JPS6244904A - Power cable - 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 (Field of Application in Industry) The present invention relates to an insulating layer formed by winding at least a portion of a polyolefin plastic film such as polyethylene, polypropylene, polybutene, polymethylpentene, etc. This invention relates to power cables such as pipe type OF cables and solid type cables impregnated with high viscosity insulating oil.

(Background of the invention) In general, in a power cable in which an insulating layer formed by winding at least a portion of a polyolefin plastic film is impregnated with insulating oil, the closer the SP value (solubility IH number) of the plastic and the insulating oil, the better the insulation. It is known that oil penetrates plastic films and causes them to swell.

On the other hand, the more the insulating oil penetrates into the plastic film, the more the amorphous parts and microvoids in the plastic are impregnated with the insulating oil, which improves the electrical properties and improves the AC breaking voltage and impulse breaking voltage. decreases.

Therefore, in order to prevent the plastic film from swelling due to insulating oil, it is already known that plastic film and kraft paper can be alternately wound, or a composite tape made by laminating plastic film and kraft paper can be wound to form an insulating layer. We decided to take measures such as winding kraft paper that has been pre-adjusted as described above, or emboss one or both of the above tapes, and then apply an embossing method to the plastic film. It is desirable to improve the electrical characteristics of the cable by absorbing the insulation.

By the way, power cables impregnated with insulating oil include OF cables with a metal sheath impregnated with low-viscosity insulating oil, and insulating layers impregnated with high-viscosity insulating oil in metal pipes such as steel pipes that have been laid in advance. Introducing a cable core with a metal pipe filled with a relatively high-viscosity insulating oil (see Figure 1), and a cable core with an insulating layer impregnated with a high-viscosity insulating oil. There is a so-called solid type cable that is used for lines without a fuel tank and is made of a metal sheath.

Among these, pipe-type OF cables and solid-type cables that use high-viscosity insulating oil are generally made with polybutene-based insulating oil alone, or mixed with tar-based insulating oil, heavy oil-based insulating oil, paraffin, wax, etc. to achieve the required viscosity. , for example, at room temperature (25°C), 30 centistokes or higher,
80°C) and Iθ centistokes or more. As a specific example, solid insulating oil used in solid type cables has approximately 8000 centistokes at room temperature.
It is approximately 150 centistokes at high temperature, and for pipe type cable bends, it is approximately 2000 centistokes at room temperature and approximately 70 centistokes at high temperature. Incidentally, the dodecylbenzene and mineral oil impregnated into the OF cable have a viscosity of 20 centistokes or less at room temperature and 4 centistokes or less at high bending temperature, and there is a clear difference in the viscosity of these two types of cable insulating oil.

However, polyolefin plastic tapes, such as polyethylene, polypropylene, polybutene, and polymethylpentene, are melt-extruded to form a film, which can be stretched alone, -axially or biaxially, or by laminating these films and kraft paper. integrated composite tape,
Furthermore, an insulating layer is formed by alternately winding the film and kraft paper in the conductor (2), and this is impregnated with the high viscosity oil to achieve low loss (low ε, low tan δ) and high In order to bring out the excellent characteristics of dielectric strength (AC1 impulse, DC), the following problems were encountered.

In other words, unless an insulating oil with a SP value close to that of the plastic film is selected, the insulating oil cannot be sufficiently impregnated into the amorphous portion and microvoid layer inside the plastic tape, making it impossible to achieve sufficient performance. Can not.

However, as shown in Table 1, most of the SP values of polyolefin-based plastics are 8 or higher, while the SP values of insulating oils are 8 or higher.
The P value is as shown in Table 2, and the insulating oils that are close to the SP value of polyolefin are dodecylbenzene (DDB) and mineral oil-based OF oil, which are commonly used for OF cables, and are suitable for pipe type cables and sled/sod type cables. The aforementioned high viscosity insulating oils used are far away from polyolefins in SP value.

Table 1 Table 2 Therefore, in order to sufficiently impregnate an insulating oil into an insulating layer having a polyolefin plastic film, it is best to use dodecylbenzene or mineral oil-based OF oil, which is used in OF cables, and especially those containing unsaturated benzene rings. Dodecylbenzene itself has better corona resistance properties and gas-in-oil absorption properties than other insulating oils, so it can be said that it is preferable to swell a polyolefin plastic film with dodecylbenzene.

(Disclosure of the Invention) The present invention has been made in consideration of the technical matters mentioned in -I- above, and its feature is that an insulating layer, at least a portion of which is wrapped with a polyolefin plastic film, is pre-coated with dodecylbenzene. The cable core is impregnated with insulating oil having a viscosity of 30 centistokes or more at room temperature (25°C) and 10 centistokes or more at high temperature (80'C) after deoiling the dodecylbenzene. It consists of a power cable.

