JP5258014B2 - DC coaxial cable for power - Google Patents

Description

  The present invention relates to a power DC coaxial cable used for a DC power transmission line.

  As shown in FIG. 3, the power direct-current coaxial cable has a main conductor 1 at the center, and a return conductor through a main inner semiconductive layer 2, a main insulating layer 3, and a main outer semiconductive layer 4 in order on the outer side. (Neutral wire conductor, also referred to as external conductor) 5 is provided, and a lead coat 9 is provided on the outer side through a return inner semiconductive layer 6, a return insulating layer 7, and a return outer semiconductive layer 8 in this order, and polyethylene is provided on the outer side. The anticorrosion layer 10 which consists of etc. is provided. The return conductor 5 is configured by concentrically twisting a large number of return conductor strands (see Patent Document 1).

  As shown in FIG. 4, the return internal semiconductive layer 6 in the conventional DC coaxial cable for electric power is composed of a semiconductive tape winding layer 6a formed by wrapping a semiconductive tape. The return external semiconductive layer 8 is also composed of a semiconductive tape winding layer.

Japanese Patent Laid-Open No. 11-12083

  In the power DC coaxial cable, the same DC current flows through the central main conductor 1 and the outer return conductor 5 in the opposite direction during normal operation. For this reason, a voltage drop (DC voltage) occurs due to the DC current flowing in the return conductor. In order to cope with this DC voltage, a return insulation layer 7 is provided between the return conductor 5 and the lead coat 9 at the ground potential outside thereof. A return inner semiconductive layer 6 and a return outer semiconductive layer 8 are provided on the inner side and the outer side of the return insulating layer 7 for electric field relaxation. Conventionally, these semiconductive layers are formed by wrapping a semiconductive tape as described above.

  On the other hand, an abnormal voltage is applied to the return insulating layer in addition to the DC voltage during normal operation. This abnormal voltage may be a lightning surge, a surge generated at the time of ground fault, an overvoltage generated due to a commutation failure of the AC-DC converter or the DC-AC converter, and greatly affects the insulation design of the return insulating layer. This abnormal voltage tends to increase as the DC coaxial cable increases in voltage and capacity (increase in power transmission capacity), so that the insulation performance required for the return insulation layer also tends to increase.

  Conventionally, the return inner semiconductive layer and the return outer semiconductive layer are formed by semiconductive tape winding. However, the semiconductive tape wound layer has poor smoothness at the interface with the return insulating layer, and the return insulation. Since the adhesion with the layer is poor, there is a problem that the insulation performance and the reliability are lowered.

  For example, at the interface between the return insulating layer and the return inner semiconductive layer, a step D occurs at the wrap portion of the semiconductive tape as shown in FIG. Further, as shown in FIGS. 4A and 4B, a semiconductive tape is wound on the return conductor 5 having a large number of return conductor strands 5a and having an uneven outer peripheral surface. Concavities and convexities also occur on the surface of the layer 6, and as a result, concavities and convexities occur at the interface between the return insulating layer 7 and the return inner semiconductive layer 6. If the current flowing through the return conductor increases due to an increase in transmission capacity, the total cross-sectional area of the return conductor needs to be increased.Thus, if the return conductor strand is thickened, the unevenness on the outer periphery of the return conductor also increases, resulting in The unevenness generated at the interface between the return insulating layer and the return inner semiconductive layer is also increased.

  On the other hand, regarding the adhesion between the return insulating layer and the return inner semiconductive layer formed by winding the semiconductive tape, there is a problem that the adhesive between the semiconductive tape and the return insulating layer is poor, so that it is easy to peel off. is there. In addition, the outer peripheral surface of the return inner semiconductive layer formed by winding the semiconductive tape has a step D of the wrap portion of the semiconductive tape and unevenness due to the return conductor element wire, and therefore the return insulating layer thereon As shown in FIGS. 4A and 4B, the extruded resin cannot completely follow the step D and the unevenness as described above, and the return inner semiconductive layer 6 and the return insulating layer 7 There is a tendency that a gap K is formed between the two.

