JP2895519B2 - Optical fiber composite power cable - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a power cable laid underwater in which optical fibers are combined.

(Conventional technology and problems to be solved) Conventional optical fiber composite submarine power cables, for example,
On the metal sheath of the power cable, a plastic sheath made of polyethylene or the like provided with a spiral or longitudinal groove on the outer periphery is provided, and an optical fiber unit containing an optical fiber in a metal pipe is stored in the groove, and Apply an iron wire sheath on the outside of the plastic sheath, or spirally or SZ twist the optical fiber unit around the outer circumference of the metal sheath of the power cable, wind it, provide a plastic sheath such as polyethylene on it, and further outside It was configured with an iron wire exterior. As still another example, an optical fiber is arranged in a gap between wires of an iron wire sheath applied on a plastic sheath.

However, in the above-described optical fiber composite submarine power cable, the optical fiber unit buckles due to the bending operation of the cable. This buckling is fatal for an optical fiber, and local bending, so-called microbending, lowers the transmission characteristics of the optical fiber. Further, the structure in which the optical fiber unit is disposed in the gap between the strands of the iron sheath has a problem that the optical fiber unit is crushed by the sheath iron wire.

(Means for Solving the Problems) The present invention provides an optical fiber composite power cable which has solved the above-mentioned problems, and is characterized in that the plastic is provided inside a plastic sheath provided on the power cable and on the outer periphery thereof. An optical fiber unit containing an optical fiber is arranged in a metal pipe provided with a coating layer of a plastic material having a melting point higher than that of a sheath material, and an iron wire is provided outside the optical fiber unit. An optical fiber composite power cable in which the coating layer is both semiconductive.

(Operation) In general, an optical fiber has low mechanical strength, and buckling is fatal. Local bending, so-called microbending, significantly reduces the transmission characteristics of the optical fiber. Accordingly, the inventors of the present application have conducted various studies in order to find a structure that can be most easily combined with a power cable and that does not impair the mechanical characteristics and transmission characteristics of the optical fiber.

Thirty metal pipes with an outer diameter of about 1.0 mmφ containing an optical fiber inside are spirally wound at a pitch of 80 × (7 to 12) times on the lead sheath of a power cable with an outer diameter of about 70 mmφ. A polyethylene sheath was provided on the upper surface, and the fiber was reciprocated 20 times with a radius of 70 mm × 20 = 1400 mm. Inspection of the optical fiber and the metal sheath revealed that several to ten or more fibers were damaged. From this, it was found that the main cause was that the buckling strength of the metal pipe was low, that is, the rigidity was low.

For this reason, a polyethylene coating layer was provided on the outer periphery to reinforce the metal pipe. If the thickness of the polyethylene coating layer is too large, the outer diameter of the cable becomes too large, and when a polyethylene sheath is provided on the arrangement layer of the optical fiber unit, the step of the optical fiber unit appears on the outside, which is not preferable. The thickness was set to 0.5 to 1.0 mm, and the outer diameter of the optical fiber unit was selected to be 2 to 3 mmφ.
Further, as shown in FIGS. 3 (a) to 3 (d), only the optical fiber unit (3) is wound, and the optical fiber unit (3) and the nylon string spacer (4) are wound together. A prototype with a polyethylene sheath was manufactured.

When a bending test was performed on such a product, and the product was dismantled and then inspected, the following facts were found.

Part of the polyethylene coating layer of the optical fiber unit is no longer melted or deformed at the extrusion temperature of the polyethylene sheath (typically, polyethylene is extruded at a melting point of 120 to 130 ° C and inside and outside 200 ° C). It turned out that it was not a great reinforcement.

Although the case of FIGS. 3 (c) and 3 (d), which have relatively little effect, was good, the phenomenon of buckling was partially observed in the optical fiber unit (3), and a stable product was obtained during mass production. Was found to be still insufficiently stiff and insufficiently rigid.

A closed winding state as shown in FIGS.
In the close-wound state as in (d), it was found that the close-wound state caused the optical fiber unit (3) to move uniformly with respect to bending, and local buckling was less likely to occur.

No abnormality was observed in the nylon string spacer (4).

