WO2011142303A1 - 超電導ケーブル - Google Patents
超電導ケーブル Download PDFInfo
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- WO2011142303A1 WO2011142303A1 PCT/JP2011/060630 JP2011060630W WO2011142303A1 WO 2011142303 A1 WO2011142303 A1 WO 2011142303A1 JP 2011060630 W JP2011060630 W JP 2011060630W WO 2011142303 A1 WO2011142303 A1 WO 2011142303A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B12/00—Superconductive or hyperconductive conductors, cables, or transmission lines
- H01B12/02—Superconductive or hyperconductive conductors, cables, or transmission lines characterised by their form
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G3/00—Compounds of copper
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/40—Electric properties
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/02—Disposition of insulation
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment
Definitions
- the present invention relates to a superconducting cable.
- Superconducting cable is attracting attention as a new power cable that is compact and capable of transmitting large-capacity power with low loss.
- a superconducting cable is generally configured by sequentially laminating a superconducting conductor layer, an insulating layer, and a superconducting shield layer on a flexible former.
- the superconducting conductor layer is formed by winding a plurality of tape-shaped oxide superconducting wires.
- the insulating layer is configured by winding an insulating tape.
- the superconducting shield layer is formed by winding a plurality of tape-shaped oxide superconducting wires.
- Patent Document 1 discloses a superconducting cable in which a superconducting conductor layer 3a, an insulating layer 51a, a superconducting shield layer 7a, and the like are sequentially laminated on a former 1a as shown in FIG.
- a superconducting conductor layer 3a for example, an yttrium-based oxide superconducting wire such as Y 1 Ba 2 Cu 3 O 7-X (0 ⁇ X ⁇ 1) is used.
- the insulating layer 51a is configured by winding insulating paper such as synthetic paper, semi-synthetic insulating paper or kraft paper. When the superconducting cable is cooled by liquid nitrogen, the insulating layer 51a retains liquid nitrogen in the insulating paper or in a gap between the insulating papers (bad gap: bad gap).
- Formula 1 shows the electric field distribution in the insulating layer 51a made of a uniform insulating material.
- the withstand voltage performance of the insulating layer 51a needs to be larger than the maximum electric field in the insulating layer 51a.
- the electric field in the insulating layer 51a becomes the maximum electric field.
- the insulation design of the superconducting cable is designed such that the maximum electric field in the insulating layer 51a is lower than the withstand voltage performance.
- Patent Document 2 discloses a configuration of an insulating layer called grading.
- the insulating layer is made up of two layers. Of the two insulating layers, the dielectric constant epsilon 1 of the inner peripheral side of the insulating layer is high, the dielectric constant epsilon 2 of the outer peripheral side of the insulating layer is low.
- Formula 2 shows the boundary voltage Va between the inner peripheral insulating layer and the outer peripheral insulating layer.
- the voltage ⁇ V borne by the inner peripheral insulating layer becomes (V ⁇ Va), in order to increase the dielectric constant ⁇ 1 of the inner peripheral insulating layer and lower the dielectric constant ⁇ 2 of the outer peripheral insulating layer ( ⁇ 1 > ⁇ 2 ), and the voltage ⁇ V decreases.
- grading has the effect of relaxing (lowering) the internal electric field. Therefore, the maximum electric field directly above the conductor can be reduced, and high withstand voltage performance can be realized.
- Table 1 shows insulating materials that are normally used as insulating layers for superconducting cables.
- dielectric constant ⁇ dielectric loss tangent tan ⁇
- material cost of each insulating material are shown. Note that the values of dielectric constant and dielectric loss tangent are those in liquid nitrogen impregnation (atmospheric pressure 77K).
- the insulating materials shown in Table 1 have a dielectric breakdown strength of 40 to 50 kV / mm for each single material.
- the insulating layer is formed in a state of being impregnated with liquid nitrogen (dielectric constant 1.43 (atmospheric pressure 77 K)).
- dielectric constant ⁇ of the insulating layer is small, the electric field applied to the liquid nitrogen existing in the bad gap becomes high, so that high withstand voltage performance cannot be realized.
- the dielectric constant ⁇ and dielectric loss tangent ⁇ of the nonwoven fabric itself are preferred, but the nonwoven fabric is a stretchable material, so the nonwoven fabric Is used as the insulating layer, or when the proportion of the nonwoven fabric in the insulating layer is large, the nonwoven fabric can be wrinkled when bending occurs in the superconducting cable. If wrinkles are formed in the insulating layer, a gap is generated in the insulating layer, resulting in a void having low electric field concentration and insulation resistance in terms of electrical insulation, which causes a problem of dielectric breakdown even when a low voltage is applied.
- a synthetic resin nonwoven fabric plastic fiber nonwoven fabric
- An object of the present invention is to provide a superconducting cable at a low material cost that suppresses dielectric loss and has high withstand voltage performance.
