JP2020155355A - Power cable - Google Patents

Abstract

To provide a power cable capable of preventing dielectric breakdown in an insulating layer even if water absorbed by a water absorbing layer is released into the cable.SOLUTION: In a power cable 10 in which at least an insulating layer 40 and a water absorbing layer 60 are formed around a central conductor 20 toward the outside, salts consisting of inorganic compounds capable of forming hydrates are disposed between the insulating layer 40 and the water absorbing layer 60. With this configuration, even if water absorbed by the water absorption layer 60 of the power cable 10 is released into the cable, the water is absorbed by the inorganic compound disposed between the insulating layer 40 and the water absorption layer 60, and the inorganic compounds form hydrates to prevent desorption of water, whereby the occurrence of dielectric breakdown in the insulating layer 40 due to water can be accurately prevented.SELECTED DRAWING: Figure 1

Description

The present invention relates to a power cable in which an insulating layer and a water absorbing layer are formed around a central conductor.

For example, a submarine power cable is provided with a water-impervious layer such as a lead cover or an aluminum cover, and under normal conditions, the water-impervious layer or the like prevents seawater or the like from entering the cable.
In addition, in order to prevent seawater from entering the cable from the accident point even if the impermeable layer is damaged when an accident occurs underwater, a central conductor should be installed inside the submarine power cable. In many cases, a water-absorbing layer containing a water-absorbing polymer for stopping water is provided on the outside of the surrounding insulating layer (see, for example, Patent Document 1).

If a water absorption layer is provided, even if seawater or the like enters the cable from the accident point, the water absorption material such as the water absorption polymer of the water absorption layer absorbs water and swells, thus blocking the water infiltration route. It comes off.
Therefore, by providing such a water absorption layer in the submarine power cable, even if water infiltrates into the cable due to damage of the water barrier layer due to an accident in water, etc., the inside of the water absorption layer It is possible to prevent the central conductor, the insulating layer, etc. from being flooded.

JP-A-2018-6227

By the way, although the temperature and humidity are thoroughly controlled in the submarine power cable manufacturing factory, it is practically impossible to reduce the humidity to 0% unless it is manufactured under vacuum conditions. Therefore, when the submarine power cable is manufactured by incorporating the water absorption layer, the water absorption layer is incorporated into the submarine power cable in a state of absorbing moisture in the air to some extent.
And such a phenomenon is a phenomenon that can occur not only in the submarine power cable but also in all power cables having a water absorption layer.

However, if the water absorption layer incorporated in the power cable during manufacturing contains water in this way, even if the above-mentioned accident does not occur (that is, the water barrier layer of the power cable is not damaged), the power is supplied. When the cable generates heat due to power transmission or the like and the temperature of the power cable rises, the water absorption layer may release the absorbed water into the power cable.
Then, when the water absorption layer releases water, it also releases it inside. Therefore, the moisture released from the water absorption layer may gradually permeate into the insulating layer, causing dielectric breakdown (so-called water tree) through insulation deterioration.

The present invention has been made in view of the above problems, and is a power cable capable of preventing dielectric breakdown in the insulating layer even if the moisture absorbed by the water absorbing layer is released into the cable. The purpose is to provide.

In order to solve the above problem, the invention according to claim 1 is
In a power cable in which at least an insulating layer and a water absorbing layer are formed around the central conductor toward the outside.
A salt made of an inorganic compound that can be a hydrate is arranged between the insulating layer and the water absorbing layer.

The invention according to claim 2 is characterized in that, in the power cable according to claim 1, the inorganic compound contains at least one of magnesium sulfate, calcium chloride and magnesium oxide.

The invention according to claim 3 is characterized in that, in the power cable according to claim 1 or 2, the salts are arranged so as to be in contact with the inside of the water absorption layer.

The invention according to claim 4 is characterized in that, in the power cable according to any one of claims 1 to 3, the salts are arranged so as to be in contact with the outside of the insulating layer. ..

The invention according to claim 5 is the power cable according to any one of claims 1 to 4.
A moisture-proof layer is provided between the insulating layer and the water-absorbing layer.
The salts are arranged so as to be in contact with the inside, outside or both sides of the moisture-proof layer, or are arranged inside the moisture-proof layer.

