EP3437111A1

EP3437111A1 - Electrical transformer with windings

Info

Publication number: EP3437111A1
Application number: EP17712527.5A
Authority: EP
Inventors: Sébastien FONTAINE; Daniel Sadarnac; Charif KARIMI
Original assignee: Safran Electronics and Defense SAS
Current assignee: Safran Electronics and Defense SAS
Priority date: 2016-03-30
Filing date: 2017-03-27
Publication date: 2019-02-06
Anticipated expiration: 2037-03-27
Also published as: US20190385782A1; FR3049759A1; FR3049759B1; WO2017167699A1; US11145454B2; EP3437111B1

Abstract

The invention relates to an electrical transformer (T, T') comprising: a primary central winding (11a) extending around an axis (X) and configured to generate a central magnetic flux when a current is passed through it circulating in a first direction around the axis (X), two peripheral primary windings (12a, 13a) extending around the axis (X), between which the central primary winding (11a) is located, and configured to generate peripheral magnetic fluxes when currents are passed through same respectively circulating in a second direction around the axis (X) which is opposite to the first direction, the peripheral magnetic fluxes superimposing on the central magnetic flux, wherein the windings are further configured in such a way that the peripheral magnetic fluxes compensate the central magnetic flux in the regions located beyond the peripheral windings.

Description

Electric transformer with windings

FIELD OF THE INVENTION

The invention relates to a winding electric transformer.

STATE OF THE ART

Electrical transformers comprising two parts in which power must be transmitted from one of the two parts to the other part are known from the state of the art.

For this purpose, a known transformer comprises at least two windings: a primary winding, generally connected to a power supply, and a secondary winding generally connected to a "load" that it supplies with energy drawn from the source.

FIGS. 1a and 1b illustrate two conventional electrical transformers, in which the primary winding P comprises 7 turns extending about an axis X, and the secondary winding S comprises n ₂ turns extending around 1 X axis and around the turns.

In such transformers, energy is transmitted from the primary winding P to the secondary winding S via a "magnetic flux" radiated by the primary winding P and partly received by the secondary winding S. A magnetic circuit M, consisting of a material with high magnetic permeability such as ferrite, is used to channel this magnetic flux and thus improve the coupling between the windings. The magnetic circuit M of the transformer of FIG. 1a has a disc-shaped section in a plane transverse to the axis X, whereas that of the transformer of FIG. 1b has an annular section in such a plane.

The windings P and S are traversed by currents i and i ₂ as shown in FIG. When the permeability of the magnetic circuit M is sufficient, the "ampere x turns" of the primary winding and the secondary winding are then almost identical, as illustrated by the following formula:

nor it 'n2 i2

However, the magnetic circuit weighs down the electrical transformer.

Moreover, in some electrical transformers, it is desirable that the power is transmitted from one part to the other without contact between the two parts. This is particularly the case of so-called "rotating" or "rotary" transformers, which are characterized by primary and secondary windings movable relative to each other. An example of a known rotating transformer is shown in Figure 2a. Figure 2b illustrates an unconventional transformer that could be theoretically considered in a process of lightening and simplification of the geometry of the parts. These transformers comprise an "air gap" e, namely a space formed in the magnetic circuit so that one winding can rotate relative to the other. Connecting wires turn in this space e if the two parts of the magnetic circuit are fixed (only one winding rotates). This space corresponds to the necessary mechanical clearance if the two parts of the magnetic circuit are each fixed to a winding (a winding then rotates with a part of the magnetic circuit). However, because of the presence of the air gap e, the magnetic flux between the two windings P and S is less well channeled. This results in a not insignificant difference between the "amps x turns" of the primary winding and the secondary winding:

neither he ≠ n2 i2

This difference occurs in the magnetic environment of the system. It is possible to rewrite the previous relation by defining the "magnetizing current" iml seen by the primary winding:

neither he = n2 i2 + nor iml

A conventional magnetic circuit M is not a linear system. However, given the gaps e, it is possible to consider the overall system as almost linear, which allows to use the superposition theorem: the magnetic environment can be considered as the sum of the two radiations emitted by the windings in the two configurations:

• 1 configuration ^era: we have "x amps towers" identical nor it i2 = n2 (imposed by the load)

· ^2nd configuration: only the winding is powered by the magnetizing current: ni il = ni iml (computable from the voltage imposed by the source).

