WO2002007189A2

WO2002007189A2 - Dielectric fabrication method for high voltage capacitor

Info

Publication number: WO2002007189A2
Application number: PCT/KR2001/001088
Authority: WO
Inventors: Soo Hwi Lee; Il Su Seo
Original assignee: Samhwa Capacitor Co., Ltd.
Priority date: 2000-07-14
Filing date: 2001-06-26
Publication date: 2002-01-24
Also published as: WO2002007189A3

Abstract

A method for fabricating a dielectric of a high voltage capacitor including the steps of: superposing an electrode film on a first plastic film having a first face and a second face formed plane with a predetermined thickness and dielectric constant, and winding them to form a winding element; and assembling the winding element inside a case and infiltrating an insulation oil into the case in a vacuum state. Since the dielectric is fabricated by using only the plastic film, the loss value, the internal pressure characteristic and the degradation characteristic caused due to the capacitor paper can be improved, so that a high pressure capacitor satisfying desired characteristics can be fabricated. In addition, by not using the capacitor paper, the production cost can be reduced.

Description

DIELECTRIC FABRICATION METHOD FOR HIGH VOLTAGE CAPACITOR

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a dielectric fabrication method for a high voltage capacitor, and more particularly, to a dielectric fabrication method for a high voltage capacitor that is capable of forming a dielectric without a capacitor paper used for facilitating infiltration of an insulation oil, to thereby improve an internal pressure characteristic o.f a high voltage capacitor and a degradation possibly occurring in using the high voltage capacitor.

Description of the Background Art

There are two types of film capacitors: one is a deposition foil type capacitor and the other is an electrode foil type capacitor as classified depending on the fabrication method of an electrode material.

The deposition foil type capacitor can be fabricated to a compact size with light weight as it forms an electrode by depositing a metal such as aluminum or zinc on a dielectric film. Meanwhile, in case of the electrode thin capacitor, since it forms an electrode by overlapping an aluminum foil or a tin foil on the dielectric film, it has a low resistance value, is thermally stable and has an excellent characteristic electrically.

These days, the electrode foil type capacitor is increasingly demanded thanks to its electrically excellent performance and a high reliability.

A method for fabricating the electrode foil type capacitor having a high performance and high reliability in accordance with a conventional art will now be described. Figure 1 is a perspective view showing how the dielectric of the high voltage capacitor is wound in accordance with a conventional art, and Figure 2 is a sectional view of a dielectric of Figure 1.

In order to fabricate a high voltage capacitor, as shown in Figure 2, a plastic film 1, a capacitor paper 2 and the plastic filml are sequentially superposed alternately, and then, as shown in Figure 1, they are wound to form a winding element 5.

In this respect, polypropylene (PP) or polyester (PET) is used for the plastic film 1, and aluminum or tin is used for the electrode film 3.

After the winding element 5 is formed, the winding element 5 is assembled in a case (not shown) , and then the capacitor paper 2 is dried to remove moisture absorbed from the atmospheric air.

When the capacitor paper 2 is completely dried, a lead line is inserted in the case. After the case is inserted, a cover (not shown) of the case covers it, of which contact faces are completely sealed. And then, an insulation oil (not shown) is infiltrated into the case in a vacuum state, thereby fabricating a high voltage capacitor.

The insulation oil is used to help the dielectric 4 of the high voltage capacitor have a high insulation, and the capacitor paper 2 is used between the plastic films 1, forming the dielectric 4, to facilitate infiltration of the insulation oil.

However, even though the capacitor paper 2 is used for the dielectric to facilitate the infiltration of the insulation oil, the high voltage capacitor adopting the capacitor paper has the following problems . For example, first, since the capacitor paper

(loss value: 0.2 ~ 0.4%) has a greater loss than that of the plastic film (loss value: below 0.01%), the dielectric loss of the dielectric made of the capacitor paper and the plastic film be comes high, causing that heat is much generated when the high voltage capacitor is operated, contaminating the electrode film. Contamination of the electrode film causes a partial corona, degrading the characteristics of a product of the high voltage capacitor. Secondly, if the insulation oil is not sufficiently infiltrated into the capacitor paper, the insulation oil would be gradually absorbed into the capacitor paper according to a temperature around it, causing a phenomenon that the dielectric is short of the insulation oil therein. Accordingly, a void is formed inside the high voltage capacitor, causing a critical result to a withstand voltage characteristic, and thus, a reliability of the product is degraded.