The invention according to claim 6 is characterized in that, in the power cable according to claim 5, the water-absorbent layer is formed of a water-absorbent polymer.

The invention according to claim 7 is the power cable according to any one of claims 1 to 6.
The central conductor is formed by twisting a plurality of conductor strands.
It is characterized in that salts made of an inorganic compound that can be hydrates are arranged in the gaps between the conductor strands.

The invention according to claim 8 comprises an inorganic compound which can be a hydrate between the central conductor and the insulating layer in the power cable according to any one of claims 1 to 7. It is characterized in that salts are arranged.

According to the present invention, even if the water absorbed by the water absorption layer of the power cable is released into the cable, it is absorbed by the inorganic compound arranged between the insulating layer and the water absorption layer, and the inorganic compound is hydrated. Since the moisture is not desorbed, it is possible to accurately prevent the insulation breakdown from occurring in the insulating layer due to the moisture.

It is sectional drawing which shows the electric power cable which concerns on this invention. It is sectional drawing which shows another structural example of the power cable which concerns on this invention. It is a graph which shows the measurement result in (A) the experiment performed at room temperature (25 ° C.), and (B) the experiment performed at 90 ° C. (A) is a graph showing the result of measuring the water absorption of each salt, and (B) is a graph showing the result of measuring the amount of water remaining in each salt. It is sectional drawing which explains the gap of a plurality of conductor strands and shows the structural example which provided the internal moisture-proof layer.

Hereinafter, the power cable according to the present invention will be described with reference to the drawings.
However, although each of the embodiments described below is provided with various technically preferable limitations for carrying out the present invention, the scope of the present invention is not limited to the following embodiments and illustrated examples. .. The power cable may have at least an insulating layer and a water absorbing layer formed around the central conductor toward the outside.

FIG. 1 is a cross-sectional view showing a power cable according to the present invention. In each diagram including FIG. 1, the relative size and thickness of the conductor strands and each layer do not necessarily reflect the relative size and thickness of the actual power cable.
In the present embodiment, the power cable 10 includes a cable core 11 formed by sequentially laminating an inner semiconductive layer 30, an insulating layer 40, and an outer semiconductive layer 50 from the outer periphery of the central conductor 20 to the outside. ing.

The power cable 10 has a water absorption layer 60 formed on the outside of the cable core 11 (outside of the outer semi-conductive layer 50).
Further, a water-impervious layer 70 is formed on the outside of the water-absorbing layer 60. An anticorrosion layer 80 is formed on the outside of the impermeable layer 70.

[Cable core: center conductor]
The central conductor 20 is formed by twisting a plurality of conductor strands 21.
Such a central conductor 20 may be a circular compressed conductor obtained by twisting and compressing a conductor wire 21. Further, a divided conductor structure (divided compression conductor) including a plurality of segment conductors composed of a bundle of twisted conductor strands 21 may be used, and various structures can be adopted for the structure of the central conductor 20.

[Cable core: Insulation layer, etc.]
An inner semi-conductive layer 30, an insulating layer 40, and an outer semi-conductive layer 50 are formed on the outside of the central conductor 20 by, for example, extrusion molding.
The method for forming the inner semi-conductive layer 30, the insulating layer 40, and the outer semi-conductive layer 50 and the materials to be used are appropriately selected according to the working voltage class and voltage form (alternating current or direct current) of the power cable. For example, in a general AC power cable, cross-linked polyethylene is used to form the insulating layer 40. Further, as the material of the inner semi-conductive layer 30 and the outer semi-conductive layer 50, for example, an ethylene vinyl acetate copolymer containing carbon particles, polyethylene, or a mixed resin thereof or the like is used.

[Water absorption layer]
A water absorption layer 60 is formed on the outside of the outer semi-conductive layer 50.
The water absorption layer 60 is formed by winding a conductive water absorption tape or a conductive water absorption cushion tape containing a water absorption powder.
As the material of the water-absorbing powder, for example, a water-absorbing polymer such as an acrylate-based crosslinked product, a vinyl acetate / acrylic acid ester copolymer saponate, and an acrylate / acrylamide copolymer is used.

