JP2008300093A - Dc coaxial power cable - Google Patents

Dc coaxial power cable Download PDF

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JP2008300093A
JP2008300093A JP2007142795A JP2007142795A JP2008300093A JP 2008300093 A JP2008300093 A JP 2008300093A JP 2007142795 A JP2007142795 A JP 2007142795A JP 2007142795 A JP2007142795 A JP 2007142795A JP 2008300093 A JP2008300093 A JP 2008300093A
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layer
return
semiconductive
conductor
coaxial cable
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JP5258014B2 (en
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Takehiko Mizuno
健彦 水野
Junichi Haraguchi
純一 原口
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Electric Power Development Co Ltd
Viscas Corp
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Electric Power Development Co Ltd
Viscas Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC coaxial power cable wherein the insulation performance of a return path insulating layer is improved. <P>SOLUTION: In this DC coaxial power cable having a main conductor 1 at the center, having a return path conductor 5 formed by concentrically stranding a large number of return path conductive strands on its outside with a main internal semiconductive layer 2, a main insulating layer 3, and a main external semiconductor layer 4 interposed in a consecutive order, and having a return path internal semiconductive layer 6, a return path insulating layer 7, and a return path external semiconductive layer 8 in a consecutive order at the outside of them, the return path internal semiconductive layer 6 is composed of a semiconductive tape wound layer 6a formed on the return path conductor 5, and a semiconductive resin extruded layer 6b molded on the wound layer by extrusion. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、直流送電線路に使用される電力用直流同軸ケーブルに関するものである。   The present invention relates to a power DC coaxial cable used for a DC power transmission line.

電力用直流同軸ケーブルは、図３に示すように、中心に主導体１を有し、その外側に主内部半導電層２、主絶縁層３、主外部半導電層４を順次介して帰路導体（中性線導体、外部導体ともいう）５を設け、その外側に帰路内部半導電層６、帰路絶縁層７、帰路外部半導電層８を順次介して鉛被９を設け、その外側にポリエチレン等からなる防食層１０を設けた構造となっている。帰路導体５は、多数の帰路導体素線を同心撚りすることにより構成されている（特許文献１参照）。   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).

従来の電力用直流同軸ケーブルにおける帰路内部半導電層６は、図４に示すように、半導電性テープのラップ巻きによる半導電性テープ巻き層６ａで構成されている。また帰路外部半導電層８も同様に半導電性テープ巻き層で構成されている。   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.

特開平１１−１２０８３６号公報Japanese Patent Laid-Open No. 11-12083

電力用直流同軸ケーブルでは、通常の運転時に、中心の主導体１とその外側の帰路導体５に逆向きに同一の直流電流が流れる。このため帰路導体には、直流電流が流れることによる電圧降下（直流電圧）が発生する。この直流電圧に対応するため、帰路導体５とその外側の接地電位にある鉛被９との間には、帰路絶縁層７が設けられている。また帰路絶縁層７の内側と外側には、電界緩和のために帰路内部半導電層６及び帰路外部半導電層８がそれぞれ設けられている。これらの半導電層は従来、前述のように半導電性テープのラップ巻きにより形成されている。   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.

一方、帰路絶縁層には、通常運転時の直流電圧のほかに、異常電圧が加わる。この異常電圧は、雷サージや地絡時に発生するサージ、ＡＣ−ＤＣ変換器及びＤＣ−ＡＣ変換器の転流失敗により発生する過電圧などが考えられ、帰路絶縁層の絶縁設計に大きく影響する。この異常電圧は、直流同軸ケーブルの高電圧化と大容量化（送電容量の増大）に伴い、大きくなる傾向にあり、このため帰路絶縁層に要求される絶縁性能も高くなる傾向にある。   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.

従来、帰路内部半導電層及び帰路外部半導電層は半導電性テープ巻きにより形成されているが、半導電性テープ巻き層は、帰路絶縁層との界面の平滑性がわるいことや、帰路絶縁層との密着性がわるいことから、絶縁性能及び信頼性の低下を引き起こす問題がある。   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.

