Epoxy resin curing process and equipment for metal armored voltage transformer

Abstract

The invention provides a metal armored voltage transformer epoxy resin curing process and equipment, and belongs to the technical field of electrical equipment manufacturing. According to the process, by optimizing the epoxy resin castable formula and adopting a stepped temperature control curing tunnel furnace system, the air gap problem of the bonding surface caused by the difference of thermal expansion coefficients of a metal shell and epoxy resin is solved. The process comprises the following steps: mixing epoxy resin, a curing agent and silica powder according to a specific ratio; in the primary curing, the stepped temperature rise from 50 DEG C (5h) to 70 DEG C (10h) to 90 DEG C (5h) to 110 DEG C (5h) is adopted; the secondary curing is 110 DEG C (12h) constant-temperature treatment; the curing tunnel furnace system designed in a matched mode comprises a plurality of curing bins with independent temperature control. According to the invention, the partial discharge performance of the product is obviously improved, the partial discharge level is below 5pC, the qualified rate of the product reaches 100%, and meanwhile, the production efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of power equipment manufacturing, and specifically discloses an epoxy resin curing process and equipment for a metal-clad voltage transformer. Background Art

[0002] Metal-clad voltage transformers are critical equipment in power systems, and their insulation performance directly impacts grid safety. Partial discharge (PD) is a defect in insulators, primarily caused by uneven electric field distribution. For example, air gaps or bubbles are prone to forming within cast, injection-molded, or layer-wound insulation. These gaps or bubbles are the first to discharge when subjected to an applied voltage.

[0003] In traditional manufacturing processes, there are two major technical difficulties in the curing process: one is the large difference in thermal expansion coefficient between the metal shell (usually aluminum alloy) and the epoxy resin (aluminum alloy is about 23.8×10 -6 / ℃, epoxy resin is about 60×10 -6 / ℃), air gaps are easily formed at the interface after curing and cooling; secondly, traditional curing equipment is an oven, and the heat is evenly distributed inside the oven through a blast device. Heat is concentrated at the blower outlet, and the temperature at the return air outlet is slightly lower. The temperature in the entire space is uneven, resulting in uneven heating of the transformers at different positions. During the curing process, there is a temperature difference of 2-6℃ on a single transformer, and there is no regular pattern to follow, resulting in inconsistent product performance.

[0004] Patent CN108597826B proposes a fully enclosed structure design without armor shielding. Under the condition of no metal shell and epoxy resin insulator interface, a conventional curing process is adopted to achieve a partial discharge electric quantity below 10pC. However, the national standard (20pC) qualification rate for mass production is 98%, which does not achieve the stable target of partial discharge electric quantity completely below 20pC. If this is used to produce metal armored voltage transformers, its partial discharge will further increase at the metal shell and insulator interface gap, and the qualification rate will further decrease. Therefore, it is urgent to develop a special curing process and equipment that can accurately control the pouring and curing process of the internal insulating material of the metal armored voltage transformer to ensure the quality of the interface bonding. Summary of the Invention

[0005] The purpose of the present invention is to provide an epoxy resin curing process and equipment for a metal-clad voltage transformer, so as to solve the problem that the interface between the metal and the epoxy resin insulating material is heated unevenly during the curing process and has a large difference in expansion coefficient, resulting in air gaps and high partial discharge in the product.

[0006] To achieve the above objectives, the present invention proposes the following technical solutions: 1. Material formula optimization: The insulating castable is formulated with a weight ratio of epoxy resin to silica powder of 100:(210-250), and a curing agent to silica powder of 80:(123-166). The silica powder is then added to the epoxy resin and the curing agent to the silica powder. The epoxy resin castable is then vacuum-mixed at a ratio of epoxy resin to curing agent of 100:(70-88). This is to adjust the thermal expansion coefficient of the epoxy resin to around 0.3% at 110°C, similar to that of an aluminum alloy housing (0.214%). The conversion ratio is epoxy resin: curing agent: silica powder of 100:(70-88):(318-432).

[0007] Premixing the silica powder epoxy resin and silica powder curing agent allows for stable placement. When pouring, a binary mix of the silica powder epoxy resin and silica powder curing agent is easier to control than a ternary mix of epoxy resin, curing agent, and silica powder. Premixing also prevents the epoxy resin and curing agent from reacting upon direct contact, which can hinder the uniform distribution of the silica powder.