- a superconducting cable having an insulating layer on the outer periphery of a conductor,
- the insulating layer has at least three layers consisting of a first insulating layer, a second insulating layer, and a third insulating layer from an inner layer to an outer layer, and the insulating layer is impregnated with liquid nitrogen,
- the product of the dielectric constant ⁇ 1 and the dielectric loss tangent tan ⁇ 1 of the first insulating layer and the product of the dielectric constant ⁇ 2 and the dielectric loss tangent tan ⁇ 2 of the second insulating layer satisfy the relationship of ⁇ 1 ⁇ tan ⁇ 1> ⁇ 2 ⁇ tan ⁇ 2.
- the product of the dielectric constant ⁇ 2 and the dielectric loss tangent tan ⁇ 2 of the second insulating layer and the product of the dielectric constant ⁇ 3 and the dielectric loss tangent tan ⁇ 3 of the third insulating layer satisfy the relationship of ⁇ 2 ⁇ tan ⁇ 2 ⁇ 3 ⁇ tan ⁇ 3.
- a superconducting cable is provided.
- FIG. 1 is a schematic sectional view of the superconducting cable 10.
- the superconducting cable 10 includes a former 1, a smoothing layer 2, a superconducting conductor layer 3, an internal semiconductive layer 4, an insulating layer 5, an external semiconductive layer 6, a superconducting shield layer 7, a shield protective layer 8, and an insulating protective layer 9. Composed.
- a smooth layer 2 is formed on the surface of a flexible copper twisted wire former 1 having a diameter of 30 mm.
- a superconducting conductor layer 3 is formed by spirally winding 20 tape-shaped superconducting wires at a pitch of 300 mm.
- the superconducting wire is, for example, a YBCO wire, and the cross-sectional dimensions are a width of 4 mm and a thickness of 0.2 mm.
- an internal semiconductive layer 4 is formed with a gap of about 1 mm made of tape-like carbon paper. The role of the internal semiconductive layer 4 is to relieve the concentration of the electric field at the corners of the YBCO wire on the conductor surface and the protrusions on the surface.
- An insulating layer 5 is formed on the inner semiconductive layer 4.
- the insulating layer 5 includes a first insulating layer 5a, a second insulating layer 5b, and a third insulating layer 5c, and the first to third insulating layers (5a to 5c) are sequentially stacked from the inner layer to the outer layer. Configured.
- the first insulating layer 5a is composed of 20 sheets of polyethylene laminated paper (width 20mm, thickness 0.15mm), which is a composite of kraft paper sandwiched between polyethylene paper, with a 1mm gap and a continuous spiral shape. It is formed by wrapping around.
- the thickness of the first insulating layer 5a is desirably 1/4 or less with respect to the entire insulating layer 5. This is because if the thickness of the first insulating layer 5a exceeds 1/4 of the total thickness of the insulating layer 5, there arises a problem that the dielectric loss increases.
- polyethylene laminated paper is used for the first insulating layer 5a.
- the present invention is not limited to this.
- the first insulating layer 5a may be made of only kraft paper.
- the first insulating layer 5a may have a dielectric loss tangent tan ⁇ 1 of 0.05% or more and a dielectric constant ⁇ 1 of 1.0 or more.
- the dielectric loss tangent tan ⁇ 1 is preferably 0.2% or less. This is because when it exceeds 0.2%, there arises a problem that the dielectric loss becomes high.
- the product of the dielectric constant ⁇ 1 and the dielectric loss tangent tan ⁇ 1 is preferably 0.1% or more and less than 0.4%.
- the product of the dielectric constant ⁇ 1 and the dielectric loss tangent tan ⁇ 1 is less than 0.1%, there arises a problem that the withstand voltage characteristics deteriorate, and if it exceeds 0.2%, the dielectric loss increases. It is.
- the second insulating layer 5b is formed by winding 20 sheets of nonwoven fabric having a width of 20 mm and a thickness of 0.15 mm in a continuous spiral with a 1 mm gap.
- the non-woven fabric is obtained by bonding or intertwining Teflon (registered trademark) fiber, polystyrene fiber, polyethylene non-woven fabric, polypropylene fiber or the like by thermal, mechanical, or chemical action.
- Teflon registered trademark
- polystyrene fiber polyethylene non-woven fabric
- polypropylene fiber or the like by thermal, mechanical, or chemical action.
- Tyvek registered trademark
- the thickness of the second insulating layer 5b is in the range of 1/10 to 1/3, and preferably in the range of 1/5 to 1/4 with respect to the entire insulating layer 5.
- the thickness of the second insulating layer 5b is desirably 5 mm or less. If the thickness of the second insulating layer 5b exceeds 5 mm, the material cost increases, which is not preferable.
- the second insulating layer 5b may have a dielectric loss tangent tan ⁇ 2 of 0.02% or less and a dielectric constant ⁇ 2 of 1.0 or more. When the dielectric loss tangent tan ⁇ 2 exceeds 0.02%, there is a problem that the dielectric loss increases.
- the product of dielectric constant ⁇ 2 and dielectric loss tangent tan ⁇ 2 is preferably 0.04% or less.
- the second insulating layer 5b is preferably calendered in order to increase the density.