例えば、帰路絶縁層と帰路内部半導電層の界面については、図４（Ｂ）に示すように半導電性テープのラップ部で段差Ｄが生じる。また図４（Ａ）、（Ｂ）に示すように、多数の帰路導体素線５ａの並びで外周面に凹凸のある帰路導体５の上に半導電性テープを巻きつけるため、帰路内部半導電層６の表面にも凹凸が生じ、結果的に帰路絶縁層７と帰路内部半導電層６の界面に凹凸が生じることとなる。送電容量の増大により帰路導体に流す電流が大きくなると、帰路導体の総断面積を大きくする必要があり、そのために帰路導体素線を太くすると、帰路導体外周面の凹凸も大きくなり、結果的に帰路絶縁層と帰路内部半導電層の界面に生じる凹凸も大きくなることになる。   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.

一方、帰路絶縁層と、半導電性テープ巻きで形成された帰路内部半導電層との密着性に関しては、半導電性テープと帰路絶縁層との接着性がわるいため、剥離しやすいという問題がある。また、半導電性テープ巻きにより形成された帰路内部半導電層の外周面には、半導電性テープのラップ部の段差Ｄや、帰路導体素線による凹凸があるため、その上に帰路絶縁層を押出成形すると、図４（Ａ）、（Ｂ）に示すように、押し出された樹脂が上記のような段差Ｄや凹凸に完全に追従しきれず、帰路内部半導電層６と帰路絶縁層７との間に空隙Ｋができる傾向がある。   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.

帰路内部半導電層と帰路絶縁層の界面に存在する空隙Ｋや凹凸は電気的弱点となるため、特に直流同軸ケーブルの高電圧化や大容量化に対応して帰路絶縁性能及びその信頼性を高める上で妨げとなる。   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.

帰路絶縁層の絶縁性能を高める手段としては、帰路絶縁層の厚さを厚くすることが考えられるが、帰路絶縁層を厚くすると、ケーブルサイズ・重量の増大、ケーブル布設・施工性の悪化、ケーブル製造・布設コストの増加といった問題が生じる。   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.

本発明の目的は、帰路絶縁層の絶縁性能を向上させた電力用直流同軸ケーブルを提供することにある。   An object of the present invention is to provide a power direct-current coaxial cable with improved insulation performance of a return insulation layer.

上記目的を達成するため本発明は、中心に主導体を有し、その外側に主内部半導電層、主絶縁層、主外部半導電層を順次介して多数の帰路導体素線を同心撚りしてなる帰路導体を有し、その外側に帰路内部半導電層、帰路絶縁層、帰路外部半導電層を順次有する電力用直流同軸ケーブルにおいて、前記帰路内部半導電層が、帰路導体上に押出成形された半導電性樹脂押出層からなることを特徴とするものである（請求項１）。   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. In the DC coaxial cable for electric power, which has a return conductor formed on the outside and a return inner semiconductive layer, a return insulating layer, and a return outer semiconductive layer in that order, the return inner semiconductive layer is extruded on the return conductor. It is characterized by comprising a semi-conductive resin extruded layer made (claim 1).

また本発明は、中心に主導体を有し、その外側に主内部半導電層、主絶縁層、主外部半導電層を順次介して多数の帰路導体素線を同心撚りしてなる帰路導体を有し、その外側に帰路内部半導電層、帰路絶縁層、帰路外部半導電層を順次有する電力用直流同軸ケーブルにおいて、前記帰路内部半導電層が、帰路導体上に設けられた半導電性テープ巻き層と、その上に押出成形された半導電性樹脂押出層とからなるものであることが好ましい（請求項２）。   In addition, the present invention provides a return conductor formed by concentrically twisting a number of return conductor wires through a main inner semiconductive layer, a main insulating layer, and a main outer semiconductive layer in order on the outer side of the main conductor at the center. A DC coaxial cable for power having a return inner semiconductive layer, a return insulating layer, and a return outer semiconductive layer on the outside thereof, the semiconductive tape provided with the return inner semiconductive layer on the return conductor It is preferable that it is composed of a wound layer and a semiconductive resin extruded layer extruded thereon.

