JP2006320115A - Connecting part of superconductive cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a connector of a superconductive cable that can smooth DC field distribution in the connector. <P>SOLUTION: The connector 30 of the superconductive cable comprises a superconductor 12; a conductor connector (conductor connecting sleeve 32) that connects the superconductor 12 and an object to be connected; an insulating layer 13 that covers a part of the superconductor by exposing the superconductor partially; and a reinforcing insulating layer 31 that covers at least the conductor connecting part, the exposed superconductor 12, and ends of the insulating layer 13. On the reinforcing insulating layer 31, there are formed places whose resistivity locally differ from one another to control the DC field distribution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a connecting portion of a superconducting cable. In particular, the present invention relates to a connection part of a superconducting cable capable of controlling a DC electric field distribution.

  As a superconducting cable, a DC superconducting cable shown in FIG. 7 has been proposed. The superconducting cable 100 has a configuration in which a multicore core obtained by twisting three cable cores 10 is housed in a heat insulating tube 20.

  Each cable core 10 includes a former 11, a superconducting conductor 12, an insulating layer 13, an outer conductor layer 14, and a protective layer 15 in order from the center. Usually, the insulating layer 13 is formed by winding insulating paper. Both the superconducting conductor 12 and the outer conductor layer 14 are formed of a superconducting wire. The outer conductor layer 14 is used as a current return path when, for example, the superconducting conductor 12 is used as a current forward path. On the other hand, the heat insulating tube 20 has a structure in which a heat insulating material (not shown) is disposed between the double tubes composed of the inner tube 21 and the outer tube 22, and the inside of the double tube is evacuated. An anticorrosion layer 23 is formed outside the heat insulating tube 20. In such a cable, a space surrounded by the inner tube 21 and each cable core 10 is usually a refrigerant flow path.

  When constructing a line over a long distance using such a superconducting cable, an intermediate connection part for connecting cable cores drawn from different cables is required in the middle of the line. An example of the intermediate connection portion is described in Patent Document 1. The intermediate connection portion is formed by stepping off the end portion of the cable core stored in the connection box to expose the superconducting conductors, connecting the superconducting conductors of each core with a connecting sleeve, and connecting the outer periphery of the exposed superconducting conductor and the connecting sleeve. It is the structure which forms a stress cone.

  On the other hand, in a normal conducting cable, local ρ grading is formed at a portion where the DC electric field in the insulating layer is high, and the DC electric field at that portion is lowered (for example, Patent Document 2).

  In a normal conducting cable, for example, a DC OF cable, a temperature gradient is generated in the radial direction of the insulating layer in accordance with the load, and the DC electric field distribution of the insulating layer changes greatly accordingly. This is because the resistivity (ρ) of the insulating layer that determines the DC electric field distribution varies greatly with temperature, and the resistivity decreases with increasing temperature. As shown in FIG. 8, for example, when there is no load, the temperature in the insulating layer is almost constant, so the electric field on the conductor side (inner side) is high due to the cylindrical coordinate structure of the electric field, and the sheath side (outer side) ) Electric field is low. On the other hand, when a load is applied, the temperature on the conductor side becomes higher than the temperature on the sheath side, the resistivity on the conductor side is small, and the resistivity on the sheath side is large. Therefore, in the DC electric field distribution depending on the resistivity, the electric field on the sheath side is high and the electric field on the conductor side is low.

  As described above, in the normal conducting cable, the position where the maximum electric field strength changes depending on the load, and since the electric field stress on the sheath side at the maximum load usually becomes a weak point of the insulating layer, the electric field strength on the sheath side in the insulating layer is reduced. In order to lower it, local ρ grading is performed by applying a kraft paper having a low resistivity on the sheath side.

JP 2000-340274 A (Fig. 1) Japanese Patent Laid-Open No. 11-224546 (FIGS. 13 and 14)

  However, in the conventional superconducting cable, the insulating layer is composed of a material having uniform electrical characteristics from the inner peripheral side to the outer peripheral side, and of course, locally relieving the electric field strength at the point where the maximum electric field strength is reached, There is no contrivance for smoothing the DC electric field distribution over the entire thickness direction of the insulating layer. The fact that such a device has not been made also applies to the intermediate connection part or the terminal connection part. Therefore, there is a demand for an insulating structure with even better insulating properties at the connection portion of the superconducting cable.

