EP0923785B1 - High voltage/low voltage transformer with thermoplastic air-core insulation - Google Patents

Description

The present invention relates to transformers and relates more particularly to transformers dry.

Transformers used in distribution of energy to the public have a rated power included between 5 kVA and 2500 kVA.

They are used to lower the voltage level of the network of "medium voltage" level between 5 and 36 kV at a low voltage level below 500 V for the supply of electrical energy to domestic customers.

Immersed type transformers, insulated in a dielectric liquid (mainly oil) represent the vast majority of usage and the current offer. Indeed, mineral oil is a inexpensive material, good insulator and good coolant for winding cooling. However, the oil mineral has the disadvantage of being a good fuel, which is harmful in the event of an internal arc in the transformer.

To mitigate the risk of fire inherent in oil mineral, high fire point dielectric liquids have been developed. Polychlorobenzene was the most used, but was later banned because of its non-biodegradability and the harmfulness of some fire decomposition products. Esters or oils silicone would be the best contenders for replacement of polychlorobenzene in transformers. However, these products are not yet popular, and their use is very marginal. Their future commercial is certainly compromised by severity growing laws regulating the use of dielectrics liquids due to the risk of cold pollution.

Solid insulation devices or devices dry have grown strongly after the ban use of polychlorobenzene. They are mostly used in establishments open to the public (buildings, workshops), to reduce the risk of fire. Their distribution use remains marginal because significant additional cost compared to oil appliances mineral.

Current dry transformers include large air gaps providing an insulation function between windings and between windings and ground, this which increases their bulk, their mass and therefore their cost. To overcome this problem, some manufacturers use a surface metallization of the windings, which allows them to reduce clutter. This technique has the disadvantage of being expensive and delicate to Implementation.

Today there are two large families of dry transformers: asphalt and impregnated. The manufacturing methods of these devices are certainly different, but the insulation materials used have common to be thermosetting and to require a hot polymerization, which induces a manufacturing cost Student.

The invention aims to remedy the drawbacks aforementioned dry transformers by creating a transformer of this type which while being of a bulk and a reduced cost price compared to transformers dry products have similar performances or even improved.

It therefore relates to a transformer with dry insulation comprising at least one high winding voltage and at least one low voltage winding fitted on at least one column of a magnetic circuit, characterized in that its high voltage winding is contained in a thermoplastic resin insulation coating coated with a surface layer of thermoplastic resin electrically conductive for fixing the potential, compatible with the insulating coating and its winding low voltage is coated in an electrically conductive resin.

• l'enrobage de l'enroulement haute tension comporte dans sa surface latérale des orifices pour le passage des bornes de connexion de l'enroulement;
• lesdits orifices pour le passage des bornes de connexion de l'enroulement haute tension sont ménagés dans une bande latérale de résine thermoplastique isolante de l'électricité compatible avec la résine thermoplastique de l'enrobage d'isolation et en surépaisseur par rapport à celle-ci;
• le transformateur comprenant des barres de couplage haute tension, chaque barre de couplage comporte une âme conductrice enrobée d'une résine thermoplastique isolante, revêtue d'une résine thermoplastique électro-conductrice;
• entre l'âme conductrice de la barre de couplage et l'enrobage isolant de celle-ci est insérée une précouche de résine thermoplastique électroconductrice destinée à éviter les décharges partielles risquant d'apparaítre entre le métal de l'âme et l'isolant de l'enrobage si l'interface métal-isolant n'est pas parfait ou s'il y a un risque de détérioration de celui-ci en raison de contraintes thermiques ou mécaniques;
• chaque barre de couplage comporte à chacune de ses extrémités un organe de raccordement de l'âme de la barre avec une borne de connexion d'un enroulement haute tension, l'un des organes de raccordement formant borne de raccordement avec l'extérieur, lesdits organes de raccordement étant chacun entourés d'une tête en résine thermoplastique moulée d'une seule pièce avec le revêtement isolant de la barre et ayant des dimensions adaptées aux orifices pour le passage des bornes de connexion de l'enroulement haute tension ménagés dans l'enrobage isolant dudit enroulement, la tête comportant en outre un revêtement en résine thermoplastique électroconductrice moulé d'une seule pièce avec le revêtement électroconducteur de l'ensemble de la barre;
• ledit au moins un enroulement basse tension est bobiné directement sur un manchon en résine électro-conductrice enrobant la colonne correspondante du circuit magnétique;
• le circuit magnétique comporte en outre des culasses réunissant les colonnes du circuit magnétique, lesdites culasses étant également revêtues d'un enrobage de résine;
• l'enrobage en résine de l'une au moins des culasses du circuit magnétique comporte des zones en surépaisseur pour la fixation des conducteurs de connexion des enroulements basse tension et pour la sortie des bornes de connexion basse tension du transformateur;
• entre les bobinages haute tension et basse tension, sont ménagés des canaux de circulation d'un fluide de refroidissement définis par des saillies venues de matière avec l'un au moins des enrobages desdits enroulements;
• des orifices supplémentaires pour la sortie de bornes de réglage sont ménagés dans la bande latérale de l'enrobage de l'enroulement haute tension, ces orifices étant obturés chacun par un bouchon isolant revêtu d'une couche de matière électroconductrice de fixation du potentiel en contact avec la couche électroconductrice de revêtement du bobinage haute tension pour assurer la continuité de la couche électroconductrice de fixation du potentiel.

