Power cable

Abstract

The purpose of the present invention is to provide a power cable having a cooling structure capable of quickly cooling conductor heat generation caused by overcurrent. As a solution, this power cable (1) is provided with a twisted wire (2) and an outer covering part (4) for insulating and covering the twisted wire (2). The outer covering part (4) comprises an inner annular part (4a), three or more rib parts (4b) extending radially from the inner annular part (4a), and an outer annular part (4c) connected to the outer ends of the rib parts (4b). The number of flow paths (5) surrounded by the inner annular part (4a), the rib parts (4b), and the outer annular part (4c) is the same as the number of the rib parts (4b). The twisted wire (2) is an aggregate of elemental wires in which an insulating layer is formed on the outer periphery of a conductor. The power cable (1) has a gap part (6) comprising an outside gap part (6a) formed on the outside of the twisted wire (2) and an inside gap part (6b) formed on the inside of the twisted wire (2). The power cable (1) has a configuration in which an increase in temperature during energization is suppressed by causing a refrigerant (7) to flow through the flow path (5) and the gap part (6).

Description

Power cable

[0001] The present invention relates to a power cable for power supply.

[0002] Conventionally, a power supply cable provided with a cooling pipe has been proposed (Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-18748). Also, a coaxial cable in which a refrigerant flows through a void formed in a hollow core body has been proposed (Patent Document 2: Japanese Unexamined Patent Application Publication No. 2015-100188).

[0003] Japanese Unexamined Patent Application Publication No. 2018-18748 Japanese Unexamined Patent Application Publication No. 2015-100188

[0004] In the power supply cable described in Patent Document 1, since the cooling pipe is provided at the center of the power line, it is not possible to sufficiently secure the cross-sectional area necessary for cooling the conductor heat generation during energization. Also, since the cross-section has a non-axisymmetric shape, it has less flexibility than the coaxial cable having an axisymmetric shape such as that of Patent Document 2.

[0005] In order to shorten the power supply time to an electric vehicle, it is necessary to increase the amount of electric power flowing through the conductor. On the other hand, when the amount of electric power is increased, the conductor heat generation increases, and if the conductor heat generation becomes excessive, there is a problem that the outer covering melts and the insulation performance cannot be maintained. For example, due to an excessive current such as an inrush current, the conductor heat generation may temporarily increase and exceed the heat-resistant temperature of the hollow core body.

[0006] In view of the above circumstances, the present invention aims to provide a power cable having a heat-resistant structure that can withstand conductor heat generation caused by an excessive current such as an inrush current and a cooling structure that can quickly cool the conductor heat generation.

[0007] The power cable according to the present invention comprises a stranded wire and an outer sheath that insulates the stranded wire, the outer sheath comprising an inner annular portion, three or more rib portions extending radially from the inner annular portion, and an outer annular portion connected to the outer end of the rib portion, the flow channels enclosed by the inner annular portion, the rib portion and the outer annular portion being formed in the same number as the rib portion, the stranded wire being an assembly of individual wires with an insulating layer formed on the outer circumference of a metal wire, and having voids, the voids comprising an outer void portion formed on the outside of the stranded wire and an inner void portion formed on the inside of the stranded wire, and the configuration is characterized in that a coolant is flowed through the flow channels and the voids to suppress the temperature rise when energized.

[0008] With this configuration, a cooling channel is provided in the outer casing, and a cooling void is provided inside the inner annular section. This ensures sufficient cross-sectional area for cooling the heat generated by the conductor when energized, and allows for direct cooling where the refrigerant comes into contact with the stranded wire and absorbs heat. As a result, the cooling efficiency is dramatically improved.

[0009] The void ratio of the void portion is preferably 27 to 35%. The void ratio is expressed as a percentage of the cross-sectional area of ​​the void portion to the inner cross-sectional area of ​​the inner annular portion. The void ratio can be calculated using the cross-sectional area obtained by adding the outer void cross-sectional area formed by the stranded wire and the inner annular portion and the inner void cross-sectional area formed inside the stranded wire. By setting the void ratio to 27% or more, the stranded wire can be sufficiently cooled. By setting the void ratio to 35% or less, sufficient power can be supplied to the stranded wire.