  At that time, it is also conceivable to divert the insulation design technology such as ρ grading already used in the normal conducting cable to the connecting portion of the superconducting cable as it is. However, in the normal conducting cable, the temperature distribution in the radial direction of the insulating layer varies greatly depending on the state of the load, whereas in the superconducting cable and its connecting portion, there is a special circumstance that the insulating layer is kept in a cryogenic state. Therefore, it is possible to unambiguously design the DC electric field distribution at the connection part of the superconducting cable regardless of whether it is loaded or not loaded. In consideration of this situation, the insulation design is performed by a method different from that of the normal conducting cable. Should be made.

  This invention is made | formed in view of said situation, The main objective is to provide the connection part of the superconducting cable which can control the DC electric field distribution in a connection part.

  The present inventor has conducted various studies on the DC electric field distribution in the superconducting cable connection, considering that there should be an insulation design method suitable for the superconducting cable connection in the superconducting cable connection. As a result, the present invention has been completed.

  The connection part of the superconducting cable of the present invention includes a superconducting conductor, a conductor connecting part that connects the superconducting conductor and a connection target, an insulating layer that partially exposes the superconducting conductor, and at least a conductor connecting part, an exposed superconducting conductor, and It is the connection part of the superconducting cable which has a reinforcement insulation layer which covers the edge part of an insulation layer. Here, the reinforcing insulating layer is characterized in that a portion where the resistivity ρ is locally different is provided so as to control the DC electric field distribution.

  A superconducting cable has an insulating layer with a very stable temperature compared to a normal conducting cable because the superconducting wire used for the cable needs to be cooled to a very low temperature and the temperature change of the insulating layer due to load fluctuations is small. Yes. Therefore, the electric field distribution is almost uniform regardless of the load in the insulation layer of the superconducting cable, and the position where the maximum electric field strength is changed between no load and maximum load like the insulation layer of the normal conduction cable. Nor. The same applies to the reinforcing insulating layer used as a constituent member of the connection portion. Therefore, by providing a location where the resistivity ρ is locally different in the reinforcing insulating layer of the connection portion, the DC electric field distribution can be appropriately controlled, and the electrical characteristics of the connection portion can be improved.

Hereinafter, the connecting portion of the present invention will be described in more detail.
The connection part of the present invention can be applied not only to the intermediate connection part but also to the terminal connection part. These connections are formed at the ends of the superconducting cable. The configuration of the superconducting cable is not particularly limited. Typically, a connection portion is formed at an end portion of a superconducting cable that includes a cable core and a heat insulating tube that houses the cable core. Among them, the cable core has a basic configuration including a former, a superconducting conductor, and an insulating layer. In either of the intermediate and terminal connection portions, the cable end portion is stripped, the superconducting conductor and the insulating layer are partially exposed, and the connection portion is formed at the exposed portion. In the case of the intermediate connection part, the superconducting conductor of one cable is usually abutted with the superconducting conductor of the other cable and connected via the conductor connecting part. In the case of a termination connection portion, the superconducting conductor of the superconducting cable is usually connected to a current lead such as copper via a conductor connecting portion. For the conductor connection part, for example, a conductive member having at least both ends hollow is used, and the superconducting conductor is fitted into the hollow part and soldered, or the current lead is fitted into the hollow part and connected by compression connection or multi-contact. Consists of. Then, at least the conductor connection portion, the exposed superconducting conductor, and the end of the insulating layer are covered with the reinforcing insulating layer.

  There are roughly two ways to control the DC electric field distribution in such a connection. One is to relieve the electric field at the location where the DC electric field is high and use a material with lower resistivity than the other location, and the other is the resistance to the location where the DC electric field is high compared to other locations. By using a material having a high rate and a high DC withstand voltage characteristic, it is possible to withstand DC electric field stress. Hereinafter, the former is called a low ρ type, and the latter is called a high ρ type.

  The locations where the DC electric field is higher than other locations at the connection include stresses formed directly above the conductor connection, outside the pencil-down portion where the end of the insulating layer is tapered, and outside the insulating layer The vicinity of the rising part of a cone is mentioned. In the case of the low rho type, an insulating material having a lower resistivity than that of the other part is applied to at least one of the parts where the DC electric field becomes high. In the case of the high ρ type, an insulating material having a high resistivity and a high DC withstand voltage characteristic is applied to at least one of the locations where the DC electric field is high, compared to other locations.

