JP3107302B2 - DC solid power cable, DC solid power cable line, and method for monitoring DC solid power cable line - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC solid power cable, a line using the cable, and a method for monitoring the line.

[0002]

2. Description of the Related Art DC power transmission methods for submarine cables include monopolar operation (monopolar) and bipolar operation (bipolar).
There is.

[0003] Of these, there are two types of unipolar operation, as shown in FIGS. 12 (A) and 12 (B). FIG. 12A shows that the AC / DC converter 6 is connected in parallel with a high-voltage cable 20 and a ground cable 21, a DC current flows through the high-voltage cable, and a return current flowing in the opposite direction at the ground potential at the ground cable. Is a method of flowing.
FIG. 12 (B) shows a case where the ground cable 21 is eliminated and the ground electrode
22 is installed in seawater, and the return current in the opposite direction flows through seawater. FIG. 12A shows an example of one-end grounding, but there is also a case of both-end grounding.

On the other hand, bipolar operation is basically performed as shown in FIG.
And (B). FIG. 13 (A) shows AC / DC
Neutral wire 23 (or neutral cable,
(Ground cable). Here, an example in which one end is grounded is shown, but there is also a case in which both ends are grounded. FIG.
(B) is a method of grounding to seawater at a neutral ground point at both ends of the cable instead of using a neutral cable. The dashed lines in FIGS. 12 and 13 indicate beaches, and indicate that a cable is laid underwater between the two dashed lines.

Further, in order to omit a neutral cable for a return circuit, a line using an outer wire of a power cable made of copper or a copper alloy and using this outer wire as a return circuit is disclosed in Japanese Unexamined Patent Publication (Kokai) No. Heisei 9 (1994) -157.
It is disclosed in JP-A-6-215638.

[0006]

However, FIG.
13A, the ground cable and the neutral cable are required, so that the number of cables is increased, which is uneconomical. In addition, the cable laying period is long, and the occupation rate of the seabed required for laying the submarine cable becomes large, which is a problem in fisheries compensation.

On the other hand, the seawater return system shown in FIGS. 12 (B) and 13 (B) is economical because the number of expensive cables can be reduced. , That is, an environmental problem and a problem of electrolytic corrosion due to inflow of stray current into an adjacent seawater facility are likely to occur.

Further, the invention of Japanese Patent Application Laid-Open No. 6-215638 has the merit that a grounding cable and a neutral cable are unnecessary, but since copper (alloy) is used for the sheathing wire, the sheathing wire is subjected to electrolytic corrosion. However, there is a problem in that when it is damaged, it cannot be used as a return current flow path. Regarding this countermeasure, the same publication discloses that the sheathing wire is coated with polyethylene or the like, but if a pinhole occurs in the coating, a means for preventing electrolytic corrosion of the sheathing wire is also required.

Accordingly, the main object of the present invention is to provide a ground (neutral)
A DC solid power cable, a DC solid power cable line, and a monitoring method of a DC solid power cable line that can suppress environmental problems and electric corrosion problems in the seawater return system without laying cables and suppress electric corrosion of the exterior line itself. To provide.

[0010]

According to the present invention, the above object is achieved by using a sheath wire used for a DC solid power cable as a neutral wire and taking measures to prevent electrolytic corrosion on the sheath wire.

That is, the cable of the present invention is a DC solid power cable comprising a conductor, an insulator, a metal sheath, an anticorrosion layer, and a sheathing wire, characterized by having the following configuration. A plurality of exterior wires serving as return current flow paths are formed, of which the inner exterior wire is a copper wire and the outer exterior wire is an iron wire. An exterior wire serving as a return current flow path is provided between the metal sheath and the anticorrosion layer, and no exterior wire is provided outside the anticorrosion layer.

In order to use the armored wire as a return current flow path, it is necessary to ensure the same current capacity as the conductor current capacity in the armored wire. For example, (1) increase the cross-sectional area of each wire constituting the armoring wire, (2) increase the number of wires, (3) configure the armoring wire with a material having high conductivity such as copper, (4) In addition, connecting each armature wire in a plurality of (for example, two) DC solid power cables in parallel at both ends.

The above configuration is effective in preventing electrolytic corrosion of the armored wire itself. When electrolytic corrosion occurs, by applying iron, which is electrically lower than copper (having a high ionization tendency), to the outer periphery,
First, electrolytic corrosion occurs from the iron wire, and the inner copper wire can be protected. In general, in the case of providing multiple exterior lines, a so-called jute layer (or yarn layer) and a coating material are applied between the exterior lines. Since these work as layers having a large electrical resistance, if the exterior wire inside the jute layer is used as the return current flow path, the return current leaks from the exterior wire that serves as the return current flow path to the seawater. It also has the effect of being less likely to occur.