[0008] 2. Step curing process: 1. Place the metal-clad voltage transformer in a mold and statically vacuum cast the insulating castable described above. After casting, remove the mold and the casting pot from the mold and place it in a heat preservation room for at least three hours to cool. During this low-temperature curing period, the castable maintains a low viscosity, allowing the epoxy resin and curing agent to react more fully. This allows the castable molecules ample time to diffuse and disperse, resulting in a uniform structure. Low-temperature curing allows for a more gradual evaporation of solvents or small molecules, minimizing bubble formation.

[0009] 2. After standing still, the metal-clad voltage transformer is transferred to the curing tunnel furnace tray and enters the primary curing tunnel furnace for step-by-step temperature increase and curing; 3. Set the process parameters of the one-step curing tunnel furnace; 4. After the primary curing is completed, it is transferred to the demoulding area for demoulding; 5. The demoulding area is kept at a constant temperature of 25±5℃ and the demoulding time is about 20 minutes; 6. After demoulding, the metal armored voltage transformer is transported into the secondary curing tunnel furnace; 7. Set the process parameters of the secondary curing tunnel furnace, and after secondary curing, cool down and enter the buffer section for assembly.

[0010] The process parameters of the curing tunnel furnace are set as follows: Insulation room: 20±5℃×3h One-time curing: 50±5℃×5h+70±5℃×10h+90±5℃×5h+110±5℃×5h Secondary curing: 110±5℃×12h During one-time curing, a step-by-step temperature increase is designed based on the temperature characteristics of the casting mixture and the aluminum shell. On the basis of sufficient internal curing, the thermal expansion coefficients of the casting mixture and the alloy aluminum shell are kept as close as possible.

[0011] 3. Metal shell design: Aluminum alloy 5052, shell thickness 2mm.

[0012] According to the thermal expansion coefficient of 5052 aluminum alloy α=23.8×10 -6 / ℃, thermal expansion coefficient = α × ΔT × 100%, the thermal expansion coefficient at each temperature relative to the reference temperature of 20℃ is calculated as follows: 50℃-ΔT=50℃-20℃=30℃ -Expansion rate = 23.8 × 10 -6 ×30×100%=0.0714% 90℃-ΔT=90℃-20℃=70℃ -Expansion rate = 23.8 × 10 -6 ×70×100%=0.1666% 110℃-ΔT=110℃-20℃=90℃ -Expansion rate = 23.8 × 10 -6 ×90×100%=0.2142% When the material is cooled from high temperature to 20℃, the shrinkage rate is the same as the expansion rate at the corresponding high temperature.

[0013] 4. Curing tunnel furnace equipment: The dedicated curing tunnel furnace equipment provided by this solution includes: a primary curing tunnel furnace, a secondary curing tunnel furnace, and a control system. The primary curing tunnel furnace is equipped with a receiving section, an observation section, and a heating section, with a double-row chain roller conveyor at the bottom that runs through each section.

[0014] The primary curing tunnel furnace has a connecting section at both ends, which is designed with product pallets. The pallets are sized to fit the entire curing tunnel furnace system. The pallets are supported and transported by two rows of powered rollers at the bottom of a double-row chain roller conveyor.

[0015] The observation section is equipped with an observation window, which can clearly observe the position of the transformer pouring mixture and exit and replenish the material in time when the material is lacking. A curing bin is set in the observation section.

[0016] The heating section has a total of 5 temperature steps, which are divided into four heating and curing chambers, namely preheating section, heating section 1 (occupying 2 temperature steps), heating section 2, and heating section 3.

[0017] Each heating and curing chamber of the one-time curing tunnel furnace is provided with a temperature sensor, a heater, an air blast device and an alarm device; The secondary curing tunnel furnace comprises: a receiving section, a heating section, a heat preservation section, a cooling section and a buffer section; Openable and closable partition sealing devices and transfer devices are set between each section and each warehouse; each solidification warehouse has an independent space.

[0018] The control system includes: a temperature control module, a partition and sealing device opening and closing module, and a transfer device speed control module; the temperature control module includes: one or a combination of temperature sensors, heaters, blowing devices, and alarm devices set in each section of the primary curing tunnel furnace and the secondary curing tunnel furnace that need to be temperature controlled, and a control system panel connected to the electrical signals of these devices.

