High current dc transmission busbar insulation and method of making same

Abstract

The application discloses a large-current direct-current transmission bus insulating layer and a preparation method thereof, and belongs to the technical field of power transmission.The large-current direct-current transmission bus insulating layer comprises a plurality of glass fiber tape layers, resin adhesive layers and insulating reinforced film layers, the glass fiber tape layers and the insulating reinforced film layers are alternately stacked, and at least one resin adhesive layer is arranged between two adjacent layers; the preparation method of the insulating reinforced film comprises the following steps: step 1, preparing a resin glue solution; step 2, coating the resin glue solution on a release film, pre-drying to form a semi-cured film, and then performing segmented curing after hot-pressing compounding of the semi-cured film and two PET films; and step 3, peeling off the release film and slitting into a roll material.The large-current direct-current bus insulating layer prepared by the application has a breakdown voltage much higher than 20kV, and has super-high insulating strength, super-long service life, excellent mechanical and heat dissipation properties.

Description

Technical Field

[0001] This invention relates to the field of power transmission technology, specifically to the insulation layer of a high-current DC transmission bus and its preparation method. Background Technology

[0002] As the "power artery" of the superconducting magnet system, the high-current DC transmission bus undertakes a dual core mission: First, under normal operating conditions, it precisely connects the magnet power supply, DC switching system, and superconducting magnet coil to construct a complete low-impedance closed loop, achieving efficient and stable transmission of variable DC power (10-50 kA) at the 10,000 ampere level; Second, when the superconducting magnet suddenly loses its quench capability, it must withstand instantaneous kilovolt-level high-voltage surges (typically 3-5 kV / m) to provide a safe channel for the rapid dissipation of magnet energy and prevent catastrophic damage to the system.

[0003] However, the existing fabrication process for DC transmission bus insulation layers faces three major challenges: First, insulation performance is unstable, with interlayer air gap exceeding 0.5% and partial discharge initiation voltage below 20 kV, leading to frequent surface flashovers under high-voltage conditions. Second, withstand voltage is insufficient, with a room-temperature power frequency withstand voltage limit of only 28 kV, and insulation strength attenuation reaching 40% in the liquid nitrogen temperature range (-196℃), failing to meet quench protection requirements. Third, the process is complex and inefficient: reliance on manual winding results in thickness deviations > ±10%, multi-segment curing causes interface delamination, product qualification rate is less than 70%, and manufacturing costs increase by 50%. These problems are particularly prominent in scenarios such as high-field-strength fusion devices (e.g., ITER longitudinal field coils) and high-precision medical imaging equipment (16T MRI)—when the bus needs to carry 50 kA current in a 4.5K superfluid helium environment, or withstand an 8 kV / m voltage gradient during quench, traditional insulation layers have become a fatal weakness in system reliability.

[0004] Insulation technology suffers from drawbacks such as high air gap ratio, low-temperature performance degradation, and poor process consistency, severely limiting its application in high-end scenarios such as fusion devices and high-field MRI. For example, the insulation strength of a certain type of accelerator busbar decreases by 40% at -196℃ compared to room temperature, causing the quench protection threshold to fail to meet the standard. Furthermore, the manual winding process makes it difficult to guarantee the uniformity of insulation layer thickness, with measured deviations often exceeding the nominal value by more than 10%. This not only weakens insulation reliability but also leads to a scrap rate of approximately 30%, further increasing the manufacturing cost of critical equipment. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing an insulation layer for a high-current DC transmission bus. The method employs an overlapping and winding scheme of fiberglass tape impregnated with resin adhesive and a pre-cured insulating reinforcement film. The breakdown voltage of the prepared insulation layer is much higher than 20kV. When used to protect DC bus carrying high current, it has extremely high safety and reliability, and improves the problems of poor strength and reliability of existing insulation layers, as well as poor process consistency during winding.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A high-current DC transmission bus insulation layer includes several fiberglass tape layers, resin adhesive layers and insulation reinforcement film layers, wherein the fiberglass tape layers and insulation reinforcement film layers are stacked alternately, and at least one resin adhesive layer is provided between adjacent layers.

[0008] The method for preparing the insulating reinforcing film includes the following steps:

[0009] Step 1: Mix epoxy resin, benzyl glycidyl ether and propylene glycol methyl ether acetate evenly, add nano-sized silica, ultrasonically disperse evenly, then add curing agent, defoamer and leveling agent and mix evenly, filter, degas to obtain resin adhesive;

[0010] Step 2: Apply resin liquid onto release film, pre-dry to form semi-cured film, hot-press semi-cured film with two layers of PET film, and then cure in sections.

[0011] Step 3: After cooling to room temperature, peel off the release film and cut it into rolls that match the fiberglass tape.

