JP2020087798A - Power cable - Google Patents

Abstract

To provide a power cable having insulation characteristics equivalent to or higher than that of a conventional power cable and having excellent adhesion between a conductor and an insulating layer.SOLUTION: There is provided a power cable comprising a conductor, an insulating layer provided on the outer periphery of the conductor and an adhesive layer in contact with the conductor and the insulating layer, wherein the conductor is a compressed twisted-wire including a plurality of wires formed of copper or a copper-based alloy and the constituent material of the insulating layer contains a crosslinked polyolefin.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to power cables.

BACKGROUND ART Conventionally, as a power cable, a cable including a conductor, an inner semiconductive layer, an insulating layer, and an outer semiconductive layer in order from the center is known (eg, Patent Document 1). A typical example of such a power cable is a crosslinked polyethylene insulated vinyl sheath cable (CV cable) (specification [0002] of Patent Document 1).

JP, 06-203651, A

Insulates from the conductor while having insulation characteristics equivalent to or higher than that of a power cable having an inner semiconductive layer, an insulating layer, and an outer semiconductive layer on the outer circumference of the conductor (hereinafter sometimes referred to as a conventional power cable) A power cable with excellent adhesion to layers is desired.

In particular, a power cable whose transmission voltage is higher than 600 V and higher than 3500 V is more likely to be in a use state in which partial discharge and insulation breakdown are more likely to occur than an electric wire whose use voltage is several hundred V or less. Therefore, a power cable that is unlikely to cause partial discharge or dielectric breakdown over a long period from the beginning of use is desired.

In addition, the power cable is typically laid and used in an underground pipe or the like. When the power cable is used, the insulating layer thermally expands and contracts due to the heat cycle that accompanies repeated energization and de-energization. In particular, it is desired that the conductor and the insulating layer can be kept in close contact with each other even when the insulating layer is thermally contracted.

Therefore, it is an object of the present disclosure to provide a power cable that has insulation characteristics equal to or higher than those of conventional power cables and that has excellent adhesion between a conductor and an insulating layer.

The power cable of the present disclosure is
A conductor,
An insulating layer provided on the outer periphery of the conductor,
An adhesive layer in contact with the conductor and the insulating layer,
The conductor is a compressed stranded wire including a plurality of strands made of copper or a copper-based alloy,
The constituent material of the insulating layer includes cross-linked polyolefin.

The power cable of the present disclosure has insulation properties equal to or higher than those of conventional power cables, and has excellent adhesion between the conductor and the insulating layer.

FIG. 1 is a schematic cross-sectional view showing a power cable of the embodiment. FIG. 2 is a diagram for explaining a method for measuring the ratio of the area of the contour of the compressed stranded wire to the area of the envelope circle of the compressed stranded wire forming the conductor in the cross section of the power cable.

[Description of Embodiments of the Present Disclosure]
First, embodiments of the present disclosure will be listed and described.
(1) A power cable according to an aspect of the present disclosure is
A conductor,
An insulating layer provided on the outer periphery of the conductor,
An adhesive layer in contact with the conductor and the insulating layer,
The conductor is a compressed stranded wire including a plurality of strands made of copper or a copper-based alloy,
The constituent material of the insulating layer includes cross-linked polyolefin.

The power cable of the present disclosure includes a compression stranded wire as a conductor, and includes an adhesive layer in contact with the conductor and the insulating layer. Therefore, the power cable of the present disclosure does not include an internal semiconductive layer between the conductor and the insulating layer, but as described below, has an insulation property equal to or higher than that of a conventional power cable including an internal semiconductive layer. Have. Moreover, the power cable of the present disclosure has excellent adhesion between the conductor and the insulating layer.

In the compressed stranded wire, the gap (twisted groove) formed between the adjacent outer peripheral strands can be made smaller (shallow) as compared with the uncompressed stranded wire (hereinafter, also referred to as non-compressed wire). Therefore, the twist groove of the compressed stranded wire is easily filled with the constituent material of the adhesive layer. In addition, typically, the adhesive layer covers the entire circumference of the compressed stranded wire. The conductor and the insulating layer can be brought into close contact with each other by the adhesive layer that fills the twist groove and covers the conductor. As a result, it is considered that there are few voids between the conductor and the insulating layer, which can be local electric field concentration points. It is considered that the small number of voids makes it difficult to cause partial discharge, water tree, and the like due to local electric field concentration, and makes it difficult to cause dielectric breakdown due to these. In addition, it is considered that the oxidative deterioration of the insulating layer due to air, water, or the like that can be present in the voids can be easily reduced because the voids are small. For these reasons, the power cable of the present disclosure has excellent insulating properties.

Further, when the power cable of the present disclosure is used, the insulating layer undergoes thermal contraction due to heat cycles associated with repeated energization and non-energization, and tends to be displaced along the axial direction of the conductor. The adhesive layer can reduce the displacement of the insulating layer. Therefore, the power cable of the present disclosure can prevent the end portion of the insulating layer from being displaced from the initial position due to the heat shrinkage of the insulating layer, and the end portion of the conductor from being exposed from the insulating layer. Therefore, the power cable of the present disclosure can maintain the state in which the conductor and the insulating layer are in close contact with each other for a long period of time.

(2) As an example of the power cable of the present disclosure,
The constituent material of the adhesive layer has a form containing at least one compound selected from the group consisting of ethylene methyl methacrylate copolymer, ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, and maleic anhydride. Can be mentioned.

Since the above-described embodiment includes the adhesive layer containing the above-mentioned specific compound as a constituent material, it has excellent adhesiveness between the conductor and the insulating layer.

