WO2017109317A1

WO2017109317A1 - Electrical transformer for remote high voltage devices

Info

Publication number: WO2017109317A1
Application number: PCT/FR2016/053224
Authority: WO
Inventors: Arnaud Allais; Albert PEREIRA; Michel Mermet-Guyennet
Original assignee: Supergrid Institute
Priority date: 2015-12-22
Filing date: 2016-12-06
Publication date: 2017-06-29
Also published as: FR3045925B1; EP3394867B1; JP2019503074A; ES2773516T3; KR20180095074A; PL3394867T3; FR3045925A1; EP3394867A1; CN108463861A

Abstract

The invention relates to an electrical transformer (1) comprising a cable (11) including: a central section (2), an intermediate section (3) and a peripheral section (4), the central section (2) comprising a first winding (21) of a primary circuit and a first winding of a secondary circuit (22), and a first insulation layer (23) between said winding of the primary circuit and said winding of the secondary circuit, the intermediate section (3) surrounding the central section (2) and comprising a magnetic core (31), the peripheral section (4) surrounding the intermediate section (3) and comprising a second winding (41) of the primary circuit and a second winding (42) of the secondary circuit, and a second insulation layer (43) between said winding of the primary circuit and said winding of the secondary circuit; electrical connections (51, 52) between the first and second windings of the primary circuit and between the first and second windings of the secondary circuit.

Description

ELECTRICAL TRANSFORMER FOR REMOTE HIGH VOLTAGE EQUIPMENT

The invention relates to equipment for high voltage networks, in particular the transmission of electrical power between remote equipment of an electrical network, the galvanic isolation between these remote devices and the transformation of the voltage level between these remote devices.

The paper by Mr. Arun Kadavelugu 'High-Frequency Design Considerations of Dual Active Bridge 1200V SiC Mosfet DC-DC converter', published in 201 1 by ΓΙΕΕΕ on pages 314-320, describes a DC / DC converter, in which two bridges in H are galvanically isolated by a coaxial transformer. The coaxial transformer includes two arms, interconnected at their ends and supported by an armature. Each arm includes an internal section provided with several windings of the primary circuit, and an outer section provided with several windings of the secondary circuit. The primary and secondary windings are isolated from each other. A magnetic core is positioned at the periphery of the primary and secondary windings. This magnetic core comprises several spaced sections, to promote the cooling of the transformer. To gain compactness, the magnetic cores of the two arms are intertwined.

If it is desired to connect two remote DC networks or equipment, the converter is connected by its input to a first network, its output being connected to the second network by electric cables.

In practice, such an installation has disadvantages, since the volume occupied by the transformer at one of the two networks is particularly bulky for high voltage applications. The cooling of the transformer induces in particular a not insignificant bulk.

Such a coaxial transformer is then inappropriate. We then choose more conventional transformers, provided with a magnetic core surrounded by primary and secondary windings. The electrical insulation is most often made by a fluid such as gas or oil circulating between the primary and secondary windings. The management of such a fluid presents problems of safety, environment, maintenance and bulk, particularly troublesome when the transformer is placed in a hostile environment, for example in a field of marine wind turbines.

Cooling and electrical isolation of such more conventional transformers is also problematic even for local processing applications. DE4318270 discloses a coaxial electric transformer, comprising a winding of a primary circuit, a magnetic core surrounding the primary circuit winding, and a winding of a secondary circuit surrounding the magnetic core.

US201 1/0291 792 discloses a coaxial transformer where the windings of the primary and secondary circuits are arranged within a magnetic core.

GB2447963 discloses a coaxial electric transformer, comprising a winding of a primary circuit, a magnetic core surrounding the primary circuit winding, and a winding of a secondary circuit surrounding the magnetic core.

The invention aims to solve one or more of these disadvantages.

The invention thus relates to an electrical transformer, as defined in appended claim 1.

The invention also relates to the variants defined in the appended dependent claims. It will be understood by those skilled in the art that each of the features of these variants may be independently combined with the features of claim 1, without necessarily constituting an intermediate generalization.

