JPH0336252B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a stranded conductor in a power cable, particularly a stranded conductor in which strands shaped in a cross-sectional shape or in a fan shape are twisted or assembled.

Generally, so-called round wires with a circular cross section are used for the stranded conductors of power cables, and the occupation rate of the completed stranded conductors after twisting or gathering is as follows:
It is as low as 78.5% (equivalent to π/4), and as a result, the outer diameter of the conductor becomes large, making it extremely uneconomical, especially in power cables and the like where a large amount of coating is applied on the conductor.

Conventionally, the following two methods have been used to overcome this problem.

First, the first method involves twisting or gathering round wires to form a predetermined stranded wire conductor, and then compressing this conductor using dies or rolls, thereby improving the space factor. This contributed to the The space factor with this can be improved to about 90% (approximately 88 to 92%). At this time, the compression ratio corresponding to the improvement in the space factor, that is, the reduction in the area within the envelope, is approximately 10
~15%. It is known from experience that even if an attempt is made to increase the compression ratio any further, the strands simply extend to the rear of the die or roll, and this does not lead to an improvement in the space factor.

The above-mentioned products are disclosed in, for example, Japanese Patent Publication No. 7-2074 and Japanese Patent Application Laid-open No. 50-147585, but in these products, the space factor after compression processing is This could only be improved to about 90%, and there was a limit to how compact this product could be.

Therefore, the following second method has been proposed to overcome the above-mentioned limitations on improving the space factor.

That is, the second method, as illustrated in FIG. By gathering or twisting the wires, a stranded wire conductor with a significantly improved space factor can be obtained. According to this, the occupancy factor is approximately 95~
This can be dramatically improved to 98%, which can be compared to the first thing above, but on the other hand, after the stranded wire conductor is completed, the formed wires may become loose or loose, resulting in poor conductor connection. or have a negative impact on
In addition, the edges of the formed strands sometimes have a fatal adverse effect on the coating applied to the erect conductor, so that the practical application of power cables using this stranded conductor has been delayed.

The method according to the second method is, for example,
It is disclosed in Publication No. 34-6337.

However, in the method disclosed in the same publication, a round wire with a circular cross section is passed through a deformed die to be preformed into a final square shape as a completed compressed conductor. Thereafter, the wires formed by the round die are assembled to obtain a round conductor with a high space factor, and the shaping and assembly of the wires are performed in the same process.

The round conductors obtained by this method are assembled after the round wires are shaped into a final completed form, so no special processing is applied after the round conductors are assembled. Therefore, the advantages that can be enjoyed by this method are limited to improving the space factor and preventing the strands from collapsing.

As explained above, the first method that improves the space factor of stranded conductors is the first method, which is obtained by gathering (twisting) round wires and then compressing them. A second method has been proposed in which a stranded wire conductor is obtained by assembling (twisting) shaped wires that have been previously shaped into a flat, fan-shaped, or square shape, and from the viewpoint of improving the space factor. The stranded wire conductor made by the second method is overwhelmingly superior.

Furthermore, according to this stranded wire conductor, since the formed wire has a so-called wedge shape, it can be structured to have a hollow part 10 as shown in FIG. 1, and if this is used as an oil passage, the conductor itself can be In order to secure the oil passage, the spiral pipe for securing the oil passage was omitted.
OF cable can be provided.

However, despite having the above-mentioned excellent features, as mentioned earlier, in the completed stranded wire conductor, the formed strands may become loose or loose due to the influence of residual stress in the formed strands. This may make the conductor connection work difficult, or, as illustrated in FIG. 6, the edge 1e of the formed wire 1 will stand up and form a protrusion on the coating applied to the conductor. There was a defect that had a fatal adverse effect on the coating. In particular, when this type of stranded conductor is used in high-voltage power cables, defects such as raised edges in the formed strands become irregularities in the electrodes, causing electric field concentration and causing electrical damage to the insulation coating applied over the stranded conductors. This may significantly reduce the insulation strength.
This was a major factor preventing its practical use as a power cable. Therefore, conventional power cables have been put into practical use mainly using stranded conductors according to the first example.