As for the method of winding the conductive water-absorbing tape or the conductive water-absorbing cushion tape, any of well-known tape winding methods such as a spiral wrap winding and a vertical wrap winding may be adopted.
Further, the thickness of the water absorption layer 60 can be increased by increasing the thickness of the water absorption layer 60, but the cable cost and weight increase due to the increase in the size of the power cable 10 and the like. Should be adjusted to the proper thickness.

[Metal coating layer and anticorrosion layer]
A lead cover is provided on the outer periphery of the water absorption layer 60 as a metal impermeable layer 70. In addition to the lead cover, the water-impervious layer 70 may be, for example, a stainless steel cover (SUS cover), an aluminum cover, or a metal cover with an annular corrugated corrugated metal, or a metal laminate tape wrapped around it. It may be a metal laminate cover that has been made to adhere with a wrap.
That is, the material of the water-impervious layer 70 is not particularly limited as long as it is a metal cover that prevents the ingress of moisture from the outside and obtains an electrical shielding effect, but has good corrosion resistance, workability, and the like. Is preferable.

An anticorrosion layer 80 is extruded on the outer periphery of the impermeable layer 70. The material of the anticorrosion layer 80 can be appropriately selected depending on the usage environment and specifications of the power cable, and for example, polyethylene or polyvinyl chloride can be used, but the material is not limited to these and protects the inner layer. Any material having strength, water resistance, durability and the like may be formed.

[Salts consisting of inorganic compounds that can be hydrates]
In the power cable 10 of the present invention, salts made of an inorganic compound that can be a hydrate are arranged.
The inorganic compound constituting the salts may be any inorganic compound that can be a hydrate, and specifically, magnesium sulfate, sodium sulfate, aluminum sulfate, calcium sulfate, copper sulfate, calcium chloride, cobalt chloride, magnesium oxide, etc. Examples thereof include iron oxide, sodium carbonate, sodium acetate and sodium thiosulfate. The above-mentioned inorganic compound preferably contains at least one of magnesium sulfate, calcium chloride and magnesium oxide.

[Arrangement of salts]
In the power cable 10 of the present invention, salts made of the above-mentioned inorganic compounds that can be hydrates are arranged between the insulating layer 40 and the water absorbing layer 60.
Various methods can be adopted as a method for arranging the salts between the insulating layer 40 and the water absorbing layer 60.

(1) Salts can be arranged so as to be in contact with the inside of the water absorption layer 60.
In this case, for example, salts may be applied to the inside of the water absorption tape or the like constituting the water absorption layer 60, or a sheet kneaded with salts may be attached to the inside of the water absorption tape or the like. By wrapping the water-absorbing tape in the state around the outer semi-conductive layer 50 to form the water-absorbing layer 60, the salts can be arranged so as to be in contact with the inside of the water-absorbing layer 60, and the salts can be arranged between the insulating layer 40 and the water-absorbing layer 60. Can be placed in between.

(2) The salts can be arranged so as to be in contact with the outside of the insulating layer 40 and the outer semi-conductive layer 50.
In this case, for example, after forming the insulating layer 40 and the outer semi-conductive layer 50, the insulating layer 40 and the outer semi-conductive layer 50 are coated with salts, or a sheet kneaded with salts is applied to the insulating layer. The salts can be arranged so as to be in contact with the outside of the insulating layer 40 and the external semi-conductive layer 50 by wrapping or sticking them around the outside of the insulating layer 40 or the external semi-conductive layer 50, and the salts can be arranged in contact with the insulating layer 40 and the water absorbing layer. It can be placed between 60 and 60.

(3) As shown in FIG. 2, a moisture-proof layer 90 is provided between the insulating layer 40 and the water-absorbing layer 60 (between the outer semi-conductive layer 50 and the water-absorbing layer 60 in FIG. 2), and salts are added to the moisture-proof layer. It can be arranged so as to be in contact with the inside, outside or both sides of the 90, or can be arranged inside the moisture-proof layer 90.
The moisture-proof layer 90 can be formed of butyl rubber (isobutylene / isoprene copolymer) as a main material. Although the moisture-proof layer 90 can be formed of a material other than butyl rubber, high waterproof / moisture-proof properties can be obtained by using butyl rubber.

