JPH0642333B2 - Optical fiber composite overhead ground wire - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in the structure of an optical fiber composite overhead ground wire.

[Prior art and problems] Optical fiber composite overhead ground wire housed inside optical fiber and overhead ground wire is used for communication by connecting to ultra high voltage transmission line by utilizing the property that optical fiber is not affected by electromagnetic effect. Since it is possible to omit the construction of the railroad, it has been widely put into practical use in recent years.

FIG. 1 shows an example of a well-known optical fiber composite overhead ground wire.
A structure in which a plurality of optical fibers 2 are twisted around the outer circumference of a core material 1 made of steel wire, FRP, aluminum or the like, and then a pipe 3 is covered, and a conductive strand 4 is twisted around the outer circumference of the pipe 3. There is.

In the optical fiber composite overhead ground wire configured as shown in FIG. 1, a particular problem is a large difference in mechanical strength between the conductive element wire 4 and the optical fiber 2. That is,
The conductive wire 4 is usually made of metal such as aluminum or aluminum-coated steel wire and has a high mechanical strength, but the optical fiber 2 is mainly made of glass and plastic, so the mechanical strength is much lower. If such a composite component is twisted and catenated under a considerable catenary tension, the optical fiber 2
Since a large tensile stress may be applied to this and an unexpected accident may occur, it is necessary to take some measures as a matter of course.

From such a meaning, the optical fiber 2 housed inside is made to have an extra length or is formed in a spiral shape so that a large load is not applied to the conductive wire 4, but There are some situations that are not always sufficient.

[Object of the Invention] In view of the above situation, it is an object of the present invention to provide a novel optical fiber composite overhead ground wire which does not receive a large tensile stress when the optical fiber composite overhead ground wire is installed. And

[Summary of the Invention] That is, the gist of the present invention is to set the twisting directions of the conductive strands arranged on the outer periphery of the pipe and the optical fibers accommodated in the pipe to the same direction, and further to set the conductive strands. , The twist pitch of the optical fiber is Pw, the core diameter of the twist layer is Dw, and the twist pitch of the optical fiber is P
f, where Dw is the core diameter of the twisted layer, it is configured to satisfy the relationship of Dw ² / Pw ≦ Df ² / Pf.

[Embodiment] An embodiment of the present invention will be described based on the optical fiber composite overhead ground wire of the structure shown in FIG.

When the optical fiber composite overhead ground wire is extended, it is commonly used to twist the conductive strand 4 in a direction in which the twist of the conductive strand 4 returns. By twisting the conductive strand 4, the optical fiber 2 housed in the pipe 3 is also twisted in the same direction at the same time.

First, assume that the twisting directions of the conductive element wire 4 and the optical fiber 2 are opposite to each other.

At this time, the twist pitch of the conductive strands 4 increases and the twist pitch of the optical fiber 2 decreases conversely, so that the actual length of the conductive strands 4 is extended with respect to the longitudinal direction of the ground line, and the optical fiber 2 is stretched.
Will be shortened. That is, two tensile stresses are applied to the optical fiber 2 due to the elongation due to the tightness of the twist and the elongation to the actual length of the ground wire caused by the elongation of the conductive element wire 4.
This tensile stress also deteriorates the transmission characteristics of the optical fiber and may cause a disconnection.

In order to provide an optical fiber composite overhead ground wire in which this tensile stress does not act on the optical fiber, the inventors twisted the conductive wire 4 and the optical fiber 2 into a ground wire in which the twisting directions are the same. Attention was paid to the case where the above was applied, and as a result, the present invention was accomplished.

It is considered that the conductive strands 4 and the optical fibers 2 are twisted in the same direction so that the amounts of change in the actual lengths of the conductive strands 4 and the optical fibers 2 when twisted are made equal. First, the conductive wire 4 in the initial state, that is, the state before being twisted
And the line length per pitch of the optical fiber 2 is l
If w and lf are given, it is given by the equation (1).

Here, Pw is the twist pitch of the conductive strand, Dw is the twist core diameter of the conductive strand, Pf is the twist pitch of the optical fiber, and Df is the twist core diameter of the optical fiber.

Next, the conductive wire 4 and the optical fiber 2 are twisted, and the wire lengths lw ′ and lf ′ per pitch of the conductive wire 4 and the optical fiber 2 after the twist pitch and the twisted amount are changed are ( It is given by the formula (2).

Here, εw is the pitch change rate of the conductive strand, εf is the pitch change rate of the optical fiber, Δw is the twist amount change rate of the conductive strand, and Δf is the twist amount change rate of the optical fiber.

Here, since it can be assumed that the conductive wire 4 is generally excellent in rigidity and that the wire length does not change, the following equation is established.

lw = lw ¹ (3) Further, assuming that the rate of change in pitch after twisting is the same between the conductive element wire 4 and the optical fiber 2, the following expression is obtained.

[epsilon] w = [epsilon] f (4) Since the ratio of the twisting amount change rate between the conductive element wire 4 and the optical fiber 2 after twisting is equal to that in the initial state, the following relationship is established.

Δw / Δf = Pw / Pf (5) The condition that the optical fiber tensile stress is not applied after the twisting is the formula (6).

lf = lf ′ (6) The following relational expressions are derived from the above expressions (1) to (6).

Dw ² / Pw = Df ² / Pf (7) The expression (7) is equal to the amount of change in the actual length that occurs when the conductive wire 4 is twisted in the direction in which the twist of the conductive wire 4 returns when it is aerial. This is a conditional expression for configuring that the tensile stress does not act on the optical fiber 2 due to the change in the actual length of the optical fiber 2. That is, since it can be said that the expression (7) is a boundary condition for achieving the object of the present invention, if the deviation from this condition is in the direction of causing the optical fiber 2 to laugh, then the tensile stress in the optical fiber 2 is reduced. Needless to say, you can avoid working. In other words, it is equation (8).

Dw ² / Pw ≦ Df ² / Pf (8) [Advantages of the Invention] As described above, according to the optical fiber composite overhead ground wire of the structure according to the present invention, the twisting of the conductive wire occurs when the overhead wire is used. On the other hand, the optical fiber is also twisted in the same direction so that the amount of change in its actual length is equal or it causes laughter in the optical fiber, so it is possible to completely avoid the tensile stress acting on the optical fiber, which is highly reliable. Information can be transmitted.

Furthermore, since the present invention clearly shows the necessary conditions therefor, it may be very useful in design, and its utility value is extremely large.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an optical fiber composite overhead ground wire. 1 ... Core material, 2 ... Optical fiber, 3 ... Pipe, 4 ... Conductive wire

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-154831 (JP, A) JP-A-57-122406 (JP, A) Actually open Sho-60-155115 (JP, U) Actual-open Sho-56- 3505 (JP, U)

Claims (1)

[Claims] 1. An optical fiber composite overhead ground wire in which a plurality of optical fibers are twisted and accommodated in a pipe accommodating chamber, and conductive wires are twisted around the outer circumference of the pipe. The twisting directions of the optical fibers are set in the same direction, and the twist pitch of the conductive wires is Pw,
The twist layer core diameter is Dw, and the twist pitch of the optical fiber is P
f, Dw ² / Pw ≦ Df, where D is the core diameter of the twisted layer
^2. An optical fiber composite overhead ground wire, characterized in that it is configured to satisfy the relationship of ² / Pf.