Cable

Abstract

This cable comprises: a conductor part; a first semiconductive layer (20) that covers the outer periphery of the conductor part; an insulating layer (30) that covers the outer periphery of the first semiconductive layer (20); and a second semiconductive layer that covers the outer periphery of the insulating layer (30). In the cable, at least one among a first gap (50) located between the first semiconductive layer (20) and the insulating layer (30) and a second gap located between the insulating layer (30) and the second semiconductive layer is formed. In the radial direction of the cable, the maximum value of the width (W1) of the first gap (50) or the maximum value of the width of the second gap is less than or equal to 100 μm. In the radial direction of the cable, the average value of the width (W1) of the first gap (50) or the average value of the width of the second gap is 0.1-100 μm inclusive.

Description

Cable

[0001] This disclosure relates to a cable.

[0002] European Patent Application Publication No. 2765581 (Patent Document 1) describes an electric cable. The electric cable described in Patent Document 1 has a conductor portion, a first semiconductive layer, an insulating layer, and a second semiconductive layer.

[0003] The conductor portion has a plurality of conductive wires. In the conductor portion, the plurality of conductive wires are bundled. The first semiconductive layer covers the outer periphery of the conductor portion. The insulating layer covers the outer periphery of the first semiconductive layer. The second semiconductive layer covers the outer periphery of the insulating layer. The first semiconductive layer is formed by extruding a resin material containing a conductive filler. The insulating layer is formed by extruding a resin material on the outer periphery of the first semiconductive layer. The second semiconductive layer is formed by extruding a resin material containing a conductive filler.

[0004] European Patent Application Publication No. 2765581

[0005] The cable of this disclosure includes a conductor portion, a first semiconductive layer covering the outer periphery of the conductor portion, an insulating layer covering the outer periphery of the first semiconductive layer, and a second semiconductive layer covering the outer periphery of the insulating layer. At least one of a first gap located between the first semiconductive layer and the insulating layer and a second gap located between the insulating layer and the second semiconductive layer is formed in the cable. In the radial direction of the cable, the maximum value of the width of the first gap or the maximum value of the width of the second gap is 100 μm or less. In the radial direction of the cable, the average value of the width of the first gap or the average value of the width of the second gap is 0.1 μm or more and 100 μm or less. [[ID=z16]]

[0006] FIG. 1 is a plan view of cable 100. FIG. 2 is a cross-sectional view taken along II-II in FIG. 1. FIG. 3 is a first partial enlarged view of FIG. 2. FIG. 4 is a second partial enlarged view of FIG. 2. FIG. 5 is a cross-sectional view of cable 300 according to a modified example. FIG. 6 is a manufacturing process diagram of cable 100. FIG. 7 is a cross-sectional view of cable 200. FIG. 8 is a first partial enlarged view of FIG. 7. FIG. 9 is a second partial enlarged view of FIG. 7. [[ID=z19]]

[0007] [Problems to be Solved by This Disclosure] In the electrical cable described in Patent Document 1, it is difficult to achieve both the suppression of partial discharge between the insulating layer and the semiconducting layer (first semiconducting layer, second semiconducting layer) and the flexibility of the cable. This disclosure has been made in view of these problems of the prior art. More specifically, this disclosure provides a cable that can ensure flexibility while suppressing partial discharge between the insulating layer and the semiconducting layer.

[0008] [Effects of this disclosure] The cable of this disclosure makes it possible to ensure flexibility while suppressing partial discharge between the insulating layer and the semiconducting layer.

[0009] [Summary of Embodiments] First, embodiments of the present disclosure are listed below.

