JPH0231933Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Technical Field] The present invention relates to improvements in electrically insulated cables immersed in electrically insulating oil. [Prior art and its problems] Conventionally, electrical insulating paper has been used as the oil-immersed insulation layer (or dielectric layer) of oil-immersed electrical cables, but recently, polyolefin film has been used in some cases. Ta. This film not only has a much higher withstand voltage than electrically insulating paper, but also has several advantages, such as a small dielectric loss tangent and a dielectric constant close to that of insulating oil. However, conventional cables covered with polyolefin film have the disadvantage of extremely large swelling due to insulating oil, and therefore have various limitations when used for oil-immersed insulation applications. For example, when a cable is made by winding a melt-extruded polymethylpentene film and immersed in insulating oil, the oil swells the film, making the cable tightly wound and hard, and the insulating oil flows between the layers. This can cause problems such as things getting worse. As an emergency measure to avoid this, there is a method of winding the cable loosely when first winding it, but if you wind it too loosely, it is likely to become misaligned, and
Wrinkles are also likely to occur. The object of the present invention is to provide an oil-immersed electrical insulated cable covered with a polymethylpentene film that overcomes the above-mentioned drawbacks. [Disclosure of the invention] In order to achieve the above object, the present invention has the following configurations: a density of 0.83 g/cm ³ or more, a strength ratio in both axial directions (longitudinal tensile strength/width direction tensile strength) of 5 to
This cable is characterized by being coated with an oil-immersed electrically insulating polymethylpentene film in the range of 15. The polymethylpentene mentioned here has a density of
It has 0.83 or more, preferably 0.84 or more,
The melt index is in the range of 0.1 to 40 g/10 minutes, preferably 0.5 to 30 g/10 minutes. If the density is lower than the above, swelling due to insulating oil will increase, which is not preferable. Furthermore, if the melt index is smaller than the above range, the swelling caused by the insulating oil will increase, and conversely, if it is larger than the above range, the amount eluted into the insulating oil will increase, causing an increase in the viscosity of the insulating oil. This is not desirable because it causes The strength of the film used in the cable of the present invention in both axial directions, that is, the value obtained by dividing the tensile strength in the longitudinal direction of the film by the tensile strength in the width direction, is in the range of 5 to 15, preferably 7 to 12. is necessary. If this strength ratio is smaller than this range, swelling due to insulating oil will increase. This is due to the following reason. Generally, when a plastic film is manufactured using a rolling roll, the film is rolled in the longitudinal direction, and the tensile strength in the longitudinal direction changes depending on the rolling ratio. On the other hand, the tensile strength in the width direction does not change significantly. Therefore, the strength of the film in both axial directions essentially means the strength in the longitudinal direction. Moreover, the fact that the strength in the longitudinal direction is high means that there are fewer amorphous portions existing between the crystals. On the other hand, swelling is a phenomenon in which oil invades the amorphous portions existing between crystals and breaks the bonds between the crystals (that is, a phenomenon in which the thickness increases). Therefore, the fact that the strength ratio in both axial directions is small, that is, the tensile strength in the longitudinal direction is small, means that there are many non-crystalline parts between the crystals, which means that there is more oil intrusion and swelling becomes large. That's why. On the other hand, if it is larger than this range, the difference in properties depending on the direction within the film plane becomes too large, resulting in significantly poor workability when winding the insulating layer (for example, when winding, elongation occurs). (The film may wrinkle easily, or tear easily.) Next, an example of a method for manufacturing the film used in the cable of the present invention will be described. Polymethylpentene resin is melt-extruded and extruded from a die into a sheet, which is then wound around a cooling drum and cooled and solidified. This polymethyl pentene sheet was inserted between a set of rolling rolls, and the rolling magnification (the value obtained by dividing the sheet thickness before rolling by the sheet thickness after rolling) was 5 to 12 times.
Preferably, it is rolled so that it becomes 7 to 10 times its size. Thickness of polymethylpentene film sheet
The reason for limiting the thickness to 70 μm to 300 μm is that if it is thinner than 70 μm, it will be difficult to obtain the mechanical strength necessary for cutting the sheet and winding the cut tape as an insulating layer, which will not only significantly reduce work efficiency, but also cause OF This is because the necessary strength cannot be maintained even when the cable is bent after being made into a cable, and abnormalities such as "wrinkles,""bumps," and "spots" may occur, which may reduce electrical performance. In addition, the necessary insulation thickness is obtained by winding tape, but if the tape is thin, the number of tape windings increases, which increases the size of the equipment, and also increases the work of installing, replacing, and connecting tapes, making the work more difficult. This will lead to poor performance and, in any case, to the detriment of economic efficiency. On the other hand, if it is thicker than 300 μm, the tape will be too stiff and will have difficulty conforming to the cylindrical shape when the tape is laminated as an insulating layer. There is a great possibility that abnormalities such as gap disturbances may occur and the electrical performance will deteriorate.Furthermore, the tape is wound in gaps as a cable insulation layer, and as the tape becomes thicker, the oil layer formed in the gaps becomes thicker. In OF cables, the electrical strength of the oil layer is lower than the insulating strength of the tape part, so it is undesirable for the oil layer, which is a weak point, to become significantly large. From the above, the film with a sheet thickness of 70 μm to 300 μm should be made with an appropriate width. Place the slit tape on the inside of the insulating layer (on the conductor side, where the electrical stress is severe), and use a thin tape that is mechanically weak but electrically superior on the outside (the electrical stress applied to the cable decreases as it goes outward). OF cables are manufactured by wrapping them in a thick tape that is somewhat weaker electrically but is mechanically strong (because it is strongly affected by bending).
In Dodeeylbenzene (abbreviated as DDB), it swells and becomes thicker as described above. Therefore, in order to maintain an appropriate film surface pressure as a cable, it is necessary to absorb the increase in thickness due to this swelling. Generally, the surface pressure of the film can be controlled by changing the tape winding tension of the tape winding machine, but this alone is not sufficient for tapes that swell. Therefore, the present inventors developed a technology in which the surface is roughened and the unevenness collapses when the tape swells, thereby absorbing the swelling of the tape. By varying the surface roughness of the film, we produced prototype cables, and by varying the surface pressure applied to the film in its film state to determine the necessary surface roughness, we found that a range of 1 to 50 μm was most suitable. If the surface roughness is less than 1μ, it will not be possible to sufficiently absorb the increase in thickness due to swelling of the tape in the insulating oil, and it will be impossible to control the surface pressure even if the tension of the tape winder is loosened. On the other hand, 50μm
If it is larger, the film itself may be damaged by roughening, and if the unevenness is too large, the unevenness of the tape will remain even after swelling, creating an oil gap between the tapes and causing a decrease in electrical strength. undesirable for this reason. Next, the results of electrical tests using model cables with only a film layer and a combination of film and kraft paper are as follows. Melt index 23g/10 minutes, density 0.83g/
cm ³ of polymethylpentene at 230℃ melt extrusion T
It was discharged in a sheet form from a letter-shaped mouthpiece. This molten sheet was wound around a cooling drum at 30°C and cooled and fixed to produce a sheet with a thickness of 1000μ. This sheet was inserted between a set of rolling rolls and rolled 10 times. The resulting film (100 μm) was
I cut it into mm width pieces and made tape. Wrap 10 pieces of tape around a ^150mm2 stranded conductor with a 1/3 wrap, and place it on top of this.
I wrapped three pieces of 0.2mm thick copper tape in 1/3 wraps. This cable (2.5 m) was immersed in alkylbenzene (viscosity 10 centistokes, 30°C) at 100°C for 48 hours. At the same time, a cable using a 100 μm tape made of the same polymethylpentene by melt extrusion was immersed. In addition, a cable made of rolled tape and 5 sheets of 100μ kraft paper (density 0.80, airtightness 5000 galley sec) alternately wound, and 1 sheet of kraft paper (density
0.80 g/cm ³ airtightness 5000 galleys/sec), and then the tape obtained by the above rolling process was wrapped twice with 1/3 laps, and this combination was applied 4 times to make a total of 12 tapes. were soaked in the same way. After winding these four types of cables around a 50cm diameter drum at room temperature, an impulse destruction test was conducted. Table 1 shows the ratio to the breaking value of cables using extruded films.

