Method for forming an electrical connection on a superconducting cable

Abstract

The invention relates to a method for forming an electrical connection (200) on a superconducting cable (100). The cable (100) comprises a cylindrical central support (110) and, around the central support (110), at least one functional layer (114) having an electrical function and at least one structural layer (112) having a mechanical function. A preloading step comprises exerting an outward axial force on the structural layer (112) from the first end of the cable. An electrical connection step comprises securing the functional layer (114) and the structural layer (112) together in an electrical connection (200), while the structural layer (112) is preloaded, such that, after the electrical connection step, when a tensile force is exerted by the cable on the electrical connection (200), deformation of the functional layer (114) is limited by the length of the structural layer (112).

Description

Description Title of the invention: Method of forming an electrical connection on a superconducting cable Technical field and technological background

[0001] The present invention relates to a method of forming an electrical connection on a superconducting cable. The invention further relates to a superconducting cable.

[0002] The invention applies typically, but not exclusively, to superconducting cables intended for the transport of electrical energy, in particular to low voltage, or medium voltage (in particular from 6 to 45-60 kV) or high voltage (in particular greater than 60 kV, and possibly up to 400 kV for example) electrical connections, whether in direct or alternating current, in different fields such as those of aerial, underwater, terrestrial electricity transport, or even aeronautics, or rail transport.

[0003] In particular, superconducting cables allow the transport of electrical currents, particularly high intensity ones, with cable sections much smaller than those of conventional transport cables made of resistive electrical conductors, while limiting electrical losses along the cable, in particular losses due to the Joule effect, since this phenomenon is non-existent in the superconducting state.

[0004] A so-called "cold dielectric" superconducting cable generally comprises a cable core comprising a central support of cylindrical shape (generally referred to as "former" in English). Around the central support extends at least one central superconducting part, a dielectric layer surrounding the superconducting part, a screen surrounding said dielectric layer. The superconducting cable further comprises a cryogenic enclosure or cryostat surrounding said cable core. The cryostat typically comprises two concentric envelopes, thermally insulated from each other by a vacuum level, of 10' 5 mbar for example. A cryogenic fluid contained inside the internal casing of the cryostat cools the cable core, in particular through the dielectric layer, hence the designation "cold dielectric", until it reaches a temperature at which the A superconductor is in a state of superconductivity. This temperature is, for example, around -200°C for so-called "high temperature" superconductors. We also know superconducting cables, called "hot dielectric" where the superconducting part is included in a hollow element, generally a tube, in which a cryogenic fluid circulates. The dielectric layer is applied in this case to this tube, which can be thermally insulated, hence the designation "hot dielectric".

[0005] Typically, a connection termination is assembled at the end of the superconducting cable to allow electrical connection with another electrical device, such as another superconducting cable or a resistive cable.

[0006] Patent application publication FR2899389 describes a connection termination comprising a resistive sleeve, for example made of copper, mounted on one end of the cable. The cable is first stripped to expose the superconducting layer and allow an electrical connection of the superconducting layer and the sleeve by soldering. Once the termination is integrated into an electrical connection, it is generally kept stationary, in particular by being fixed to the ground. However, the superconducting cable can exert a force on the termination, generally an axial force along the axis of the cable. This force can be due, among other things, to a contraction of the cable linked to a drop in temperature, or to the weight of the cable suspended at height, or to a pull exerted on the cable from an opposite end.Such an effort can lead to degradation of the electrical connection between the superconducting layer and the sleeve, or even to a tear in the superconducting layer in or near the electrical connection.

[0007] There is therefore a need to mechanically protect the electrical connection between the superconducting layer of a superconducting cable and an electrical connection of the superconducting cable from a force, in particular an axial force, exerted by the cable. Summary of the invention

[0008] For this, the invention proposes a method of forming an electrical connection on a superconducting cable, said cable comprising a cylindrical central support, and around said support central, at least one functional layer having an electrical function and at least one structural layer having a mechanical function, said layers being exposed at a first end of the cable, said method comprising: - a prestressing step comprising the exertion of an outward axial force on the structural layer from the first end of the cable, - an electrical connection step comprising joining the functional layer and the structural layer in an electrical connection at the first end of the cable, while the structural layer is prestressed, such that, after the electrical connection step, when a tensile force is exerted by the cable on the electrical connection, a deformation of the functional layer is limited by the length of the structural layer.