[0019] The air blowing device includes a fan on the top of the silo, a porous return air plate and a heater; The fan is located at the top of the bin and is used to inhale hot air from the top of the curing bin, guide the hot air into the air ducts on the left and right sides through the porous return air plate, exchange heat with the heaters in the air ducts on both sides, and then blow it out from the lower parts of both sides of the curing bin to heat the mutual inductor, and then be inhaled by the fan, forming a repetitive hot air cycle.

[0020] The curing chamber partition sealing device is sealed with ceramic fiber rope and / or asbestos tape; the transfer device is a double-row chain roller set through the bottom of each section of the curing tunnel furnace; the partition sealing device and the transfer device are both controlled by the control system and automatically opened according to the set curing program.

[0021] The heating section curing chamber can be operated in a divided chamber; when more temperature steps need to be subdivided, the chamber is separated and controlled by the partition sealing device to form two independent curing chambers.

[0022] Beneficial effects: It can be seen from the above technical solutions that the technical solution of the present invention optimizes the material formula and adjusts the thermal expansion coefficient of the epoxy resin so that the thermal expansion coefficient of the insulating material is close to that of the metal shell.

[0023] Epoxy resin curing is an exothermic reaction. If the starting temperature is too high or the temperature rises too quickly, a strong heat release will occur in the early stages of the reaction. If the starting temperature is too high and the reaction is too rapid, the heat release will be concentrated, leading to localized overheating. This sudden temperature rise can cause material degradation or the rapid precipitation of volatiles, resulting in bubbles.

[0024] The curing reaction is slow at low temperatures and accelerates as the temperature rises. If the temperature rises too quickly, the surface cures too quickly before the internal reaction occurs, leading to high internal stress. Heat dissipation within the transformer is difficult, and the internal temperature may even be much higher than the external temperature. Stepped heating allows sufficient time for heat to dissipate, avoiding large temperature differences between the inside and outside, which can lead to inconsistent shrinkage, stress, and even cracking.

[0025] After the gel point, the epoxy resin material hardens. If the temperature continues to rise, the unreacted portion inside shrinks, but this is constrained by the hardened portion outside, generating stress. Therefore, it is important to fully react before the gel point to avoid excessive internal shrinkage later.

[0026] Excessive local temperatures may cause: Scorch / Degradation: Resin or curing agent decomposes, discolors, and carbonizes at high temperatures.

[0027] Internal bubbles / voids: Low-boiling-point components or solvents vaporize violently, and small molecules (such as water and aldehyde) produced by internal reactions do not have time to escape and form bubbles.

[0028] Thermal stress cracking: Severe temperature gradients and uneven reactions lead to excessive thermal stress and cracking.

[0029] Use step-by-step heating: Start the reaction at a lower temperature to make the initial reaction rate moderate, the heat release small and gradual, and there is enough time for the heat to be conducted away to avoid local overheating.

[0030] During the cooling and static stage in the insulation room, the reaction is carried out at a temperature far below the glass transition temperature Tg of the epoxy resin (initial Tg = 80°C), ensuring that the system maintains a low viscosity before the gel point, which is conducive to molecular diffusion, bubble escape and stress relaxation, while avoiding premature glass transition and inhibition of the reaction.

[0031] During the step-up temperature ramp, sufficient holding time at low temperatures promotes full diffusion of the epoxy resin and ensures a uniform reaction. At low temperatures, the resin's viscosity is relatively low, allowing for better mobility of the molecular chains and curing agent. During the step-up temperature ramp, sufficient holding time at lower temperatures allows for full mixing and diffusion of the reactants, ensuring a uniform reaction within the system.

[0032] Subsequent temperature-raising curing: After gelation, the temperature is gradually raised to 110°C to continue to increase the Tg of the system, while providing sufficient molecular activity to complete a deeper cross-linking reaction and achieve the designed final curing degree and Tg.

[0033] Each curing chamber is heated in stages to reach the predetermined temperature before the product enters. There is no significant temperature increase after the product enters. The hot air circulation system in the auxiliary chamber improves the temperature uniformity in the chamber and minimizes the local temperature difference of the product.

