JPS6137729B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes the hygroscopic properties of the plastic film to form an electrically insulating paper by combining a plastic film with a fibrous paper having hygroscopic properties, such as natural cellulose. This invention relates to a composite of fiber paper and plastic film for oil-immersed electrical equipment, which has fine irregularities added to it.

BACKGROUND ART In recent years, as power cables have become increasingly ultra-high voltage and large-capacity, there has been a demand for smaller cable sizes and reduced dielectric loss in order to reduce construction and operating costs. One of the means to achieve these objectives is to improve the insulators used. In this case, they not only have excellent electrical properties such as breakdown strength and dielectric loss tangent against impulse voltage and AC voltage, but also mechanical properties. Materials with excellent strength are required. For these purposes, attempts have been made to use plastic film instead of conventional natural cellulose paper and oil-impregnated paper made of insulating oil, but there are problems with the temperature characteristics specific to plastic, the polarity effect on impulse voltage, the drop in withstand voltage against repeated voltage, and the film's unique temperature characteristics. There are drawbacks such as difficulty in following excessive oil pressure fluctuations due to poor oil flow between layers. In order to compensate for this drawback, provide a barrier effect against impulse voltage, and ensure the flow of oil between the layers of the insulating layer, a composite technology was developed that combines plastic film and insulating paper, which is natural cellulose fiber paper. The plastic film used for this needs to have excellent impulse voltage characteristics, AC voltage characteristics, dielectric properties, etc. From this point of view, polyolefin films are desirable. However, a composite using polyolefin film and insulating paper swells with the oil used (mineral oil, DDB, hydrocarbon oil such as alkylnaphthalene) and becomes thicker than when only insulating paper is used. The insulating paper in between is pressed against it, increasing the resistance to oil flow through its surface irregularities and fiber gaps, impairing oil flow in the radial direction of the cable, and reducing the insulation required for bending cables. Mechanical properties may be deteriorated. In order to minimize the increase in thickness due to swelling of polyolefin films, it is preferable to use polyolefin films that have small changes in thickness due to swelling, but at present there are limits to this, and increases in thickness must be avoided. I can't.

However, even if it is impossible to essentially suppress the swelling, it is possible to suppress the apparent increase in thickness due to swelling, and recent developments have been made in this direction. One of them is as known from Japanese Patent Publication No. 52-38273, in which when a plastic film and insulating paper are combined, the thickness can be increased by controlling the humidity of the insulating paper in advance by utilizing the hygroscopic swelling property of the insulating paper. This is a method in which insulating paper is increased in size, wound on a cable conductor, dried to a certain degree, and then thinned, and then interposed between plastic films and impregnated with oil. In this way, by compensating for the increase in the thickness of the plastic film due to swelling with the tolerance of the insulating paper whose thickness has decreased due to drying, the flow of the insulating oil is inhibited even when the film is in a swollen state after being impregnated with insulating oil. It never happens. Another method is to forcibly give a predetermined unevenness to a composite of plastic film and fiber paper, so-called embossing, as known in Japanese Patent Application Laid-Open No. 54-66498, and then apply an insulating oil to the plastic film. The increase in thickness due to swelling after impregnation is absorbed by the deformation of these irregularities. However, since this method involves mechanical embossing, the composite of plastic film and fiber paper is susceptible to local damage, which may lead to a decrease in mechanical and electrical strength.

The present invention is particularly directed to a laminated insulating paper in which a plastic film and a fiber paper are integrated into one, which can effectively suppress the increase in thickness due to swelling of the plastic film after impregnation with an insulating oil by utilizing the hygroscopic swelling properties of the fiber paper. It provides:

The present inventors have conducted various studies on the effects of the above-mentioned laminate paper, which is a composite of a wet-treated plastic film and fiber paper, on suppressing the increase in thickness caused by swelling of the plastic film in insulating oil. Ta. As a result, even if the same amount of moisture is applied, the suppression effect differs depending on how the moisture is applied. In other words, if the fiber paper is unevenly moistened by spraying water droplets with a wide particle size distribution, The effect of suppressing the increase in plastic film thickness is greater than when uniform humidification is achieved by dispersing microscopic water droplets with a narrow particle size distribution or by balancing the water vapor in a gas with high relative humidity with the moisture in fiber paper. The present invention was based on the discovery that this phenomenon becomes significant.

That is, the present invention is characterized in that water droplets with a wide particle size distribution are sprinkled on the surface of a laminated insulating paper that is a composite of a plastic film and a fiber paper, thereby moistening the fiber paper. Laminated insulating paper for electrical equipment is rolled, then dried and soaked in oil.

To explain the present invention with reference to drawings, Fig. 1 shows the same polypropylene laminated paper as used in Example 1, which will be described later. The water was then collided with a wire mesh to form water droplets of various sizes, which were then sprayed (the moisture content of the paper after spraying was 11.2%), and then heated to 100°C.
This is a full-sized photograph of the surface of the kraft paper after drying for one hour. The entire surface of the kraft paper is pocked, with unevenness of various sizes. The diameter of the unevenness is determined by the particle size of the applied water droplets (20 to 500
It is much larger than 10 μm) and reaches more than 10 mm.