According to other characteristics of the invention:

• the coating of the high-voltage winding has in its lateral surface orifices for the passage of the connection terminals of the winding;
• said orifices for the passage of the connection terminals of the high-voltage winding are formed in a lateral strip of electrically insulating thermoplastic resin compatible with the thermoplastic resin of the insulation coating and in excess thickness with respect thereto ;
• the transformer comprising high voltage coupling bars, each coupling bar comprises a conductive core coated with an insulating thermoplastic resin, coated with an electrically conductive thermoplastic resin;
• between the conductive core of the coupling bar and the insulating coating thereof is inserted a precoat of electroconductive thermoplastic resin intended to avoid partial discharges which risk appearing between the metal of the core and the insulator of the '' coating if the metal-insulator interface is not perfect or if there is a risk of deterioration thereof due to thermal or mechanical stresses;
• each coupling bar comprises at each of its ends a member for connecting the core of the bar with a connection terminal for a high-voltage winding, one of the connection members forming a connection terminal with the outside, the said connection members each being surrounded by a head of thermoplastic resin molded in one piece with the insulating coating of the bar and having dimensions adapted to the orifices for the passage of the connection terminals of the high-voltage winding formed in the an insulating coating of said winding, the head further comprising a coating of electroconductive thermoplastic resin molded in one piece with the electroconductive coating of the entire bar;
• said at least one low-voltage winding is wound directly on a sleeve of electroconductive resin coating the corresponding column of the magnetic circuit;
• the magnetic circuit further comprises yokes joining the columns of the magnetic circuit, said yokes also being coated with a resin coating;
• the resin coating of at least one of the yokes of the magnetic circuit includes areas with extra thickness for fixing the connection conductors of the low voltage windings and for the output of the low voltage connection terminals of the transformer;
• between the high voltage and low voltage windings are formed channels for the circulation of a cooling fluid defined by protrusions made from one material with at least one of the coatings of said windings;
• additional orifices for the output of adjustment terminals are provided in the lateral strip of the coating of the high-voltage winding, these orifices each being closed by an insulating plug coated with a layer of electrically conductive material for fixing the potential in contact with the electroconductive coating layer of the high voltage winding to ensure the continuity of the electroconductive potential fixing layer.