The invention also relates to an electrical infrastructure as defined in the appended claims.

Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which:

FIG 1 is a schematic representation of an example of implantation of a transformer according to the invention;

FIG. 2 is a schematic cross-sectional view illustrating different sections of a cable of an exemplary transformer according to the invention;

FIG. 3 is a cross-sectional view of a first embodiment of cable for a transformer according to the invention;

FIG 4 is a sectional view along a longitudinal plane of the cable of Figure 3;

FIG 5 is a cross-sectional view of a second embodiment of cable for a transformer according to the invention;

FIG 6 is a sectional view along a longitudinal plane of the cable of Figure 5;

FIG. 7 is a longitudinal sectional view of an example of interconnections at the end of a cable; FIGS. 8 and 9 are diagrammatic representations of an example of wiring between windings of a secondary circuit;

FIG 10 is a cross-sectional view of a variant of the first embodiment of cable for a transformer according to the invention.

The invention provides an electrical transformer in which the windings of the primary circuit and the secondary circuit are housed in a single cable, for example for the connection of two remote devices of a high voltage network. The cable of such a transformer comprises a central section, an intermediate section and a concentric peripheral section. The central section comprises at least one winding of the primary circuit, a winding of the secondary circuit and a galvanic isolation between this winding of the primary circuit and this winding of the secondary circuit. The intermediate section surrounds the central section and has a magnetic core. The peripheral section surrounds the intermediate section and comprises a winding of the primary circuit and a winding of the secondary circuit. The peripheral section also comprises a galvanic isolation between this winding of the primary circuit and this winding of the secondary circuit. These two windings of the primary circuit, included respectively in the central section and in the peripheral section, are electrically connected at an axial end of the cable. These two windings of the secondary circuit, included respectively in the central section and in the peripheral section, are electrically connected at an axial end of the cable.

FIG. 1 illustrates an example of implantation of a transformer 1 according to the invention. The transformer 1 comprises an elongated cable 11 having axial ends 11 1 and 11.2. The cable 11 includes windings of a primary transformer circuit, windings of a secondary transformer circuit, and a core. magnetic, as detailed later. At the end 1 1 1, the cable 1 1 has connection terminals 1 21 and 1 23 forming the terminals of the primary circuit of the transformer 1. At the end 1 1 2, the cable 1 1 has connection terminals 1 22 and 124 forming the terminals of the secondary circuit of the transformer 1.

In this particular example, the transformer 1 is used for the transmission of electrical energy and the transformation of voltage level between two equipment 82 and 84 remote from a high-voltage network. The terminals 1 21 and 1 23 of the primary circuit are connected to an alternating interface of a DC / AC converter 81. The equipment 82 is connected to a continuous interface of the DC / AC converter 81. Terminals 1 22 and 1 24 of the secondary circuit are connected to an alternating interface of a DC / AC converter 83. The equipment 84 is connected to a DC interface of the DC / AC converter 83. Fig. 2 is a schematic cross-sectional view illustrating different sections of a cable 1 1 of an exemplary transformer 1 according to the invention. In this cable 1 1, it is possible to define a central section 2, an intermediate section 3 and a peripheral section 4, the sections 2, 3 and 4 being concentric. The peripheral section 4 surrounds the intermediate section 3, which surrounds the central section 2.

Figure 3 is a cross-sectional view of a first exemplary embodiment of the cable 1 1 of a transformer 1 according to the invention. Figure 4 is a sectional view along a longitudinal plane of the cable January 1.

The central section 2 of the cable 1 1 comprises several windings 21 of the primary circuit of the transformer 1, several windings 22 of the secondary circuit of the transformer 1, and a solid galvanic isolation 23.

The galvanic isolation 23 is in the form of an electrically insulating layer (solid at room temperature) surrounding the windings 21 of the primary circuit. The windings 22 of the secondary circuit are positioned in contact with the outer surface of this insulating layer 23. The windings 21 are distributed radially around the axis of the cable January 1. The different windings 21 are separated and insulated by insulating walls 25 (solid at ambient temperature), extending in a radial direction between these windings 21. The windings 22 are distributed radially around the axis of the cable January 1. The different windings 22 are separated and insulated by insulating walls 26 (solid at room temperature), extending in a radial direction between these windings 22.