The present invention has been made based on the above circumstances, and is directed to a stranded wire conductor in which shaped wires having a flat or fan-shaped cross section are assembled or twisted, that is, a stranded wire conductor obtained by the second method. The stranded wire is based on its use as a conductor of power cables, and is improved to prevent defects such as loosening and laughter in the stranded wire conductor obtained by the second method, as well as to prevent the occurrence of edges. By what the conductor does,
The aim is to promote the practical use of power cables that can be made even more compact. Therefore, this point is the problem (object) to be solved by the present invention.

According to the present invention, as a result of tireless trial and error and efforts by the inventors of the present invention, they have finally found a solution that can eliminate the defects in the stranded wire conductor made of the shaped strands.

The method is that a stranded wire conductor constructed by twisting or assembling shaped wires with a substantially flat or fan-shaped cross section is sufficient from the point of view of the space factor, and there is no need for anything more. Breaking away from the common sense that there is no need for additional processing, we intentionally apply slight compression to each formed strand after it has been twisted or assembled to improve the space factor, causing plastic deformation to occur in each formed strand. be.

Such mild compression is different from conventional compression processing performed from the perspective of improving the space factor of stranded wire conductors using round strands, and it is not possible to improve the space factor that flat or fan-shaped strands already have. This is done from the viewpoint of eliminating residual stress in the formed wire without affecting the significance of the wire. Therefore, processing is performed on the formed wire after satisfying two contradictory conditions: retaining its original shape even if plastic deformation is applied to it.

As for light compression that satisfies the above conditions, the inventors have made various studies and, after repeated failures, have discovered for the first time that it is effective only within a certain specific range.

In other words, the degree of compression is as follows, assuming that the formed wires are compressed by twisting or gathering.
(1), (2) and (3).

(1) The outer diameter of the stranded conductor after compression (see d' in B in Figure 2) is reduced by 0.1 to 2.5% compared to the outer diameter before compression (see d in A in Figure 2). Range (2) The area within the envelope of the stranded wire conductor after compression processing, that is,
Area hatched in d of Figure 2
S ₀ ′ is the inner envelope area before compression processing, that is, with respect to the hatched surface line S ₀ in d of Fig. 2,
Range of 0.2 to 5.0% reduction (3) Actual conductor cross-sectional area of stranded wire conductor after compression processing ΣS′=
S ₁ ′+S ₂ ′+S ₃ ′+…Sn′ (see Fig. 2) is the actual conductor cross-sectional area before compression ΣS=S ₁ +S ₂ +S ₃ +…Sn (second
1.0 to 5.0% reduction range compared to (see E in the figure).

The optimum degree of compression selected within such a specific range varies depending on the configuration, shape, and material of the formed wire.

Therefore, regardless of the composition, shape, or material of the formed wire, the degree of compression falls below the range where the conductor outer diameter decreases by 0.1%, the conductor envelope inner area decreases by 0.2%, and the conductor actual cross-sectional area decreases by 1.0%. If it is too small, the residual stress in each formed strand cannot be sufficiently eliminated, and even if loosening and breakage prevention is achieved, edge standing still tends to occur.

On the other hand, if the degree of compression exceeds the range where the conductor outer diameter is reduced by 2.5%, the conductor envelope inner area is reduced by 5.0%, and the conductor actual cross-sectional area is reduced by 5.0%, and the degree of compression is increased to the extent that it is further reduced, work hardening will complete the process. The bending rigidity of the stranded conductor increases, and the flexibility originally required of the cable becomes insufficient, resulting in extremely poor handling when bending or the like.

As described above, the degree of compression in the present invention is such that the compression rate is the same as the outer diameter of the stranded wire conductor for the purpose of improving the space factor, as in the stranded wire conductor obtained by the first conventional method. It is impossible for the reduction rate to exceed 5 to 8%, the area within the envelope to be reduced by 10 to 15%, and the reduction rate for the actual cross-sectional area of the conductor to exceed 5%, which has been independently determined.

In addition, in order to ensure that the formed wire does not easily undergo plastic deformation due to mild compression processing, and that even if compression becomes excessive, the rigidity of the completed conductor does not increase significantly. It is desirable to use an annealed material as the shaped wire.