• les Fig. 1A à 1E sont des vues schématiques en perspective montrant les phases de montage d'un transformateur triphasé sec suivant l'invention;
• la Fig.2 est une vue en coupe à plus grande échelle du transformateur sec de la Fig.1E;
• la Fig.3 est une section suivant la ligne 3-3 de la Fig.2;
• la Fig.4 est une vue en coupe suivant la ligne 4-4 de la Fig.2;
• la Fig.5 est une vue en perspective de la culasse supérieure du transformateur de la Fig.1E pourvue d'un enrobage isolant;
• la Fig.6 est une vue en perspective de la culasse inférieure du transformateur de la Fig.1E pourvue d'un enrobage isolant;
• la Fig.7 est une vue en coupe d'une barre droite de couplage entre bobinage haute tention des transformateurs de la Fig.1; et
• la Fig.8 est une vue en coupe d'une barre coudée de construction analogue à celle de la Fig.7.

The invention will be better understood on reading the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

• Figs. 1A to 1E are schematic perspective views showing the assembly phases of a dry three-phase transformer according to the invention;
• Fig.2 is a sectional view on a larger scale of the dry transformer of Fig.1E;
• Fig.3 is a section along line 3-3 of Fig.2;
• Fig.4 is a sectional view along line 4-4 of Fig.2;
• Fig.5 is a perspective view of the upper yoke of the transformer of Fig.1E provided with an insulating coating;
• Fig.6 is a perspective view of the lower yoke of the transformer of Fig.1E provided with an insulating coating;
• Fig.7 is a sectional view of a straight bar for coupling between high voltage winding of the transformers of Fig.1; and
• Fig.8 is a sectional view of a bent bar of construction similar to that of Fig.7.

In Figs. 1A to 1E, the various mounting phases of a three-phase transformer dry insulation according to the invention.

FIG. 1A shows a winding low voltage 1 placed on a column 2 of the magnetic circuit a three-phase transformer shown more fully in Figures 1D and 1E.

To carry out the arrangement of FIG. 1A, we begins by assembling according to a usual process the laminated column 2 of the magnetic circuit of the transformer by stacking pre-cut steel sheets at conventional silicon. On the central part of the column 2, i.e. outside the end portions 2A and 2B beveled, for the subsequent meeting of column 2 with circuit closing yokes magnetic, a sleeve 3 of polymer resin is molded.

This operation is carried out by injection, or by hot strip compression, if the polymer used is thermoplastic.

However, the material used can also be a thermosetting resin. It is important that the material be conductive of heat and this as much as possible. AT for this purpose, it may contain in adequate proportion a carbon load, for example, which has the advantage additional to make it also weakly conductive electricity, according to a variant preferred of the invention which will be explained later.

After fitting compression rings 4 (Fig. 4) at the ends of the sleeve 3 made of polymer resin, coil on the surface of the sleeve an electrical conductor metallic 5 which will form the low voltage winding of the transformer as shown in particular in FIG. 1D and also in FIGS. 2, 3 and 4.

This conductor 5 can be in the form of wide strips or flat in aluminum or copper. he is conventionally wrapped in oiled insulating paper.

Each of its ends extends outside by conventional connection bars 6.

The low voltage winding thus produced is then encapsulated in a layer 7 of polymer resin dielectric a few millimeters thick, by example of 3mm. This resin envelope 7 is produced by hot pressing of superimposed sheets of material thermoplastic, also thermally conductive in order to promote heat exchange with the surrounding air. This resin is also slightly conductive electricity, which improves the overall safety of the device to be produced, by earth potential at point 7A shown in figure 1A.

This completes the manufacture of a winding low voltage of the transformer according to the invention.

The sleeve 3, although being an intermediate entity which will disappear as such in the realization completed shown in Figure 1A, nevertheless fulfills several essential roles.

First, thanks to its rigidity, it ensures the necessary mechanical maintenance of the stacking of sheets forming column 2 while conventionally this cohesion is ensured by means of bolts and nuts.

Then, the sleeve 3 fulfills a major role heat exchanger which promotes the cooling of column 2 or winding 5 by conduction of the heat through the thermally conductive material of which said sleeve is made up.