また本発明に係る電力用直流同軸ケーブルにおいては、帰路内部半導電層の半導電性樹脂押出層と、帰路絶縁層とが、２層同時押出により形成されていることが好ましい（請求項３）。   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 3). .

また本発明に係る電力用直流同軸ケーブルにおいては、 帰路外部半導電層が、帰路絶縁層上に押出成形された半導電性樹脂押出層からなることが好ましい（請求項４）。   In the DC coaxial cable for electric power according to the present invention, it is preferable that the return external semiconductive layer is a semiconductive resin extruded layer formed by extrusion on the return insulating layer.

また本発明に係る電力用直流同軸ケーブルにおいては、帰路外部半導電層が、帰路絶縁層上に押出成形された半導電性樹脂押出層と、その上に設けられた半導電性テープ巻き層とからなることが好ましい（請求項５）。   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 5).

また本発明に係る電力用直流同軸ケーブルにおいては、帰路内部半導電層の半導電性樹脂押出層と、帰路絶縁層と、帰路外部半導電層の半導電性樹脂押出層とが、３層同時押出により形成されていることが好ましい（請求項６）。   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 6).

請求項１の発明によれば、帰路内部半導電層が半導電性樹脂押出層で形成されているので、帰路内部半導電層の外周面に、半導電性テープ巻き層の場合のような段差が生じることがなく、したがって電気的弱点が発生しにくくなり、従来よりも帰路絶縁性能及びその信頼性を向上させることができる。特に、帰路内部半導電層用の半導電性樹脂押出層と帰路絶縁層とを２層同時押出により形成すると（請求項３）、両層の接着性が高まり、帰路内部半導電層と帰路絶縁層の界面での空隙の発生をなくすことができることから、電気的弱点がさらに発生しにくくなり、帰路絶縁性能及びその信頼性をさらに向上させることができる。   According to the invention of claim 1, since the return inner semiconductive layer is formed of a semiconductive resin extruded layer, a step difference as in the case of the semiconductive tape winding layer is formed on the outer peripheral surface of the return inner semiconductive layer. Therefore, electrical weak points are less likely to occur, and the return insulation performance and its reliability can be improved as compared with the conventional case. In particular, when two layers of the semiconductive resin extrusion layer and the return insulating layer for the return inner semiconductive layer are formed by coextrusion (Claim 3), the adhesion between the two layers is improved, and the return inner semiconductive layer and the return insulation are improved. Since the generation of voids at the interface of the layers can be eliminated, electrical weak points are less likely to occur, and the return insulation performance and its reliability can be further improved.

また請求項２の発明によれば、帰路内部半導電層が、帰路導体上に設けられた半導電性テープ巻き層と、その上に押出成形された半導電性樹脂押出層で形成されているので、半導電性テープ巻き層の外周面の段差や凹凸が半導電性樹脂押出層で覆われ、帰路内部半導電層の外周面に段差や凹凸が現れなくなる。したがって、帰路内部半導電層と帰路絶縁層の界面が平滑になり、電気的弱点が少なくなるため、より一層帰路絶縁性能とその信頼性を向上させることができる。特に、帰路内部半導電層の半導電性樹脂押出層と帰路絶縁層とを２層同時押出により形成すると（請求項３）、両層の接着性が高まり、帰路内部半導電層と帰路絶縁層の界面での空隙の発生をなくすことができることから、電気的弱点がさらに少なくなり、帰路絶縁性能とその信頼性をさらに向上させることができる。   According to the invention of claim 2, the return internal semiconductive layer is formed of a semiconductive tape winding layer provided on the return conductor and a semiconductive resin extruded layer formed thereon by extrusion. Therefore, the steps and irregularities on the outer peripheral surface of the semiconductive tape winding layer are covered with the semiconductive resin extruded layer, and the steps and irregularities do 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 3), 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.