  The gaps K and irregularities that exist at the interface between the return semiconductive layer and the return insulation layer are electrical weak points. Therefore, the return insulation performance and reliability are particularly suitable for higher voltage and larger capacity of the DC coaxial cable. It becomes a hindrance in raising.

  As a means to improve the insulation performance of the return insulation layer, it is conceivable to increase the thickness of the return insulation layer. However, increasing the return insulation layer increases the cable size and weight, deteriorates the cable laying and workability, Problems such as an increase in manufacturing / laying costs arise.

  An object of the present invention is to provide a power direct-current coaxial cable with improved insulation performance of a return insulation layer.

In order to achieve the above object, the present invention has a main conductor at the center, and a plurality of return conductor strands are concentrically twisted sequentially through the main inner semiconductive layer, main insulating layer, and main outer semiconductive layer on the outer side. A DC coaxial cable for power having a return conductor inside and a return insulation layer, a return insulation layer, and a return exterior semiconducting layer in order on the outside of the return conductor. And a semiconductive tape winding layer and a semiconductive resin extrusion layer extruded thereon . (Claim 1)

In the DC coaxial cable for electric power according to the present invention, it is preferable that the semiconductive resin extruded layer of the return inner semiconductive layer and the return insulating layer are formed by two-layer coextrusion ( Claim 2 ). .

In the power direct-current coaxial cable according to the present invention, return outer semiconducting layer is preferably made of a semiconductive resin extruded layer which is extruded on the return insulating layer (claim 3).

In the power direct-current coaxial cable according to the present invention, the return external semiconductive layer is formed by extruding a semiconductive resin extruded layer on the return insulating layer, and a semiconductive tape winding layer provided thereon. ( Claim 4 ).

Further, in the power DC coaxial cable according to the present invention, the semiconductive resin extruded layer of the return inner semiconductive layer, the return insulating layer, and the semiconductive resin extruded layer of the return outer semiconductive layer are simultaneously formed in three layers. It is preferably formed by extrusion ( Claim 5 ).

According to the first aspect of the present invention, the return inner semiconductive layer is formed of the semiconductive tape winding layer provided on the return conductor and the semiconductive resin extruded layer formed thereon by extrusion. The step or unevenness on the outer peripheral surface of the semiconductive tape winding layer is covered with the semiconductive resin extruded layer, and the step or unevenness does not appear on the outer peripheral surface of the return inner semiconductive layer. Therefore, the interface between the return internal semiconductive layer and the return insulation layer becomes smooth and the electrical weakness is reduced, so that the return insulation performance and its reliability can be further improved. In particular, when the semiconductive resin extruded layer and the return insulating layer of the return inner semiconductive layer are formed by two-layer coextrusion ( Claim 2 ), the adhesion between the two layers is improved, and the return inner semiconductive layer and the return insulating layer are increased. Since the generation of voids at the interface can be eliminated, the electrical weakness is further reduced, and the return insulation performance and its reliability can be further improved.

Therefore, according to the first aspect of the present invention, even if the required return insulation performance is increased by increasing the voltage or capacity of the DC coaxial cable, the insulation performance of the interface between the return inner semiconductive layer and the return insulation layer is increased. This can be dealt with by improving the thickness of the return insulating layer. From this, it is possible to reduce the cable size / weight, improve the cable laying / installability, and reduce the cable manufacturing / laying cost. Furthermore, in the connection processing part of the return insulation layer at the connection part between the cables and the terminal treatment part of the return insulation layer at the cable terminal part, the internal semiconductive layer on the return path and the return insulation layer are peeled off and the gap is generated between both layers. Therefore, it is possible to improve the return insulation performance and reliability of the cable connection portion and terminal portion.