In addition, in the configuration described above, the anticorrosion layer located on the outer periphery of the armoring line functions as a thermal insulating layer, which is disadvantageous for increasing the power transmission capacity. However, since the exterior line is protected in the anticorrosion layer, there is no worry about electrolytic corrosion,
The return current does not leak into seawater. Further, since the exterior line is provided inside the anticorrosion layer, it is not necessary to provide the exterior line outside the anticorrosion layer. It is effective to use a plastic material having excellent heat resistance for the insulating layer in order to solve the problem that the temperature of the outer wire rises due to the return current and the conductor allowable temperature substantially decreases.

Here, the above-mentioned cable may be configured as follows, or the respective configurations may be appropriately combined.

(1) The outer sheathing line made of iron wire is wound in a loose winding, and the number of outer sheathing lines is a sufficient number as a sacrificial electrode against electrolytic corrosion. In this configuration, the outer sheath is used exclusively as a sacrificial electrode in electrolytic corrosion, and the inner sheath (copper wire) is used as a return conductor. Therefore, the number of iron wires only needs to be sufficient as a sacrificial electrode, and it is not necessary to densely wind the iron wire around the outer periphery of the copper wire as long as the purpose is achieved.

(2) An anticorrosion coating layer is formed only on the inner armoring lines, and no anticorrosion coating layer is formed on the outer armoring lines. Since the inner sheathing line is protected by the anticorrosion coating layer, it is effectively protected from electrolytic corrosion and also completely prevents return current from leaking into seawater. Even if a pinhole occurs in this anticorrosion coating layer, the outer sheathing line made of iron serving as a sacrificial electrode is located on the outer periphery, and the outer sheathing line is preferentially eroded so that the inner sheathing line is protected from electrolytic corrosion. protect. As the material of the anticorrosion coating layer, polyethylene, polypropylene and the like are preferable. In addition, inside
If the anticorrosion coating layer is formed on both of the outer sheathing lines, if only the anticorrosion coating layer of the inner sheathing line is damaged, the outer sheathing line cannot be a sacrificial electrode because it is covered with the anticorrosion coating layer,
If only the anticorrosion coating layer of the outer sheath line is damaged , the outer sheath line can be used as a sacrificial electrode.

(3) A plurality of outer wires are formed, and at least the innermost outer wire has a rectangular cross section. This configuration is an effective structure when the outer diameter of the entire cable is not to be increased as much as possible and the cross-sectional area of the entire armoring wire is desired to be large. In addition, when the rectangular outer wire is used, a wedge effect is obtained between the adjacent outer wires, and it is possible to suppress the narrowing of the outer wire when tension is applied to the cable.

(4) A high-strength resin layer is provided on the outer periphery of the exterior wire. Specific examples of the high tension resin layer include polyamide and polyimide fibers. For example, an aramid fiber (trade name: Kevlar) may be wound around the outer periphery of the exterior wire. By forming such a high-tensile resin layer, it is possible to suppress the electrolytic corrosion of the exterior wire and the leak of the return current, and to increase the tensile strength of the entire cable.

(5) A material containing a plastic film is wound around at least a part of the insulating layer, and the insulating layer is impregnated with high-viscosity oil. In this case, the material containing a plastic film includes, in addition to the plastic film itself, a composite tape in which kraft paper is attached to one or both sides of the plastic film. Specific materials of the plastic film include polyolefin resins such as polyethylene and polypropylene, polystyrene, polydimethylbenzene, and fluoroethylene terephthalate. In the existing kraft paper insulated solid cable, the insulating oil is easy to flow because the fiber of the insulating paper is porous (porous). It is possible to suppress the decrease in power transmission capacity due to heat generation when the exterior wire is a return current conductor. As the high-viscosity oil, oil having a viscosity of about 25 to 150 cst at 120 ° C. can be used.

(6) An optical fiber composite unit and a spacer are interposed between the anticorrosion layer and the sheath line. Since the optical fiber generally dislikes high heat, it is preferable to dispose the optical fiber outside the anticorrosion layer, that is, between the anticorrosion layer and the sheath line.

In the power cable line according to the present invention, in the DC solid power cable line using the DC solid power cable described above, the sheath line is formed with an anticorrosion coating layer and serves as a return current flow path. Are grounded via a switch, the switch at one end of the sheathing line is opened, and the switch at the other end of the sheathing line is closed, so that the return potential becomes negative with respect to seawater.
According to such a method, electrons can be caused to flow in instead of flowing out of the armoring line, and it is possible to suppress electrolytic corrosion of the armoring line.

In addition, in the DC solid power cable line using the DC solid power cable, a seawater return electrode is provided at both ends of the DC solid power cable,
The exterior wire may be used as a return current flow path, and both ends of the exterior wire may be grounded. If the sheathing line is electrolytically eroded by the monitoring method described below, the return current flow path can be automatically shifted from the sheathing line to the seawater return electrode.

Further, the method for monitoring a DC power line according to the present invention is a method for monitoring a DC solid power cable line using a DC solid power cable having an outer wire, wherein the outer wire is provided with an anticorrosion coating layer, and And measuring the current or resistance of the armored wire and monitoring the degree of corrosion of the armored wire from changes in these measured values.

