JPS58209008A - Method of producing electrically insulating paper - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrical insulating paper, particularly insulating paper made of porous plastic film.0 Electrical insulating paper used for electric cables, transformers, capacitors, etc. is conventional cellulose paper. are being replaced by plastic film or paper.

When using plastic film, in order to obtain the same flexibility, tensile strength, elongation, compressibility, etc. as cellulose paper, plastic film is often processed to have a large number of micropores. When forming an insulator by laminating layers, similar processing is performed to improve impregnation with insulating oil or gas.

The porous plastic film used at this time is produced by various methods, but none of the methods have so-called open pores in which all of the micropores communicate with the outside of the insulating paper. There are some confined micropores. By laminating such porous films, dehumidifying and degassing them, and then applying insulating oil or inert gas pressure, independent closed micropores are created in the insulator, which is designed to have a certain level of dielectric strength. Then, the inside is not sufficiently replaced with insulating oil or inert scum, and air, plastic, decomposed gas of insulating oil, etc. remain inside, resulting in deterioration due to micro discharge in this part, or deterioration caused by this part. In some cases, dielectric breakdown may occur and the original dielectric strength cannot be demonstrated.

An object of the present invention is to alleviate the drawbacks of conventional porous plastic films and to provide electrically insulating paper with improved performance.

In other words, the gist of the present invention is that after manufacturing a conventional porous plastic film, a gas pressure or liquid pressure is applied to the existing closed micropores from the outside such as the surface of the plastic film or the open pores around it, and the process is continued for a relatively long period of time. By diffusing these gases or liquids inside the plastic part around the closed micropores, increasing the pressure inside the micropores and conversely reducing the external pressure in a short time, the micropores expand due to the internal pressure inside the micropores. The plastic film is ruptured to form a passageway that connects to the open pores on or around the plastic film.

Figure 1 is a cross-sectional model of electrical insulating paper 1 made of a conventional porous plastic film, with open holes 2 reaching the film surface, micropores 3 connected to other open holes, and closed microscopic holes with no passages. Hole 4 is present.

FIG. 2 is a model diagram showing a state in which high pressure gas 5 is applied to the conventional porous plastic film 1 as shown in FIG.
However, the pressure inside the closed micropore 4 becomes P' and P
>P'.

Figure 3 shows the external pressure P after adding the high pressure gas in Figure 2.
This shows a situation in which P is suddenly changed to P', and the gas pressure inside the open hole 2゜3 immediately becomes ■''', whereas if P'>P',
An outward pressure (P′〉1) acts inside the closed micropore 4, and a part of the wall surface is mechanically destroyed in 6 parts by this pressure, and the internal debris is removed, for example, as shown in Fig. 3. It will be released by following the path of the arrow. That is, the closed micropores become open holes. In this process, if the temperature of the film is raised within a range that does not cause the micropores to collapse, which is generally lower than the melting point of the plastic material, the diffusion of gas or liquid due to external pressure will be promoted, and the high pressure holding time will be extended. Since the tensile strength of the plastic film generally decreases, it is possible to destroy the wall surface even if the internal pressure inside the closed hole is low when the external pressure suddenly decreases, making it practical. is an important additional condition. Further, the applied pressure value, pressure medium, and application time should be changed depending on the temperature, the material of the porous plastic film, and the condition of the pores.

In this case, the scum that liquefies at low temperature is applied at high temperature and high pressure to hasten the filling of the closed micropores, which is then lowered to a low temperature and liquefied. It is also possible to use heating to cause the internal liquid to boil, thereby increasing the internal pressure. Furthermore, by repeating high temperature and low temperature conditions, it is possible to promote the storage of liquid inside the micropores, and then to obtain a high internal pressure by the same process as described above.

As an example, we used a porous polypropylene film with a thickness of 100 μm as a sample, and in a model cable created by winding 10 sheets of this, vacuum-drying it, and then impregnating it with alkylbenzene oil. At 1rlG, the partial discharge inception voltage is 30kv/m, and the dielectric breakdown stress is 52k.
It was v/mm.

On the other hand, as an example of the present invention, nitrogen gas pressure of 100 atm is
When the partial discharge inception voltage of a similar model cable was measured using insulating paper that had been exposed to atmospheric pressure for 1 hour at ℃ and then released to atmospheric pressure for about 20 seconds, the inception voltage was 45 kV. /am, and the dielectric breakdown stress was 7Qkv/m+n or more. This means that in the former cable, minute closed holes remained in the cable insulation, and discharge started inside them under a stress of 30 kv/mm, whereas in the latter cable, those closed holes were opened.
Internal discharge starting voltage was 45kv/M due to penetration of insulating oil.
As n increases, the dielectric breakdown stress also improves. However, at 45 kV/throat, a small discharge still remained, but this was because an extremely small closed hole was not opened and the discharge occurred inside the hole. However, the discharge starting voltage is 30
The 50% increase from 45kv/m+n to 45kv/m+n is a major improvement from an industrial perspective, and can be said to be a revolutionary improvement in the performance of insulating paper.

In the present invention, a porous plastic film is used as the electrically insulating paper, but in practical terms, it can also be processed in the form of a laminated structure, a roll-wound structure, or an adhesive structure with other insulating papers or films. A new insulating paper can be obtained.

Furthermore, it is also possible to improve the performance of an insulating paper using an ordinary plastic film having minute closed voids, rather than a porous plastic film, by the same method as the insulating paper according to the present invention.

The present invention dramatically improves the voltage resistance of insulating paper made of porous plastic film, which was previously discouraged from practical use due to remaining closed micropores, and provides stable electrical insulation for many years with sufficient deaeration, drying, and impregnation. You can get paper.

As a result, an insulating paper with high voltage resistance and low dielectric loss characteristics, especially under high stress conditions, was obtained, which will promote the ultra-high voltage and compactness of future high voltage equipment, and will greatly contribute to the development of power equipment. It is.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing an example of the cross-section of insulating paper made from a conventional porous plastic film. Figure 2 is a cross-sectional view showing a state in which high gas pressure is applied to the conventional porous plastic film. FIG. 2 is a cross-sectional view of an embodiment of the method of the present invention, showing a situation in which after adding dregs, the external pressure is suddenly removed, and the walls of the closed micropores are ruptured by the internal pressure, resulting in open pores. 1... Porous plastic film, 2... Open pores, 3... Micropores connected to other open pores, 496. Closed micropore, 5... high pressure medium, 6... rupture port due to internal pressure.

Claims (1)

[Claims] (1) After applying high pressure with clean gas or liquid to electrical insulating paper made of a porous plastic film with many micropores, the pressure is reduced in a short time,
A method for producing electrical insulating paper, characterized by breaking closed micropores to form open pores.