EP0258362A1

EP0258362A1 - High voltage transformer

Info

Publication number: EP0258362A1
Application number: EP87901500A
Authority: EP
Inventors: Günter Menge
Original assignee: General Electric CGR SA; Thomson CGR
Current assignee: General Electric CGR SA
Priority date: 1986-02-21
Filing date: 1987-02-17
Publication date: 1988-03-09
Also published as: US4814733A; DE3605629C2; WO1987005148A1; DE3605629A1

Abstract

Un transformateur haute tension (20) dont les dimensions sont particulièrement réduites par rapport à l'art antérieur. Le transformateur selon l'invention comporte un circuit magnétique (1) et un corps de bobines (5). Un enroulement secondaire est bobiné sur le corps de bobines (5) en plusieurs bobinages (3a, 3b) séparés. Chaque bobinage secondaire (3a, 3b) est contenu dans une gorge (4a, 4b) fermée par un anneau isolant (23a, 23b). L'anneau isolant (23a, 23b) est constitué par deux tronçons (7a, 7b) qui sont assemblés autour de la gorge (4a) par un mouvement effectué dans un même plan que celui de la gorge.A high voltage transformer (20) whose dimensions are particularly reduced compared to the prior art. The transformer according to the invention comprises a magnetic circuit (1) and a coil body (5). A secondary winding is wound on the coil body (5) in several separate windings (3a, 3b). Each secondary winding (3a, 3b) is contained in a groove (4a, 4b) closed by an insulating ring (23a, 23b). The insulating ring (23a, 23b) is made up of two sections (7a, 7b) which are assembled around the groove (4a) by a movement carried out in the same plane as that of the groove.

Description

HIGH VOLTAGE TRANSFORMER

The invention relates to a high voltage transformer, in particular for a radiodiagnostic generator and high voltage power supplies. The high voltage transformer is of the type supplied by a converter capable of operating at relatively high frequencies, up to 100 Hertz for example.

A high voltage transformer must not only have the characteristics required for the intended operation, but also, and particularly in the case of industrial manufacturing, its raw materials and its manufacturing must be inexpensive. These conditions are all the more difficult to fulfill as the high voltage transformer must be more compact and of a small footprint. The dimensions of a high voltage transformer can be reduced, in particular thanks to an optimization -5 of the dimensions of the magnetic circuit or core used, to the material of which the latter is made, and to the operating frequency which can be made much higher than that of the supply network, by the use of a converter.

Indeed, one of the determining parameters in the manufacturing 0 of a transformer, and the loss due to the sheets of the magnetic circuit

: the lower the losses, the higher the induction can be chosen, without the iron losses exceeding the allowable tolerance. The high frequency converter technique makes it possible to use relatively small magnetic cores or circuits, which facilitates compact construction of the high voltage transformer.

In a current manner, the high frequency converter delivers in a load circuit comprising the primary winding of the high voltage transformer and comprising an oscillating circuit; the resonant frequency of the oscillating circuit being linked to the operating frequency 0 of the converter. The frequency limits, within which the converter can operate, are set terminated in particular by the semiconductors used; the current thyristors make it possible to master functions without problems at frequencies up to 100 hertz.

However, for a given high voltage value, the smaller the dimensions of the high voltage transformer and the more difficult it is to achieve electrical insulation between the secondary winding, and the primary winding and the core of the transformer; so that for small dimensions of the transformer, the cost of the latter becomes very high both for the price of the materials used and for the complexity of the assembly work.

The invention relates to a high voltage transformer, of the type intended to operate with a high frequency converter, having particularly reduced dimensions compared to the prior art. This is obtained by a new arrangement, in particular in terms of electrical insulation, which makes it possible both to use elements which are simple to assemble and of low cost, and to improve the conditions of electrical insulation.