Thirdly, in the case of forming the dielectric by using the capacitor paper, since the capacitor paper absorbs moisture contained in the air during the process or fabricating the dielectric of the high voltage capacitor, it is difficult to completely dry the capacitor paper. Also, in this case, a process for drying the capacitor paper is inevitably added, and a production cost of the high voltage capacitor is increased because of using a natural pulp for the capacitor paper.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a method for fabricating a dielectric of a high voltage capacitor by using only a plastic film without a capacitor paper which has been used to facilitate infiltration of an insulation oil. Another object of the present invention is to provide a method for fabricating a dielectric of a high voltage capacitor that is capable of improving an internal pressure characteristic of a high voltage capacitor by not using a capacitor paper which has been typically used in fabricating a dielectric and improving a degradation occurring in using of a high voltage capacitor.

Yet another object of the present invention is to provide a method for fabricating a dielectric of a high voltage capacitor that is capable of simplifying a fabrication process of a high voltage capacitor and reducing a production cost of the high voltage capacitor by not using a capacitor paper using natural pulp and thus omitting a process required for drying the capacitor paper.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a method for fabricating a dielectric of a high voltage capacitor including the steps of: superposing an electrode film on a first plastic film having a first face and a second face formed plane with a predetermined thickness and dielectric constant, and winding them to form a winding element; and assembling the winding element inside a case and infiltrating an insulation oil into the case in a vacuum state. In the above method, at least one of the first face and the second face of the first plastic film is formed uneven, the first plastic film is made of one selected from the group consisting of polypropylene, polyester, polycarbonate and polyethylene and has the thickness of 4 -800 μm.

In the above method, a dielectric constant of the first plastic film is 2 ~4, a space factor of the first plastic film is below 25%, and the electrode film is made by selecting one of aluminum (Al) or tin (Sn) . The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings .

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

In the drawings :

Figure 1 is a perspective view showing how a dielectric of a high voltage capacitor is wound in accordance with a conventional art;

Figure 2 is a sectional view of the dielectric of Figure 1 in accordance with the conventional art; Figures 3A through 3C are drawings illustrating a method for fabricating a dielectric of a high voltage capacitor in accordance with a first embodiment of the present invention; Figures 4A and 4B show another example of a plastic film of Figure 3B in accordance with the first embodiment of the present invention;

Figure 5 is a table showing material characteristics of the plastic film as adopted in accordance with the preferred embodiment of the present invention;

Figures 6A through 6G are drawings illustrating a method for fabricating a dielectric of a high voltage capacitor in accordance with a second embodiment of the present invention;

Figure 7 is a graph showing a test result of a loss variation by temperatures of a capacitor adopting a dielectric and a capacitor adopting a capacitor paper; and Figures 8A and 8B are drawings illustrating a method for fabricating a dielectric of a high voltage capacitor in accordance with a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Figures 3A through 3C are drawings illustrating a method for fabricating a dielectric of a high voltage capacitor in accordance with a first embodiment of the present invention.

As shown in Figures 3A through 3C, a method for fabricating a dielectric of a high voltage capacitor includes the steps of: superposing an electrode film 3 on a first plastic film 11 of which a first face (a) and a second face (b) are formed plane and have a predetermined thickness and dielectric constant, and winding it to form a winding element 10; and assembling the winding element 10 inside a case 21 and infiltrating an insulation oil into the case in a vacuum state.

The construction and operation of the present invention will now be described in detail.

The dielectric of a high voltage capacitor includes the first plastic film 11 and the insulation oil (not shown) . As the insulation oil, a petroleum refining oil, a mineral oil, a vegetable oil may be used solely or by mixing together.

