JPH04267509A - Capacito0r bushing and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture a resin impregnated bushing leaving no void at a capacitor core. CONSTITUTION:An impregnated body 1a to be a bushing core is formed by interposing conductive material sheets 4 between the insulating material sheets 3 wound up in multiple rounds around the axial line of a central conductor. Next, the title capacitor bushing leaving no void at all can be manufactured by a method wherein the impregnated body la inserted into a metallic mold 11 is filled up with liquid resin jetted from an injection pipe 15 so that the liquid resin level may be lifted at the lifting rate 0.5-2.5 times of the initial lifting rate of the capillary liquid level lifted by the capillarity in the insulating material sheets 3 for the manufacture of the title capacitor bushing leaving no void at all.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to capacitor bushings used in electric power equipment such as transformers and reactors, and more particularly to capacitor bushings impregnated with resin and a method for manufacturing the same.

0002

BACKGROUND OF THE INVENTION As shown in FIG. 7, a capacitor core 1 of a capacitor bushing impregnated with resin includes a central conductor 2 and an insulating material sheet 3 which is the main part of internal insulation, and a large number of sheets of conductive material each having a thickness of about 10 μm. 4 are arranged in a concentric cylindrical shape and impregnated with thermosetting resin 5. In particular, if voids (holes) are formed in the resin 5,
The structure is designed to be free of voids, which can cause corona to occur. In other words, in order to prevent the generation of voids in the insulating material sheet 3 and to quickly impregnate the resin when impregnating the resin, the conventional insulating material sheet 3 has an actual thickness of about 150μ as shown in FIG. Crepe paper was used, which was folded into a finely uneven shape and shrunken to have an apparent thickness of 500 μm. Then, in the step of impregnating the resin, the object to be impregnated is set in an upright state in a mold, and the
Under a high vacuum of 1 to 0.01 mmHg, a void-free capacitor core 1 was manufactured by gently impregnating the capacitor core 1 using a conduit 7 formed by unevenness of crepe paper communicating in the axial direction.

0003

[Problems to be Solved by the Invention] However, as shown in Fig. 8, crepe paper is crepe-like, wavy, and uneven, so the rolled and laminated crepe paper meshes with each other, causing the winding diameter to change. Not only was this uneven, but the thin conductive material sheet 4 sandwiched between them was also wavy, making the electrodes as a capacitor substantially thicker. Therefore, in order to obtain a predetermined electric field relaxation effect, it is necessary to increase the number of layers of the insulating material sheet 3 between the electrodes to make the capacitor core thicker, and there is also the technical problem of not being able to accurately control the electric field distribution. there were.

On the other hand, if a smooth insulating material sheet that is not crepe-like is used, the laminated insulating material sheet 3 and conductive material sheet 4 will come into close contact with each other. Route 7) disappeared, and it was not possible to prevent the generation of voids during impregnation with resin. For this reason, it has not been possible to manufacture a capacitor bushing using the smooth insulating sheet 3.

[0005]An object of the invention is to provide a capacitor bushing that can sufficiently alleviate electric field concentration despite having a small diameter and has no variation in electric field distribution. Another object of the invention is to provide a method for manufacturing a capacitor bushing that does not produce voids even when conventional crepe paper or a smooth insulating sheet is used.

[0006]

[Means for Solving the Problems] In order to achieve the above object, in the invention as claimed in claim 1, a smooth insulating material sheet having a slit where capillary force acts is continuously wound around the central conductor a plurality of times. A conductive material sheet is wound into a cylindrical shape between the insulating material sheets at a predetermined number of turns, and the insulating material sheet is impregnated with resin.

[0007] Furthermore, in the invention of claim 2, when impregnating the liquid resin, the rising speed is 0.5 to 2.5 times the initial rising speed of the capillary liquid level that rises in the insulating material sheet due to capillary phenomenon. A method is used to raise the resin liquid level.

[0008]

According to the first aspect of the invention, since the insulating material sheet has a smooth surface, the conductive material sheet can be arranged smoothly. Therefore, the thickness of each sheet of conductive material can be substantially reduced, and even if the capacitor bushing has a small diameter, electric field concentration can be sufficiently alleviated. Also, the gap between the insulation sheets can be precisely controlled.