[0034] Close thermal expansion coefficients, uniform temperatures, and low temperature differences make the thermal expansion rates tend to be consistent, thereby achieving: The interface is tightly bonded, with no bubbles or air gaps. The local discharge peak at 48.6kV is ≤5pC (national standard 20pC). The product qualification rate increased from 91.67% to 100%.

[0035] Continuous step-by-step production, no waiting process for heating, and production efficiency increased by 10%.

[0036] It should be appreciated that all combinations of the foregoing concepts, as well as additional concepts described in greater detail below, to the extent such concepts are not mutually inconsistent, can be considered to be part of the inventive subject matter of this disclosure.

[0037] The foregoing and other aspects, embodiments, and features of the present invention will be more fully understood from the following description in conjunction with the accompanying drawings. Other additional aspects of the present invention, such as features and / or beneficial effects of the exemplary embodiments, will become apparent from the following description or through practice of specific embodiments according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings are not drawn to scale. In the accompanying drawings, each identical or nearly identical component shown in various figures may be represented by the same reference numeral. For clarity, not every component is labeled in every figure. Embodiments of various aspects of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 This is the process flow chart for epoxy resin curing of metal armored voltage transformer; Figure 2 This is a schematic diagram of a metal armored voltage transformer; Figure 3 Schematic diagram of a tunnel furnace for primary curing of epoxy resin for metal-clad voltage transformers; Figure 4 Schematic diagram of the secondary curing tunnel furnace for epoxy resin curing of metal-clad voltage transformers.

[0039] Description of markings: double-row chain roller 10, receiving section 11, observation section 12, preheating section 13, primary curing heating section one 14, primary curing heating section two 15, primary curing heating section three 16, out-of-furnace transfer track 17, pallet 18, control system panel 19, secondary curing heating section two 21, secondary curing insulation section 22, cooling section 23, cache section 24. DETAILED DESCRIPTION

[0040] To further clarify the objectives, technical solutions, and advantages of the embodiments of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only a portion of the embodiments of the present invention, not all of them. Based on the described embodiments of the present invention, all other embodiments derived by persons of ordinary skill in the art without requiring creative effort are within the scope of protection of the present invention. Unless otherwise defined, technical or scientific terms used herein shall have the ordinary meanings understood by persons of ordinary skill in the field to which the present invention pertains.

[0041] The terms "first," "second," and similar words used in the patent specification and claims of this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular forms of "a," "an," or "the" and similar words do not indicate a limitation of quantity, but rather indicate the presence of at least one. Terms such as "include" or "comprising" mean that the elements or objects preceding "include" or "comprising" encompass the features, integers, steps, operations, elements, and / or components listed after "include" or "comprising," and do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0042] Example 1: like Figure 3 、 Figure 4 As shown, the tunnel furnace curing equipment used in this embodiment includes: a primary curing tunnel furnace, a secondary curing tunnel furnace, and a corresponding intelligent control system.

[0043] like Figure 3 As shown, the one-time curing tunnel furnace is provided with a receiving section 11, an observation section 12, a heating section (13-16) divided into four independent temperature-controlled chambers, and a double-row chain roller conveyor 10 transfer device is provided at the bottom that runs through each section.

[0044] The first and last ends of the primary curing tunnel furnace are provided with a connecting section 11, which is provided with a pallet 18 for transferring products. The size of the pallet 18 is suitable for the entire curing tunnel furnace system. The pallet 18 is supported and transported by two rows of power rollers at the bottom of the double-row chain roller conveyor 10.

[0045] The observation section 12 is equipped with an observation window, which can clearly observe the pouring position of the metal armored voltage transformer and promptly withdraw and replenish the material when a shortage of material is found.

[0046] The heating section is divided into five temperature steps and four heating and curing chambers, namely preheating section 13, primary curing heating section 1 14 (occupying 2 steps), primary curing heating section 2 15, and primary curing heating section 3 16.

[0047] Each heating section maintains the set temperature unchanged, and the product goes through a temperature step every 5 hours. After completing a step, the next batch of products can be continuously cured without adjusting the temperature of the heating section. The cast metal armored voltage transformer is scheduled according to the curing step, and the cast metal armored voltage transformer is continuously cured, which improves the production efficiency of the curing process.