In one configuration ^age, the effects of the two windings P, S compensate around the system. All the magnetic flux is practically contained in the system. Magnetic leakage to the outside of the transformer is limited. Figure 3 illustrates this compensation effect. The left part of Figure 3 shows a single conductor in space, rectilinear and infinite length: the induction lines are circular with an induction that decreases inversely proportional to the radial distance to the conductor. The central part of FIG. 3 shows the association of two such conductors, arranged in parallel and traversed by currents of opposite directions. Their effects are superimposed on the right side of Figure 3: induction is reinforced between drivers as it decreases very rapidly towards the outside, as one moves away from the drivers. Magnetic circuit portions placed around the conductors are sufficient in this 1 ^st configuration to channel these low external leakage fluxes.

Figures 4a and 4b show the magnetic flux generated by the transformers of Figures 2a and 2b in the 2 ^nd configuration (the only current imposed on the transformer is the magnetizing current in the primary winding). In this 2 ^nd configuration, there is no more compensation effect. Magnetic leakage propagates to the outside of these transformers, the leakage being all the more important as the air gaps e are wide.

Figure 5 details the profile of the induction obtained along the line D of the transformer of Figure 4b for a given magnetizing current imposed on the primary winding. This figure shows the presence of magnetic leaks outside the transformer. Inside the transformer, the induction profile is computable simply by approximating the internal induction lines to parallel lines: the 2 lines drawn in a thicker line on this figure surround part of the "amps x turns"; the induction on these two lines is proportional to these encircled "ampere x towers". The fact that the induction is not zero along the line D in regions adjacent to the transformer is the manifestation of the aforementioned magnetic leakage.

However, these magnetic leaks are likely to disrupt the operation of other components located near the transformer or outside the system in which it is implanted.

Moreover, even if the magnetic circuit M can contribute to reducing these magnetic leaks, this magnetic circuit remains an imperfect solution to remove them in the case of an electrical transformer whose two parts do not touch, such as a transformer of the rotary type, since an air gap remains.

In addition, as indicated above, the magnetic circuit weighs down the electrical transformer. SUMMARY OF THE INVENTION

An object of the invention is to reduce the magnetic disturbances generated by a transformer operating on the basis of windings, while allowing to significantly reduce this transformer.

In order to achieve this object, the invention proposes an electrical transformer comprising: A central primary winding extending around an axis and configured to generate a central magnetic flux, when it is traversed by a current rotating in a first direction about the axis,

Two peripheral primary windings extending about the axis, between which the central primary winding is located, and configured to generate peripheral magnetic fluxes when they are traversed by respective currents rotating in a second direction around the axis which is opposite to the first direction, the peripheral magnetic flux superimposed on the central magnetic flux,

In which the windings are further configured so that the peripheral magnetic fluxes compensate the central magnetic flux in regions located beyond the peripheral windings.

In the transformer thus proposed, a phenomenon of magnetic flux compensation is obtained by the addition of peripheral windings on either side of the primary winding. This compensation makes it possible to reduce or even eliminate magnetic leakage in the peripheral regions of the transformer without necessarily having to integrate a magnetic circuit that can weigh down the transformer.

The invention may also be supplemented by the following features, taken alone or in combination when technically possible.

• The primary windings are connected in series.

The central primary winding is wound around the axis in a first winding direction, and the peripheral primary windings are wound around the axis in a second direction of winding opposite the first direction of winding.

• The peripheral primary windings together have a cumulative number of turns equal to the number of turns of the central primary winding.

Each primary winding has at least one helical portion around and along the axis, the helical portions of the three primary windings extending in different ranges of respective positions along the axis.