- the third insulating layer 5c is formed by winding 66 sheets of polyethylene laminated paper having a width of 20 mm and a thickness of 0.15 mm, similar to the first insulating layer 5a.
- the third insulating layer 5c is not limited to polyethylene laminated paper.
- the thickness of the third insulating layer 5c is a thickness obtained by subtracting the thicknesses of the first insulating layer 5a and the second insulating layer 5c from the total thickness of the insulating layer 5.
- the third insulating layer 5c may have a dielectric loss tangent tan ⁇ 3 larger than 0.02% and a dielectric constant ⁇ 3 of 1.0 or more.
- the product of dielectric constant ⁇ 3 and dielectric loss tangent tan ⁇ 3 is preferably greater than 0.04% and less than 0.3%.
- the product of the dielectric constant ⁇ 3 and the dielectric loss tangent tan ⁇ 3 is less than 0.04%, the withstand voltage characteristic is deteriorated.
- the product exceeds 0.3% the dielectric loss is increased. It is.
- FIG. 2 shows the electric field distribution inside the insulating layer 5.
- the electric field is concentrated because the dielectric constant ⁇ is generally small, the electric field rise is smaller than that of the first insulating layer 5a because it is thinner than the entire thickness of the insulating layer 5. Therefore, even when the second insulating layer 5b is formed using synthetic paper or the like having low withstand voltage performance, the voltage performance of the insulating layer 5 as a whole is not impaired.
- the configuration outside the insulating layer 5 is different from the main subject of the present invention.
- the external semiconductive layer 6 is formed on the insulating layer 5.
- a superconducting shield layer 7 formed by winding 30 superconducting wires on the external semiconductive layer 6 is formed.
- the material, dimensions and winding method of the superconducting wire used for the superconducting shield layer 7 are the same as those of the superconducting conductor layer 3.
- a shield protection layer 8 is formed on the upper surface of the superconducting shield layer 7.
- the shield protective layer 8 is formed by winding a plurality of copper tapes, and plays a role of protecting the superconducting wire of the superconducting shield layer 7 and protecting the conductor by dividing the current when an overcurrent flows through the shield layer. Further, an insulating protective layer 9 having a thickness of 1 mm is formed outside the shield protective layer 8. The insulating protective layer 9 is formed by winding four layers of tape-shaped kraft paper in a spiral manner with a gap of about 1 mm, and plays a role of insulating between the cable core and the heat insulating tube.
- the first experiment will be described with reference to Table 2.
- the first experiment was performed by applying an AC voltage of 275 kV class to the superconducting cable 10 including the three insulating layers 5 according to this embodiment and the comparative example.
- the maximum electric field means that the voltage gradient per mm in the insulator forming the insulator layer is the highest, and the dielectric loss was determined by measuring the dielectric constant and the dielectric loss tangent.
- the dielectric breakdown strength confirmed the presence or absence of dielectric breakdown and partial discharge when an alternating voltage was applied at 275 kV. A was evaluated when neither dielectric breakdown nor partial discharge occurred when an AC voltage was applied, B was evaluated when partial discharge was generated, and C was evaluated when both were generated.
- Example 1 is a superconducting cable including an insulating layer in which a first insulating layer is made of polyethylene laminated paper, a second insulating layer is made of polyethylene nonwoven fabric, and a third insulating layer is made of polyethylene laminated paper.
- the thickness of the first insulating layer 5a was 5 mm
- the thickness of the second insulating layer 5b was 5 mm
- the thickness of the third insulating layer 5c was 14 mm.
- an insulating layer was formed using an insulating material as shown in Table 2, and the thickness of each insulating layer was configured as shown in Table 2.
- Example 1 the first insulating layer and the third insulating layer were formed using the same insulating material. In Examples 5 to 7, the first insulating layer and the third insulating layer were formed using different insulating materials. In Example 8, the first to third insulating layers of the present embodiment were disposed on the second to fourth layers, and the insulating material having a large product of dielectric constant ⁇ and dielectric loss tangent ⁇ was disposed on the first layer. In Example 9, the first to third insulating layers of the present embodiment are arranged on the first to third layers, and the insulating material having a large product of dielectric constant ⁇ and dielectric loss tangent ⁇ is arranged on the fourth layer.
- a superconducting cable (Comparative Example 1) provided with a single insulating layer having a large product of dielectric constant ⁇ and dielectric loss tangent ⁇ , and a single insulating layer having a small product of dielectric constant ⁇ and dielectric loss tangent ⁇ .
- Superconducting cable provided (Comparative Example 2), and superconducting cable (Comparative Example 3) provided with two insulating layers using the insulating layers of Comparative Example 1 and Comparative Example 2, dielectric from the inner side toward the outer insulating layer
- a similar experiment was performed on a superconducting cable (Comparative Example 4) having three insulating layers in which the product of the rate ⁇ and the dielectric loss tangent ⁇ increases.
- Comparative Example 3 the thickness of the inner insulating layer (first insulating layer) is 10 mm, and the thickness of the outer insulating layer (second insulating layer) is 14 mm.
