EP0430755B1 - High voltage unit for X-ray tube with a secondary circuit integrated cooling tank - Google Patents

Description

The invention relates to electrical devices which are used to power X-ray tubes and, more particularly in such devices, means for supporting and cooling the various elements of electrical circuits.

An X-ray tube includes a filament type cathode which emits an electron beam towards an anode or anti-cathode. The anode is made of a material such as tungsten or molybdenum which emits X-rays when it is bombarded by the electron beam from the cathode. To obtain a high energy electron beam, the electrons are accelerated by an intense electric field created between the cathode and the anode. To this end, the anode is brought to a positive potential of several tens of kilovolts relative to the cathode, this potential being able to exceed one hundred kilovolts and reach one hundred and forty kilovolts.

Such voltages are supplied by so-called high voltage power supply devices which include, as shown in FIG. 1, a transformer 10 which is connected to voltage rectifier-doubler circuits 11. More specifically, the transformer 10 comprises a single winding primary 12 to which an alternating voltage is applied and a secondary circuit 13 which is connected to the rectifier-doubling circuits 11. Each rectifier-doubling circuit 11 consists, in a conventional manner, in a secondary winding 14, two diodes D1 and D2 and two capacitors C1 and C2 which are connected together according to the diagram in Figure 1. Each voltage rectifier-doubler circuit is connected to the next one so that their output voltages add up, which makes it possible to obtain a very high voltage on the last doubler circuit of the assembly .

More specifically, the transformer comprises a primary winding 12 and twelve secondary windings S1 to S12 which have been shown as the windings S1, S5, S6 and S12. Likewise, it comprises twenty-four identical rectifying diodes D1 to D24 of which it has been shown that the elements D1, D2, D3 ... D12, D13, D14 ... D22, D23, D24.

It also includes twenty-four filter capacitors C1 to C24 of which the elements C1, C2, C3 ... C12, C13, C14 ... C23, C24 have been shown.

Each secondary winding S1 to S12 has two output terminals. All the output terminals bear the references B1 to B24, only the terminals B1, B2, B3 ... B5, B6, B7, B8 ... B23, B24 having been represented.

In FIG. 1, the common point of the capacitor C1 and the diode D1 constitutes the high voltage output terminal HT through a resistor R while the common point of the capacitor C24 and the diode D24 constitutes the ground output terminal with which a spark gap 9 is associated.

To measure the amplitude of the high voltage, the HT output terminal is connected to a measuring device (not shown) connected to point M via a resistor R ′ and a variable capacitor C ′. The point M is connected to earth by a spark gap 9 ′.

In a typical embodiment, each rectifier-doubler circuit has an output voltage of six kilovolts so that at the output of the twelfth rectifier-doubler circuit, the voltage is seventy-two kilovolts.

It will be noted that to obtain a potential difference of the order of 140 kilovolts between the cathode and the anode of an X-ray tube, it suffices to connect the cathode to a negative potential of 70 kilovolts relative to the mass and the anode has a positive potential of 70 kilovolts relative to the mass. For this purpose, two supply devices identical to that of FIG. 1 are used.

It is understood that the production of a high-voltage supply device according to the diagram in FIG. 1 leads to insulation problems which are often resolved by separating from each other the conductors with very different potentials and by interposing between them a insulating medium such as oil which also serves as a coolant. This then leads to large devices which are bulky.

In addition, X-ray tubes are used more and more in impulse mode according to increasingly higher repetition frequencies. In the circuit of FIG. 1, this means that the primary winding is supplied by an alternating voltage of high frequency, of the order of several tens of kilohertz. In these new operating conditions, the performance of the circuit of FIG. 1 is limited by the parasitic capacities and inductors of the conductors and the windings of the transformer, the values of which are difficult to know and to compensate for.