• The transformer further comprises a magnetic circuit having two opposite ends having different longitudinal positions in a direction parallel to the axis, and the primary windings are strictly confined between and at a distance from these two longitudinal positions.

• Each primary winding has at least one spiral part wound on itself transversely to the axis, the spiral parts of the three windings primary members extending in respective ranges of annular positions with respect to the axis.

• Primary windings are coplanar.

• The transformer further comprises a magnetic circuit having two opposite ends having different radial positions in a direction perpendicular to the axis, and the primary and secondary windings are strictly confined between and at a distance from these two radial positions.

• The electrical transformer further comprises a central secondary winding configured to receive at least a portion of the central magnetic flux.

"The electrical transformer further comprises two peripheral secondary windings, between which the central secondary winding is located, each peripheral secondary winding being configured to receive at least partially one of the peripheral magnetic flux.

• The transformer comprises a primary housing to which each primary winding is fixed, and a secondary housing to which the or each secondary winding is fixed, the two housings being rotatable relative to each other relative to the axis.

• The transformer comprises a primary housing having a primary annular surface extending perpendicular to the axis, each primary winding being fixed to the primary annular surface, a secondary housing having a secondary annular surface extending perpendicular to the axis and vis-à-vis the primary annular surface, each secondary winding being fixed on the secondary annular surface so as to be facing a primary winding. DESCRIPTION OF THE FIGURES

Other features, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings in which:

• Figures 1a, 1b, 2a, 2b are sectional views of three conventional winding transformers.

• Figure 3 schematically illustrates the superposition of two magnetic flux generated by two rectilinear conductors.

• Figures 4a, 4b illustrate magnetic flux lines generated by the transformers of Figures 2a and 2b respectively. • Figure 5 comprises a sectional view of the transformer of Figure 4b in combination, and an induction profile obtained when the transformer is supplied with current.

FIG. 6 comprises a sectional view of a transformer according to a first embodiment of the invention, and an induction profile along a line D obtained when the transformer is supplied with current.

FIGS. 7a and 7b include sectional views of the transformer according to the first embodiment of the invention, and induction profiles along a line D obtained when specific and different windings of the transformer are supplied with current. .

• Figure 8 comprises a longitudinal sectional view of a transformer according to a second embodiment of the invention, and an induction profile along a line D obtained when the transformer is supplied with current.

Fig. 9 is a cross-sectional view of the transformer of Fig. 8 detailing primary windings.

• Figures 10 and 1 1 show other primary windings seen transversely.

In all the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

With reference to the left-hand part of FIG. 6, a transformer T comprises two parts: a primary part A and a secondary part B.

In the remainder of this text, an element relating to Part A will be qualified as "primary" and designated in the figures by a reference suffixed by "a"; similarly, an element relating to Part B will be described as "secondary" and designated in the figures by a reference suffixed by "b".

The primary portion A comprises three primary windings 11a, 12a, 13a and the secondary portion B comprises three secondary windings 11b, 12b, 13b.

Although it does not appear in the figures, which are only schematic, each winding mentioned in this document comprises one or more turns. A turn is defined as a winding portion extending 360 degrees about an axis in a given direction. Formally, the following defines a "winding" as a turn or a set of consecutive turns wound in the same direction. As a result, a change of direction marks a separation between two adjacent windings. The six windings 11a, 12a, 13a, 11b, 12b, 13b extend around a reference axis X.

The primary winding 11a, said central primary winding, is arranged between the primary windings 12a and 13a, said peripheral primary windings.

The primary windings 11a, 12a, 13a are intended to be connected to one or more electrical power sources (not shown in the figures). These primary windings January 1, 12a, 13a are therefore supplied with current by such electric sources.

The central primary winding 11a is configured to be traversed by a current rotating in a first direction about the axis X. The two peripheral primary windings 12a, 13a are configured to be traversed by a current rotating in a second direction around of the X axis which is opposite to the first sense. In other words, the flow directions of the current in the different primary windings are alternated.