Also, if we also make it slightly conductor of electricity, we can improve safety of use of the final device by simple setting sleeve earth. This provision is facilitated if, as we understand, we plan to exceed the sleeve 3 of the end of the winding 5 in order to have then a fully coated coil 5.

Furthermore, as already indicated, it serves as winding support for the electrical conductor metallic 5 intended to be energized. So between other advantages, the oiled paper insulation that envelops driver 5 no longer risks being injured during winding. So far indeed, we have been led to avoid this risk by interposing between the columns of the circuit magnetic and low voltage windings wound around these columns, wooden spacers which kept the driver away from sharp corners sometimes injuries to the magnetic circuit.

As shown in Figure 1A, on the surface exterior of the electrically conductive polymer resin coating 7 are provided projections 8 in the form of longitudinal ribs forming spacers for the coil high voltage shown in Figure 1B and which will be placed around the low voltage stage of FIG. 1A.

These ribs, 3 to 50 mm high by example, are also used to define channels 9 for circulation of a coolant by convection such as air between the low voltage stage and the high voltage stage as can be seen for example at Figure 1C.

In this example, the outer surface of the dielectric polymer resin coating 7 comprises four ribs 8 distributed at 90 ° one with respect to the other along the periphery of the coating envelope 7.

As already indicated above, the envelope of coating or encapsulation resin 7 present preferably some ability to conduct electricity, especially when formed from a resin polymer charged with electrically conductive particles or a naturally conductive polymer resin electricity.

Thanks to such an arrangement, an effect is obtained antistatic to prevent dust, inevitably present in the air are deposited on the wall cooling channels 9. It is also possible to put the resin envelope 7 to the ground by connecting it electrically grounded, as shown in 7A, which improves transformer safety in the event of failure or local degradation of oiled paper for insulating the metallic conductor 5 under voltage.

In fact, all of the resin parts polymer including sleeve 3 and protective cover 7 can safely be slightly conductive, since the electrical voltage of the conductor 5 at the level of the low voltage stage of a transformer does not exceed usually not 400 to 500 volts.

The compression rings 4 are in fact end plates intended to laterally contain the metallic conductor wound 5 in multi-layer turns and are shaped to take into account the helical winding of this last. It is necessary that the end turns of each layer of the preformed conductor winding 5 continuously wear against these flanges over all their length. This implies a re-entrant ramp shape or outgoing from the bearing face of each ring 4 according to the orientation of the coil winding propeller.

This is the reason why we have two concentric rings with inverted ramps for windings two layers usually used.

Such rings have an advantage here major, i.e. forming a mass of stuffing at the ends sleeve 3 which allows compression molding sheets of thermoplastic resin 7 satisfactorily. Otherwise, the volume to be filled with the molded resin would require an injection operation which is not not generally intended for massive parts and which is much less economical than compression.

The low voltage stage shown in Figure 1A is of course produced in as many copies as the transformer to be built has phases.

Figures 1B to 1E schematically show the stages of construction of a three-phase dry transformer.

In Figure 1B, we show a high winding voltage intended to cooperate with the low voltage winding of Figure 1A.

To make this high-voltage winding 10, we begins by winding an electrical conductor coated with a insulating sheath to constitute a winding formed of coaxial turns of circular, oval or polygonal shape on one or more layers. The metallic conductor 11 (Fig.1D) is usually made of copper or aluminum and the insulating sheath is generally an enameling or a covering in an insulator generally made of paper, to insulate between they contiguous turns.

The winding thus obtained is coated with injection or compression into a resin layer electrically insulating thermoplastic 12 (Fig. 2).

The coating 12 has on its lateral surface holes 14 for the passage of connection terminals 15 of the winding.

The holes 14 for the passage of the terminals of high voltage winding connection are provided in a side strip 16 of insulating thermoplastic resin electricity, compatible with thermoplastic resin of the insulation coating 12 and in excess thickness by compared to this one.

Advantageously, the side strip 16 is made by molding in one piece with the coating 12. It can also be produced by compression at hot on coating 12.