[0010] (1) The cable according to the embodiment comprises a conductor portion, a first semiconducting layer covering the outer circumference of the conductor portion, an insulating layer covering the outer circumference of the first semiconducting layer, and a second semiconducting layer covering the outer circumference of the insulating layer. The cable has at least one of a first gap located between the first semiconducting layer and the insulating layer, and a second gap located between the insulating layer and the second semiconducting layer. In the radial direction of the cable, the maximum width of the first gap or the maximum width of the second gap is 100 μm or less. In the radial direction of the cable, the average value of the width of the first gap or the average value of the width of the second gap is 0.1 μm or more and 100 μm or less. According to the cable of (1) above, it is possible to ensure flexibility while suppressing partial discharge between the insulating layer and the first semiconducting layer.

[0011] (2) In the cable described in (1) above, the average value of the width of the first gap in the radial direction of the cable may be greater than the average value of the width of the second gap in the radial direction of the cable.

[0012] (3) In the cable described in (1) or (2) above, the conductor portion may consist of multiple bundled wires.

[0013] (4) In the cables described in (1) to (3) above, the first semiconducting layer, the insulating layer, and the second semiconducting layer may each contain fluororesin.

[0014] (5) In the cable described in (4) above, the fluororesin constituting the first semiconducting layer, the insulating layer, and the second semiconducting layer may be any of PFA, FEP, and ETFE.

[0015] (6) In the cable described in (4) or (5) above, the fluororesin constituting the first semiconducting layer, the insulating layer, and the second semiconducting layer may be crosslinked.

[0016] [Details of Embodiments] Details of embodiments of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions will not be repeated. The cable according to the embodiment will be referred to as cable 100.

[0017] (Configuration of cable 100) The configuration of cable 100 is described below.

[0018] <Basic Configuration of Cable 100> Figure 1 is a plan view of cable 100. As shown in Figure 1, cable 100 extends in a straight line. The direction in which cable 100 extends is defined as the axial direction of cable 100. Figure 2 is a cross-sectional view taken along line II-II in Figure 1. Figure 2 shows a cross-section perpendicular to the axial direction of cable 100. As shown in Figure 2, cable 100 has a conductor portion 10, a first semiconducting layer 20, an insulating layer 30, and a second semiconducting layer 40.

[0019] The conductor portion 10 has, for example, a plurality of conductors 11. The plurality of conductors 11 are bundled together to constitute the conductor portion 10. The plurality of conductors 11 may be simply bundled together, or they may be bundled while being twisted together. The conductors 11 are made of a conductive material. The conductors 11 are made of, for example, copper, copper alloy, aluminum, aluminum alloy, nickel, silver, iron, steel, stainless steel, etc. The surface of the conductors 11 may be silver plated, tin plated, nickel plated, copper plated, etc. The conductors 11 are, for example, circular in cross-section. However, the cross-sectional shape of the conductors 11 is not limited to this.

[0020] The first semiconducting layer 20 covers the outer circumference of the conductor portion 10. Since the conductor portion 10 is formed by bundling multiple conductors 11 together, a recess exists on the outer circumference of the conductor portion 10 in cross-sectional view. Therefore, a partial void may exist between the inner circumference of the first semiconducting layer 20 and the outer circumference of the conductor portion 10.

[0021] The first semiconducting layer 20 is semiconductive. Semiconductivity means that the volume resistivity is between 1 Ω·cm and 100,000 Ω·cm. The first semiconducting layer 20 comprises a first resin material and a first conductive filler mixed in the first resin material. The first resin material is, for example, a fluororesin. Specific examples of fluororesins used as the first resin material include PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and ETFE (ethylene-tetrafluoroethylene copolymer). The first resin material may or may not be crosslinked. The first conductive filler is formed from a conductive material. The first conductive filler is, for example, made from carbon black, carbon nanotubes, or a metal material.

[0022] The insulating layer 30 covers the outer periphery of the first semiconducting layer 20. The insulating layer 30 has electrical insulating properties. Electrical insulating properties mean that the volume resistivity is greater than 100,000 Ω·cm. The insulating layer 30 is formed of a second resin material. The second resin material is, for example, a fluororesin. Specific examples of fluororesins used as the second resin material include PFA, FEP, and ETFE. The second resin material may or may not be crosslinked.