Specific means for applying mild compression include hard dies, rolls, or other means.

An embodiment of the present invention will be described with reference to FIGS. 3 and 4. In this embodiment, the shaped wires 21, 2
This is the case of a so-called hollow twisted conductor which has two layers formed by twisting or aggregating layers 2, 23, . . . and has a hollow portion 200.

That is, formed wires 21, 22, 23 having a fan-shaped cross section
... are twisted together, and a predetermined twisted wire conductor 20 is formed while forming a hollow portion 200 in the center that can be used as an oil passage due to their wedge effect.

After twisting, each formed wire 21, 22, 23... is compressed to a degree selected from the range specified in (1), (2), and (3) above. The residual stress in each formed strand is eliminated by applying plastic deformation to each formed strand while maintaining its original shape.

An example of a specific means for doing so is shown in FIG. That is, the formed wires 21, 22, 23... having a fan-shaped cross section are twisted from bobbins 41, 42, 43... equipped in a twisting machine (not shown), and are bundled into a metal die 40. After each formed wire is twisted in the die 40, it is immediately subjected to slight compression processing in the metal die 400 within the range specified in (1), (2), and (3) above to undergo plastic deformation. It is something that will be done. Once the first layer configured as described above is constructed, the second layer is formed on top of the formed wire 210 having a fan-shaped cross section,
220, 230... are focused by another metal die 41 and twisted on the circumference of the first layer of twisted strands, and immediately thereafter, by the metal die 410, the above-mentioned (1), (2) and (3), which undergoes slight compression processing and plastic deformation within the range specified in (3).

FIG. 3 shows a stranded wire conductor 20 manufactured in this way, and on its circumference an internal shielding layer S ₁ of shielding carbon paper, an insulating layer Z of insulating paper, shielding carbon paper, and metal. External shielding layer S ₂ with synthetic paper
This is an example in which an OF cable is constructed by sequentially applying a metal sheath SH and a sheath B. According to such an OF cable, there is no looseness or looseness of the formed strands, so even if the conductor 20, which is exposed by stripping off all the covering on the conductor, is cut, the strands will not fall apart and the conductor Connection work can be easily performed. In addition, since the edges of the formed strands are eliminated, there is no need to form protrusions that would cause electric field concentration on the coating, especially on the insulating layer Z, and the insulating layer Z can maintain a predetermined electrical insulation strength. becomes possible.

In order to confirm the above-mentioned effects, the inventors used a copper fan-shaped wire with a conductor cross-sectional area of 630 mm ²
Two types of 130KVOF cables (oil-immersed paper insulated oil-filled power cables) using hollow conductors were manufactured: one based on the above example and one using a conventional method. And both of them are shielding carbon paper,
Insulating paper (9mm thick), shielding carbon paper, and metal chemical paper were applied in sequence, and after vacuum drying, a lead coating was applied, and after lubricating the lead coating with insulating oil, a metal tape was wrapped to reinforce the internal pressure. Furthermore, a polyvinyl chloride coating was applied as an anti-corrosion layer.

In order to confirm the electrical insulation strength of these cables, a dielectric breakdown test using lightning impulse voltage was conducted. The test method was to apply a negative lightning impulse voltage from 400KV to 50KV three times at room temperature. The results of the test were as follows.

Conventional hollow conductor → Dielectric breakdown at 550KV second time.

Due to the hollow conductor of the present invention → dielectric breakdown at 800KV for the third time.

As is clear from the above results, it was confirmed that the electrical insulation strength of the power cable using a hollow conductor according to the present invention was improved by about 45% compared to the conventional cable. This is because the insulation strength against lightning impulse voltage required for 132KVOF cable is generally 650KV.
It was confirmed that the cable according to the present invention fully satisfies the requirements and can be put to practical use.

In order to confirm why the above-mentioned difference in electrical strength occurs, we disassembled the two types of cables mentioned above and carefully observed their internal structures. As a result, in the conventional conductor, not only the wires were slightly loose and loose, but also the formed wire 1 tended to have an edge 1e as shown in Fig. 6, and the insulation The breaking point occurred at the edge of the formed wire. This is considered to be a fatal adverse effect caused by residual stress not completely disappearing in the completed stranded wire conductor. On the other hand, the conductor according to the invention includes:
Of course, there was no evidence of any looseness or looseness between the strands, and there was also no sign that the edges of the formed strands were standing.