[0048] Except for the receiving section 11, the observation section 12 and the heating section are set as sealed spaces, and the observation section 12 is provided with a curing chamber; the heating section (13-16) is provided with four step-by-step heating curing chambers, each of which has an independent space and is respectively provided with two temperature sensors, a heater, a blower device, and an alarm device.

[0049] Each section and each bin is provided with an openable and closable partition sealing device and a transfer device, which is controlled by a control system and automatically opened according to a set curing program. The control system panel 19 can also be manually operated to open or adjust.

[0050] like Figure 4 As shown, the secondary curing tunnel furnace is provided with a receiving section 11, a secondary curing heating section 21, a secondary curing insulation section 22, a cooling section 23 and a buffer section 24, and a double-row chain roller 10 is provided at the bottom running through each section.

[0051] The double-row chain roller conveyor 10 is connected to the external transfer track 17 outside the furnace.

[0052] After the primary curing is completed, the product is transferred to the demoulding area via the transfer track 17 outside the furnace.

[0053] The products demoulded in the demoulding area are transported via the tray 18 to the double-row chain roller conveyor 10 of the secondary curing section 11 via the external transfer track 17 .

[0054] Intelligent control system: monitors and adjusts the temperature in real time, and issues drive commands for partition devices and transfer devices according to the program.

[0055] A control system panel 19 is provided on one side of the observation section 12 of the primary curing tunnel furnace, which can select or set different curing programs to meet the curing process parameter requirements of different types of products.

[0056] The two temperature steps of the primary curing heating section 14 can also be operated in separate compartments. When more temperature levels need to be subdivided, the compartment can be separated and controlled by a partition device to become two independent curing compartments.

[0057] A control system panel 19 is provided on one side of the secondary curing tunnel furnace receiving section 11 , and the secondary curing process parameters are set through the control system panel 19 .

[0058] The operating temperature control module includes temperature sensors, heaters, and air blowers in each curing chamber, as well as alarms above each heating section. If the chamber temperature exceeds the set temperature, an audible and visual alarm sounds, and the heaters are automatically switched on and off to adjust the room temperature. If the temperature exceeds the control limit, or if the temperature difference between two locations within the same curing chamber exceeds 5°C, the alarm will activate, alerting you to the abnormality.

[0059] The cooling section 23 is arranged after the secondary curing insulation section 22. A temperature sensor is provided at the very end to directly detect the surface temperature of the transformer. When the cooling section 23 detects that the temperature of the transformer in the frontmost tray 18 drops below 45°C, the transfer switch will be triggered and the transformer will be transferred into the cache section.

[0060] The buffer section 24 provides a static area for the transformers, caching at least 100 products waiting to enter the assembly area.

[0061] Specific operation process: Castable preparation: Epoxy resin: Hubei Jiangte Insulation Materials Co., Ltd. JT8024A modified liquid epoxy resin (epoxy content, mol / kg [ASTM D-1652]: 4.5-5.0; non-volatile component, wt% [DOWM 101188-TE]: 100; viscosity @ 25°C (77°F), mPa.s [ASTM D-2983]: 3800-6000; density @ 25°C, g / cm 3 [ASTM D-1475]: 1.10-1.20); Curing agent: Hubei Jiangte Insulation Materials Co., Ltd. JT8024B pre-catalyzed liquid anhydride curing agent (viscosity @ 25 ° C (77 ° F), mPa.s [ASTM D-2983]: 200-500; density @ 25 ° C, g / cm 3 [ASTM D-1475]: 1.15-1.25); Filler: Silane treated silicon powder, moisture content should be less than 0.2%; The above raw materials were mixed in a mass ratio of (epoxy resin:silica powder = 100:225) and (curing agent:silica powder = 82:145) to obtain an epoxy resin mixture and a curing agent mixture; The above mixture is vacuum stirred and mixed according to the mass ratio of epoxy resin: curing agent = 100:82 to obtain a casting material, and static vacuum casting is performed on the metal-clad voltage transformer.

[0062] Curing process: 1. The metal armored voltage transformer set mold is statically vacuum poured. After pouring is completed, it is taken out of the tank and placed in an insulation room to cool to 20℃ and stand for 3 hours.

[0063] 2. After the static process in the insulation room, the metal-clad voltage transformer is loaded into the curing tunnel furnace tray 18, the tray size is 500mm*800mm, and is transferred to the primary curing tunnel furnace receiving section 11 through the external transfer track 17.