In the second aspect of the invention, when the liquid resin is impregnated from below, the rising speed is 0.5 to 2.5 times the rising speed of the capillary liquid level that rises in the insulating material sheet due to capillary phenomenon. Since the resin liquid level is raised, the resin can be impregnated without creating voids.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. 1 to 6. Generally, the impregnating properties of resin vary depending on the type of insulating material sheet, the type and viscosity of the resin to be impregnated, etc. For this reason, the inventor conducted a resin impregnation test using capillary force and obtained the test results shown in FIGS. 3 to 5. First, we will explain this test and its results.

3(a) to 3(b), each sample is held upright in a Petri dish (not shown) under atmospheric pressure, and liquid epoxy resin (viscosity: 20 cpoise) is poured into it to a predetermined depth. The results of a test were shown in which the material was poured into the glass and impregnated by capillary force. Here, sample a in FIG. 3(a) has a thickness of 24
It is a polyester nonwoven fabric with a smooth surface and a bulk density of 477 (g/cm2.m2). Sample b in FIG. 3(b) is a polyester nonwoven fabric with a thickness of 320 μm and a bulk density of 441 (g/cm 2 .m 2 ) and a smooth surface. Also, Figure 3(c)
Sample C has an apparent thickness of 500μ and a bulk density of 6500 (g/cm), which is conventionally used for resin-impregnated bushings.
．． This is crepe paper made of plant fibers. According to this, no void formation was observed at a depth of about 5 mm or less from the liquid surface in all of samples a to c. The reason for this is that inside the sheets of samples a to c, there are differences in density and density in the gaps where capillary force acts, but this difference is not so large, so the resin rises at a relatively uniform rate of rise, and no voids are generated. .

[0012] On the other hand, the portions 5 mm or more from the liquid level are impregnated with voids formed therein. This is because as the rising height increases, the difference in impregnation height increases, and as a result, the resin that rose earlier surrounds the slower part,
This is thought to be because air bubbles are trapped here. Also,
The voids in samples a and b are small, and the voids in sample c are large. This is because the nonwoven fabric surfaces of samples a and b are smooth, and the gaps formed between the nonwoven fabrics are not much different from the internal gaps, so the rise is uniform as a whole, whereas crepe paper Since the paper surface is uneven, large gaps and small gaps are formed between the crepe papers. For this reason, the rising speed is fast in small gaps, and slow in large gaps, and the difference in rising speed is large, which is considered to be the cause of large voids.

[0013] From the results of this test, it was confirmed that voids do not occur within 5 mm from the resin liquid level when resin is impregnated by capillary force without being affected by the surface shape. Moreover, FIGS. 4 and 5 show the relationship between the rising height of the epoxy resin liquid that rises due to capillary force and time after conducting a test similar to the test conditions shown in FIG. 3. FIG. 5 shows the rising height of the epoxy resin liquid until 5 minutes have elapsed, and the initial rising speed of each sample was determined.

Furthermore, the inventor held each sample with a length of 10 cm upright in a glass cylinder under atmospheric pressure, and measured the difference between the epoxy resin liquid rising due to capillary force and the liquid level of the poured epoxy resin liquid. A test was conducted in which epoxy resin was poured to ensure that no difference occurred. As a result, it was confirmed that each sample having a length of 10 cm was impregnated without generating any voids.

From the above tests, (1) Impregnation using only capillary force does not produce voids at a depth of 5 mm or less from the liquid level. ■ According to the impregnation speed due to capillary force,
Raising the liquid level will prevent voids from forming. Two findings were obtained.

[0016] An example based on this knowledge is shown in Fig. 1 below.
, 2. FIG. 1 shows a molding die 11 and a capacitor core 1 assembled therein before impregnation (hereinafter referred to as an impregnated object 1a). The molding die 11 is a cylindrical die 12
and a lower cap mold 13 screwed to the lower and upper parts thereof.
and an upper cap mold 14, forming a molding surface inside. This molding die 11 is installed upright within a heating device (not shown).

An injection pipe 15 for injecting resin is attached to the lower cap mold 13, and a recess 16 is formed to accommodate the lower end of the central conductor 2 of the object to be impregnated 1a. The upper cap mold 14 is fitted with an exhaust pipe 17 for evacuating the inside of the mold 11, and a recess 18 is formed to accommodate the upper end of the central conductor 2 of the object to be impregnated 1a. As shown in FIG. 2, this molding die 11 is connected to a resin tank 19 that supplies resin to be injected through an injection pipe 15, and an exhaust pipe 17 is connected to a vacuum pump 20. A resin made of liquid thermosetting epoxy resin is stored in the resin tank 19 . Further, the resin tank 19 is provided with a vacuum pump 21 for discharging air caught in the resin, and a resin stirring device 22.