[0010] The aforementioned stranded wire is preferably a rope twist. Rope twisting provides excellent shape stability. Furthermore, since the void is formed in a spiral shape, sufficient surface area and volume of the void through which the refrigerant flows can be secured.

[0011] This configuration provides excellent flexibility while easily accommodating power supply methods with currents of 300A or more, power supply methods with a power of 3000VA, and known charging standards such as CHAdeMO and SAE. As an example, the power cable according to the present invention constitutes a power supply line from the power supply unit to the battery in an electric vehicle.

[0012] According to the present invention, a power cable having a cooling structure capable of rapidly cooling conductor heat generated by excessive currents such as inrush current can be realized.

[0013] Figure 1 is a schematic cross-sectional view showing an example of a power cable according to this embodiment. Figure 2 is a schematic structural diagram showing an example of the power cable in Figure 1. Figure 3A is a schematic diagram showing the arrangement of the air gaps when the final strand of the stranded wire is 3 strands. Figure 3B is a schematic diagram showing the arrangement of the air gaps when the final strand of the stranded wire is 4 strands. Figure 3C is a schematic diagram showing the arrangement of the air gaps when the final strand of the stranded wire is 5 strands. Figure 3D is a schematic diagram showing the arrangement of the air gaps when the final strand of the stranded wire is 6 strands. Figure 4 is a schematic configuration diagram showing an application example of the power cable according to this embodiment.

[0014] Embodiments of the present invention will now be described in detail with reference to the drawings. As an example, the power cable 1 according to this embodiment constitutes a power supply line from the power supply unit 51a to the battery 51b in an electric vehicle 51, as shown in Figure 4. Connectors for external connection are attached to both ends of the power cable 1. The coolant flows through the cable via the connectors. In the diagrams illustrating the embodiments, components having the same function are denoted by the same reference numerals, and repeated explanations may be omitted.

[0015] [Power Cable] As shown in Figure 1, the power cable 1 of this embodiment comprises a stranded wire 2 and an outer sheath 4 that insulates the stranded wire 2. The outer sheath 4 is made of a thermoplastic resin with an integral structure comprising an inner annular portion 4a, three or more rib portions 4b extending radially from the inner annular portion 4a, and an outer annular portion 4c connected to the outer end of the rib portions 4b. The number of flow channels 5 surrounded by the inner annular portion 4a, the rib portions 4b, and the outer annular portion 4c is the same as the number of rib portions 4b. In order to achieve both heat dissipation efficiency and mechanical strength, the number of rib portions 4b is set to 3 to 9. By setting the number of rib portions 4b to 3 or more, sufficient mechanical strength of the outer sheath 4 can be ensured. By setting the number of rib portions 4b to 9 or less, sufficient cross-sectional area of ​​the flow channels 5 necessary for cooling by flowing a refrigerant can be ensured. More preferably, the number of rib portions 4b is set to 5 to 7. In other words, it is preferable that the number of flow channels 5 be set to 5 to 7.

[0016] In the example shown in Figure 1, the power cable 1 has six rib sections 4b extending radially from the inner annular section 4a, and six flow channels 5 are formed at these locations. As will be described later, the power cable 1 has a void section 6 consisting of a plurality of outer void sections 6a formed by the outer circumferential surface of the composite twisted structure in the stranded wire 2 and the inner circumferential surface of the inner annular section 4a, and a plurality of inner void sections 6b formed inside the stranded wire 2.

[0017] As shown in Figure 2, the power cable 1 of this embodiment is configured to suppress the temperature rise when energized by flowing a refrigerant 7 through the flow path 5 and the gap 6. For example, the refrigerant 7 is air or an inert gas. This prevents an increase in the weight of the power cable 1. For example, outside air is used as the refrigerant 7. The refrigerant 7 is then taken in from one end of the power cable 1, allowed to flow, and released outside the machine from the other end of the power cable 1. This allows the power cable 1 to be easily cooled. The arrows in Figure 2 indicate the direction of flow of the refrigerant 7. In addition to the above, the refrigerant 7 may be an inert liquid or antifreeze.