From these results, it was concluded that it is most preferable to use a plastic material having a higher melting point and higher rigidity than polyethylene as the plastic sheath of the power cable as the coating layer on the metal pipe of the optical fiber unit. 3 (a) to (d), a similar experiment was conducted by applying a nylon coating layer instead of the polyethylene coating layer on the metal pipe of the optical fiber unit (3).

As a result, it was found that any of the structures shown in FIGS. 3 (a) to 3 (d) was satisfactory. Dare to see the difference between (a) to (d), that (c) and (d) are still excellent, and when the lateral pressure and crushing of the cable were carried out,
(C) and (d) were also found to be excellent. Further, the same experiment was performed on materials other than nylon, polybutene, and polypropylene, and the same result as that of nylon was obtained.

Thereafter, an iron wire sheath was applied on the polyethylene sheath, and a bending test similar to the above was performed. However, the above conclusion did not change.

On the basis of the above results, experiments were also conducted on a case where the optical fiber unit was wound on a polyethylene sheath of a power cable. In this case, at the same time as the loose winding shown in FIGS. 3 (a) and 3 (b), a close-wound structure shown in FIGS. 3 (c) and 3 (d) in which a nylon string spacer was appropriately added to the optical fiber unit was also produced. It is considered that the close winding is preferable when the iron wire sheathing is applied thereon, because the external force from the iron wire does not depend on it, and the optical fiber unit does not bend or move locally, and local abnormality hardly occurs. Was.

In FIG. 3C, the optical fiber unit diameter is 2
In the case of 44 mm, the outer diameter of the nylon string spacer was increased by 1 to 2 mm to 3 to 6 mm. In FIG. 4D, both the optical fiber unit and the nylon string spacer have the same outer diameter of 2 to 4 mm. All winding pitches are lower diameter x (7 ~ 12
Times). On top of this, a wound layer of polypropylene yarn, a single iron wire sheath (iron wire outer diameter 8 mmφ), and a serving layer of polypropylene yarn were applied as a seating floor, which are the same as existing submarine cable technology.

Use such a cable with a radius of 20 times the outer diameter of the
When the optical fiber unit was bent twice and examined for the degree of damage to the optical fiber unit, all of the structures were sound. However, if it were to be expected, the close winding was more stable as expected.

After that, the optical fiber unit was subjected to lateral pressure and crushing, and the proof stress of the optical fiber unit was examined. As a result, although the optical fiber unit had sufficient performance, the pressure in the nylon string spacer was higher in FIG. 3 (c) than in FIG. It is found that the structure (c) is preferable in the case where the optical fiber unit has a high proof stress and a large lateral pressure. When side pressure performance is not required,
Figure (d) showing the optical fiber unit and nylon string spacer
If the diameters are the same, the production is easy and the number of windings can be reduced even a little, so that the productivity is improved. Further, when the lateral pressure performance may be low, the structure shown in FIGS. 3A and 3B may be used, which is economical. These may be appropriately used depending on use conditions.

In addition, nylon, polybutene, and polypropylene as the plastic coating layers of the optical fiber unit were not affected at all by the paint applied on the outermost polypropylene yarn serving layer.

Further, in the cable having this structure, seawater or the like reaches the optical fiber unit through the iron wire sheath. In terms of resistance to this, it has been shown that polyethylene has the highest track record in the past and there is no problem, but at least elongation due to long-time water infiltration, breaking strength reduction test confirmed that both nylon, polybutene and polypropylene were good. I have. However, polyethylene may be preferable to nylon in the vicinity of the surface of seawater due to the effects of ultraviolet rays, repeated wetting by seawater, and repeated dryness. In such a case, it is preferable that the nylon layer spacer and the coating layer of the optical fiber unit are further coated with polyethylene of about 0.5 to 2.0 mm outside the nylon.

In both of the two structures described above, the winding method of the optical fiber unit and the nylon string is not limited to helical winding, but the essence does not change even with SZ twist, but from the viewpoint of ease of manufacture, SZ
Spiral winding is preferred over twisting.

(Embodiment) FIG. 1 is a cross-sectional view of a specific example of an optical fiber composite submarine power cable according to the present invention.

In the drawings, (1) is a power cable, (2) is a metal sheath of a power cable such as a lead sheath, and (3) is sparsely disposed on the outer periphery of the metal sheath (2) together with a plastic spacer (4) such as a nylon string spacer. Alternatively, the optical fiber unit is tightly wound, and in this case, the plastic spacer (4) may be omitted and only the optical fiber unit (3) may be wound. (5) is a press winding tape, (6) is a plastic sheath such as polyethylene, (7) is an iron wire sheath, and (8) is a serving layer such as polypropylene yarn.