(3) As an example of the power cable of (2) above,
An example is a mode in which the electrical resistivity of the adhesive layer at room temperature is 1×10 ⁴ Ω·cm or more.

The above-described embodiment has an adhesive layer having a high electric resistivity and therefore has excellent electric insulation.

(4) As an example of the power cable of the present disclosure,
The thickness of the adhesive layer may be 0.5 mm or less.

The adhesive layer in the above form is very thin. Therefore, the said form can make an insulating layer thicker compared with the conventional electric power cable provided with the conductor of the same conductor cross-sectional area. From this point of view, the above-described form is likely to enhance the insulating property.

(5) As an example of the power cable of the present disclosure,
In the cross-section, there is a form in which an envelope circle of the compressed stranded wire and a contour of the compressed stranded wire are taken, and a ratio of an area in the outline to an area of the envelope circle is more than 85%.

In the above embodiment, the ratio of the area in the contour of the compressed twisted wire to the area of the envelope circle of the compressed twisted wire (hereinafter, also referred to as conductor occupancy ratio) is large in the cross section. It can be said that such a twisted wire has a shallow twist groove. Therefore, it is considered that the above-described embodiment can more reliably reduce the voids that can be local electric field concentration points between the conductor and the insulating layer. Therefore, in the above-described embodiment, dielectric breakdown due to the voids, oxidative deterioration of the insulating layer, and the like are less likely to occur, and excellent insulating characteristics can be easily maintained for a long period of time.

(6) As an example of the power cable of the present disclosure,
Examples of the constituent material of the insulating layer include a form containing an antioxidant.

The antioxidant in the above-mentioned embodiment has a function of suppressing acceleration of oxidation (copper damage) due to contact of the cross-linked polyolefin forming the insulating layer with copper or a copper-based alloy forming the conductor. Therefore, in the above embodiment, even if there is a portion where the conductor and the insulating layer are in direct contact with each other, oxidative deterioration of the insulating layer does not easily occur, and it is easy to maintain excellent insulating characteristics for a long period of time.

(7) As an example of the power cable of (6) above,
The antioxidant is phenolic,
Examples of the constituent material of the insulating layer include a form containing the antioxidant in an amount of 0.05% by mass or more and 0.5% by mass or less.

Since the said form contains the above-mentioned specific antioxidant in the above-mentioned specific range, the oxidation deterioration of an insulating layer does not occur easily, and it is easy to maintain the outstanding insulating characteristic for a long period of time.

(8) As an example of the power cable of the present disclosure,
In the partial discharge test, a mode in which the discharge generation voltage of 10 pC is 15 kV or more can be mentioned.

In the above embodiment, the discharge generation voltage of 10 pC is as high as 15 kV or more, and partial discharge is difficult.

(9) As an example of the power cable of the present disclosure,
In the AC breakdown test, a form in which the breakdown voltage is 20 kV/mm or more can be mentioned.

In the above embodiment, the breakdown voltage is as high as 20 kV/mm or more, and it is difficult to cause dielectric breakdown.

(10) As an example of the power cable of the present disclosure,
In the AC breakdown test after flooding and charging, the breakdown voltage is 15 kV/mm or more.

In the above-mentioned embodiment, the breakdown voltage after flooding is as high as 15 kV/mm or more, and it is difficult to cause dielectric breakdown for a long period of time.

(11) As an example of the power cable of the present disclosure,
An example is a mode in which the transmission voltage is 6.6 kV or higher.

The above-mentioned form has excellent insulation characteristics as described above, and can be suitably used for a high-voltage cable having a transmission voltage of 6.6 kV or more.

[Details of the embodiment of the present disclosure]
Hereinafter, embodiments of the present disclosure will be specifically described with reference to the drawings. The same reference numerals in the drawings indicate the same names.

[Embodiment]
(Outline)
Hereinafter, the power cable according to the embodiment will be described with reference to FIGS. 1 and 2 as appropriate.
The power cable 1 of the embodiment includes a conductor 2 and an insulating layer 3. The insulating layer 3 is provided on the outer periphery of the conductor 2. The power cable 1 is a rubber/plastic insulated power cable in which the main constituent material of the insulating layer 3 is a crosslinked polyolefin. Typically, the power cable 1 includes an outer semiconductive layer 5 on the outer periphery of the insulating layer 3, and further includes a shielding layer and a sheath (neither is shown) on the outer periphery thereof.

Particularly, in the power cable 1 of the embodiment, the conductor 2 is a compression stranded wire including a plurality of strands 20 made of copper or a copper-based alloy. The power cable 1 of the embodiment also includes the adhesive layer 4 that contacts the conductor 2 and the insulating layer 3. That is, the power cable 1 of the embodiment does not include an internal semiconductive layer as compared with a conventional power cable such as a CV cable. However, in the power cable 1 of the embodiment, the entire inner peripheral surface of the insulating layer 3 does not contact the entire outer peripheral surface of the conductor 2, and typically, the adhesive layer 4 is provided between the conductor 2 and the insulating layer 3. Intervene.
Hereinafter, each component will be described in detail.

(Power cable)
<conductor>
The power cable 1 of the embodiment includes a conductor 2 made of a compressed stranded wire. The compression stranded wire is a kind of stranded wire in which a plurality of strands 20 are twisted together, and is further compression-molded after twisting.

When the cross-sectional shape of the compressed stranded wire is a shape close to a circle as shown in FIG. 1, the following effects are obtained. The cross-sectional shape or outer shape of the compression stranded wire can be changed depending on the molding die used for compression molding. In addition, the horizontal cross section here means a cross section taken along a plane orthogonal to the axial direction of the power cable 1.