[0023] The second semiconducting layer 40 covers the outer periphery of the insulating layer 30. The second semiconducting layer 40 is semiconductive. The second semiconducting layer 40 comprises a third resin material and a second conductive filler mixed in the third resin material. The third resin material is, for example, a fluororesin. Specific examples of fluororesins used as the third resin material include PFA, FEP, and ETFE. The third resin material may or may not be crosslinked. The second conductive filler is formed of a conductive material. The second conductive filler is formed of, for example, carbon black, carbon nanotubes, or a metal material.

[0024] <Detailed Configuration of Cable 100> Figure 3 is a first enlarged view of Figure 2. As shown in Figure 3, a gap 50 can be formed between the first semiconducting layer 20 and the insulating layer 30. The radial direction of the cable 100 is perpendicular to the axial direction of the cable 100 and passes through the center of the cable 100. The width of the gap 50 in the radial direction of the cable 100 is denoted as width W1. The maximum value of width W1 is 100 μm or less. The maximum value of width W1 may be 50 μm or less, or 10 μm or less.

[0025] The average width W1 is 0.1 μm or more. The average width W1 may be 0.15 μm or more, or 3 μm or more. The average width W1 is 100 μm or less. The average width W1 may be 50 μm or less, or 10 μm or less.

[0026] The maximum and average values ​​of the width W1 are measured by taking a cross-sectional image of the cable 100 using a microscope (optical microscope or electron microscope) in a cross-section perpendicular to the axial direction of the cable 100, and then analyzing the boundary between the first semiconducting layer 20 and the insulating layer 30 of the cross-sectional image using image processing software. As an alternative method for measuring the width W1, measurement points may be selected from any number of locations at the boundary between the first semiconducting layer 20 and the insulating layer 30, and the maximum and average values ​​of the width W1 may be calculated from the width W1 at those measurement points. The average value of the width W1 can be calculated by dividing the sum of the measured width W1 values ​​by the number of measurement points. The number of measurement points should preferably be 10 or more.

[0027] Furthermore, the gap 50 does not need to be formed over the entire boundary between the first semiconducting layer 20 and the insulating layer 30. To put this in other words, the first semiconducting layer 20 and the insulating layer 30 may be in contact with each other in a portion of the boundary between them. However, the ratio of the length of the portion in which the first semiconducting layer 20 and the insulating layer 30 are in contact with each other to the total circumference of the boundary between the first semiconducting layer 20 and the insulating layer 30 should be 50 percent or less. By making this ratio 50 percent or less, the cable 100 can be made flexible. Also, it is preferable that the gap 50 be in multiple locations rather than just one. It is preferable that the gap 50 be evenly distributed along the circumferential direction of the cable 100 rather than being concentrated in a portion of the boundary between the first semiconducting layer 20 and the insulating layer 30. The length of the portion of the boundary between the first semiconducting layer 20 and the insulating layer 30 that is in contact with each other, out of the total circumference length of the boundary between the first semiconducting layer 20 and the insulating layer 30, is measured by taking a cross-sectional image in the same manner as the measurement method for the width W1, and analyzing the said cross-sectional image with image processing software.

[0028] Figure 4 is a second enlarged view of Figure 2. As shown in Figure 4, a gap 51 can be formed between the second semiconducting layer 40 and the insulating layer 30. The width of the gap 51 in the radial direction of the cable 100 is denoted as width W2. The maximum value of width W2 is 100 μm or less. The maximum value of width W2 may be 50 μm or less, or 10 μm or less.

[0029] The average value of width W2 is 0.1 μm or more. The average value of width W2 may be 0.5 μm or more, or 3 μm or more. The average value of width W2 may be less than the average value of width W1.

