a three-dimensional gradient structure, and an efficient fabrication process. Summary of the Invention

[0005] To overcome the problems of fixed gradient structure and lack of dynamic electric field-temperature adaptive capability in existing technologies, this invention discloses a gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission and its manufacturing process, which can effectively solve the above-mentioned technical problems.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: The manufacturing process of gradient conductivity anti-corona insulators used in ultra-high voltage direct current transmission includes: A composite slurry is injected into a mold with electrodes. The composite slurry comprises a dielectrophoretic active core-shell filler, a nonlinear conductivity-responsive filler, a thermotropic adaptive filler, and an epoxy resin matrix. During the curing and molding process, an alternating electric field is applied through the electrodes, causing the filler in the composite slurry to migrate along the direction of the electric field under the action of dielectric force and form a filler density gradient distribution in the insulator body; The frequency of the alternating electric field applied when forming a high-fill-density region is greater than the frequency of the alternating electric field applied when forming a low-fill-density region.

[0007] Furthermore, the frequency of the alternating electric field applied when forming the high filler density region is 300 kHz to 1 MHz, and the frequency of the alternating electric field applied when forming the low filler density region is 100 Hz to 5 kHz; the curing temperature when forming the high filler density region is 100 to 120°C, and the curing temperature when forming the low filler density region is 70 to 90°C.

[0008] Furthermore, the dielectric electrophoretic active core-shell filler is a Fe3O4@SiO2 / C core-shell structured nanofiller, the nonlinear conductivity-responsive filler is a mixture of micron-sized silicon carbide and nano-sized zinc oxide with a mass ratio of 2:3, and the thermotropic adaptive filler is a temperature-sensitive conductive microcapsule with a paraffin / carbon nanotube composite core; the volume ratio of the three is 8-15 vol% : 12-20 vol% : 3-8 vol%.

[0009] Furthermore, the dielectric electrophoretic active core-shell filler, nonlinear conductivity responsive filler, and thermo-adaptive filler are respectively surface functionalized before injection into the mold; The surface modification of the dielectric electrophoretic active core-shell filler is a composite modification of oxygen-containing plasma treatment and silane coupling agent grafting; the surface modification of the nonlinear conductivity responsive filler is dielectric barrier discharge plasma modification; and the surface modification of the thermotropic adaptive filler is a multi-layer shell encapsulation of a melamine resin inner layer and a polyurea elastomer outer layer.

[0010] Furthermore, after forming the high filler density region, the process also includes rotating the mold 180° and applying a low-frequency alternating electric field after rotation for secondary induction, so that the filler forms a multi-dimensional gradient network structure in the radial and axial directions.

[0011] Furthermore, the frequency of the secondary induced low-frequency alternating electric field is 1–5 kHz, and the curing temperature of the secondary induced curing is 70–90 °C.

[0012] Furthermore, after applying the alternating electric field and before curing is completed, a step of applying a high-frequency pulse voltage to the mold electrodes for gradient locking is included; the amplitude of the high-frequency pulse voltage is 15-20 kV, the pulse width is 50-200 μs, the number of pulses is 5-10, and the pulse interval is 0.5-2 seconds.

[0013] Furthermore, the waveform of the high-frequency pulse voltage is a square wave or a sharp pulse wave, which is used to locally and rapidly solidify the epoxy matrix under the action of the pulse electric field, instantly lock the spatial gradient distribution of the filler and prevent the filler from agglomerating again.

[0014] Furthermore, after gradient locking and curing, a gradient post-curing treatment step is also included; the gradient post-curing treatment involves sequentially holding at 80°C for 2 hours, at 120°C for 4 hours, and at 150°C for 2 hours, followed by natural cooling to room temperature.

[0015] Furthermore, the gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission is manufactured using the gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission and its manufacturing process described above.