Also, when also formed with a semi-conductive resin extruded layer retrace Michigaibu semiconductive layer (claim 3), it is possible to enhance the smoothness of the interface between the return insulating layer and the return outer semiconducting layer, further return insulation performance And the reliability can be improved.

The same applies to the case where the return external semiconductive layer is formed of a semiconductive resin extruded layer formed by extrusion on the return insulating layer and a semiconductive tape winding layer provided thereon ( Claim 4 ). The effect is obtained.

In particular, when the return external semiconductive layer is formed of a semiconductive resin extruded layer ( Claim 3 ) or a semiconductive resin extruded layer and a semiconductive tape winding layer ( Claim 4 ), If the semiconductive resin extruded layer of the semiconductive layer, the return insulating layer, and the semiconductive resin extruded layer of the return external semiconductive layer are formed by three-layer coextrusion ( Claim 5 ), the return insulating layer and Since the smoothness and adhesiveness of the interface of the return external semiconductive layer can be improved and the generation of voids can be eliminated, the return insulation performance and its reliability can be further improved. Furthermore, in the connection processing part of the return insulation layer at the cable connection part and the terminal treatment part of the return insulation layer at the cable terminal part, separation of the return insulation layer and the return external semiconductive layer and generation of voids between both layers are prevented. Therefore, it is possible to improve the return insulation performance and the reliability of the cable connection part and the terminal part.

Embodiment 1 FIG. 1 shows an embodiment of a power direct-current coaxial cable according to the present invention. In the figure, 1 is a main conductor, 2 is a main internal semiconductive layer, 3 is a main insulating layer, 4 is a main external semiconductive layer, 5 is a return conductor, 6 is a return internal semiconductive layer, 7 is a return insulating layer, 8 Is a return external semiconductive layer, 9 is a lead coating, and 10 is an anticorrosion layer. This DC coaxial cable is different from the conventional DC coaxial cable in that the return inner semiconductive layer 6 includes a semiconductive tape winding layer 6a provided on the return conductor 5 and a semiconductive extrusion formed thereon. It is comprised from the resin extrusion layer 6b. Hereinafter, the configuration of each part will be described in detail.

  For the main conductor 1, a copper stranded wire is usually used. The main inner semiconductive layer 2, the main insulating layer 3, and the main outer semiconductive layer 4 are usually formed by three-layer coextrusion, and these three layers are integrated. As the material of the main insulating layer 3, a polymer insulating material for direct current resistance (60 to 500 kV) can be used. For example, as the insulating material for the main insulating layer 3, DC cross-linked polyethylene, cross-linked polyethylene with carbon filler, modified polyolefin, or the like can be used.

  The return conductor 5 is formed by twisting a large number of copper wires (return conductor strands) 5 a on the main outer semiconductive layer 4. The configuration of the return conductor 5 (the diameter and number of copper wires) is determined by the rated current passed through the main conductor 1 and the return conductor 5 of the DC coaxial cable, but the rigidity of the copper wire increases as the diameter of the copper wire increases. As a result, the manufacturability of the cable, the mechanical properties of the cable, and the workability of the return conductor processing at the cable connection part and the cable terminal part are disturbed. Good.

  On the outside of the return conductor 5, a return inner semiconductive layer 6, a return insulating layer 7, and a return outer semiconductive layer 8 are provided. The return inner semiconductive layer 6 is formed by extruding a semiconductive tape winding layer 6a formed by wrapping a semiconductive tape on the return conductor 5 and a semiconductive resin thereon. And a semiconductive resin extruded layer 6b. The semiconductive resin extruded layer 6 b can be extruded separately from the return insulating layer 7, but is preferably formed by two-layer coextrusion together with the return insulating layer 7. When formed by two-layer coextrusion, the integrity of the semiconductive resin extruded layer 6b and the return insulating layer 7 is improved, and it is difficult for voids to occur at the interface between the two layers, and foreign matter can be prevented from entering the interface. .