The intermediate section 3 surrounds the central section 2. The intermediate section 3 comprises a core or magnetic circuit 31. The magnetic core 31 here surrounds the central section 2. The magnetic core 31 here occupies the entire volume of the intermediate section 3.

The peripheral section 4 of the cable 1 1 comprises several windings

41 of the primary circuit of the transformer 1, several windings 42 of the secondary circuit of the transformer 1, and a solid galvanic isolation 43.

Galvanic isolation 43 is in the form of an electrically insulating layer (solid at room temperature) surrounding the windings.

42 of the secondary circuit. The windings 42 are distributed radially around the axis of the cable January 1. The windings 42 are here in contact with the magnetic core 31. The different windings 42 are separated and isolated by insulating walls 46 (solid at room temperature), extending in a radial direction between these windings 42. The windings 41 of the primary circuit are positioned in contact with the outer surface of this insulating layer 43. The windings 41 are distributed radially around of the cable axis 1 1. The different windings 41 are separated and isolated by insulating walls 45 (solid at room temperature), extending in a radial direction between these windings 41.

Such a transformer 1 has a convection cooling along the entire length of the cable January 1. The length of the cable 1 1 thus promotes the cooling of the transformer 1, which avoids or limits the need to plunge the cable 1 1 in a flow of cooling fluid. Furthermore, the galvanic isolation is here obtained by solid materials, which limits the risk of leakage maintenance constraints for the transformer 1. In addition, the electrical transformation being performed along the length of the cable 1 1 also used for the transmission of energy, the size of the transformer 1 is particularly reduced at the remote equipment to which it is connected.

In this embodiment, it is intended to promote the ease of manufacture of the cable January 1, by arranging the windings of the primary circuit and the windings of the secondary circuit in different layers. In addition, the manufacture of such a cable is facilitated, the galvanic insulation 23 and 43 can easily be made by extrusion or wrapping, by methods known per se. Moreover, this embodiment makes it easy to achieve galvanic insulation of significant thickness between the different windings.

The peripheral section 4 of the cable 1 1 further comprises an insulating wall 48 (solid at ambient temperature) surrounding the windings 41. The peripheral section 4 of the cable 1 1 also advantageously comprises a conductive layer 49 (for example a metal layer forming a screen or electromagnetic shielding) The screen layer 49 surrounds the insulating wall 48.

In the illustrated embodiment, the cable 1 1 advantageously comprises a mechanical reinforcement 29. The mechanical reinforcement advantageously extends over the entire length of the cable 1 1 (or protrude from the cable 1 1, to allow its attachment by its ends). The mechanical reinforcement 29 is advantageously positioned in the center of the central section 2, at the axis of the cable 1 1, in order to undergo less deformation during bending of the cable January 1. The mechanical reinforcement 29 may for example include insulated wire rope, synthetic fiber or fiber reinforced polymer.

In the illustrated embodiment, the insulating walls 25 extend radially between the mechanical reinforcement 29 and the insulating layer 23. In the exemplary illustrated embodiment, the insulating walls 26 extend radially between the insulating layer 23 and the magnetic core 31. In the illustrated exemplary embodiment, the insulating walls 46 extend between the magnetic core 31 and the insulating layer 43. In the exemplary illustrated embodiment, the insulating walls 45 extend between the insulating layer 43 and the insulating layer 43. and the insulating layer 48.

The magnetic core 31 has for example a shape that can be obtained by extrusion or concentric wrapping. The magnetic core 31 may for example be formed from a polymer resin loaded with magnetic powder. The magnetic core 31 may for example also be formed of rolled sheet and coated with an insulator. Such a material may for example be chosen to have a relative magnetic permeability of at least 1 50, preferably at least 200, advantageously 500. According to simulations, the magnetic coupling is at least 0.99 for magnetic permeability. relative to at least 1 50 of the magnetic core 31.