[0012] This invention employs an alternating layering scheme of fiberglass tape layers impregnated with resin adhesive and pre-cured insulating reinforcement film layers. The resulting high-current DC transmission bus insulation layer exhibits a breakdown voltage far exceeding 20kV, providing extremely high safety margin and reliability when used to protect DC buses carrying high currents. The resin-impregnated fiberglass tape layers ensure full wetting of the bus surface and interlayer, forming a gapless whole that provides excellent mechanical strength, adhesion, and basic insulation. The insulating reinforcement film layer, as a pre-prepared, highly controllable solid insulating barrier, is placed between the fiberglass tape layers to withstand and share extremely high electric field stresses, particularly suppressing partial discharge and surface flashover.

[0013] In existing technologies, directly coating PET with liquid resin results in solvent residue and uneven thickness; fully cured films lack adhesion. This invention first creates a "semi-cured film," which, during hot pressing, possesses a certain degree of fluidity to ensure perfect adhesion to PET, expel air, and maintain shape stability. The resulting PET / resin / PET three-layer structure provides excellent mechanical strength, tear resistance, and dimensional stability through the top and bottom PET film layers, while the middle epoxy resin layer provides extremely high dielectric strength and adhesion. The insulation reinforcement film itself has a thickness of 0.150 ± 0.001 mm.

[0014] Further, in step 1, the resin solution, by weight, comprises the following components:

[0015] 45-55 parts of bisphenol A type epoxy resin, 12-15 parts of modified alicyclic amine curing agent, 2.5-5 parts of benzyl glycidyl ether, 0.15-0.3 parts of organosilicon defoamer, 0.1-0.25 parts of fluorocarbon modified leveling agent, 1-3 parts of nano-sized silica, and 40-50 parts of propylene glycol methyl ether acetate;

[0016] The resin adhesive has a solid content of 48-52%.

[0017] Further, in step 1, the mixture is stirred at 50~60℃ until completely dissolved and mixed evenly; nano-sized silica is added and ultrasonically dispersed at 250~350W for 25~35min; then curing agent, defoamer and leveling agent are added, and the mixture is cooled to 35~42℃ and stirred at low speed for 8~12min; the mixture is filtered through a 350~450 mesh filter and allowed to stand for degassing for 25~35min to obtain the resin solution.

[0018] Stir at low speed at 35~42℃ for 8~12 minutes. Separate the step of adding the exothermic curing agent from the high-energy dispersion step. Solve the filler dispersion first, and then process the mixing to ensure the storage stability of the adhesive.

[0019] Further, in step 2, the resin solution is coated onto the release film, with a wet film thickness of 90~110μm. It is pre-baked at 75~85℃ for 5~8min to form a semi-cured film. The semi-cured film is then hot-pressed with two layers of PET film at 125~135℃ and 0.7~1.0MPa for 25~35min; cured at 95~105℃ for 0.8~1.2h, and then cured at 145~150℃ for 1.5~2.5h. The thickness of a single PET film layer is 0.05mm.

[0020] Segmented curing: The low-temperature stage allows the resin to gel slowly, forming a preliminary network structure and reducing internal stress caused by rapid curing; the high-temperature stage promotes complete reaction, reaching the highest crosslinking density, thereby obtaining optimal mechanical properties, heat resistance, and electrical properties. Simultaneously, it ensures good bonding between nano-SiO2 and the resin interface. Segmented curing avoids the problems of excessive internal stress leading to film warping or microcracks caused by single-stage high-temperature curing, and the freezing of molecular chains due to excessively rapid reaction, preventing the formation of a complete network.

[0021] A method for preparing an insulation layer for a high-current DC transmission bus includes the following steps:

[0022] S100, Pretreatment of resin adhesive: Mix all components of the insulating material evenly and degas under vacuum until no bubbles are present;

[0023] S200: Fiberglass tape and insulating reinforcement film, both impregnated with resin adhesive, are interleaved and wound around the outer surface of the busbar.

[0024] S300, under vacuum conditions, stepped temperature rise curing; nitrogen replacement is carried out during the curing process to obtain the busbar with cured insulation layer;

[0025] S400. Fix the two cured busbars in parallel, wrap them with a metal armor layer, inject potting compound to fill the gaps, and cure to obtain the target busbar insulation layer.

[0026] In existing technologies, high temperatures are required for complete resin curing, but high temperatures also reduce resin viscosity, making residual air bubbles more prone to aggregation and expansion, causing defects. In this invention, air bubbles are removed to the maximum extent possible under vacuum conditions when the resin viscosity is low (in the initial stage of heating); step-by-step heating and curing ensures a stable and complete cross-linking reaction of the resin, avoiding violent exothermic reactions that could lead to internal cracks; and during the optimal time window when the resin viscosity has decreased but before violent reactions, nitrogen is used to replace oxygen, controlling the oxygen content to an extremely low level of <50ppm. This fundamentally inhibits the thermal oxidative degradation and ion-catalytic aging of the resin, greatly improving long-term insulation life and reliability.