[0018] The stranded wire 2 according to this embodiment is made by twisting together copper or aluminum strands. For example, the stranded wire 2 is an assembly of strands in which an insulating film, such as an oxide film, is formed on the outer circumference of a metal wire made of copper or a copper alloy. For example, the stranded wire 2 is a composite stranded structure having a first stranded wire made by twisting strands, a second stranded wire made by twisting the first stranded wire, and a third stranded wire made by twisting the second stranded wire. The insulating film in the stranded wire 2 is made of a material that does not interfere with soldering. For example, the insulating film in the stranded wire 2 is made of polyurethane or polyester.

[0019] As an example, the porosity α of the void portion 6 is 27-35%. The porosity α is expressed as the percentage of the cross-sectional area of ​​the void portion 6 to the inner cross-sectional area of ​​the inner annular portion 4a. Since the outer circumference of the stranded wire 2 is inscribed inside the inner annular portion 4a, the porosity α can be calculated from the relationship between the two.

[0020] Figure 3A schematically shows the arrangement of the voids 6 when the final strand of the stranded wire 2 is 3 strands. The void ratio α when the final strand of the stranded wire 2 is 3 strands is 35%. Figure 3B schematically shows the arrangement of the voids 6 when the final strand of the stranded wire 2 is 4 strands. The void ratio α when the final strand of the stranded wire 2 is 4 strands is 31%. Figure 3C schematically shows the arrangement of the voids 6 when the final strand of the stranded wire 2 is 5 strands. The void ratio α when the final strand of the stranded wire 2 is 5 strands is 31%. Figure 3D schematically shows the arrangement of the voids 6 when the final strand of the stranded wire 2 is 6 strands. The void ratio α when the final strand of the stranded wire 2 is 6 strands is 33%.

[0021] When the final strand of stranded wire 2 is 7 strands, the void ratio α is 33%. When the final strand of stranded wire 2 is 8 strands, the void ratio α is 27%. When the final strand of stranded wire 2 is 9 strands, the void ratio α is 31%. Furthermore, when the final strand of stranded wire 2 is 10 strands, the void ratio α is 31%. And when the final strand of stranded wire 2 is 11 strands, the void ratio α is 29%.

[0022] In the example shown in Figure 2, the stranded wire 2 is a rope twist. In a rope twist, the twist direction of the final (n+1)th twist in the stranded wire 2 is in the opposite direction to the twist directions from the first twist to the nth twist. Here, n is a natural number of 2 or greater. Preferably, n is 2 or 3.

[0023] As an example, multiple strands are Z-twisted to form a first strand, multiple first strands are Z-twisted to form a second strand, and multiple second strands are S-twisted to form a third strand. As another example, multiple strands are Z-twisted to form a first strand, multiple first strands are Z-twisted to form a second strand, multiple second strands are Z-twisted to form a third strand, and multiple third strands are S-twisted to form a fourth strand. As yet another example, multiple strands are S-twisted to form a first strand, multiple first strands are S-twisted to form a second strand, and multiple second strands are Z-twisted to form a third strand. As yet another example, multiple strands are S-twisted to form a first strand, multiple first strands are S-twisted to form a second strand, multiple second strands are S-twisted to form a third strand, and multiple third strands are Z-twisted to form a fourth strand. Here, Z-twist is synonymous with left-hand twist, and S-twist is synonymous with right-hand twist.

[0024] As an example, stranded wire 2 uses strands consisting of metal wire made of copper or a copper alloy and an insulating coating made of polyurethane. The total cross-sectional area of ​​the conductor is 20 to 120 mm². ２ The insulating film has a radial thickness of 0.006 to 0.018 mm.

[0025] As an example, 3 to 12 strands of wire are twisted together to create strand 2. As an example, 10 to 20 strands of wire are twisted together to create the first strand, and then 4 to 7 strands of the first strand are twisted together to create strand 2. As an example, 27 strands of wire are twisted together to create the first strand, and then 7 strands of the first strand are twisted together to create strand 2. As an example, 30 strands of wire are twisted together to create the first strand, and then 8 strands of the first strand are twisted together to create strand 2. As an example, 35 strands of wire are twisted together to create the first strand, and then 10 strands of the first strand are twisted together to create strand 2. As an example, 10 to 35 strands of wire are twisted together to create the first strand, and then 4 to 10 strands of the first strand are twisted together to create strand 2.