  As a specific form of locally forming a portion having a different resistivity in the reinforcing insulating layer, a layer having a different resistivity over the thickness direction of the reinforcing insulating layer is formed and ρ grading is performed, or a high DC electric field is applied. It can be mentioned that ρ grading is performed by using a material having a partially different resistivity only at a certain point.

  When layers having different resistivity over the thickness direction of the reinforcing insulating layer are formed, the reinforcing insulating layer is composed of a plurality of layers having different resistivities stepwise or continuously. In that case, the number of layers is not particularly limited. Practically, two or three layers are preferable, but by increasing the number of layers, a reinforcing insulating layer whose resistivity changes substantially continuously in the thickness direction of the reinforcing insulating layer can be configured. .

  In the low ρ type, if the ρ grading is applied throughout the thickness direction so that the resistivity on the inner peripheral side of the reinforcing insulating layer is low and the resistivity on the outer peripheral side is high, the entire thickness of the reinforcing insulating layer is The DC electric field distribution can be smoothed, and the thickness of the reinforcing insulating layer can be reduced. In particular, it is desirable that the thickness of each layer constituting the reinforcing insulating layer be as uniform as possible. If the thicknesses of the layers having different resistivity are equal, the DC electric field distribution in the thickness direction of the insulating layer can be smoothed more effectively.

  On the other hand, when a material with a partially different resistivity is used only at a location where the DC electric field is high, the low ρ type relaxes the DC electric field at that location, and the high ρ type has a high DC electric field at that location, DC withstand voltage characteristics that can sufficiently withstand the electric field are provided.

  In order to distribute materials having different resistivity only at the location where the DC electric field is high, for example, the main part of the reinforcing insulating layer having resistivity ρ1 having both ends tapered is formed, and only on the tapered portion. For example, an insulating material having a resistivity ρ2 (where ρ2 <ρ1) is wound to a substantially uniform thickness to alleviate the DC electric field stress at the rising portion of the stress cone. In general, since the material of the reinforcing insulating layer is a tape material, a portion having a different resistivity can be easily formed locally by using a plurality of tape materials having different resistivity.

In addition, an epoxy bell mouth may be used. In the case of an epoxy bell mouth, since the main part of the reinforcing insulating layer is formed in advance in a predetermined shape, it can be locally attached to this main part, and the resistivity is high only in a portion where the DC electric field is high with good workability. Different materials can be arranged. The resistivity ρ of epoxy resin is about 2.0 × 10 ¹⁷ Ω · cm (0 ° C) for the quartz compound material, about 7.0 × 10 ¹⁷ Ω · cm (0 ° C) for the fused silica compound material, and about 5.0 × for the alumina compound material. 10 ¹⁷ Ω · cm (0 ° C). Therefore, the resistivity of the epoxy bell mouth may be selected as appropriate depending on whether the low ρ type or the high ρ type.

  Of course, in addition to forming layers having different resistivities in the radial direction, a combination of locally dissipating materials having different resistivities may be combined at locations where the DC electric field is high.

  In order to perform ρ grading, it is necessary to use insulating materials having different resistivity (ρ). Typical means for changing the resistivity include the following.

In the case of insulating paper, for example, the resistivity can be changed by changing the density of kraft paper. Further, by adding dicyandiamide to kraft paper or forming kraft paper with cyanoethyl paper, a low resistance kraft paper having a resistivity lower than that of general kraft paper can be obtained. The resistivity ρ (20 ° C.) of general kraft paper is about 10 ¹⁴ to 10 ¹⁷ Ω · cm, and the resistivity of low resistance kraft paper is about half of the resistivity of general kraft paper.

A composite paper made of insulating paper and plastic film typically includes a polypropylene film laminated with kraft paper (PPLP: registered trademark of Sumitomo Electric Industries, Ltd.). In this type of composite paper, composite paper having different resistivity can be obtained by changing the ratio of the thickness tp of the plastic film to the thickness T of the composite paper (tp / T) × 100. Here, the ratio (tp / T) × 100 is set as a k value, and the resistivity may be changed by changing the value of the ratio k in a range of about 40% to 90%, for example. Usually, the resistivity ρ increases as the ratio k increases. For example, the resistivity ρ (20 ° C) of composite paper with a ratio k of 40% is about 10 ¹⁶ to 10 ¹⁸ Ω · cm, and the resistivity ρ (20 ° C) of 60% composite paper is 10 ¹⁷ to 10 ¹⁹ Ω.・ The resistivity ρ (20 ° C.) of the composite paper of about 80% is about 10 ¹⁸ to 10 ²⁰ Ω · cm. Furthermore, the resistivity of the composite paper can also be changed by changing the density, material, additive, etc. of the insulating paper constituting the composite paper.