(1) Easy to bend.
(2) Of the strands 20, the gaps (twisted grooves) provided between the outer circumferential strands forming the contour of the stranded wire are likely to be small.
(3) It is easy to form the adhesive layer 4 and the insulating layer 3 by extrusion in the manufacturing process.
(4) The thickness t of the adhesive layer 4 and the thickness of the insulating layer 3 can be easily manufactured uniformly as compared with the case where the cross-sectional shape is an angular shape such as a hexagon. As a result, it is easy to reduce the cable diameter.

As an example of the compressed stranded wire, seven concentric stranded compressed stranded wires shown in FIG. 1 can be cited. The number of the strands 20, the cross-sectional area of each strand 20, the twisting method, and the like can be appropriately selected within the range of the conductor 2 that satisfies the predetermined cross-sectional area according to the transmission voltage. For example, in the power cable 1 having a transmission voltage of 6.6 kV, the conductor 2 has a nominal cross-sectional area of 14 mm ² or more and 1200 mm ² or less. The outer diameter of the conductor 2 is 4.4 mm or more and 41.7 mm or less.

The constituent material of each strand 20 is copper or a copper-based alloy. "Copper" is so-called pure copper. The "copper-based alloy" is an alloy containing an additive element and the balance of Cu and impurities. A known composition can be used for the copper-based alloy. The conductivity of copper or a copper-based alloy is higher than that of aluminum or an aluminum-based alloy, for example. Therefore, if the conductor 2 is provided with a compression strand of the wire 20 made of copper or a copper-based alloy, the conductor cross-sectional area can be easily reduced. As a result, it is easy to reduce the cable diameter.

It is preferable that the twist groove of the compressed stranded wire forming the conductor 2 is shallow. Quantitatively, in the cross section of the power cable 1, as shown in FIG. 2, the envelope circle 25 of the compressed stranded wire forming the conductor 2 and the contour of this compressed stranded wire are taken. The ratio of the area in the contour of the compressed twisted wire to the area of the envelope circle 25 (conductor occupancy ratio) is more than 85%. The area within the contour of the compressed stranded wire includes the area of the plurality of strands 20 and the area of the gap 22 formed by the plurality of strands 20 in addition to the area of the plurality of strands 20. In FIG. 2, the envelope circle 25 is virtually shown by a chain double-dashed line. Further, in FIG. 2, a region (hereinafter, referred to as an intervening region 27) of the envelope circle 25 excluding the area within the contour of the compression twisted wire is hatched, and the gap 22 is cross-hatched. In FIG. 2, the hatching of the wires 20 is omitted. The intervening region 27 is filled with the constituent material of the adhesive layer 4 (FIG. 1 ).

When the above-mentioned conductor occupancy rate exceeds 85%, the power cable 1 is likely to suppress deterioration of the insulating characteristics of the insulating layer 3 in combination with the provision of the adhesive layer 4, as described below. Therefore, the power cable 1 can easily maintain excellent insulation characteristics for a long period of time.

It can be said that the compressed stranded wire in which the conductor occupancy ratio exceeds 85% has an outer shape with shallow twisted grooves and small unevenness as compared with the non-compressed wire. Further, it can be said that the cross-sectional shape of such a compressed stranded wire is close to a circle. If the twist groove is shallow, it is easy to reduce the formation of voids in the twist groove by filling the constituent material of the adhesive layer 4. The compression stranded wire forming the conductor 2 and the insulating layer 3 can be adhered to each other by the adhesive layer 4 filled in the twist groove. Further, typically, the entire circumference of the compressed stranded wire is covered with the adhesive layer 4, and the adhesive layer 4 is interposed between the compressed stranded wire forming the conductor 2 and the insulating layer 3. Due to such an adhesive layer 4, the conductor 2 and the insulating layer 3 are more easily brought into close contact with each other. Therefore, it is considered that there are few gaps between the conductor 2 made of the compressed stranded wire and the insulating layer 3, which can be local electric field concentration points. Since the number of voids is small, it is easy to reduce dielectric breakdown due to electric field concentration in the voids. Further, it is considered that since the voids are small, inclusions such as air and water that may exist in the gaps are also small. Therefore, oxidative deterioration due to the insulating layer 3 being in contact with the inclusions for a long period of time is easily reduced. For these reasons, the power cable 1 can easily maintain a predetermined insulation characteristic.

It is expected that the larger the conductor occupancy rate is, the less the voids are. Therefore, the conductor occupancy ratio is preferably 88% or more, more preferably 90% or more, further preferably 95% or more.

Examples of methods for increasing the conductor occupancy ratio include the following.
(1) Increase the degree of compression during compression molding.
(2) A wire having a relatively large cross-sectional area (a wire having a certain thickness) is used as a wire to be twisted before compression molding.

<Insulation layer>
The constituent material of the insulating layer 3 includes crosslinked polyolefin. For example, when the constituent material of the insulating layer 3 is 100% by mass, the content of the crosslinked polyolefin is 95% by mass or more. Specific examples of the polyolefin include polyethylene (PE) and polypropylene (PP). Cross-linked polyethylene is an example of the constituent material of the insulating layer 3.

The constituent material of the insulating layer 3 may include an additive in addition to the crosslinked polyolefin. For example, the constituent material of the insulating layer 3 may include an antioxidant. By including the antioxidant, the oxidative deterioration of the insulating layer 3 can be effectively prevented. As an example of the constituent material of the insulating layer 3, cross-linked polyethylene containing an antioxidant can be mentioned.

Various antioxidants can be used. Particularly, phenolic antioxidants are preferable from the following points.
(1) The antioxidant effect of the crosslinked polyolefin is high in a wide temperature range.
(2) A copper damage prevention effect can be expected.
Copper damage is a phenomenon in which the constituent material of the conductor 2, copper, accelerates the oxidation of the insulating layer 3. When there is a portion where the conductor 2 and the insulating layer 3 are in direct contact with each other, copper damage may occur, but it is easy to prevent by including an antioxidant in the insulating layer 3.