[0030] The maximum and average values ​​of the width W2 are measured by taking a cross-sectional image of the cable 100 using a microscope (optical microscope or electron microscope) in a cross-section perpendicular to the axial direction of the cable 100, and then analyzing the boundary between the insulating layer 30 and the second semiconducting layer 40 of the cross-sectional image using image processing software. As an alternative method for measuring the width W2, measurement points may be selected from any multiple locations at the boundary between the insulating layer 30 and the second semiconducting layer 40, and the maximum and average values ​​of the width W2 may be calculated from the width W2 at those measurement points. The average value of the width W2 can be calculated by dividing the sum of the measured width W2 values ​​by the number of measurement points. The number of measurement points should preferably be 10 or more.

[0031] Furthermore, the gap 51 does not need to be formed along the entire boundary between the second semiconducting layer 40 and the insulating layer 30. To put this in other words, the second semiconducting layer 40 and the insulating layer 30 may be in contact with each other in a portion of the boundary between them. However, the ratio of the length of the portion in which the second semiconducting layer 40 and the insulating layer 30 are in contact with each other to the total circumference of the boundary between the second semiconducting layer 40 and the insulating layer 30 should be 50 percent or less. By making this ratio 50 percent or less, the cable 100 can be made flexible. Also, it is preferable that the gap 51 be in multiple locations rather than just one. It is preferable that the gap 51 be evenly distributed along the circumferential direction of the cable 100 rather than being concentrated in a portion of the boundary between the insulating layer 30 and the second semiconducting layer 40. The length of the portion of the boundary between the insulating layer 30 and the second semiconducting layer 40 that is in contact with each other, out of the total circumference length of the boundary between the insulating layer 30 and the second semiconducting layer 40, is measured by taking a cross-sectional image in the same manner as the width W2 measurement method and analyzing the said cross-sectional image with image processing software.

[0032] The circumferential direction of cable 100 is the direction along the circumference of the cable 100 when viewed in a cross-section perpendicular to the axial direction of cable 100. To put this in other terms, the circumferential direction of cable 100 is the direction perpendicular to the radial direction of cable 100 when viewed in a cross-section perpendicular to the axial direction of cable 100.

[0033] The index used to compare the length of the gap 50 in the circumferential direction of cable 100 is R1 (unit: rad), as shown in Figure 3. R1 is defined as the angle between a virtual line passing through one end of the gap 50 in the circumferential direction of cable 100 and the center of cable 100, and a virtual line passing through the other end of the gap 50 in the circumferential direction of cable 100 and the center of cable 100. The index used to compare the length of the gap 51 in the circumferential direction of cable 100 is R2 (unit: rad), as shown in Figure 3. R2 is defined as the angle between a virtual line passing through one end of the gap 51 in the circumferential direction of cable 100 and the center of cable 100, and a virtual line passing through the other end of the gap 51 in the circumferential direction of cable 100 and the center of cable 100. R1 and R2 are measured by analyzing the cross-sectional image with image processing software, similar to the widths W1 and W2.

[0034] <Modified Example> Figure 5 is a cross-sectional view of the modified cable 300. Figure 5 shows a cross-section at a position corresponding to Figure 2. As shown in Figure 5, the conductor portion 10 may be composed of a single thick conductor 12 instead of a bundle of multiple thin conductors 11.

[0035] (Method for manufacturing cable 100) The method for manufacturing cable 100 is described below.

[0036] Figure 6 is a diagram of the manufacturing process for cable 100. As shown in Figure 6, the manufacturing method for cable 100 includes a preparation step S1, a first coating step S2, a second coating step S3, and a third coating step S4. The first coating step S2 is performed after the preparation step S1. The second coating step S3 is performed after the first coating step S2. The third coating step S4 is performed after the second coating step S3.

[0037] In preparation step S1, the conductor portion 10 is prepared. At this stage, the first semiconducting layer 20, the insulating layer 30, and the second semiconducting layer 40 have not yet been formed.