[0025]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 is a partial sectional view of a DC solid power cable according to the present invention. This power cable is
Conductor, insulating layer, metal sheath 1, anticorrosion layer 2
Equipped. A bedding jute layer (or yarn layer) 3 is provided on the outer periphery of the anticorrosion layer 2, and a sheathing wire 4 is wound thereon, and a serving jute layer (or yarn layer) 5 is further formed on the sheathing wire. It has been subjected.

The insulating layer is formed by winding a composite paper obtained by laminating a polypropylene film and kraft paper on a conductor and impregnating with a high-viscosity insulating oil. Usually, lead (pure lead or alloy lead) is used for the metal sheath, and polyethylene is used for the anticorrosion layer.

The outer wire 4 is made of an iron wire or a copper wire. In the present invention, this exterior wire is used as a return current flow path. FIG. 2 shows a cable line using the outer wire as a return conductor. This line shows a case where two DC solid power cables 10 are arranged in parallel to form a bipolar configuration. AC / D
The C converter 6 is grounded at one end at a neutral ground point, and the armoring wires 4 of both cables are converged at their ends to function as a neutral wire (ground wire).

When the armoring wire 4 is an iron wire, the conductivity of the iron wire is usually smaller than that of a conductor made of copper.
Is usually higher than the conductivity of a single cable conductor, and can sufficiently function as a neutral conductor.

When the outer wire 4 is made of a copper wire, the cost is slightly higher than that of an iron wire, but the total effective cross-sectional area of the outer copper wire in one cable is usually larger than the cross-sectional area of the conductor of one cable. Therefore, the electrical conductivity of the armored copper wire is higher than that of the cable conductor, so that the return current of the conductor current in one cable can sufficiently flow even with only the copper wire armored wire of one cable. Needless to say, it is preferable to connect the copper outer wires of the two cables in parallel as described above, since the conductivity of the entire return conductor can be further increased.

Here, the current flows through the neutral conductor during bipolar operation because of the accident occurring in one of the two cables
This is the case where half the power is transmitted by book. In this case, as much current as the current flowing through the conductor of the normal cable runs through the neutral conductor. In the case of the track shown in FIG. 2, if one of the cables becomes unusable due to an accident, the return current of the remaining normal cable will flow through both the outer wires of the normal cable and the accident cable. Therefore, armoring wire 4 is cable 2
As a result, the return current of the normal cable can sufficiently flow. Of course, if the accident cable is repaired, the return current does not flow in the bipolar system, so that no current flows in the parallel-connected armored wires. On the other hand, in the monopolar system, a current having the same magnitude as the current flowing through the conductor of each cable always flows as a return current through the neutral wire (the exterior wire 4).

Here, when the parallel-connected exterior wire 4 is grounded at one or both ends to the ground or seawater, a part of the return current may flow into the seawater (ground) or may flow as a stray current into a nearby facility. obtain. However, since the resistance of the armoring wire 4 serving as a return circuit is smaller than the grounding resistance of seawater or the ground and the leakage resistance of seawater from the armoring wire to the seawater, most of the return current flows through the armoring wire 4, resulting in environmental problems. The adverse effects are extremely small.

In FIG. 1, the bedding jute layer 3 and the serving jute layer 5 are conventionally made of twisted strings of natural jute.
In recent years, synthetic plastic strings such as polypropylene strings, cloths, and rubber-based materials have often been substituted. In that case,
The bedding jute layer 3 and the serving jute layer 5 are often coated with an asphalt-based, tar-based, or artificial paint. In this case, since the electric resistance of these paint-coated layers is higher than that of seawater or armor lines, they also serve as an electrical protection layer for the armor lines. Therefore, the effect of increasing the leakage resistance of the sheathing line against seawater and effectively confining the return current by the sheathing line can be expected. Further, in this specification, a structural portion inside the anticorrosion layer 2 is referred to as a cable core. These points are common to other embodiments described below.

(Embodiment 2) When a return current is applied to the sheathing line, the sheathing line may be electrically corroded (corroded) in seawater. The following are effective measures against such electrolytic corrosion.

A submarine cable is buried in submarine soil. In this case, wear due to external force of the serving layer and corrosion caused by seawater itself and microorganisms in seawater can be almost prevented,
Since the leakage resistance from the sheath wire to the seabed soil and seawater around the cable is much higher than the iron wire and copper wire constituting the sheath wire, the return current hardly leaks into the seawater.
Therefore, even in the case of an armored wire without an anticorrosion coating layer, the electrolytic corrosion can hardly cause a problem.

Even in the case of a non-buried submarine cable, the cable itself may be housed in a protective tube or covered with sand cement. Also in this case, since the serving layer can be prevented from being damaged, the electrolytic corrosion can hardly cause a problem.

However, if none of the above is satisfied, the return current leaks from the armoring line, causing electrolytic corrosion, and the armoring line may become thinner, making it impossible to flow the return current that should be passed. In such a case, a configuration as shown in FIGS.

