Method for improving breakdown performance of oil immersed capacitor film

Abstract

The invention discloses a method for improving the breakdown performance of a thin film of an oil-immersed capacitor. The method comprises the following steps: obtaining a winding thin film for the oil-immersed capacitor; applying pressure to the radial direction of the winding film to obtain a capacitor core; the capacitor core and the core immersion medium are dried; the dried capacitor core is placed in the dried core immersion medium to be immersed, and an oil immersed capacitor core is obtained; and after the oil immersed capacitor core is taken out and treated, the immersed film is obtained. According to the method, pressure is applied to the rolled film in the radial direction, the pressing degree of the rolled film during dipping is changed, the crystallization characteristic of the polypropylene film in the rolled film can be regulated and controlled, score chain arrangement of the polypropylene film is more ordered, the direct-current breakdown field strength of the polypropylene film is improved, and the method is easy and convenient to operate, easy to implement and suitable for industrial production. The method has a good application effect in the field of oil immersed capacitors.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer dielectric films, and in particular to a method for improving the breakdown performance of an oil-immersed capacitor film. Background Art

[0002] Oil-immersed capacitors, as a key energy storage and reactive power compensation device, are widely used in all aspects of power transmission and distribution, fully ensuring the long-term stable operation of power systems. Biaxially oriented polypropylene film, due to its high breakdown performance and low dielectric loss, has gradually become the core material for oil-immersed capacitors. However, during the impregnation process of oil-immersed capacitors, the degree of compression of the wound film changes the crystallization characteristics of the polypropylene film, thereby affecting its breakdown performance. At the same time, the harmonic effects in the power system can also cause the operating temperature of the oil-immersed capacitor to increase significantly, which places higher demands on the performance of the polypropylene film. Currently, the degree of compression can only be determined through experience, and there is no uniformity, and the breakdown performance cannot be guaranteed every time. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0004] In view of this, the present invention provides a method for improving the breakdown performance of oil-immersed capacitor film, wherein the improvement method regulates the crystallization characteristics of the polypropylene film by changing the compression degree of the wound film during immersion, making its molecular chains more orderly, thereby improving its DC breakdown field strength. The method is simple to operate and easy to implement.

[0005] Specifically, the following technical solutions are included:

[0006] The present invention provides a method for improving the breakdown performance of an oil-immersed capacitor film, the method comprising the following steps:

[0007] Obtaining wound film for oil-impregnated capacitors;

[0008] applying pressure in a radial direction of the wound film to obtain a capacitor core;

[0009] Drying the capacitor core and the core immersed medium;

[0010] placing the dried capacitor core into the dried core immersion medium to immerse it, thereby obtaining an oil-immersed capacitor core;

[0011] The oil-immersed capacitor core is taken out and processed to obtain the immersed film.

[0012] Optionally, obtaining a wound film for an oil-immersed capacitor includes:

[0013] Preparation of polypropylene film for oil-immersed capacitors based on biaxial stretching process;

[0014] The polypropylene film and the aluminum foil are alternately wound to prepare the wound film for the oil-immersed capacitor.

[0015] Optionally, the thickness of the polypropylene film is 11.2 μm, and the thickness of the aluminum foil is 5 μm.

[0016] Optionally, the alternating winding is performed by alternating 3 layers of the polypropylene film and 1 layer of aluminum foil, and the number of winding turns is 80 to 90 turns.

[0017] Optionally, obtaining a capacitor core includes:

[0018] Using hard cardboard to apply radial pressure on the wound film;

[0019] The capacitor core is obtained by adjusting the spacing of the cardboards by screws.

[0020] Optionally, the spacing between the battery core cardboards is 15 mm to 20 mm.

[0021] Optionally, the core immersion medium is benzyltoluene oil, and the capacitor core and the benzyltoluene oil are placed in two ovens for drying respectively, the drying temperature is 60° C. to 80° C., and the drying time is 18 h to 24 h.

[0022] Optionally, the step of placing the dried capacitor core into a dried core immersion medium for immersion is performed under high temperature and vacuum conditions;

[0023] The high temperature is 100° C. to 105° C., and the immersion time is 105 h to 110 h.