- Comparative Example 4 the insulation of the first layer The thickness of the layer was 5 mm, the thickness of the second insulating layer was 5 mm, and the thickness of the third insulating layer was 14 mm. The total thickness of the insulating layer was 24 mm in all of Examples 1 to 9 and Comparative Examples 1 to 4.
- Example 1 it was possible to suppress the dielectric loss to 0.4 W / m while realizing high withstand voltage performance.
- the dielectric loss was reduced to about 70%.
- the cost can be suppressed by reducing the thickness of the expensive second insulating layer 5b to 5 mm.
- even when an alternating voltage was applied not only dielectric breakdown, but also a phenomenon that caused problems in insulation such as partial discharge did not occur.
- Comparative Example 1 the dielectric loss was higher than in Example 1 and other Comparative Examples 2, 3, and 4.
- Comparative Example 2 a voltage of 10 kV / mm is applied at the maximum electric field in spite of the insulating layer having a low withstand voltage performance, which is not preferable as the withstand voltage performance.
- the dielectric loss is low, but the cost is high.
- Comparative Example 3 since an expensive insulating layer having a small dielectric constant ⁇ and dielectric loss tangent ⁇ is used as much as 14 mm, the cost is high.
- Tyvek registered trademark
- Tyvek which is a stretchable nonwoven fabric on the outside, is used, when the superconducting cable is bent, the outer insulating layer is wrinkled.
- the comparative example 4 has a three-layer structure and the dielectric breakdown strength is sufficient, the dielectric loss is slightly higher than those of the first example and the first and second comparative examples, and the cost is increased.
- Example 2 as in Example 1, the dielectric loss could be suppressed to 0.4 W / m. However, partial discharge occurred when an AC voltage was applied. However, the material cost could be reduced compared to Comparative Examples 2-4. Compared with Comparative Example 3, the dielectric loss and the dielectric breakdown strength are equal, but the material cost can be suppressed as compared with Comparative Example 3, which is advantageous. In Example 3, as in Example 1, the dielectric loss could be suppressed to 0.4 W / m. Furthermore, partial discharge did not occur even when an AC voltage was applied. The material cost was higher than those of Examples 1 and 2, but could be suppressed as compared with Comparative Examples 2-4. In Example 4, the dielectric loss could be suppressed to 0.5 W / m, and no partial discharge occurred even when an AC voltage was applied. Moreover, the material cost is also equivalent to that of Example 1, which is preferable.
- Example 5 the dielectric loss was 0.6 W / m, which was slightly higher than Examples 1 to 4. In addition, partial discharge occurred when an alternating voltage was applied. However, the material cost could be reduced compared to Examples 1 to 4. Compared to Comparative Example 4, the dielectric loss is equivalent, but the dielectric breakdown strength is slightly inferior. However, the material cost is reduced to half that of Comparative Example 4, which is preferable. In Example 6, the dielectric loss could be suppressed to 0.5 W / m. However, both dielectric breakdown and partial discharge occurred when an AC voltage was applied. The material cost is higher than those of Examples 1 to 5, but can be reduced by 30% as compared with Comparative Example 2.
- Example 7 the dielectric loss could be suppressed to 0.2 W / m, and no partial discharge occurred even when an AC voltage was applied. However, the material cost has increased. However, it is preferable because the dielectric loss equivalent to that in Comparative Example 2 can be realized and the dielectric breakdown strength can be sufficiently increased.
- Example 8 the dielectric loss was 0.6 W / m, which was slightly higher than Examples 1 to 4, 6, and 7. However, partial discharge did not occur even when an AC voltage was applied. Moreover, the material cost could be suppressed to the same level as in Examples 1 and 4. Compared with Comparative Example 4, the dielectric loss and the dielectric breakdown strength are equal, but the material cost can be reduced by 40%, which is preferable. In Example 9, the dielectric loss could be suppressed to 0.4 W / m, and no partial discharge occurred even when an AC voltage was applied. Furthermore, the material cost can be suppressed lower than that in the first embodiment, which is preferable.
- Example 1 a preferable range of the product of the dielectric constant ⁇ and the dielectric loss tangent tan ⁇ of each insulating layer will be described.
- the product of the dielectric constant ⁇ and the dielectric loss tangent tan ⁇ of the second insulating layer ( ⁇ 2 ⁇ tan ⁇ 2) is 0.04% or less, so that the reduction rate of dielectric loss It can be seen that is improved.
- the value of ⁇ 2 ⁇ tan ⁇ 2 is in the range of 0.04% or less, the dielectric loss and the dielectric breakdown strength do not change, but the material cost increases by using the fluororesin film as in Example 3. I understand that.