[0009] The functional layer can be a superconducting layer or an electrically insulating layer. By prestressing the structural layer, it is ensured that it supports the majority of the force exerted by the cable on the first end.

[0010] According to one embodiment, the prestressing step comprises: - a contact sub-step comprising the engagement of one end of the structural layer, then - a pulling sub-step comprising an axial pulling of the structural layer outwards from said end of the structural layer.

[0011] According to one embodiment, the end of the structural layer is engaged against a first contact flange, and said axial pull is exerted between the first contact flange and the central support, taking as support one end of the central support included in the first end of the cable.

[0012] According to one embodiment, said central support is axially set back relative to the end of the structural layer. The contact sub-step comprises positioning the first contact flange so that a central surface of the first contact flange axially faces the end of the structural layer and the central support; fixing the end of the structural layer to the central surface of the first contact flange. The pulling sub-step comprises forming a pulling device housed between the central support and the end of the structural layer, said pulling device comprising an axis extending in the extension of the central support and a support plane movable in translation along said axis; the movement of the support plane of the pulling device along the axis of the pulling device until a force is exerted on the central surface of the first contact flange.

[0013] According to one embodiment, the contact sub-step comprises mounting the first contact flange in the form of a crown, such that the central support passes right through said first contact flange; fixing the end of the structural layer to the first contact flange. The pulling sub-step comprises: mounting a pulling flange such that one end of the central support included in the first end of the cable comes against a central shoulder of the pulling flange; and bringing the first contact flange towards the pulling flange to stretch the structural layer.

[0014] According to one embodiment, the contact sub-step comprises: - the mounting, before the first contact flange, of a second contact flange in the form of a crown, so that the central support passes right through said second contact flange, and - wedging the end of the structural layer with surfaces of the first contact flange and the second contact flange to achieve its fixation.

[0015] According to one embodiment, the method comprises a prior step of mounting an electrical connection sleeve on the first end of the cable, said sleeve being intended to be secured to the functional layer and the structural layer, for an electrical connection of the structural layer.

[0016] According to one embodiment, the sleeve is attached to the first contact flange, directly or via the second contact flange.

[0017] The invention further relates to a superconducting cable, said cable comprising a cylindrical central support, and around said central support, at least one functional layer and at least one structural layer, said structural layer having a mechanical function, said layers being exposed at a first end of the cable. An axial force is exerted on the structural layer from the first end of the cable outwards. The functional layer and the structural layer are intended to be secured in an electrical connection at the first end of the cable, while the structural layer is prestressed, such that when a tensile force is exerted by the cable on the first end, a deformation of the functional layer is limited by the length of the structural layer.

[0018] According to one embodiment, the central support is axially set back relative to the end of the structural layer. Said cable further comprises: - a first contact flange, a central surface of said first contact flange coming axially opposite the end of the structural layer and the central support, the end of the structural layer being fixed on the central surface of the first contact flange, - a pulling device housed between the central support and the end of the structural layer, said pulling device comprising an axis extending in the extension of the central support and a support plane movable in translation along said axis, said support plane of the pulling device exerting a force on the central surface of the first contact flange.

[0019] According to one embodiment, the superconducting cable comprises: - a first contact flange in the form of a crown crossed from one side to the other by said central support, the end of the structural layer being fixed to the first contact flange; and - a pulling flange, one end of the central support included in the first end of the cable coming against a central shoulder of the pulling flange, the pulling flange being connected to the first contact flange so as to tension the structural layer.

[0020] According to one embodiment, the superconducting cable comprises a second crown-shaped contact flange traversed from one side to the other by said central support, said second flange being axially positioned upstream of the first flange in a direction going from the inside of the cable towards the first end. The end of the structural layer is wedged with surfaces of the first contact flange and the second contact flange.