As shown in FIG. 2, the optical fiber unit (3) has a stainless steel pipe provided with a coating layer having a melting point higher than that of the polyethylene sheath (6), for example, nylon, polybutene, polypropylene, etc., on its outer periphery. The optical fiber (32) is housed in a metal pipe (31) such as the above.

In the case of a submarine power cable, for example, when a switch on land is operated, a switching surge enters. Also, when a lightning strike occurs on an overhead power line connected to both ends of the submarine power cable, a lightning impulse enters the submarine power cable (these are collectively called surges).

When the surge enters the conductor and the metal sheath of the submarine power cable, a large potential may be generated on the metal body wound in the longitudinal direction of the cable on the outside thereof. In the case of submarine power cables, these metal bodies are usually grounded at both ends and the potential is zero, but the longer the cable is, the larger the potential is generated in proportion to it, and the further away from the ground point, the larger the potential is generated The possibilities increase. In the case of the armored wire, such potential is not generated because it is uniformly grounded in seawater. However, in the case of the optical fiber unit according to the present invention, which is protected by plastic to prevent corrosion by seawater, a large electric potential is generated as the distance from the ground point at both ends increases, as described above. Breakage may occur, and seawater may enter the inside, corroding the metal pipe, or damaging the optical fiber with electrical breakdown energy.

As a countermeasure, as shown in FIG. 1, the plastic coating layer (33) of the optical fiber unit (3) and the plastic sheath (6) of the cable are made semiconductive so that the surge induction potential can be reduced over the entire length of the optical fiber unit ( 3) Metal pipe (31) → plastic coating layer (33) → plastic sheath of cable (6) → escape to seawater to prevent surge voltage from rising.

(Effects of the Invention) As described above, according to the optical fiber composite submarine power cable of the present invention, it is possible to prevent the buckling of the optical fiber unit caused by the bending of the cable, and to achieve stable performance for a long period of time. Can be held.

Also, by making the plastic sheath of the cable and the plastic coating layer of the optical fiber unit a semiconductive layer,
No matter how long the power cable becomes, an abnormal induced potential caused by the intrusion surge can be prevented from being generated in the metal pipe of the optical fiber unit, and the effect of the optical fiber unaffected by such a potential can be utilized as it is.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment of an optical fiber composite submarine power cable according to the present invention. FIG. 2 is a cross-sectional view of a specific example of the optical fiber unit according to the present invention. 3 (a) to 3 (d) are explanatory diagrams of experiments on the arrangement of the optical fiber units. DESCRIPTION OF SYMBOLS 1 ... Power cable core, 2 ... Metal sheath, 3 ... Optical fiber unit, 31 ... Metal pipe, 32 ... Optical fiber, 33 ... Plastic coating layer, 4 ... Plastic spacer, 5 ... Holding tape, 6 ... Plastic sheath, 7 ... iron wire exterior, 8 ... serving layer.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Masayuki Hirose 1-3-1 Shimaya, Konohana-ku, Osaka-shi, Osaka Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Toshiyuki Amaga, Shimaya, Konohana-ku, Osaka-shi, Osaka 1-3-1 Sumitomo Electric Industries, Ltd., Osaka Works (72) Inventor Masayoshi Yamaguchi 1-3-1, Shimaya, Konohana-ku, Osaka-shi, Osaka Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Hiroyuki Kimura Osaka 1-3-3 Shimaya, Konohana-ku, Osaka-shi Sumitomo Electric Industries, Ltd. Osaka Works (56) References JP-A-59-29305 (JP, A) JP-A-57-124315 (JP, A) 1-178906 (JP, A) JP-A-1-189812 (JP, A) JP-A-63-38220 (JP, U)

Claims (1)

(57) [Claims] 1. An optical fiber unit in which an optical fiber is accommodated in a metal pipe provided with a coating layer of a plastic material having a melting point higher than that of the plastic sheath material on the outer periphery, inside a plastic sheath provided on the power cable, An optical fiber composite power cable having an outer surface covered with an iron wire, wherein the plastic sheath and the plastic coating layer around the optical fiber unit are both semiconductive.