The material used for one of the solid insulators 23, 25, 26, 43, 45 or 46 is for example chosen from the group comprising insulating crosslinked polyethylene, polypropylene, rubber (EPR, HEPR) or silicone.

The material used for the windings 21, 22, 41 or 42 is for example chosen from the group comprising copper and its alloys or aluminum and its alloys.

An example of dimensioning for a cable 1 1 of transformer 1 according to the first embodiment can be as follows. We plan:

the transmission of a power of 10MW by the transformer 1;

a voltage of 10 kV at the terminals of the primary circuit, a voltage of 100 kV at the terminals of the secondary circuit;

a current of 1000 A through the primary circuit, a current of 100 A through the secondary circuit, with a frequency of 20 kHz;

a current density of 1 A / mm ² ;

a magnetic induction of 0.2T.

As a reminder, the sinusoidal voltage V across a wound coil is calculated by the Boucherot formula:

With N: the number of turns of the winding, B: magnetic induction,

S: the section of the magnetic circuit,

F: the operating frequency. The material chosen for the windings 21, 22, 41 and 42 is copper.

The material chosen for the screen layer 49 is aluminum.

The material used for the solid insulators 23, 26, 43 and 46 is crosslinked polyethylene.

The number of windings of the primary circuit in the central section 2 (and in the peripheral section 4) is 1. The number of windings of the secondary circuit in the central section 2 (and in the peripheral section 4) is 1 0.

An air passage (not shown in Figure 3) is provided in the center of the central section 2 instead of the mechanical reinforcement 29 and has a radius of 1 0 mm. The thickness of the winding 21 is 1 0.5 mm. The thickness of the insulating layer 23 is 5 mm. The thickness of the windings 22 is 5.6 mm. The width of the insulating walls 26 is at least 1 mm, preferably at least 2 mm. The thickness of the magnetic core 31 is 10 mm. The thickness of the windings 42 is 3.7 mm. The thickness of the insulating layer 43 is 5 mm. The thickness of the winding 41 is 3.1 mm. The thickness of the insulating layer 48 is 5 mm. The thickness of the screen layer 49 is 2.75 mm. The cable 1 1 has a length of 62.5 m.

The winding pitch of the windings 21 and 41 (here identical to the pitch for the windings 22 and 42) is for example between 5 and 30 times the diameter of the cable January 1.

In the examples previously illustrated, the terminals 1 21 and 1 23 on the one hand and 1 22 and 1 24 on the other hand, are disposed at opposite ends of the cable January 1. However, the transformer 1 can also be used for local application, with terminals 121 to 24 positioned at the same end of the cable 11. Such a transformer 1 also makes it possible to benefit from the cooling over the length of the cable and the insulating capacity of the solid galvanic insulation.

An exemplary structure for the end of a cable January 1, with terminals at the same end, is illustrated in a longitudinal sectional view in Figure 7. This illustration aims to represent interconnections between windings of the primary circuit of the central section 2 and the peripheral section 4, or between windings of the secondary circuit of the central section 2 and the peripheral section 4. A tip 5 is thus attached to one end of the cable January 1. The tip 5 may include connection terminals of the primary or secondary, not shown here. The tip 5 comprises an electrical connector 52, electrically connecting a winding 42 of the peripheral section to a winding 22 of the central section 2. The electrical connector 52 is for example fixed by welding to its respective windings 22 and 42.

The electrical connector 52 is covered at its periphery by an insulator 53. The insulator 53 is disposed in the continuity of the insulating layers 23 and 43 and covers the axial end of the electrical connector 52. The insulator 53 envelopes the electrical connector 52 .

The tip 5 also comprises an electrical connector 51, electrically connecting a winding 41 of the peripheral section to a winding

21 of the central section 2. The electrical connector 51 is for example fixed by welding to its respective windings 21 and 41. The electrical connector 51 is covered at its periphery by an insulator 54. The insulator 54 is disposed in the continuity of the insulating layer 48 and covers the axial end of the electrical connector 51.

The mechanical reinforcement 29 here extends axially through the end piece 5 and beyond.