[0016] Compared with existing technologies, the advantages of this invention are as follows: This invention abandons the traditional preset gradient manufacturing mode and uses an alternating electric field to drive the dielectrophoretic active filler to actively migrate in situ and distribute as needed, forming a gradient structure in which the filler density automatically matches the electric field strength. When the operating conditions change (such as voltage polarity reversal or overvoltage impact), the filler can undergo a slight rearrangement response under the applied or induced electric field, so that the conductivity gradient dynamically adapts to the current electric field distribution, thereby continuously suppressing corona. At the same time, the nonlinear conductive filler (SiC / ZnO) automatically increases conductivity to dissipate charge when the local electric field exceeds the threshold, and the thermally adaptive microcapsules enhance the conductivity path through phase transition when corona heating occurs, forming a closed-loop control of electric field and temperature dual parameters, overcoming the fundamental defect of fixed gradient in existing technologies. Through a multi-physics synergistic process of high-temperature, high-frequency primary induction → mold flipping → low-temperature, low-frequency secondary induction, the filler not only forms a density gradient from the high-voltage side to the ground side axially, but also achieves directional arrangement and hierarchical distribution radially, obtaining a three-dimensional gradient network with a continuous transition between the inner high-density charge-conducting layer and the surface low-density electric field buffer layer. Compared with the simple gradients formed by existing surface coatings or centrifugation methods, this invention can reduce the maximum electric field intensity on the insulator surface, increase the corona initiation voltage, and control the surface electric field distortion rate within a low range. The single electric field induction molding time is only 30~120 seconds, and the gradient solidification is completed instantly by high-frequency pulse locking, shortening the overall preparation cycle compared to 3D printing. The pulse electric field anchoring process effectively prevents secondary agglomeration of the filler, and the gradient resolution reaches the sub-micron level. All processes are completed in one integrated manner within the mold, eliminating the need for multi-layer casting or complex post-assembly, resulting in a high yield rate and suitability for large-scale manufacturing in ultra-high voltage projects. After modification by plasma and coupling agents, the filler surface is tightly bonded to the epoxy matrix, reducing interface defects. In environmentally friendly insulating gas environments such as SF6 or C4F7N, the performance degradation rate is lower than that of traditional surface coating technologies. After cycling and curing, internal stress is fully released. This invention provides an anti-corona insulator solution for UHVDC transmission that combines dynamic intelligent response, high gradient efficiency, and long lifespan. Attached Figure Description

[0017] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary. For those skilled in the art, other embodiments can be derived from the provided drawings without creative effort.

[0018] Figure 1 A flowchart illustrating the manufacturing process of a gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission provided in this application embodiment. Detailed Implementation

[0019] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent. To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It will be understood by those skilled in the art that certain well-known structures and their descriptions may be omitted in the accompanying drawings.

[0020] The embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples.

[0021] It is understood that the specific embodiments described herein are merely illustrative of the embodiments of this application and are not intended to limit the embodiments of this application. Furthermore, it should be noted that, for ease of description, the accompanying drawings only show the parts related to the embodiments of this application, not all structures. Those skilled in the art, after reading this specification, should be able to realize that any combination of technical features can constitute an optional implementation method, provided that the technical features do not contradict each other.

[0022] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship. In the description of this application, "multiple" means two or more, and "several" means one or more.

[0023] This invention discloses a gradient conductivity anti-corona insulator for ultra-high voltage direct current (UHVDC) transmission, its manufacturing process, and corresponding insulator products. It aims to solve the technical problems of existing UHVDC transmission insulators, such as easy corona discharge, uneven electric field distribution, and insufficient aging resistance. By manufacturing insulators with a gradient conductivity distribution, the internal electric field distribution of the insulator is optimized, corona discharge is suppressed, and the insulator's corona resistance, mechanical properties, and long-term operational stability are improved, meeting the stringent operational requirements of UHVDC transmission projects.