[0038] In the first coating step S2, a first semiconducting layer 20 is formed by extrusion molding to cover the outer circumference of the conductor portion 10. In the second coating step S3, an insulating layer 30 is formed by extrusion molding to cover the outer circumference of the first semiconducting layer 20. In the third coating step S4, a second semiconducting layer 40 is formed by extrusion molding to cover the outer circumference of the insulating layer 30. In other words, in the manufacturing method of the cable 100, the first semiconducting layer 20, the insulating layer 30, and the second semiconducting layer 40 are not formed simultaneously (co-extruded), but are formed sequentially and individually.

[0039] The characteristics of the gap 50 (width W1 and R1) are adjusted by changing the magnitude of the pressure applied when supplying the softened resin onto the first semiconducting layer 20 within the crosshead of the extruder, and by changing the timing of the application of that pressure. The characteristics of the gap 50 can also be adjusted, for example, by applying oil to the outer circumference of the first semiconducting layer 20 before performing the second coating process S3. Alternatively, the characteristics of the gap 50 can also be adjusted by introducing compressed air from the rear of the crosshead of the extruder. The characteristics of the gap 51 (width W2 and R2) are adjusted in a similar manner.

[0040] (Effects of Cable 100) The effects of Cable 100 will be explained below in comparison with the cable of the comparative example. The cable of the comparative example will be referred to as Cable 200.

[0041] Figure 7 is a cross-sectional view of cable 200. Figure 7 shows a cross-section at a position corresponding to Figure 2. As shown in Figure 7, cable 200 has a conductor portion 10, a first semiconducting layer 20, an insulating layer 30, and a second semiconducting layer 40. In this respect, the configuration of cable 200 is the same as that of cable 100.

[0042] FIG. 8 is a first partial enlarged view of FIG. 7. FIG. 9 is a second partial enlarged view of FIG. 7. As shown in FIGS. 8 and 9, in cable 200, no gap 50 is formed at the boundary between the first semiconductive layer 20 and the insulating layer 30, and no gap 51 is formed at the boundary between the second semiconductive layer 40 and the insulating layer 30. In this regard, the configuration of cable 200 is different from that of cable 100. In cable 200, as a result of co-extrusion molding of the first semiconductive layer 20, the insulating layer 30, and the second semiconductive layer 40, no gap 50 and no gap 51 are formed.

[0043] In cable 200, since no gap 50 is formed, the adhesion between the first semiconductive layer 20 and the insulating layer 30 is high, and since no gap 51 is formed, the adhesion between the second semiconductive layer 40 and the insulating layer 30 is high. As a result, cable 200 is difficult to bend and lacks flexibility. On the other hand, in cable 100, a gap 50 is formed such that the average value of the width W1 is 0.1 μm or more, and a gap 51 is formed such that the average value of the width W2 is 0.1 μm or more. Therefore, the adhesion between the first semiconductive layer 20 and the insulating layer 30 and the adhesion between the second semiconductive layer 40 and the insulating layer 30 are moderately reduced. Therefore, according to cable 100, it is possible to ensure ease of bending.

[0044] When a gap exists between the first semiconductive layer 20 and the insulating layer 30 or between the second semiconductive layer 40 and the insulating layer 30, partial discharge may occur in the gap. The larger the gap, the more likely partial discharge is to occur. In cable 200, since no gap 50 or gap 51 is formed, partial discharge is unlikely to occur. On the other hand, in cable 100, gaps 50 and 51 are formed. However, in cable 100, the maximum value of the width W1 and the maximum value of the width W2 are set to 100 μm or less, and since the widths W1 and W2 are within a range where partial discharge is unlikely to occur, it is possible to suppress the occurrence of partial discharge while ensuring ease of bending.