[0027] Integrating two independent insulated busbars into a robust single unit using metal armor and potting compound provides not only mechanical protection but also optimization at the electromagnetic and insulation levels. The potting compound effectively balances the electric field distribution between the two busbars, reducing edge effects, while providing an excellent heat conduction path to promptly dissipate Joule heat generated by high currents, preventing localized overheating and insulation failure. Step S200 can be performed using a multi-axis winding machine, such as the CNCFW-4-2000. The metal armor layer in step S400 can be made of stainless steel or aluminum alloy.

[0028] After step S300 passes the inspection, the single-insulation-layer cured busbar can be obtained. The inspection standard is as follows: High voltage withstand voltage test (100% inspection): Apply AC 20kV for 1 minute. Judgment: No breakdown, no flashover, leakage current less than 10μA.

[0029] After passing the inspection in step S400, the target busbar insulation layer is obtained. The inspection standards are: high voltage DC test, DC34 kV, leakage current <1μA; thermal cycling test -196℃~100℃, no cracking after 3 cycles.

[0030] Further, in step S100, the resin adhesive, by weight, comprises the following components:

[0031] 95-105 parts epoxy resin, 85-95 parts methyltetrahydrophthalic anhydride, 0.5-0.6 parts coupling agent, and 0.85-1 part defoamer.

[0032] Further, in step S100, the vacuum degree of the vacuum degassing is -0.11 to -0.09 MPa, and the time is 28 to 35 minutes.

[0033] Further, in step S200, the winding method of the fiberglass tape and the insulating reinforcement film is as follows: a 0.9~1.1mm thick fiberglass tape is wound on the busbar, a 0.4~0.5mm thick insulating reinforcement film is wound on the surface of the fiberglass tape, a 1.9~2.1mm thick fiberglass tape is wound on the surface of the insulating reinforcement film, a 0.4~0.5mm thick insulating reinforcement film is wound on the surface of the fiberglass tape, and finally a 2.9~3.1mm thick fiberglass tape is wound on the surface of the insulating reinforcement film.

[0034] Each layer of insulating reinforcement film covers the outside of the fiberglass tape, with an edge overlap ratio ≥50%. The winding method of this invention employs a flexible buffer layer (fiberglass tape) and a rigid shielding layer (insulating film) as basic units, and this unit is stacked twice and thickened once in the radial direction, forming a five-layer structure. Unlike traditional single-material uniform thickening or simple 1+1 structures, this is a system-level topology optimization.

[0035] The distribution of a DC electric field within an insulating layer is non-uniform, and its field strength is inversely proportional to the material's conductivity. By placing an insulating film with extremely high electrical performance but mechanical fragility in specific locations, the electric field distribution is actively guided and optimized. The first insulating film (0.4~0.5mm) is responsible for withstanding the highest electric field strength on the conductor surface; the middle insulating film further equalizes the internal electric field, preventing electric field distortion. These two insulating film barriers divide the entire insulation system into multiple electric field regions. Even if a local breakdown occurs in one layer due to extreme conditions (such as overvoltage or aging), it is difficult for the next barrier to continuously break down, effectively preventing the fault from escalating and providing multiple layers of protection.

[0036] The thinner inner layer of 0.9~1.1mm fiberglass tape ensures good flexibility, better transmits and absorbs the thermal expansion stress of the conductor, and reduces the risk of interface delamination. The outer layer gradually thickens, providing great structural strength and stiffness, resisting external mechanical impact and internal expansion stress, and protecting the fragile but critical inner insulating film layer.

[0037] Furthermore, in step S200, the tension of the spiral winding is 20~30N, the winding angle is 30℃~60℃; the surface roughness of the busbar before winding is Ra=3.2~6.3μm, and it is cleaned by acetone-plasma.

[0038] Further, in step S300, the vacuum degree is -0.1 MPa to -0.095 MPa; the step-by-step temperature curing method includes: 75~85℃, 0.8~1.2h; 110~130℃, 1.5~2.5h; 140~160℃, 3.5~4.5h; wherein, nitrogen is injected at 80~90℃ to replace residual oxygen, so that the oxygen content is <50 ppm.

[0039] Stepped temperature curing:

[0040] The first stage, at 75-85℃, is the induction and degassing stage. This stage allows the resin viscosity to be sufficiently reduced, facilitating continued flow, wetting, and removal of deep air bubbles, but without reacting too quickly and causing the air bubbles to be locked in.

[0041] The second stage, at 110-130℃, is the main curing and gelation stage, which is the fastest and most intense stage of the curing reaction. A vacuum environment is used to promptly remove reaction byproducts and small molecules, preventing the formation of microbubbles.