FIG. 3 shows a case in which a bedding jute layer is provided on a cable core, and an inner armoring line made of a copper wire is successively provided thereon.
4A, an intermediate yarn layer 7, an outer armoring wire 4B made of iron wire, and a serving jute layer 5. Since iron is electrically "base" compared to copper, even if electrolytic corrosion occurs, corrosion first occurs from the outer iron wire, and the inner copper wire is protected, so that for a sufficiently long period of time, Copper wires can be used as return conductors. Of course, both the inner armoring wire 4A and the outer armoring wire 4B may be made of copper wire so that the corrosion reduction years of both of them sufficiently satisfy the design life years.

The cable of FIG. 4 differs from the cable of FIG. 3 in that the outer sheath line 4B made of iron wire is loosely wound. The outer sheathing wire 4B may be wound by a sufficient number to serve as a sacrificial electrode and to protect the inner sheathing wire 4A from electrolytic corrosion. The close winding state of the inner sheathing wire 4A and the loose winding state of the outer sheathing wire 4B are appropriately determined according to the structure of the submarine cable (conduction current and required conductor cross-sectional area and the thickness and number of the sheathing wires), laying conditions, and seawater conditions. Just design.

(Embodiment 3) As described above, when the armored wire is used as the return conductor, Joule heat is generated in the armored wire, and the outer peripheral serving jute layer or the outer layer through which the heat flow is radiated from the return wire. The cable temperature rises due to the thermal resistance of the buried soil, and eventually a large transmission current flowing through the cable conductor cannot be taken, or the conduction current needs to be reduced by an amount corresponding to the temperature rise. Such a problem has little effect on an OF cable in which the maximum allowable temperature of the conductor is high, for example, 80 to 90 ° C. However, for example, a solid cable (MI or MIND cable) used for long-distance power transmission of 50 km or more, in which it is difficult to supply insulating oil from both ends of the cable line, has a large effect. That is, the solid cable is generally made by impregnating the insulating layer of kraft insulating paper with high-viscosity insulating oil, and the maximum allowable temperature of the conductor is about 50 to 55 ° C. For this reason, it is necessary to devise a device for compensating for the decrease in the conductor current due to the heat generation of the exterior wire, and the following measures are recommended.

In existing kraft paper insulation layers, the fibers of the insulation paper are porous, through which the high viscosity insulating oil flows. Therefore, the cable cannot be used at a temperature where the viscosity of the insulating oil becomes lower than a certain value due to the temperature rise,
About 50-55 ° C was the maximum allowable temperature.

The present inventors have filed a Japanese Patent Application No. 10-38173.
As described in detail above, if a plastic film is used as the insulating layer, it is possible to suppress the flowing dripping of the insulating oil and to set the allowable temperature of the conductor high, so that the adverse effect accompanying the heat generation of the return conductor according to the present invention can be offset. Obtained knowledge. Therefore, it is preferable to use a plastic film for at least a part of the insulating layer of the solid cable. Examples of the material containing a plastic film include a composite tape in which kraft paper is attached to one or both sides of the plastic film in addition to the plastic film itself.

In such a cable, a return conductor 4C may be provided between the anticorrosion layer 2 and the metal sheath 1 in the cable core as shown in FIG. In particular, it is preferable that the return conductor 4C be of a rectangular type because a sufficient return current capacity can be easily secured and an increase in the cable outer diameter can be suppressed as much as possible. In such a cable, the return conductor 4C is arranged inside the anticorrosion layer 2 usually made of polyethylene.
Can be considered as a thermal insulating layer against the heat generated by the return conductor 4C, and it is conceivable that a higher temperature rise is exhibited and the conductor allowable current is greatly reduced. However, as mentioned above, by including a plastic film in the insulating layer, the allowable conductor temperature is 80 to 85 ° C.
If it can be used, it is considered that there is a case where the reduction of the conductor allowable current due to the heat generation of the return conductor 4C can be made sufficiently small and there is no problem in practical use. Further, in this cable, since the return conductor 4C is housed inside the anticorrosion layer, there is no concern about electrolytic corrosion of the return conductor 4C and leakage of return current from the return conductor to seawater. Further, since the return conductor 4C is provided in the anticorrosion layer 2, it is not necessary to further provide it on the outer periphery of the anticorrosion layer 2.

(Test Example) Soil specific thermal resistance g = 100 ° C. cm /
DC solid cable (see Fig. 1) 1m below the seabed of W
It will be buried in Article 1 to construct a seawater return monopolar system. Let us consider an example in which the exterior wire is used as a return conductor in this system. The power transmission conditions and cable configuration are as follows.