On the coating layer 12 is further plated by hot compression, a layer 18 of a few millimeters thick of an electrically conductive thermoplastic resin covering all surfaces of the winding high voltage both outside and inside of it.

This resin forming a surface layer 18 (Fig. 2) is loaded with carbon particles for the conduct electricity and it is the same nature that the insulating polymer forming the coating 12.

Thus, the interfaces with the insulators can be free from vacuoles.

The high voltage coil is then finished.

It remains to be specified that the thicknesses of insulation on the winding are sufficient to hold the maximum dielectric stresses that can be applied between the winding and the electrically conductive layer 18 connected to earth, or between the internal connections of the winding and the electrically conductive layer 18 connected to the earth, between the terminals 15 of the winding and the layer electrically conductive 18 connected to earth.

The side band 16 in thermoplastic resin formed of a stack of insulating thermoplastic material similar or identical to that of the insulating coating 12 and an electrically conductive surface layer 18, covers the internal connections and the terminals 15, of the winding. The orifices 14 formed around the conductors of outlet 15 are intended to allow the connection of the high voltage coil to the network, or to connect the coil high voltage to other high voltage coils of so as to make an electrical coupling as it will be described with reference to FIG. 1E, and to be connected to the high voltage coil, adjustable connectors such as the set of conductors 20 appearing in FIG. 1B in a hole 22 of square shape made in the strip side 16 between the holes 14 for passage of the conductors of the high voltage winding.

The high voltage winding 10 is then placed on the low voltage winding 1 as shown in Figure 1C.

For this purpose, the low voltage winding 1 mounted on its column 2 is introduced into the upper winding tension 10. The ribs 8 present on the periphery of the conductive coating 7 of the low-voltage winding, allow to center the high voltage stage on the axis of the magnetic column 2 of the low voltage winding and provide an ambient air cooling channel 9 between the low voltage 1 and high voltage 10 windings, the ribs 8 thus forming spacers between the two windings.

We thus created a high voltage stage - low voltage coupled.

Such stages are used to achieve a three-phase transformer such as that shown in Figures 1D and 1E.

For this purpose, we assemble three low floors voltage - high voltage and we assemble the columns 2 of these stages by upper and lower yokes 24 and 26 as clearly shown in Figure 2.

Cylinder heads 24 and 26 are also produced made of laminated magnetic sheet.

The cylinder heads 24 and 26 being put in place so as to cooperate with vertical columns 2 bearing each a low voltage winding 1 and a winding high voltage 10, form a closed magnetic circuit comprising a central column and two lateral columns.

With a view to their assembly, the lateral columns 2 have beveled ends 2A, 2B, while that the central column has 2C, 2D ends in symmetrical tips. Cylinder heads 24 and 26 are shaped complementary to the ends of columns 2 with which they are assembled.

As shown in Figure 1E, each of cylinder heads 24 and 26 have a coating 28, 30 of resin thermoplastic. The coatings 28 and 30 which are represented in Figure 1E and which also appear in Figures 2,5 and 6 have the main function of ensuring the mechanical holding together of the sheets forming the cylinder heads 24 and 26 and the assembly of these cylinder heads with the corresponding ends of columns 2. Resin forming the coatings 28 and 30 preferably has the same chemical base than that used for coating columns 2 so as to obtain a good weld between the two materials.

The second function of cylinder head coating is to protect them against external aggressions.

The coating of cylinder heads 24 and 26 also has the following additional functions.

It ensures the positioning of the high windings tension and low tension 1 and 10 compared to the cylinder heads 24 and 26.

It also ensures the mechanical maintenance of low voltage conductors 6 between the outputs of the windings low voltage and the low voltage terminals of the transformer.

For this purpose, the coating 28 of the upper cylinder head has zones 32 in excess thickness for the fixing of low voltage connection conductors 6 and for the output of the low voltage connection terminals the transformer.

The coating 28 of the upper cylinder head 24 forms also base for the low voltage terminals of the transformer.