[0021] According to one embodiment, the superconducting cable comprises an electrical connection sleeve on the first end of the cable, said sleeve being intended to be secured to the functional layer and the structural layer, for an electrical connection of the structural layer.

[0022] According to a variant, the sleeve is fixed directly to the first contact flange, or is fixed to the first contact flange via the second contact flange integral with the sleeve.

[0023] According to one variant, the sleeve, the functional layer and the structural layer are secured, in particular by brazing. Brief description of the figures

[0024] The following description with reference to the attached drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented. In the attached figures: - figure 1 illustrates a first example according to the invention; - figure 2 illustrates a second example according to the invention; - figure 3 illustrates a third example according to the invention. Detailed description

[0025] Examples of the method according to the invention are illustrated in Figures 1 to 3.

[0026] A first example of the method will be described in relation to Figure 1, in which views a), b), c) d) illustrate steps of the example of the method. The characteristics of the first example which are common with the other examples will be described in the following.

[0027] Like the other exemplary methods, the first exemplary method forms an electrical connection 200 on a superconducting cable 100.

[0028] The superconducting cable 100 comprises a central support 110 of cylindrical shape. For example, the central support 110 is made of an electrically conductive but non-superconductive material, such as steel or copper. In the figures, the central support 110 has corrugations on its surface, but the latter could be different, for example smooth.

[0029] The superconducting cable 100 further comprises at least one functional layer 112 and at least one structural layer 114, which extend in particular around the central support 110.

[0030] The functional layer 112 has an electrical function. For example, the functional layer is a superconducting layer or a layer dielectric configured to provide electrical insulation of the superconducting cable 100.

[0031] The structural layer 112 has a mechanical function. In particular, the structural layer 112 ensures mechanical strength of the cable 100. In particular, it is not a superconducting layer or an electrical insulation layer intended to ensure an electrical function of the cable 100.

[0032] The functional 114 and structural 112 layers are exposed at a first end of the cable 110. For this purpose, the cable 100 may have been stripped of its radially external layers 116, 118 at the first end. Such radially external layers are in particular an internal enclosure 116 and an external enclosure of a cryostat, or other layers.

[0033] The first exemplary method comprises a prestressing step illustrated in views b) and c) of FIG. 1 in which an outward axial force is exerted on the structural layer 112 from the first end of the cable 100. In particular, the axial force is exerted only on the structural layer 112.

[0034] In an electrical connection step illustrated in view d) of FIG. 1, the functional layer 112 and the structural layer 114 are secured in the electrical connection 200, at the first end of the cable. This electrical connection step is carried out while the structural layer 112 is prestressed. Thus, the structural layer 112 is secured while it is subjected to the effect of the axial force described above. The structural layer 112 is therefore fixed in a state of tension. Subsequently, when a tensile force, in particular in the longitudinal direction of the cable, is exerted by the cable 100 on the electrical connection 200, a deformation of the structural layer 114 will be limited by the length of the structural layer 112.

[0035] The method examples therefore make it possible to concentrate on the structural layer 112, the majority or all of the force exerted by the cable 100 on the electrical connection 200. The functional layer 114 is therefore mechanically protected. Degradation of its electrical connection in the electrical connection 200 or tearing at the electrical connection 200 is avoided.

[0036] In particular, the prestressing step comprises a contact sub-step in which an end 112e of the structural layer 112 is engaged. In other words, the end 112e of the structural layer 112 is grasped to be manipulated in the remainder of the method. Then, in a pulling sub-step, the structural layer 112 is pulled axially outward from the end 112e of the structural layer 112.

[0037] More particularly, a first contact flange 151 is used in the contact sub-step. The end of the structural layer 112 is engaged against the first contact flange 151. Then, the axial pulling is exerted between the first contact flange 151 and the central support 110, taking as support an end 110e of the central support 110 included in the first end of the cable.

[0038] In the first example, the prestressing step is implemented differently from that of the other process examples.