  When the ρ grading is formed on the reinforcing insulating layer using the above insulating paper and composite paper, for example, the following configuration can be considered.

A: When using only insulating paper
(1) A low rho layer is formed of insulating paper having a low density, and a high rho layer is formed of insulating paper having a high density on the outside thereof.
(2) A low rho layer is formed with insulating paper made of a material having a low resistivity, and a high rho layer is formed outside with an insulating paper made of a material with a high resistivity.
(3) A low ρ layer is formed with insulating paper having a low resistivity by adding an additive, and a high ρ layer is formed with insulating paper having no additive on the outside thereof.

B: When only composite paper is used
(1) A low rho layer is formed with composite paper having a low ratio k, and a high rho layer is formed with composite paper having a high ratio k on the outside thereof.
(2) The resistivity of the insulating paper constituting the composite paper is changed by the method A, and a low ρ layer is formed inside the insulating layer, and a high ρ layer is formed outside the insulating layer.

C: When combining insulating paper and composite paper
(1) A low ρ layer is formed by alternately winding insulating paper and composite paper, and a high ρ layer is formed by winding only composite paper around the periphery of the low ρ layer.
(2) Insulating paper and composite paper are alternately wound to form an insulating layer, and the low ρ layer is formed inside the insulating layer by changing the resistivity of the insulating paper or composite paper by the above method A or B. A high ρ layer is formed on the outside. For example, insulating paper and composite paper having a low ratio k are alternately wound to form a low ρ layer, and insulating paper and composite paper having a high ratio k are alternately wound on the outer side to form a high ρ layer.
(3) A low rho layer is formed only with insulating paper, and a high rho layer is formed only with composite paper on the outside. In that case, the low ρ layer is preferably wrapped with insulating paper so that the resistivity increases from the inside toward the outside.

  In each of the above-described configurations, the structure in which the reinforcing insulating layer is configured only with insulating paper is the lowest cost. If composite paper and insulating paper are used in combination, the amount of expensive composite paper used can be reduced and the cost of the material constituting the connecting portion can be reduced compared to the case where the reinforcing insulating layer is composed of only composite paper. it can.

  When composite paper is used for the reinforcing insulating layer, it is preferable to form ρ grading using composite paper having a ratio k of 60% or more. More preferably, all of the reinforcing insulating layers are composed of composite paper having a ratio k of 60% or more. Due to the difference in resistivity between the insulating paper and the plastic film constituting the composite paper, the DC electric field stress is greatly applied to the plastic film having excellent DC withstand voltage characteristics. Therefore, by increasing the ratio of the plastic film in the reinforcing insulating layer, it is possible to improve the DC withstand voltage characteristics of the reinforcing insulating layer and reduce the thickness of the reinforcing insulating layer. More preferably, the ρ grading may be formed using a composite paper having a ratio k of 70% or more.

  According to the connecting portion of the superconducting cable of the present invention, the following effects can be obtained.

  (1) By providing the reinforcing insulating layer with portions having locally different resistivities, it is possible to control the DC electric field distribution at the connecting portion and reinforce the electrical weak point. In particular, form ρ grading directly above the conductor connection, outside the pencil-down part where the end of the cable insulation layer is tapered, and around the rising part of the stress cone formed outside the insulation layer. Thus, the DC electric field distribution at the connection can be effectively adjusted.

(2) By reducing the resistivity of the portion where the DC electric field is high in the reinforcing insulating layer to be lower than the resistivity of the other portions, it is possible to alleviate the directly collected electric field stress at the portion that tends to be an electrical weak point. Accordingly, the tolerance of electric field design can be increased, and the outer diameter and length of the connection portion can be reduced. In particular, by applying ρ grading so that the resistivity on the inner peripheral side of the connection portion is low and the resistivity on the outer peripheral side is high, the DC electric field distribution can be smoothed over the entire thickness direction of the reinforcing insulating layer. it can.
(3) Of the reinforced insulating layer, the part where the DC electric field is high is made of a material having a higher DC resistivity than that of the other parts, and it is sufficient even if the DC electric field stress is high. It can be set as the connection part which has a DC withstand voltage characteristic.