The content of the antioxidant is, for example, 0.05% by mass or more and 0.5% by mass or less, with 100% by mass of the constituent material of the insulating layer 3 (the total amount of the crosslinked polyolefin and the additive such as the antioxidant). Is mentioned.

When the content of the antioxidant is 0.05% by mass or more, it is easy to prevent oxidation of the insulating layer 3 and copper damage. The greater the content of the antioxidant, the easier it is to prevent oxidation of the insulating layer 3 and copper damage. Therefore, the content of the antioxidant may be 0.08% by mass or more, further 0.10% by mass or more, and further 0.12% by mass or more.

When the content of the antioxidant is 0.5% by mass or less, defects such as foaming and discoloration of the insulating layer 3 can be reduced. Therefore, the content of the antioxidant may be 0.45 mass% or less, further 0.40 mass% or less, and further 0.30 mass% or less.

For example, various analysis methods can be used to measure the content of the antioxidant in the constituent material of the insulating layer 3. One example of the analysis method is gas chromatography analysis.

The thickness of the insulating layer 3 may be appropriately selected depending on the conductor cross-sectional area so as to satisfy predetermined insulating characteristics. The power cable 1 of the embodiment does not have an internal semiconductive layer. Therefore, a thickness of (the thickness of the inner semiconductive layer-the thickness t of the adhesive layer 4) can be added to the insulating layer 3 with respect to the conventional power cable. By increasing the thickness of the insulating layer 3 as described above, the power cable 1 is likely to have improved insulation characteristics. For example, in the power cable 1 having a transmission voltage of 6.6 kV, the thickness of the insulating layer 3 may be 4.0 mm or more and 6.0 mm or less.

<Adhesive layer>
The adhesive layer 4 contributes to the improvement of the adhesiveness between the conductor 2 and the insulating layer 3. Here, the power cable 1 is typically laid and used in an underground conduit or the like. Therefore, in the power cable 1, the tension resulting from the installed state does not substantially act. However, when the power cable 1 is used, the insulating layer 3 thermally expands and contracts due to a heat cycle that accompanies repeated energization and de-energization. In particular, when the insulating layer 3 thermally contracts, it is possible that the end of the insulating layer 3 is displaced from the initial position at the end of the power cable 1 and the end of the conductor 2 is exposed from the insulating layer 3. Therefore, it is desired that the adhesive layer 4 be able to maintain the state in which the conductor 2 and the insulating layer 3 are in close contact with each other, even when the tension resulting from the heat shrinkage during use acts on the insulating layer 3. The constituent material of such an adhesive layer 4 is preferably a material having excellent adhesiveness to both the conductor 2 made of copper or a copper-based alloy and the insulating layer 3 having a crosslinked polyolefin as a main material. For example, as the constituent material of the adhesive layer 4, a material other than the cross-linked polyolefin and having a higher adhesiveness with the conductor 2 than the cross-linked polyolefin can be suitably used.

An example of the constituent material of the adhesive layer 4 is selected from the group consisting of ethylene methyl methacrylate copolymer (EMMA), ethylene vinyl acetate copolymer (EVA), ethylene ethyl acrylate copolymer (EEA), and maleic anhydride. Are included. All the compounds listed above have high adhesiveness to the conductor 2. Therefore, the adhesive layer 4 made of the compounds listed above can bring the conductor 2 and the insulating layer 3 into close contact with each other. In addition, all of the above-listed compounds have appropriate fluidity when dissolved, and thus extrusion coating is easy to perform. In this respect, the manufacturability of the power cable 1 is also excellent. The constituent material of the adhesive layer 4 may be one kind of the compounds listed above, or may include two or more kinds of compounds.

The electrical resistivity of the adhesive layer 4 at room temperature (for example, 20° C.±15° C.) is, for example, 1×10 ⁴ Ω·cm or more. When the electric resistivity of the adhesive layer 4 is 1×10 ⁴ Ω·cm or more, the electric insulation is excellent. When good electrical insulation is desired, the electrical resistivity may be 5×10 ⁴ Ω·cm or more, and further 1×10 ⁵ Ω·cm or more. Such an adhesive layer 4 having an excellent electric insulation property may be constituted substantially by, for example, a compound such as EMMA described above to which a conductive substance (eg, carbon black) is not added.

The adhesive layer 4 includes a portion (hereinafter referred to as a filling portion) filled in the twist groove (the intervening region 27) of the compressed stranded wire forming the conductor 2. In addition to the filling portion, the adhesive layer 4 typically includes a portion (hereinafter, referred to as a covering portion) that surrounds at least a part of the outer circumference of the compressed stranded wire. The covering portion is a portion that covers at least a part of the envelope circle 25 described above. The adhesive layer 4 preferably includes the filling portion and the covering portion, and the covering portion preferably has an annular shape covering the entire circumference of the envelope circle 25.

As long as each twist groove of the compressed stranded wire is provided with the filling portion of the adhesive layer 4 described above, the outer peripheral surface of each filling portion and the insulating layer 3 By bonding the peripheral surface, the conductor 2 and the insulating layer 3 can be in close contact with each other. Therefore, the adhesive layer 4 allows the case without the covering portion and the case with the covering portion but not the annular shape. In other words, it is allowed that there is a portion where the conductor 2 and the insulating layer 3 are in direct contact with each other. On the other hand, when the filling portion and the covering portion are provided, the contact area with the adhesive layer 4 on the inner peripheral surface of the insulating layer 3 increases as the covering portion further approximates a ring, and the conductor 2 and the insulating layer 3 are provided. And are easily adhered, which is preferable. Further, when the covering portion is annular, the conductor 2 and the insulating layer 3 are in direct contact with each other by the interposition of the adhesive layer 4 between the entire circumference of the compressed stranded wire forming the conductor 2 and the insulating layer 3. Can be prevented. Therefore, the effect of preventing copper damage due to the interposition of the adhesive layer 4 can be expected.