The document US Pat. No. 3,541,424 describes a high voltage supply device for an X-ray tube, comprising a volume comprising a transformer which comprises at least one primary winding, a plurality of secondary windings and a magnetic circuit, the two output terminals of each of said secondary windings being connected to a voltage rectifier-doubler circuit which consists of two diodes and two filter capacitors, said rectifier-doubler circuits being connected together so that their output voltages add up, and a closed enclosure enclosing said volume in an insulating and refrigerating medium.

In patent application EP-A-0 381 580, which belongs to the state of the art defined in paragraph 54 (3) EPC and which is entitled: "SUPPLY DEVICE HIGH VOLTAGE FOR X-RAY TUBE ", the Applicant has described a supply device in which the relative positions of the various elements tend to minimize the parasitic capacities and inductors and contribute to reducing the overall size while presenting a large ease of assembly.

In addition, by producing the secondary circuit in the form of concentric windings, only the parasitic capacitance between the first secondary winding and the mass has an influence because the other parasitic capacitances between the secondary windings between them do not intervene because they are at an alternating voltage.

In order to limit the lengths of the connection conductors which connect the output terminals B1 to B24 of the secondary windings S1 to S12, on the one hand, to the diodes D1 to D24 and, on the other hand, to the capacitors C1 to C24, the The invention described in the aforementioned patent application first provides for making secondary windings whose similar output terminals of odd rank B1, B3 ... B23, are arranged on a first lateral side of the windings while the output terminals of even rank B2, B4 ... B24 are arranged on the other or second lateral side of the secondary windings.

It is then planned to group the diodes D1 to D24 on the same support which is arranged on the side of the output terminals B1, B3 ... B23 of the secondary windings. It is also planned to place the capacitors C1 to C24 on the external periphery of the secondary windings and to make their connections, on the one hand, to the diodes D1 to D24 on the first lateral side of the secondary windings and, on the other hand, at the output terminals B2, B4 ... B24 on the second side side of the secondary windings.

This particular arrangement of the various elements will be better understood with the aid of the description of FIGS. 2 and 3 in which the elements identical to those of FIG. 1 have the same references.

The device comprises two half-shells 20 and 21 in which are provided housings for placing the primary winding 12, the secondary windings S1 to S12, the capacitors C1 to C24 and the diodes D1 to D24. To this end, each half-shell 20 (or 21) comprises three annular compartments 22, 23 and 24 (or 26, 27, 28) around a cylindrical central part 25 (or 29).

The first annular compartment 22 (or 26) is at the periphery of the central part 25 (or 29) while the second annular compartment 23 (or 27) is at the external periphery of the first compartment 22 (or 26). The third compartment 24 (or 29) is arranged laterally with respect to the first two 22 and 23 (or 26 and 27) and is separated from it by partitions 30 and 31 respectively (or 32 and 33) pierced with orifices.

The central parts 25 and 29 are provided for housing, in particular, the primary winding 12 and a branch 34 of the magnetic circuit 35 of the transformer 10. The first annular compartments 22 and 26 are provided for housing the secondary windings 13 which are wound so concentric on a mandrel 36. The external periphery of the mandrel 36 is closed by a cover constituted by a cylindrical ring 37. The mandrel 36 and its cover 37 fit into compartments 22 and 26. The second annular compartments 23 and 27 comprise twenty-four cells A1, A2, A3 ... A14, A15, A16..A24 which are designed to house the twenty-four capacitors C1 respectively to C24.

The third compartment 24 of the half-shell 20 is provided for housing the diodes D1 to D24 and making their connections to one another, with the capacitors C1 to C24 and to certain output terminals of the secondary windings S1 to S12. This arrangement will be described below in relation to FIG. 4.

The third compartment 28 of the half-shell 21 is provided for making the various connections between certain output terminals of the secondary windings S1 to S12 and the capacitors C1 to C24 as will be described below in relation to FIG. 5.

Each annular compartment 24 or 28 is closed respectively by an annular cover 40 or 41 which comes to fit on the outer periphery of the associated compartment.