Transmission voltage: DC 350 kV Transmission current: DC 1000 A Transmission capacity: 350 MW Conductor size: 1100 mm²  Insulation thickness: 17mm Single outer wire diameter: 6mm

If the exterior wire is an iron wire, its electric resistance is about 1.0 × 10 ⁻⁶ Ω / cm, and if it is a copper wire, the electric resistance is
1.7 × 10 ⁻⁷ Ω / cm. Therefore, when a return current of 1000 A is applied to these sheath wires, the temperature rise ΔT of the sheath wires is as follows: iron wire → ΔT _Fe ≒ 64.5 ° C. copper wire → ΔT _Cu ≒ 11 ° C.

<Case 1> In the case of a solid cable using conventional kraft paper, the maximum conductor temperature (Tmax) is 50 to 55.
Since the temperature in the seabed soil where this cable is laid is assumed to be Tc, Tc <Tmax−ΔT _{Fe (Cu)} −ΔT where ΔT is the rising temperature of the conductor flowing 1000A.

Therefore, when the armored wire is an iron wire, Tc <(50 to 55) −64.5−ΔT = − (9.5 to 14.5) −ΔT (° C.) That is, if the temperature of the seafloor soil is not a minus temperature environment, power transmission of 1000 A is impossible, and it cannot be used unless the power transmission capacity is significantly reduced.

<Case 2> When PPLP (composite paper obtained by laminating a polypropylene film and kraft paper) is used for the cable insulating layer, Tmax is 80 to 85 ° C., so that Tc <(80 to 85) −64.5 −ΔT = (15.5 to 20.5) −ΔT (° C.) Therefore, ΔT at the time of power transmission of 1000 A is within 30 ° C., and therefore, when the cable of the present invention is laid in a cold region where Tc is within 0 ° C. or less, electric power almost barely required can be transmitted. However, when laying cables in general seawater with a Tc of 5 to 25 ° C, the transmission current will need to be greatly reduced.

<Case 3> When copper wire is used as a conventional kraft paper insulated solid cable, Tc <(50-55) -11-ΔT = (39-45) -ΔT (° C.) . Therefore, it is considered that applicable cases will increase in areas other than warm regions.

<Case 4> When PPLP is used for the cable insulating layer and the outer wire is a copper wire, Tc <(80-85) -11-ΔT = (69-74) -ΔT (° C.) Assuming that ΔT when transmitting 1000A is about 30 ° C, Tc <(39
~ 44) ° C. Therefore, it is understood that the cable of the present invention can be used globally. Further, the present invention can be applied to more severe environments, for example, when the burial depth is deeper, and the power transmission capacity can be further increased according to the temperature in seawater and soil.

(Embodiment 4) In general, in the case of an AC submarine cable, an AC current flows through the armored line by electromagnetic induction. Therefore, if an anticorrosion coating layer made of polyethylene or the like is applied to the armoring line to maintain insulation from seawater, an induced voltage is generated in the armoring line, and there is a high possibility that the anticorrosion coating layer will cause dielectric breakdown. Once insulation breakdown occurs in a spot shape somewhere in the anticorrosion coating layer of the exterior wire, the exterior wire and seawater conduct at that spot, and the induced current concentrates at this conduction location.
Then, the electrolytic corrosion largely progressed around the spot, and when the progress was remarkable, the exterior line was sometimes disconnected. Therefore, it is common sense that insulation protection is not applied to the exterior wire.

However, in the case of a DC cable, there is no guidance for these outer wires. Therefore, an extremely reliable and environmentally friendly submarine cable line can be realized if an anticorrosion coating layer is formed on the exterior wire to completely prevent electrolytic corrosion of the return conductor and leakage of return current. Specific examples are shown in FIGS.

FIG. 6 shows a structure in which a bedding jute layer 3 is provided on a cable core, a single exterior wire 4 is provided thereon, and a serving jute layer 5 is further formed. Each element wire 4D of this sheathing wire 4 has an anticorrosion coating layer of polyethylene on the outer periphery.
4E is formed. Here, a sheath wire 4 was formed by using a 4 mm diameter copper wire coated with a 2 mm thick polyethylene and using a wire having an outer diameter of 8 mm. These dimensions are, for example, 0.5 to 2 mm in polyethylene coating thickness and 2 to 8 m in copper wire diameter depending on the cable distance, installation conditions, and the like.
The optimum value may be selected after changing to about m.

In the case where the cable is composed of multiple wires, it is effective if the armoring wire 4 is made of an iron wire having a higher material strength than copper and is economical, and the armoring wire 4 of each cable is connected in parallel at both ends to form a return conductor. This is preferable because the resistance can be sufficiently reduced.
In the case where the number of strips is small or a return current is always supplied to the armoring line in a monopolar system, it is preferable to use a copper wire having higher conductivity than iron for the armoring line.

FIG. 7 shows a double outer wire around the cable core.
This is an example in which 4A and 4B are formed. Inner sheath 4A and outer sheath 4
Between B and the intermediate yarn layer 7 is formed. Here, the inner sheath wire 4A was used as a return conductor, and a polyethylene-coated copper wire was used. Also, if the outer sheathing wire 4B is an iron wire without coating,
The cable is easily protected from the tensile force by the high tensile strength iron wire against the tension at the time of laying, and is excellent in economy. Furthermore, even if the coating of the inner sheath wire 4A is damaged, the outer sheath wire 4B made of iron is preferentially electrolytically eroded, so that the inner sheath wire 4A is protected from electrolytic corrosion.