[0039] First, as for example illustrated in view a) of FIG. 1, the central support 110 is axially set back relative to the end 112e of the structural layer 112. In other words, the structural layer 112 protrudes from the end 110e of the central support 110, so that a space is created between the end 112e of the structural layer and the end 110e of the central support 110.

[0040] Referring to view b), a pulling device 160 is housed in this space to implement the axial force on the structural layer 112. The pulling device 160 comprises an axis which extends in the extension of the central support 100, in particular from the end 110e of the central support 100. The pulling device 160 further comprises a support plane which is movable in translation along the axis of the pulling device 160.

[0041] The first contact flange 151 is then positioned so that its central surface axially faces the end 112e of the structural layer 122 and the central support 110. The end 112e of the structural layer 112 is then fixed to the central surface of the first contact flange 151, for example by welding or brazing.

[0042] The support plane of the pulling device 160 is then moved along the axis of the pulling device 160 to come into contact with the central surface of the first contact flange 151 and exert a force thereon. The first contact flange 151 is therefore pushed away from the central support 110, which tensions the structural layer 112. The pulling device 160 may take the form of a piston. It may be actuated remotely or through an opening provided in the central surface of the first flange 151, in particular opposite the pulling device 160.

[0043] As in the other method examples, the first method example may comprise a preliminary step of mounting an electrical connection sleeve 170. In particular, the electrical connection sleeve 170 is mounted on a portion of the first end of the cable comprising the central support 110 provided with the functional layer 114 and the structural layer 112. The sleeve 170 may subsequently be secured to the functional layer 114, the structural layer 112 to form the electrical connection 200, as for example illustrated in view d) of FIG. 1. Preferably, the sleeve 170 is formed from a material that can be soldered to ensure an electrical connection. For example, the sleeve 170 is made of copper. In particular, the sleeve 170 is secured to the functional layer 114 and the structural layer 112 by a solder 210. The solder 210 can further contribute to securing the sleeve to the central support 110.

[0044] More particularly, in the first example, the sleeve 170 is an independent part. In particular, the sleeve 170 is fixed directly to the first flange 151. For example, screws 172 come into corresponding openings of the first flange 151 and of the sleeve 170 to secure the sleeve 170 with the first flange 151. This makes it possible in particular to hold the sleeve 170 in place, without effort or mechanical connection with the functional layer 112, until the electrical connection step.

[0045] In the following, the differences of the other process examples from the first example will be described.

[0046] In the second example illustrated in Figure 2 and the third example illustrated in Figure 3, the prestressing step is implemented differently from that of the first process example.

[0047] In the contact sub-step illustrated in view a) in Figure 2 and in views a), b) of Figure 3, the first contact flange 151 is crown-shaped. Once mounted on the first end of the cable, the first contact flange 151 is traversed right through by the central support 110. The end 112e of the structural layer 112 is then fixed on the first contact flange 151.

[0048] In particular, to fix the end 112e of the structural layer 112 on the first contact flange 151, a second contact flange 152 in the form of a crown is mounted on the first end of the cable before the first contact flange 151. Once mounted on the first end of the cable, the second contact flange 152 is crossed right through by the central support 110. The end 112e of the structural layer 112 is then wedged between surfaces of the first contact flange 151 and the second contact flange 152. For this purpose, screws 153 can be used to bring the flanges 151, 152 closer to each other. In particular, the functional layer 114 stops before the second contact flange 152 so as not to be engaged with the structural layer 112.

[0049] More particularly, in the second example method illustrated in FIG. 2, a ring 154 is mounted on the central support 110 to be clamped between the contact flanges 151, 152, the end 112e of the structural layer 112 being wedged at the interface between the first flange 151 and the ring 154 and at the interface between the second flange 152 and the ring 154. In particular, the ring 154, as well as its clamping by the contact flanges 151, 152, are as disclosed in the patent application publication EP 2 424 058 A1.

[0050] More particularly, in the third exemplary method illustrated in FIG. 3, the end 112e of the structural layer 112 is wedged between corresponding surfaces 151s, 152s of the first contact flange 151 and the second contact flange 152. In particular, these surfaces 151s, 152s are profiled to facilitate the insertion of the end 112e of the structural layer 112 between the contact flanges 151, 152.