Furthermore, when using the cable of the present invention to expose and cut the conductor for use in conductor connection work, there was no phenomenon that each formed wire became loose or unraveled, and the rigidity was It was also not found that handling would be significantly difficult. In addition, the specified conductor connection work was able to proceed smoothly.

What can be said from these results is that compared to conventional cables, the cable according to the present invention, that is, the molded wires are subjected to a slight compression process in a specific range in the process of gathering (twisting) them, and each molded wire is It was confirmed that residual stress in the strands could be completely eliminated only by causing mild plastic deformation, and the importance of the effect of mild compression processing according to the present invention was recognized.

Because of this, the hollow part of the self can be used as an oil passage without the need for a spiral pipe, and the space factor can be reduced.
We were able to successfully create an OF cable that fully exploits the excellent features of this type of conductor, with a ratio of 95 to 98%, and the economic effects can be said to be extremely large.

In the above embodiments, hollow conductors have been described, but the present invention is also applicable to solid conductors. That is, as an example is shown in FIG. 5, the above-described formed wires are twisted and arranged around a central round conductor 500 having a circular cross section as an axis. In this embodiment, the same elements as those in FIG. 3 are referred to by the reference numerals assigned thereto, so please refer to the above description for the characteristics of these elements.

As explained above, according to the method for manufacturing a power cable conductor of the present invention, a stranded wire conductor is produced in which formed wires having a flat or fan-shaped cross section are assembled or twisted, that is, the second method described at the beginning. Based on the fact that the stranded conductor obtained by the method is used as a cable conductor,
And of course, it is possible to prevent defects, that is, loosening and laughter, in the stranded conductor obtained by the second method.
This is the first time that the intended purpose of creating a practical power cable that can be made even more compact has been achieved by using a stranded conductor that has been improved to prevent the formation of edges.
This makes it possible to provide an economical power cable, and the practical benefits can be said to be truly great.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional explanatory diagram showing an example of a stranded wire conductor made of formed wires having a fan-shaped cross section, and A, B, C, D, H and F of FIG. 2 are manufactured according to the present invention. A cross-sectional explanatory diagram showing the state before and after compression of a stranded conductor by a cross-sectional fan-shaped wire in the method, and FIG. 3 is an example of a power cable employing a stranded conductor manufactured according to the present invention. 4th cross-sectional explanatory diagram showing
The figure is an explanatory diagram showing an example of assembly and mild compression processing using fan-shaped wires in the manufacturing method of the present invention.
The figure is an explanatory cross-sectional view showing an application example of a power cable employing the stranded conductor manufactured according to the present invention, and FIG. 6 is an explanatory cross-sectional view showing the situation after the fan-shaped wires are assembled. . In the figure, 21, 22, 23 are shaped wires with a fan-shaped cross section, 20 is a twisted wire conductor, 200 is a hollow part used as an oil passage, Z is an insulating layer, 40, 41 are assembled dies, 400, 410 is a metal die for mild compression.

Claims (1)

[Claims] 1. When twisted or assembled formed wires having a flat or fan-shaped cross section to form a stranded conductor, the stranded conductor can be further compressed slightly. Production of a stranded conductor for a power cable, characterized in that a molded wire is subjected to slight plastic deformation, and the degree of said slight compression is within the following ranges (1), (2), and (3). Method. (1) The outer diameter d′ of the stranded conductor after compression is the same as d before compression.
(2) Range in which the area within the envelope of the stranded conductor after compression S ₀ ′ decreases by _0.2 to 5.0% compared to that before compression (3) After compression Actual conductor cross-sectional area of stranded wire conductor ΣS′=S ₁ ′+
S ₂ ′+S ₃ ′+…+Sn′ is that before compression ΣS=S ₁ +S ₂
+S ₃ +...Range of 1.0 to 5.0% reduction relative to +Sn.