The inner sheath 4A and the outer sheath 4B may be provided with a polyethylene anticorrosive coating layer. In this case, any of "the inner sheathing wire and the outer sheathing wire are both iron wires", "the inner sheathing wire is a copper wire and the outer sheathing wire is an iron wire", and "the inner sheathing wire and the outer sheathing wire are both copper wires" may be used. In particular, in the case of high power transmission, the conductor cross-sectional area in the cable core becomes large, and the use of polyethylene-coated copper wire for both the inner and outer sheathing lines reduces power transmission loss from the viewpoint of suppressing cable temperature rise. Is also preferable in many cases. Further, when the outer conductor serving as the return conductor is sufficient, it is preferable that the return conductor is formed of an inner outer wire, and a polyethylene coating layer is applied to the inner outer wire 4A in order to protect the return wire.

The laying conditions of the submarine cable are, for example,
When the sea depth is more than 500m, the cable underwater weight at the time of cable laying (the weight of the entire underwater cable suspended from the laying ship to the bottom of the sea and considering the buoyancy) must be reduced as much as possible. Must. In that case, it is preferable to use a high-strength resin wire having a specific gravity several times lower than that of the steel material for the exterior wire. For example, the use of aramid fibers for the outer sheathing line may be mentioned. As a result, protection of the inner sheath line can be achieved.

FIG. 8 shows an example in which each of the double exterior wires 4A and 4B is formed in a rectangular shape. When it is desired to increase the cross-sectional area of the entire exterior wire without increasing the outer diameter of the cable, or when sufficient protection of the cable is required during installation, the cross-sectional shape of the exterior wire is preferably a flat shape rather than a circular shape. When the required cross-sectional area of the return conductor is sufficient, it is preferable that only the inner sheath line 4A be coated with polyethylene to be used as the return conductor. Of course, only the inner armored wire 4A may be a rectangular wire, and the outer armored wire 4B may be a round wire.

FIG. 9 shows an example in which a triple armoring line, which is optimal for laying in an ultra-deep sea such as 1000 m, is provided. Here, the innermost outer wire 41 is a return conductor, and a rectangular copper wire coated with polyethylene is used. Middle and outermost sheath lines
For 42 and 43, it is preferable to use iron wire or aramid fiber. With this configuration, the innermost outer wire 41 serving as a return conductor is protected by the middle and outermost outer wires 42 and 43. When the intermediate outer wire 42 is an iron wire and the outermost outer wire 43 is an aramid fiber, a high tensile strength is obtained by the aramid fiber, and even when a pinhole is generated in the coating of the innermost outer wire 41, the iron intermediate wire is used. The outermost wire 41 is protected by preferential electrolytic corrosion, thereby protecting the innermost outer wire 41. When both the outer and outer layers 42 and 43 are made of aramid fiber, higher tensile strength is obtained, and the outer and outer layers 42 and 43 are protected from the outer layer 41. Layer.

In the constructions shown in FIGS. 6 to 9, since the wire itself of the sheathing wire is covered with a polyethylene coating having a high heat insulating effect, and the double or triple sheathing wire is provided, the return conductor is provided. It becomes more difficult to dissipate the heat of the exterior wire as compared with the configuration of FIGS. As a result, the temperature rise in the return conductor becomes large, and it becomes difficult to secure the power transmission capacity of the conventional kraft paper insulated solid cable. In that case, it is more effective to use a material containing a plastic film for at least a part of the cable insulating layer. In particular, when a plastic material such as Kevlar is used for the intermediate and outermost armoring wires, since the thermal resistance of these materials is greater than that of iron, a conductor using a material containing a plastic film for at least a portion of the cable insulating layer is further used. It is important to use a combination of solid DC cables with a high allowable temperature.

(Embodiment 5) Next, FIG. 10 shows an example of an optical fiber composite single core DC submarine cable described in Japanese Patent No. 2573694 by the present applicant. A bedding jute layer 3 is formed on a cable core, and an optical fiber composite layer on which an optical fiber unit 8 and a spacer 9 are arranged is formed thereon. First intermediate yarn layer 7 on top
A, inner sheath line 4A, second intermediate yarn layer 7B, outer sheath line 4
B, a serving jute layer 5 is sequentially formed. The inner sheath wire 4A was used as a return conductor, and was a polyethylene-coated copper wire. The outer sheath wire 4B was an aramid fiber assuming deep laying. Of course, the case where the inner sheath wire 4A does not have a polyethylene coating may be used. Since the optical fiber composite layer functions as a heat insulating layer, it becomes difficult for heat generated from the conductor to escape. In addition, since there is an inner armoring wire 4A outside that as a return conductor, the cable consists of an insulating layer made of plastic film material, and the solid conductor has a high conductor allowable temperature.
It is even more important to use a combination of DC cables.