  (4) The ρ grading of the reinforcing insulating layer can be designed with a high degree of freedom by changing the ratio of the thickness of the plastic film in the composite paper or the combination of the insulating paper and the composite paper. Therefore, connection portions having various characteristics can be manufactured according to the required characteristics of the connection portions.

  (5) Improve the DC withstand voltage characteristics and Imp. Withstand voltage characteristics of the reinforcing insulating layer by using composite paper with a high ratio k for the reinforcing insulating layer and increasing the proportion of the plastic film in the reinforcing insulating layer. In addition, the thickness of the insulating layer can be reduced.

  Embodiments of the present invention will be described below. Here, the following embodiments will be described by taking the intermediate connection portion of the DC superconducting cable as an example. In the drawings referred to in each embodiment, common members are denoted by the same reference numerals.

(Embodiment 1)
First, an embodiment of the present invention capable of smoothing a radial DC electric field distribution will be described with reference to FIG.

[Configuration of connection part]
This intermediate connection part has a structure in which a pair of cable cores of a DC superconducting cable are abutted and the cable cores are connected to each other.

  Although each cable core is shown in a simplified manner in FIG. 1, it includes a former, a superconducting conductor 12, an insulating layer 13, an outer conductor layer, and a protective layer in order from the center as in the core of FIG. As the former, a stranded wire formed by twisting a plurality of insulated copper wires was used. Bi2223-based Ag-Mn sheath tape wire was used for the superconducting conductor 12 and the outer conductor layer. This tape wire is wound in multiple layers on the former to form a superconducting conductor, and wound on the insulating layer 13 in multiple layers to form an external conductor layer. The insulating layer 13 was formed by winding PPLP (registered trademark). Similarly to the reinforcing insulating layer 31 described later, this insulating layer 13 is preferably subjected to ρ grading so that the resistivity on the inner peripheral side is low and the resistivity on the outer peripheral side is high. The protective layer was formed by winding insulating paper.

  The end of such a cable core is stepped off, and the superconducting conductor 12 and the insulating layer 13 are exposed stepwise. Actually, other layers are also exposed in stages, but FIG. 1 shows a state in which the superconducting conductor 12 and the insulating layer 13 are exposed for convenience of explanation. At that time, a tapered pencil down portion 13A having a diameter that decreases toward the tip end is formed at the end of the insulating layer 13.

  Here, the end portions of the cores are compression-connected between the formers via a connection sleeve (not shown), and the superconducting conductors 12 on the outer periphery thereof are inserted into the conductor connection sleeve 32 and connected with solder. Has been. The outer diameter of the conductor connection sleeve 32 is small at both end sides and large at the central portion, and the outer diameter of the central portion is substantially equal to the outer diameter of the insulating layer. The reinforcing insulating layer 31 is formed so as to cover the range of the end portions of the conductor connecting sleeve 32, the exposed superconducting conductor 12, and the insulating layer 13.

  The reinforcing insulating layer 31 is composed of three layers having different resistivity ρ. That is, the insulating material of the reinforcing insulating layer 31 was selected so that the resistivity ρ of the inner layer 31A, the intermediate layer 31B, and the outer layer 31C was such that the inner layer 31A <the intermediate layer 31B <the outer layer 31C. Each layer is constituted by winding a composite paper tape (PPLP: registered trademark) in which kraft paper is laminated on polypropylene.

  More specifically, the inner layer 31A covers the outer periphery of the taper portions at both ends of the pencil-down portion 13A of the insulating layer, the exposed superconducting conductor 12 and the conductor connection sleeve 32, and the outer diameter of the inner layer 31A is the insulating layer of the cable core. Almost corresponds to 13 outer diameters. Next, the intermediate layer 31B covers a range from a portion other than the pencil down portion in the insulating layer 13 of one cable core to a portion other than the pencil down portion in the insulating layer 13 of the other cable core. At this time, both end portions of the intermediate layer 31B are formed in a tapered shape so that the outer diameter decreases as the distance from the conductor connection sleeve 32 increases. Both end portions of the intermediate layer 31B correspond to rising portions of an electric field relaxation layer (not shown) formed of a semiconductive material thereon. Further, the outer layer 31C is formed so as to cover the intermediate layer 31B. The outer layer 31C is also formed in a tapered shape so that the outer diameter becomes smaller as both end portions are separated from the conductor connection sleeve 32. Then, the outer layer 31C was formed so that the taper at both ends of the intermediate layer 31B and the taper at both ends of the outer layer 31C were continuous with the same inclination.