The adhesive layer 4 may be thin as long as the conductor 2 and the insulating layer 3 can be kept in close contact with each other when the power cable 1 is used as described above. For example, the thickness t of the adhesive layer 4 is 0.5 mm or less.

The thickness t of the adhesive layer 4 here is the thickness of the above-mentioned covering portion. The thickness t is measured as follows. In the cross section of the power cable 1, the envelope circle 25 of the compression strand forming the conductor 2 and the contour line of the adhesive layer 4 are extracted. The distance between the envelope circle 25 and the contour line is measured along the diameter direction of the envelope circle 25. The above distances are measured at a plurality of measurement points (eg, 4 points to 5 points) and averaged. This average value is taken as the thickness t. If the covering portion is annular, it is advisable to take measurement points at equal intervals in the circumferential direction of the envelope circle 25. Alternatively, if the covering portion is annular, the distance may be measured over the entire circumference of the envelope circle 25 and averaged. If the covering portion is not annular, the measurement point is taken from the place where the covering portion is present.

The thinner the thickness t of the adhesive layer 4, the thicker the insulating layer 3 as described above, and the easier it is to improve the insulating property. This is because the value of (thickness of inner semiconductive layer-thickness t of adhesive layer 4) becomes large, and a large increase amount of the insulating layer 3 can be secured. Further, the thinner the thickness t, the more the material of the adhesive layer 4 can be reduced. From this point, the material cost can also be reduced. The thickness t may be 0.4 mm or less, and more preferably 0.3 mm or less when it is desired to improve the insulating property by increasing the insulating layer 3.

On the other hand, when the thickness t of the adhesive layer 4 is 0.01 mm or more, it is possible to improve the adhesion between the conductor 2 and the insulating layer 3 by including the above-mentioned covering portion. Further, the thicker the thickness t is, the easier the adhesive layer 4 has the above-mentioned covering portion, and more easily the annular covering portion. Therefore, it is easy to obtain the effect of improving the adhesion between the conductor 2 and the insulating layer 3 and the effect of preventing copper damage. The thickness t may be set to 0.05 mm or more, further 0.08 mm or more, 0.10 mm or more in order to improve the adhesion and prevent copper damage.

<Other constituent layers>
Known materials can be used for the outer semiconductive layer 5, the shielding layer, the sheath, and the like. The outer semiconductive layer 5 may be omitted.

<Insulation characteristics>
Although the power cable 1 of the embodiment does not include the inner semiconductive layer, it has an insulating property equivalent to or higher than that of the conventional power cable including the inner semiconductive layer.

For example, the power cable 1 of the embodiment may have a discharge generation voltage of 10 pC of 15 kV or more in the partial discharge test. It can be said that partial discharge is difficult if the discharge generation voltage of 10 pC is 15 kV or more. It is considered that such a power cable 1 has a small gap between the conductor 2 and the insulating layer 3 that can be a starting point of partial discharge. From this, for the power cable that does not include the internal semiconductive layer, the index "the discharge generation voltage of 10 pC is 15 kV or more" indicates that there is a gap between the conductor 2 and the insulating layer 3 that may be a starting point of partial discharge. It can be used as one of the indicators that indirectly indicate that there is little. The higher the discharge generation voltage of 10 pC, the more difficult partial discharge is, and the more excellent the insulation characteristics are. Therefore, the discharge generation voltage of 10 pC is preferably 15.3 kV or higher, more preferably 15.5 kV or higher. The test conditions of the partial discharge test, the AC destructive test described later, and the AC destructive test after immersion in water will be described in detail in Test Example 1.

Alternatively, the power cable 1 of the embodiment may have a breakdown voltage of 20 kV/mm or more in the AC breakdown test. If the breakdown voltage is 20 kV/mm or more, it can be said that dielectric breakdown is difficult. It is considered that such a power cable 1 has few insulating layers 3 and voids between the conductors 2 and the insulating layers 3 that can be the starting points of dielectric breakdown. From this, with respect to the power cable that does not include the internal semiconductive layer, the index "breakdown voltage is 20 kV/mm or more" is defined as the above-mentioned gap between the insulating layer 3 and the conductor 2 and the insulating layer 3. It can be used as one of the indicators that indirectly indicate that there is little. The higher the breakdown voltage is, the more difficult the dielectric breakdown is and the more excellent the insulation property is. Therefore, the breakdown voltage is preferably 20.2 kV/mm or more, more preferably 20.5 kV/mm or more.

Alternatively, the power cable 1 of the embodiment may have a breakdown voltage of 15 kV/mm or more in the AC breakdown test after the flooding. If the breakdown voltage is 15 kV/mm or more after flooding, it can be said that even if moisture is kept in contact for a long period of time, oxidative deterioration, water tree, etc. are less likely to occur, and dielectric breakdown is less likely to occur. It is considered that such a power cable 1 has few insulating layers 3 and a gap between the conductor 2 and the insulating layer 3 in which water can be accumulated. From this, for the power cable that does not include the internal semiconductive layer, the index "the breakdown voltage after flooding is 15 kV/mm or more" indicates that the insulation layer 3 or the conductor 2 and the insulation layer 3 are It is considered that this can be used as one of the indicators indirectly indicating that the above gap is small. The higher the breakdown voltage is, the more difficult it is to cause dielectric breakdown even after long-term use, and the more excellent the insulation characteristics are. Therefore, the breakdown voltage is preferably 16 kV/mm or more, more preferably 18 kV/mm or more.

