JPH03190015A - Power cable laid in duct - Google Patents

Abstract

PURPOSE:To form a power cable laid in a duct integrated with a sheath, by forming a filament material, wound around a cable core in spiral and capable of being pressed with the sheath. CONSTITUTION:A filament material 3 having a high rigidity and flexibility, for example, a metal steel wire, is wound around the periphery of a cable core 2 in spiral with a predetermined pitch, and this periphery is formed by integral extrusion molding and covering of the plastic sheath 4 to form a cable 1 laid in a duct. Consequently, a projection 5 is formed on the periphery of the spiral filament material 3, and since the filament material 3 is buried in the projection 5, the strength of the projection 5 is considerably stronger than in the case of integral formation only with the plastic sheath. Consequently, a danger that a pitch of the spiral projection is changed at the time of pulling the cable 1 into a duct is eliminated, and a snake can be expected in the duct.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a power cable installed in a conduit, and more particularly to a single-conductor power cable that tends to naturally generate snakes in a conduit.

[Prior art] In recent years, it has been common practice to draw in and install power cables using existing conduits, but in this case, there is often insufficient space in the entry hole, which places restrictions on the offset dimensions that can be set there. be. Therefore, thermal contraction of the offset portion at the entrance hole is suppressed and the power cable is snaked within the conduit to absorb the heat shrinkage of the power cable itself.

In general, as a means of giving the power cable itself a snake shape in a conduit, a filament is spirally wound around the circumference of the power cable body at a predetermined pitch, and when the power cable undergoes heat contraction, the filament is A well-known method is to help the electric cable form a snake state by winding it around itself.

Figure 3 shows an outline of such a power cable installed in a conduit.In the conduit P between the entrance hole MH and MH, the power cable C is passed in a straight line when being led in. The end of the power cable C is prevented from moving by a gripping device (not shown) at the conduit mouth, and protrudes from the end to enter the inlet M H+ , M
Junction box J, taking an offset shape within Hz,
J, is terminated.

An expansion/contraction suppressing device is attached to the offset portion of the electric cable C in the entrance holes M HI and M HR to suppress movement of the electric cable C due to thermal expansion and contraction.

S is a filament body spirally wound around the electric cable C in the conduit P at a predetermined pitch, and its presence causes a snake to occur in the electric cable C during thermal expansion and contraction.

By the way, if such a striatum S is simply wrapped around an electric cable C, the electric cable C will have a snake shape (<, therefore, various modifications have been made to the striatum S etc. .

For example, as disclosed in Japanese Patent Publication No. 39-20972, weights are connected to both ends of a filament wrapped around an electric cable, and tension is applied to the filament to generate snakes when the cable thermally expands and contracts. How to make it easier to wake up,
As disclosed in Japanese Patent No. 7-27641, a method has been proposed in which a wire body thickened in some places in the length direction is spirally wound around an electric cable, and the cable is supported by the thickened portion of the wire body. Ta.

[Problems to be Solved by the Invention] By the way, according to the method disclosed in the above-mentioned Japanese Patent Publication No. 39-20972, the wire body to which tension is applied is attached to the surface of the electrical cable (PV
There is a risk that the cable's life will be significantly shortened by biting into the outer sheath (such as the anti-corrosion layer) and causing damage to the surface of the cable, leading to water intrusion into the cable.

■In order to apply tension to the striatum, a weight connected to the end of the striatum is placed inside the inlet, but there is no room and it is difficult to find such an installation space within the narrow inlet. And it's not realistic.

Furthermore, according to the method disclosed in Japanese Patent Publication No. 57-27641, it is difficult to produce filament bodies that are thick at regular intervals, and special manufacturing equipment is required. It is not practical to provide such services.

■By wrapping a filament around the electric cable, the outer diameter of the electric cable including the filament increases, and when installing using an existing empty pipe, it can be applied depending on the pipe diameter. In some cases, it may disappear, and its range of use is limited.

Furthermore, in any of the above, the filament is wound around the circumference of the electric cable main body, so even if the filament is wound around the circumference of the electric cable main body at a predetermined pitch, When such power cables are drawn into the pipe and installed, there is a risk that the filament will rub strongly against the inner surface of the pipe and the pitch of the winding will be disordered. There were times when I couldn't expect any transformation. In such a case, thermal expansion and contraction of the power cable cannot be sufficiently absorbed or bending stress is applied to local parts of the power cable, which impairs the long-term reliability of the power cable.

For this reason, the present applicant has proposed a power cable installed in a conduit that can be extremely easily formed into a snake when the power cable is thermally expanded and contracted without wrapping the filament.
It has been filed as No.-207549.

This is made by integrally extruding spiral protrusions containing filaments with the sheath at an optimal pitch that is most likely to cause cable snakes, and these spiral protrusions give the power cable a natural snake.

However, in this invention as well, (1) the protrusions are generally soft, and there is a risk that the protrusions may be deformed when wrapped around a drum or during installation.