So that the magnetic circuit 35 is disposed near the secondary windings, each half-shell 20 (or 21) has its periphery interrupted by a notch 42 (or 43) and it is the same for each cover 40 (or 41). Such a notch allows the passage of a branch of said magnetic circuit.

As shown in FIG. 4, the diodes D1 to D24 are arranged on a printed circuit in the form of an annular wafer sector which makes their connections with one another, with one end of the capacitors C1 to C24 and with the output terminals B1, B3. ..B23 in accordance with the electric diagram of FIG. 1. Thus, by way of example, the diode D1 has its cathode which is connected to the terminal B1 of the winding S1 and its anode which is connected to a of the ends of the capacitor C1. Furthermore, terminal B1 is connected to the anode of diode D2, the cathode of which is connected, on the one hand, to the anode of diode D3 and, on the other hand, at one end of the capacitors C2 and C3, and to the latter by a printed conductor CI1. It will be noted that the other printed conductors CI2 to CI11 connect the other common points of the diodes equivalent to D2, D3 to the capacitors equivalent to C3.

Figure 5 is a top view, cover 41 partially broken away, on the other side of the secondary windings. In this figure, it has been shown that the connection conductors CC5 to CC10 between the terminals B6, B8, and B10 and the associated capacitors (C5, C6), (C7, C8) and (C9, C10). Of course, these conductors CC5 to CC10 can be produced in the form of conductors of a printed circuit analogous to the printed circuit 38 carrying the diodes or in the form of bars.

FIG. 5 also shows three of the four branches of the magnetic circuit 35, one of which is disposed in the notch 43.

The various elements which have just been described in relation to FIGS. 1 to 5 are assembled by interlocking into each other and held together with each other by assembly elements so as to obtain the assembly shown in partial section. in FIG. 6. The assembly elements, not shown in FIGS. 1 to 5, consist of threaded tie rods and nuts and plates for supporting and holding the various branches of the magnetic circuit 35.

Thus the elements of Figure 2 are held by two threaded tie rods and nuts such as those referenced 50, 51 and 52 (Figure 6), the tie rods being housed in holes 53 and 54 (Figure 5) passing through the elements of Figure 2 right through along an axis parallel to the x′x axis.

Furthermore, to support and maintain the magnetic circuit 35, there are provided plates 55 and 56 (FIG. 6) these plates being held respectively against the covers 41 and 40 by threaded tie rods and nuts such as those bearing the references 57, 58 and 59 in FIGS. 2 and 6. These plates 55 and 56 are provided to each house and hold a branch of the magnetic circuit. Thus, the plate 55 supports the branch 60 of the U-shaped part while the plate 56 supports the branch 46 of the magnetic circuit which closes the opening of the U.

The device of FIG. 6 is placed in an enclosure 61 (FIG. 7) filled with an insulating cooling fluid. For this purpose, it is mounted on a support plate 62 which constitutes the cover of the enclosure 61. The mounting on the support plate 62 is carried out by means of two feet 63 and 64 which cooperate with the plates holding 55 and 56 by fitting into housings (not shown) provided inside. These feet 63 and 64 are pierced with holes, such as that referenced 65, for the passage of screws (not shown) which are screwed into a thread in the cover 62.

The cover 62 also supports an insulating pad 66 which supports the high voltage output terminal of the supply device. The other electrical terminals of the supply device have not been shown in this figure 7.

Despite the significant reduction in the size of the supply device, the enclosure 61 must be large enough to contain a large volume of coolant, approximately 15 to 20 liters, which volume leads to a high-voltage block assembly. quite bulky.

The object of the present invention is therefore to produce a supply device for an X-ray tube of the type described in the aforementioned patent application, in which the enclosure containing the coolant is of reduced dimensions so as to obtain an assembly more compact and lighter.