The power cable 1 of the embodiment has a discharge generation voltage of 10 pC of 15 kV or more in a partial discharge test, a breakdown voltage of 20 kV/mm or more in an AC breakdown test, and a breakdown in an AC breakdown test after water immersion. It is preferable to satisfy at least one of the voltage being 15 kV/mm or more. It is more preferable that at least two of the three listed items are satisfied, and further that all three are satisfied.

In order to further increase the above-mentioned discharge generation voltage, breakdown voltage, and breakdown voltage after immersion in water, it is necessary to increase the above-mentioned conductor occupancy ratio, increase the antioxidant content, and increase the thickness of the adhesive layer 4. Increasing t can be mentioned.

<Transmission voltage>
Since the power cable 1 of the embodiment has the conductor 2 having a specific shape as described above and the adhesive layer 4 is less likely to cause partial discharge or dielectric breakdown, the power cable 1 can be suitably used for a higher transmission voltage. .. For example, the power cable 1 can be suitably used for applications in which the transmission voltage is more than 600 V, further 3500 V or more, and particularly 6.6 kV or more.

(Power cable manufacturing method)
The power cable 1 of the embodiment can be manufactured by, for example, a manufacturing method including the following steps.
(Conductor preparation step) A step of forming a compressed stranded wire by twisting a plurality of wires and further compression-molding the wires.
(Extrusion step) A step of immediately extruding a first raw material to be an adhesive layer and a second raw material to be an insulating layer directly above the compressed stranded wire.
(Crosslinking step) A step of crosslinking the extruded layer with the second raw material.
Hereinafter, each step will be described in detail.

<Conductor preparation process>
In this step, a compressed stranded wire to be the conductor 2 is manufactured. The wire rod used for the compression stranded wire is made of copper or a copper-based alloy, and a wire rod having a predetermined cross-sectional area and outer diameter can be used. Typically, the wire may be a round wire made of copper or a copper-based alloy. The wire rod can be manufactured by a known method for manufacturing a copper wire or a copper-based alloy wire. If a relatively thick wire is used as the wire, the degree of compression can be easily increased, and the conductor occupancy rate can be easily increased. For manufacturing the stranded wire, a twisting method such as concentric twisting or collective twisting can be used. For compression molding, a molding die that can obtain a predetermined cross-sectional shape can be used. Further, the compression molding is preferably performed by adjusting the degree of compression within the range where the conductor occupancy rate exceeds 85%.

<Extrusion process>
In this step, the first raw material and the second raw material are extruded onto the outer periphery of the prepared compressed stranded wire to simultaneously form an extruded layer of the first raw material and an extruded layer of the second raw material. To form the extruded layer, the equipment used for coextruding the inner semiconductive layer and the insulating layer in the conventional power cable can be used.

As the first raw material, the compound or the like described in the section of the constituent material of the adhesive layer 4 can be used. The polyolefin (which may include an antioxidant or the like) described in the section of the constituent material of the insulating layer 3 can be used as the second raw material. For details of the constituent materials of the adhesive layer 4 and the insulating layer 3, refer to the above-mentioned items. Both the first raw material and the second raw material are in a molten state so that they can be extruded.

The thickness of each extruded layer is adjusted so that the thickness t of the adhesive layer 4 and the thickness of the insulating layer 3 become a predetermined thickness. Since the thickness t of the adhesive layer 4 may be thin as described above, the thickness of the extruded layer serving as the adhesive layer 4 can also be thin.

The extrusion temperature is, for example, 180° C. or higher. The higher the extrusion temperature, the higher the fluidity of the raw material and the easier it is for the compressed stranded wire and the molten raw material (extruded layer) to adhere to each other. The extruded layer made of the first raw material and the extruded layer made of the second raw material are easily adhered to each other. As a result, it is easy to reduce the formation of minute voids between the conductor 2 and the insulating layer 3, which can be local electric field concentration points. When it is desired to improve the adhesion, the extrusion temperature may be 190° C. or higher, more preferably 200° C. or higher, depending on the composition of the raw material, the thickness of the extruded layer, and the like. In addition to or instead of adjusting the extrusion temperature, the extrusion pressure may be increased. Also in this case, it is expected that the above-mentioned voids will be reduced and the compressed stranded wire and the extruded layer and the extruded layers will be easily brought into close contact with each other.

<Crosslinking process>
In this step, the extruded layer made of the second raw material, that is, the extruded layer mainly made of polyolefin is crosslinked to form the insulating layer 3 mainly made of crosslinked polyolefin. Crosslinking conditions can be appropriately selected depending on the type of polyolefin, the type and content of additives such as antioxidants, the thickness of the extruded layer, and the like. By this step, it is possible to obtain the conductor 2 including the compressed stranded wire, which has the insulating layer 3 mainly composed of the cross-linked polyolefin and the adhesive layer 4 in contact with the conductor 2 and the insulating layer 3 on the outer periphery of the conductor 2.

<Other processes>
When the outer semiconductive layer 5 is provided, the outer semiconductive layer 5 is formed on the outer periphery of the insulating layer 3. For example, the outer semiconductive layer 5 may be formed by winding a semiconductive tape. Alternatively, for example, the outer semiconductive layer 5 may be formed by coextrusion with the adhesive layer 4 and the insulating layer 3.

A shield layer, a sheath, etc. (none of which are shown) are formed on the outer periphery of the insulating layer 3 or the outer periphery of the outer semiconductive layer 5. Known conditions can be used for manufacturing conditions of the shielding layer and the sheath.