[0026] As an example, six strands of wire are Z-twisted to form the first strand, four strands of the first strand are Z-twisted to form the second strand, and four strands of the second strand are S-twisted to form strand 2. As an example, six strands of wire are Z-twisted to form the first strand, four strands of the first strand are Z-twisted to form the second strand, and five strands of the second strand are S-twisted to form strand 2. As an example, six strands of wire are Z-twisted to form the first strand, five strands of the first strand are Z-twisted to form the second strand, and seven strands of the second strand are S-twisted to form strand 2. As an example, eight strands of wire are Z-twisted to form the first strand, five strands of the first strand are Z-twisted to form the second strand, and seven strands of the second strand are S-twisted to form strand 2. For example, 10 strands of wire are twisted together in a Z-shape to form the first stranded wire, 5 strands of the first stranded wire are twisted together in a Z-shape to form the second stranded wire, and 7 strands of the second stranded wire are twisted together in an S-shape to form the second stranded wire. For example, 12 strands of wire are twisted together in a Z-shape to form the first stranded wire, 6 strands of the first stranded wire are twisted together in a Z-shape to form the second stranded wire, and 10 strands of the second stranded wire are twisted together in an S-shape to form the second stranded wire. For example, 6 to 12 strands of wire are twisted together in a Z-shape to form the first stranded wire, 4 to 6 strands of the first stranded wire are twisted together in a Z-shape to form the second stranded wire, and 4 to 10 strands of the second stranded wire are twisted together in an S-shape to form the second stranded wire.

[0027] As an example, six strands of wire are Z-twisted to form the first strand, four strands of the first strand are Z-twisted to form the second strand, four strands of the second strand are Z-twisted to form the third strand, and four strands of the third strand are S-twisted to form strand 2. As an example, seven strands of wire are Z-twisted to form the first strand, six strands of the first strand are Z-twisted to form the second strand, five strands of the second strand are Z-twisted to form the third strand, and five strands of the third strand are S-twisted to form strand 2. As an example, eight strands of wire are Z-twisted to form the first strand, six strands of the first strand are Z-twisted to form the second strand, five strands of the second strand are Z-twisted to form the third strand, and seven strands of the third strand are S-twisted to form strand 2. As an example, 10 strands of wire are Z-twisted to form the first stranded wire, 6 strands of the first stranded wire are Z-twisted to form the second stranded wire, 5 strands of the second stranded wire are Z-twisted to form the third stranded wire, and 7 strands of the third stranded wire are S-twisted to form stranded wire 2. As an example, 12 strands of wire are Z-twisted to form the first stranded wire, 6 strands of the first stranded wire are Z-twisted to form the second stranded wire, 6 strands of the second stranded wire are Z-twisted to form the third stranded wire, and 7 strands of the third stranded wire are S-twisted to form stranded wire 2. As an example, 12 strands of wire are Z-twisted to form the first stranded wire, 7 strands of the first stranded wire are Z-twisted to form the second stranded wire, 6 strands of the second stranded wire are Z-twisted to form the third stranded wire, and 7 strands of the third stranded wire are S-twisted to form stranded wire 2. For example, 6 to 12 strands of wire are twisted together in a Z-shape to form the first stranded wire, 4 to 10 strands of the first stranded wire are twisted together in a Z-shape to form the second stranded wire, 4 to 6 strands of the second stranded wire are twisted together in a Z-shape to form the third stranded wire, and 4 to 10 strands of the third stranded wire are twisted together in an S-shape to form stranded wire 2.

[0028] The outer covering 4 can be made of olefin resins such as polyethylene and polypropylene. Crosslinked polyethylene is particularly preferred because it has a heat resistance temperature of 120°C. The outer covering 4 can also be made of fluororesins such as PTFE, PFA, FEP, PCTFE, ETFE, and ECTFE. These fluororesins have better heat resistance than olefin resins.