The moisture-proof layer 90 can be formed by extrusion molding of, for example, butyl rubber in the manufacturing process of the power cable 10. Extrusion molding has high processability and productivity, and each wet layer 90 formed by this can easily obtain high waterproof / moisture-proof performance by seamlessness.
Further, the moisture-proof layer 90 is formed by wrapping a tape made of butyl rubber or the like, or a tape coated or laminated with butyl rubber or the like on a fiber such as cloth or cotton as a base material, around the outside of the outer semiconductive layer 50. Is also possible.
It is also possible to configure the moisture-proof layer 90 to have conductivity, but refer to Patent Document 1 described above for this.

When the salts are arranged so as to be in contact with the inside, outside or both sides of the moisture-proof layer 90, the salts may be applied to the moisture-proof layer 90 or a sheet kneaded with salts may be applied to the inside or outside of the moisture-proof layer 90 in the same manner as described above. , Can be placed by pasting or wrapping on both sides.
When the salts are arranged inside the moisture-proof layer 90, the salts can be arranged by kneading the salts into butyl rubber or the like constituting the moisture-proof layer 90.
Then, by arranging the salts so as to be in contact with the inside, the outside, and both sides of the moisture-proof layer 90 or inside the moisture-proof layer 90 in this way, the salts are arranged between the insulating layer 40 and the water absorption layer 60. It becomes possible.

When salts made of an inorganic compound that can be hydrates are arranged between the insulating layer 40 and the water absorbing layer 60 in the power cable 10 as in the present invention, the salts function as follows.
That is, as described above, the water absorption layer 60 incorporated in the power cable 10 at the time of manufacturing the power cable 10 may already contain water. In that case, after the power cable 10 is installed, when the power cable 10 generates heat due to power transmission or the like and the temperature of the power cable 10 rises (for example, about 90 ° C.), the water absorption layer 60 absorbs the water absorbed by the power cable. It may be released within 10.

However, when salts composed of inorganic compounds that can be hydrates as in the present invention are arranged between the insulating layer 40 and the water absorbing layer 60, the water released from the water absorbing layer 60 is more than the water absorbing layer 60. When the water released to the inside reaches the portion where the salts are arranged, it is taken up as hydrated water by the inorganic compound and absorbed by the salts. At that time, the inorganic compound becomes a hydrate (note that some of the water may be adsorbed by the inorganic compound).
Then, the reaction in which the inorganic compound takes in water and becomes a hydrate occurs even in a temperature environment of about 90 ° C. Further, since the temperature at which the hydrated water is desorbed from the hydrate is usually higher than 90 ° C., the hydrated water is not desorbed from the hydrated inorganic compound in a temperature environment of about 90 ° C.

Therefore, even if the temperature of the power cable 10 rises due to power transmission or the like and water is released from the water absorption layer 60 into the power cable 10, at least the water released inward from the water absorption layer 60 exists inside the water absorption layer 60. Since it is reliably absorbed by the salts, the water does not reach the insulating layer 40 inside the insulating layer 40.
Therefore, even if the moisture absorbed by the water absorbing layer 60 is released into the power cable 10, the moisture does not permeate into the insulating layer 40, causing insulation deterioration or dielectric breakdown (so-called water) in the insulating layer 40. It is possible to reliably prevent the occurrence of a tree).

An experiment conducted by the present inventors to confirm the above will be described.
[Experiment 1]
First, an experiment was conducted to confirm whether or not the salts could remove the water contained in the water absorbing material constituting the water absorbing layer 60 of the power cable 10 from the water absorbing material.