The subject of the invention is a high-voltage supply device for an X-ray tube as defined in claim 1.

This closed enclosure is produced using two half-shells which have cells to set up and maintain the various elements of the secondary circuit as well as other elements which are connected to high voltages such as the transformer (s) of the supply circuit for the cathode filament (s).

Each half-shell has opposite two tunnels which pass right through them and which serve as support, on the inside of the enclosure, for the secondary windings and, on the outside of the enclosure, for the primary winding and magnetic circuit.

• la figure 1 est un schéma électrique classique d'un dispositif d'alimentation haute tension pour tube à rayons X.
• la figure 2 est une vue en coupe éclatée d'une partie du dispositif d'alimentation selon l'art intérieur suivant un axe longitudinal x′x passant par l'axe de symétrie des bobines des enroulements du transformateur.
• la figure 3 est une vue éclatée en perspective cavalière d'une partie des éléments constituant le dispositif d'alimentation selon l'art antérieur.
• la figure 4 est une vue de dessus de l'élément sur lequel sont disposées et connectées électriquement les diodes du circuit de la figure 1,
• la figure 5 est une vue de dessus, en partie arrachée, montrant notamment les alvéoles de rangement des condensateurs de la figure 1,
• la figure 6 est une vue en coupe de l'ensemble du dispositif d'alimentation selon l'art antérieur suivant l'axe x′x et passant par le circuit magnétique du transformateur,
• la figure 7 est une vue en perspective, en partie arrachée, du dispositif d'alimentation selon l'art antérieur tel qu'il est placé dans un compartiment rempli de liquide isolant et réfrigérant.
• la figure 8 est une vue éclatée en perspective cavalière du bloc haute tension pour tube à rayons X selon l'invention.

Other characteristics and advantages of the present invention will appear on reading the following description of a particular embodiment, said description being made in relation to the accompanying drawings in which:

• FIG. 1 is a conventional electrical diagram of a high voltage supply device for an X-ray tube.
• Figure 2 is an exploded sectional view of a portion of the supply device according to the interior art along a longitudinal axis x′x passing through the axis of symmetry of the coils of the transformer windings.
• Figure 3 is an exploded perspective view of a portion of the elements constituting the supply device according to the prior art.
• Figure 4 is a top view of the element on which are arranged and electrically connected the diodes of the circuit of FIG. 1,
• FIG. 5 is a top view, partially broken away, showing in particular the storage cells of the capacitors of FIG. 1,
• FIG. 6 is a sectional view of the entire supply device according to the prior art along the axis x′x and passing through the magnetic circuit of the transformer,
• Figure 7 is a perspective view, partially broken away, of the supply device according to the prior art as it is placed in a compartment filled with insulating and cooling liquid.
• Figure 8 is an exploded perspective view of the high voltage block for X-ray tube according to the invention.

FIGS. 1 to 7, which have been used in the preamble to describe a high voltage supply device for x-ray tubes according to the prior art, will not be described again, but they nevertheless form an integral part of the description of the invention. The invention, with the exception of FIG. 7, with regard to the particular arrangement of the electrical and magnetic elements and of the transformer voltage doubler circuits. Thus the elements of Figure 8 identical or similar to those of Figures 1 to 6 have the same references. However, it should be noted that the two half-shells 20 and 21 of the embodiment of Figures 2 to 6 have been combined into a single shell which has been referenced (20, 21) in Figure 8.

The invention is based on the observation that the energy dissipated in a feeder for an X-ray tube is due for about a first third to the primary circuit, about a second third to the circuit secondary and about a third to the magnetic circuit but that the insulation problems due to high voltage only exist for the elements of the secondary circuit. For this reason, it is necessary to use a cooling medium which is also a very good insulator, a quality which is not required to isolate the elements of the primary and magnetic circuits which can therefore remain in the open air.