It of course also ensures the maintenance mechanics of low voltage coupling bars which are also protected by the extra thickness zones 32 above.

This coating finally ensures an increase in the cylinder head heat exchange area beneficial for cooling if the resin used is thermally conductive.

As can be seen in Figure 1E, the whole including the magnetic circuit including the cylinder heads upper and lower 24 and 26 are coated with a coating and whose columns 2 each carry a winding low voltage 1 and a high voltage winding 10, is then mounted on a frame 34. The main function of frame 34 is the positioning of the transformer relative to the ground. The axis of the transformer windings is preferably close to vertical to improve transformer cooling by convection natural ambient air.

The frame 34 can also be used to reinforce the timing of the windings. This setting is necessary for to oppose the electro-dynamic forces which are exerted on windings, in particular during short circuits, network.

We can then mount the coupling bars 35 and 36 high voltage windings as shown in Figure 1E.

In Figure 7, there is shown a bar of rectilinear coupling such as the bar 35 of FIG. 1E. This high voltage coupling bar has a core conductive 37 coated with a thermoplastic resin insulation 38, coated with an electrically conductive thermoplastic resin 39.

Between the conductive core 37 of the bar coupling and the insulating coating 38 thereof, is inserted an electrically conductive thermoplastic resin prelayer 40 intended to avoid partial discharges risking to appear between the metal of the core 37 and the insulation of the coating 38 if the metal-insulator interface is not perfect or if there is a risk of deterioration of it due to thermal or mechanical constraints.

The busbar 36 shown in Figure 8, is a bar comprising elbows 42 intended for it pass over straight bars 35 as clearly shown in Figure 1E.

The constitution of the coupling bar 36 is otherwise the same as that of the coupling bars 35.

Each coupling bar each has its ends, a connecting member 43.44 of the core 37 of the bar with a connection terminal of a winding high tension. The connecting member 43.44 is surrounded by a 45,46 head in molded thermoplastic resin in one piece with the insulating coating 38 and having dimensions adapted to the orifices 14 for passage terminals 15 for connecting a high-voltage winding formed in the coating 12 of said winding. Each of heads 45,46 further includes a coating 47,48 in electrically conductive thermoplastic resin molded from single piece with electrically conductive coating 39 of the whole bar.

Thanks to the arrangement which has just been described, the accessible area of coupling rods 35.36 present a potential referenced to mass provided that the mounting ensures electrical continuity between the electrically conductive layers 39, 47, 48 of the bars and the electrically conductive layers 18 of the high windings tension 10.

In addition, each bar has one of its ends, a connecting member 50 with the outside consisting of a junction plug and at both ends a connection member 52 with a terminal of a winding high voltage, this member comprising a spring socket.

Considering more particularly the figures 6 and 7, it can be seen that the coating 28.30 of each of the transformer upper and lower heads 24.26 three-phase according to the invention, has on its faces facing the winding assemblies constituting the transformer, pads 54 for positioning the windings compared to cylinder heads.

Furthermore, the coating 28.30 of the cylinder heads 24 and 26 covers a few millimeters long, the sleeve 3 molding the magnetic columns 2.

To the right of this overlap there is a welding watertight between the coating 28.30 and the sleeve 3 during molding of the coating 28.30 on the sleeve 3.

• le maintien mécanique des culasses 24,26 sur les colonnes 2,
• la protection contre les agressions externes du circuit magnétique constitué des culasses 24,26 et des colonnes 2.

This welding allows:

• mechanical maintenance of the cylinder heads 24, 26 on the columns 2,
• protection against external aggressions of the magnetic circuit consisting of the yokes 24, 26 and of the columns 2.

Referring again to Figure 1E, we sees that the orifices 22 formed in the side bands 16 of the coatings of the high voltage windings 10 carried by each column of the transformer are intended for the output high voltage winding adjustment terminals 20 correspondents. These orifices are advantageously closed off each by an insulating plug 64 coated with a layer 65 of electrically conductive material for fixing potential in contact with the electrically conductive coating layer 18 corresponding high-voltage winding to ensure continuity of the electrically conductive fixing layer of potential.