[0024] Optionally, removing the oil-immersed capacitor core for processing includes:

[0025] The oil-immersed capacitor core is disassembled, washed and dried to obtain an impregnated polypropylene film.

[0026] Optionally, anhydrous ethanol is used in the washing process, the drying temperature is 60° C. to 80° C., and the drying time is 8 hours to 12 hours.

[0027] The embodiment of the present invention provides a method for improving the breakdown performance of the oil-immersed capacitor film. The improvement method of the present application regulates the breakdown performance of the wound film and applies it to the oil-immersed capacitor, which can further improve the capacitance of the capacitor and ensure the operational stability of the oil-immersed capacitor. At the same time, the present application applies radial pressure to the wound film to change the degree of compression of the wound film during immersion. In other words, whether the degree of compression is appropriate can be judged based on the test results of the capacitor core after immersion. The increase in crystallinity and DC breakdown field strength indicates that the degree of compression is good. The improvement method of the present application can regulate the crystallization characteristics of the polypropylene film in the wound film, so that its value chain arrangement is more orderly, thereby improving its DC breakdown field strength. The method is simple to operate and easy to implement, and has a good application effect in the field of oil-immersed capacitors.

[0028] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 A flowchart of a method for improving the breakdown performance of an oil-immersed capacitor film according to an embodiment of the present invention;

[0031] Figure 2 The differential scanning calorimetry test results of the polypropylene films before and after immersion in Examples 1 to 3 and the comparative example are shown;

[0032] Figure 3 The calculated results of the crystallinity of the polypropylene films before and after immersion in Examples 1 to 3 and the comparative example are as follows;

[0033] Figure 4 The DC breakdown field strength test results of the polypropylene films before and after immersion in Examples 1 to 3 and the comparative example are shown. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] Before further describing the embodiments of the present invention in detail, the directional terms involved in the embodiments of the present invention, such as "upper part", "lower part" and "side part", do not have the meaning of limiting the scope of protection of the present invention.

[0036] To make the technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0037] Figure 1 The figure is a flowchart of a method for improving the breakdown performance of an oil-immersed capacitor film according to an embodiment of the present invention.

[0038] like Figure 1 As shown, one embodiment of the present invention provides a method for improving the breakdown performance of an oil-immersed capacitor film, the improvement method comprising the following steps:

[0039] Step 1, obtaining a wound film for an oil-immersed capacitor;

[0040] Step 2, applying radial pressure to the wound film to obtain a capacitor core;

[0041] Step 3, drying the capacitor core and the core immersed in the medium;

[0042] Step 4, placing the dried capacitor core into the dried core immersion medium to immerse it, thereby obtaining an oil-immersed capacitor core;

[0043] Step 5: Take out the oil-immersed capacitor core and process it to obtain the impregnated film.

[0044] The improvement method of the present application regulates the breakdown performance of the wound film and applies it to the oil-immersed capacitor, which can further improve the capacitance of the capacitor and ensure the operational stability of the oil-immersed capacitor. At the same time, the present application applies radial pressure to the wound film to change the degree of compression of the wound film during immersion. In other words, whether the degree of compression is appropriate can be judged based on the test results of the capacitor core after immersion. The increase in crystallinity and DC breakdown field strength represents a good degree of compression. The improvement method of the present application can regulate the crystallization characteristics of the polypropylene film in the wound film, making its value chain arrangement more orderly, thereby improving its DC breakdown field strength. The method is simple to operate and easy to implement, and has a good application effect in the field of oil-immersed capacitors.

[0045] By varying the number of turns of the film, the film's overall radial thickness changes. Since the distance between the components applying radial pressure remains constant, a greater number of turns, and therefore an increase in radial thickness, indicates increased compression. The impregnated polypropylene film obtained by disassembling the capacitor core is then tested to determine if the compression is adequate.

[0046] Specifically, obtaining a wound film for an oil-immersed capacitor includes:

[0047] Preparation of polypropylene film for oil-immersed capacitors based on biaxial stretching process;

[0048] Polypropylene film and aluminum foil are alternately wound to prepare wound films for oil-immersed capacitors.