According to the invention, a high voltage transformer of the type supplied by a high frequency converter, comprising, a magnetic circuit, a primary winding, a coil body disposed around a longitudinal axis of the magnetic circuit, a high voltage secondary winding wound around of the coil body, the secondary winding comprising at least one secondary winding, the secondary winding being contained in a groove produced in the coil body in a plane substantially per¬ pendicular to the longitudinal axis, is characterized in that the groove containing the secondary winding is closed by an insulating ring constituted by the assembly of at least two sections, the sections having ends which fit into one another so as, on the one hand, to form at their junctions a joint in the form of a labyrinth, and on the other hand so as to assemble the sections by a movement of the latter in substantially the same plane as c throat. The invention will be better understood thanks to the description which follows, given by way of nonlimiting example, and to the four appended figures among which:

- Figure 1 is an overview of the transformer according to the invention, particularly showing a magnetic circuit and insulating rings surrounding a coil body;

- Figure 2 is a sectional view which shows in more detail the coil body shown in Figure 1, and which shows separate secondary windings constituting a secondary winding;

- Figure 3 is an enlarged view of a box shown in Figure 2, and showing details of embodiment of a secondary winding;

- Figure Ψ is a view along a plane perpendicular to a longitudinal axis of the magnetic circuit shown in Figure 1, and which shows an insulating ring formed of two sections whose junctions constitute joints in the form of a labyrinth.

FIG. 1 shows a high voltage transformer 20 according to the invention. The transformer 20 comprises a core or magnetic circuit 1 in itself conventional. In the nonlimiting example described, the magnetic circuit 1 comprises a central core (not shown in FIG. 1) arranged along a longitudinal axis 2, and two external branches 70, 71 parallel to the central core and closed on the latter. 20 comprises a coil body 5 having, in the non-limiting example described, a circular section (the section of the coil body 5 being in a plane perpendicular to that of the figure, it does not appear in the figure). The coil body 5 is arranged along the longitudinal axis 2, between the outer branches 70, 71 of the magnetic circuit 1, and substantially centered around the longitudinal axis 2, and of a primary winding (not shown in FIG. 1 ) which is arranged around the central core.

The coil body 5 is intended to carry a secondary winding (not shown in FIG. 1) formed by at least one secondary winding. The secondary winding (s) are isolated electrically with respect to the magnetic circuit 1, on the one hand by the coil body 5 which is made of an electrically insulating material, each secondary winding being on the other hand electrically insulated by an insulating ring 23a, 23b. In the nonlimiting example described and shown in Figure 1, two insulating rings 23a, 23b are shown, that is to say that the secondary winding is constituted by two separate secondary windings; but it should be understood that, in the spirit of the invention, the secondary winding can equally well consist of a single secondary winding or of a plurality of separate secondary windings, but electrically connected together, so that only the two extreme ends 25, 26 of the secondary winding are extended outside the insulation rings 23a, 23b, as shown in FIG. 1, thanks to openings 13 made in the insulating rings 23a, 23b. The openings 13 also allow the passage of an oil (not shown) of the conventional type, used for electrical insulation, and in which the transformer 20 is immersed; the isolation oil and the transformer 20 being contained in a manner known per se in an enclosure (not shown). The magnetic circuit 1 is cut into two parts 1a, 1b according to a separation plane 72 perpendicular to the longitudinal axis 2. The two parts 1a, 1b of the magnetic circuit 1 are joined and clamped one against the other at the using a band tightening device 22, after mounting in the magnetic circuit of the primary winding, and of the coil body 5 equipped with the secondary winding (s) as well as the insulating rings 23a, 23b.

As is further explained in a continuation of the description, each isolation ring 23a, 23b is intended to surround at least one secondary winding, and according to a characteristic of the invention, each isolation ring 23a, 23b is formed by the assembly of at least two sections of rings 7a, 7b, the ends of which 27, 28 have a complementary shape so as to constitute, on the one hand, at their junctions on their sides 30 , a joint called in labyrinth 9 (further described with reference to the figure which shows an insulating ring 23a, according to its section), and on the other hand so as to allow the assembly of the sections 7a, 7b by a movement of the latter carried out in a radial direction illustrated by the arrows 31, that is to say to say by a movement in a plane substantially perpendicular to the longitudinal axis 2; assembling the sections 7a, 7b to produce an insulating ring 23a, 23b being carried out before the coil body 5 is mounted in the magnetic circuit 1. On an outer face 32 of the insulating rings 23a, 23b, the junction of the sections 7a, 7b takes place along lines 11 and 12 respectively for the first and the second insulating rings 23a, 23b; these lines