The three primary windings 11a, 12a, 13a can be connected in series, that is to say that they form different portions of the same primary electrical conductor. In this way, the primary windings can be traversed by a current of the same intensity, for example provided by a single electrical source.

An alternation of directions of the currents flowing through the three primary windings 11a, 12a, 13a can for example be obtained by alternating the direction in which these windings 11a, 12a, 13a are wound around the axis X. The peripheral primary windings 12a, 13a are then wound around the axis X in a first direction of winding (for example hourly), and the central primary winding 11a is wound around the axis X in a second direction of winding opposite to the first direction of winding (counterclockwise). This is such as to minimize the length of conductor needed to connect the central primary winding to each of the adjacent peripheral primary windings, when these are connected in series.

In this case, the central primary winding 11a and the peripheral primary winding 12a are directly connected to one another via a junction 14a forming a hairpin: it is at this junction 14a that the winding direction about the reference axis X is reversed between the two primary windings 11a and 12a. It is the same for the junction 15a between the windings 1 1a and 13a.

The three windings can be contiguous two by two. In other words, the windings are in contact two by two (the junctions 14a and 15a can then form a simple fold). Alternatively, the three primary windings are at a distance from each other; in this case, the junction 14a passes through a space between the two windings 11a and 12a, and the junction 15a passes through a space between the two windings 11a and 13a. This space is useful (but not essential) to maximize the magnetic flux closing through the primary and secondary windings, thus to maximize the resulting magnetization inductance. Maximization of the magnetization inductance is useful (but not necessary) to minimize the no-load (no load) current of the transformer.

Moreover, the peripheral primary windings 12a, 13a of FIG. 6 comprise the same number of turns and together have a cumulative number of turns equal to the number of turns of the central primary winding 11a.

Similarly, the secondary winding 11b, said central secondary winding, is arranged between the secondary windings 12b and 13b, said peripheral secondary windings.

The secondary windings 11b, 12b, 13b are intended to be connected to one or more electrical devices to supply energy, also designated as "charges" (not shown in the figures).

The central primary winding 11a is configured to generate a central magnetic flux in cooperation with the central secondary winding 11b. The peripheral primary winding 12a (respectively 13a) is configured to generate a central magnetic flux in cooperation with the secondary winding 12b (respectively 13b).

The central secondary winding 11b is configured to be traversed by a current rotating in the second direction around the axis X (thus in a direction opposite to the direction of the current rotating in the central primary winding 1 1a with which it cooperates ). The two peripheral secondary windings 12b, 13b are configured to be traversed by a current rotating in the first direction about the axis X which is opposite to the second direction. In other words, the flow directions of the current in the different secondary windings 11b-13b are also alternated.

The three secondary windings 11b, 12b, 13b can be connected in series, that is to say that they form different portions of the same secondary electrical conductor.

Alternate sense of currents flowing through the three secondary windings

1 1 b, 12b, 13b can for example be obtained by alternating the direction in which these windings are wound around the axis X. The peripheral secondary windings 12b, 13b are then wound around the axis X in a certain sense of winding (for example counterclockwise), and the central secondary winding 11b is wound around the axis X in the other direction (for example hourly). In this case, the central secondary winding 1 1b and the peripheral secondary winding 12b are directly connected to one another, via a junction 14b forming a hairpin: it is at this junction 14b that the winding direction around the reference axis X is reversed between the two secondary windings 11b and 12b. Similarly, the central secondary winding 11b and the secondary winding 13b are directly connected to each other, via another junction 15b forming a half-turn: it is at this junction 15b that the sense of winding around the reference axis X is reversed between the two secondary windings 11b and 13b.

Furthermore, the peripheral secondary windings 12b, 13b of FIG. 6 comprise the same number of turns and together have a cumulative number of turns equal to the number of turns of the central secondary winding 11b.

There can be provided a number n of turns in the primary and secondary windings in the secondary windings, distributed as follows: n / 4 turns for each of the peripheral primary windings, n / 2 turns for the central primary winding, m / 4 turns for each of the peripheral secondary windings and m / 2 turns for the central secondary winding. For example, we can have n = m or n different from m (in which case the transformer will have a transformation ratio different from 1).