[0049] It should be noted that the aluminum foil is connected to the terminal of the capacitor by welding. As the electrode material of the capacitor, the aluminum foil is on the outside of the polypropylene film.

[0050] The thickness of the polypropylene film is 11.2 μm, and the thickness of the aluminum foil is 5 μm. It should be noted that the thickness of the polypropylene film and the aluminum foil is the thickness of the product when it leaves the factory, which is also the thickness commonly used in capacitor cores at present, and will not be repeated here.

[0051] Furthermore, the film is alternately wound with three layers of polypropylene film and one layer of aluminum foil, and the number of winding turns is 80 to 90 turns.

[0052] It should be noted that three layers of polypropylene film are placed adjacent to each other, with the outermost layer of polypropylene film adjacent to a layer of aluminum foil, resulting in a four-layer winding, with the aluminum foil positioned on the outermost side of each winding. This alternating winding of polypropylene film and aluminum foil ensures high capacitance while reducing the size of the capacitor core, meeting the requirements for device miniaturization and expanding the device's applicability.

[0053] In a feasible implementation manner, obtaining the capacitor core includes:

[0054] Use hard cardboard to apply radial pressure on the wound film;

[0055] Adjust the spacing of the cardboard using screws to obtain the capacitor core.

[0056] It should be noted that the wound film of polypropylene film and aluminum foil is clamped by two pieces of upper and lower cardboards, and the distance between the two pieces of cardboards is fixed with long screws and matching nuts to adapt to polypropylene films with different requirements for compression levels.

[0057] The spacing between the two sheets of cardboard is typically 15mm to 20mm. The distance between the two sheets of cardboard is typically fixed, and the degree of compression of the polypropylene film within the winding is controlled by adjusting the number of wraps of the film.

[0058] In a feasible embodiment, the core is immersed in a medium of benzyl toluene oil, and the capacitor core and the benzyl toluene oil are placed in two ovens for drying, respectively, at a drying temperature of 60° C. to 80° C. and a drying time of 18 h to 24 h.

[0059] The drying time ensures that the water evaporates fully, thus improving the drying effect. The core immersion medium may also be PXE oil. It should be noted that the advantage of benzyl toluene oil as the core immersion medium is that it has good thermal stability and excellent antioxidant properties, and the benzyl toluene oil has a low pour point, that is, it has better fluidity and performance in low temperature environments, thereby improving the scope of application of the core immersion medium.

[0060] In a feasible embodiment, the dried capacitor core is placed in a dried core immersion medium and immersed under high temperature and vacuum conditions;

[0061] The high temperature is 100° C. to 105° C., and the immersion time is 105 h to 110 h.

[0062] Among them, under the conditions of high temperature of 100°C to 105°C and immersion time of 105h to 110h, benzyltoluene oil can be fully incorporated into the capacitor core to form an oil-immersed capacitor core, thereby improving the performance of the polypropylene film and effectively improving the DC breakdown field strength of the polypropylene film.

[0063] In a feasible embodiment, removing the oil-immersed capacitor core for processing includes:

[0064] The oil-impregnated capacitor core is disassembled, washed and dried to obtain the impregnated polypropylene film.

[0065] Among them, anhydrous ethanol is used in the washing process, the drying temperature is 60°C to 80°C, and the drying time is 8h to 12h.

[0066] It should be noted that the advantage of using anhydrous ethanol for washing is that it removes excess cores from the surface of the polypropylene film and allows it to be immersed in the medium (impregnant) without damaging the molecular structure within the impregnated polypropylene film. Cyclohexane is also a commonly used degreasing solvent, but it is generally used in the field of transformer oil-paper insulation.

[0067] The drying temperature and drying time are set to remove the unvolatile anhydrous ethanol on the surface of the polypropylene film. Setting this time can better allow the anhydrous ethanol to evaporate completely, thereby improving the accuracy of the performance test of the polypropylene film.