In order to fabricate a dielectric of the present invention constructed with the first plastic film 11 and the insulation oil, first, as shown in Figures 3A and 3B, the electrode film 3 is overlapped on the first plastic film 11 having a predetermined thickness and dielectric constant and having the first plane face (a) and the second plane face (b) , which are then wound to form a winding element 10. The electrode film 3 is made of aluminum or tin. Thereafter, as shown in Figure 3C, the winding element 10 as formed is assembled inside of the case 21, and then, a lead line 24 is assembled at the electrode film 3 of the winding element 10.

As the lead line 24 is completely assembled, the case 21 is covered to be sealed by the cover 22, the insulation oil is infiltrated into the case 21 in a vacuum state through the insulation oil inlet 23, thereby forming a dielectric of high voltage capacitor.

In the dielectric fabrication of the present invention only using the first plastic film 11 having the flat surface as shown in Figure 3B, the surface area of the first plastic film 11 can be enlarged. Figures 4A and 4B show another example of a plastic film of Figure 3B in accordance with the first embodiment of the present invention.

As shown in Figures 4A and 4B, at least one face of the first face (a) and the second face (b) of the first plastic film 11 is formed uneven, thereby having a rough surface. That is, Figure 4A shows a state that the second face (b) of the first plastic film 11 is formed uneven, and Figure 4B shows a state that both the first face (a) and the second (b) of the first plastic film 11 are formed uneven. The uneven face (p) may be formed by performing a semiconductor etching process or injection- molding. In case that the first plastic film 11 is formed uneven, a space factor of the first plastic film 11 is set below 25% to make the film to have uneven face. In this respect, as shown in Figure 4B, the space factor is computed by using the thickness (Tl) according to measurement of a micrometer of the first plastic film 11 and the thickness (T2) according to the weight of the first plastic film 11. That is, the space factor is computed by a formula of ( (T2-T1) /T2 ) xlOO .

Referring to a computing reference of the space factor, the space factor of the first plastic film 11 is set below 25% on the assumption that the high voltage capacitor is adopted to a microwave oven.

If the space factor of the first plastic film 11 of the high voltage capacitor for use in the microwave oven is set above 25%, it is hard to maintain the state of the winding element 10 and assemble the winding element 10 in the case 21. Accordingly, the space factor is set below 25% to form the uneven face.

Thus, setting the space factor of the first plastic film 11 by below 25% is limited to the case of adopting the high voltage capacitor using the dielectric of the present invention to the microwave oven, and when applied to other instruments, the space factor may be above 25%.

With reference to Figure 5, the first plastic film 11 having the space factor of below 25% is made of one selected from the group consisting of polypropylene, polyester, polycarbonate, polyethylene and mixtures thereof.

The first plastic film 11 has a dielectric constant of 2 ~ 4 according to its material. The first plastic film 11 made of a material having a predetermined dielectric constant has the thickness of 4 ~ 800 μm . For example, if polypropylene is used as a material of the first plastic film 11, its dielectric constant is 2.2 and its thickness is 4 ~ 50 μm . Besides the method for fabricating a dielectric by using only the first plastic film 11 as in the first embodiment, a dielectric can be fabricated by using a plurality of first plastic film 11 and second plastic film 12. Figures 6A through 6G are drawings illustrating a method for fabricating a dielectric of a high voltage capacitor in accordance with a second embodiment of the present invention.

As shown in Figures 6A through 6G, a second plastic film 12 having a predetermined thickness and dielectric constant with a first face (a) and a second face (b) formed plane is superposed on a first plastic film 11 having a predetermined thickness and dielectric constant with a first face (a) and a second face (b) formed plane. And then, an electrode film 3 is superposed on the second plastic film 12, to thereby form a winding element 10 (as shown in Figure 3A) .

After the winding element 10 is assembled inside the case 21 (as shown in Figure 3C) , the insulation oil is infiltrated into the case 21 in a vacuum state, to thereby fabricate a dielectric. In the second embodiment in which the plurality of first plastic film 11 and second plastic film 12 are used to fabricate a dielectric, the surface area of the first and the second plastic film 11 and 12 can be enlarged as follows. That is, as shown in Figures 6B through 6G, at least one of the first face (a) and the second face (b) of at least one of the first plastic film 11 and the second plastic film 12 is formed uneven.