したがって、請求項１、２の発明によれば、直流同軸ケーブルの高電圧化や大容量化により、要求される帰路絶縁性能が高まっても、帰路内部半導電層と帰路絶縁層との界面の絶縁性能を向上させることで対応することができ、帰路絶縁層の厚さの増大を抑えることができる。このことから、ケーブルサイズ・重量の低減、ケーブル布設・施工性の向上、ケーブル製造・布設コストの低減を図ることができる。さらに、ケーブル同士の接続部での帰路絶縁層の接続処理部やケーブル端末部での帰路絶縁層の端末処理部において、帰路内部半導電層と帰路絶縁層の剥離や両層間での空隙の発生を防止できるため、ケーブルの接続部や端末部での帰路絶縁性能及びその信頼性を向上させることができる。   Therefore, according to the first and second aspects 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 interface between the return inner semiconductive layer and the return insulation layer is increased. This can be dealt with by improving the insulating performance, and an increase in the thickness of the return insulating layer can be suppressed. 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.

また、帰路内部半導電層だけでなく帰路外部半導電層も半導電性樹脂押出層で形成すると（請求項４）、帰路絶縁層と帰路外部半導電層の界面の平滑性を高めることができるので、さらに帰路絶縁性能及びその信頼性を向上させることができる。   Further, when not only the return inner semiconductive layer but also the return outer semiconductive layer is formed of a semiconductive resin extruded layer (Claim 4), the smoothness of the interface between the return insulating layer and the return outer semiconductive layer can be improved. As a result, the return insulation performance and its reliability can be further improved.

また、帰路外部半導電層を、帰路絶縁層上に押出成形された半導電性樹脂押出層と、その上に設けられた半導電性テープ巻き層とで形成した場合（請求項５）も同様の効果が得られる。   The same applies to the case where the return external semiconductive layer is formed of a semiconductive resin extruded layer extruded on the return insulating layer and a semiconductive tape winding layer provided thereon (Claim 5). The effect is obtained.

特に、帰路外部半導電層を、半導電性樹脂押出層で形成する場合（請求項４）あるいは半導電性樹脂押出層と半導電性テープ巻き層で形成する場合（請求項５）、帰路内部半導電層の半導電性樹脂押出層と、帰路絶縁層と、帰路外部半導電層の半導電性樹脂押出層とを、３層同時押出により形成すれば（請求項６）、帰路絶縁層と帰路外部半導電層の界面の平滑性、接着性を高め、空隙の発生をなくすことができるので、帰路絶縁性能及びその信頼性をさらに向上させることができる。さらに、ケーブル接続部での帰路絶縁層の接続処理部やケーブル端末部での帰路絶縁層の端末処理部において、帰路絶縁層と帰路外部半導電層の剥離や両層間での空隙の発生を防止できるため、ケーブルの接続部や端末部での帰路絶縁性能の向上及び信頼性の向上を図ることができる。   Particularly, when the return external semiconductive layer is formed of a semiconductive resin extruded layer (Claim 4) or when formed of a semiconductive resin extruded layer and a semiconductive tape winding layer (Claim 5), 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 6), 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.

＜実施形態１＞ 図１は本発明に係る電力用直流同軸ケーブルの一実施形態を示す。図において、１は主導体、２は主内部半導電層、３は主絶縁層、４は主外部半導電層、５は帰路導体、６は帰路内部半導電層、７は帰路絶縁層、８は帰路外部半導電層、９は鉛被、１０は防食層である。この直流同軸ケーブルが従来の直流同軸ケーブルと異なる点は、帰路内部半導電層６が、帰路導体５上に設けられた半導電性テープ巻き層６ａと、その上に押出成形された半導電性樹脂押出層６ｂとから構成されていることである。以下、各部の構成について詳述する。 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.