[0068] In this example, polypropylene was prepared from Borealis, HC-312BF, with a melt flow rate of 3.2 g / 10 min at 230°C and 2.16 kg, as measured according to ISO 1133. Benzyl toluene oil was prepared from Yantai Jinzheng Fine Chemicals Co., Ltd., with a density of 0.980 to 1.020 g / cm⁻³, a water content of ≤50 mg / kg, and a chlorine content of ≤30 mg / kg, as measured according to GB 21221-2007.

[0069] Example 1

[0070] Based on the biaxial stretching process, 11.2 μm polypropylene film for oil-immersed motors was prepared and alternately wound with 5 μm aluminum foil. The film was alternately wound in the order of 3 layers of polypropylene film and 1 layer of aluminum foil. The cycle was 6 layers of polypropylene film and 2 layers of aluminum foil. The number of windings was 86 to prepare the wound film for oil-immersed capacitors.

[0071] A hard cardboard was used to apply radial pressure to the wound film, and the spacing between the cardboards was adjusted to 17 mm using screws to obtain a capacitor core.

[0072] The capacitor core and benzyltoluene oil were placed in two ovens for drying at 80°C for 24 hours.

[0073] The capacitor core was immersed in benzyltoluene oil at 105°C under vacuum conditions for 108 hours to obtain an oil-immersed capacitor core.

[0074] The impregnated oil-immersed capacitor core was taken out and disassembled, washed with anhydrous ethanol, and then dried at 80° C. for 12 h to obtain an impregnated polypropylene film.

[0075] Example 2

[0076] Compared with Example 1, the difference is that the number of winding turns is changed from 86 turns to 83.5 turns, and the other steps remain unchanged.

[0077] Example 3

[0078] Compared with Example 1, the difference is that the number of winding turns is changed from 86 turns to 88 turns, and the other steps remain unchanged.

[0079] Comparative Example

[0080] In this comparative example, commercially available Borealis HC-312BF polypropylene was used to prepare an 11.2 μm polypropylene film for oil-impregnated capacitors based on a biaxial stretching process. After drying at 80° C. for 12 h, an unimpregnated polypropylene film was obtained.

[0081] Performance testing:

[0082] (1) The polypropylene films prepared in the above examples and comparative examples were placed in a differential calorimeter for testing. The test was conducted in a nitrogen atmosphere. First, the temperature was raised from 25°C to 200°C at a rate of 10°C / min and held for 5 minutes. Then, the temperature was lowered from 200°C to 25°C at a rate of -10°C / min and held for 5 minutes to eliminate the thermal history. On this basis, the temperature was raised from 25°C to 200°C again at a rate of 10°C / min. The test curve was obtained as shown in FIG. Figure 2 shown.

[0083] The crystallinity of the above examples and comparative examples was calculated according to formula (1), as follows: Figure 3 shown.

[0084]

[0085] Where, X c is the crystallinity, %; ΔH is the melting enthalpy, which is obtained by integrating the results obtained from the DSC test (differential scanning calorimetry test) of the polypropylene film or directly measuring it, J / g, ΔH t is the melting enthalpy when the PP crystallinity is 100%, 209 J / g, obtained based on historical data.

[0086] (2) The polypropylene films prepared in the above examples and comparative examples were placed in a DC breakdown test apparatus for testing. A copper electrode with a diameter of 3 mm was used for the test. The voltage rise rate during the test was 1 kV / mm. Each sample was tested 10 times at room temperature and analyzed using a two-parameter Weibull distribution. Figure 4 shown.

[0087] from Figure 2 It can be seen that the melting peaks of the polypropylene film before and after impregnation are both located around 145°C and 160°C, representing the melting processes of the β and α crystals in the polypropylene, respectively. Compared to the comparative document, the melting temperature of the α crystals in Example 1 is higher, indicating that the molecular chain segments are less mobile at high temperatures, resulting in better high-temperature resistance of the polypropylene film.

[0088] from Figure 3 It can be seen that the crystallinity of Examples 1 to 3 is improved compared to the comparative example, with Example 1 having the highest crystallinity of 47.23%. This indicates that the impregnation process can fully improve the crystallization characteristics of the polypropylene film. However, due to the different degrees of compression of the polypropylene film, the benzyl toluene oil in Examples 2 and 3 was unable to fully penetrate the film, resulting in poor impregnation effect, resulting in a decrease in crystallinity and a decrease in DC breakdown field strength.