[Table] The results show that cables using rolled film have a large failure value, and when kraft paper is used in combination, the impulse strength increases even more. Next, a cable with 5 sheets of the above-mentioned kraft paper spread over the conductor and 5 sheets of rolled film spread over the conductor, and a cable with 5 sheets of rolled film spread over the conductor. A total of four types of cables were made and the same tests as Sample 1 were conducted at the same time as the above sample 1. The results are shown in Table-2.

[Effect of idea]

The cable of this invention is based on the density of the polymethylpentene film used in the cable, the strength ratio in both axial directions, the roughening of the polymethylpentene film, and the skillful combination of the polymethylpentene film and kraft paper. This results in a cable with the following excellent features. (1) Less swelling due to insulating oil. (2) Good flow of insulating oil between the insulating layers. (3) Excellent mechanical properties as an insulating layer and workability during winding. (4) The insulating layer is less likely to tighten or loosen. (5) Excellent dielectric loss tangent, dielectric constant, and breakdown voltage characteristics. (6) Less polarity effect. (7) Optimal cable design is possible by combining economic efficiency and electrical performance. Therefore, the oil-immersed power cable of the present invention is a power cable with excellent economic efficiency, mechanical properties, and electrical properties, and has a wide range of applications from EHV to UHV class.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an oil-immersed insulated power cable. FIGS. 2-A to 2-C are cross-sectional views showing examples of the insulating structure of the present invention, and are schematic enlarged views of the Z portion in FIG. 1. DESCRIPTION OF SYMBOLS 1...Oil passage, 2...Conductor, 3...Oil-immersed insulating layer, 4...Metal sheath, 3a...Polymethylpentene film layer, 3b...Kraft paper layer.

Claims (1)

[Scope of claims for utility model registration] (1) Density 0.83g/ ^cm3 or more, strength ratio in both axial directions (longitudinal tensile strength/width direction tensile strength) 5 to 15
1. A power cable comprising an insulating layer having a polymethylpentene film layer having a thickness of 70 μm to 300 μm, and impregnated with insulating oil. (2) The power cable according to claim (1) of the utility model registration, wherein the insulating layer is composed of polymethylpentene film and kraft paper. (3) The power cable according to claim (1) or (2) of the utility model registration, characterized in that the surface roughness of one or both sides of the polymethylpentene film is in the range of 1 to 50 μm. (4) The power cable according to claim (2) or (3) of the utility model registration, characterized in that polymethylpentene film and kraft paper are alternately wound. (5) The power cable according to claim (2) or (3) of the utility model registration, characterized in that it is alternately wound with two sheets of polymethylpentene film and one sheet of kraft paper. (6) The power cable according to claim (1), wherein the insulating layer is entirely composed of a polymethylpentene film layer. (7) The power cable according to claim (6), wherein the polymethylpentene film has a surface roughness of 1 to 50 μm on one or both sides. (8) Scope of utility model registration claims characterized by the use of raw paper as kraft paper, paragraph (2) or paragraph
Power cables described in paragraph (4) or (5).