主導体１には通常、銅撚線が使用される。主内部半導電層２、主絶縁層３及び主外部半導電層４は通常、３層同時押出により形成され、この３層は一体化されている。主絶縁層３の材料には、耐直流用（６０〜５００ｋＶ）の高分子絶縁材料を使用することができる。例えば、主絶縁層３の絶縁材料としては、直流用架橋ポリエチレンや、カーボン充填剤入り架橋ポリエチレン、変性ポリオレフィン等を使用することができる。   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.

帰路導体５は、主外部半導電層４上に多数の銅線（帰路導体素線）５ａを撚り合わせることにより形成される。帰路導体５の構成（銅線の直径と本数）は、直流同軸ケーブルの主導体１と帰路導体５に流す定格電流で決定されるが、銅線の直径が太くなるに従って銅線の剛性が強くなり、ケーブルの製造性やケーブルの機械的特性、ケーブル接続部やケーブル端末部での帰路導体処理の作業性がわるくなるため、通常、銅線の直径は２〜６mmの範囲で設計するのがよい。   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.

帰路導体５の外側には、帰路内部半導電層６、帰路絶縁層７、帰路外部半導電層８が設けられる。帰路内部半導電層６は、帰路導体５上に半導電性テープをラップ巻きすることにより形成された半導電性テープ巻き層６ａと、その上に半導電性樹脂を押出成形することにより形成された半導電性樹脂押出層６ｂとで構成されている。半導電性樹脂押出層６ｂは、帰路絶縁層７とは別に単独で押出成形することもできるが、帰路絶縁層７と共に２層同時押出で形成することが好ましい。２層同時押出で形成すると半導電性樹脂押出層６ｂと帰路絶縁層７との一体性が向上し、両層の界面に空隙が発生しにくく、界面への異物の混入も防止することができる。   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. .

帰路内部半導電層６の半導電性テープ巻き層６ａに使用する半導電性テープの厚さは、テープ巻きのラップ部の段差Ｄを小さくでき、かつ帰路導体５の緩みを抑えられるだけの強度を持ち合わせる厚さが選択され、通常、０．１〜０．３mmである。帰路内部半導電層６の半導電性樹脂押出層６ｂの厚さは、当該押出層６ｂと帰路絶縁層７の界面に、帰路導体５の銅線の並びでできる凹凸の影響、及び半導電性テープ巻き層６ａのラップ部の段差Ｄの影響がでない厚さであって、半導電性樹脂の押出時に発生する押出層の偏肉の影響を考慮した厚さが選択され、通常、１〜３mmである。   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.

帰路絶縁層７は、例えばポリエチレン等のポリオレフィン系樹脂の押出成形により形成することができる。帰路絶縁層７の厚さは、直流同軸ケーブルの送電電圧及び異常電圧で決定されるが、通常、３〜８mmである。   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.

帰路外部半導電層８は、半導電性テープのラップ巻きにより形成することができるが、半導電性樹脂の押出成形により形成することもできる。帰路外部半導電層８を半導電性樹脂の押出により形成する場合、その厚さは、帰路内部半導電層の半導電性樹脂押出層のように帰路導体の凹凸の影響や半導電性テープ巻き層のラップ部の段差の影響がないため、主に半導電性樹脂の押出時に発生する偏肉の影響を考慮した厚さが選択され、通常、１〜２mmである。帰路外部半導電層８を半導電性樹脂の押出により形成する場合は、帰路内部半導電層の半導電性樹脂押出層６ｂと帰路絶縁層７と帰路外部半導電層の半導電性樹脂押出層の３層を同時押出により形成することが好ましい。   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 part 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.