In a particularly advantageous application, the transformer is of rotary type, in that the primary windings 11a, 12a, 13a are rotatable about the X axis relative to the secondary windings 11b, 12b, 13b (or Conversely).

The primary part A of the transformer is for example a stator comprising a primary casing 2a extending around the reference axis X. The primary casing 2a has a generally annular shape, for example cylindrical and / or of revolution.

The abutment B is furthermore a rotor rotating about the reference axis

X with respect to the stator A. The rotor B comprises a secondary casing 2b having a generally annular shape, for example cylindrical and / or of revolution.

The secondary casing 2b is inside the primary casing 2a, or vice versa. In the figures, the casing closest to the X axis is hollow; it is understood that this housing can alternatively be full.

The primary windings are fixed to the stator A, and the secondary windings are fixed to the rotor B.

In what follows, will be detailed two different embodiments each comprising the characteristics discussed above. Embodiment with "cylindrical" windings

The left part of FIG. 6 schematically illustrates an embodiment of transformer T, called a "cylindrical" winding, in which each winding extends in volume around and along the axis X. More precisely, each winding comprises a succession of turns located at different positions along the reference axis X (for better readability, there is shown in Figure 6 only one turn of each primary winding).

The primary conductor in which the primary windings are formed is wound along a substantially helical path around and along the X axis, and occupies a generally annular volume centered on the reference axis X. The primary windings are wound at a first radial distance from the reference axis X.

In this embodiment, the junction 14a between the peripheral primary winding 12a and the central primary winding 11a is a portion of the primary conductor which is confined between the two windings 11a, 12a in a direction parallel to the axis. X. The same is true for the junction 15a which connects the primary windings 11a and 13a.

The foregoing features also apply to the secondary conductor, in which the secondary windings 11b, 12b, 13b and the junctions 14b-15b are formed. This secondary conductor is wound in a substantially helical path around and along the axis X, and occupies a generally annular volume centered on the reference axis X. The secondary windings January 1, b, 12b, 13b are wound to a second radial distance from the reference axis X, different from the first radial distance.

For example, the secondary windings 11b, 12b, 13b are wound around the primary windings 11a, 12a, 13a with respect to the axis X, or vice versa. More specifically, each secondary winding is wound around a primary winding, and facing it.

The "cylindrical" winding transformer T may be of rotary type. The windings radially further from the axis X can then be fixed to the outer annular casing 2b, and the windings radially closer to the X axis be fixed to the inner annular casing 2a as shown in FIG. 6, the two housings being movable. in rotation with respect to each other.

When the primary windings 11a, 12a, 13a are supplied with current, it is possible, as a first approximation, to consider that each of these windings creates a magnetic flux, all three flows superimposed to form the overall flow. resulting. This is how the induction lines in the left part of Figure 6 and the induction pattern in the right part can be traced.

The left part of FIG. 6 shows the induction lines which result from the magnetizing current flowing in the primary conductor in the cylindrical winding transformer T, and the right part of FIG. 6 shows the induction profile measured along the a line D parallel to the axis X and located between the annular structure formed by the primary windings and the annular structure formed by the secondary windings.

There are three regions of space: a central region centered at the center windings 11a and 11b, containing a segment D0 of the line D, and two peripheral regions containing the two remaining half-lines of the line D.

In the central region, energy is transferred from the primary windings to the secondary windings.

The central secondary winding 1 1 b receives at least in part the central magnetic flux generated by the central primary winding 1 1 a, the secondary peripheral winding 12b (respectively 13b) receives the peripheral magnetic flux generated by the peripheral primary winding 12a (respectively 13a).