[0051] In the pulling sub-step of the second example illustrated in Figure 2 and the third example illustrated in Figure 3, a pulling flange 180 is mounted on the first end of the cable. The end 110e of the central support 100 included in the first end of the cable comes against a shoulder 180p located in a central area of ​​the pulling flange 180. The pulling flange 180 then makes it possible to pull the first contact flange 151 by bearing on the end 110e of the central support 100, which causes the structural layer 112 to be pulled outwardly. For example, screws 182 come into corresponding openings of the pulling flange 180 and the first flange 151 to pull the first contact flange 151 towards the pulling flange 180.

[0052] As in the first exemplary method, the second exemplary method illustrated in Figure 2 and the third exemplary method illustrated in Figure 3 may include a prior step of mounting an electrical connection sleeve 170.

[0053] More particularly, in the second and third method examples, the sleeve 170 is integral with the second contact flange 152. This makes it possible in particular to keep the sleeve 170 in place until the electrical connection step, the sleeve 170 being fixed to the first contact flange 151 via the second contact flange 152.

[0054] Preferably, the structural layer 114 and / or the functional layer 112 each form a bundle of strands wound regularly along the central support 110, in particular with a transposition pitch. The strands may be wires or ribbons.

[0055] In the figures, the structural layer 112 is in particular radially internal relative to the functional layer 114. It is in particular comprised between the central support 110 and the functional layer 114. However, the structural layer 112 could be radially external relative to the functional layer 114.

[0056] The structural layer may be a mechanical reinforcement layer specifically added into the superconducting cable 100 for axial pulling as described above.

[0057] The cable and method examples have been described with an electrical connection 200 comprising a sleeve 170. However, the electrical connection 200 could be different, in particular without a sleeve 170. For example, the electrical connection 200 could be made by a single solder deposited on the first end of the cable, and secured to the structural layer 112 and the functional layer 114.

[0058] In particular, a termination is assembled at the end of the superconducting cable 100. The termination comprises an electrical part including, among other things, the electrical connection 200. The termination further comprises a mechanical part ensuring the fixing of the termination, in particular to the ground. In particular, the termination comprises a cryogenic box connected to the cryostat 116, 118 of the cable 100. The termination may also comprise, among other things, other elements of electric field management or inputs of a cooling medium such as nitrogen.

Claims

Claims

1. A method of forming an electrical connection (200) on a superconducting cable (100), said cable (100) comprising a cylindrical central support (110), and around said central support (110), at least one functional layer (114) having an electrical function and at least one structural layer (112) having a mechanical function, said layers being exposed at a first end of the cable, said method comprising: - a prestressing step comprising exerting an outward axial force on the structural layer (112) from the first end of the cable, - an electrical connection step comprising securing the functional layer (114) and the structural layer (112) in an electrical connection (200) at the first end of the cable, while the structural layer (112) is prestressed, so that, after the electrical connection step, when a tensile force is exerted by the cable on the electrical connection (200), a deformation of the functional layer (114) is limited by the length of the structural layer (112).

2. The method of claim 1, wherein the prestressing step comprises: a contacting substep comprising engaging one end (112e) of the structural layer, and then a pulling substep comprising axially pulling the structural layer (112) outwardly from said end (112e) of the structural layer.

3. Method according to claim 2, in which the end (112e) of the structural layer is engaged against a first contact flange (151), and said axial pulling is exerted between the first contact flange (151) and the central support (110), taking as support an end (110e) of the central support (110) included in the first end of the cable.

4. Method according to the preceding claim, said central support (110) being axially set back relative to the end (112e) of the layer structural, process in which the contact sub-step comprises: - positioning the first contact flange (151) so that a central surface of the first contact flange (151) comes axially opposite the end (112e) of the structural layer and the central support (110), - fixing the end (112e) of the structural layer on the central surface of the first contact flange (151), the drawing sub-step comprises: - the formation of a pulling device (160) housed between the central support (110) and the end (112e) of the structural layer, said pulling device (160) comprising an axis extending in the extension of the central support (110) and a support plane movable in translation along said axis, - moving the support plane of the pulling device (160) along the axis of the pulling device (160) until a force is exerted on the central surface of the first contact flange (151).