[Experiment 1-1]
Specifically, the water-absorbing material for cables (VT-403 (trade name), manufactured by Fukuoka Cross Industry Co., Ltd.) is cut into appropriate amounts, and each water-absorbing material piece, the bottle and lid of the sample tube are separated into appropriate amounts, and the temperature is 25 ° C. Exposed to the environment for more than 24 hours. At that time, the amount of water absorbed by the water absorbing material (water absorbing material piece) at room temperature (25 ° C.) was 8 [wt%].
After that, one piece of water-absorbing material and 1 g of magnesium sulfate (an inorganic compound that can become a hydrate) are placed in a bottle so as not to come into contact with each other and covered (Sample A1), and the other bottle absorbs water. A piece of wood and 1 g of calcium chloride (an inorganic compound that can become a hydrate) were placed in the same manner and covered (Sample A2). In addition, as a control experiment, 1 g of porous calcium silicate and a piece of water-absorbing material were put in another bottle and covered (Sample B), and further, only a piece of water-absorbing material was put and the bottle was not covered (Sample C1). , A bottle with a lid (Sample C2) containing only a piece of water absorbing material was prepared.
Then, each sample A1 to C2 was stored in a precision chamber (25 ° C.), and the amount of water [wt%] remaining in each water-absorbing material piece was measured over time.
The measurement results after one week (7 days) and after 30 days are shown in FIG. 3 (A).

[Experiment 1-2]
Further, for each of the samples A1 to C2 prepared in the same manner, the same experiment was conducted with the temperature of the precision chamber set to 90 ° C. The measurement results after one week (7 days) and after 30 days are shown in FIG. 3 (B).

From the experimental results at room temperature (25 ° C.) and high temperature (90 ° C.) in sample C1 (without lid) and sample C2 (with lid), first, a certain amount of water can be released from the water absorbing material even at room temperature (25 ° C.). However, it can be seen that a large amount of water is released when the temperature rises to 90 ° C.
Further, from the results of Sample A1 and Sample A2, it can be seen that magnesium sulfate and calcium chloride can sufficiently deprive the water absorbing material of water contained in the water absorbing material at both normal temperature and high temperature.
On the other hand, from the result of sample B, porous calcium silicate can deprive the water absorbing material of water contained in the water absorbing material at high temperature, but has the ability to deprive the water absorbing material of water contained in the water absorbing material at room temperature. It turns out that it is weak (or the water contained in the water absorbing material cannot be taken from the water absorbing material).

[Experiment 2]
Next, an experiment was conducted to confirm whether the salts released the absorbed water under high temperature and low humidity conditions.
[Experiment 2-1]
Specifically, 1 g of each salt was placed on an aluminum foil tray, and the water absorption [wt%] was measured after 1 hour, 24 hours, and 7 days in a constant temperature bath at a temperature of 40 ° C. and a humidity of 85%. The measurement results of each salt are shown in FIG. 4 (A).

[Experiment 2-2]
After 7 days, the temperature of the constant temperature bath was 90 ° C. and the humidity was 0%, and each salt was left to stand, and the amount of water [wt%] remaining in each salt was measured after 24 hours and 7 days. The measurement results of each salt are shown in FIG. 4 (B).
In each sample in FIGS. 4 (A) and 4 (B), samples A1, A2 and B are magnesium sulfate, calcium chloride and porous calcium silicate as in the case of the above experiment 1, and sample A3 is oxidized. Magnesium (an inorganic compound that can be a hydrate).

As a result, magnesium sulfate (Sample A1) absorbed about 100 [wt%] of water. Further, when magnesium sulfate was dried at 90 ° C. for 7 days, water was removed from magnesium sulfate, but about 30 [wt%] of water remained, and this state continued thereafter.
Calcium chloride (Sample A2) absorbed water up to about 350 [wt%] and dissolved (deliquescent). Further, when calcium chloride was dried at 90 ° C. for 7 days, water was removed from calcium chloride, but about 20 [wt%] of water remained, and this state continued thereafter.
Magnesium oxide (Sample A3) absorbed about 30 [wt%] of water. Further, when magnesium oxide was dried at 90 ° C. for 7 days, water was removed from magnesium oxide, but about 25 [wt%] of water remained, and this state continued thereafter.