The ratio k of the constituent materials of each layer 31A-31C (the ratio of the thickness of the polypropylene film to the thickness of the entire composite paper), the resistivity ρ, and the dielectric constant ε are as follows. A and B below are constants.
Inner layer: Ratio k = 60%, resistivity ρ1 (20 ℃) = AΩ ・ cm, dielectric constant ε = B
Intermediate layer: Ratio k = 70%, resistivity ρ2 (20 ° C) = about 1.2 AΩ · cm, dielectric constant ε = about 0.95B
Outer layer: Ratio k = 80%, resistivity ρ3 (20 ° C) = about 1.4 AΩ · cm, dielectric constant ε = about 0.9B

  According to this configuration, since PPLP (registered trademark) having a higher ratio k is used on the outer peripheral side of the reinforcing insulating layer 31, the outer peripheral side of the reinforcing insulating layer 31 becomes higher ρ and at the same time the outer peripheral side becomes lower ε. Yes.

  In the connection portion having this configuration, for example, the DC electric field distribution in the thickness direction outside the exposed superconducting conductor 12 in the reinforcing insulating layer 31 is a distribution having three stages corresponding to the difference in resistivity as shown in FIG. Become. Therefore, the DC electric field distribution in the thickness direction of the reinforcing insulating layer 31 can be smoothed, and the thickness of the reinforcing insulating layer 31 can be reduced.

  Further, according to the present embodiment, (1) just above the conductor connection sleeve 32, (2) the outside of the pencil down portion 13A in which the end portion of the insulating layer of the cable is tapered, (3) the outside of the insulating layer 13 Since the ρ grading is also applied to the rising portion of the electric field relaxation layer formed in (1), the electric field relaxation can be effectively performed at the portion where the electric field stress is likely to be high. In particular, by configuring the reinforcing insulating layer 31 with PPLP (registered trademark) having a high ratio k, the proportion of polypropylene having excellent DC withstand voltage characteristics in the reinforcing insulating layer 31 can be increased, and the thickness of the reinforcing insulating layer 31 can be reduced. The effect can be expected even more.

(Embodiment 2)
An embodiment of the present invention for relieving the DC electric field stress at the rising portion of the electric field relaxation layer will be described with reference to FIG.

  The present embodiment also includes a reinforcing insulating layer 31 consisting of three layers as in the first embodiment, but the outer diameter of the intermediate portion of the conductor connection sleeve 32 is smaller than the outer diameter of the insulating layer 13 of the cable. The difference from Embodiment 1 is that the resistivity of the inner layer 31A and the outer layer 31C is the same, and only the resistivity of the intermediate layer 31B is low.

  First, the inner layer 31A covers the pencil down portion 13A, the exposed superconducting conductor 12, and the conductor connection sleeve 32, and is formed to have an outer diameter equivalent to the outer diameter of the insulating layer 13 of the cable. Next, the intermediate layer 31B is formed on the insulating layer 13 and the inner layer 31A, with both end portions being tapered and the intermediate portion having an equal thickness. Further, the outer layer 31C is formed on the intermediate layer 31B, with both end portions formed in a tapered shape that is continuous with both end portions of the intermediate layer 31B, with the intermediate portion having an equal thickness.

  The resistivity ρ1 to ρ3 of the inner layer 31A, the intermediate layer 31B, and the outer layer 31C are set to satisfy ρ1 = ρ3> ρ2. For example, the inner layer 31A and the outer layer 31C are made of PPLP having a high ratio k, and the intermediate layer 31B is made of kraft paper or PPLP having a low ratio k.

  According to the connection portion having this configuration, the low ρ insulating material is disposed at the rising portion of the electric field relaxation layer, so that the DC electric field stress at this portion can be reduced. Further, the low ρ intermediate layer 31B can be formed in a layer having a substantially uniform thickness, and the forming operation of the reinforcing insulating layer 31 can be easily performed. Furthermore, the reinforcing insulating layer 31 can be composed of two types of materials having different resistivity.

(Embodiment 3)
Another embodiment of the present invention for relieving the DC electric field stress at the rising portion of the electric field relaxation layer will be described with reference to FIG.