For example, Figure 6B shows an example of formation of an uneven face (p) at the second face (b) of the first plastic film 11. Figure 6C shows an example of formation of an uneven face (p) at both first face (a) and second face (b) of the first plastic film 11. Figure 6D shows an example of formation of an uneven face (p) at the second face (b) of the first plastic film 11 and the first face (a) of the second plastic film 12. Figure 6E shows an example of formation of an uneven face (p) both at the first face (a) of the first plastic film 11 and the second face (b) of the second plastic film 12. Figure 6F shows an example of formation of an uneven face (p) at the second face (b) of the first plastic film 11 and the second face (b) of the second plastic film 12. Figure 6G shows an example of formation of an uneven face (p) formed both at the first face (a) and the second face (b) of the first plastic film 11 and at the first face (a) and the second face (b) of the second plastic film 12.

In case that a high voltage capacitor together with the first plastic film 11 as shown in Figure 4B is adopted to a microwave oven, the uneven face (p) for enlarging the surface area of the first and the second plastic film 11 and 12 is formed with a space factor set by below 25%.

The material, the dielectric constant and the thickness of the first plastic film 11 and the second plastic film 12 of the second embodiment are selected, set and formed the same as those of the first plastic film 11 as shown in Figure 3A.

In this manner, in the case that a dielectric is fabricated by overlapping the plurality of first plastic film 11 and second plastic film 12 to form the winding element 10 (as shown in Figure 3A) and selectively forming the first plastic film 11 and the second plastic film 12 to be uneven, its loss value is below 0.01% in every case, which is quite low (measuring equipment: automatic schering bridge, model name: DAC-ASC-3S, manufacturer : SOKEN, Japan) . A loss variation by temperatures of the dielectric having the very low loss value by using only the first plastic film 11 and the second plastic film 12 will now be described with reference to Figure 7.

Figure 7 is a graph showing a test result of a loss variation by temperatures of a capacitor adopting a dielectric and a capacitor adopting a capacitor paper.

As shown in Figure 7, in case of the high voltage capacitor having the conventional dielectric using a capacitor paper (mesh) , when the temperature goes up, its loss value was much increased by 0.2% at the temperature 85°C. However, in the case of the high voltage capacitor only using the plastic film (PF) as in the present invention, the loss value was maintained at the very low degree, so that the high voltage capacitor is stably operated.

A method for fabricating a dielectric which is capable of rendering a high voltage capacitor to maintain a stable operation regardless of change in the temperature by using the first plastic film 11 and the second plastic film 12 will now be described with reference to Figures 8A and 8B. Figures 8A and 8B are drawings illustrating a method for fabricating a dielectric of a high voltage capacitor in accordance with a third embodiment of the present invention.

As shown in Figures 8A and 8B, a plurality of first plastic film 11 and the nth plastic film (n) each having a first face (a) and a second face (b) formed plane with a predetermined thickness and dielectric constant are sequentially superposed. And then, after an electrode film 3 is superposed on the nth plastic film (n) , which are then wound to form a winding element 10 (as shown in Figure 3A) . Thereafter, the winding element 10 is assembled in a case 21 (as shown in Figure 3C) , and an insulation oil is infiltrated into the case 21 in a vacuum state, to thereby obtain a dielectric.

In the case of fabricating a dielectric by using the plurality of first plastic film 11 through the nth plastic film (n) , the plurality of first plastic film 11 through the nth plastic film (n) are made of the same material, have the same dielectric constant and thickness as those of the first plastic film 11 as shown in Figure 3B.

That is, the first plastic film 11 through the nth plastic film (n) are made of one selected from the group consisting of polypropylene, polyester, polycarbonate, polyethylene and mixtures thereof.

In order to enlarge the surface area of the first plastic film 11 through the nth plastic film (n) , each being made of the same material and having the same dielectric constant and thickness as those of the first plastic film 11 as shown in Figure 3B, at least one of the first plastic film 11 through the nth plastic film (n) is formed uneven, and at the same time, at least one of the first face (a) and the second face (b) of the plastic film formed uneven is formed uneven.