■Since this method uses integral extrusion molding, it is difficult to stabilize the shape of the protrusion.

There were other drawbacks.

This invention was made in view of the above points, and it eliminates the above-mentioned drawbacks of the prior art, and provides a novel method that effectively generates snakes within the pipe and forms strong spiral protrusions. The purpose is to provide power cables installed in pipelines.

[Means for Solving the Problems] In the present invention, when a highly rigid filament is spirally wound around the core of a cable and a corrosion-resistant layer is coated thereon, a spiral-shaped filament is inevitably formed on the cable. This is an in-duct power cable that is characterized by having protrusions formed thereon so as to naturally generate snakes.

It is also an in-duct power cable in which the filament is made of a metal vibrator, and an optical fiber and a communication cable are inserted into the filament to form a composite cable.

[Example] Hereinafter, the present invention will be described in detail based on the drawings. 1st
The figure is a cross-sectional view showing the configuration of a conduit-like laid cable. That is, the conduit-type cable 1 is constructed by winding a highly rigid and flexible filament 3 made of a metal steel wire, for example, in a spiral shape at a predetermined pitch around the outer periphery of a cable core 2. It is formed by integrally extruding and covering the plastic sheath 4. Therefore, a protrusion 5 is formed on the outer periphery of the spiral-shaped filament 3, and the strength of this protrusion 5 is due to the filament 3 embedded therein, so that it can be integrally molded with only a plastic sheath. It will be held much stronger than before.

The material of the filamentary body 3 is not limited to metal, but may be any other material as long as it has high rigidity, flexibility, and is not affected by heat during coating with a plastic sheath.

Next, another embodiment of the present invention will be described based on FIG. In this example, the striatum is made up of tubes. That is, the conduit-based cable 10 is constructed by winding a metal tube 9 into which an optical fiber 8 is inserted in advance around the outer periphery of the cable core 2 in a spiral shape at a predetermined pitch, and then evacuating the outer periphery of the plastic sheath 4'. The spiral protrusion 5' is then integrally extruded and covered. Here, the predetermined pitch is a pitch that allows the cable 10 to be bent in a snake shape due to the weight of the cable itself. Therefore, the spiral protrusion 5 formed by covering the sheath 4' with the metal tube 9 will not break the spiral bit irregularly, and there is no risk of it being crushed.

This not only protects the optical fiber inserted into the metal tube, but also provides a composite cable that has both an electrical cable and a communication system. Note that what is inserted into the metal tube 9 is not limited to an optical fiber, and it goes without saying that a communication cable may be used.

In this way, since the filament 3 is wound around the outer periphery of the cable core 2 and the plastic sheath 4 is coated on the outer periphery, it is very easy to form the projections 5, 5'.

Next, FIG. 2 shows a state in which this conduit-like laid cable 1.10 is installed in the conduit 6.
After being pulled in, the lower end portions of the protrusions 5 at a predetermined pitch contact the inner surface of the conduit, and between them the cable 1 changes from a floating state to a naturally snaked state due to its own weight. Since this protrusion 5 has high rigidity and a stable pitch, there is no fear of it being crushed by the gravity of the cable and it is ensured that it exists, so that the cables 1 and 10 are naturally and reliably formed in a snake state. Moreover, the filament body 3 is pushed in by the plastic sheath 4, so that there is no pitch deviation and regular snakeing is possible.

[Effects of the Invention] As explained above, in the in-duct power cable of the present invention, since the filament body spirally wound around the cable core is held down by the sheath, it has an integral structure with the sheath, and the cable can be There is no risk that the pitch of the spiral protrusion will change when the bow is large in the conduit (and a snake in the conduit can definitely be expected. Also, since the spiral protrusion contains a filamentous body, the rigidity of the protrusion is There is no risk of deformation such as crushing of protrusions as there is no risk of deformation such as crushing of protrusions as there is no need to worry about deformation such as crushing of protrusions. It's easy and
The extrusion speed can be improved.

If the filament to be wound around this cable is formed into a tubular shape, it is possible to easily incorporate optical fibers, communication cables, etc. into the filament to form a composite cable.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the configuration of a conduit-like installed cable according to an embodiment of the present invention, FIG. 2 is a side view showing the state in which the conduit-like installed cable is drawn into the conduit, and FIG. 3 FIG. 4 is a diagram schematically showing a conduit-like laid cable by snake laying; FIG. 4 is a perspective view showing the configuration of a conduit-like laid cable according to another embodiment of the present invention. 6... Conduit 8... Optical fiber 9... Metal tube

Claims (2)

[Claims] (1) When a highly rigid filament is spirally wound around the core of a cable and coated with a corrosion-resistant layer, a spiral protrusion is inevitably formed on the cable, and a snake naturally forms. A power cable installed in a conduit, characterized in that the power cable is configured to generate the following: (2) Claim 1, wherein the filamentous body is formed into a tubular body, into which an optical fiber cable or a communication cable is inserted.
Power cable installed in the pipeline as described.