In order to limit the electric field applied to the different insulating walls 26 and 46, FIGS. 8 and 9 illustrate an example of interconnection for the windings 22 and 42 of a secondary circuit according to the numerical application detailed above (FIG. windings of the secondary circuit in each of sections 2 and 4). Figures 8 and 9 illustrate the interconnections at respective opposite ends of the cable January 1. The interconnections illustrated here make it possible to limit the potential difference between adjacent windings 22, or between adjacent windings 42. The interconnections are here schematically illustrated in dashed lines. In FIG. 9, only the terminations of the interconnections have been illustrated for the sake of readability. The windings 22 and 42 are numbered with an index n, windings

22 and 42 of index n being positioned radially opposite. The windings 22, identified by their index n (and by analogy the windings 42), are positioned radially in the following order: 1 -2-4-6-8-10-9-7-5-3. The interconnections between the windings are as follows:

the windings 22 and 42 of index 1 are electrically connected by the interconnection 521;

the windings 22 of index 1 and 42 of index 2 are electrically connected by the interconnection 61 2; the windings 22 and 42 of index 2 are electrically connected by the interconnection 522;

the windings 22 of index 2 and 42 of index 3 are electrically connected by the interconnection 623;

the windings 22 and 42 of index 3 are electrically connected by the interconnection 523;

the windings 22 of index 3 and 42 of index 4 are electrically connected by the interconnection 634;

the windings 22 and 42 of index 4 are electrically connected by the interconnection 524;

the windings 22 of index 4 and 42 of index 5 are electrically connected by the interconnection 645;

the windings 22 and 42 of index 5 are electrically connected by the interconnection 525;

the windings 22 of index 5 and 42 of index 6 are electrically connected by the interconnection 656;

the windings 22 and 42 of index 6 are electrically connected by the interconnection 526;

the windings 22 of index 6 and 42 of index 7 are electrically connected by the interconnection 667;

the windings 22 and 42 of index 7 are electrically connected by the interconnection 527;

the windings 22 of index 7 and 42 of index 8 are electrically connected by the interconnection 678;

the windings 22 and 42 of index 8 are electrically connected by the interconnection 528;

the windings 22 of index 8 and 42 of index 9 are electrically connected by the interconnection 689;

the windings 22 and 42 of index 9 are electrically connected by the interconnection 529;

the windings 22 of index 9 and 42 of index 10 are electrically connected by the interconnection 690;

the windings 22 and 42 of index 10 are electrically connected by the interconnection 520.

In the case where the primary circuit comprises several windings in the central section 2 and in the peripheral section 4, a similar interconnection mode can be used for the windings 21 and 41 in order to limit the electric field applied to the insulating walls 25 and 45. Another example of dimensioning for a cable 1 1 of transformer 1 according to the first embodiment may be the following. We plan:

the transmission of a power of 1 MW by the transformer 1;

a voltage of 5 kV across the primary circuit, a voltage of 5 kV across the secondary circuit;

a current of 200 A through the primary circuit, a current of 200 A through the secondary circuit, with a frequency of 5 kHz;

a current density of 1 A / mm ² ;

a magnetic field of 0.2T.

The material chosen for the windings 21, 22, 41 and 42 is copper. The material chosen for the screen layer 49 is aluminum.

The material used for the solid insulators 23 and 43 is cross-linked polyethylene.

The number of windings of the primary circuit in the central section 2 (and in the peripheral section 4) is 1. The number of windings of the secondary circuit in the central section 2 (and in the peripheral section 4) is 1.

An air passage (not shown in Figure 3) is provided in the center of the central section 2 instead of the mechanical reinforcement 29 and has a radius of 1 0 mm. The thickness of the winding 21 is 2.8 mm. The thickness of the insulating layer 23 is 5 mm. The thickness of the winding 22 is 1.7 mm. The thickness of the magnetic core 31 is 10 mm. The thickness of the winding 42 is 1.1 mm. The thickness of the insulating layer 43 is 5 mm. The thickness of the winding 41 is 0.9 mm. The thickness of the insulating layer 48 is 5 mm. The thickness of the screen layer 49 is 2.75 mm. The cable 1 1 has a length of 125 m.