[0024] It should be noted that, unless otherwise specified, the equipment, raw materials, and reagents involved in this embodiment are all commercially available conventional products; the operating steps and process parameters involved are all optimized selections based on the technical solution of this invention, and can be appropriately adjusted according to the actual production scale, product specifications, etc., and all fall within the protection scope of this invention. The room temperature mentioned in this embodiment refers to 25±5℃, "vol%" is volume percentage, kHz is kilohertz, MHz is megahertz, kV is kilovolt, μs is microsecond, and the volume ratio of all fillers is calculated based on the epoxy resin matrix to ensure precise control of the gradient conductivity. The gradient conductivity anti-corona insulator prepared in this embodiment is mainly used in insulator strings of ±800kV and ±1100kV ultra-high voltage DC transmission lines, which can effectively suppress electromagnetic interference, noise pollution, and insulation aging caused by corona discharge, extend the service life of the insulator, and ensure the safe and stable operation of the ultra-high voltage DC transmission system.

[0025] First, the core principle and overall process of the preparation process of this invention will be explained. The core innovation of this process is that by using dielectric electrophoresis induction technology, combined with gradient curing, gradient locking and post-processing, various fillers in the composite slurry form a density gradient distribution along the electric field direction, thereby realizing the gradient conductivity control of the insulator body. At the same time, through the synergistic effect of various fillers, the insulator is endowed with nonlinear conductivity response and thermal adaptive performance, thereby improving its anti-corona effect and operational stability. The overall process flow is as follows: raw material preparation and pretreatment (preparation of various fillers, surface functionalization modification, formulation of epoxy resin matrix, and mixing of composite slurry), mold preparation and slurry injection (pretreatment of special molds with electrodes, and injection of composite slurry after vacuum degassing), dielectric electrophoresis induction and gradient curing (applying alternating electric fields of different frequencies in stages, combined with gradient temperature control, to form a density gradient distribution of fillers; optional mold flipping secondary induction to form a multidimensional gradient), gradient locking (applying high-frequency pulse voltage to instantaneously lock the gradient distribution of fillers to prevent agglomeration), gradient curing (stage-wise heating and heat preservation to improve curing degree and performance stability), demolding and finished product inspection (demolding treatment, appearance inspection, performance testing), and finished gradient conductivity anti-corona insulator.

[0026] Please see Figure 1 Raw material preparation and pretreatment. This step mainly includes the preparation and surface functionalization modification of dielectrophoretic active core-shell fillers, nonlinear conductivity-responsive fillers, and thermotropic adaptive fillers, as well as the formulation of epoxy resin matrix and the mixing of composite slurry. The dielectrophoretic active core-shell filler is selected from Fe3O4@SiO2 / C core-shell structured nanofillers, and its preparation method is as follows: Fe3O4 nanoparticles were prepared by dissolving FeCl3·6H2O and FeSO4·7H2O in deionized water at a molar ratio of 2:1. After stirring until homogeneous, 25wt% ammonia solution was slowly added dropwise to adjust the pH of the solution to 9-10. The reaction was carried out in a 60℃ water bath with stirring for 2 hours to generate black Fe3O4 nanoparticles. After centrifugation, the nanoparticles were repeatedly washed with deionized water and ethanol until neutral, and then vacuum dried at 80℃ for 12 hours to obtain Fe3O4 nanocores. Subsequently, a SiO2 shell was coated on the surface of the Fe3O4 nanocores. The Fe3O4 nanoparticles were then dispersed in a mixed solvent of ethanol and deionized water (volume ratio 3:1), and tetraethyl orthosilicate was added as silicon. The pH value was adjusted to 4-5 by adding dilute hydrochloric acid, and the reaction was stirred at room temperature for 8 hours. After centrifugation, washing, and drying, Fe3O4@SiO2 core-shell structured particles were obtained. Finally, a carbon layer was coated on the surface of the SiO2 shell, and the Fe3O4@SiO2 particles were dispersed in a glucose aqueous solution and ultrasonically dispersed for 30 minutes. The particles were then transferred to a hydrothermal reactor and hydrothermally reacted at 180℃ for 12 hours. After cooling, the particles were centrifuged and calcined at 500℃ under a nitrogen atmosphere for 2 hours to obtain Fe3O4@SiO2 / C core-shell structured nanofiller with a particle size controlled at 50-100 nm to ensure excellent dielectric electrophoretic activity and rapid migration under an alternating electric field.