A voltage is generated in the secondary windings connected to the load or loads used. The central secondary winding 1 1 b is then traversed by a current rotating in a third direction about the axis X, and the two peripheral secondary windings 12b, 13b are traversed by a current rotating in a fourth direction about the axis X who is opposed to the third sense. In other words, the flow directions of the current in the different secondary windings 11b, 12b, 13b are alternated as is the case for the primary conductors 11a, 12a, 13a. Whatever the type of load, in the peripheral regions, the peripheral magnetic flux generated by the primary peripheral windings 12a, 13a, compensate for the effects of the central magnetic flux generated by the primary central winding 11a. By way of example, the induction is in particular zero along the two half-lines of the line D starting from the two opposite ends of the segment DO. Equipment located in these peripheral regions, and in particular located along the line D or the X axis, are thus very effectively protected against radiation emitted by the windings of the transformer, without the need for recourse a magnetic circuit weighing the transformer or complicating its shape in order to minimize the air gap discussed in the introduction.

The phenomenon of compensation of the inductions in the peripheral regions illustrated in the right part of FIG. 6 can be explained by means of FIGS. 7a and 7b. The Figure 7a shows the central magnetic induction obtained in the transformer T when power is supplied to the central primary winding January 1 (the peripheral primary windings 12a, 13a, located on either side, being disconnected). FIG. 7b shows the magnetic inductions obtained in the transformer T when the primary primary windings 12a, 13a are supplied with current only (the central primary winding 11a being disconnected). By superimposing the magnetic inductions shown in FIGS. 7a and 7b, the compensation phenomenon illustrated on the right-hand part of FIG. 6 in the aforementioned peripheral regions occurs.

It will be understood that the compensation phenomenon is not limited to the line D but is generalizable outside a ball. Compensation occurs at every point of the space farther from this center of the radius of the ball, in all directions of space. The center of the ball is the intersection between the X axis and a plane intersecting the central conductors 11a, 11b in the particular embodiment in FIG. 6.

Thanks to this compensation phenomenon, magnetic leaks are thus avoided in the peripheral regions without having to resort absolutely to a magnetic circuit. However, even if this is no longer absolutely necessary, the transformer T may comprise such a magnetic circuit. The magnetic circuit is for example made of mu-metal (single sheet or stacked sheets (laminating)) or ferrite. In Figures 6, 7a and 7b, the magnetic circuit is formed by the casings 2a and 2b.

The magnetic circuit has two opposite ends having different positions along the X axis. Preferably, the primary and secondary windings are confined strictly between these two positions.

In other words, the magnetic circuit extends beyond the peripheral windings in a direction parallel to the X axis. This makes it possible to improve the coupling between the windings of the transformer T.

"Planar" embodiment

Figure 8 schematically illustrates a transformer T 'according to another embodiment, said "planar".

This embodiment differs from the cylindrical winding embodiment in that the windings are arranged differently.

In this embodiment, each winding comprises at least one spiral portion arranged transversely to the axis X, that is to say that each winding comprises several spirals wound around each other transversely to the axis X. The two ends of the spiral portion thus have different radial positions with respect to the X axis.

It is understood that a given winding may consist of a single spiral with several turns wound around each other, or may comprise several spiral parts stacked on each other in a direction of stacking parallel to the axis. X, each spiral portion comprising a plurality of turns wrapped around the others.

In what follows, we will consider a particularly simple but non-limiting embodiment in which each winding has a planar spiral shape extending perpendicular to the X axis.

The primary windings 11a, 12a, 13a are coplanar. The secondary windings 11b, 12b, 13b are also coplanar.

Each primary winding 11a, 12a, 13a is located in an annular sector around the axis X which is specific to it, the annular sectors being located in ranges of different radial positions with respect to the reference axis X.

The transformer T 'may further comprise a magnetic circuit. The magnetic circuit is for example made of mu-metal (single sheet or stacked sheets (laminating)) or ferrite. The magnetic circuit is for example formed by the casings 2a and 2b.

With reference to FIG. 9 (in a plane perpendicular to the X axis), the peripheral primary winding 13a is located in an outer annular sector, and the central primary winding 11a is located in an intermediate annular sector, closer of the reference axis X as the outer annular sector, and the peripheral primary winding 12a is located in an inner annular sector, closer to the X axis than the intermediate annular sector.