[0042] The second stage, at 140-160℃, is the post-curing and performance optimization stage. After the reaction is basically completed, a long period of high-temperature treatment is still required to promote the interfacial bonding between the nanofiller and the resin; relax the internal stress of curing, so that the molecular chain segments can rearrange and relax at high temperature, reducing internal microcracks; and increase the glass transition temperature (Tg) and crosslinking density, thereby improving long-term heat resistance.

[0043] During the curing process, oxygen molecules may attack amine curing agents, generating quinone structures and peroxides, leading to epoxy resin degradation; O2 may cause the breakage of unsaturated bonds in the resin, generating alkyl free radicals and initiating free radical chain reactions; Cu dissolved from the busbar copper material may also contribute to the degradation. 2+ Catalytic resin oxidation in the presence of oxygen, etc. Nitrogen gas can effectively suppress the above-mentioned oxidation side reactions by replacing residual oxygen.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] The high-current DC bus insulation layer prepared by this invention adopts a scheme of overlapping and winding fiberglass tape impregnated with resin adhesive and pre-cured insulation reinforcement film. The breakdown voltage of the prepared insulation layer is much higher than 20kV. When used to protect DC bus carrying high current, it has extremely high safety and reliability, and also has ultra-high insulation strength, ultra-long life, and excellent mechanical and heat dissipation performance. Detailed Implementation

[0046] Example 1

[0047] The resin adhesive comprises the following components:

[0048] Bisphenol A type epoxy resin (EPON 828) 5kg, modified alicyclic amine curing agent (Ancamine 2280) 1.35kg, benzyl glycidyl ether 380g, organosilicon defoamer (BYK-A530) 22g, fluorocarbon modified leveling agent (BYK-354) 17g, nano-grade silica (Aerosil R812) 200g, propylene glycol methyl ether acetate 4.5kg;

[0049] The resin adhesive has a solid content of 50%.

[0050] The method for preparing the insulating reinforcing film includes the following steps:

[0051] Step 1: Stir at 55℃ until completely dissolved and mixed evenly; add nano-sized silica and ultrasonically disperse at 300W for 30 minutes; then add curing agent, defoamer and leveling agent, cool to 38℃ and stir at low speed for 10 minutes; filter with a 400-mesh filter and let stand to degas for 30 minutes to obtain resin solution.

[0052] Step 2: Apply the resin solution onto the release film, with a wet film thickness of 100 μm. Pre-bake at 80℃ for 6 min to form a semi-cured film. Hot-press the semi-cured film with two layers of PET film at 130℃ and 0.85 MPa for 30 min; cure at 100℃ for 1 h, and then at 148℃ for 2 h. The thickness of a single layer of PET film is 0.05 mm.

[0053] Step 3: After cooling to room temperature (25°C), peel off the release film and cut into rolls with a width of 5cm.

[0054] Example 2

[0055] The resin adhesive comprises the following components:

[0056] Bisphenol A type epoxy resin (EPON 828) 45g, modified alicyclic amine curing agent (Ancamine 2280) 12g, benzyl glycidyl ether 2.5g, silicone defoamer (BYK-A530) 0.15g, fluorocarbon modified leveling agent (BYK-354) 0.1g, nano-grade silica (Aerosil R812) 1g, propylene glycol methyl ether acetate 40g;

[0057] The resin adhesive has a solid content of 48%.

[0058] The method for preparing the insulating reinforcing film includes the following steps:

[0059] Step 1: Stir at 50℃ until completely dissolved and mixed evenly; add nano-sized silica and ultrasonically disperse at 250W for 25 minutes; then add curing agent, defoamer and leveling agent, cool to 35℃ and stir at low speed for 8 minutes; filter with a 350-mesh filter and let stand to degas for 25 minutes to obtain resin solution.

[0060] Step 2: Apply the resin solution onto the release film, with a wet film thickness of 90 μm. Pre-bake at 75°C for 5 min to form a semi-cured film. Hot-press the semi-cured film with two layers of PET film at 125°C and 0.7 MPa for 25 min; cure at 95°C for 0.8 h, and then at 145°C for 1.5 h. The thickness of a single layer of PET film is 0.05 mm.

[0061] Step 3: After cooling to room temperature of 23°C, peel off the release film and cut it into rolls with a width of 5cm.

[0062] Example 3

[0063] The resin adhesive comprises the following components:

[0064] Bisphenol A type epoxy resin (EPON 828) 5.5kg, modified alicyclic amine curing agent (Ancamine 2280) 1.5kg, benzyl glycidyl ether 500g, organosilicon defoamer (BYK-A530) 30g, fluorocarbon modified leveling agent (BYK-354) 25g, nano-grade silica (Aerosil R812) 3g, propylene glycol methyl ether acetate 5kg;

[0065] The resin adhesive has a solid content of 52%.