[0027] The nonlinear conductivity response filler is a mixture of micron-sized silicon carbide and nano-sized zinc oxide, with a strictly controlled mass ratio of 2:3. The micron-sized silicon carbide has a particle size of 5-10 μm and a purity of ≥99%, while the nano-sized zinc oxide has a particle size of 50-80 nm and a purity of ≥99.5%. This ratio is chosen because the synergistic effect of the two can endow the composite system with excellent nonlinear conductivity characteristics. When the electric field strength inside the insulator is too high, the conductivity rises rapidly first, alleviating electric field concentration, suppressing corona discharge, and avoiding the decrease in insulation performance caused by excessive conductivity. The thermosensitive conductive microcapsules with a paraffin / carbon nanotube composite core are prepared as follows: Paraffin is used as the core material (melting point 50-60℃), and carbon nanotubes (diameter 10-20nm, length 1-5μm) are used as the conductive medium. The paraffin is melted by heating, and then carbon nanotubes are added and stirred until homogeneous to form the paraffin / carbon nanotube composite core. Melamine resin and polyurea elastomer are used as the shell material. An in-situ polymerization method is employed. First, the composite core is dispersed in deionized water, and an emulsifier (sodium dodecylbenzenesulfonate) is added. The mixture is ultrasonically emulsified for 30 minutes to form a stable emulsion. Then, melamine resin and polyurea elastomer are added... Amine resin prepolymer is adjusted to pH 8-9 and reacted at 70℃ for 2 hours to form a melamine resin inner shell. Then, polyurea elastomer monomer is added and the reaction continues for 3 hours to form a polyurea elastomer outer shell. After centrifugation, washing, and drying, temperature-sensitive conductive microcapsules are obtained with a particle size controlled at 1-5 μm. These microcapsules are in an insulating state at room temperature. When the insulator is in operation and local overheating occurs due to corona discharge (temperature exceeds the melting point of paraffin), the paraffin melts, and carbon nanotubes form conductive pathways, increasing the local conductivity and further alleviating the electric field concentration, thus achieving thermo-induced adaptive anti-corona regulation.

[0028] To improve the compatibility of various fillers with the epoxy resin matrix, prevent filler agglomeration, and ensure uniform migration of fillers during dielectric electrophoresis, each filler needs to undergo surface functionalization modification before injection into the mold. Specifically, the dielectric electrophoretic active core-shell filler undergoes a composite modification using oxygen-containing plasma treatment and silane coupling agent grafting. First, Fe3O4@SiO2 / C nanofiller is placed in a plasma treatment instrument, oxygen is introduced, the plasma power is 100-150W, and the treatment time is 10-15 minutes, generating oxygen-containing functional groups such as hydroxyl and carboxyl groups on the filler surface. Then, the treated filler is dispersed in ethanol, and a silane coupling agent (KH-550) is added at 3-5% of the filler mass. The mixture is stirred at 80℃ for 4 hours, centrifuged, and dried to complete the surface modification. This modification significantly improves the interfacial bonding force between the filler and the epoxy resin, reducing agglomeration. Nonlinear conductivity-responsive fillers are modified using dielectric barrier discharge plasma. A mixture of micron-sized silicon carbide and nano-sized zinc oxide is placed in a dielectric barrier discharge plasma device, argon gas is introduced, the discharge power is 80-100W, and the treatment time is 8-12 minutes. This increases the surface roughness of the filler and introduces active functional groups, improving its compatibility with epoxy resin and promoting uniform dispersion of the filler in the matrix. Thermotropic adaptive fillers are modified using a multi-layer shell encapsulation of a melamine resin inner layer and a polyurea elastomer outer layer. This modification is completed simultaneously during microcapsule preparation. The multi-layer shell structure not only protects the paraffin / carbon nanotube composite core but also improves the compatibility of the microcapsules with epoxy resin, while enhancing the mechanical strength of the microcapsules and preventing breakage during dielectric electrophoresis induction and curing.