(Example) Figures 1 and 2 show pipe type O to which the present invention is applied.
2 shows cross-sectional views of examples of F cables (FIG. 1) and solid type cables (FIG. 2); FIG.

In the drawing, (1) is a conductor, and (■) is a polyolefin plastic film that is individually wound, but a composite tape made by laminating the above plastic film and kraft paper is wound, or a plastic film and kraft paper are alternately wound. An insulating layer formed by winding. Usually, the insulating layer (1) is impregnated with polybutene-based insulating oil, or insulating oil mixed with tar-based insulating oil, heavy oil-based insulating oil, paraffin, wax, etc. .

In the pipe type OF cable shown in Fig. 1, three cable cores (3) described above are introduced into a metal pipe (4) such as a steel pipe that has been laid in advance, and the same high viscosity as described above is inserted into the metal pipe (4). It is filled with insulating oil ■.

1 The solid type cable shown in Fig. 2 shows the case of a three-core bundle type cable, but the three strands of the cable core (3) are twisted together with an inclusion (6) such as a paper string or a short, and then It is constructed by applying a metal sheath such as lead coating. Although not shown, there is also a single-core solid cable in which each core is coated with a metal sheath and laid as is, or a solid cable in which three cores are twisted together after each core is coated with a metal sheath.

However, in the power cable of the present invention, the insulating layer ■
Before the step of impregnating the insulating oil with the high viscosity insulating oil, the insulating layer (1) is impregnated with dodecylbenzene in advance, and in that state, it is heated for example at 60° C. to 120° C. for 3 to 48 hours, preferably 70° C.
°C to 80 °C, 12 to 24 hours, more preferably 0 to 5
Hold it while applying pressure with kg/c♂G to create a sufficient insulation layer■
The plastic film is impregnated with decylbenzene. As a result, the polyolefin film has 5 to 20
Absorbs % by weight of dodecylbenzene. Generally, if the absorption amount is less than 5% by weight, the absorption of insulating oil is insufficient.
If it exceeds 20% by weight, the plastic film will begin to decompose and melt, which is not preferable. In this case, since dodecylbenzene is a low viscosity oil, it is extremely easy to impregnate it after wrapping with tape and drying, and pressurization and heating can also be easily carried out using an ordinary dry impregnation tank.

Dodecylbenzene is removed from the tank to perform what is called deoiling. To remove oil, if you vacuum the tank at room temperature and suck the oil out of the tank, it will naturally escape from the insulating layer.
Once dodecylbenzene is absorbed into the plastic film layer, it does not easily escape, so it will not be removed from the plastic film during this oil removal process.

After the deoiling process with pipe type O
For F cables, the cable core is formed by impregnating the insulating layer with polybutene-based insulating oil, and in the case of solid cables, impregnating the insulating layer with the above-mentioned mixed insulating oil.

The pipe type OF cable or solid type cable obtained through the above processing becomes a high quality power cable with excellent corona resistance properties and electrical properties (AC, impulse, DC1 tan δ).

On the other hand, in manufacturing such cables, conventional manufacturing equipment can be used almost as is, so it is also highly economical.

Incidentally, the electrical properties of a 125 μm thick composite tape laminated with polypropylene film and kraft paper were measured as shown in Table 3, and the effect was fully confirmed.

Table 3 (Effects of the Invention) According to the power cable having two consecutive polyolefin plastic insulation layers impregnated with high viscosity insulating oil of the present invention, the preheated plastic film is heated before being impregnated with high viscosity insulating oil. Because it absorbs dodecylbenzene, it becomes a high-quality electrical cable with excellent corona resistance and electrical properties.

Furthermore, in manufacturing such cables, most of the conventional manufacturing equipment can be used as is, making it highly economical.

[Brief explanation of drawings]

Figures 1 and 2 show pipe type O, which is the object of the present invention.
2 shows cross-sectional views of examples of F cables (FIG. 1) and solid type cables (FIG. 2); FIG. DESCRIPTION OF SYMBOLS 1... Conductor, 2... Insulating layer, 3... Cable core, 4... Metal pipe, 5... Insulating oil, 7... Metal sheath.

Claims (1)

[Claims] (1) At least a portion of the insulating layer wrapped with a polyolefin plastic film is pre-impregnated with dodecylbenzene, and then the dodecylbenzene is deoiled, and the temperature is increased to 30 centistokes or more at room temperature (25°C). 1. A power cable comprising a cable core impregnated with an insulating oil having a viscosity of 10 centistokes or more at (80° C.).