  The thickness of the semiconductive tape used for the semiconductive tape winding layer 6a of the return inner semiconductive layer 6 is strong enough to reduce the step D of the wrap portion of the tape winding and to suppress the looseness of the return conductor 5. Is selected and is usually 0.1 to 0.3 mm. The thickness of the semiconductive resin extruded layer 6b of the return inner semiconductive layer 6 is determined by the influence of unevenness formed by the arrangement of copper wires of the return conductor 5 on the interface between the extruded layer 6b and the return insulating layer 7, and the semiconductive property. The thickness is not affected by the step D of the wrap portion of the tape winding layer 6a, and the thickness is selected in consideration of the influence of the uneven thickness of the extruded layer generated when the semiconductive resin is extruded. It is.

  The return insulation layer 7 can be formed by extrusion molding of polyolefin resin such as polyethylene, for example. The thickness of the return insulation layer 7 is determined by the transmission voltage and abnormal voltage of the DC coaxial cable, but is usually 3 to 8 mm.

  The return external semiconductive layer 8 can be formed by wrapping of a semiconductive tape, but can also be formed by extrusion molding of a semiconductive resin. When the return outer semiconductive layer 8 is formed by extruding the semiconductive resin, the thickness thereof is influenced by the unevenness of the return conductor or the semiconductive tape winding as in the case of the semiconductive resin extruded layer of the return inner semiconductive layer. Since there is no influence of the level difference of the lap portion of the layer, the thickness is selected mainly considering the influence of uneven thickness generated during extrusion of the semiconductive resin, and is usually 1 to 2 mm. When the return external semiconductive layer 8 is formed by extruding the semiconductive resin, the semiconductive resin extruded layer 6b of the return internal semiconductive layer, the return insulating layer 7, and the semiconductive resin extruded layer of the return external semiconductive layer are used. These three layers are preferably formed by coextrusion.

Moreover, the return external semiconductive layer 8 can also be comprised by the semiconductive resin extrusion layer extrusion-molded on the return insulation layer 7, and the semiconductive tape winding layer provided on it.
A lead coat 9 is provided outside the return outer semiconductive layer 8, and a corrosion protection layer 10 is provided outside the lead coat 9. When the power DC coaxial cable is used as a submarine cable, a floor, an iron wire armor, and a serving layer are further provided outside the anticorrosion layer 10.

  When the DC coaxial cable is configured as described above, the return insulation performance can be improved as compared with the conventional one. As an example, a return conductor composed of a large number of copper wires having a diameter of 5 mm, a return insulation layer made of polyethylene having a thickness of 6 mm, and a return external semiconductive layer (thickness 1.5 mm) formed by semiconductive tape winding. DC coaxial cable A), a conventional DC coaxial cable A in which the return inner semiconductive layer is formed only by a semiconductive tape winding layer (thickness 0.5 mm), and the return inner semiconductive layer is a semiconductive tape. Consists of a wound layer (thickness 0.5 mm) and a semiconductive resin extrusion layer (thickness 2 mm) thereon, and forms the semiconductive resin extrusion layer and the return insulating layer thereon by two-layer coextrusion. The DC coaxial cable B of the present invention was prototyped, and the lightning impulse breakdown characteristics of the return insulation layer were measured for both cables A and B. The results are shown in Table 1.

  As apparent from Table 1, the lightning impulse breakdown electric field of the return insulation layer of the DC coaxial cable B is improved by about 30% with respect to the lightning impulse breakdown electric field of the return insulation layer of the DC coaxial cable A.

  At the interface between the return inner semiconductive layer and the return insulation layer of the DC coaxial cable A, as shown in FIGS. 4 (A) and 4 (B), the unevenness caused by the arrangement of the copper wires of the return conductor 5, and FIG. As shown in FIG. 4, there are irregularities due to the step D of the wrap portion of the semiconductive tape, and the destruction start point of the lightning impulse tends to be located at the lap of the semiconductive tape. From this, it can be said that the level difference between the wraps of the semiconductive tape is an electrical weak point.