[0029] The epoxy resin matrix is ​​made of bisphenol A type epoxy resin (E-51), which is formulated with curing agent (diaminodiphenylmethane, DDM) and accelerator (2-methylimidazole). The mass ratio of epoxy resin, curing agent and accelerator is 100:25:1. The formulation process is as follows: The epoxy resin is placed in a constant temperature stirring tank and heated to melt at 60°C. After stirring evenly, the curing agent and accelerator are slowly added and stirred for 30 minutes to ensure that the three are mixed evenly to obtain the epoxy resin matrix. Subsequently, according to the defined volume ratio, the modified dielectrophoretic active core-shell filler, nonlinear conductivity-responsive filler, and thermotropic adaptive filler were added to the epoxy resin matrix. The volume ratio of the three was 8–15 vol% : 12–20 vol% : 3–8 vol%. In this embodiment, the preferred volume ratio was 12 vol% : 16 vol% : 5 vol%. After adding the fillers, the mixture was first mechanically stirred (at a speed of 500–800 r / min) for 1 hour, and then ultrasonically dispersed (at a power of 300 W) for 30 minutes to ensure that the fillers were uniformly dispersed in the epoxy resin matrix. The mixed composite slurry was then placed in a vacuum degassing chamber at a vacuum degree ≤10. -3Degas at 60°C for 20 minutes to remove air bubbles from the slurry, preventing them from affecting the insulation and mechanical properties of the insulator after curing. Once degassing is complete, the slurry is ready for use.

[0030] Mold preparation and slurry injection are crucial steps in ensuring the molding quality and uniform gradient distribution of insulators. This step mainly includes the preparation and pretreatment of a specialized mold with electrodes, and the precise injection of the composite slurry. The mold is made of high-strength aluminum alloy. The mold cavity is designed according to the actual specifications of the UHVDC transmission insulator (such as skirt structure, length, diameter, etc.). A pair of parallel metal electrodes (copper electrodes, 2-3mm thick) are embedded inside the mold. The electrode arrangement direction is consistent with the insulator's axis, and the electrode spacing is set to 50-100mm according to the mold cavity size. The electrode surfaces are polished to ensure uniform electric field distribution and avoid localized electric field concentration affecting filler migration. The inner wall of the mold needs to be demolded by applying a release agent (silicone-based release agent). After even application, the mold is placed in an oven at 80℃ for 30 minutes to remove moisture from the release agent, ensuring smooth demolding and preventing the release agent from affecting the curing of the composite slurry and the surface quality of the insulator. After the mold is pre-treated, it is fixed on a special tooling table to ensure that the mold is placed horizontally, so as to avoid skewing after the slurry is injected, which would affect the gradient distribution.

[0031] The grout injection process must be carried out in a constant temperature and clean environment (ambient temperature 25±2℃, cleanliness level 1000). Using precision grouting equipment, the vacuum-degassed composite grout is slowly injected into the mold cavity at a controlled injection speed of 5-10 mL / min to avoid air bubbles from excessive speed, while ensuring the grout completely fills the mold cavity without gaps or missing material. After grouting, excess grout on the mold surface is scraped smooth with a scraper to ensure a flat insulator surface. A sealing cap is then placed on top of the mold to prevent dust from entering during curing and to facilitate the subsequent application of alternating electric fields and high-frequency pulse voltages. After injection, allow the mold to stand for 10-15 minutes to allow the grout to fully wet the inner wall of the mold and the electrode surface.