A tube 15 is installed at the bottom of the resin tank 19.
is connected to enable resin to be supplied to the molding die 11. A tube pump 24 is disposed in the middle of the tube 15, and is capable of supplying a constant amount of resin into the molding die 11. Further, a reservoir 26 for collecting resin overflowing from the mold 11 is arranged in the middle of the exhaust pipe 17 connecting the molding mold 11 and the vacuum pump 20. 2
7 to 31 are valves.

Next, a method for manufacturing a capacitor bushing using the apparatus configured as described above will be explained. First, the impregnated object 1a to be impregnated with resin in the molding die 11 is formed according to a conventional method. That is,
A predetermined number of elongated insulating sheets 3 having a narrower width are wound around the axial center of the rod-shaped central conductor 2. The insulating material sheet 3 is different from the conventionally used crepe paper, and is made of a smooth polyester nonwoven fabric having slits on which capillary force acts. This insulating material sheet 3 has a thickness of 320μ and a bulk density of 4.
41 (g/cm m2) was used.

Next, after wrapping the insulating material sheet 3 a predetermined number of times, a conductive material sheet 4 (made of aluminum foil with a thickness of about 10 μm) is wound.
When rolled up, cut it into a length that will go around once) and place it on the insulating material sheet 3 and roll it up together. Furthermore, after winding the insulating material sheet 3 a predetermined number of times, the next conductive material sheet 4 is placed on the insulating material sheet 3 and rolled up together, and this operation is repeated sequentially to wind the conductive material sheet 4 in a concentric cylindrical shape. , a predetermined number (10 to 15) of conductive material sheets 4
Insert. The mutual gap between the conductive material sheets 4 inserted in a concentric cylindrical shape is approximately 1.7 to 2.0 mm in the thickness direction.

As described above, the insulating material sheet 3 and the conductive material sheet 4 are wrapped around the central conductor 2 in the axial direction, thereby forming the impregnated body 1a (the capacitor core 1 before impregnation) (see FIG. 1). ). In particular, in this embodiment, since the insulating material sheet 3 is made of a smooth polyester nonwoven fabric that is not creped, a sufficient number of conductive material sheets 4 are wound compactly.

The capacitor core 1 thus formed has a recess 16 formed in the lower cap mold 13 and a recess 18 formed in the upper cap mold 14, as shown in FIG.
Both upper and lower ends of the central conductor 2 are respectively fitted into the molding die 11 and erected within the molding die 11. Next, a method of impregnating the capacitor bushing with resin using the molding apparatus configured as described above will be described.

The vacuum pump 20 is driven, and the mold 11
While the air inside is exhausted, the inside of the molding die 11 is heated by a heating device (not shown), and the stirring device 22 and the vacuum pump 21 are driven with the liquid resin stored in the resin tank 19. , the resin is vacuum stirred and degassed. After the vacuum stirring and degassing is completed, the valve 30 is closed, the stirring device 22 and the vacuum pump 21 are stopped, and the valves 31 and 32 are opened.

Next, the tube pump 24 is driven to supply a predetermined amount of liquid resin into the molding die 11. After the liquid resin is filled into the molding die 11, the tube pump 24 is stopped and the valve 32 is closed. Valve 27 is then closed, vacuum pump 20 is stopped, and valve 28
is opened, and the liquid resin is cured in this state.

After sufficient heat curing, the upper cap mold 1
4 was removed, the impregnated capacitor core 1 was taken out from the molding die 11, and the presence or absence of voids was examined. An impregnation test was conducted on Samples 1 to 13 by the method described above. Each sample is as shown in Table 1.

[0026]

[Table 1]

Here, the supplied resin was a mixture of diglycidyl ether type resins having different epoxy resin contents to adjust the viscosity, and an acid anhydride curing agent was added thereto to obtain an impregnated resin. In addition, the initial velocity of capillary rise was determined from the relationship between the capillary rise height and elapsed time for each sample in the same manner as when the data in FIG. 5 was obtained.