Also the invention relates to a feed device for an X-ray tube in which only the elements of the secondary circuit are arranged in a tank 80 filled with a cooling and insulating medium, the tank being shaped to serve as a support inside. elements of the secondary circuit and outside the support of the elements of the primary and magnetic circuits.

As shown in FIG. 8, the tank 80 comprises two half-shell parts 81 and 81 ′ which are assembled together using tie rods (not shown) passing through holes, such as those referenced 82 and 82 ′, drilled respectively in the thickness of the half-shells 81 and 81 ′. A seal, not shown, is provided to seal the tank after assembly of the two half-shells. The interior of each half-shell 81 and 81 ′ is shaped in substantially the same way to serve as a mounting support for a certain number of elements, in particular those of the secondary circuit. Thus, each half-shell 81 or 81 ′ has a bottom wall 83 or 83 ′ and side walls 84 or 84 ′, 85 or 85 ′, 86 or 86 ′, 87 or 87 ′. Each bottom wall 83 or 83 ′ is pierced, substantially in the middle, with a hole 88 or 88 ′, to produce a tunnel 89 or 89 ′ which passes through each half-shell 81 or 81 ′. Circular ends inside the tunnels 89, 89 ′ abut one on the other during the assembly of the two half-shells by means of a seal not shown.

Each half-shell has a notch 90 or 90 ′ in the shape of a letter L, the vertical arm of which is located on the bottom wall 83 or 83 ′ while the horizontal arm is situated on the side wall of 87 or 87 ′. The vertical arm has a depth less than that of the thickness of the half-shell and the horizontal arm has a depth less than the distance from the tunnel to the side wall 87 or 87 ′.

The internal volume of each half-shell has cells to allow the establishment and maintenance of the elements of the secondary circuit as well as other elements. Thus a first cell 91 or 91 ′ is provided around the tunnel 89 or 89 ′ for the support and the maintenance of the secondary windings 13 and of the shell (20, 21) containing the capacitors, the diodes and the circuits of connection between these different elements carried by printed circuits in the shape of a horseshoe such as the shell (20, 21). A second cell 92, arranged in the half-shell 81 and a third cell 92 ′, arranged in the half-shell 81 ′, are used to set up, respectively, the high-voltage connectors 93 and 93 ′. These connectors 93 and 93 ′ are each produced in a conventional manner, by a sleeve, one closed end of which carries the connection pads located in the cell near the output terminal of the secondary winding, and the open end of which serves to passage of the output conductors via a male connector not shown in FIG. 8. The sleeve is hermetically sealed in a orifice in the side wall 85 or 85 ′ using a gasket 94 or 94 ′ and a plate 95 or 95 ′ screwed to the side wall.

A fourth cell 96, arranged in the shell 81, allows the establishment of a vase 97 filled with air to absorb the expansions of the insulating and cooling medium. The interior of this expansion vessel communicates with the exterior of the tank by a conduit 98. A fifth cell 96 ′, disposed in the half-shell 81 ′, allows the installation of an electrical circuit 99 for measuring voltage.

This electrical circuit 99 consists, as indicated in relation to the description of FIG. 1, of a resistor R ′ and of a variable capacitor C ′ in parallel and of a spark gap 9 ′.

A sixth cell 100 in the half-shell 81 and a seventh cell 100 ′ in the half-shell 81 ′ are provided for positioning and maintaining the transformers 101 and 101 ′ of the filament supply circuits of the cathode of the tube, respectively. X-ray.

The different cells which have just been described are separated by walls, such as that referenced 102, whose shapes match those of the elements which they must maintain. These walls are pierced with orifices such as that referenced 103 ′ in the wall 102 ′ to allow the flow of coolant.

For the filling of the tank 80 formed of the two half-shells 81 and 81 ′, by the cooling and insulating medium, two orifices 104 and 104 ′ are provided, drilled respectively in the side walls 85 and 85 ′ and provided with plugs 105 and 105 ′.