- Examples 8 and 9 when forming a four-layer insulating layer, an insulating material having a larger product of dielectric constant ⁇ and dielectric loss tangent ⁇ was disposed in the fourth layer than in the first layer. It can be seen that the dielectric loss reduction is improved and the material cost can be further reduced. When the dielectric loss, dielectric breakdown strength, and material cost are comprehensively evaluated, Examples 1, 4, and 9 are most preferable. In other words, semi-synthetic paper (polypropylene laminate paper) is used for the first insulating layer, synthetic resin nonwoven fabric is used for the second insulating layer, and the same material as the first insulating layer is used for the third insulating layer. Most preferably, it is used.
- the relationship between the dielectric loss and the thickness of the insulating layer will be described.
- the thickness of the first insulating layer 5a and the thickness of the second insulating layer 5b of the superconducting cable 10 including the insulating layer 5 according to the present embodiment are changed, and in each case, the AC voltage of 275 kV class is changed.
- the value of dielectric loss when is applied is shown.
- the dielectric loss is reduced, but the reduction rate is reduced from about 8 mm.
- the cost increases.
- the thickness of the first insulating layer 5a is reduced, the dielectric loss is reduced, but when the thickness of the first insulating layer 5a is 5 mm, the maximum electric field applied to the second insulating layer 5b is 8 kV / mm.
- the maximum electric field applied to the second insulating layer 5b is as high as about 9.5 kV / mm, which is a factor that impairs reliability in terms of dielectric strength.
- the range in which the effect of this configuration is produced is that the thickness of the first insulating layer 5a is 2 mm to 6 mm with respect to the insulating layer 5 having a thickness of 24 mm. ), The thickness of the second insulating layer 5b is 2 mm to 8 mm (1/10 to 1/3 of the thickness of the entire insulating layer 5), and the thickness of the third insulating layer 5c is the remaining thickness. It should be configured.
- the dielectric loss can be reduced by making the insulating layer 5 in the superconducting cable 10 the grading of the three-layer structure. Furthermore, the voltage distribution of the second insulating layer 5b having a small dielectric loss tangent tan ⁇ but low withstand voltage performance can be kept low, and the insulation layer is made thick without impairing the withstand voltage performance of the entire superconducting cable 10. Therefore, dielectric loss can be reduced.
- the thickness of the whole insulating layer 5 can be made the same thickness as the conventional polyethylene laminated paper with high insulation performance, and the compactness of the superconducting cable is not impaired.
- the dielectric loss can be reduced to 80% compared to the superconducting cable made of polyethylene laminated paper, and in addition to reducing the transmission loss due to the power transmission of the cable itself, in order to remove the heat generated by the loss, The required capacity can be lowered and the construction cost of the refrigeration system can be reduced.
- the thickness of what uses an expensive nonwoven fabric for the 2nd insulating layer 5b can be suppressed, and the whole total system cost can be reduced.
- the reliability of electrical insulation is equivalent to that of conventional insulation layers, so long-term use of cables and insulation breakdown of cables cause obstacles to urban functions and citizen living functions caused by suspension of power transmission to urban areas. To maintain a reliable social infrastructure.
- the product of the dielectric constant ⁇ 1 and the dielectric loss tangent tan ⁇ 1 of the first insulating layer and the dielectric constant ⁇ 2 of the second insulating layer is ⁇ 1 ⁇ tan ⁇ 1> ⁇ 2 ⁇ tan ⁇ 2, and the withstand voltage strength F1 of the first insulating layer and the withstand voltage strength F2 of the second insulating layer have a relationship of F1> F2,
- the magnitude of the dielectric constant is not limited.
- the relationship between the product of the dielectric constant ⁇ 2 and the dielectric loss tangent tan ⁇ 2 of the second insulating layer and the product of the dielectric constant ⁇ 3 and the dielectric loss tangent tan ⁇ 3 of the third insulating layer is as long as ⁇ 2 ⁇ tan ⁇ 2 ⁇ 3 ⁇ tan ⁇ 3.
- ⁇ 1 ⁇ tan ⁇ 1 and ⁇ 3 ⁇ tan ⁇ 3 do not have to be the same.
- RE-based superconducting wires such as YBCO wires and HoBCO wires
- Bi-based superconducting wires obtained by applying a silver sheath to Bi-based superconductors such as Bi2223
- RE is a rare earth element
- the Re-based superconducting material is a superconducting material composed of one or more elements selected from Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu. It is.
- the present invention is configured as described above, it can be used as a superconducting cable.
