JPH0538614U - Optical fiber unit - Google Patents

Abstract

(57) [Summary] [Structure] The optical fiber unit 9 has a structure in which the optical fiber core wire 1 is covered with a sheath 8 made of linear low-density polyethylene. Then, this unit is pneumatically fed and inserted into the pipe arranged in parallel with the power cable. [Effect] The sheath 8 has a small increase rate of the coefficient of friction with the pipe and a small decrease rate of its rigidity even when the temperature of the pipe becomes high due to the heat received from the power cable. Therefore, the resistance when air is pneumatically fed is small, and the pressure feeding characteristics are excellent.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to an optical fiber unit that is pneumatically fed and inserted into a pipe.

[0002]

[Prior Art]

 When laying an optical fiber cable along a certain route, in addition to the one that is laid while pulling the pre-formed cable, the force of compressed air is used for the pipe that is previously placed along the laying route. There is a configuration that inserts an optical fiber unit. Some optical fiber cables, which are installed in parallel on the power cable line and used for information transmission between substations, have such a configuration for convenience of maintenance and exchange.

FIG. 3 shows a cross-sectional view of this type of optical fiber unit and the installed state. In the figure, a plurality of optical fiber core wires 1 are covered with a sheath 3 after being pressed and wound to form an optical fiber unit 4. On the other hand, the optical fiber unit 4 is configured to be inserted into a pipe 6 arranged along a power cable 5 made of, for example, a triplex CV cable. When the power cable 5 is a CV cable, the maximum conductor temperature used is about 90 ° C., and the pipes 6 arranged in parallel with the power cable 5 are also heated to about 70 ° C., for example. Even under such a high temperature, the optical fiber unit 4 as described above may be pneumatically fed into the pipe 6.

[0004]

[Problems to be solved by the device]

 However, when pneumatically feeding the optical fiber unit 4 under the high temperature as described above, the following problems have conventionally occurred. First, the sheath 3 of the optical fiber unit 4 is conventionally composed of an extruded coating layer of, for example, low density polyethylene or expanded polyethylene. Here, when the temperature of the pipe 6 rises, the coefficient of friction between the pipe 6 and the sheath 3 increases.

FIG. 4 shows the coefficient of friction with the optical fiber unit 4 when the pipe 6 is made of polyethylene. As shown in the figure, for example, low density polyethylene (LDPE) has a friction coefficient of 0.25 with a polyethylene pipe at 20 ° C. However, when the temperature of polyethylene pipe rises to 70 ° C, the friction coefficient increases to 0.84, which is more than about three times. This increases the resistance when the optical fiber unit 4 is inserted into the pipe 6 by the compressed air. For this reason, it becomes difficult to carry out pressure feeding over a long distance, and there is a problem that the working time until the optical fiber unit 4 is completely inserted into the pipe 6 becomes longer.

In order to solve such a problem, it can be considered that the material used for the sheath 3 of the optical fiber unit 4 is high density polyethylene (HDPE). In this case, as shown in FIG. 4, the coefficient of friction is 0.20 at 20 ° C., and the coefficient of friction is 0.33 at 70 ° C., which is a characteristic that the increase in the coefficient of friction is relatively small. However, when the sheath 3 of the optical fiber unit 4 is made of high density polyethylene, there is a problem that so-called microbending is likely to occur this time. That is, during manufacture of the optical fiber unit, the sheath 3 is extruded and coated on the core wire 1. At that time, a certain strain occurs, and the strain remains in the sheath even after cooling. However, the action of alleviating this strain works for a long time, and the sheath 3 contracts in the longitudinal direction. As a result, so-called microbending occurs.

FIG. 5 shows an explanatory diagram of comparison of rigidity of units. As shown in the figure, low-density polyethylene (LDPE) has a rigidity of 8. 0, and when the temperature rises to 70 ° C., its rigidity decreases to 2.5. On the other hand, high-density polyethylene (HDPE) has a high rigidity at 20 ° C. of 18, and reaches about 4.8 at 70 ° C. The unit is kilogram / square millimeter. In this way, high-density polyethylene has high rigidity and has less undulations when it is inserted into the pipe 6, so it has the advantage of less friction when laying, but considering the increase in transmission loss due to the occurrence of micro-bending, However, there was a problem that it could not be used as it was. The present invention has been made in view of the above points, and an object thereof is to provide an optical fiber unit which is free from the risk of microbending and has better layability.