[0032] Dielectrophoretic induction and gradient curing are the core steps of this process. Their purpose is to induce the filler in the composite slurry to migrate along the electric field direction under the action of dielectric force by applying an alternating electric field, forming a filler density gradient distribution. Simultaneously, gradient temperature control ensures stable curing of the filler after migration, forming a gradient conductivity structure. Specifically, the high filler density region is first induced and cured. This region corresponds to the electric field concentration area of ​​the insulator (such as the insulator end and shed root). This region requires higher conductivity to alleviate electric field concentration and suppress corona discharge. Therefore, the alternating electric field frequency applied when forming the high filler density region is greater than that applied when forming the low filler density region. Specific parameters are: alternating electric field frequency controlled between 300kHz and 1MHz (preferably 500kHz in this embodiment); electric field strength controlled between 5-10kV / cm; and the mold placed in a constant temperature oven while the electric field is applied, with the curing temperature controlled between 100-120℃ (preferably 110℃ in this embodiment); and curing time of 2-3 hours. Under these conditions, the dielectrophoretic active core-shell filler is subjected to a strong dielectrophoretic force under the action of a high-frequency alternating electric field, and migrates rapidly in the direction of the electric field. At the same time, it drives the nonlinear conductivity response filler and the thermally adaptive filler to migrate together, forming a high filler density region near the electrode, with a filler volume fraction of 30-40%. The conductivity of this region will be significantly higher than that of other regions.

[0033] After the high-filler-density region is cured, the low-filler-density region is induced and cured. This low-filler-density region corresponds to the non-electric field-concentrated area of ​​the insulator. This region needs to maintain a low conductivity to ensure the overall insulation performance of the insulator. Therefore, a low-frequency alternating electric field is applied. Specific parameters are: the alternating electric field frequency is controlled between 100Hz and 5kHz (preferably 2kHz in this embodiment); the electric field strength is controlled between 2-5kV / cm; and the oven temperature is adjusted to 70-90℃ (preferably 80℃ in this embodiment). The curing time is 3-4 hours. Under the action of the low-frequency alternating electric field, the remaining filler is subjected to a weak dielectric force and slowly migrates, forming a low-filler-density region with a filler volume fraction of 15-25%. This creates a filler density gradient distribution along the electric field direction (axial direction) within the insulator body, thereby achieving gradient control of conductivity. To further optimize the gradient distribution and improve the corona resistance of the insulator, a secondary induction treatment can be performed after forming the high filler density area. The specific operation is as follows: The mold is rotated 180° to ensure the insulator is axially inverted. Then, a low-frequency alternating electric field is applied for secondary induction. The frequency of the low-frequency alternating electric field for secondary induction is 1–5 kHz, preferably 3 kHz in this embodiment, with an electric field strength of 2–3 kV / cm. The curing temperature for secondary induction is 70–90°C, preferably 80°C in this embodiment, and the secondary induction time is 1–2 hours. Through mold rotation and secondary induction, a multi-dimensional gradient network structure can be formed in the radial and axial directions of the filler, further optimizing the electric field distribution inside the insulator, avoiding radial electric field concentration, and improving the overall corona resistance effect. This step can be selected for implementation according to actual product requirements, and all are within the scope of protection of this invention.

[0034] During the dielectrophoresis-induced and gradient curing process, it is necessary to monitor the electric field parameters, temperature parameters, and curing state of the slurry in real time to ensure uniform filler migration and a reasonable gradient distribution. The electric field parameters are precisely controlled using a high-frequency signal generator, with fluctuations in frequency and electric field strength not exceeding ±5%. The temperature is controlled by the temperature control system of a constant-temperature oven, with fluctuations not exceeding ±2℃. The curing state is monitored by sampling every 30 minutes to check the gel time of the slurry, ensuring the curing process meets requirements and avoiding either excessively rapid curing leading to insufficient filler migration or excessively slow curing causing secondary filler agglomeration. Simultaneously, the mold must be kept fixed during the curing process to avoid vibration and prevent disruption of the filler gradient distribution.