[0066] The method for preparing the insulating reinforcing film includes the following steps:

[0067] Step 1: Stir at 60℃ until completely dissolved and mixed evenly; add nano-sized silica and ultrasonically disperse at 350W for 35 minutes; then add curing agent, defoamer and leveling agent, cool to 42℃ and stir at low speed for 12 minutes; filter with a 450 mesh filter and let stand to degas for 35 minutes to obtain resin solution.

[0068] Step 2: Apply the resin solution onto the release film, with a wet film thickness of 110 μm. Pre-bake at 85°C for 8 minutes to form a semi-cured film. Then, hot-press the semi-cured film with two layers of PET film at 135°C and 1.0 MPa for 35 minutes; cure at 105°C for 1.2 hours and then at 150°C for 2.5 hours. The thickness of a single PET film layer is 0.05 mm.

[0069] Step 3: After cooling to room temperature of 27°C, peel off the release film and cut it into rolls with a width of 5cm.

[0070] Comparative Example 1

[0071] In the resin adhesive formulation, nano-silica was removed. Other formulation components and preparation methods were the same as in Example 1.

[0072] Comparative Example 2

[0073] In step 2, the stepped curing process was omitted, and the product was directly cured at 148°C for 3 hours. The formulation components and other preparation methods were the same as in Example 1.

[0074] Comparative Example 3

[0075] In the resin adhesive formulation, the amount of propylene glycol methyl ether acetate was reduced to 3 kg, and the solid content of the resin adhesive was adjusted to 60%. Other formulation components and preparation methods were the same as in Example 1.

[0076] The performance parameters of the insulating reinforcing films prepared in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0077] Table 1 Performance parameters of the insulating reinforcement films prepared in Examples 1-3 and Comparative Examples 1-3

[0078]

[0079] As shown in Table 1, in Examples 1 to 3, the DC breakdown field strength is 131~136kV / mm, the PDIV is 9.5~9.8kV, the volume resistivity at 150℃ reaches 6.2E+14Ω·m, the corona resistance life is ≥220h, the MIT folding resistance can reach 2850 cycles, and the SAT defect-free rate is ≥99.3%.

[0080] In Comparative Example 1, the removal of nano-SiO2 resulted in the loss of the deep-level charge traps it introduced, making it impossible to effectively suppress space charge injection and accumulation, leading to electric field distortion and a decline in electrical performance. Simultaneously, corona resistance deteriorated drastically due to the loss of this barrier. The DC breakdown field strength dropped to 118 kV / mm, PDIV dropped to 8.5 kV, the volume resistivity at 150 °C dropped to 4.5E+14 Ω·m, and the corona resistance lifetime was only 85 hours.

[0081] In Comparative Example 2, direct high-temperature curing was used, resulting in a violent reaction and concentrated heat release, which led to: high internal stress and a MIT flexural strength of only 1800 cycles; internal microbubbles could not be expelled, the SAT defect-free rate dropped to 95.5%, and the PDIV dropped to 7.2kV; the molecular chains were frozen, the curing network was imperfect, the DC breakdown field strength dropped to 105kV / mm, and the volume resistivity at 150℃ dropped to 3.0E+14Ω·m.

[0082] In Comparative Example 3, increasing the solid content of the resin resulted in excessively high viscosity. High viscosity led to poor ultrasonic dispersion, nanoparticle agglomeration, poor coating leveling, uneven film thickness, and difficulty in degassing, resulting in a large number of residual bubbles. These manufacturing defects became weak points under the electric field, comprehensively lowering performance. The DC breakdown field strength dropped to 96 kV / mm, PDIV decreased to 6.8 kV, the volume resistivity at 150℃ dropped to 2.8E+14 Ω·m, the corona resistance life was only 95 hours, the MIT flexural strength was 2050 cycles, and the SAT defect-free rate was only 92%.

[0083] Example 4

[0084] The resin adhesive comprises the following components:

[0085] 10 kg of epoxy resin (model 0164), 9 kg of methyltetrahydrophthalic anhydride (ATM-120), 55 g of coupling agent (BYK-C-8001), and 92 g of defoamer (BYK-A-535).

[0086] A method for preparing the insulation layer of a high-current DC transmission bus includes the following steps:

[0087] S100, Pretreatment of resin adhesive: Mix all components of the insulating material evenly, degas under vacuum at -0.1 MPa for 32 min;

[0088] S200. After processing the surface roughness of the busbar to Ra=5μm and cleaning it with acetone-plasma for 10min, fiberglass tape and insulating reinforcement film impregnated with resin adhesive are overlapped and wrapped around the outer surface of the busbar.

