Thin film capacitor for flexible direct current power transmission

Abstract

The utility model discloses a film capacitor for flexible direct current power transmission, which belongs to the technical field of capacitors and comprises a shell, a plurality of capacitor cores and extraction electrodes, the shell is made of metal materials, the plurality of capacitor cores are grouped to form a plurality of capacitor core independent groups, and the extraction electrodes are arranged in the shell. Each capacitor core independent group is connected with a tinned copper plate, the lead-out electrode is provided with a laminated busbar and is connected with the tinned copper plate in a matched manner through the laminated busbar, and the plurality of capacitor core independent groups are packaged in the shell through a potting material. The thin-film capacitor can simultaneously meet the performance requirements of low self-inductance, low temperature rise, high energy density, light weight and long service life, thereby effectively improving the safety and reliability of the thin-film capacitor for flexible direct-current power transmission.

Description

Technical Field

[0001] This utility model relates to the field of capacitor technology, specifically a flexible DC power transmission film capacitor. Background Technology

[0002] Flexible DC transmission technology was first proposed by Boon-Teck Ooi et al. in Canada in 1990. It is a new generation of high voltage DC transmission technology based on voltage source converters, self-turn-off devices (IGBTs), and pulse width modulation (PWM) technology.

[0003] The converter valve is the core equipment of the flexible DC transmission converter station, which plays the role of AC / DC conversion. It converts AC to DC at the sending end and DC to AC at the receiving end.

[0004] The DC-Link capacitor, one of the key components in the converter valve, plays a crucial role in supporting DC voltage in the DC transmission system. It is a core component that ensures the quality of DC transmission and the normal and stable operation of the converter valve.

[0005] Currently, the DC-link capacitors used in flexible DC transmission projects mostly use products from Hitachi Energy (formerly ABB Power Grids), which is monopolized by foreign manufacturers. This results in long supply cycles, high product prices, and a risk of supply disruption under the current complex international situation, making it the most prominent weakness in my country's flexible DC transmission project construction. Therefore, my country urgently needs to conduct technical research on high-end capacitors for flexible DC transmission to achieve independent control and domestic substitution of key technologies.

[0006] Support capacitors used on the DC side of flexible DC transmission face complex electric fields caused by superimposed high voltage DC, harmonics and transient overvoltages, as well as operating conditions with rising internal temperatures. There is also a rigid requirement for high reliability of the capacitors (more than 40 years of operation in the grid). The progress of domestic DC capacitors in replacing imported products in the field of flexible DC transmission is very slow.

[0007] Because flexible DC transmission projects operate continuously, the failure rate of film capacitors must be ≤30 FIT over a continuous service life of up to 40 years. Therefore, the safety of such a large number of capacitors installed in the valve hall must be guaranteed. Flexible DC capacitors are characterized by high voltage, large capacitance, and high current, and require low loss tangent, low self-inductance, and low temperature rise. Furthermore, to reduce the footprint of the valve hall and the load on valve tower components, the capacitors should be as small and lightweight as possible. More importantly, while meeting the above conditions, extremely low failure rates are also required over the expected 40-year lifespan. This can only be achieved through a perfect match between the capacitor design, manufacturing process, equipment, and materials. Therefore, further improvements are necessary. Utility Model Content

[0008] The present invention aims to provide a flexible thin-film capacitor for DC power transmission to overcome the shortcomings of the prior art.

[0009] A flexible DC transmission film capacitor designed for this purpose includes a shell, a capacitor core, and lead electrodes. The shell is made of metal. Several capacitor cores are provided, and the several capacitor cores are grouped to form multiple individual capacitor core groups. Each individual capacitor core group is connected to a tin-plated copper plate. The lead electrodes are provided with a stacked busbar and are connected to the tin-plated copper plate through the stacked busbar. The multiple individual capacitor core groups are encapsulated in the shell by potting compound.

[0010] The outer casing has an opening, through which multiple capacitor cores are individually placed inside the casing. An opening end plate is provided on the opening, and the opening end plate is fixed to the opening with potting compound to achieve encapsulation of multiple capacitor cores individually.