When laying a cable in the deep sea exceeding 500 m, it is difficult to form the optical fiber unit in a rectangular shape, so if the optical fiber unit is arranged in a circular shape, it is pulled down in the direction in which the cable extends by the gravity of the water at the time of laying. In order to prevent this, it is preferable that the inner armoring wire 4A in FIG. 10 is a rectangular wire to prevent the optical fiber unit from being squeezed by the wedge effect.

(Embodiment 6) In the case where the sheath wire serving as the return conductor is insulated and coated with a polyethylene coating layer or the like, it is possible to devise a method of grounding. Generally, metal causes electrolytic corrosion when the metal is eluted as ions into seawater and emits electrons as in the following formula. A (metal) → A ⁺ (metal ion) + e ⁻

Since the current flows in the opposite direction to the electron e ⁻ , if a pinhole is formed in the anticorrosion coating layer of the outer cable in the submarine cable, it is necessary to prevent disconnection of the outer cable due to electrolytic corrosion near the pinhole. In this case, the electrons e ⁻ may flow in instead of being eluted.

The DC power line shown in FIG. 11 will be described. The outer conductor 4 of the DC solid power cable 10 is a return conductor having an anticorrosion insulating coating layer, and both ends of the return conductor are grounded via switches 11 and 12. The left end in FIG. 11 is the power transmission side AC / DC converter 6, and when power is transmitted at + A (V), a current flows to the right through the cable conductor. Where the load
Z consumes power, and the current flows to the left through
Return to the DC converter 6. Assuming that the voltage corresponding to the voltage drop due to the return conductor conduction is α (α is plus), the switch 12 on the load side is grounded, and the terminal of the return current, that is, the switch 11 on the power transmission end side is opened. Armoring line 4) is 0 to-all over ground (ground potential) zero potential.
The potential becomes negative in the range of α. Therefore, if a wound point 13 occurs in a part of the return conductor, the potential β at the wound point 13
Becomes −α <β <0 (V). Therefore, electrons flow into the injury point 13 through the seawater, and no metal is eluted from the injury point 13 in the armoring line 4.

As described above, even if a part of the exterior line is damaged and a part of the exterior line is connected to the seawater, if the grounding is made at one of the two ends of the cable so that electrons flow into the exterior line at the point of the injury, Can prevent electrolytic corrosion.

Furthermore, in order to forcibly maintain the potential at the injury point at a negative potential, a power supply is provided between both ends of the armoring line and the ground, and the potential β at the injury point is forcibly maintained at the negative potential. If it can be constituted, it is more effective in suppressing electrolytic corrosion.

(Embodiment 7) Further, in order to further secure long-term reliability, the current or resistance value of the armoring wire is measured as needed, and the resistance value of the armoring wire increases and unbalanced. It is only necessary to monitor whether the resistance value becomes infinite or the resistance value becomes infinite. If such monitoring reveals that the corrosion of the outer conductor that will be the return conductor has progressed, as an example of the countermeasures, separate seawater return electrodes are provided at both ends of the cable, and the return current is switched to flow through the seawater return circuit. It is desirable. If the installation environment allows, it is appropriate to connect the seawater return electrode and the sheath wire in advance in parallel, ground both ends of the sheath wire, and use both the return routes together.
Since the resistance of the outer wire is usually smaller than the seawater return resistance,
When the sheathing line is normal, the return current mainly flows to the sheathing line, and when the sheathing line is corroded, the return current automatically flows through the seawater return electrode and seawater according to the degree of the corrosion. Become.

[0070]

As described above, the power cable of the present invention uses the armored wire as the return conductor, thereby eliminating the necessity of laying a neutral wire and minimizing the return current leaking to the surrounding environment. Can be suppressed. In addition, it is possible to effectively suppress the electrolytic corrosion of the exterior wire serving as the return flow path.

In addition, in the case of the power cable line of the present invention, in particular, when a sheath line serving as a return conductor is covered with a corrosion-resistant insulating coating, even if the sheath of the sheath line is damaged and a portion which is electrically connected to seawater is formed on the way, the damage point is not affected. By maintaining the voltage with respect to the seawater of the armoring line negative so as to keep the electrons on the side where the electrons flow into the armoring line, the electrolytic corrosion of the armoring line can be suppressed.

Further, the monitoring method of the power cable line according to the present invention can monitor the corrosion state of the armoring line serving as the return conductor by a simple method such as resistance and current measurement. In particular, if the seawater return electrode and the sheath wire forming the return conductor are connected in parallel and both are used at the same time, if the sheath wire is normal, the return current flows through the sheath wire and the sheath wire is corroded. In such a case, the return current automatically flows to the seawater side via the seawater return electrode in response to this, which is convenient.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of a cable according to the present invention.

FIG. 2 is a schematic view of the cable line of the present invention.