[0089] A 1mm thick fiberglass tape is wound around the busbar. A 0.45mm thick insulating reinforcing film is then wound around the surface of the fiberglass tape. A 2mm thick fiberglass tape is then wound around the surface of the insulating reinforcing film. Another 0.45mm thick insulating reinforcing film is then wound around the surface of the fiberglass tape. Finally, a 3mm thick fiberglass tape is wound around the surface of the insulating reinforcing film. The spiral winding tension is 25N, and the winding angle is 45°.

[0090] S300, under a vacuum of -0.098 MPa, was cured by stepwise temperature increase: 80℃, 1h; 120℃, 2h; 150℃, 4h.

[0091] Nitrogen gas was injected at 85℃ to replace residual oxygen, resulting in an oxygen content of 40 ppm. After curing, the test results met the standard, and the busbar with cured insulation layer was obtained.

[0092] S400. Fix two cured busbars in parallel with a spacing of 50mm, wrap them with an aluminum alloy armor layer, inject potting compound (LD-100) to penetrate the gap at -0.08 MPa, cure at 80℃ for 4 hours, grind off the excess potting compound, and ensure the surface flatness Ra=2.8μm; if the test is qualified, the target busbar insulation layer is obtained.

[0093] The high-current DC transmission bus insulation layer includes three fiberglass tape layers with thicknesses of 1 mm, 2 mm, and 3 mm, respectively. The fiberglass tape is of type ET100 and has a width of 50 mm. There are two insulating reinforcement film layers, each with a thickness of 0.45 mm. The insulating reinforcement film layers are prepared by the method in Example 1. The fiberglass tape layers and the insulating reinforcement film layers are stacked alternately, and adjacent layers are bonded to each other by a resin adhesive layer. The 1 mm thick fiberglass tape layer is bonded to the bus surface by a resin adhesive.

[0094] Example 5

[0095] The resin adhesive comprises the following components:

[0096] 9.5 kg of epoxy resin (model 0164), 8.5 kg of methyltetrahydrophthalic anhydride (ATM-120), 50 g of coupling agent ((BYK-C-8001)), and 85 g of defoamer (BYK-A-535).

[0097] A method for preparing the insulation layer of a high-current DC transmission bus includes the following steps:

[0098] S100, Pretreatment of resin adhesive: Mix all components of the insulating material evenly, degas under vacuum at -0.11 MPa for 28 min;

[0099] S200, the surface roughness of the busbar is treated to Ra=3.5μm, and after acetone-plasma cleaning, fiberglass tape and insulating reinforcement film impregnated with resin adhesive are overlapped and wound on the outer surface of the busbar.

[0100] A 0.9mm thick fiberglass tape is wound around the busbar, followed by a 0.4mm thick insulating reinforcement film. Then, a 1.9mm thick fiberglass tape is wound around the insulating reinforcement film, and another 0.4mm thick insulating reinforcement film is wound around the fiberglass tape. Finally, a 2.9mm thick fiberglass tape is wound around the insulating reinforcement film. The spiral winding tension is 20N, and the winding angle is 30°.

[0101] S300, under -0.1 MPa vacuum conditions, stepped temperature curing: 75℃, 0.8h; 110℃, 1.5h; 140℃, 3.5h;

[0102] Nitrogen gas was injected at 80℃ to replace residual oxygen, resulting in an oxygen content of 48 ppm. After curing, the test results met the standard, and the busbar with cured insulation layer was obtained.

[0103] S400. Fix two cured busbars in parallel with a spacing of 50mm, wrap them with an aluminum alloy armor layer, inject potting compound (LD-100) to penetrate the gap at -0.08 MPa, cure at 80℃ for 4 hours, grind off the excess potting compound, and ensure the surface flatness Ra=3.2μm; if the test is qualified, the target busbar insulation layer is obtained.

[0104] The high-current DC transmission bus insulation layer includes three fiberglass tape layers with thicknesses of 0.9 mm, 1.9 mm, and 2.9 mm, respectively. The fiberglass tape is of type ET100 and has a width of 50 mm. There are two insulating reinforcement film layers, each with a thickness of 0.4 mm. The insulating reinforcement film layers are prepared by the method in Example 1. The fiberglass tape layers and the insulating reinforcement film layers are stacked alternately, and adjacent layers are bonded to each other by a resin adhesive layer. The 0.9 mm thick fiberglass tape layer is bonded to the bus surface by a resin adhesive.

[0105] Example 6

[0106] The resin adhesive comprises the following components:

[0107] Epoxy resin (model 0164) 10.5kg, methyltetrahydrophthalic anhydride (ATM-120) 9.5kg, coupling agent (BYK-C-8001) 60g, defoamer (BYK-A-535) 100g.

[0108] A method for preparing the insulation layer of a high-current DC transmission bus includes the following steps:

[0109] S100, Pretreatment of resin adhesive: Mix all components of the insulating material evenly, degas under vacuum at -0.09 MPa for 35 min;

[0110] S200, the surface roughness of the busbar is treated to Ra=6.3μm, and after acetone-plasma cleaning, fiberglass tape and insulating reinforcement film impregnated with resin adhesive are overlapped and wound on the outer surface of the busbar.