[0035] The gradient locking and post-treatment steps are used to ensure the stability of the filler gradient distribution and improve the curing degree and performance stability of the insulator. Specifically, these steps include high-frequency pulsed voltage gradient locking and gradient-based post-curing treatment, performed sequentially. The gradient locking step is performed after applying the alternating electric field and before curing is complete. The purpose is to use high-frequency pulsed voltage to rapidly cure the epoxy matrix locally, instantly locking the spatial gradient distribution of the filler and preventing secondary agglomeration during subsequent curing, thus ensuring the stability of the gradient distribution. The specific parameters for gradient locking are as follows: a high-frequency pulse voltage is applied between the mold electrodes, with a voltage amplitude of 15–20 kV (preferably 18 kV in this embodiment), a pulse width of 50–200 μs (preferably 100 μs in this embodiment), a number of pulses of 5–10 (preferably 8 in this embodiment), and a pulse interval of 0.5–2 seconds (preferably 1 second in this embodiment). The waveform of the high-frequency pulse voltage is a square wave or a sharp pulse wave, with a square wave being preferred in this embodiment. Square wave pulses have the advantages of stable voltage and uniform effect, enabling the epoxy matrix to undergo rapid cross-linking reaction and local curing under the action of the pulsed electric field, thereby firmly locking the gradient distribution of the filler and ensuring that the filler position does not change during subsequent curing. During gradient locking, the application speed of the pulse voltage needs to be controlled to avoid excessive voltage causing cracks inside the insulator. At the same time, the temperature change inside the mold should be monitored. If the temperature is too high, the pulse interval can be appropriately extended to ensure process stability.

[0036] After gradient locking is completed, a gradient post-curing treatment is performed to improve the curing degree of the insulator, eliminate internal stress, and enhance the mechanical, insulating, and aging resistance properties of the insulator. The post-treatment process adopts a staged heating and holding method, with the following specific steps: First, the mold and the insulator are placed together in a constant temperature oven and held at 80℃ for 2 hours. This stage mainly eliminates the internal stress generated during the curing process, allowing the epoxy matrix to cure slowly and preventing cracks. Then, the oven temperature is raised to 120℃ and held for 4 hours. This is the main curing stage, promoting full cross-linking of the epoxy matrix, improving the curing degree, and ensuring the mechanical strength and insulating performance of the insulator. Finally, the oven temperature is raised to 150℃ and held for 2 hours to further improve the curing degree and enhance the aging resistance and thermal stability of the insulator. After the post-treatment is completed, the oven is closed, and the insulator is allowed to cool naturally to room temperature. The cooling rate is controlled at 5-10℃ / hour to avoid excessively rapid cooling that could cause thermal stress, cracks, or damage to the insulator. After natural cooling to room temperature, the post-treatment steps are completed.

[0037] Demolding inspection and product verification are the final steps to ensure the quality of insulator products meets standards. This includes demolding, visual inspection, performance testing, and product verification to ensure that the prepared gradient conductivity anti-corona insulators meet the application requirements of UHVDC transmission projects. Demolding: After the insulators have cooled naturally to room temperature, open the mold seal and slowly disassemble the mold. Since the inner wall of the mold has undergone demolding treatment, the insulators can be demolded smoothly. During demolding, handle the insulators gently to avoid collisions and scratches on the surface, preventing damage. After demolding, conduct a visual inspection of the insulators using a combination of visual observation and a magnifying glass (10x magnification). Check whether the surface of the insulator is flat and smooth, and whether there are defects such as cracks, bubbles, missing material, and scratches. Also check whether the skirt structure is intact and whether the dimensions meet design requirements. If defects are found, repair or scrapping is required. Qualified products proceed to the subsequent performance testing stage.