FIG. 3 is a partial cross-sectional view of the cable of the present invention in which an outer wire is doubled.

FIG. 4 is a partial cross-sectional view of the cable of the present invention in which the outer sheath line is doubled and the outer sheath line is loosely wound.

FIG. 5 is a partial cross-sectional view of the cable of the present invention using a rectangular wire as an exterior wire.

FIG. 6 is a partial cross-sectional view of the cable of the present invention in which an anticorrosion coating layer is formed on an exterior wire.

FIG. 7 is a partial cross-sectional view of the cable of the present invention in which the outer wire is doubled and an anticorrosion coating layer is formed on the inner outer wire.

FIG. 8 is a partial cross-sectional view of the cable of the present invention in which the outer wire is doubled with a rectangular wire and the inner outer wire is coated with anticorrosion.

FIG. 9 is a partial cross-sectional view of the cable of the present invention in which the exterior wire has a triple structure, the inner two layers are flat exterior wires, and the outermost layer is a resin exterior wire such as Kevlar.

FIG. 10 is a partial sectional view of a cable of the present invention in which an optical fiber is combined.

FIG. 11 is a schematic explanatory view of a method of monitoring the degree of corrosion at a damage point and preventing the progress of corrosion in the power transmission line according to the present invention.

12A and 12B are explanatory diagrams showing a monopolar transmission line, where (A) shows a case where a ground wire is used and (B) shows a case where a seawater return route is used.

13A and 13B are explanatory diagrams showing a bipolar transmission line, where (A) shows a case where a neutral wire is used and (B) shows a case where a seawater return route is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal sheath 2 Anticorrosion layer 3 Beding jute layer 4 Armoring line 5 Serving jute layer 6 AC / DC converter 7 Intermediate yarn layer 8 Optical fiber unit 9 Spacer 10 DC solid power cable 11, 12 Switch 13 Injury point 20 High voltage cable 21 Ground wire 22 Ground electrode 23 Neutral wire

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI H01B 7/32 H01B 11/22 11/22 H02G 1/10 F H02G 1/10 9/00 D 9/00 H01B 7/18 G (58) Field surveyed (Int. Cl. ⁷ , DB name) H01B 9/00 H01B 7/14 H01B 7/17

Claims (11)

(57) [Claims] 1. A DC solid power cable comprising a conductor, an insulator, a metal sheath, an anticorrosion layer, and a sheathing wire, wherein the sheathing wire has a current capacity serving as a return current flow path, and the sheathing wire is formed in multiples. A DC solid power cable, wherein the inner armor is made of copper wire and the outer armor is made of iron wire. 2. The direct-current solid power cable according to claim 1, wherein the outer sheath wire is sparsely wound, and the number of the outer sheath wires is a sufficient number as a sacrificial electrode against electrolytic corrosion. 3. The DC solid power cable according to claim 1, wherein an anticorrosion coating layer is formed on the inner armoring wire, and no anticorrosion coating layer is formed on the outer armoring wire. 4. The DC solid power cable according to claim 1, wherein at least the outermost layer of the innermost layer has a rectangular cross section. 5. A DC solid power cable comprising a conductor, an insulator, a metal sheath, an anticorrosion layer and an armoring wire, wherein the armoring wire has a current capacity to be a return current flow path, and the metal sheath and the anticorrosion layer A direct-current solid power cable, which is provided between the inner and outer surfaces of the anticorrosion layer and has no outer wire. 6. The DC solid power cable according to claim 1, wherein a material containing a plastic film is wound around at least a part of the insulating layer. 7. The DC solid power cable according to claim 1, wherein a high-strength resin layer is provided on an outer periphery of the armoring wire. 8. The DC solid power cable according to claim 1, wherein an optical fiber composite unit and a spacer are interposed between the anticorrosion layer and the armoring wire. 9. A DC solid power cable line using a DC solid power cable having an armoring wire, wherein the DC solid power cable comprises the cable according to claim 1 or 2, wherein the armoring wire is formed with an anticorrosive coating layer. And a return current flow path, both ends of the sheath wire are grounded via a switch, a switch at one end of the sheath wire is opened, a switch at the other end of the sheath wire is closed, and the return potential is negative with respect to seawater. A DC solid power cable line, characterized in that: 10. A DC solid power cable line using a DC solid power cable having an armored wire, wherein the DC solid power cable comprises the cable according to claim 1 or 2, and a seawater return path at both ends of the DC solid power cable. A DC solid power cable line comprising electrodes, a sheath wire serving as a return current flow path, and both ends of the sheath wire grounded. 11. A method for monitoring a DC solid power cable line using a DC solid power cable having a sheathing line, wherein the DC solid power cable comprises the cable according to claim 1 or 5, wherein the sheathing line is a corrosion protection coating layer. A DC solid power cable line characterized by measuring the current or resistance of the sheath and monitoring the degree of corrosion of the sheath from a change in these measured values. Monitoring method.