In this embodiment, the junction 14a between the primary winding 11a and the primary winding 12a is a portion of the primary hairpin conductor. This portion 14a may be rectilinear or curved (for example U-shaped). It is the same for the junction 15a which connects the primary windings 11a and 13a.

The three annular sectors can be contiguous two by two. In other words, the windings are in contact two by two (the junctions 14a and 15a can then form a simple fold).

Alternatively, the three primary windings are at a distance from each other; in this case, the junction 14a passes through an annular space between the two windings 11a and 12a, and the junction 15a passes through an annular space between the two windings 1 1a and In the pancake embodiment, one way of optimizing the compensation phenomenon is to provide for the two annular spaces crossed by the junctions 14a and 15a to be of approximately the same area in a plane perpendicular to the X axis.

The primary windings 11a, 12a, 13a can be made on a plate-shaped washer (or "slab") centered on the axis X. The plate is for example made of an electrically insulating material such as the epoxy.

All the above is equally applicable to secondary windings 11b, 12b, 13b (replacing "a" with "b" in the references mentioned in the foregoing paragraphs referring to Figure 8).

Each secondary winding 11b, 12b, 13b is arranged opposite a primary winding 11a, 12a, 13a, in a direction parallel to the axis X.

The transformer according to the "pancake" embodiment can also be of the rotary type.

The two housings 2a, 2b have two annular surfaces 22a, 22b facing each other, which extend in two parallel planes offset from one another along the reference axis X .

The primary windings 11a, 12a, 13a are fixed to the annular surface 22a of the primary casing 2a, and the secondary windings 11b, 12b, 13b are fixed to the annular surface 22b of the secondary casing 2b, facing each other. . Each primary winding faces a secondary winding, regardless of the angular position of the rotor when it rotates relative to the stator around the reference axis X.

The phenomenon of induction compensation, already described for the "cylindrical" winding transformer T, also occurs in the planar transformer T ', when the primary windings 11a, 12a, 13a are supplied with current. By way of example, an induction profile is shown in FIG. 8 along a straight line D extending radially (perpendicularly) to the axis X.

Compensation can be optimized by dissymmetrizing certain parameters related to peripheral windings (number of turns, dimensions, spacing ...) because these peripheral windings are by nature asymmetrical (the average radii are different).

In this embodiment, the central region is located between two concentric spheres: a first sphere and a second sphere surrounding the first sphere. Peripheral regions where induction is canceled include: A ball-shaped region centered on the X axis and delimited by the first sphere,

An outer region farther from the X axis than the windings (thus of infinite dimensions and going towards the outside of the transformer), which is delimited internally by the second sphere.

This embodiment is particularly advantageous when equipment sensitive to magnetic radiation must be arranged along the reference axis X, in the ball-shaped region.

The transformer T 'may further comprise a magnetic circuit. The magnetic circuit is for example formed by the housings 2a, 2b which extend radially with respect to the axis X.

The magnetic circuit has two opposite ends having different radial positions with respect to the axis X. Preferably, the primary and secondary windings occupy a space whose ends are strictly confined between and at a distance from these two radial positions. In other words, the magnetic circuit extends beyond the peripheral windings in a direction radial to the X axis. This makes it possible to improve the coupling between the windings of the transformer T '.

In addition, the planar spiral shape of the windings results in different sections offered to the passage of the magnetic flux through the turns. This results in a differential flow which closes outside the transformer T '.

A first option to improve the reduction of magnetic leaks is to opt for a number of turns different from the distribution n / 4, n / 2 and n / 4, between the inner side and the outer side (see Figure 10) , so that the peripheral inductions exactly compensate the central induction.

Another option is to space the windings differently, according to Figure 1 1.

The invention is not limited to the embodiments that have just been described. In particular :

• The transformer is not necessarily of rotary type (in other words, parts A and B are not necessarily mobile with each other, but can be fixed relative to each other).

• Positioning of the stator and rotor can be reversed.