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Abstract
Description
絶縁層51aの耐電圧性能は、絶縁層51a内の最大電界よりも大きい必要がある。下記式1によれば、r=r1のときに絶縁層51a内の電界は最大電界となる。超電導ケーブルの絶縁設計は、絶縁層51a内の最大電界が耐電圧性能よりも低くなるようにして設計される。
均一な絶縁材料により構成される特許文献1に記載の絶縁層に対して、グレーディングでは絶縁層が2層により構成される。2層の絶縁層のうち、内周側の絶縁層の誘電率ε1は高く、外周側の絶縁層の誘電率ε2は低い。
内周側の絶縁層で負担する電圧ΔVは、(V-Va)となり、内周側の絶縁層の誘電率ε1を高くし、外周側の絶縁層の誘電率ε2を低くするため(ε1>ε2)、電圧ΔVは小さくなる。その結果、グレーディングは内部の電界を緩和する(低下させる)効果がある。よって、導体直上の最大電界を下げることができ、高い耐電圧性能を実現することができる。
超電導ケーブルの誘電損失は、下記式3及び4で表される。
上記表1によれば、(1)クラフト紙を絶縁層として用いた場合、誘電率εが大きいため高い耐電圧性能を実現し得るが、誘電率ε及び誘電正接δの両方が大きいため誘電損失が大きくなる問題がある。
また、(2)半合成紙(ポリプロピレンラミネート紙:クラフト紙とプラスチックフィルムの複合されたテープ材料)を絶縁層として用いた場合、誘電率ε及び誘電正接δは比較的好ましいが、誘電率εが小さいため、高い耐電圧性能を実現することができない。
また、(3)合成樹脂製不織布(プラスチック繊維製の不織布)を絶縁層として用いた場合、不織布自体の誘電率ε及び誘電正接δは好ましいが、不織布は伸縮性のある材料であるため、不織布を絶縁層として用いた場合や不織布が絶縁層に占める割合が大きい場合、超電導ケーブルに曲げが生じると不織布に皺ができる。絶縁層中に皺ができると絶縁層に隙間が生じ、電気絶縁的に電界集中と耐絶縁の低いボイドができ、これにより低電圧が印加された場合でも絶縁破壊する問題がある。これ以外にも、不織布を絶縁層に用いることは、コスト面で問題がある。
また、(4)合成樹脂製フィルム(プラスチックフィルム)を絶縁層として用いた場合、誘電率ε及び誘電正接δの特性とコスト面で適用が難しい。ポリイミド樹脂、ポリアミド合成繊維のナイロン(登録商標)、塩化ビニル樹脂を用いた場合は、誘電率ε及び誘電正接δの両方が大きいため誘電損失が大きくなるという問題を有しており、フッ素樹脂のテフロン(登録商標)やABS樹脂を用いた場合には、誘電率ε及び誘電正接δは比較的好ましいが、コスト面で大きな問題があり、更に、誘電率εが小さいため、高い耐電圧性能を実現することができない。
なお、ここでのコスト評価は、構成材料自体の価格を意味する。
前記絶縁層は、内層から外層にかけて第1の絶縁層、第2の絶縁層及び第3の絶縁層からなる三層を少なくとも有し、前記絶縁層は液体窒素が含浸された状態であり、
前記第1の絶縁層の誘電率ε1と誘電正接tanδ1の積と前記第2の絶縁層の誘電率ε2と誘電正接tanδ2の積とは、ε1×tanδ1>ε2×tanδ2の関係を満たし、
前記第2の絶縁層の誘電率ε2と誘電正接tanδ2の積と前記第3の絶縁層の誘電率ε3と誘電正接tanδ3の積とは、ε2×tanδ2<ε3×tanδ3の関係を満たすことを特徴とする超電導ケーブルが提供される。
超電導ケーブル10は、フォーマ1、平滑層2、超電導導体層3、内部半導電層4、絶縁層5、外部半導電層6、超電導シールド層7、シールド保護層8、絶縁保護層9を備えて構成される。
なお、実施例では第1の絶縁層5aにポリエチレンラミネート紙を用いたがこれに限らず、例えば第1の絶縁層5aは、クラフト紙だけで構成してもよい。
ここで、第1の絶縁層5aは、誘電正接tanδ1が0.05%以上であり、誘電率ε1は1.0以上であればよい。誘電正接tanδ1が0.05%未満の場合には、耐電圧特性が悪くなるという問題がある。また、誘電正接tanδ1は好ましくは0.2%以下であることが好ましい。0.2%を超えた場合には、誘電損失が高くなるという問題が生じるためである。また、誘電率ε1と誘電正接tanδ1の積は好ましくは0.1%以上0.4%未満であることが好ましい。誘電率ε1と誘電正接tanδ1の積が、0.1%未満の場合には耐電圧特性が悪くなるという問題が生じる、0.2%を超える場合には誘電損失が高くなるという問題が生じるためである。
ここで、第2の絶縁層5bは、誘電正接tanδ2が0.02%以下であり、誘電率ε2は1.0以上であればよい。誘電正接tanδ2が0.02%を超えた場合には、誘電損失が高くなるという問題がある。また、誘電率ε2と誘電正接tanδ2の積は好ましくは0.04%以下であることが好ましい。誘電率ε2と誘電正接tanδ2の積が、0.04%を超える場合には誘電損失が高くなるという問題が生じるためである。