[0064] 3. Set the process parameters of the one-step curing tunnel furnace through the control system panel 19: The preheating section 13, primary curing heating section 1 14, primary curing heating section 2 15, and primary curing heating section 3 16 are cured in a stepwise manner: 50°C (5 hours) → 70°C (10 hours) → 90°C (5 hours) → 110°C (5 hours). Products are transported between these sections within the furnace by a double-row chain roller conveyor 10 carrying pallets 18.

[0065] 4. After the primary curing is completed, the mold is transferred to the demoulding area through the connecting section 11 and the external transfer track 17 for demoulding.

[0066] 5. The demoulding area is kept at a constant temperature of 25°C and the demoulding time is 20 minutes.

[0067] 6. After demoulding, the product passes through the external transfer track 17 and enters the secondary curing tunnel furnace. The secondary curing process parameters are set through the control system panel 19: the secondary curing heating section 21 and the secondary curing insulation section 22 are both set to 110°C, and the cumulative insulation time is 12 hours.

[0068] 7. After secondary curing, the steel is cooled to 45°C in the cooling section 23 and transported to the buffer section 24. Twelve transformers are extracted to test the partial discharge performance.

[0069] Observation results of the temperature of each chamber of the primary curing furnace and the outlet temperature of the cooling section during the implementation process: The temperature difference between each chamber of the primary curing furnace is ≤1.5℃ Cooling section outlet temperature ≤45℃ Test results of 12 35kV products: Measuring voltage 28.1kV Discharge ≤ 2pC Qualified rate 100% Measuring voltage 48.6kV Discharge ≤ 5pC Qualified rate 100% Example 2: The curing device used is the same as that in Example 1, with only the specific operation process being different.

[0070] The epoxy resin, curing agent, and filler are the same as those in Example 1. The above raw materials are mixed in a mass ratio of (epoxy resin:silica powder = 100:250) and (curing agent:silica powder = 70:145) to obtain an epoxy resin mixture and a curing agent mixture; The above mixture is mixed by vacuum stirring at the ratio of epoxy resin to curing agent = 100:70 to obtain a casting material, and static vacuum casting is performed on a metal-clad voltage transformer mold.

[0071] Curing process: 1. The metal armored voltage transformer set mold is statically vacuum poured. After it is unloaded from the tank, it is placed in an insulation room and cooled to 16°C and left to stand for 2.5 hours.

[0072] 2. After the static process in the insulation room, the metal-clad voltage transformer is loaded into the curing tunnel furnace tray 18, the tray size is 500mm*800mm, and is transferred to the primary curing tunnel furnace receiving section 11 through the external transfer track 17.

[0073] 3. Set the process parameters of the one-step curing tunnel furnace through the control system panel 19: The preheating section 13, primary curing heating section 1 14, primary curing heating section 2 15, and primary curing heating section 3 16 are cured in a stepwise manner from 45°C (5 hours) to 65°C (10 hours) to 85°C (5 hours) to 110°C (5 hours). Products are transported between these sections within the furnace by a double-row chain roller conveyor 10 carrying pallets 18.

[0074] 4. After the primary curing is completed, the mold is transferred to the demoulding area through the connecting section 11 and the external transfer track 17 for demoulding.

[0075] 5. The demoulding area is kept at a constant temperature of 20°C, and the demoulding time for each tray of transformers is approximately 20 minutes.

[0076] 6. After demoulding, the product passes through the external transfer track 17 and enters the secondary curing tunnel furnace. The temperature of the secondary curing heating section is set to: the secondary curing heating section 21 and the secondary curing insulation section 22 are both set to 105°C, and the cumulative insulation time is 12 hours.

[0077] 7. After secondary curing, the product is cooled to 45°C in the cooling section 23 and transported to the buffer section 24 for assembly. Twelve transformers are selected to test their partial discharge performance.

[0078] Observation results of the temperature of each chamber of the primary curing furnace and the outlet temperature of the cooling section during the implementation process: The temperature difference between each chamber of the primary curing furnace is ≤1.8℃ Cooling section outlet temperature ≤45℃ Test results of 12 35kV products: Measuring voltage 28.1kV, discharge capacity ≤ 2pC, qualified rate 100% Measuring voltage 48.6kV, discharge capacity ≤5pC, qualified rate 100% Example 3: The curing device used is the same as that in Example 1, with only the specific operation process being different.