[0011] The open end plate has an electrode connection hole. The lead-out electrode is set on the electrode connection hole and placed outside the housing. The stacked busbar and the lead-out electrode are integrated or separate and then fixed to each other by fasteners, threads or buckles. The stacked busbar is placed inside the housing through the electrode connection hole and connected to the tin-plated copper plate.

[0012] The open end plate is also provided with a pressure relief valve connection hole, and a pressure relief valve is connected through the pressure relief valve connection hole.

[0013] Each capacitor core group consists of multiple capacitor cores that are positioned back-to-back and side-to-side. The positive and negative terminals of the capacitor cores that are positioned side-to-side are connected to transverse connecting copper plates. Each capacitor core group is positioned longitudinally, with tin-plated copper plates positioned longitudinally and connected to the transverse connecting copper plates of the capacitor core groups that are longitudinally adjacent to each other.

[0014] An insulating sleeve is also fitted onto the tin-plated copper plate.

[0015] The outer shell is made of lightweight aluminum alloy, and its outer surface is coated with a graphene thermally conductive coating.

[0016] A manufacturing process for a flexible DC transmission film capacitor includes the aforementioned flexible DC transmission film capacitor, and the manufacturing process includes the following steps:

[0017] Step 1: The capacitor core is formed by metallization film through evaporation, slitting, winding, heat setting and electrode gold sputtering. The metallization film is a double T-shaped safety film made of high crystallinity BOPP base film and is formed by gradient sheet resistance evaporation.

[0018] Step 2: Arrange several formed capacitor cores back-to-back and side-to-side with each other, and then horizontally weld the horizontal connecting copper plate to the positive and negative terminals of the capacitor cores that are side-to-side with each other to form a separate capacitor core group.

[0019] Step 3: Arrange multiple capacitor cores in a longitudinally adjacent group, and longitudinally weld tin-plated copper plates onto the transverse connecting copper plates of the longitudinally adjacent capacitor core groups.

[0020] Step 4: Assemble the lead-out electrodes and stacked busbars onto the open end plate;

[0021] Step 5: Place multiple connected capacitor cores individually inside the housing, and fill the housing with potting compound under vacuum conditions in a vacuum machine. Then, assemble the open end plate onto the housing and connect the tin-plated copper plate to the laminated busbar.

[0022] Step Six: Remove the semi-finished product from the vacuum machine and allow the potting compound to cure under positive pressure. Finally, apply a graphene thermally conductive coating to the outer shell to produce a flexible DC transmission film capacitor.

[0023] In step one, before the capacitor core is wound, the entire roll of metallized film undergoes failure treatment to eliminate the stress generated during the coating and slitting of the metallized film.

[0024] In step one, the capacitor core is wound using two metallized thin films with staggered edges, and the winding machine used for the winding operation employs variable tension.

[0025] In step five, the potting compound uses polyurethane components A and B. After degassing, the polyurethane components A and B are mixed and then poured into the outer shell under vacuum conditions and cured under positive pressure.

[0026] In step one, the capacitor core is a flat core. During heat setting, a heat setting fixture is used to apply a fixed pressure to the capacitor core, and it is placed in an oven for gradient heat setting. The control process is as follows:

[0027] Heat from room temperature to 60℃ and hold for 3 hours, with the heating time taking 10 minutes;

[0028] Heat to 65℃ and maintain for 5 hours; heating time is 30 minutes.

[0029] Heat to 70℃ and hold for 30 minutes; heating time is 10 minutes.

[0030] Heat to 75℃ and hold for 30 minutes; heating time is 10 minutes.

[0031] Heat to 80℃ and hold for 30 minutes; heating time is 10 minutes.

[0032] Heat to 85℃ and hold for 30 minutes; heating time is 10 minutes.

[0033] Heat to 90℃ and hold for 30 minutes; heating time is 10 minutes.

[0034] Heat to 95℃ and hold for 30 minutes; heating time is 10 minutes.

[0035] Heat to 100℃ and hold for 30 minutes; heating time is 10 minutes.