It is considered that the water remaining in each of the inorganic compounds of Samples A1 to A3 became hydrated water (each inorganic compound became hydrate).
As described above, calcium chloride is deliquescent and dissolves when it absorbs sufficient water, but since the amount of water in the power cable 10 is very small, even if calcium chloride is placed as salts in the power cable 10. , Calcium chloride does not deliquesce and dissolve.

On the other hand, the porous calcium silicate (Sample B) absorbed about 10 [wt%] of water, but when the porous calcium silicate was dried at 90 ° C. for 7 days, the amount of water remaining in the porous calcium silicate. Was almost 0 [wt%], almost all the water was removed, and no water remained in the salts.
That is, in the case of porous calcium silicate (Sample B), when the water absorption layer 60 of the power cable 10 releases water, the water can be absorbed, but when the amount of water in the power cable 10 decreases, it is absorbed. It can be seen that there is a high possibility of releasing water.

[effect]
As described above, according to the power cable 10 according to the present invention, salts composed of inorganic compounds (magnesium sulfate, calcium chloride, magnesium oxide, etc.) that can be hydrates between the insulating layer 40 and the water absorbing layer 60. Is arranged, the power cable 10 becomes hot (about 90 ° C.) due to power transmission or the like, and even if the water absorbed in the water absorption layer 60 at the time of manufacture is released from the water absorption layer 60, at least from the water absorption layer 60. The water released to the inside is surely absorbed by the salts arranged inside the water absorption layer 60. Therefore, the salts prevent the moisture from reaching the insulating layer 40 further inside.

Further, among the water absorbed by the salts, the water taken into the inorganic compound as hydrated water does not desorb from the inorganic compound (hydrate) at a temperature of about 90 ° C.
Therefore, even if the water absorbed by the water absorption layer 60 is released into the power cable 10, the water is taken into the inorganic compound as hydrated water and does not desorb from the inorganic compound, so that the water no longer penetrates into the insulating layer 40. Insulation deterioration and dielectric breakdown (so-called water treeing) in the insulating layer 40 can be reliably prevented.

Hereinafter, an appropriate amount of salts to be arranged in the power cable 10 will be described.
As described above, it is assumed that about 8 [wt%] of water absorbed by the water absorbing layer 60 of the power cable 10 at room temperature is released when the power cable 10 becomes hot, and further released. Assuming that all the water is taken up as hydrated water by the inorganic compounds of salts, when all the inorganic compounds become hydrates, the water taken up as hydrated water is tentatively 25 [wt%] of the inorganic compound as described above. If this is the case, the amount of salts required is (8/25 =) 0.32 times that of the water absorbing material of the water absorbing layer 60.

As described above, the amount of water absorbed by the water absorbing material of the water absorbing layer 60 of the power cable 10 (that is, the amount of water that can be released from the water absorbing layer 60) is α [wt%], and all the inorganic compounds constituting the salts are contained. When the amount of water taken in when becoming hydrate is β [wt%] with respect to the inorganic compound, salts are arranged in the power cable 10 in an amount of α / β times that of the water absorbing material of the water absorbing layer 60. I know what to do.
However, even if the power cable 10 becomes hot, not all the water absorbed by the water absorption layer 60 is released, and the water is not only released from the water absorption layer 60 to the inside (insulation layer 40 side) but also to the outside. It is possible that the amount of salts to be placed in the power cable 10 may be less than the above amount, considering that it is also released.
The amount of salts to be arranged in the power cable 10 is appropriately determined in consideration of the above circumstances.

[Modification example]
Further, salts made of an inorganic compound that can be a hydrate can be arranged not only between the insulating layer 40 and the water absorbing layer 60 of the power cable 10 as described above, but also inside the insulating layer 40. It is possible.
For example, as shown in FIG. 5, a salt made of an inorganic compound that can be a hydrate is arranged in a gap 22 between a plurality of conductor strands 21 formed by twisting the central conductor 20. It is also possible.