  In the present embodiment, the configuration of the reinforcing insulating layer 31 is different from that of the second embodiment, and other configurations are the same as those of the second embodiment. The reinforcing insulating layer 31 here includes a main part 31D and an inclined end part 31E. The main part 31D covers a part of the outer periphery of the insulation layer of each cable core, the pencil down part 13A, the exposed superconducting conductor 12 and the conductor connection sleeve 32, both ends are tapered, and the middle part is cylindrical. It is configured. On the other hand, the inclined end portion 31E covers a part of the insulating layer and both end portions of the tapered main portion 31D, and is formed to have a substantially constant thickness along the taper at both ends of the main portion.

  Here, the resistivity ρ1 of the main portion 31D and the resistivity ρ2 of the inclined end portion 31E are set to satisfy ρ1> ρ2. For example, the main part 31D is composed of PPLP with a high ratio k, and the inclined end part 31E is composed of kraft paper or PPLP with a low ratio k.

  According to the connection portion having this configuration, since the low ρ insulating material is locally disposed on the rising portion of the electric field relaxation layer, the DC electric field stress at this portion can be reduced. The reinforcing insulating layer 31 can be made of two types of materials having different resistivity.

(Embodiment 4)
Next, an embodiment of the present invention for alleviating DC electric field stress immediately above the conductor connection sleeve, outside the pencil down portion, and the rising portion of the electric field relaxation layer will be described with reference to FIG.

  In the present embodiment, the main part in the third embodiment is constituted by an inner main part 31DI and an outer main part 31DO, and the inner main part 31DI is also constituted by a low ρ insulating material. The inner main portion 31DI covers the pencil down portion 13A, the exposed superconducting conductor 12, and the conductor connection sleeve 32, and has an outer diameter equivalent to the outer diameter of the insulating layer 13 of the cable. The outer main portion 31DO has both ends tapered and a middle portion formed in a cylindrical shape on a part of the insulating layer 13 and the inner main portion 31DI. The inclined end portion 31E is formed along the taper at both ends of the outer main portion 31DO, as in the second embodiment.

  Here, the resistivity ρ1 to ρ3 of the inner main portion 31DI, the outer main portion 31DO, and the inclined end portion 31E are set to satisfy ρ1 = ρ3 <ρ2. For example, the outer main portion 31DO is made of PPLP having a high ratio k, and the inner main portion 31DI and the inclined end portion 31E are made of kraft paper or PPLP having a low ratio k.

  According to the connecting portion having this configuration, the low ρ insulating material is disposed immediately above the conductor connecting sleeve 32, outside the pencil down portion 13A, and the rising portion of the electric field relaxation layer. World stress can be relieved. The reinforcing insulating layer 31 can be made of two types of materials having different resistivity.

(Embodiment 5)
Next, an embodiment of the present invention using an epoxy bell mouth will be described with reference to FIG.

  In the present embodiment, the shape of the main part 31D in the third embodiment is slightly changed, and a part of the inclined end part 31E is replaced with an epoxy bell mouth 31F. The main part 31D covers a part of the outer periphery of the insulating layer of each cable core, the pencil down part 13A, the exposed superconducting conductor 12 and the conductor connection sleeve 32. The intermediate part of the main part 31D is formed in a cylindrical shape, and both end parts are formed as a conical tapered part on the inner peripheral side and a stepped part on the outer peripheral side continuing to the tapered part. On the other hand, the inclined end portion 31E covers a part of the insulating layer 13 and the tapered portion, and is formed to have a substantially constant thickness along the taper of the tapered portion. Further, the epoxy bell mouth 31F is formed in an annular shape so as to be fitted into the step portion of the main portion 31D.

  Here, the resistivity ρ1 to ρ3 of the main portion 31D, the inclined end portion 31E, and the epoxy bell mouth 31F are set to satisfy ρ1> ρ2≈ρ3. For example, the main part 31D is made of PPLP with a high ratio k, the inclined end part 31E is made of kraft paper or PPLP with a low ratio k, and the epoxy bell mouth 31F is made of an epoxy resin containing quartz.

  According to the connection portion having this configuration, the DC electric field stress at the rising portion of the electric field relaxation layer can be alleviated by the composite of the inclined end portion 31E and the epoxy bell mouth 31F. In addition, by using the epoxy bell mouth 31F molded in advance according to the DC electric field distribution, the DC electric field stress can be more effectively reduced and the connection portion can be easily formed.

(Embodiment 6)
Next, in contrast to the first to sixth embodiments, an embodiment of the present invention in which a high ρ insulating material is used at a location where the DC electric field is high will be described.

