JPH0354403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overhead power transmission line that can suppress sag and a method for manufacturing the same.

BACKGROUND OF THE INVENTION With the recent increase in demand for electric power, methods have been put into practice that attempt to achieve large-capacity power transmission by replacing steel-core aluminum stranded aluminum wires with heat-resistant aluminum alloys and increasing the maximum operating temperature of the wires. As a result, the operating temperature of conventional electric wires has been reduced from 90℃ to 150℃ to 200℃.
Alternatively, it has become possible to raise the temperature to 230 degrees Celsius, making it possible to transmit large amounts of power, but the higher operating temperature causes an increase in the sag of the wires due to the rise in temperature, making it necessary to make the towers taller. Moreover, when existing steel towers are used, this increased sag creates a new problem in that the long-awaited allowable capacity cannot be fully utilized. For this reason, a method was adopted in which the overhead wire tension was shared only with the steel core with a low coefficient of linear expansion, thereby minimizing the increase in sag.Gap wires, rotating loose wires, roll compression wires, etc. were proposed and put into practical use. has been done.

FIG. 2 is a sectional view of a known overhead power transmission line 10, in which aluminum wires 2 are twisted around the outer periphery of a steel core 1. In this case, the coefficient of linear expansion of steel core 1 is 11.5×10 ^-6
and that of aluminum wire 2 is 23×10 ^-6 , and the conventional steel core aluminum stranded wire shows a composite value of these, which is almost
It will be about 20×10 ^-6 . Therefore, it can be seen that if the tension can be shared only by the steel core, the increase in sag can be significantly suppressed.

Conventional techniques such as the above-mentioned gap-type electric wires, rotary loose electric wires, and roll-compressed electric wires required special work to be carried out during the wire tensioning process or after the wire extension, which caused major problems in overhead line construction. On the other hand, as a means to solve this problem, JP-A No. 53-103052
There is a technique disclosed in the publication No. That is, the twisting direction of the aluminum wire of the steel core aluminum stranded wire is a mixed twist of S twist and Z twist, and by giving the aluminum wire an extra length with respect to the effective length of the electric wire, it is possible to suppress the slackness. .

However, the work of mixing and twisting the S twist and the Z twist at a predetermined ratio is extremely difficult because it involves reversing the twist direction, and the aluminum wire tends to be damaged at the part where the twist direction is reversed, making it difficult to handle it. The disadvantage is that it is inconvenient.

An object of the present invention is to provide an overhead power transmission line that does not have such problems and can more simply and reliably suppress slack, and a method for manufacturing the same.

Hereinafter, embodiments of the present invention will be described based on the drawings. As shown in _FIG . As shown in part _P2 , the twist pitch is different in size. To manufacture such an electric wire 10, when twisting the aluminum wires around the steel core 10 in a fixed direction, the rotational speed of the wire twisting machine that twists the aluminum wires must be adjusted while maintaining the wire take-off speed constant. If the rotational speed is changed, that is, the rotational speed is made faster, slower, or stopped in some cases, the pitch changes in size depending on the rotational speed, making it easier to obtain the desired electric wire 10. can.

If tension is applied to the electric wire 10 configured in this way, vibration is applied, etc. to make the twist pitch uniform in the longitudinal direction, the aluminum wire will have extra length and slack, and the overhead wire will become loose. The tension is now shared only by the steel core, without being shared by the aluminum wire.

By the way, when the core diameter of the stranded wire (referring to the diameter of the circle formed by connecting the center points of each strand in the outermost layer of the stranded wire) is D, and the twist pitch is P, the strands per pitch are The length X can be expressed by the following formula.

X=√() ² + ² Now, let us schematically consider the case where the first half of the length of 2P is twisted with P=10D, and the second half is not twisted. P
If the length of the aluminum wire at the = 10D part is X ₁ , then from the above formula, X ₁ = 1.0482P, and the length of the aluminum wire at the untwisted part is
If X ₂ , then X ₂ = P, so the length of aluminum wire X ₁ for the above 2P is the sum of X ₁ (1.0482P) and X ₂ (P), that is, 2.0482P, and per pitch. The average strand length X ₃ is 1.0241P.

On the other hand, in another part, the length of 2P is twisted at P = 20D, and the length of aluminum wire per 1P at this time is X _0. From the above formula, X ₀ = 1.01226P (Length of 2P 2.02452P).

Therefore, when comparing the length of the aluminum wire per pitch in the above two twisted configurations, that is, the configuration with different twisted pitches and the configuration with the same pitch, X ₃ −X ₀ = 0.01184P, and the length per pitch The length of the aluminum wire in the former becomes longer by 1.184%. This will give slack to the aluminum wire.

The above calculation is of course calculated schematically, and differs from the actual case, but it should help you understand why the aluminum wire becomes slack when the twist pitch is varied.

When the twist pitch is varied in size in this way, there is no problem in the inner layer, but in the outermost layer the strands become slightly slack, so it may be necessary to wrap them with restraining tape or the like. Then, this tape can be unwound after the overhead wire is finished.

As described above, according to the electric wire according to the present invention, there is no need for a special structure such as a conventional gap type, and there is no need to use special methods such as rotation or compression.
During the manufacturing of electric wires, slack is created in the aluminum stranded wire layer, and after that, the slack can be suppressed by simply connecting the wire to the wire.This simplification is revolutionary, and its effectiveness is significant. There are some things that are worth mentioning.

[Brief explanation of drawings]

FIG. 1 is a partial sketch of the electric wire according to the present invention, and FIG.
The figure is a cross-sectional view of a steel-core aluminum stranded wire. 1: Steel core, 2: Aluminum wire.

Claims (1)

[Scope of Claims] 1. In a steel-core aluminum stranded wire in which aluminum wires are twisted in a constant direction around the outer periphery of a steel core, the aluminum wires are twisted with different twisting pitches in the longitudinal direction of the stranded wires. An overhead power line. 2. When twisting the aluminum wires on the outer periphery of the steel core in a constant twisting direction, the twisting pitch of the aluminum wires is changed by changing the rotational speed of the twisting machine that twists the aluminum wires while keeping the stranding speed constant. A method for manufacturing overhead power transmission lines in which stranded wires vary in size in the longitudinal direction.