In this case, for example, salts may be arranged so as to fill the gaps 22 of the plurality of conductor strands 21, and a tape-shaped or string-shaped water absorbing member (not shown) containing salts may be arranged as a conductor element. It is also possible to arrange the salts by winding them around the wire 21, or to arrange the water absorbing member along the conductor wire 21, and the method of arranging the salts is not limited.
By arranging salts made of inorganic compounds that can be hydrates in the gaps 22 between the plurality of conductor strands 21 constituting the central conductor 20 in this way, when water enters the central conductor 20 or the central conductor When water tries to enter the 20, the salts accurately absorb the water, so that it is possible to effectively prevent the water from entering the central conductor 20 and moving along the longitudinal direction of the central conductor 20. It becomes.

Further, it is also possible to arrange salts made of an inorganic compound that can be hydrates between the central conductor 20 of the power cable 10 and the insulating layer 40.
In this case, for example, salts can be arranged inside the insulating layer 40 or inside or outside the inner semi-conductive layer 30 by applying salts or attaching a sheet kneaded with salts. ..

Alternatively, as shown in FIG. 5, for example, an internal moisture-proof layer 100 is provided between the central conductor 20 and the internal semi-conductive layer 30, and salts are arranged so as to be in contact with the inside, outside, or both sides of the internal moisture-proof layer 100. , Or it may be configured to be arranged inside the internal moisture-proof layer 100.
In this case, the internal moisture-proof layer 100 can be formed of butyl rubber (isobutylene / isoprene copolymer) as a main material, similarly to the moisture-proof layer 90 (see FIG. 2) described above. Although it is possible to form the internal moisture-proof layer 100 with a material other than butyl rubber, high waterproof / moisture-proof properties can be obtained by using butyl rubber.

Then, in the same manner as in the case of the moisture-proof layer 90 described above, the salts can be arranged so as to be in contact with the inside, outside or both sides of the internal moisture-proof layer 100, or can be arranged inside the internal moisture-proof layer 100.
Even with this configuration, when moisture enters the central conductor 20 or when moisture tries to enter the central conductor 20, the salts accurately absorb the moisture, so that the moisture enters the central conductor 20. It is possible to effectively prevent the conductor 20 from entering and moving along the longitudinal direction of the central conductor 20.

Although the moisture-proof layer 90 is not shown in FIG. 5, the moisture-proof layer 90 is provided between the insulating layer 40 and the water-absorbing layer 60 (for example, between the external semi-conductive layer 50 and the water-absorbing layer 60) in the above modification. It goes without saying that the layer 90 can be provided and the salts can be arranged so as to be in contact with the inside, outside or both sides of the moisture-proof layer 90, or can be arranged inside the moisture-proof layer 90.
Needless to say, the present invention is not limited to the above-described embodiments and modifications, and can be appropriately modified as long as the gist of the present invention is not deviated.

10 Power cable 20 Center conductor 21 Conductor wire 22 Gap between conductor wires 40 Insulation layer 60 Water absorption layer 90 Moisture-proof layer

Claims (8)

In a power cable in which at least an insulating layer and a water absorbing layer are formed around the central conductor toward the outside.
A power cable characterized in that salts made of an inorganic compound that can be a hydrate are arranged between the insulating layer and the water absorbing layer. The power cable according to claim 1, wherein the inorganic compound contains at least one of magnesium sulfate, calcium chloride and magnesium oxide. The power cable according to claim 1 or 2, wherein the salts are arranged so as to be in contact with the inside of the water absorption layer. The power cable according to any one of claims 1 to 3, wherein the salts are arranged so as to be in contact with the outside of the insulating layer. A moisture-proof layer is provided between the insulating layer and the water-absorbing layer.
Any one of claims 1 to 4, wherein the salts are arranged so as to be in contact with the inside, the outside, or both sides of the moisture-proof layer, or are arranged inside the moisture-proof layer. The power cable described in. The power cable according to claim 5, wherein the water-absorbent layer is formed of a water-absorbent polymer. The central conductor is formed by twisting a plurality of conductor strands.
The power cable according to any one of claims 1 to 6, wherein salts made of an inorganic compound that can be a hydrate are arranged in the gaps between the conductor wires. The power cable according to any one of claims 1 to 7, wherein salts made of an inorganic compound that can be a hydrate are arranged between the central conductor and the insulating layer. ..

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