[0008]

[Means for Solving the Problems]

 An optical fiber unit of the present invention is pneumatically fed and inserted into a pipe installed in parallel with a power cable, and comprises an optical fiber core wire and a sheath coated on the core wire. It is characterized by being composed of low-density polyethylene.

[0009]

[Action]

 This optical fiber unit has a structure in which the core of the optical fiber is covered with a sheath made of linear low-density polyethylene. Then, this unit is pneumatically fed and inserted into the pipe arranged in parallel with the power cable. The sheath has a small increase in the coefficient of friction with the pipe and a small decrease in its rigidity even when the temperature of the pipe becomes high due to the heat received from the power cable. Therefore, the resistance when air is pneumatically fed is small, and the pressure feeding characteristics are excellent.

[0010]

【Example】

 Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 is a sectional view showing an embodiment of the optical fiber unit of the present invention. As shown in the figure, the optical fiber core wire 1 is formed by applying a presser winding 2 and then covering a sheath 8 made of linear low-density polyethylene. Such an optical fiber unit 9 is pneumatically fed and inserted into a pipe 6 made of, for example, polyethylene, which is laid along the power cable 5 as described with reference to FIG. When the optical fiber unit is configured as described above, the sheath 8 of the unit has an increase in friction coefficient at high temperature sufficiently lower than that of low density polyethylene or the like. For example, at 20 ° C, the friction coefficient is about 0.25, but at 70 ° C it is about 0.65, and although the increase rate is slightly higher than that of high-density polyethylene, the increase rate is less than that of low-density polyethylene. Further, there is little decrease in rigidity at high temperatures. That is, at 20 ° C, it is 8 kilograms per square millimeter, whereas at 70 ° C, it is about 4 kilograms.

Therefore, as shown in FIG. 2, in the case of the conventional optical fiber unit 4 shown in (a), the unit undulates at a small pitch inside the pipe 6, but the optical fiber unit 9 of the present invention is As shown in FIG. 2B, the pitch of the waviness becomes long. As a result, the area in which the unit 9 is in contact with the pipe 6 is also reduced, and the increase in resistance during pneumatic feeding at high temperature is suppressed to a sufficiently low level, including the fact that the increase rate of the friction coefficient is small. Furthermore, when such a linear low-density polyethylene is used as a sheath, shrinkage strain is less than when high-density polyethylene is used, and the increase in transmission loss due to micro-bending can be suppressed sufficiently low. .. The sheath 8 of the optical fiber unit as described above may have a structure in which linear low-density polyethylene is extrusion-coated as it is, or may be foamed and then extrusion-coated. .

[0012]

[Effect of the device]

 In the optical fiber unit of the present invention described above, the sheath coated on the optical fiber core wire is made of the linear low-density polyethylene even when the optical fiber unit is installed side by side in the power cable and pneumatically fed into the pipe where the temperature becomes relatively high. As a result, the friction coefficient does not increase at high temperatures and the rigidity does not decrease so much that the pumping characteristics do not deteriorate significantly compared to room temperature. Therefore, very good characteristics can be obtained for this type of cable.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an optical fiber unit of the present invention.

2A and 2B show a comparison between a conventional optical fiber unit and a conventional optical fiber unit when installed, FIG. 2A is a longitudinal sectional view of a pipe showing a conventional optical fiber unit installed state, and FIG. 2B is an optical fiber unit of the present invention. It is a pipe longitudinal cross-sectional view showing a laid state.

FIG. 3 is a cross-sectional view of a conventional optical fiber unit.

FIG. 4 is an explanatory diagram showing a comparison of a friction coefficient between a polyethylene pipe and an optical fiber unit.

FIG. 5 is an explanatory diagram of comparison of rigidity rates of units.

[Explanation of symbols]

 1 Optical fiber core wire 2 Presser winding 6 Pipe 8 Sheath 9 Optical fiber unit

Claims (1)

[Scope of utility model registration request] 1. A power cable, which is inserted into a pipe provided in parallel by pneumatic feeding, and comprises an optical fiber core wire and a sheath covered with the core wire, wherein the sheath has a straight chain and low density. An optical fiber unit made of polyethylene.