11,12 materialize vanishing lines which we note that they are not aligned with each other, this being obtained by means of different positioning of the two rings 23a, 23b around the longitudinal axis 2. The figure 2 shows by way of nonlimiting example, the manner in which the secondary winding, previously mentioned, is produced and arranged around the coil body 5. The coil body 5 is substantially centered around the longitudinal axis 2, and around of the primary winding 35 and of the central core 36 previously mentioned. According to a characteristic of the invention, the secondary winding is formed by secondary windings 3a, 3b, separated, two in number in the nonlimiting example described, and each contained in a housing where they are electrically isolated from the rest of the transformer. Each housing is constituted by a groove Ψa, Ψb, produced in the periphery of the coil body 5. The grooves a, Ψb are successively arranged along the longitudinal axis 2, in planes substantially parallel to each other and substantially perpendicular to l 'longitudinal axis 2. Each groove, 4b containing a secondary winding 3a, 3b, is closed by an insulating ring 23a, 23b. Such a distribution of the high-voltage secondary winding into several secondary windings 3a, 3b each arranged in a groove 4a, b makes it possible, on the one hand, to perfectly electrically isolate each of these windings from the primary winding 35 and by with respect to magnetic circuit 1, and also allows the tension between lower layers and upper layers of a winding to be reduced.

The coil body 5 and the insulating rings 23a, 23b are made of an electrically insulating material, having in particular a high dielectric strength and a dielectric constant; so as to allow the reduction of the thickness of the rings 23a, 23b and of the walls which constitute the grooves 4a, 4b, in order to reduce the dimensions and the weight of the transformer according to the invention. Another characteristic, which in the invention plays an important role in reducing the size of the transformer along the longitudinal axis 2, is that each insulating ring 23a, 23b is made up of at least two ring sections 7a, 7b as was previously mentioned, and that these two sections are assembled to one another in a movement as represented by the arrows 31, that is to say in a movement which takes place in the same plane as that of the groove 4a, 4b which is to be closed. This results on the one hand, a great ease of assembly, and a simplification of manufacture, because the secondary windings 3a, 3b can be produced together or successively on the coil body 5 which is common to them, and that thereafter each of these secondary windings can be encapsulated independently of the other secondary coils, that is to say that each groove 4a, 4b can be closed by an isolation ring 23a, 23b in any order. It results on the other hand, due to the radial movement which is accomplished by the sections 7a, 7b to form a ring

23a, 23b, to close a groove 4a, 4b, that the distance D between two successive secondary windings 3a, 3b can be considerably reduced; whereas in the prior art when it is desired to encapsulate a coil on all sides and to increase the lengths of the creepage distances by a labyrinth seal, a box is formed formed of two half-boxes which are assembled to one another by an axial movement; so that in the prior art, when it is desired to produce a secondary winding by several separate windings, a great distance must be left between the windings, parallel to the axis of these. With the present invention, on the contrary, the distance D between two successive secondary windings 3a, 3b, can correspond to the thickness which is just necessary to ensure electrical isolation by a wall 40 situated between the two grooves 4a, 4b; to the point that the side edges 30 of two insulating rings

23a, 23b can be joined, as shown in FIG. 2. This allows a significant reduction in the size of the transformer according to the invention, all the more advantageous since the secondary winding is formed by a number more important secondary windings; the secondary windings 3a, 3b may be, in the spirit of the invention, in a number greater than two.

According to another characteristic of the invention, which makes it possible to improve the electrical insulation, a secondary winding 3a, 3b inside a groove 4a, 4b, has a trapezoidal shape whose base 41 is oriented towards the body coil 5, and the top of which

42 is oriented towards the insulating ring 23a, 23b. This form of a secondary winding allows, thanks to projections 8 which is provided on the inner face 45 of each insulating ring 23a, 23b, to increase the efficiency of an electrical insulation, produced using insulating layers ( not shown in Figure 2) arranged between the plies of electrical conductors which form a secondary winding 3a, 3b.