Figure 5 is a cross-sectional view of a second exemplary embodiment of the cable 1 1 of a transformer 1 according to the invention. Figure 6 is a sectional view along a longitudinal plane of the cable January 1.

The central section 2 of the cable 1 1 comprises several windings 21 of the primary circuit of the transformer 1, several windings 22 of the secondary circuit of the transformer 1. The central section 2 here comprises an alternation of windings distributed around the axis of the cable January 1. The number of windings 22 here is twice the number of windings 21. The cable 1 1 further comprises a galvanic isolation in the form of insulating elements 27 (solid at room temperature). The insulating elements 27 are distributed radially around the axis of the cable January 1. The insulating elements 27 separate two adjacent windings from the central section 2. The insulating elements 27 here form insulating walls extending in a radial direction between two adjacent windings 21 or 22.

The peripheral section 4 of the cable 1 1 comprises several windings 41 of the primary circuit of the transformer 1 and several windings 42 of the secondary circuit of the transformer 1. The peripheral section 4 here comprises an alternation of windings distributed around the axis of the cable January 1. The number of windings 42 here is twice the number of windings 41.

The cable 1 1 further comprises a galvanic isolation in the form of insulating elements 47 (solid at room temperature). The insulating elements 47 are distributed radially around the axis of the cable January 1. The insulating elements 47 separate two adjacent windings from the peripheral section 4. The insulating elements 47 form here insulating walls extending in a radial direction between two adjacent windings 41 or 42.

The windings 41 of the primary circuit and the windings 42 of the secondary circuit are positioned in contact with the outer surface of the magnetic core 31.

The peripheral section 4 of the cable 1 1 further comprises an insulating wall 48 (solid at ambient temperature) surrounding the windings 41 and 42. The peripheral section 4 of the cable 1 1 also advantageously comprises a conductive layer 49 (for example a metallic layer forming a screen or electromagnetic shielding The screen layer 49 surrounds the insulating wall 48.

In the illustrated embodiment, the cable 1 1 advantageously comprises a mechanical reinforcement 29. The mechanical reinforcement advantageously extends over the entire length of the cable 1 1 (or protrude from the cable 1 1, to allow its attachment by its ends). The mechanical reinforcement 29 is advantageously positioned in the center of the central section 2, at the axis of the cable 1 1, in order to undergo less deformation during bending of the cable January 1. The mechanical reinforcement 29 may have the same composition as for the first exemplary embodiment.

In the illustrated embodiment, the insulating walls 27 extend radially between the mechanical reinforcement 29 and the magnetic core 31. In In the exemplary embodiment illustrated, the insulating walls 47 extend between the magnetic core 31 and the insulating layer 48.

The various embodiments of the cable 1 1 of a transformer 1 according to the invention have been illustrated described with a cable 1 1 having a rectilinear axis, for the sake of simplification. However, such a cable 1 1 will be flexible in most configurations. The axis of the cable 1 1 may thus be curvilinear, for example when the cable 1 1 is wound in a coil or when the middle portion of the cable 1 1 has deformations by bending.

In the different embodiments described, the primary circuit and the secondary circuit of the transformer 1 each include several windings in the central section 2, and several windings in the peripheral section 4. However, it is also possible to envisage that the primary circuit and / or the Secondary circuit of the transformer 1 includes a single winding in the central section 2 and a single winding in the peripheral section 4.

To promote the cooling of the cable 1 1 and serve for power transmission between remote network equipment, the length of the cable 1 1 is advantageously at least 100 times greater than its outer diameter.

In the illustrated examples, the transformer 1 is used for power transmission between remote high voltage equipment. The distance between the high voltage equipment may be greater than the length of the cable 1 1. In such a case, it is possible to connect a power transmission cable to the terminals of the primary circuit and / or to the terminals of the secondary circuit to adapt to the distance separating these high voltage equipment.

Figure 10 is a cross-sectional view of a variant of the first exemplary embodiment of the cable 1 1 of a transformer 1 according to the invention. The cable 1 1 differs from that of FIG.