In addition, each of the impregnated samples 1 to 13 was observed to investigate the presence of voids. As a result, the liquid level rise rate (
In Samples 1 and 9 where the ratio B/A between B) and the initial velocity of capillary rise (A) was 3.0, cylindrical voids were generated. Also ratio B
In samples 5 and 13 where /A was less than 0.5, spherical voids were generated. On the other hand, no voids were observed in samples 2 to 4, 6 to 8, and 10 to 12 in which the ratio B/A was in the range of 0.5 to less than 3.0.

From now on, samples 2 to 4 and 6 in which the resin liquid level rose at a rising speed within the range of 0.5 to 3.0 of the rising speed of the capillary liquid level rising in the insulating material sheet 3 due to capillary phenomenon. It was found that impregnation was possible without generating voids in samples 8 and 10 to 12. In this example,
Since the insulating material sheet 3 is made of a smooth polyester nonwoven fabric having a thin gap of 320 μm in thickness, the conductive material sheet 4 can be smoothly arranged in close contact with the insulating material sheet 3, and
Even if a sufficient number of conductive material sheets 4 are interposed, the capacitor core 1 can have a small diameter.

Although this embodiment shows an example of a capacitor bushing made entirely of smooth insulating material sheets 3, only the portion where the conductive material sheet 4 is sandwiched may be made smooth. In addition, in this example, a method for impregnating the object 1a to be impregnated with a resin using a smooth insulating sheet 3 has been described, but even when applied to the object 1a to be impregnated using crepe paper, a void-free capacitor bushing can be obtained. can be manufactured.

Furthermore, although this embodiment shows an example in which the inside of the molding mold 11 is evacuated during resin impregnation, it is not necessarily necessary to create a vacuum, and an air vent may be provided in the upper part of the cap mold 14. You can also use it as

[0032]

As described in detail above, in the invention of claim 1, the conductive material sheet is smoothly arranged in close contact with the insulating material sheet, and electric field concentration can be sufficiently alleviated despite the small diameter. At the same time, it has the effect of eliminating variations in electric field distribution and allowing a sufficient number of conductive material sheets to be interposed even if the diameter is small.

Further, in the invention of claim 2, the object to be impregnated inserted and set in the mold is filled with liquid resin, and the initial velocity of the capillary liquid level rising through the insulating material sheet due to capillary phenomenon is zero. By raising the resin liquid level at a rate of rise of .5 to 2.5 times, a void-free capacitor bushing can be manufactured.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a molding die with an object to be impregnated attached thereto.

FIG. 2 is a pipeline diagram of the manufacturing device.

[Fig. 3] Fig. 3(a) is an explanatory diagram showing the state of resin permeated through a nonwoven fabric with a thickness of 240μ by capillary force, Fig. 3(b)
) is an explanatory diagram showing the state of the resin permeating through a nonwoven fabric with a thickness of 320 μm by capillary force, and FIG.
FIG. 2 is an explanatory diagram showing the state of resin permeated through 00μ crepe paper by capillary force.

FIG. 4 is a graph showing the relationship between the resin liquid level rising due to capillary force and time.

FIG. 5 is a graph showing the relationship between the resin liquid level rising due to capillary action and time.

FIG. 6 is an enlarged cross-sectional view of a portion of the capacitor core.

FIG. 7 is a schematic diagram of a capacitor core.

FIG. 8 is an enlarged cross-sectional view of a portion of a conventional capacitor core.

[Explanation of symbols]

1 capacitor core, 2 center conductor, 3
Insulating material sheet, 4 Conductive material sheet, 5 Resin, 1
1 Molding mold, 13 Cylindrical mold, 14 Lower cap mold, 15 Upper cap mold.

Claims (2)

[Claims] 1. Wrapping a smooth insulating material sheet having a slit where capillary force acts around a central conductor multiple times in succession, and winding a conductive material sheet between the insulating material sheets in a cylindrical shape every predetermined number of turns, A capacitor bushing characterized in that the insulating material sheet is impregnated with resin. 2. A body to be impregnated consisting of an insulating sheet wrapped around a central conductor and a conductive sheet interposed between the insulating sheets is inserted and set in a mold, and liquid resin is applied. Manufacture of a capacitor bushing characterized in that during impregnation, the resin liquid level rises at an initial rising speed of 0.5 to 2.5 times the initial rising speed of the capillary liquid level that rises in the insulating material sheet by capillary action. Method.