<Other manufacturing methods>
Instead of the co-extrusion, the first raw material to be the adhesive layer may be extruded directly above the compression stranded wire, and then the second raw material to be the insulating layer may be extruded. That is, the extrusion process may be performed multiple times. However, when the above-mentioned coextrusion is performed, the number of extrusion steps is small and the manufacturability is excellent.

(Main actions/effects)
In the power cable 1 of the embodiment, the conductor 2 is composed of a compression stranded wire, and includes an adhesive layer 4 that contacts the conductor 2 and the insulating layer 3. Although the power cable 1 of the embodiment does not include the inner semiconductive layer, it has insulation properties equal to or higher than those of the conventional power cable including the inner semiconductive layer. Also, the adhesion between the conductor 2 and the insulating layer 3 is excellent. These effects will be specifically described in Test Example 1 below.

[Test Example 1]
The following power cables were examined for insulation properties and adhesion between conductors and insulation layers.
Each power cable is equivalent to a single-core CV cable (6600V, CV, 1X60SQ) having a transmission voltage of 6.6 kV and a conductor cross-sectional area of 60 mm ² . The conductor shall be made of copper. In addition, each power cable includes an insulating layer having the same thickness, and an outer semiconductive layer, a shielding layer, and a sheath.

<Sample No. 1 No internal semi-conductive layer, adhesive layer, conductor occupancy ratio: large>
Sample No. The power cable of No. 1 includes a conductor made of a compressed stranded wire, an adhesive layer made of EMMA, and an insulating layer made of crosslinked polyethylene containing an antioxidant.
Here, a plurality of copper wires having a wire diameter of 1.0 mmφ or more are twisted together, and then compression molded to produce a compressed twisted wire. The degree of compression is adjusted so that the conductor occupancy rate is 91%. The conductor occupancy ratio is the ratio of the area in the contour of the compressed stranded wire to the area of the envelope circle of the compressed stranded wire in the cross section of the obtained power cable (or the compressed stranded wire).
The raw material of the insulating layer is polyethylene containing 0.15% by mass of a phenolic antioxidant. The raw material (EMMA) for the adhesive layer and the raw material for the insulating layer are melted and coextruded onto the outer periphery of the compression stranded wire. The extrusion temperature is 210°C. After the extrusion, the extruded layer made of the raw material of the insulating layer is cross-linked. The thickness of the adhesive layer is 0.1 mm.
The electrical resistivity of the adhesive layer at room temperature (here, about 20° C.) is 1×10 ⁴ Ω·cm or more.

<Sample No. 100 No internal semi-conductive layer, adhesive layer, conductor occupancy ratio: small>
Sample No. The power cable of No. 100 is sample No. Sample No. 1 except that the conductor occupancy ratio was made smaller than that of Sample No. 1. Produced in the same manner as 1. Sample No. The conductor occupancy of 100 power cables is 85%.

<Sample No. 200 With internal semi-conductive layer, without adhesive layer>
Sample No. The 200 power cable is a conventional power cable with an internal semiconductive layer and is commercially available.

The following test was performed about the power cable of each sample.
In the following tests (1) to (3), take a cable piece of an appropriate length from the power cable of each sample, and take sufficient measures to prevent partial discharge from the end (cut end surface) of the cable piece. The test piece is used.

(1) Partial discharge test (Evaluation of initial characteristics)
This test is performed at room temperature (here, about 20° C.).
The prepared test piece was bent 180° along the circumference of about 10 times the outer diameter of the wire core, and an AC voltage was applied between the conductor and the shielding layer provided on the test piece to generate the partial discharge voltage. With a measuring instrument. The alternating voltage applied is close to a sine wave with a frequency of 50 Hz or 60 Hz. As the measuring instrument, a measuring instrument having an accuracy capable of measuring a discharge charge amount of 10 pC or less is used.

(2) AC breakdown test (evaluation of initial characteristics)
Similarly to the above-mentioned (1) partial discharge test, the prepared test piece was bent at 180° along the circumference of about 10 times the outer diameter of the core, and the conductor and the shielding layer were bent. AC voltage is applied between them. The applied AC voltage has a substantially sinusoidal waveform with a frequency of 50 Hz or 60 Hz. Gradually increase the AC voltage and check the voltage that causes dielectric breakdown.

(3) Water immersion voltage application test In this test, a voltage is applied with the inside and outside of the insulating layer being in a water immersion state. Specifically, install a test piece in the waterway. A hole is made in the sheath provided in the test piece to allow water to enter the sheath, and electricity is applied in a state where water is injected into the conductor from both ends of the cable. After the above voltage application, the AC breakdown voltage (residual performance) is measured in the same manner as in the above (2) AC breakdown test. The above-mentioned voltage application is performed under the accelerated deterioration condition in which the applied voltage is 12.7 kV and the frequency is 50 Hz, and the application of the voltage under the accelerated deterioration condition is 120 days.

(4) Heat cycle test In this test, a cable piece of an appropriate length is taken from the power cable of each sample, and a terminal metal fitting is attached to the end of the cable piece to form a circuit close to the actual line, and the current is turned on and off. repeat. As the energization condition, a current value is set such that the conductor temperature is 90° C., and the current value is energized for 4 hours and then deenergized for 4 hours (energization is cut off). Energization and de-energization are repeated under the above energization conditions until the shrinkage amount of the insulating layer is saturated. When the contraction amount of the insulating layer is saturated, it is visually checked whether the end of the conductor is exposed from the insulating layer.