-the presence of a galvanic isolation 91 surrounding the central section 2. The galvanic isolation 91 advantageously isolates the windings 22 relative to the magnetic core 31;

by the presence of a galvanic isolation 92 surrounding the intermediate section 3. The galvanic isolation 92 advantageously isolates the windings 42 from the magnetic core 31.

Claims

Electrical transformer (1), comprising a cable (1 1) having first and second axial ends (1 1 1, 1 12), characterized in that the cable comprises:

-a central section (2), an intermediate section (3) and a concentric peripheral section (4);

-the central section

(2) comprising at least one first winding (21) of a primary circuit and at least one first winding of a secondary circuit (22), and at least one first solid galvanic insulation (23) between said first winding of the primary circuit and said first winding of the secondary circuit;

-the intermediate section

(3) surrounding the central section (2) and comprising a magnetic core (31);

-the peripheral section

(4) surrounding the intermediate section (3) and comprising at least one second winding (41) of the primary circuit and at least one second winding (42) of the secondary circuit, and at least one second solid galvanic insulation (43) between said second winding of the primary circuit and said second winding of the secondary circuit;

-an electrical connection (51) to one of said axial ends of the cable between the first and second windings of the primary circuit;

-an electrical connection (52) to one of said axial ends of the cable between the first and second windings of the secondary circuit.

Electrical transformer (1) according to claim 1, comprising two connection terminals (121, 123) to the primary circuit arranged at the first end (1 1 1) of the cable (1 1), and comprising two connection terminals (122 , 123) to the secondary circuit arranged at the second end (1 12) of the cable (1 1).

Electrical transformer (1) according to claim 1 or 2, in which the central section (2) comprises a mechanical reinforcement (29) extending over the entire length of the cable (1 1), said mechanical reinforcement (29) being positioned at the level of the center of the central section.

Electrical transformer (1) according to any one of the preceding claims, in which the central section (2) comprises an insulating layer (23) surrounding several windings of one of the primary circuit and the secondary circuit, the other of the primary circuit and the secondary circuit comprising several windings in contact with the external surface of the insulating layer (23).

5. Electrical transformer (1) according to claim 4, wherein said windings (22) in contact with the external surface of the insulating layer (23) are separated from each other by insulating walls (26) having a width at least equal to 1 mm.

6. Electrical transformer (1) according to any one of claims 1 to 3, in which the central section (2) comprises an alternation of windings of the primary circuit and windings of the secondary circuit distributed radially around the axis of the cable, the first galvanic insulation comprising insulating elements (27) distributed radially around the axis of the cable and separating the windings of this alternation.

7. Electrical transformer (1) according to any one of the preceding claims, wherein said first galvanic insulation comprises a material chosen from the group including polypropylene, or crosslinked polyethylene.

8. Electrical transformer (1) according to any one of the preceding claims, in which the magnetic core (31) comprises a material chosen from the group including the material sold under the reference Vitroperm 500F nanocrystalline, or the material sold under the reference Molypermalloy Powder Core.

9. Electrical transformer (1) according to claim 8, wherein the magnetic core (31) extends continuously over the entire length of the cable (1 1).

1 0. Electrical transformer (1) according to any one of the preceding claims, wherein the cable (1 1) has a length at least 100 times greater than its diameter.

1 1 . Electrical transformer (1) according to any one of the preceding claims, wherein said first galvanic insulation has a thickness of at least 2mm.

1 2. Electrical transformer (1) according to any one of the preceding claims, wherein said windings of the primary circuit are wound with an axial pitch of between 5 and 30 times the diameter of the cable of circular section.

1 3. Electrical infrastructure, comprising:

-a transformer according to claim 2; -a first electrical equipment (81) connected to the connection terminals (121,

123) to the primary circuit at the first end of the cable (1 1);

-a second electrical equipment (83) connected to the connection terminals (122,

124) to the secondary circuit at the second end of the cable (1 1), the first or second electrical equipment applying a voltage at least equal to 1 kV between the connection terminals to which it is connected.