なお、第2の絶縁層5bは、高密度化処理するためカレンダー処理されていることが望ましい。
ここで、第3の絶縁層5cは、誘電正接tanδ3が0.02%より大きく、誘電率ε3は1.0以上であればよい。誘電正接tanδ3が0.02%以下の場合には、耐電圧特性が悪くなるという問題がある。また、誘電率ε3と誘電正接tanδ3の積は好ましくは0.04%より大きく0.3%以下であることが好ましい。誘電率ε3と誘電正接tanδ3の積が、0.04%未満の場合には耐電圧特性が悪くなるという問題が生じる、0.3%を超える場合には誘電損失が大きくなるという問題が生じるためである。
第2の絶縁層5b内は、一般的に誘電率εが小さいので電界が集中するところ、絶縁層5全体の厚さに対して薄いため電界上昇は第1の絶縁層5aに比べて小さい。よって、耐電圧性能の低い合成紙等を用いて第2の絶縁層5bを形成した場合でも、絶縁層5全体として電圧性能を損なうものではない。
第1の実験は、本実施形態に係る3層の絶縁層5を備えた超電導ケーブル10及び比較例に対して275kV級の交流電圧を印加させて行った。
実験結果として、絶縁層5の各層(5a~5c)の最大電界、誘電損失及び絶縁破壊強度を得た。
なお、ここでの最大電界とは、絶縁体層を形成する絶縁体中の1mm当たりの電圧勾配が最も高いところを意味し、誘電損失は、誘電率と誘電正接を測定することによって求めた。また、絶縁破壊強度は、交流電圧を275kV印加した際の絶縁破壊及び部分放電の有無を確認した。Aは交流電圧を印加した際の絶縁破壊及び部分放電の両方が生じなかった場合、Bは部分放電が生じた場合、Cは両方とも生じた場合として評価を行った。
実施例2~9についても、表2に記載したような絶縁材を用いて絶縁層を形成し、各絶縁層の厚みについても表2に記載したように構成した。
実施例5~7は、第1の絶縁層と第3の絶縁層を異なる絶縁材を用いて形成した。
実施例8は、2~4層目に本実施形態の第1~3の絶縁層を配し、1層目に誘電率εと誘電正接δの積が大きい絶縁材を配した。
実施例9は、1~3層目に本実施形態の第1~3の絶縁層を配し、4層目に誘電率εと誘電正接δの積が大きい絶縁材を配した。
なお、絶縁層全体の厚さは、実施例1~9及び比較例1~4の全てにおいて24mmとした。
また、比較例2では、耐電圧性能の低い絶縁層にもかかわらず、最大電界で10kV/mmの電圧がかかっており、耐電圧性能としては好ましくない。また、誘電損失は低いものの、コストがかかる。
また、比較例3では、誘電率ε及び誘電正接δが小さい高価な絶縁層を厚さ14mmも用いるためコストがかかる。また、外側に伸縮性のある不織布のタイベック(登録商標)を用いるため、超電導ケーブルに曲げが生じると外側の絶縁層に皺ができる。絶縁層中に皺ができると絶縁層に隙間が生じ、電気絶縁的に電界集中と耐絶縁の低いボイドができ、これにより低電圧が印加された場合でも絶縁破壊する問題があるため、好ましくない。
更に、比較例4では、3層の構成とし、絶縁破壊強度は十分ではあるが、誘電損失が実施例1や比較例1,2に比べてやや高く、更にコストがかかってしまった。
実施例3では、実施例1と同様に誘電損失を0.4W/mまで抑制することができた。更に、交流電圧を印加した場合でも部分放電は生じなかった。材料コストは実施例1,2に比べると高いが、比較例2~4に比べれば抑えることができた。
実施例4では、誘電損失を0.5W/mまで抑制でき、更に、交流電圧を印加した場合でも部分放電は生じなかった。また、材料コストも実施例1と同等であり、好ましい。
実施例6では、誘電損失を0.5W/mまで抑制できた。しかし、交流電圧を印加した際の絶縁破壊及び部分放電の両方が生じてしまった。材料コストは、実施例1~5に比べて高いが、比較例2と比べると30%削減することができる。
実施例7では、誘電損失を0.2W/mまで抑制でき、更に、交流電圧を印加した場合でも部分放電は生じなかった。ただし、材料コストが高くなってしまった。しかし、比較例2と比べると同等の誘電損失を実現し、更に絶縁破壊強度も十分とすることができ、好ましい。
実施例9では、誘電損失を0.4W/mまで抑制でき、更に、交流電圧を印加した場合でも部分放電は生じなかった。更に、材料コストについても実施例1よりも低く抑えることができ、好ましい。
実施例1と実施例3,4を比較すると、第2の絶縁層の誘電率εと誘電正接tanδの積(ε2×tanδ2)は、0.04%以下とすることで、誘電損失の低減率が向上していることがわかる。また、ε2×tanδ2の値が0.04%以下の範囲内であれば誘電損失及び絶縁破壊強度は変化しないが、実施例3のようにフッ素樹脂フィルムを用いることで材料コストが上昇してしまうことが判る。