[0036] Heat to 105℃ and hold for 10 hours; heating time is 60 minutes.

[0037] Heat to 110℃ and hold for 5 hours, with a heating time of 60 minutes.

[0038] Through the structural improvements described above, this invention can simultaneously meet the performance requirements of low self-inductance, low temperature rise, high energy density, light weight, and long lifespan, thereby effectively improving the safety and reliability of thin-film capacitors used in flexible DC transmission. Attached Figure Description

[0039] Figure 1 This is an exploded structural diagram of an embodiment of the present invention.

[0040] Figure 2 This is an exploded structural diagram from another perspective of an embodiment of the present invention.

[0041] Figure 3 This is a schematic diagram of the assembly structure of an embodiment of the present utility model.

[0042] Figure 4 This is a schematic diagram of the assembly structure for a separate capacitor core assembly.

[0043] Figure 5 This is a schematic diagram of the current density of a metallized thin film with a gradient sheet resistance.

[0044] Figure 6 This is a schematic diagram of the structure of a double-T-shaped safety membrane.

[0045] Figure 7 This is a schematic diagram of a T-shaped fuse circuit. Detailed Implementation

[0046] To make the above-mentioned objects, features, and advantages of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a full understanding of this utility model. However, this utility model can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this utility model. Therefore, this utility model is not limited to the specific embodiments disclosed below.

[0047] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0048] See Figures 1-7 This flexible DC transmission film capacitor includes a housing 1, a capacitor core 2, and lead-out electrodes 3. The housing 1 is made of metal. Several capacitor cores 2 are provided, and several capacitor cores 2 are grouped to form multiple individual capacitor core groups. Each individual capacitor core group is connected to a tin-plated copper plate 4. The lead-out electrodes 3 are provided with a stacked busbar 5 and are connected to the tin-plated copper plate 4 through the stacked busbar 5. Multiple individual capacitor core groups are encapsulated in the housing 1 by potting compound.

[0049] This embodiment can simultaneously meet the performance requirements of low self-inductance, low temperature rise, high energy density, light weight, and long life, thereby effectively improving the safety and reliability of thin-film capacitors for flexible DC transmission.

[0050] The outer casing 1 is provided with an outer casing opening 6. Multiple capacitor cores are placed in the outer casing 1 through the outer casing opening 6. An opening end plate 7 is provided on the outer casing opening 6. The opening end plate 7 is fixed on the outer casing opening 6 by potting material to realize the encapsulation of multiple capacitor cores in a single group.

[0051] An electrode connection hole 8 is provided on the open end plate 7. The lead-out electrode 3 is set on the electrode connection hole 8 and placed outside the outer shell 1. The stacked busbar 5 is integrally set with the lead-out electrode 3 or separately set and then fixed to each other by fasteners, threads or buckles. The stacked busbar 5 is placed inside the outer shell 1 through the electrode connection hole 8 and is connected to the tin-plated copper plate 4.

[0052] The open end plate 7 is also provided with a pressure relief valve connection hole 9, and a pressure relief valve 10 is connected through the pressure relief valve connection hole 9.

[0053] Each capacitor core group consists of multiple capacitor cores 2 that are positioned back-to-back and side-to-side. The positive and negative terminals of the capacitor cores 2 that are positioned side-to-side are connected to transverse connecting copper plates 11. Each capacitor core group is arranged longitudinally, and a tin-plated copper plate 4 is arranged longitudinally and connected to the transverse connecting copper plates 11 of the capacitor core group that is longitudinally adjacent to it.

[0054] An insulating sleeve 12 is also fitted onto the tin-plated copper plate 4.

[0055] The outer shell 1 is made of lightweight aluminum alloy material, and its outer surface is coated with a graphene thermally conductive coating.

[0056] The manufacturing process of the aforementioned flexible DC transmission film capacitor includes the following steps:

[0057] Step 1: The capacitor core 2 is formed by metallization film through evaporation, slitting, winding, heat setting and electrode gold sputtering. The metallization film is a double T-shaped safety film made of high crystallinity BOPP base film and is formed by gradient sheet resistance evaporation.