5. The method of claim 3, wherein the contacting substep comprises: - mounting the first contact flange (151) in the form of a crown, so that the central support (110) passes right through said first contact flange (151), - fixing the end (112e) of the structural layer on the first contact flange (151), the drawing sub-step comprises: - mounting a pull flange (180) so that one end (110e) of the central support included in the first end of the cable comes against a central shoulder (180p) of the pull flange, and - bringing the first contact flange (151) closer to the pulling flange (180) to split the structural layer (112).

6. Method according to the preceding claim, in which the contact sub-step comprises: - the assembly, before the first contact flange (151), of a second crown-shaped contact flange (152), such that the central support (110) passes right through said second contact flange (152), and - wedging the end (112e) of the structural layer with surfaces of the first contact flange (151) and the second contact flange (152) to achieve its fixing.

7. Method according to one of the preceding claims, comprising a prior step of mounting an electrical connection sleeve (170) on the first end of the cable, said sleeve (170) being intended to be secured to the functional layer (114) and the structural layer (112), for an electrical connection of the structural layer (112).

8. Method according to the preceding claim, in which the sleeve (170) is fixed to the first contact flange (151), directly or via the second contact flange (152).

9. Superconducting cable (100), said cable (100) comprising a cylindrical central support (110), and around said central support (110), at least one functional layer (114) and at least one structural layer (112), said structural layer (112) having a mechanical function, said layers being exposed at a first end of the cable, an axial force being exerted on the structural layer (112) from the first end of the cable outwards, the functional layer (114) and the structural layer (112) being intended to be secured in an electrical connection (200) at the first end of the cable, while the structural layer (112) is prestressed, so that, when a tensile force is exerted by the cable on the first end, a deformation of the functional layer (114) is limited by the length of the structural layer (112).

10. A superconducting cable (100) according to the preceding claim, wherein the central support (110) is axially recessed relative to the end (112e) of the structural layer, said cable (100) further comprising: a first contact flange (151), a central surface of said first contact flange (151) axially facing the end (112e) of the structural layer and the central support (110), the end (112e) of the structural layer being fixed on the central surface of the first contact flange (151), a pulling device (160) housed between the central support (110) and the end (112e) of the structural layer, said pulling device (160) comprising an axis extending in the extension of the central support (110) and a support plane movable in translation along said axis, said support plane of the pulling device (160) exerting a force on the central surface of the first contact flange (151).

11. Superconducting cable (100) according to claim 9, comprising: a first contact flange (151) in the form of a crown crossed from one side to the other by said central support (110), the end (112e) of the structural layer being fixed on the first contact flange (151), and a pulling flange (180), one end (110e) of the central support included in the first end of the cable coming against a central shoulder (180p) of the pulling flange, the pulling flange (180) being in connection with the first contact flange (151) so as to tension the structural layer (112).

12. Superconducting cable (100) according to the preceding claim, comprising a second contact flange (152) in the form of a crown crossed from one side to the other by said central support (110), said second flange being axially positioned upstream of the first flange in a direction going from the inside of the cable towards the first end; the end (112e) of the structural layer being wedged with surfaces of the first contact flange (151) and of the second contact flange (152).

13. Superconducting cable (100) according to one of claims 9 to 12, comprising an electrical connection sleeve (170) on the first end of the cable, said sleeve (170) being intended to be secured to the functional layer (114) and the structural layer (112), for an electrical connection of the structural layer (112).

14. Superconducting cable (100) according to the preceding claim, wherein the sleeve (170) is fixed directly to the first contact flange (151), or is fixed to the first contact flange (151) via the second contact flange (152) integral with the sleeve (170).

15. Superconducting cable (100) according to the preceding claim, wherein the sleeve (170), the functional layer (114) and the structural layer (112) are integral, in particular by brazing.

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