[0111] A 1.1mm thick fiberglass tape is wound around the busbar, followed by a 0.5mm thick insulating reinforcement film. A 2.1mm thick fiberglass tape is then wound around the insulating reinforcement film, followed by another 0.5mm thick insulating reinforcement film. Finally, a 3.1mm thick fiberglass tape is wound around the insulating reinforcement film. The spiral winding tension is 30N, and the winding angle is 60°.

[0112] S300, under a vacuum of -0.095 MPa, was cured by stepwise temperature increase: 85℃, 1.2h; 130℃, 2.5h; 160℃, 4.5h.

[0113] Nitrogen gas is injected at 90℃ to replace residual oxygen, so that the oxygen content is 35ppm. After curing, the test results meet the standard, and the busbar with cured insulation layer is obtained.

[0114] S400. Fix two cured busbars in parallel with a spacing of 50mm, wrap them with stainless steel armor, inject potting compound (LD-100) to penetrate the gap at -0.08 MPa, cure at 80℃ for 4 hours, grind off the excess potting compound, and ensure the surface flatness Ra=2.5μm; if the test is qualified, the target busbar insulation layer is obtained.

[0115] The high-current DC transmission bus insulation layer comprises three layers of fiberglass tape with thicknesses of 1.1 mm, 2.1 mm, and 3.1 mm, respectively. The fiberglass tape is of type ET100 and has a width of 50 mm. It also includes two 0.5 mm thick insulating reinforcement film layers, prepared using the method described in Example 1. The fiberglass tape layers and the insulating reinforcement film layers are staggered and bonded together with adjacent layers using a resin adhesive. The 1.1 mm thick fiberglass tape layer is bonded to the bus surface using resin adhesive. The thickness of a single fiberglass tape layer is 0.05 mm.

[0116] Comparative Example 4

[0117] The nitrogen purging step was omitted, and curing was carried out in air with an oxygen content of 210,000 ppm. The formulation components and other preparation methods were the same as in Example 4.

[0118] Comparative Example 5

[0119] The stepped heating and vacuum process was omitted, and the product was cured at ambient pressure, 80°C, and for 12 hours. The formulation components and other preparation methods were the same as in Example 4.

[0120] Comparative Example 6

[0121] The winding structure was changed to traditional uniform winding: 7.9 mm thick impregnated fiberglass tape was directly wound. The formulation components and other preparation methods were the same as in Example 4.

[0122] The performance parameters of the high-current DC transmission bus insulation layers prepared in Examples 4-6 and Comparative Examples 4-6 are shown in Table 2.

[0123] Table 2 Performance parameters of the high-current DC transmission bus insulation layers prepared in Examples 4-6 and Comparative Examples 4-6

[0124]

[0125] As shown in Table 2, in Examples 4-6, the system DC breakdown voltage is >158kV, the PD value at 24kV is <5 pC, the glass transition temperature Tg is 148~155℃, the radial thermal conductivity of the insulation layer is 0.35~0.38W / m·K, the withstand voltage retention rate after thermal cycling is ≥97.8%, the temperature rise after short-circuit thermal shock is <62℃, and the condition is intact after short circuit.

[0126] Comparative Example 4 was cured in air. Oxygen caused thermal oxidative degradation of the resin, resulting in molecular chain breakage, decreased crosslinking density, and a drop in glass transition temperature (Tg) to 138°C. Oxidation products and micropores became channels for electron and ion conduction, leading to a decrease in insulation resistance. The PD at 24kV increased to 25pC, and long-term aging performance deteriorated sharply.

[0127] Comparative Example 5 exhibited defects in its atmospheric pressure low-temperature curing process: extremely incomplete curing, with a Tg of only 115℃, resulting in poor mechanical strength and heat resistance; a large amount of solvent and bubble residue caused the PD value to rise to 85pC; and internal stress concentration. Under the severe test of short-circuit thermal shock, its internal defects expanded, leading to direct cracking and failure.

[0128] In Comparative Example 6, a conventional uniform winding method was used. Although the total thickness was the same, its structure was simple. The advantages of the staggered layered structure in this embodiment are: the insulating reinforcement film provides extremely high bulk dielectric strength, effectively suppressing the electric field and resulting in lower PD; the nanofillers in the insulating reinforcement film provide better lateral heat conduction paths, leading to faster heat dissipation; and it provides better stress distribution. In Example 6, the system's DC breakdown voltage dropped to 140kV, the PD at 24kV increased to 12pC, and the temperature rise after a short-circuit thermal shock was 70°C.

[0129] The high-current DC transmission bus insulation layer of the present invention exhibits significant and consistent superiority in electrical strength, long-term reliability, heat dissipation capacity, and resistance to extreme working conditions.