[0058] Step 2: Arrange several formed capacitor cores 2 back-to-back and left-to-right against each other, and then horizontally weld the horizontal connecting copper plate 11 to the positive and negative terminals of the capacitor cores 2 that are left-to-right against each other to form a separate capacitor core group.

[0059] Step 3: Arrange multiple capacitor cores in a longitudinally adjacent group, and longitudinally weld the tin-plated copper plate 4 onto the transverse connecting copper plate 11 of the longitudinally adjacent capacitor core groups.

[0060] Step 4: Assemble the lead-out electrode 3 and the stacked busbar 5 onto the open end plate 7;

[0061] Step 5: Place multiple connected capacitor cores individually inside the housing 1, and fill the housing 1 with potting compound under vacuum conditions in a vacuum machine. Then, assemble the open end plate 7 onto the housing 1, and connect the tin-plated copper plate 4 to the laminated busbar 5.

[0062] Step 6: Remove the semi-finished product from the vacuum machine and allow the potting compound to cure under positive pressure. Finally, apply a graphene thermally conductive coating to the surface of the outer shell 1 to ultimately produce a flexible DC transmission film capacitor.

[0063] In step one, before winding the capacitor core 2, the entire roll of metallized film is subjected to failure treatment to eliminate the stress generated during the coating and cutting of the metallized film.

[0064] In step one, when the capacitor core 2 is wound, two metallized thin films are wound with staggered edges, and the winding machine used for the winding operation is operated with variable tension.

[0065] In step five, the potting compound is polyurethane of materials A and B. After degassing, the polyurethane of materials A and B are mixed and then poured into the outer shell 1 under vacuum conditions and cured under positive pressure conditions.

[0066] In step one, capacitor core 2 is a flat core. During heat setting, a fixed pressure is applied to capacitor core 2 using a heat setting fixture, and it is placed in an oven for gradient heat setting. The control process is as follows:

[0067] Heat from room temperature to 60℃ and hold for 3 hours, with the heating time taking 10 minutes;

[0068] Heat to 65℃ and maintain for 5 hours; heating time is 30 minutes.

[0069] Heat to 70℃ and hold for 30 minutes; heating time is 10 minutes.

[0070] Heat to 75℃ and hold for 30 minutes; heating time is 10 minutes.

[0071] Heat to 80℃ and hold for 30 minutes; heating time is 10 minutes.

[0072] Heat to 85℃ and hold for 30 minutes; heating time is 10 minutes.

[0073] Heat to 90℃ and hold for 30 minutes; heating time is 10 minutes.

[0074] Heat to 95℃ and hold for 30 minutes; heating time is 10 minutes.

[0075] Heat to 100℃ and hold for 30 minutes; heating time is 10 minutes.

[0076] Heat to 105℃ and hold for 10 hours; heating time is 60 minutes.

[0077] Heat to 110℃ and hold for 5 hours, with a heating time of 60 minutes.

[0078] In the existing technology, low sheet resistance films have a significant advantage in withstanding large current surges. However, low sheet resistance metallized safety films require a large amount of self-healing energy during self-healing, which can easily lead to thermal bonding between multiple layers of films and shorten the life of the capacitor.

[0079] High sheet resistance films can withstand higher voltage and release much less self-healing energy. Capacitance loss and loss changes are smaller than conventional products. However, if the entire coating is high sheet resistance, its obvious weakness is poor high current carrying capacity, large equivalent series resistance, and increased capacitor temperature, which leads to a shortened capacitor life.

[0080] In this embodiment, the metallized film is a graded sheet resistance film. This graded sheet resistance film combines the advantages of both low and high sheet resistance films, increasing the capacitor's overcurrent capability while reducing the product's self-healing energy. It can withstand higher electric field strengths and overcome the shortcomings of conventional high sheet resistance films, balancing overcurrent capability and self-healing properties. This graded sheet resistance design improves the film's withstand voltage level while maintaining superior overcurrent capability compared to conventional high sheet resistance films. The sheet resistance gradually increases from the thickened area to the edge area, while the current density during capacitor operation gradually decreases from the thickened area to the edge area, resulting in a more uniform current. Its structure is as follows... Figure 5As shown.