Although in the example just described the invention is applied to a three-phase transformer, it is of course possible to apply it to the realization a single-phase transformer comprising at least one set of low-voltage windings, high-voltage carried by a column of a closed magnetic circuit.

Claims (12)

1. Transformer with air-core insulation comprising at least one primary coil and at least one secondary coil mounted on at least one column of a magnetic circuit, characterised in that its high voltage coil (10) is contained in a thermoplastic resin insulating encapsulation (12) coated with a surface layer (18) in an electroconductive thermoplastic resin for fixing the potential compatible with the insulating encapsulation and its low voltage coil (1) is encapsulated in an electroconductive resin (7).
2. Transformer according to Claim 1, characterised in that the encapsulation of the high voltage coil has passages (14) in its side area for terminals (15) to pass through for connecting the coil.
3. Transformer according to Claim 2, characterised in that the said passages (14) for the high voltage coil connection terminals (15) to pass through are made in an electrical insulating thermoplastic resin side strip (16) compatible with the thermoplastic resin of the insulating encapsulation (12) and thicker than it, and acting as covering for the internal connections of the high voltage coil.
4. Transformer according to one of the Claims 1 to 3, comprising high voltage coupling rods (35, 36), characterised in that each coupling rod has a conductive core (37) encapsulated in an insulating thermoplastic resin (38), coated with an electroconductive thermoplastic resin (39).
5. Transformer according to Claim 4, characterised in that between the conductive core (37) of the coupling bar and the latter's insulating encapsulation (38) a primer coat (40) of electroconductive thermoplastic resin (40) is put on designed to prevent partial discharges which might occur between the metal of the core and the insulating material of the encapsulation if themetal/insulation material interface is not perfect or if there is a risk of damage due to heat or mechanical stresses.
6. Transformer according to one of the Claims 4 and 5, characterised in that each coupling rod (35, 36) has at each of its ends a part (43, 44) for connecting the core (37) of the rod with a terminal connecting a high voltage coil, the said connection part being surrounded by a thermoplastic resin head (45, 46) moulded in one piece with the insulating coating (38) of the rod and with dimensions suitable for the passages (14) for the terminals (15) connecting the high voltage coil to pass through, made in the encapsulation of the said coil, the head (45, 46) having in addition an electroconductive thermoplastic resin coating (47, 48) moulded in one piece with the electroconductive coating (39) of the rod assembly,
7. Transformer according to one of the Claims 1 to 6, characterised in that at least one low voltage coil (1) is wound directly on an electroconductive resin sleeve (3) encapsulating the corresponding column (2) of the magnetic circuit.
8. Transformer according to one of the Claims 1 to 7, characterised in that the magnetic circuit has in addition yokes (24, 26) joining the columns (2) of the magnetic circuit, the said yokes being also coated with a resin encapsulation (28, 30).
9. Transformer according to Claim 8, characterised in that the resin encapsulation (28) of at least one of the yokes (24) of the magnetic circuit has thicker areas (32) for fixing leads for connecting the coils and for the outlet of the terminals (6) for low voltage connection of the transformer.
10. Transformer according to one of the Claims 8 and 9, characterised in that the resin for coating the yokes (24, 26) is a thermoconductive resin.
11. Transformer according to one of the Claims 1 to 10, characterised in that between the high voltage and low voltage windings there are channels (9) for cooling fluid to circulate, defined by the projections (8) which are made in one piece with at least one of the encapsulations (7 or 12) of the said coils.
12. Transformer according to any one of the Claims 3 to 11, characterised in that extra passages (22) for the setting terminals (20) to exit are made in the side strip of the encapsulation (16) of the high voltage coil, each of these passages being blanked off by an insulating plug (64) covered with a coat (65) of electroconductive material for fixing the potential in contact with the electroconductive coat (18) covering the high voltage coil (10) to ensure continuity of the electroconductive coat for fixing the potential.

Images