[0038] The same or similar labels correspond to the same or similar parts; The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent. Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A manufacturing process for gradient conductivity anti-corona insulators used in ultra-high voltage direct current transmission, characterized in that, include: A composite slurry is injected into a mold with electrodes. The composite slurry comprises a dielectrophoretic active core-shell filler, a nonlinear conductivity-responsive filler, a thermotropic adaptive filler, and an epoxy resin matrix. During the curing and molding process, an alternating electric field is applied through the electrodes, causing the filler in the composite slurry to migrate along the direction of the electric field under the action of dielectric force and form a filler density gradient distribution in the insulator body; The frequency of the alternating electric field applied when forming a high-fill-density region is greater than the frequency of the alternating electric field applied when forming a low-fill-density region.

2. The manufacturing process of the gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission as described in claim 1, characterized in that, The frequency of the alternating electric field applied when forming the high filler density region is 300 kHz to 1 MHz, and the frequency of the alternating electric field applied when forming the low filler density region is 100 Hz to 5 kHz; the curing temperature when forming the high filler density region is 100 to 120°C, and the curing temperature when forming the low filler density region is 70 to 90°C.

3. The manufacturing process of the gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission as described in claim 1 or 2, characterized in that, The dielectric-active core-shell filler is a Fe3O4@SiO2 / C core-shell structured nanofiller; the nonlinear conductivity-responsive filler is a mixture of micron-sized silicon carbide and nano-sized zinc oxide in a mass ratio of 2:3; and the thermotropic adaptive filler is a thermosensitive conductive microcapsule with a paraffin / carbon nanotube composite core. The volume ratio of the three components is 8–15 vol% : 12–20 vol% : 3–8 vol%.

4. The manufacturing process of the gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission as described in claim 3, characterized in that, The dielectric-active core-shell filler, nonlinear conductivity-responsive filler, and thermo-adaptive filler are all surface-functionalized before being injected into the mold. The surface modification of the dielectric electrophoretic active core-shell filler is a composite modification of oxygen-containing plasma treatment and silane coupling agent grafting; the surface modification of the nonlinear conductivity responsive filler is dielectric barrier discharge plasma modification; and the surface modification of the thermotropic adaptive filler is a multi-layer shell encapsulation of a melamine resin inner layer and a polyurea elastomer outer layer.

5. The manufacturing process of the gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission as described in claim 1, characterized in that, After forming the high filler density region, the process also includes rotating the mold 180° and applying a low-frequency alternating electric field after rotation to induce a secondary reaction, so that the filler forms a multi-dimensional gradient network structure in the radial and axial directions.

6. The manufacturing process of the gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission as described in claim 5, characterized in that, The frequency of the secondary induced low-frequency alternating electric field is 1–5 kHz, and the curing temperature of the secondary induced curing is 70–90℃.

7. The manufacturing process of the gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission as described in claim 1, characterized in that, After applying the alternating electric field and before curing is completed, the process also includes a step of applying a high-frequency pulse voltage between the mold electrodes for gradient locking; the amplitude of the high-frequency pulse voltage is 15-20 kV, the pulse width is 50-200 μs, the number of pulses is 5-10, and the pulse interval is 0.5-2 seconds.

8. The manufacturing process of the gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission as described in claim 7, characterized in that, The waveform of the high-frequency pulse voltage is a square wave or a sharp pulse wave, which is used to locally and rapidly solidify the epoxy matrix under the action of the pulse electric field, instantly lock the spatial gradient distribution of the filler and prevent the filler from agglomerating again.

9. The manufacturing process of the gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission as described in claim 1, characterized in that, After gradient locking and curing, a gradient post-curing process is also included; the gradient post-curing process involves sequentially holding at 80°C for 2 hours, at 120°C for 4 hours, and at 150°C for 2 hours, followed by natural cooling to room temperature.

10. A gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission, characterized in that, The gradient conductivity anti-corona insulator for ultra-high voltage direct current transmission and its manufacturing process, as described in any one of claims 1-9, are used to obtain the insulator.

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