[0081] In this embodiment, the double T-shaped safety film is formed by depositing a pattern of a specific shape onto the surface of an organic dielectric film as an electrode plate. The area units separated in the electrode plate are connected together by numerous T-shaped fuses 200 that can ensure the safety of the capacitor.

[0082] In existing technologies, the electrode of a conventional metallized film is a single, monolithic unit. When a conventional metallized film successfully self-heals, the energy generated causes the thin metal plating around the breakdown point to evaporate, forming an irregular annular insulating region that isolates the breakdown point, thus essentially restoring the overall electrical performance of the capacitor. Successful self-healing of the breakdown point depends primarily on the energy released during breakdown, which is mainly influenced by factors such as the thickness of the metallized plating, the composition of the dielectric material, and the static pressure at the breakdown point. In many cases, conventional metallized films fail to self-heal successfully. During the self-healing process, the multilayer dielectric adjacent to the self-healing point is often burned, resulting in continuous self-healing breakdown with a constant hissing sound. Under the high temperature of the arc generated by continuous breakdown, the local film softens, causing thermal melting, which binds the multilayer dielectric together, accompanied by the generation of a large amount of gas, leading to short-circuit failure of the capacitor, or even smoke and explosion.

[0083] In this embodiment, the metallized double-T-shaped safety film has multiple inverted T-shaped fuses 200 disposed on its film 100, with adjacent T-shaped fuses 200 spaced apart. Furthermore, the upper and lower edges of the film 100 are respectively cut with wavy portions 300. Therefore, during the self-healing process of the metallized double-T-shaped safety film, due to the sensitive response of the T-shaped fuses 200, at the instant of self-healing breakdown, current flows through the T-shaped fuses 200 into the electrode unit where the breakdown point is located. The moment the current reaches a certain value, the energy generated by the heat generated by the T-shaped fuses 200 themselves causes the T-shaped fuses 200 in the electrode unit to melt immediately, thus isolating the electrode unit where the breakdown point is located from the capacitor substrate and promptly preventing a large inrush current from entering the breakdown point. The breakdown discharge time is particularly short, preventing continuous self-healing breakdown and avoiding the phenomenon of multi-layer breakdown and large-area burns that easily occur in ordinary films. Large currents and high temperatures are not generated inside the capacitor. Even if most of the T-shaped fuses (200) blow, it will only cause a rapid decrease in capacitance until the capacitor opens and fails; it will not overheat, generate a large amount of gas, and explode, thus achieving the purpose of explosion protection. Its structure is as follows: Figure 6 As shown.

[0084] Among them, multiple T-shaped fuses 200 are connected in parallel, and their structure is as follows: Figure 7 As shown.

[0085] Before winding, the metallized film of capacitor core 2 is aged to effectively eliminate the stress generated during the coating and slitting of the metallized film.

[0086] In this embodiment, the capacitor core 2 is a flat core to improve energy density and reduce capacitor volume. During the heat setting process, tooling fixtures are used in conjunction with a gradient heat setting process to ensure that the flat core is subjected to uniform stress. This avoids problems such as inconsistent shape due to thermal shrinkage of the metallized film and poor product voltage withstand consistency caused by uneven stress distribution of the metallized film during the heat setting process.

[0087] In this embodiment, a discharge tube test is added during the energizing stage of capacitor core 2. The capacitor core 2 is subjected to a large pulse current (dv / dt) impact to test the performance of the metallized thin film coating. If the gold spraying or welding is not good during the process, the contact resistance will increase. Under the impact of a large pulse current, such defects with poor internal connection can be selected.

[0088] To reduce self-inductance and improve the capacitor's overcurrent capability, this embodiment adopts the following optimized structural design:

[0089] The capacitor has a built-in multilayer busbar 5, and the lead electrode 3 is integrally formed with the multilayer busbar 5. The input and output terminals are respectively soldered to the corresponding tin-plated copper plates 4. ESL can be reduced by eliminating the magnetic field of the current.