  In contrast, at the interface between the semiconductive tape winding layer of the return inner semiconductive layer and the semiconductive resin extruded layer of the DC coaxial cable B, the return conductor 5 is formed as shown in FIGS. 1 (A) and 1 (B). Although there are unevenness caused by the copper wire and unevenness due to the step D of the wrap portion of the semiconductive tape as shown in FIG. 5B, the extruded layer 6b of the return inner semiconductive layer 6 and the return insulating layer 7 In many cases, the breakdown start point of the lightning impulse is at the interface between the extruded layer 6b of the return inner semiconductive layer 6 and the return insulating layer 7, but the semiconductive tape winding of the return inner semiconductive layer 6 is performed. There was no correlation in the positional relationship between the irregularities at the interface between the layer 6a and the semiconductive resin extruded layer 6b. From this, it can be said that the smoothing of the interface between the return inner semiconductive layer 6 and the return insulating layer 7 has an effect of improving the lightning impulse breakdown electric field of the return insulating layer.

  Moreover, the return inner semiconductive layer and the return insulating layer of the conventional DC coaxial cable A have low adhesive strength and can be peeled relatively easily by hand, and thus are easily peeled off. Further, as shown in FIGS. 4 (A) and 4 (B), unevenness due to the arrangement of the copper wires of the return conductor 5 causes unevenness in the semiconductive tape winding layer 6a, so that the conductors were pushed out there. The resin of the return insulating layer 7 cannot follow the recess of the semiconductive tape winding layer 6 a, and a gap K is generated between the semiconductive tape winding layer 6 a and the return insulating layer 7. As the diameter of the copper wire of the return conductor 5 increases, the concave portion of the semiconductive tape winding layer 6a increases, so that the gap K tends to be formed. Such weak adhesive strength between the internal semiconductive layer on the return path and the return insulation layer (ease of peeling) and the presence of voids are electrical weaknesses, and the higher the required return insulation performance, the better the insulation performance. A problem arises in the reliability of. Also, in the connection processing part of the return insulation layer at the cable connection part and the terminal treatment part of the return insulation layer at the cable terminal part, peeling of the return semiconductive layer and the return insulation layer is likely to occur, so the required return insulation is required. As the performance increases, a problem arises in the reliability of the cable connection portion and the cable end portion with respect to the return insulation performance. In addition, there are problems such as the possibility of peeling of the return inner semiconductive layer and the return insulating layer and the increase of the air gap due to the thermomechanical behavior of the cable.

  On the other hand, the DC coaxial cable B of the present invention has better adhesion and smoothness at the interface between the extruded inner layer 6b of the return inner semiconductive layer and the return insulating layer 7, and is better than the conventional DC coaxial cable A. The return insulation performance and its reliability can be improved. In the DC coaxial cable B, as shown in FIG. 1, peeling due to weak adhesive force between the semiconductive tape winding layer 6 a and the semiconductive resin extruded layer 6 b of the return inner semiconductive layer 6, There will be a gap K due to the irregularities on the surface of the conductive tape winding layer, but this is in the return inner semiconductive layer 6, so it does not affect the electrical performance and is not a problem. Even in the connection processing part of the return insulation layer in the cable connection part and the terminal treatment part of the return insulation layer in the cable terminal part, peeling does not occur because the adhesion between the return semiconductive layer and the return insulation layer is good. High reliability for the return insulation performance can be realized. Furthermore, peeling and voids between the return inner semiconductive layer and the return insulation layer do not occur due to the thermomechanical behavior of the cable, and high reliability with respect to the return insulation performance can be realized.

  In the above example, a semiconductive resin extrusion layer is provided on the return inner semiconductive layer to improve the smoothness and adhesion of the interface with the return insulation layer, thereby improving the return insulation performance and reliability. However, it is also possible to realize higher return insulation performance and reliability by forming the return outer semiconductive layer with a semiconductive resin extrusion layer and improving the smoothness and adhesion of the interface with the return insulation layer. Needless to say.