Other entry orifices can also be provided and outlet in the case where a circulation of the coolant is provided.

After mounting and wiring the various elements of the secondary circuit in the half-shells 81 and 81 ′, the latter are assembled to one another so as to produce a sealed tank on which the various elements of the primary circuit and the magnetic circuit.

Thus the primary winding 12 is disposed inside the tunnel 89, 89 ′, that is to say on the side outside the enclosure 80, while the branch 34 of the magnetic circuit 35 passes through the tunnel 89, 89 ′ Inside the primary winding 12. The branch 60 is placed in the vertical part of the notch 90 and the branch 44 in the horizontal part of said notch. Finally, the fourth branch 46 is placed in the vertical part of the notch 90 ′ at the ends of the branches 34 and 44.

Alternatively, instead of being supported by the tunnel, the primary winding can be supported by the magnetic circuit itself.

To maintain these different elements of the magnetic circuit between them, there are provided plates, such as that referenced 106, associated with the half-shell 81, which are fixed to the bottom walls 83 and 83 ′. These plates serve as support for connection pads 107 of the primary winding. The plate 106 can also serve as a support for a fan 108 or a pump for cooling the primary winding and the magnetic circuit by effecting a forced and rapid flow of air or a refrigerant fluid such as a gas inside the tunnel (89, 89 ′).

The two half-shells 81 and 81 ′ of the enclosure 80 are made of an insulating material made of plastic, for example. In order to achieve electrical protection, the outer wall of each half-shell 81 and 81 ′ is coated with a metal casing or a conductive layer which is produced so as not to short-circuit the secondary winding disposed inside the half-shells. The metallic envelope or the conductive layer are connected to the ground potential.

The insulating and cooling fluid with which the enclosure 80 is filled can be produced by an insulating and curable resin which, in combination with the two half-shells 81 and 81 ′, forms the encapsulation mold for the elements which they contain. By operating in this way, it is not necessary to use, during manufacture, an encapsulation mold whose assembly and disassembly are long.

The invention has been described in relation to a particular embodiment in which only the enclosure 80 was filled with an insulating and cooling liquid, the outside of the enclosure being in the open air. However, nothing prevents the enclosure 80 and the elements that it supports from being placed in a tank, similar to tank 61 in FIG. 7, which would be filled with a refrigerant. Such an arrangement applies as well to the case of an enclosure 80 filled with an insulating and cooling liquid with or without circulation of said liquid as to that of an enclosure 80 filled with a resin as indicated above.

• il ne comporte pas de cuve métallique mais une enceinte en matériau isolant revêtue d'une enveloppe conductrice ou d'une couche conductrice, d'où une réduction du coût de fabrication;
• le volume et le poids du bloc haute tension ont été sensiblement réduits par une diminution du volume du liquide isolant et réfrigérant et par l'utilisation d'une enceinte 80 en matériau isolant tel qu'une matière plastique;
• les calories dégagées par les éléments électriques et magnétiques des circuits primaire et secondaire peuvent être évacuées par une circulation forcée ou non d'un fluide réfrigérant; ce liquide réfrigérant peut être différent selon qu'il s'agit du circuit secondaire ou du circuit primaire, ce qui permet une adaptation spécifique.

The high voltage block according to the invention has the following advantages:

• it does not include a metal tank but an enclosure made of insulating material coated with a conductive envelope or a conductive layer, hence a reduction in the manufacturing cost;
• the volume and weight of the high-voltage block have been significantly reduced by a reduction in the volume of the insulating and cooling liquid and by the use of an enclosure 80 made of insulating material such as a plastic material;
• the calories released by the electrical and magnetic elements of the primary and secondary circuits can be removed by forced or non-forced circulation of a refrigerant; this coolant can be different depending on whether it is the secondary circuit or the primary circuit, which allows specific adaptation.