  In the present embodiment, a high ρ insulating material is used at a location where a low ρ insulating material is used in FIGS. 1 and 3 to 6. In other words, in the configuration of FIG. 1, the inner layer 31A, the intermediate layer 31B, and the outer layer 31C are formed so that the height ρ sequentially increases from the outer periphery toward the inner periphery. In the configuration of FIG. 3, the resistivity of the intermediate layer 31B is made higher than the resistivity of the inner layer 31A and the outer layer 31C. In the configuration of FIG. 4, the resistivity of the inclined end portion 31E is made higher than the resistivity of the main portion 31D. In the configuration of FIG. 5, the resistivity of the inner main portion 31DI and the inclined end portion 31E is made higher than the resistivity of the outer main portion 31DO. In the configuration of FIG. 6, the resistivity of the inclined end portion 31E and the epoxy bell mouth 31F is made higher than the resistivity of the main portion 31D.

  In any configuration, the high ρ insulating material is a material having higher DC withstand voltage characteristics than other parts. For example, PPLP (registered trademark) with a high ratio k is used as an insulating material with high ρ, and PPLP (registered trademark) with a low ratio k is used in other places. In addition, PPLP (registered trademark) may be used as a high ρ insulating material, and craft paper may be used in other places.

  With these configurations, a portion using a high ρ insulating material has a high direct-current withstand voltage characteristic even when a direct-current electric field stress is higher than other portions. .

  The connection part of the superconducting cable of the present invention can be used for a superconducting cable line used as a DC power transportation means.

It is a model partial longitudinal cross-sectional view which shows the connection part of Embodiment 1 of this invention. It is a graph which shows DC electric field distribution in the reinforcement insulation layer of this invention connection part. It is a model partial longitudinal cross-sectional view which shows the connection part of Embodiment 2 of this invention. It is a model partial longitudinal cross-sectional view which shows the connection part of Embodiment 3 of this invention. It is a model partial longitudinal cross-sectional view which shows the connection part of Embodiment 4 of this invention. It is a model partial longitudinal cross-sectional view which shows the connection part of Embodiment 5 of this invention. It is a cross-sectional view of a superconducting cable. It is a graph which shows DC electric field distribution in the insulating layer of OF cable.

Explanation of symbols

100 superconducting cable
10 core
11 Former 12 Superconducting conductor 13 Insulating layer
13A Pencil down part 14 Outer conductor layer 15 Protective layer
20 Insulated pipe
21 Inner pipe 22 Outer pipe 23 Anticorrosion layer
30 Intermediate connection
31 Reinforcing insulation layer 31A Inner layer 31B Middle layer 31C Outer layer
31D Main part 31DI Inner main part 31DO Outer main part 31E Inclined end
31F Epoxy bell mouth
32 Conductor connection sleeve

Claims (7)

A superconducting conductor, a conductor connecting part connecting the superconducting conductor and the connection target, an insulating layer covering the superconducting conductor partially exposed, and a reinforced insulation covering at least the conductor connecting part, the exposed superconducting conductor and the end of the insulating layer A superconducting cable connection having a layer,
A superconducting cable connecting portion, wherein the reinforcing insulating layer is provided with a portion having a locally different resistivity so as to control a DC electric field distribution.   The superconducting cable connection part according to claim 1, wherein, in the reinforcing insulating layer, the resistivity at a location where the direct-current electric field becomes higher is lower than the resistivity at other locations.   2. The superconducting cable according to claim 1, wherein in the reinforcing insulating layer, a portion where the DC electric field is high is made of a material having a higher resistivity than that of the other portion and having a high DC withstand voltage characteristic. Connection part.   The location where the DC electric field is high is at least one location immediately above the conductor connection portion, outside the pencil down portion where the end portion of the insulating layer is tapered, and near the rising portion of the stress cone formed outside the insulating layer The connection part of a superconducting cable according to claim 2 or 3, wherein   5. The superconducting cable according to claim 1, wherein the difference in local resistivity is formed by a combination of insulating paper, a composite paper made of a plastic film, and insulating paper. Connection part.   The difference in local resistivity is formed by a combination of composite papers having different ratios k of the thickness of the plastic film to the thickness of the composite paper made of insulating paper and plastic film. The connection part of the superconducting cable in any one of 1-4.   The superconducting cable connection portion according to claim 6, wherein composite paper having the ratio k of 60% or more is used.

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