For example, as shown in Figure 8B, the uneven face (p) shown in a dotted line may be formed at the first face (a) or the second face (b) of the first plastic film 11 or may be formed at both faces (a and b) . In addition, all the first plastic film 11, the second plastic film 12, the third plastic film 13, ..., the nth plastic film (n) may be formed uneven.

Accordingly, the dielectric of the present invention is fabricated only by using the plastic film, it has a very low loss value by below 0.05%. In addition, by removing the capacitor paper which has been used for fabricating the conventional dielectric, a degradation of an internal pressure characteristic due to contamination of the capacitor paper is improved, the deterioration occurring in using of the high voltage capacitor is improved, a process for drying the capacitor paper is not necessary, and a production cost because of using of the capacitor paper is reduced. As so far described, the dielectric of the present invention has many advantages .

For example, since the dielectric is fabricated by using only the plastic film, the loss value, the internal pressure characteristic and the degradation characteristic caused due to the capacitor paper can be improved, so that a high pressure capacitor satisfying desired characteristics can be fabricated. In addition, by not using the capacitor paper, the production cost can be reduced. As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of • the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalence of such meets and bounds are therefore intended to be embraced by the appended claims.

Claims

What is claimed is:

1. A method for fabricating a dielectric of a high voltage capacitor comprising the steps of: superposing an electrode film on a first plastic film having a first face and a second face formed plane with a predetermined thickness and dielectric constant, and winding them to form a winding element; and assembling the winding element inside a case and infiltrating an insulation oil into the case in a vacuum state .

2. The method of claim 1, wherein at least one of the first face and the second face of the first plastic film is formed uneven.

3. The method of claim 1, wherein the first plastic film is made of one selected from the group consisting of polypropylene, polyester, polycarbonate, polyethylene, and mixtures thereof.

4. The method of claim 1, wherein the first plastic film has the thickness of 4 ~ 800 m.

5. The method of claim 1, wherein the first plastic film has a dielectric constant of 2 ~ 4.

6. The method of claim 1, wherein a space factor of the first plastic film is below 25%.

7. The method of claim 1, wherein/ the electrode film is made of aluminum (Al) or tin (Sn) .

8. A method for fabricating a dielectric of a high voltage capacitor comprising the steps of: superposing a second plastic film having a first face and a second face formed plane with a predetermined thickness and dielectric constant on a first plastic film having a first face and a second face formed plane with a predetermined thickness and dielectric constant, superposing an electrode film on the second plastic film, and winding them to form a winding element; and assembling the winding element inside a case and infiltrating an insulation oil into the case in a vacuum state.

9. The method of claim 8, wherein at least one of the first and the second faces of at least one of the first and the second plastic films is formed uneven.

10. The method of claim 8, wherein the first plastic film and the second plastic film are made of one selected from the group consisting of polypropylene, polyester, polycarbonate, polyethylene, and mixtures thereof .

11. The method of claim 8, wherein the first and the second plastic films have the thickness of 4 ~ 800 m, respectively.

12. The method of claim 8, wherein the first and the second plastic films have a dielectric constant of 2 ~ 4, respectively.

13. The method of claim 8, wherein a space factor of the first and the second plastic film is below 25%, respectively.

14. A method for fabricating a dielectric of a high voltage capacitor comprising the steps of: sequentially superposing a plurality of first plastic film through the nth plastic film each having a first face and a second face formed plane with a predetermined thickness and dielectric constant, superposing an electrode film on the nth plastic film, and winding them to form a winding element; and assembling the winding element inside a case and infiltrating an insulation oil into the case in a vacuum state.

15. The method of claim 14, wherein at least one of the first and the second faces of at least one of the first through the nth plastic films is formed uneven.

16. The method of claim 14, wherein the first through the nth plastic films are made of one selected from the group consisting of polypropylene, polyester, polycarbonate and polyethylene.

17. The method of claim 14, wherein the first through the nth plastic films have the thickness of 4 ~ 800 μm_r respectively.

18. The method of claim 14, wherein the first through the nth plastic films have a dielectric constant of 2 ~ 4, respectively.

19. The method of claim 14, wherein a space factor of the first through the nth plastic film is below 25%, respectively.