FIG. 3 is an enlarged view of a box 75 in FIG. 2, which shows in more detail the action of the projections S on the insulating layers which the first secondary winding 3a comprises, the example also being valid for the second winding secondary 3b.

For the sake of clarity in FIG. 3, the first secondary winding 3a has been moved away from the first groove 4a, which groove is partially shown, and the first insulating ring 23a shown above the first secondary winding 3a, has also been removed from the latter, and was only partially represented.

The secondary winding 3a comprises between its base 1 and its apex 42, a succession of layers of wires N1, N2 ..., Nn. In S

the nonlimiting example described, between each sheet NI to Nn is arranged at least one layer Cl, C2, ..., Cn of an electrically insulating material. The insulating layers C1 to Cn have substantially the same width L, so that these insulating layers have ends 52 which, relative to the limits 53 of the secondary winding 3a, extend all the more as they are closer to the vertex 42. Arrows 54 illustrate by way of nonlimiting example, the direction in which the first secondary winding 3a is wound.

This arrangement where the insulating layers C1 to Cn have a constant width L, corresponding substantially to the width of the groove 4a, while the secondary winding 3a has a trapezoidal shape, in itself increases the electrical insulation. between the various layers NI to Nn, and this in a manner all the greater the closer to the apex 42. On the other hand, the insulating ring 23a has two projections 8, each arranged on its inner face 45 and near a side edge 30, and these projections 8 penetrate into the groove 4a when the latter is closed by the insulating ring 23a. As a result, the insulating ends 52 situated towards the top 42 are pushed back by the projections 8 towards the base 41, as symbolized by second arrows 55, so that the insulating layers located near the top 42 are closed towards the base. 41, and the top 42 of the winding where the highest voltage exists is thus surrounded by the largest mass of insulating material. This allows, in addition to the insulating rings 23a, 23b which close the grooves 4a, 4b and which are closed on themselves by joints 9 forming a labyrinth, to make the lines of flight infinitely long at each secondary winding 3a, 3b , despite the small dimensions of the high voltage transformer according to the invention. Figure 4 shows an insulating ring 23a, 23b, seen by its section along an arrow 56 shown in Figure 1. The longitudinal axis 2 being perpendicular to the plane of Figure 4, it is seen at a point in the center of the insulating ring 23a. As previously mentioned, the insulating ring 23a is formed by the assembly of two sections of rings 7a, 7b joined by their ends 27,28.

The meeting of the ends 27, 28 of each section 7a, 7b makes two junctions 9. As it appears in FIG. 1, the shapes of the ends 27, 28 considered according to the thickness E of the insulating ring 23a, are irregular and complementary, so that their junctions 9 each constitute a labyrinth seal (which materializes a line of flight), the length of which is much greater than the thickness E. An important feature lies in that the sections 7a, 7b can be assembled to each other by a radial movement of at least one of these two sections, along an assembly axis 60; the assembly axis 60 being contained in a plane perpendicular to the longitudinal axis 2. In the nonlimiting example shown in FIG. 1, it can be seen that the two junctions 9 progress in the same way from the external face 32 towards the inner face 45 of the ring 23a; it results in particular that the sections 7a, 7b are interchangeable to form an isolation ring 23a, 23b. The ends 27, 28 of the sections 7a, 7b, by interlocking with one another, constitute an effective closure, of the type called "snap in" according to an expression in English.

It should be understood that, in the spirit of the invention, different profiles of labyrinth seals 9 can be produced, the important thing being to allow .. 'radial assembly of at least two elements to constitute an insulating ring 23a, 23b.