Claims (23)

1. High voltage supply device for an X-ray tube comprising a space (20, 21) comprising a transformer which has at least one primary winding (12), a plurality of secondary windings (S1-S12) and a magnetic circuit (35), the two output terminals (B1-B24) of each of the said secondary windings being connected to a voltage rectifying and doubling circuit which consists of two diodes (D1-D24) and two filter capacitors (C1-C24), the said rectifying and doubling circuits being connected together so that their output voltages are added to each other, and a closed chamber (80) enclosing the said space in an insulating and refrigerating medium, characterised in that in the space the secondary windings are mounted on concentric coils and have their output terminals distributed on each lateral edge of the coils, the capacitors are disposed on the outer periphery of the coils and the diodes are disposed on a lateral edge of the coils, and in that the primary winding, mounted on a coil concentrically with the secondary windings, and the magnetic circuit are disposed outside the chamber.
2. Device according to Claim 1, characterised in that the chamber also includes at least one transformer (101, 101′) for supplying one filament of the cathode of the X-ray tube.
3. Device according to Claim 1 or 2, characterised in that the chamber also includes an expansion vessel (97) for the cooling liquid.
4. Device according to one of Claims 1 to 3, characterised in that the chamber also includes an electric circuit (99) for the measurement of the high voltage.
5. Device according to one of Claims 1 to 4, characterised in that the chamber also includes high-tension connectors (93, 93′) which are mounted by means of orifices made in the lateral walls.
6. Device according to one of Claims 1 to 5, characterised in that the chamber is made of two half shells (81, 81′) with cells for mounting and holding the secondary windings.
7. Device according to Claim 6, characterised in that the walls of the cells fit the shape of the components which they hold and have orifices (103′) for the flow of a refrigerating and insulating liquid.
8. Device according to Claim 6 or 7, characterised in that the central part of each half shell has a tunnel (89, 89′) which passes through it from one side to the other and serves as a support for the secondary windings inside the chamber and as a support for the primary winding outside the chamber.
9. Device according to Claim 8, characterised in that a branch (34) of the magnetic circuit passes through the tunnel.
10. Device according to Claim 8 or 9, characterised in that each half shell has, at the level of the tunnel, recesses for mounting and holding the other branches (44, 46, 60) of the magnetic circuit.
11. Device according to Claim 10, characterised in that the different branches of the magnetic circuit are held with respect to each other and to the half shells by plates (106) fixed to their walls, the plates carrying the connection pins for the primary winding.
12. Device according to Claim 11, characterised in that at least one of the plates supports a pump for circulating a refrigerating fluid inside the tunnel.
13. Device according to Claim 12, characterised in that, the refrigerating fluid being air, the pump is a fan (108).
14. Device according to one of Claims 1 to 13, characterised in that the chamber is made of insulating material.
15. Device according to Claim 14, characterised in that the insulating material is a plastic.
16. Device according to Claim 14 or 15, characterised in that the chamber is covered with a metal enclosure providing electrical protection without short-circuiting the secondary windings.
17. Device according to Claim 14 or 15, characterised in that the chamber is covered with a conductive layer providing electrical protection without short-circuiting the secondary windings.
18. Device according to one of Claims 1 to 17, characterised in that the insulating and refrigerating medium contained in the chamber is a fluid.
19. Device according to one of Claims 1 to 17, characterised in that the insulating and refrigerating medium contained in the chamber is a setting resin.
20. Device according to Claim 18 or 19, characterised in that it is placed in a tank (61) filled with a refrigerating fluid.
21. Device according to Claim 20, characterised in that the refrigerating fluid in the tank is different from the insulating and refrigerating medium contained in the chamber.
22. Device according to one of Claims 1 to 21, characterised in that it also includes means for circulating and cooling the insulating and refrigerating fluid contained in the chamber.
23. Device according to one of Claims 20 to 22, characterised in that it also comprises means for circulating and cooling the refrigerating fluid contained in the tank containing the chamber.

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