また、帰路外部半導電層８は、帰路絶縁層７上に押出成形された半導電性樹脂押出層と、その上に設けられた半導電性テープ巻き層とで構成することもできる。
帰路外部半導電層８の外側には、鉛被９が設けられ、鉛被９の外側には防食層１０が設けられる。なお、電力用直流同軸ケーブルを海底ケーブルとして使用する場合には、防食層１０の外側に、さらに座床、鉄線鎧装、サービング層が設けられる。 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 an anticorrosion layer 10 is provided outside the lead coat 9. In addition, when using the direct current | flow coaxial cable for electric power as a submarine cable, a floor, an iron wire armor, and a serving layer are further provided in the outer side of the anticorrosion layer 10. FIG.

直流同軸ケーブルを以上のような構成にすると、帰路絶縁性能を従来よりも向上させることができる。その一例として、直径５mmの多数の銅線で構成された帰路導体と、厚さ６mmのポリエチレンの帰路絶縁層と、半導電性テープ巻きにより形成された帰路外部半導電層（厚さ１．５mm）を有する直流同軸ケーブルにおいて、帰路内部半導電層を半導電性テープ巻き層（厚さ０．５mm）のみで形成した従来型の直流同軸ケーブルＡと、帰路内部半導電層を半導電性テープ巻き層（厚さ０．５mm）とその上の半導電性樹脂押出層（厚さ２mm）とで構成し、その半導電性樹脂押出層とその上の帰路絶縁層を２層同時押出により形成した本発明型の直流同軸ケーブルＢとを試作し、両ケーブルＡ、Ｂについて帰路絶縁層の雷インパルス破壊特性を測定した。その結果を表１に示す。   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.

Figure 2008300093
Figure 2008300093

表１から明らかなとおり、直流同軸ケーブルＢの帰路絶縁層の雷インパルス破壊電界は、直流同軸ケーブルＡの帰路絶縁層の雷インパルス破壊電界に対して約３０％向上している。   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.

直流同軸ケーブルＡの帰路内部半導電層と帰路絶縁層の界面には、図４（Ａ）、（Ｂ）に示すように帰路導体５の銅線の並びにより生じる凹凸と、同図（Ｂ）に示すように半導電性テープのラップ部の段差Ｄによる凹凸が存在し、雷インパルスの破壊起点は半導電性テープのラップ目に位置することが多いという傾向がある。このことから半導電性テープのラップ目の段差が電気的弱点になっているといえる。   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.

これに対し、直流同軸ケーブルＢの帰路内部半導電層の半導電性テープ巻き層と半導電性樹脂押出層の界面には、図１（Ａ）、（Ｂ）に示すように帰路導体５の銅線の並びにより生じる凹凸と、同図（Ｂ）に示すように半導電性テープのラップ部の段差Ｄによる凹凸が存在するものの、帰路内部半導電層６の押出層６ｂと帰路絶縁層７との界面は滑らかであり、雷インパルスの破壊起点は帰路内部半導電層６の押出層６ｂと帰路絶縁層７の界面にある場合が多いが、帰路内部半導電層６の半導電性テープ巻き層６ａと半導電性樹脂押出層６ｂの界面の凹凸との位置関係には相関はなかった。このことから、帰路内部半導電層６と帰路絶縁層７の界面の平滑化が、帰路絶縁層の雷インパルス破壊電界を向上させる効果を奏しているといえる。   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.

また、従来型の直流同軸ケーブルＡの帰路内部半導電層と帰路絶縁層は接着力が弱く、手で比較的容易に剥がすことができるため、剥離しやすい。さらに、図４（Ａ）、（Ｂ）に示すように帰路導体５の銅線の並びによる凹凸により、その上の半導電性テープ巻き層６ａにも凹凸が生じるため、その上に押し出された帰路絶縁層７の樹脂は半導電性テープ巻き層６ａの凹部に追従しきれず、半導電性テープ巻き層６ａと帰路絶縁層７との間に空隙Ｋが生じる。帰路導体５の銅線の直径が太くなるほど、半導電性テープ巻き層６ａの凹部が大きくなるため、空隙Ｋが形成されやすくなる傾向がある。このような帰路内部半導電層と帰路絶縁層との接着力の弱さ（剥離のしやすさ）や、空隙の存在は、電気的弱点となり、要求される帰路絶縁性能が高くなるほど、絶縁性能に対する信頼性に問題が出てくる。また、ケーブル接続部での帰路絶縁層の接続処理部やケーブル端末部での帰路絶縁層の端末処理部において、帰路内部半導電層と帰路絶縁層の剥離が生じやすいため、要求される帰路絶縁性能が高くなるに従ってケーブル接続部やケーブル端末部の帰路絶縁性能に対する信頼性に問題が出てくる。さらに、ケーブルの熱機械的挙動によって帰路内部半導電層と帰路絶縁層の剥離や空隙が増長される可能性があるなどの問題もある。   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.