[0089] from Figure 4It can be seen that compared to the comparative example, the DC breakdown field strength of Examples 1 to 3 is significantly improved, wherein the DC breakdown field strength of Example 1 is the highest, at 536.89 kV / mm, which is 9.9% higher than the 483.81 kV / mm of the comparative example. At the same time, the DC breakdown field strength results of the embodiments and the comparative example are completely consistent with the change in crystallinity, and the higher the crystallinity, the larger the DC breakdown field strength. Wherein, β is the shape parameter of the Weibull distribution, which is calculated by the probability diagram brought by the origin software. The higher the shape parameter, the more concentrated the distribution of the breakdown data is, and the higher the credibility of the experimental results.

[0090] Therefore, the oil-immersed capacitor film of the present invention can fully improve the film breakdown performance by regulating the crystallization characteristics. Applying it to oil-immersed capacitors can further increase the capacitance of the capacitor while ensuring the operational stability of the capacitor.

[0091] In the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. The term "plurality" refers to two or more than two, unless otherwise clearly defined.

[0092] Other embodiments of the present invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as illustrative only.

[0093] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for improving the breakdown performance of oil-immersed capacitor film, characterized in that: The lifting method comprises the following steps: Obtaining wound film for oil-impregnated capacitors; applying pressure in a radial direction of the wound film to obtain a capacitor core; Drying the capacitor core and the core immersed medium; placing the dried capacitor core into the dried core immersion medium to immerse it, thereby obtaining an oil-immersed capacitor core; The oil-immersed capacitor core is taken out and processed to obtain the immersed film.

2. The method for improving the breakdown performance of oil-immersed capacitor film according to claim 1, characterized in that: Get wound film for oil-impregnated capacitors including: Preparation of polypropylene film for oil-immersed capacitors based on biaxial stretching process; The polypropylene film and the aluminum foil are alternately wound to prepare the wound film for the oil-immersed capacitor.

3. The method for improving the breakdown performance of oil-immersed capacitor film according to claim 2, characterized in that: The thickness of the polypropylene film is 11.2 μm, and the thickness of the aluminum foil is 5 μm.

4. The method for improving the breakdown performance of oil-immersed capacitor film according to claim 2, characterized in that: The alternating winding is performed by alternating three layers of the polypropylene film and one layer of aluminum foil, and the number of winding turns is 80 to 90 turns.

5. The method for improving the breakdown performance of oil-immersed capacitor film according to claim 2, characterized in that: The obtaining of the capacitor core comprises: Using hard cardboard to apply radial pressure on the wound film; The capacitor core is obtained by adjusting the spacing of the cardboards by screws.

6. The method for improving the breakdown performance of oil-immersed capacitor film according to claim 5, characterized in that: The spacing between the battery core cardboards is 15 mm to 20 mm.

7. The method for improving the breakdown performance of oil-immersed capacitor film according to claim 1, characterized in that: The core is immersed in a medium of benzyl toluene oil. The capacitor core and the benzyl toluene oil are placed in two ovens for drying respectively. The drying temperature is 60° C. to 80° C., and the drying time is 18 hours to 24 hours.

8. The method for improving the breakdown performance of oil-immersed capacitor film according to claim 1, characterized in that: The dried capacitor core is placed in a dried core immersion medium and immersed in the medium under high temperature and vacuum conditions; The high temperature is 100° C. to 105° C., and the immersion time is 105 h to 110 h.

9. The method for improving the breakdown performance of oil-immersed capacitor film according to claim 2, characterized in that: Taking out the oil-immersed capacitor core for processing includes: The oil-immersed capacitor core is disassembled, washed and dried to obtain an impregnated polypropylene film.

10. The method for improving the breakdown performance of oil-immersed capacitor film according to claim 9, characterized in that: The washing process uses anhydrous ethanol, the drying temperature is 60° C. to 80° C., and the drying time is 8 hours to 12 hours.

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