Claims

1. An insulation layer for a high-current DC transmission busbar, characterized in that, It includes several fiberglass tape layers, resin adhesive layers and insulating reinforcement film layers, wherein the fiberglass tape layers and insulating reinforcement film layers are stacked alternately, and at least one resin adhesive layer is provided between adjacent layers; The method for preparing the insulating reinforcing film includes the following steps: Step 1: Mix epoxy resin, benzyl glycidyl ether and propylene glycol methyl ether acetate evenly, add nano-sized silica, ultrasonically disperse evenly, then add curing agent, defoamer and leveling agent and mix evenly, filter, degas to obtain resin adhesive; Step 2: Apply resin liquid onto release film, pre-dry to form semi-cured film, hot-press semi-cured film with two layers of PET film, and then cure in sections. Step 3: After cooling to room temperature, peel off the release film and cut it into rolls that match the fiberglass tape.

2. The high-current DC transmission bus insulation layer according to claim 1, characterized in that, In step 1, the resin solution, by weight, includes the following components: 45-55 parts of bisphenol A type epoxy resin, 12-15 parts of modified alicyclic amine curing agent, 2.5-5 parts of benzyl glycidyl ether, 0.15-0.3 parts of organosilicon defoamer, 0.1-0.25 parts of fluorocarbon modified leveling agent, 1-3 parts of nano-sized silica, and 40-50 parts of propylene glycol methyl ether acetate; The resin adhesive has a solid content of 48-52%.

3. The high-current DC transmission bus insulation layer according to claim 1, characterized in that, In step 1, stir at 50~60℃ until completely dissolved and mixed evenly; add nano-sized silica, and ultrasonically disperse at 250~350W for 25~35min; then add curing agent, defoamer and leveling agent, cool to 35~42℃ and stir at low speed for 8~12min; filter with a 350~450 mesh filter, let stand to degas for 25~35min to obtain resin solution.

4. The high-current DC transmission bus insulation layer according to any one of claims 1 to 3, characterized in that, In step 2, the resin solution is coated onto the release film, with a wet film thickness of 90~110μm. It is pre-baked at 75~85℃ for 5~8min to form a semi-cured film. The semi-cured film is then hot-pressed with two layers of PET film at 125~135℃ and 0.7~1.0MPa for 25~35min. It is then cured at 95~105℃ for 0.8~1.2h and at 145~150℃ for 1.5~2.5h.

5. A method for preparing an insulation layer for a high-current DC transmission bus as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S100, Pretreatment of resin adhesive: Mix all components of the insulating material evenly and degas under vacuum until no bubbles are present; S200: Fiberglass tape and insulating reinforcement film, both impregnated with resin adhesive, are interleaved and wound around the outer surface of the busbar. S300, under vacuum conditions, stepped temperature rise curing; nitrogen replacement is carried out during the curing process to obtain the busbar after the insulation layer is cured; S400. Fix the two cured busbars in parallel, wrap them with a metal armor layer, inject potting compound to fill the gaps, and cure to obtain the target busbar insulation layer.

6. The preparation method according to claim 5, characterized in that, In step S100, the resin adhesive, by weight, comprises the following components: 95-105 parts epoxy resin, 85-95 parts methyltetrahydrophthalic anhydride, 0.5-0.6 parts coupling agent, and 0.85-1 part defoamer.

7. The preparation method according to claim 5, characterized in that, In step S100, the vacuum degree of the vacuum degassing is -0.11 to -0.09 MPa, and the time is 28 to 35 min.

8. The preparation method according to claim 5, characterized in that, In step S200, the fiberglass tape and the insulating reinforcement film are wound as follows: a 0.9~1.1mm thick fiberglass tape is wound on the busbar, a 0.4~0.5mm thick insulating reinforcement film is wound on the surface of the fiberglass tape, a 1.9~2.1mm thick fiberglass tape is wound on the surface of the insulating reinforcement film, a 0.4~0.5mm thick insulating reinforcement film is wound on the surface of the fiberglass tape, and finally a 2.9~3.1mm thick fiberglass tape is wound on the surface of the insulating reinforcement film.

9. The preparation method according to claim 5, characterized in that, In step S200, the tension of the spiral winding is 20~30N, and the winding angle is 30℃~60℃; the surface roughness of the busbar before winding is Ra=3.2~6.3μm, and it is cleaned with acetone-plasma.

10. The preparation method according to claim 5, characterized in that, In step S300, the vacuum level is -0.1 MPa to -0.095 MPa; The step-by-step temperature curing method includes: 75~85℃, 0.8~1.2h; 110~130℃, 1.5~2.5h; 140~160℃, 3.5~4.5h; wherein, nitrogen is injected at 80~90℃ to replace residual oxygen, so that the oxygen content is <50 ppm.

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