Figure 2 uses the same laminated paper as in Figure 1, and leaves it in a humidity control box with a relative humidity of 90% for 4 hours to almost equilibrate the water vapor in the gas and the moisture in the kraft paper ( The moisture content of paper at moisture equilibrium is 10.5
%), and is a full-sized photograph of the surface of the kraft paper after it was dried at 100°C for 1 hour. The appearance of the surface is markedly different from that shown in FIG. 1, and although some irregularities are observed, it is generally smooth.

Figure 3 shows the wet treated, untreated polypropylene laminated paper (moisture 5.4
%) is a full-sized photograph of the surface of kraft paper. It can be seen that the surface is even more gentle than in Figure 2.

As described above, the wet-treated laminated paper of FIG. 1 and the wet-treated laminated paper of FIG. 2 have moisture content similar to that of kraft paper. However, after each of these is dried, the polypropylene layer is immersed in insulating oil to swell, the thickness of the entire laminate paper is determined when the swelling reaches an equilibrium state, and the thickness increase rate before and after swelling is compared. A clear difference appears between them. In other words, when comparing the thickness increase rates of the wet-treated laminated paper in FIG. 2 and the untreated laminated paper in FIG. 3, the rate of increase in thickness is significantly smaller in the case of FIG. When compared with the wet-treated laminated paper shown in FIG. 1, the thickness increase rate is even more reduced in the case of FIG. This is considered as follows.

In other words, when kraft paper is moistened by humidifying water droplets using a nozzle, as in the case of the treated paper in Figure 1, water droplets of various sizes with a wide particle size distribution are randomly scattered and applied to the kraft paper. Therefore, depending on the presence and size of water droplets on the surface of the kraft paper, the difference in the size of the local swelling caused by the water droplets on the kraft paper becomes significant, and after drying, irregular irregularities are formed on the kraft paper surface and remain. On the other hand, when kraft paper is moistened by equilibrating it with water vapor, as in the case of the wet-treated laminated paper shown in Figure 2, the kraft paper is almost uniformly moistened with water vapor from the beginning. There is little difference in the size of local swelling due to uneven distribution of water on the surface, and the formation of unevenness after drying is small. The effect of reducing the rate of increase in thickness due to swelling of the polypropylene film layer after impregnation with insulating oil in the wet-treated laminated paper shown in Figure 2 is due to the uniform thickness increase/decrease effect when the kraft paper simply wets and dries. However, in the case of the wet-treated laminated paper shown in Figure 1, there is not only a compensation effect due to the uniform increase and decrease in the thickness of the kraft paper, but also the unevenness formed on the surface of the kraft paper. It has the same effect as the mechanical embossing described above, and also has the effect of absorbing the increase in thickness due to the swelling of the polypropylene layer in the insulating oil by deforming the unevenness. It seems to be.

The method of applying water droplets of various sizes with a wide particle size distribution in the present invention is not limited to the method using a nozzle, but also the method of scattering the water droplets ejected from the nozzle by colliding with a wire mesh, or the method of spraying water droplets by spraying. good. The width of the particle size distribution of water droplets can be changed depending on the diameter of the nozzle and the water pressure, but as mentioned above, when the water flow through the nozzle collides with the wire mesh, the width of the particle size distribution can be expanded from about 10 μm to several thousand μm, which is preferable.

The degree of moisture on the surface of laminated paper is 6 to 6 in terms of moisture content.
Around 12% is suitable. Although the effect is observed even when the moisture content is in the range of 3 to 6%, the degree of effect is small. while 25
% or more of water does not significantly improve the effect, and adding too much water leads to a decrease in the mechanical strength of the laminated paper, which may worsen the work of winding it onto a conductor.

In addition, the laminated paper that can be applied to the present invention may be one in which insulating papers made of natural cellulose such as kraft paper are integrated by melt extrusion of polyolefin resin or the like using an extruder, or one in which a polyolefin film or the like and natural cellulose are combined under heat pressure. Examples include things that are integrated. The fiber paper used in the present invention is natural cellulose 100
Of course, not only % paper but also paper made by mixing synthetic fibers or synthetic pulp with natural cellulose can be used.

The present invention will be explained in more detail below using Examples. The degree of swelling of the laminated paper in Examples and other cases was measured by applying spring pressure to the sample as described in the Institute of Electrical Engineers of Japan, Materials of the Insulating Materials Study Group, Material No. EIM-75-51 (published on December 9, 1975). The test was carried out using a device that can directly read the change in thickness of the laminated paper immersed in insulating oil while applying a predetermined pressure (pressure range 1 to 15 kg/cm ^{2 )} .