[0090] Tin-plated copper plates 4 are soldered onto individual capacitor core groups. The capacitor contains multiple independent individual capacitor core groups, and each individual capacitor core group is individually connected to the stacked busbar 5.

[0091] In the vacuum casting process of the potting and sealing process, the capacitor is first vacuum dried, then the polyurethane is degassed, and then polyurethane components A and B are mixed using a mechanical metering and mixing potting machine. The mixture is then poured under vacuum, with positive pressure applied during the curing process. This achieves the key potting and sealing treatment of the product.

[0092] This embodiment performs reliability screening tests on the products before they leave the factory. The conditions used are: powering on for 12 to 24 hours at the highest operating temperature and rated operating voltage. Products that may fail prematurely are screened out, ensuring product reliability.

[0093] This embodiment provides key technologies for DC-supported thin-film capacitors used in flexible DC transmission. It focuses on improving and enhancing key processes for the design optimization of key capacitor materials and the structural optimization of capacitors. At the same time, more comprehensive testing technologies ensure product consistency and reliability, resulting in high-performance capacitors that can replace imported products.

[0094] The above describes the preferred embodiments of this utility model, illustrating and describing its basic principles, main features, and advantages. Those skilled in the art should understand that this utility model is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this utility model. Various changes and modifications can be made without departing from the spirit and scope of this utility model, and all such changes and modifications fall within the scope of protection of this utility model as defined by the appended claims and their equivalents.

Claims

1. A film capacitor for flexible HVDC power transmission, characterized by: The device includes a housing (1), a capacitor core (2), and lead-out electrodes (3). The housing (1) is made of metal. There are several capacitor cores (2). Several capacitor cores (2) are grouped to form multiple individual capacitor core groups. Each individual capacitor core group is connected to a tin-plated copper plate (4). The lead-out electrodes (3) are provided with a stacked busbar (5) and are connected to the tin-plated copper plate (4) through the stacked busbar (5). Multiple individual capacitor core groups are encapsulated in the housing (1) with potting compound.

2. The film capacitor for flexible HVDC power transmission according to claim 1, characterized by: The outer casing (1) is provided with an outer casing opening (6). Multiple capacitor cores are placed in the outer casing (1) through the outer casing opening (6). An opening end plate (7) is provided on the outer casing opening (6). The opening end plate (7) is fixed on the outer casing opening (6) by potting material to realize the encapsulation of multiple capacitor cores in a single group.

3. The film capacitor for flexible HVDC power transmission according to claim 2, characterized by: An electrode connection hole (8) is provided on the open end plate (7). The lead-out electrode (3) is set on the electrode connection hole (8) and placed outside the outer shell (1). The stacked busbar (5) is integrated with the lead-out electrode (3) or set separately and then fixed to each other by fasteners, threads or buckles. The stacked busbar (5) is placed inside the outer shell (1) through the electrode connection hole (8) and connected to the tin-plated copper plate (4).

4. The film capacitor for flexible HVDC power transmission according to claim 3, characterized by: The open end plate (7) is also provided with a pressure relief valve connection hole (9), and a pressure relief valve (10) is connected through the pressure relief valve connection hole (9).

5. The film capacitor for flexible HVDC power transmission according to claim 4, characterized by: Each capacitor core group consists of multiple capacitor cores (2) that are positioned back-to-back and left-to-right. The positive and negative terminals of the capacitor cores (2) that are positioned left-to-right are connected to a transverse connecting copper plate (11). Each capacitor core group is positioned longitudinally and is connected to the transverse connecting copper plate (11) of the capacitor core group that is longitudinally adjacent to it.

6. The film capacitor for flexible HVDC power transmission according to claim 5, characterized by: An insulating sleeve (12) is also fitted on the tin-plated copper plate (4).

7. The film capacitor for flexible HVDC power transmission according to claim 6, characterized by: The outer shell (1) is made of lightweight aluminum alloy material, and its outer surface is coated with a graphene thermal conductive coating.

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