[0045] (Example) Samples 1 to 27 of the cable were prepared to evaluate the relationship between the maximum and average values of width W1 (width W2), bendability, and partial discharge inception voltage. As shown in Table 1, the maximum and average values of width W1 and width W2 were changed from Sample 1 to Sample 27. In the prepared samples, cross-sectional images were obtained by cutting along the radial direction at three arbitrary positions in the axial direction of the cable, and the maximum and average values of width W1 and width W2 were measured by analyzing the cross-sectional images. For Samples 1 to 27, evaluation of the partial discharge inception voltage (PDIV) and bendability was performed. The partial discharge inception voltage was evaluated by applying an AC voltage of 60 Hz between the conductor part 10 and the second semiconductive layer 40 and measuring the voltage at the time when a discharge of 100 pC or more was detected. Bendability was evaluated by measuring the bending rigidity according to the method described in International Publication No. 2015 / 159788. In the sample for measuring the bending rigidity, 19 strands of stranded wire obtained by stranding 7 wires with a diameter of 0.35 mm were used as the conductor part 10, and the thicknesses of the first semiconductive layer 20, the insulating layer 30, and the second semiconductive layer 40 were 0.2 mm, 0.7 mm, and 0.2 mm, respectively.

[0046]

[0047] As shown in Table 1, in the samples where the maximum value of width W1 (width W2) was greater than 100 μm, the partial discharge inception voltage was less than 2500 V. This result was consistent with the calculation result using simulation. Also, in the samples where the average value of width W1 (width W2) was less than 0.1 μm, the bending rigidity was 200 N·mm ２ or more. On the other hand, in the samples where the maximum value of width W1 (width W2) was 100 μm or less, the partial discharge inception voltage was 2500 V or more. Also, in the samples where the average value of width W1 (width W2) was 0.1 μm or more, the bending rigidity was less than 200 N·mm ２ From this comparison, it was found that by setting the maximum value of width W1 (width W2) to 100 μm or less and the average value of width W1 (width W2) to 0.1 μm or more, both a high partial discharge inception voltage and bendability can be achieved.

[0048] (Modification) Although not shown, the cable 100 may further have a shield layer or sheath layer located outside the second semiconducting layer 40. The conductive layer may also be wrapped with insulating tape or the like. Furthermore, the cable 100 only needs to have at least one of the gaps 50 and 51.

[0049] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the embodiments described above, and all modifications within the meaning and scope of equivalents of the claims are intended to be included.

[0050] 100, 200, 300 Cable, 10 Conductor part, 11, 12 Wire, 20 First semiconducting layer, 30 Insulating layer, 40 Second semiconducting layer, 50, 51 Gap, S1 Preparation process, S2 First coating process, S3 Second coating process, S4 Third coating process, W1, W2 Width.

Claims

1. A cable comprising: a conductor portion; a first semiconducting layer covering the outer circumference of the conductor portion; an insulating layer covering the outer circumference of the first semiconducting layer; and a second semiconducting layer covering the outer circumference of the insulating layer, wherein the cable has at least one of a first gap located between the first semiconducting layer and the insulating layer, and a second gap located between the insulating layer and the second semiconducting layer, wherein in the radial direction of the cable, the maximum value of the width of the first gap or the maximum value of the width of the second gap is 100 μm or less, and in the radial direction of the cable, the average value of the width of the first gap or the average value of the width of the second gap is 0.1 μm or more and 100 μm or less.

2. The cable according to claim 1, wherein the average value of the width of the first gap in the radial direction of the cable is greater than the average value of the width of the second gap in the radial direction of the cable.

3. The cable according to claim 1 or claim 2, wherein the conductor portion is composed of a plurality of bundled conductors.

4. The cable according to any one of claims 1 to 3, wherein each of the first semiconducting layer, the insulating layer, and the second semiconducting layer comprises a fluororesin.

5. The cable according to claim 4, wherein the fluororesin is one of PFA, FEP, and ETFE.

6. The cable according to claim 4 or claim 5, wherein the fluororesin is crosslinked.

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