これに対し、本発明型の直流同軸ケーブルＢは、帰路内部半導電層の押出層６ｂと帰路絶縁層７の界面の接着性及び平滑性が良好であり、従来型の直流同軸ケーブルＡよりも帰路絶縁性能及びその信頼性を向上させることができる。なお、直流同軸ケーブルＢでは、図１に示すように帰路内部半導電層６の半導電性テープ巻き層６ａと半導電性樹脂押出層６ｂの間に、接着力の弱さによる剥離や、半導電性テープ巻き層表面の凹凸による空隙Ｋが存在することになるが、これは、帰路内部半導電層６内のことであるので、電気性能に影響を与えることはなく、問題とならない。ケーブル接続部での帰路絶縁層の接続処理部やケーブル端末部での帰路絶縁層の端末処理部においても、帰路内部半導電層と帰路絶縁層の接着性がよいため剥離が生じることはなく、帰路絶縁性能に対する高い信頼性を実現することができる。さらに、ケーブルの熱機械的挙動によっても帰路内部半導電層と帰路絶縁層の剥離や空隙が生じることはなく、帰路絶縁性能に対する高い信頼性を実現することができる。   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.

上記の実施例では、帰路内部半導電層に半導電性樹脂押出層を設けて帰路絶縁層との界面の平滑性と接着性を向上させ、帰路絶縁性能の向上及びその信頼性の向上を実現したが、さらに帰路外部半導電層も半導電性樹脂押出層で形成して、帰路絶縁層との界面の平滑性と接着性を向上させることで、より高い帰路絶縁性能と信頼性を実現できることはいうまでもない。   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.

＜実施形態２＞ 図２は本発明に係る電力用直流同軸ケーブルの他の実施形態を示す。図において、図１と同一部分には同一符号を付してある。この直流同軸ケーブルが実施形態１の直流同軸ケーブルと異なる点は、帰路内部半導電層が半導電性樹脂押出層６ｂのみで構成されていることである。 <Embodiment 2> FIG. 2 shows another embodiment of the power DC coaxial cable according to 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 of only the semiconductive resin extruded layer 6b.

この直流同軸ケーブルの場合は、帰路導体５上に半導電性樹脂を直接押出成形するため、半導電性樹脂押出層６ｂの表面が帰路導体５の銅線の並びによる凹凸の影響を受けて周方向に若干波打つ状態となるが、従来の直流同軸ケーブルのように半導電性テープのラップ部の段差の影響を受けることはなく、かつ半導電性樹脂押出層６ｂと帰路絶縁層７の界面に空隙が発生するおそれも少ないので、従来よりも帰路絶縁性能及びその信頼性を向上させることができる。特に、半導電性樹脂押出層６ｂと帰路絶縁層７を２層同時押出により形成すれば、半導電性樹脂押出層６ｂと帰路絶縁層７の界面に空隙が発生するおそれがないので、より帰路絶縁性能及びその信頼性を向上させることができる。   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.