< Related Art 1 > FIG. 2 shows a related technique of the present invention. In the figure, the same parts as those in FIG. This DC coaxial cable is different from the DC coaxial cable of Embodiment 1 in that the return inner semiconductive layer is composed only of the semiconductive resin extruded layer 6b.

  In the case of this DC coaxial cable, since the semiconductive resin is directly extruded on the return conductor 5, the surface of the semiconductive resin extruded layer 6 b is affected by unevenness due to the arrangement of the copper wires of the return conductor 5. However, unlike the conventional DC coaxial cable, it is not affected by the level difference of the wrap portion of the semiconductive tape, and at the interface between the semiconductive resin extruded layer 6 b and the return insulating layer 7. Since there is little possibility that a space | gap will generate | occur | produce, return path insulation performance and its reliability can be improved compared with the past. In particular, if the semiconductive resin extruded layer 6b and the return insulating layer 7 are formed by two-layer coextrusion, there is no possibility that voids are generated at the interface between the semiconductive resin extruded layer 6b and the return insulating layer 7. Insulation performance and its reliability can be improved.

Also in this related technique , the return external semiconductive layer 8 can be formed by winding a semiconductive tape, can be formed by extrusion molding of a semiconductive resin, or can be formed by extrusion of a semiconductive resin. It can also be formed by providing a semiconductive tape winding layer on the substrate. When the return external semiconductive layer 8 is formed by extruding the semiconductive resin, the semiconductive resin extruded layer 6b of the return internal semiconductive layer, the return insulating layer 7, and the semiconductive resin extruded layer of the return external semiconductive layer are used. These three layers are preferably formed by coextrusion.

The principal part of one Embodiment of the direct-current coaxial cable for electric power which concerns on this invention is shown, (A) is a cross-sectional view, (B) is a longitudinal cross-sectional view. The cross-sectional view which shows the principal part of the direct-current coaxial cable for electric power as a related technique of this invention. The cross-sectional view which shows the DC coaxial cable for electric power. The principal part of the conventional DC coaxial cable for electric power is shown, (A) is a cross-sectional view, and (B) is a vertical cross-sectional view.

Explanation of symbols

1: Main conductor 2: Main inner semiconductive layer 3: Main insulating layer 4: Main outer semiconductive layer 5: Return conductor 6: Return inner semiconductive layer 6a: Semiconductive tape winding layer 6b: Semiconductive resin extruded layer 7: Return insulation layer 8: Return external semiconductive layer 9: Lead coating 10: Anticorrosion layer

Claims (5)

It has a main conductor at the center and a return conductor formed by concentrically twisting a number of return conductor strands through the main inner semiconductive layer, main insulating layer, and main outer semiconductive layer in order. In the DC coaxial cable for power having a return inner semiconductive layer, a return insulating layer, and a return outer semiconductive layer in turn, the return inner semiconductive layer includes a semiconductive tape winding layer provided on the return conductor, and A DC coaxial cable for electric power, characterized by comprising a semiconductive resin extruded layer extruded thereon. A return inner semiconducting layer the semi-conductive resin extruded layer of the return insulating layers, claim 1 Symbol placement DC coaxial cable power, characterized in that it is formed by co-extrusion two-layer. Return outer semiconducting layer, according to claim 1 or 2 Symbol placement DC coaxial cable power, characterized in that it consists of semi-conductive resin extruded layer which is extruded on the return insulating layer. Return outer semiconducting layer, return insulating and semiconductive resin extruded layer extruded onto the layer, according to claim 1 or 2 SL, characterized in that it consists of a semi-conductive tape wound layer provided thereon DC coaxial cable for power. The semiconductive resin extruded layer of the return inner semiconductive layer, the return insulating layer, and the semiconductive resin extruded layer of the return outer semiconductive layer are formed by three-layer coextrusion. 3 or 4 SL placement of a power direct-current coaxial cable.

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