[0029] As an example, the outer sheath portion 4 has a radial thickness of 0.6 to 2.4 mm for the inner annular portion 4a, a radial thickness of 0.6 to 2.4 mm for the outer annular portion 4c, and a circumferential thickness of 0.7 to 2.1 mm for the rib portion 4b. This configuration allows for a small diameter, robust, and highly flexible structure. However, the configuration is not limited to the above.

[0030] [Manufacturing Method for the Outer Sheath] The outer sheath 4 is manufactured using a die. The die has a central hole, an inner annular hole formed adjacent to its outer edge so as to surround the central hole, six or more predetermined shaped holes extending radially from the outer circumference of the inner annular hole and wider than the inner annular hole, and an outer annular hole connecting the outer ends of the predetermined shaped holes and wider than the inner annular hole. Molten resin is extruded using the die from the inner annular hole, the predetermined shaped holes and the outer annular hole and slowly cooled and solidified. By forming the outer sheath 4 through this extrusion molding, an inner annular portion 4a, rib portions 4b extending radially from the inner annular portion 4a, and an outer annular portion 4c connecting the outer ends of the rib portions 4b are integrally formed around the stranded wire 2 using thermoplastic resin. Furthermore, a flow channel 5 is formed that is continuous in the longitudinal direction, surrounded by the inner annular portion 4a, the rib portions 4b and the outer annular portion 4c. Furthermore, an outer void 6a is formed that is continuous in the longitudinal direction, surrounded by the outer circumferential surface of the stranded wire 2 and the inner circumferential surface of the inner annular portion 4a. According to the manufacturing method of this embodiment, a power cable 1 that is small in diameter, robust, and highly flexible can be produced.

[0031] [Air Cooling Test] Next, a sample was prepared and an air cooling test was conducted to confirm the cooling capacity of the power cable 1 described above. The test standard was JIS C2805:2010.

[0032] (Example) The stranded wire 2 in the sample of the example is a rope stranded wire made by twisting together 2520 strands of Type 2 polyurethane copper wire, each strand having an outer diameter of 0.12 mm. The stranded wire 2 is made by Z-twisting 12 strands together to form the first stranded wire, Z-twisting 6 strands of the first stranded wire to form the second stranded wire, Z-twisting 5 strands of the second stranded wire to form the third stranded wire, and S-twisting 7 strands of the third stranded wire. The stranded wire 2 has a void portion 6 consisting of a plurality of outer void portions 6a formed by the outer circumferential surface of the stranded wire 2 and the inner circumferential surface of the inner annular portion 4a, and an inner void portion 6b formed on the inside of the stranded wire 2, with a void ratio α of the void portion 6 being 33%. The outer sheath portion 4 is made of cross-linked polyethylene resin. The outer sheath 4 has a radial thickness of 0.8 mm in the inner annular portion 4a, a circumferential thickness of 1.4 mm in the rib portion 4b, and a radial thickness of 1.2 mm in the outer annular portion 4c. The outer sheath 4 has six flow channels 5 formed in it. The power cable 1 of Example 1 has an outer diameter of 16.0 mm and a total length of 3.3 m.

[0033] In the first air-cooling test, an air coupler was attached to one end of the sample, the other end was left open, and a DC current of 50A was continuously applied to the stranded wire 2. The surface temperature of each part of the sample was measured using a non-contact thermometer. As a result of continuous energization, the surface temperature of the stranded wire 2 reached 154°C, and the surface temperature of the outer sheath 4 reached 121°C. Subsequently, room temperature air was introduced as the refrigerant 7 at a flow rate of 70 liters per minute from one end of the sample, and the air was released to the outside from the other end of the sample. The temperature was measured using a non-contact thermometer after 10 minutes of continuous air cooling. As a result, the surface temperature of the stranded wire 2 reached 95°C, and the surface temperature of the outer sheath 4 reached 45°C. Therefore, the example confirmed that by flowing the refrigerant 7, the surface temperature of the stranded wire 2 was cooled by 59°C, and the surface temperature of the outer sheath 4 was cooled by 76°C.