Sample No. The test results of the power cable No. 1 are as follows.
(1) Partial discharge did not occur at 15 kV in the partial discharge test, but occurred at 15.8 kV. That is, the discharge generation voltage of 10 pC is 15 kV or more.
(2) In the AC breakdown test, the initial AC breakdown voltage is 21 kV/mm, which is 20 kV/mm or more.
(3) In the water immersion voltage test, the AC breakdown voltage after the water immersion voltage test is 19.2 kV/mm, which is 15 kV/mm or more.
(4) In the heat cycle test, the insulating layer contracted, but the contraction amount was small (about 6 mm or less), and the conductor was not exposed from the insulating layer.

Sample No. The test results of 100 power cables are as follows.
(1) In the partial discharge test, partial discharge occurred at 6.0 kV, and the discharge generation voltage of 10 pC was less than 15 kV, and further 10 kV or less.
(2) In the AC breakdown test, the initial AC breakdown voltage was less than 20 kV/mm.
(3) In the water immersion voltage test, the AC breakdown voltage after the water immersion voltage test was 12 kV or less.
(4) In the heat cycle test, the insulating layer contracted, but the contraction amount was small (about 6 mm or less), and the conductor was not exposed from the insulating layer.

Sample No. The test results for 200 power cables are as follows.
(1) Partial discharge occurred at 5.0 kV to 12 kV in the partial discharge test.
(2) In the AC breakdown test, the initial AC breakdown voltage was 26 kV/mm.
(3) In the water immersion voltage test, the AC breakdown voltage after the water immersion voltage test was 13 kV/mm to 31 kV/mm.
(4) In the heat cycle test, the insulating layer contracted, but the contraction amount was small (about 6 mm or less), and the conductor was not exposed from the insulating layer.
Sample No. With respect to 200, a plurality of samples were measured, and the results have variations as shown in (1) and (3).

Sample No. 1 and sample No. By comparing with No. 200, the sample No. The power cable of No. 1 has a partial discharge characteristic equal to or higher than that of a conventional power cable including an internal semiconductive layer, has an AC breakdown characteristic of an equivalent degree, and has an equivalent degree or an equal degree or more even after a water immersion test. Even though it has AC breakdown characteristics, it has excellent insulation characteristics. In addition, the sample No. Although the power cable No. 1 does not have an internal semiconductive layer, it has excellent adhesion between the conductor and the insulating layer.

Sample No. 1 and sample No. Comparing with 100, when the internal semiconductive layer is omitted, if the conductor occupancy rate is increased to some extent (more than 85% in this test), the discharge generation voltage of 10 pC, the AC breakdown voltage, and the water immersion test after It can be said that it is easy to increase the AC breakdown voltage. In addition, the sample No. As shown in 200, even if an internal semiconductive layer is provided, the discharge generation voltage of 10 pC may be less than 15 kV, or there may be variations in the AC breakdown voltage after a water immersion voltage application test, resulting in less than 15 kV/mm. is there. On the other hand, the sample No. One of the reasons why the power cable of No. 1 is excellent in the insulation characteristics as described above is that the conductor including the compression stranded wire is provided and the adhesive layer that is in contact with the conductor and the insulating layer is provided. It is considered that this is because there are sufficiently few voids that can be local electric field concentration points.

From the above test results, by providing the conductor made of the compressed stranded wire and the adhesive layer in contact with the conductor and the insulating layer, the conventional electric power having the internal semiconductive layer is provided even if the internal semiconductive layer is not provided. It has been shown that the conductor and the insulating layer have excellent adhesion while having insulation properties equal to or higher than those of the cable.

The present invention is not limited to these exemplifications, but is defined by the scope of the claims, and is intended to include meanings equivalent to the scope of the claims and all modifications within the scope.

1 Power Cable 2 Conductor, 20 Elementary Wire, 22 Gap, 25 Envelope Circle, 27 Intervening Area 3 Insulating Layer 4 Adhesive Layer 5 External Semiconductive Layer

Claims (11)

A conductor,
An insulating layer provided on the outer periphery of the conductor,
An adhesive layer in contact with the conductor and the insulating layer,
The conductor is a compressed stranded wire including a plurality of strands made of copper or a copper-based alloy,
The constituent material of the insulating layer includes a crosslinked polyolefin,
Power cable. The constituent material of the adhesive layer contains at least one compound selected from the group consisting of ethylene methyl methacrylate copolymer, ethylene vinyl acetate copolymer, ethylene ethyl acrylate copolymer, and maleic anhydride. The power cable according to 1. The power cable according to claim 2, wherein the electrical resistivity of the adhesive layer at room temperature is 1×10 ⁴ Ω·cm or more. The power cable according to claim 1, wherein the adhesive layer has a thickness of 0.5 mm or less. The cross-sectional view, wherein an envelope circle of the compressed stranded wire and an outline of the compressed stranded wire are taken, and a ratio of an area in the outline to an area of the envelope circle is more than 85%. The power cable according to any one of 1. The power cable according to any one of claims 1 to 5, wherein a constituent material of the insulating layer contains an antioxidant. The antioxidant is phenolic,
The power cable according to claim 6, wherein the constituent material of the insulating layer contains the antioxidant in an amount of 0.05% by mass or more and 0.5% by mass or less. The power cable according to any one of claims 1 to 7, wherein a discharge generation voltage of 10 pC is 15 kV or more in a partial discharge test. The power cable according to any one of claims 1 to 8, which has a breakdown voltage of 20 kV/mm or more in an AC breakdown test. The power cable according to any one of claims 1 to 9, which has a breakdown voltage of 15 kV/mm or more in an AC breakdown test after flooding. The power cable according to any one of claims 1 to 10, wherein the transmission voltage is 6.6 kV or more.

Images