• Each winding can be supplied with current independently of the other windings. The winding direction of the turns of the primary windings around the X axis is not necessarily alternated. In order to obtain the desired induction compensation phenomenon, it suffices for the currents flowing in the peripheral primary windings to be opposite to the current flowing in the central primary winding. It is the same for secondary windings.

Two adjacent windings (primary or secondary) are connected to each other by two immediately adjacent extreme turns, thereby reducing the length of the junction between two windings adjacent to a single hairpin. Alternatively, more complex junctions between two adjacent windings may be provided.

Claims

An electrical transformer (T, T ') comprising:

A central primary winding (11a) extending around an axis (X) and configured to generate a central magnetic flux, when traversed by a current rotating in a first direction about the axis (X) ,

characterized by :

Two peripheral primary windings (12a, 13a) extending around the axis (X), between which the primary primary winding (11 a) is located, and configured to generate peripheral magnetic fluxes when they are traversed by respective currents rotating in a second direction around the axis (X) which is opposite to the first direction, the peripheral magnetic flux superimposed on the central magnetic flux,

wherein the windings are further configured such that the peripheral magnetic fluxes compensate the central magnetic flux in regions located beyond the peripheral windings.

2. Transformer (T, T ') according to the preceding claim, wherein the primary windings (11a, 12a, 13a) are connected in series.

3. Transformer (T, T ') according to one of the preceding claims, wherein:

The central primary winding (1 1 a) is wound around the axis (X) in a first winding direction,

The peripheral primary windings (12a, 13a) are wound around the axis (X) in a second direction of winding opposite to the first direction of winding.

4. Transformer (T, T ') according to one of the preceding claims, wherein the peripheral primary windings (12a, 13a) together have a cumulative number of turns equal to the number of turns of the central primary winding (11 a) .

5. Transformer (T) according to one of the preceding claims, wherein each primary winding has at least a helical portion around and along the axis (X), the helical portions of the three primary windings extending in ranges respective different positions along the axis (X).

6. Transformer (T) according to the preceding claim, further comprising a magnetic circuit having two opposite ends having different longitudinal positions in a direction parallel to the axis (X), and wherein the primary windings are strictly confined between and to distance of these two longitudinal positions.

7. Transformer (Τ ') according to one of claims 1 to 4, wherein each primary winding has at least a spiral portion wound on itself transversely to the axis (X), the spiral parts of the three windings. primary members extending in respective ranges of annular positions with respect to the axis (X).

8. Transformer (Τ ') according to the preceding claim, wherein the primary windings (11a, 12a, 13a) are coplanar.

9. Transformer (Τ ') according to one of claims 7 to 8, further comprising a magnetic circuit having two opposite ends having different radial positions in a direction perpendicular to the axis (X), and wherein the primary windings. and secondary are strictly confined between and at a distance from these two radial positions.

Electrical transformer (T, T ') according to one of the preceding claims, further comprising:

A central secondary winding (1 1b) configured to receive at least part of the central magnetic flux.

1 1. Electrical transformer (T, T ') according to the preceding claim, further comprising:

Two peripheral secondary windings (12b, 13b), between which the central secondary winding (12b) is located, each peripheral secondary winding being configured to receive at least partially one of the peripheral magnetic fluxes.

12. Transformer (T, T ') according to one of claims 10 to 1 1, comprising a primary housing (2a) to which each primary winding (11a, 12a, 13a) is fixed, and a secondary housing (2b). to which the or each secondary winding (11b, 12b, 13b) is fixed, the two housings (2a, 2b) being movable in rotation with respect to each other with respect to the axis (X).

13. Transformer (Τ ') according to one of claims 10 to 12, comprising:

A primary casing (2a) having a primary annular surface (22a) extending perpendicularly to the axis (X), each primary winding (11a, 12a) being fixed on the primary annular surface,

A secondary casing (2b) having a secondary annular surface (22b) extending perpendicularly to the axis (X) and facing the primary annular surface (22a), each secondary winding (1 1 b, 12b) being fixed on the secondary annular surface so as to face a primary winding.