実施例2と6を比較すると、第1の絶縁層の誘電率εと誘電正接tanδの積(ε1×tanδ1)は、0.1%以上とすることで、絶縁破壊強度が向上することが判る。
実施例1と5、実施例3と7をそれぞれ比較すると、第3の絶縁層の誘電率εと誘電正接tanδの積(ε3×tanδ3)が、0.3%以下であれば、絶縁破壊強度が好ましいことが判る。また、ε3×tanδ3の値が、ε2×tanδ2の値よりも高い範囲内であれば、ε3×tanδ3の値が低ければ低いほど誘電損失の低減が向上していることが判る。
誘電損失、絶縁破壊強度、材料コストを総合評価した場合には、実施例1、4、9が最も好ましいことが判る。つまり、第1の絶縁層には半合成紙(ポリプロピレンラミネート紙)を用い、第2の絶縁層には合成樹脂製不織布を用い、第3の絶縁層には第1の絶縁層と同じ材料を用いることが最も好ましい。
図3に、本実施形態に係る絶縁層5を備えた超電導ケーブル10の第1の絶縁層5aの厚さと第2の絶縁層5bの厚さとを変化させ、それぞれの場合に275kV級の交流電圧を印加させた場合の誘電損失の値を示す。
また、誘電損失をポリエチレンラミネート紙による超電導ケーブルに比べて80%に低減することができ、ケーブル自身の電力送電による送電損失を低減できることに加えて、その損失による発熱を除去するために冷凍機の必要能力を下げることができ、冷凍システムの建設コストを抑えることができる。
また、第2の絶縁層5bに高価な不織布を使用するものの厚さを抑えることができ、全体のトータルシステムコストを低減することができる。
また、電機絶縁の信頼性も従来の絶縁層と同等であることから、ケーブルの長期間の使用とケーブルの絶縁破壊により、都市部への送電の停止によりおこる都市機能、市民生活機能への障害をなくし、信頼ある社会的基盤の維持を図ることができる。
2 超電導層
3 超電導導体層
4 半導電層
5 絶縁層
5a 第1の絶縁層
5b 第1の絶縁層
5c 第1の絶縁層
6 半導電層
7 超電導層
8 シールド保護層
9 絶縁保護層
10 超電導導体
Claims (9)
- 導体の外周に絶縁層を有する超電導ケーブルであって、
前記絶縁層は、内層から外層にかけて第1の絶縁層、第2の絶縁層及び第3の絶縁層からなる三層を少なくとも有し、前記絶縁層は液体窒素が含浸された状態であり、
前記第1の絶縁層の誘電率ε1と誘電正接tanδ1の積と前記第2の絶縁層の誘電率ε2と誘電正接tanδ2の積とは、ε1×tanδ1>ε2×tanδ2の関係を満たし、
前記第2の絶縁層の誘電率ε2と誘電正接tanδ2の積と前記第3の絶縁層の誘電率ε3と誘電正接tanδ3の積とは、ε2×tanδ2<ε3×tanδ3の関係を満たすことを特徴とする超電導ケーブル。 - 前記第2の絶縁層の誘電率ε2と誘電正接tanδ2の積は、0.04%以下であることを特徴とする請求項1に記載の超電導ケーブル。
- 前記第1の絶縁層の誘電率ε1と誘電正接tanδ1の積は、0.1%以上であり、
前記第2の絶縁層の誘電率ε2と誘電正接tanδ2の積は、0.04%以下であり、
前記第3の絶縁層の誘電率ε3と誘電正接tanδ3の積は、0.04%より大きく0.3%以下の範囲であることを特徴とする請求項1に記載の超電導ケーブル。 - 前記第1の絶縁層は、クラフト紙又はクラフト紙とプラスチックフィルムの複合されたテープ材料が複数枚巻きつけられて構成され、
前記第2の絶縁層は、プラスチック繊維製の不織布からなるテープ材料が複数枚巻きつけられて構成され、
前記第3の絶縁層は、クラフト紙又はクラフト紙とプラスチックフィルムの複合されたテープ材料が複数枚巻きつけられて構成されることを特徴とする請求項1~3の何れか一項に記載の超電導ケーブル。 - 前記第3の絶縁層がクラフト紙とプラスチックフィルムの複合されたテープ材料であって、前記第3の絶縁層の外周に、更に、クラフト紙が複数枚巻きつけられていることを特徴とする請求項4に記載の超電導ケーブル。
- 前記第2の絶縁層を構成するプラスチック繊維製の不織布は、無極性プラスチックであることを特徴とする請求項4又は5に記載の超電導ケーブル。
- 前記第2の絶縁層を構成するプラスチック繊維製の不織布は、高密度化処理するためにカレンダー処理されていることを特徴とする請求項4~6の何れか一項に記載の超電導ケーブル。
- 前記第1の絶縁層は、前記絶縁層全体の厚さに対して1/4以下の厚さであり、
前記第2の絶縁層は、前記絶縁層全体の厚さに対して1/10から1/3の範囲の厚さであり、
前記第3の絶縁層は、前記絶縁層全体の厚さから前記第1の絶縁層の厚さ及び前記第2の絶縁層の厚さを除いた厚さであることを特徴とする請求項1~7の何れか一項に記載の超電導ケーブル。 - 前記第2の絶縁層は、5mm以下の厚さであることを特徴とする請求項1~7の何れか一項に記載の超電導ケーブル。
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