この実施形態の場合も、帰路外部半導電層８は、半導電性テープ巻きにより形成することもできるし、半導電性樹脂の押出成形により形成することもできるし、半導電性樹脂の押出層の上に半導電性テープ巻き層を設けることにより形成することもできる。帰路外部半導電層８を半導電性樹脂の押出により形成する場合は、帰路内部半導電層の半導電性樹脂押出層６ｂと帰路絶縁層７と帰路外部半導電層の半導電性樹脂押出層の３層を同時押出により形成することが好ましい。   Also in this embodiment, 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.

本発明に係る電力用直流同軸ケーブルの一実施形態の要部を示す、（Ａ）は横断面図、（Ｂ）は縦断面図。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. 本発明に係る電力用直流同軸ケーブルの他の実施形態の要部を示す横断面図。The cross-sectional view which shows the principal part of other embodiment of the direct-current coaxial cable for electric power which concerns on this invention. 電力用直流同軸ケーブルを示す横断面図。The cross-sectional view which shows the DC coaxial cable for electric power. 従来の電力用直流同軸ケーブルの要部を示す、（Ａ）は横断面図、（Ｂ）は縦断面図。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.

符号の説明Explanation of symbols

１：主導体
２：主内部半導電層
３：主絶縁層
４：主外部半導電層
５：帰路導体
６：帰路内部半導電層
６ａ：半導電性テープ巻き層
６ｂ：半導電性樹脂押出層
７：帰路絶縁層
８：帰路外部半導電層
９：鉛被
１０：防食層 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 (6)

中心に主導体を有し、その外側に主内部半導電層、主絶縁層、主外部半導電層を順次介して多数の帰路導体素線を同心撚りしてなる帰路導体を有し、その外側に帰路内部半導電層、帰路絶縁層、帰路外部半導電層を順次有する電力用直流同軸ケーブルにおいて、前記帰路内部半導電層が、帰路導体上に押出成形された半導電性樹脂押出層からなることを特徴とする電力用直流同軸ケーブル。   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 is formed of a semiconductive resin extruded layer extruded on the return conductor. DC coaxial cable for electric power characterized by this. 中心に主導体を有し、その外側に主内部半導電層、主絶縁層、主外部半導電層を順次介して多数の帰路導体素線を同心撚りしてなる帰路導体を有し、その外側に帰路内部半導電層、帰路絶縁層、帰路外部半導電層を順次有する電力用直流同軸ケーブルにおいて、前記帰路内部半導電層が、帰路導体上に設けられた半導電性テープ巻き層と、その上に押出成形された半導電性樹脂押出層とからなることを特徴とする電力用直流同軸ケーブル。   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. 帰路内部半導電層の半導電性樹脂押出層と、帰路絶縁層とが、２層同時押出により形成されていることを特徴とする請求項１又は２記載の電力用直流同軸ケーブル。   The DC coaxial cable for electric power according to claim 1 or 2, wherein the semiconductive resin extruded layer of the return internal semiconductive layer and the return insulating layer are formed by two-layer coextrusion. 帰路外部半導電層が、帰路絶縁層上に押出成形された半導電性樹脂押出層からなることを特徴とする請求項１ないし３のいずれかに記載の電力用直流同軸ケーブル。   4. The power direct-current coaxial cable according to claim 1, wherein the return external semiconductive layer is formed of a semiconductive resin extruded layer extruded on the return insulating layer. 帰路外部半導電層が、帰路絶縁層上に押出成形された半導電性樹脂押出層と、その上に設けられた半導電性テープ巻き層とからなることを特徴とする請求項１ないし３のいずれかに記載の電力用直流同軸ケーブル。   4. The return external semiconductive layer comprises a semiconductive resin extruded layer extruded on a return insulating layer, and a semiconductive tape winding layer provided thereon. A direct-current coaxial cable for power according to any one of the above. 帰路内部半導電層の半導電性樹脂押出層と、帰路絶縁層と、帰路外部半導電層の半導電性樹脂押出層とが、３層同時押出により形成されていることを特徴とする請求項４又は５記載の電力用直流同軸ケーブル。   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. 4. A DC coaxial cable for power as described in 4 or 5.
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