Each section 7a, 7b comprises on the outer face 32, a flat 10a, 10b intended to be opposite the external branches 70, 71, of the magnetic circuit 1. These two flats 10a, 10b make it possible to define the angular position labyrinth seals 9 and first junctions 11, 12 shown in FIG. 1. The two flats 10a, 10b are centered on a positioning axis 61 arranged along a diameter of the isolation ring 23a, 23b, and which has with the assembly axis 60 an angle a little less than 90 °. This makes it possible in particular to obtain that the first junctions 11, 12 (shown in FIG. 1) which symbolize vanishing lines, are not aligned for two successive insulating rings 23a, 23b. All these provisions, as well as low manufacturing tolerances for each part, make it possible to obtain, minimum wall thicknesses, tight assemblies and a casing which is almost homogeneous around the secondary windings 3a, 3b, so that it does not voltage bypass may occur.

If, despite the low manufacturing tolerances of each part of the coil body 5, and the rings 23a, 23b, appear too large gaps, these are eliminated during a vacuuming process, in particular for filling. high voltage transformer with insulating oil; the high voltage transformer can also be heated, to a temperature of around 80 ° for example, so that during this operation the polypropylene is steamed and acquires a homogeneous form.

Claims

1. High voltage transformer of the type supplied by a converter, comprising, a magnetic circuit (1), a primary winding (35), a coil body (5) disposed around a longitudinal axis (2) of the magnetic circuit (1), a high voltage secondary winding (3a, 3b) wound around the coil body (5), the secondary winding comprising at least one secondary winding (3a) contained in a groove (4a) produced in the body coil (5) in a plane substantially perpendicular to the longitudinal axis (2), charac¬ terized in that the groove (4a) containing the secondary winding (3a) is closed by an insulating ring (23a) constituted by assembly of at least two ring sections (7a, 7b), the sections (7a, 7b) having ends (27, 28) which fit into one another so as, on the one hand, to form at their junctions a joint in the form of a labyrinth (9), and on the other hand so as to allow the sections (7a, 7b) to be assembled by a movement ement (31) of the latter performed substantially in the same plane as that of the groove (4a).

2. Transformer according to claim 1, characterized in that the secondary winding is formed by a plurality of separate secondary bobi¬ swimming (3a, 3b), each contained in a groove (4a, 4b) similar to the first groove (4a ).

3. Transformer according to claim 2, characterized in that each groove (3a, 3b) is closed by an insulating ring (23a, 23b) similar to the first insulating ring (23a).

4. Transformer according to claim 1, characterized in that the movement (31) for assembling the sections (7a, 7b) takes place only along an assembly axis (61) contained in a plane perpendicular to the longitudinal axis (2).

5. Transformer according to claim I, characterized in that the isolation ring (23a, 23b) has on its external surface two flats (10a, 10b) diametrically opposite and intended each to be opposite an external branch (70,71) of the magnetic circuit (1).

6. Transformer according to claim 5, characterized in that the flats (10a, 10b) are centered on a positioning axis (61) which forms an angle () less than 90 ° with a radial axis (60) passing through it longitudinal axis (2) and the ends (27,28) of the sections (7a, 7b).

7. Transformer according to claim 1, characterized in that at least one secondary winding (3a) has a trapezoidal shape, and in that sheets (NI to Nn) which constitute the secondary winding (3a) from its base (41) up to its top (42) are separated by layers (CI to Cn) of insulating material whose width (L) is constant.

8. Transformer according to claim 7, characterized in that at least one insulating ring (23a) has, on its inner face

(45), protrusions (8) which penetrate into the groove (4a) in order to push towards the bottom of the groove protruding parts (52) of the insulating layers (Cl to Cn).

9. Transformer according to claim 7, characterized in that a top (42) of the secondary winding (3a) is oriented towards the insulating ring (23a).

10. Transformer according to claim 1, characterized in that the coil body (5) is made of polypropylene.

11. Transformer according to claim 1, characterized in that at least one insulating ring (23a) is made of prolypolylene.

12. Transformer according to claim 1, characterized in that the magnetic circuit (1) is cut into two parts (la, lb) along a plane perpendicular to the longitudinal axis (2), the two parts (la, lb) being joined together after assembly of the coil body (5) equipped with at least one secondary winding (3a) and at least one insulating ring (23a).

13. Transformer according to claim 2, characterized in that the coil body (5) is common to all the secondary windings (3a, 3b).

14. Transformer according to claim 1, characterized in that the two sections (7a, 7b) are interchangeable.