[0079] The epoxy resin, curing agent, and filler are the same as those in Example 1. The above raw materials are mixed in a mass ratio of (epoxy resin:silica powder = 100:210) and (curing agent:silica powder = 88:136) to obtain an epoxy resin mixture and a curing agent mixture; The above mixture is vacuum stirred and mixed according to the ratio of epoxy resin to curing agent = 100:88 to obtain a casting material, and static vacuum casting is performed on the metal-clad voltage transformer.

[0080] Curing process: 1. The metal armored voltage transformer set mold is statically vacuum cast. After it is taken out of the tank, it is placed in an insulation room and cooled to 25℃ and left to stand for 3 hours.

[0081] 2. After the static process in the insulation room, the metal-clad voltage transformer is loaded into the curing tunnel furnace tray 18, the tray size is 500mm*800mm, and is transferred to the primary curing tunnel furnace receiving section 11 through the external transfer track 17.

[0082] 3. Set the process parameters of the one-step curing tunnel furnace through the control system panel 19: The preheating section 13, primary curing heating section 1 14, primary curing heating section 2 15, and primary curing heating section 3 16 are cured in a stepwise manner from 55°C (5 hours) to 75°C (10 hours) to 95°C (5 hours) to 115°C (5 hours). Products are transported between these sections within the furnace by a double-row chain roller conveyor 10 carrying pallets 18.

[0083] 4. After the primary curing is completed, the mold is transferred to the demoulding area through the connecting section 11 and the external transfer track 17 for demoulding.

[0084] 5. The demoulding area is kept at a constant temperature of 30°C and the demoulding time is 25 minutes.

[0085] 6. After demoulding, the product passes through the external transfer track 17 and enters the secondary curing tunnel furnace. The temperature of the secondary curing heating section is set to: the secondary curing heating section 21 and the secondary curing insulation section 22 are both set to 115°C, and the cumulative insulation time is 12 hours.

[0086] 7. After secondary curing, the product is cooled to 45°C in the cooling section 23 and transported to the buffer section 24 for assembly. Twelve transformers are selected to test their partial discharge performance.

[0087] Observation results of the temperature of each chamber of the primary curing furnace and the outlet temperature of the cooling section during the implementation process: The temperature difference between each chamber of the primary curing furnace is ≤2.2℃ Cooling section outlet temperature ≤45℃ Test results of 12 35kV products: Measuring voltage 28.1kV, discharge capacity ≤ 2pC, qualified rate 100% Measuring voltage 48.6kV, discharge capacity ≤5pC, qualified rate 100% Comparative Example 1 The curing device used is the same as that in Example 1, with only the specific operation process being different.

[0088] The epoxy resin, curing agent, and filler are the same as those in Example 1. The above raw materials are mixed in a mass ratio of (epoxy resin:silica powder = 100:250) and (curing agent:silica powder = 72:145) to obtain an epoxy resin mixture and a curing agent mixture; The above mixture is vacuum stirred and mixed according to the ratio of epoxy resin to curing agent = 100:72 to obtain a casting material, and static vacuum casting is performed on the metal armored voltage transformer mold.

[0089] Curing process: 1. The metal armored voltage transformer set mold is statically vacuum poured. After it is taken out of the can, it is placed in an oven and cured according to the program of 50℃ (5h) → 70℃ (10h) → 90℃ (5h) → 110℃ (5h).

[0090] 2. Enter the demoulding area for demoulding and keep warm at 110℃ for 12 hours after demoulding.

[0091] 3. Cool to 45°C and transfer to the buffer section for assembly. Take 12 transformers to test the partial discharge performance.

[0092] Test results of 12 35kV products: Measuring voltage 28.1kV, discharge capacity ≤10pC, qualified rate 100% The measurement voltage is 48.6kV, the discharge capacity is ≤20pC, and the qualified rate is 91.7%. Table 1: Partial discharge pass rate statistics

[0093] While the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Those skilled in the art and with ordinary skill in the art will readily appreciate that various modifications and alterations may be made without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the claims. The term "holding time" used in the present patent application specification and claims should be understood as a contiguous range.