[0034] In the second air-cooling test, an air coupler was attached to one end of the sample, the other end was left open, and a DC current of 70A was continuously applied to the stranded wire 2. The surface temperature of each part of the sample was measured using a non-contact thermometer. As a result of continuous energization, the surface temperature of the stranded wire 2 reached 164°C, and the surface temperature of the outer sheath 4 reached 131°C. Subsequently, room temperature air was introduced as the refrigerant 7 at a flow rate of 70 liters per minute from one end of the sample, and the air was released to the outside from the other end of the sample. The temperature was measured using a non-contact thermometer after 10 minutes of continuous air cooling. As a result, the surface temperature of the stranded wire 2 reached 85°C, and the surface temperature of the outer sheath 4 reached 47°C. Therefore, the example confirmed that by flowing the refrigerant 7, the surface temperature of the stranded wire 2 was cooled by 79°C, and the surface temperature of the outer sheath 4 was cooled by 84°C.

[0035] (Reference Example) The sample in the reference example is a bundle of 2520 strands of Type 2 polyurethane copper wire, each with an outer diameter of 0.12 mm, used as a conductor. The outer sheath of the reference example is the same as in the example. The outer diameter and total length of the cable in the reference example are the same as in the example.

[0036] In the first air-cooling test, an air coupler was attached to one end of the sample, the other end was left open, and a DC current of 50A was continuously applied to the stranded wire 2. The surface temperature of each part of the sample was measured using a non-contact thermometer. As a result of continuous current application, the surface temperature of the conductor reached 154°C, and the surface temperature of the outer sheath reached 121°C. Subsequently, room temperature air was introduced as refrigerant 7 at a flow rate of 70 liters per minute from one end of the sample, and the air was released to the outside from the other end of the sample. The temperature was measured using a non-contact thermometer after 10 minutes of continuous air cooling. As a result, the surface temperature of the conductor reached 105°C, and the surface temperature of the outer sheath reached 49°C. Therefore, it was confirmed that in the reference example, the surface temperature of the conductor was cooled by 49°C and the surface temperature of the outer sheath was cooled by 72°C by flowing refrigerant 7.

[0037] In the second air-cooling test, an air coupler was attached to one end of the sample, the other end was left open, and a DC current of 70A was continuously applied to the stranded wire 2. The surface temperature of each part of the sample was measured using a non-contact thermometer. As a result of continuous current application, the surface temperature of the conductor reached 164°C, and the surface temperature of the outer sheath reached 131°C. Subsequently, room temperature air was introduced as refrigerant 7 at a flow rate of 70 liters per minute from one end of the sample, and the air was released to the outside from the other end of the sample. The temperature was measured using a non-contact thermometer after 10 minutes of continuous air cooling. As a result, the surface temperature of the conductor reached 94°C, and the surface temperature of the outer sheath reached 52°C. Therefore, it was confirmed that in the reference example, the surface temperature of the conductor was cooled by 70°C and the surface temperature of the outer sheath 4 was cooled by 79°C by flowing refrigerant 7.

[0038] The results of the above-mentioned air cooling tests confirmed that in both the embodiment and the reference example, the temperature rise could be suppressed by flowing the refrigerant 7 through the flow path 5. Furthermore, it was confirmed that the embodiment could suppress the temperature rise during energization even more effectively than the reference example which does not have the air gap 6.

Claims

1. A power cable comprising a stranded wire and an outer sheath that insulates the stranded wire, wherein the outer sheath consists of an inner annular portion, three or more rib portions extending radially from the inner annular portion, and an outer annular portion connected to the outer end of the rib portion, and a flow channel enclosed by the inner annular portion, the rib portion, and the outer annular portion is formed in the same number as the rib portion, the stranded wire is an assembly of individual wires with an insulating layer formed on the outer circumference of a metal wire, and has voids formed therein, the voids consisting of an outer void portion formed on the outside of the stranded wire and an inner void portion formed on the inside of the stranded wire, and the configuration is such that a coolant is flowed through the flow channels and the voids to suppress the temperature rise when energized.

2. The power cable according to claim 1, characterized in that the void ratio of the void portion is 27 to 35%.

3. The power cable according to claim 2, characterized in that the stranded wire is rope-stranded.

4. The power cable according to any one of claims 1 to 3, characterized in that it constitutes a power supply line from the power supply unit to the battery in an electric vehicle.

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