Example 1 Ion-exchanged water with an electrical conductivity of 5μΩ or less was heated to 1.5mmφ
A stream of small water droplets of 20 to 500 μm was formed by colliding with a 300-mesh wire mesh through a nozzle at a water pressure of 0.51 Kg/ ^cm2 , and kraft insulating paper (43 μm thick) was bonded to both sides of a polypropylene film (55 μm thick). It was applied to both the front and back sides of polypropylene laminated paper with a total thickness of 125 μm to obtain a sample with a moisture content of 11.2%. After leaving this in a room with a relative humidity of 65% for 24 hours, we stacked 10 sheets and set it in a swelling meter to determine the thickness at a pressure of 1Kg/ ^cm2.1206
It was μm. Dry this set for 24 hours at a temperature of 100℃ or higher, thoroughly remove moisture, and then heat the insulating oil (hard type alkylbenzene) to 100℃.
The thickness of the polypropylene laminated paper at the time when it was impregnated with and equilibrium was determined to be 1197 μm, and the thickness increase rate was -0.75%.

Comparative Example 1 Regarding the polypropylene laminated paper to which no small water droplets were applied in Example 1, the thickness increase rate after oil impregnation was determined in the same manner and was found to be +1.14%.

Comparative Example 2 Instead of applying a small stream of water in Example 1, polypropylene laminated paper was left in a humidity control box with a relative humidity of 90% and humidified with water vapor.
A sample of 10.5% was obtained. The thickness increase rate after oil impregnation was found to be 0.0% in the same way as this sample.
It was hot.

Example 2 In the polypropylene laminated paper of Example 1, instead of the 55 μm thick polypropylene film,
A small stream of water droplets was applied under the same conditions except that the film was 105 μm thick and the entire film was made of 170 μm thick laminated paper, and the moisture content was 11.9%. The thickness increase rate of this sample after oil impregnation was determined to be −0.72.
It was hot.

Comparative Example 3 When the same thickness increase rate was determined for the polypropylene laminated paper to which no small water droplets were applied in Example 2, it was +1.84%.

Comparative Example 4 Instead of applying a small stream of water in Example 2, the laminated paper was left in a humidity control box at a relative humidity of 90%, and the moisture content was 10.4%. The thickness increase rate of this sample after oil impregnation was +1.09%.

Example 3 In the polypropylene laminated paper of Example 1, 68 μm was used instead of the 55 μm thick polypropylene film.
Moisture content of the sample in which a small water droplet flow was applied under the same conditions except that a polypropylene film with a thickness of 155 μm was used, one sheet of insulating paper was 43 μm thick, and one sheet of insulating paper was 70 μm thick. was 10.7%. The thickness increase rate of this material after oil impregnation was -1.60%.

Comparative Example 5 The thickness increase rate after oil impregnation was determined for the polypropylene laminated paper to which no small water droplets were applied in Example 3, and it was +1.26%.

Comparative Example 6 Instead of applying a small stream of water in Example 3, the polypropylene laminated paper was left in a humidity control box at a relative humidity of 90%, and the moisture content was 10.5%. The thickness increase rate of this sample after oil impregnation was -0.75.

Example 4 The same laminated paper as in Example 3 was used except that a 134 μm thick polypropylene film was used instead of the 68 μm polypropylene film to make the overall 220 μm thick laminated paper, and a small water droplet stream was applied to reduce the water content to 11.5. % samples were created. The thickness increase rate of this sample after oil impregnation was determined to be -0.68%.

Comparative Example 7 The thickness increase rate after oil impregnation was determined for the polypropylene laminated paper to which no small water droplets were applied in Example 4, and it was +2.30%.

In the above embodiments, the case of polypropylene laminated paper was shown, but the plastic film material is of course not limited to polypropylene, and other laminated papers such as polyethylene and polybutene can be used as well.

As explained above, according to the present invention, water droplets with a particle size distribution width in the range of 10 to 1000 μm are dispersed to locally create unevenness on a fiber paper such as kraft paper, and the entire fiber paper is uniformly distributed by absorbing moisture. Wet-treated laminated insulating paper, which is a composite of fiber paper and plastic film that has been swollen by the insulating oil, absorbs the increase in thickness due to swelling of the plastic film layer in insulating oil, and increases the overall thickness of the laminated insulating paper. It has an extremely large effect in suppressing the increase rate, and has not only dramatically improved the manufacturing technology for electrical equipment such as OF-type power cables and OF-type power capacitors, but also further increased the proportion of plastic film in laminated insulating paper. The effects are truly significant, such as making it possible to develop laminated insulating paper that is larger and has higher performance.

[Brief explanation of the drawing]

The figures are actual-size photographs of the surface of the laminated insulating paper. Figure 1 is the surface of the laminated insulating paper of the present invention, Figure 2 is the surface of the laminated insulating paper left in a humidity control box with a relative humidity of 90%, and Figure 3 is a photograph of the surface of untreated laminated insulating paper.

Claims (1)

[Scope of Claims] 1. A wet state characterized by spraying water droplets with a wide particle size distribution on the surface of a laminated insulating paper that is a composite of a plastic film and a fiber paper to moisten the fiber paper. Laminated insulating paper for electrical equipment that is wrapped around a conductor, then dried and soaked in oil. 2. The laminated insulating paper for oil-immersed electrical equipment according to claim 1, wherein the fiber paper is moistened to a moisture content of 5 to 25%. 3. Claim 1, characterized in that water droplets having a particle size distribution width in the range of 10 to 1000 μm are sprayed.
Laminated insulating paper for oil-immersed electrical equipment as described in .