Claims

1. A metal armored voltage transformer epoxy resin curing process, characterized in that: The following steps are involved: A. Mix epoxy resin and silica powder in a weight ratio of 100:(210-250), curing agent and silica powder in a ratio of 80:(123-166), add silica powder to epoxy resin and curing agent to silica powder, and then vacuum mix and prepare epoxy resin casting material in a ratio of 100:(70-88). B. The metal-clad voltage transformer is placed in a mold and the epoxy resin casting material prepared in step A is poured into the mold under static vacuum. After pouring, the mold is taken out of the tank and placed in a heat preservation room for cooling and standing. C. After standing still, the metal-clad voltage transformer is transferred to a primary curing tunnel furnace for curing by step-by-step temperature increase; D. Demolding after the primary curing is completed; E. After demoulding, the metal armored voltage transformer is transported to the secondary curing tunnel furnace for secondary curing; F. After secondary solidification, it cools down and enters the buffer section for assembly.

2. The process according to claim 1, characterized in that: The metal armored voltage transformer in step B is cooled to 20±5℃ in the insulation room after the tank is removed; let it stand for more than 3 hours; The step C one-step curing tunnel furnace adopts a step-by-step temperature rising process, and the step-by-step temperature rising process parameters of the one-step curing tunnel furnace are set to 50±5°C for 5 hours, 70±5°C for 10 hours, 90±5°C for 5 hours, and 110±5°C for 5 hours. The demoulding area in step D is kept at a constant temperature of 25±5°C; The process parameters of the secondary curing tunnel furnace in step E are to maintain the temperature at 110±5°C for 12 hours; In the cooling section of step F, it is detected that the transformer temperature drops below 45° C. and is transferred to the buffer section.

3. The process according to claim 1, characterized in that In step A, before vacuum mixing the epoxy resin and the curing agent, silicon micropowder is added and vacuum mixed. The silicon micropowder is added in a weight ratio of epoxy resin: silicon micropowder = 100: (210-250), and curing agent: silicon micropowder = 80: (123-166).

4. The process according to claim 1, characterized in that The metal shell of the metal-clad voltage transformer is made of 5052 aluminum alloy with a thickness of 2 mm. The difference in thermal expansion coefficient between the metal-clad aluminum alloy and the epoxy resin at 110° C. is controlled within 0.1%.

5. The process according to claim 1, characterized in that The partial discharge level of the metal-clad voltage transformer produced by the process is lower than 10pC.

6. A curing tunnel furnace device for the process according to claims 1-5, characterized in that: include: Primary curing tunnel furnace, secondary curing tunnel furnace and corresponding control systems; The one-step curing tunnel furnace comprises: a receiving section, an observation section and a heating section; the heating section has at least four independently temperature-controlled curing chambers, and the observation section is provided with one curing chamber; each curing chamber has an independent space; The secondary curing tunnel furnace comprises: a receiving section, a heating section, a heat preservation section, a cooling section and a buffer section; Each section and each warehouse is equipped with an openable and closable partition sealing device and a transfer device; The control system includes: a temperature control module, a partition sealing device opening and closing module and a transfer device speed regulation module.

7. The device according to claim 6, characterized in that The temperature control module includes: one or more combinations of temperature sensors, heaters, air blowing devices and alarm devices set in each section of the primary curing tunnel furnace and the secondary curing tunnel furnace that need to be temperature controlled, and a control system panel connected to these devices with electrical signals.

8. The device according to claim 7, characterized in that The air blowing device includes a fan on the top of the silo, a porous return air plate and a heater; The fan is located at the top of the bin and is used to inhale hot air from the top of the curing bin, guide the hot air into the air ducts on the left and right sides through the porous return air plate, exchange heat with the heaters in the air ducts on both sides, and then blow it out from the lower parts of both sides of the curing bin to heat the mutual inductor, and then be inhaled by the fan, forming a repetitive hot air cycle.

9. The device according to claim 6, characterized in that The curing chamber partition sealing device is sealed with ceramic fiber rope and / or asbestos tape; the transfer device is a double-row chain roller set through the bottom of each section of the curing tunnel furnace; the partition sealing device and the transfer device are both controlled by the control system and automatically opened according to the set curing program.

10. The device according to claim 6, characterized in that The heating section curing chamber can be operated in a divided chamber; when more temperature steps need to be subdivided, the chamber is separated and controlled by the partition sealing device to form two independent curing chambers.

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