JPH0457048B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a pipe type OF in which an insulating layer formed by winding at least a portion of a polyolefin plastic film such as polyethylene, polypropylene, polybutene, polymethylpentene, etc. is impregnated with high viscosity insulating oil. The present invention relates to a method of manufacturing power cables such as cables and solid type cables. (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 index) of the plastic and insulating oil are, the more the insulating oil is. It is known that it penetrates into plastic film and causes it 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, the swelling of the plastic film due to insulating oil can be prevented by alternately wrapping plastic film and kraft paper, or by wrapping a composite tape made of plastic film and kraft paper as an insulating layer. As is known, we decided to take measures such as winding kraft paper that has been pre-conditioned, or emboss one or both of the above tapes, and insulate the tape with plastic film. It is desirable to improve the electrical properties of the cable by absorbing oil. By the way, power cables impregnated with insulating oil are impregnated with low-viscosity insulating oil and have a metal sheath.
OF cable is a pipe type in which a cable core with an insulating layer impregnated with high viscosity insulating oil is introduced into a metal pipe such as a steel pipe that has been laid in advance, and the metal pipe is filled with relatively high viscosity insulating oil.
There are cables (see FIG. 1), and furthermore, there are so-called solid type cables used for lines without oil tanks, which are made by providing a metal sheath on a cable core having an insulating layer impregnated with high-viscosity insulating oil. Of these, pipe types that use high viscosity insulating oil
OF cables and solid type cables are generally made using 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, e.g. 30 centistokes at room temperature (25°C). The temperature is increased to 10 centistokes or more at high temperatures (80℃). As a specific example, the solid insulating oil used in solid type cables has approximately 8,000 centistokes at room temperature, and approximately 8,000 centistokes at high temperatures.
150 centistokes, and for pipe type cable oils, approximately 2000 centistokes at room temperature and approximately 70 centistokes at high temperatures are used. Incidentally, the dodecylbenzene and mineral oil impregnated into OF cables are less than 20 centistokes at room temperature and less than 4 centistokes at high temperatures, 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 is then stretched alone, uniaxially or biaxially, or these films and kraft paper are laminated together. The film and kraft paper are alternately wound on a conductor to form an insulating layer, and this is impregnated with the high viscosity oil to create a low loss (low ε, low tan δ) However, the following problems arose in trying to bring out the excellent characteristics of high dielectric strength (AC, impulse, DC). In other words, if an insulating oil with a SP value similar to that of the plastic film is not selected, the insulating oil will not be able to sufficiently impregnate the amorphous parts and microvoid layers inside the plastic tape, making it impossible to achieve sufficient performance. Can not. However, polyolefin plastic
As shown in Table 1, most of the SP values are 8 or higher, while the SP values of insulating oils are as shown in Table 2. ) and mineral oil OF
The above-mentioned high viscosity insulating oil used in pipe type cables and solid type cables is far from polyolefin in terms of SP value.

【table】

[Table] Therefore, in order to sufficiently impregnate an insulating layer with polyolefin plastic film with insulating oil,
It is best to use dodecylbenzene and mineral oil-based OF oils used in OF cables. In particular, dodecylbenzene, which has an unsaturated benzene ring, has superior corona resistance properties and gas-in-oil absorption properties compared to other insulating oils. Therefore, it is preferable to swell polyolefin plastic film with dodecylbenzene. (Disclosure of the Invention) The present invention has been developed in consideration of the above-mentioned technical matters, and its characteristics are that at least part of the film is wrapped with a polyolefin plastic film and the rest is made of kraft paper. A power cable impregnated with dodecylbenzene, then deoiled from the dodecylbenzene, and impregnated with an 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). It's in the manufacturing method. (Example) FIGS. 1 and 2 show cross-sectional views of an example of a pipe type OF cable (FIG. 1) and a solid type cable (FIG. 2) to which the present invention is applied. In the drawings, 1 is a conductor, 2 is a polyolefin plastic film wound individually,
The insulating layer 2 is formed by winding a composite tape made by laminating the plastic film and kraft paper, or by alternately winding the plastic film and kraft paper, and the insulating layer 2 is usually filled with polybutene-based insulating oil or It is impregnated with 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, the three cable cores 3 described above are introduced into a metal pipe 4 such as a steel pipe, which has been laid in advance, and the metal pipe 4 is filled with the same high-viscosity insulating oil 5 as described above. It is configured as follows. The solid cable shown in Fig. 2 is a three-core cable, in which the three strips of the cable core 3 are twisted together with an inclusion 6 such as a paper string or a jacket, and a lead sheath or the like is placed on top of the cable. It is configured with a metal sheath 7. Although not shown, there is also a single-core solid cable in which a metal sheath is applied to each core and laid as is, or a solid cable in which a metal sheath is applied to each core and three cores are twisted together. However, in the power cable of the present invention,
Before the step of impregnating the insulating layer 2 with the high viscosity insulating oil, the insulating layer 2 is impregnated with dodecylbenzene in advance, and in that state, for example, 60°C to 120°C, 3 to 48°C
The plastic film of the insulating layer 2 is sufficiently impregnated with dodecylbenzene by holding the plastic film at a temperature of preferably 70° C. to 80° C. for 12 to 24 hours, more preferably 0 to 5 kg/cm ² G while applying pressure. As a result, the polyolefin film absorbs 5 to 20% by weight of dodecylbenzene. In general, if the absorption amount is less than 5% by weight, the absorption of insulating oil is insufficient;
If it exceeds this, the plastic film will begin to decompose and melt, which is undesirable. 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. When the dodecylbenzene absorption process is completed, the dodecylbenzene is removed from the tank to perform so-called oil removal. Oil removal can be done by vacuuming the tank at room temperature and sucking the oil out of the tank, allowing it to naturally escape from the insulating layer, but once dodecylbenzene has been absorbed into the plastic film layer, it will not come out easily, so this It will not be removed from the plastic film during the oil process. After this oil removal process, use the conventional method to remove polybutene-based insulating oil for pipe type OF cables.
In the case of a solid cable, the cable core is formed by impregnating the insulating layer with the above-mentioned mixed insulating oil. Pipe type obtained through the above processing
OF cables or solid type cables have corona resistance properties, electrical properties (AC, impulse, DC,
This is a high-quality power cable with excellent tanδ).
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 results of measuring the electrical properties of a 125 μm thick composite tape made by laminating polypropylene film and kraft paper are shown in Table 3, and the effect was fully confirmed.

[Table] (Effects of the Invention) According to the method of manufacturing a power cable having a polyolefin plastic insulation layer impregnated with a high viscosity insulating oil of the present invention described above, a plastic film is preliminarily coated before being impregnated with a 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 the drawing]

FIGS. 1 and 2 show cross-sectional views of examples of a pipe type OF cable (FIG. 1) and a solid type cable (FIG. 2), both of which are objects of the present invention. 1... Conductor, 2... Insulating layer, 3... Cable core, 4... Metal pipe, 5... Insulating oil, 7... Metal sheath.

Claims (1)

[Claims] 1 An insulating layer made of polyolefin-based plastic film wrapped around at least a portion and the rest made of kraft paper is pre-impregnated with dodecylbenzene, then the dodecylbenzene is deoiled and the insulating layer is heated to 30 centistokes at room temperature (25°C). or higher, high temperature (80
A method for manufacturing a power cable, characterized in that the power cable is impregnated with an insulating oil having a viscosity of 10 centistokes or more at ℃).