EP3945533A1 - Inductive filtering device with limitation of heating - Google Patents

Abstract

The invention relates to an inductive filtering device comprising:
- a magnetic core (12)
- at least one electric cable (14) wound around the magnetic core (12) forming at least one turn, the electric cable (14) being intended to convey an electric signal having at least one undesirable alternating component superimposed on a fundamental frequency electrical signal and
- an electrically conductive screen (20), electrically insulated from the electric cable (14) and from the magnetic core (12),
the screen (20) being arranged between the magnetic core (12) and the electric cable (14) so as to allow the generation in the screen (20), by electromagnetic induction, of a current whose frequency is greater than the fundamental frequency,
the screen (20) being configured so as not to allow the flow of a current in a direction parallel to that of the turn or turns formed by the winding of the electric cable (14) around the magnetic core.

Description

The invention relates to an inductive filtering device. This type of filtering is commonly used in order to reduce any disturbances present on a signal conveyed on an electric cable. The device is then placed in series on the cable. The invention finds particular utility in the aeronautical field where the current trend is to increase the number of electrical equipment items and therefore the number of filtering devices associated with the equipment items. In this field, on-board mass reduction is a recurring problem that arises. The invention proposes to reduce the mass of the filtering devices.

Conventionally, a filtering device can be formed by an inductance connected in series on an electrical conductor. The value of the impedance of an inductor is proportional to the frequency of the current flowing through it. An inductor is therefore well suited to filtering the high frequency components of the current flowing in the electrical conductor.

The inductor can be made by means of an electrical conductor wound around a magnetic core making it possible to channel the magnetic flux induced by the current flowing in the electrical conductor. In order to optimize the circulation of the magnetic flux, it is possible to implement a closed magnetic core without air gap. This type of core is called by many manufacturers: "ring core". It is formed around a central recess. The torus qualification for the magnetic core goes far beyond the mathematical definition of a torus. There are in particular so-called toroidal magnetic cores with a circular or rectangular section, etc. The inductance is made by winding an electrical conductor around the magnetic core by crossing the central recess in order to form one or more turns.

The applicant has found that during the filtering of harmonics from a current whose fundamental component is at low frequency, the harmonics and more generally the high frequency components, being superimposed on the fundamental component of the current, generate significant induced electric currents in the magnetic core. Indeed, although the materials of the magnetic cores are chosen for their magnetic properties, in particular for their permeability, they are also conductors of electricity. This electrical property allows the generation of induced currents. The higher the frequency of the current flowing in the conductor, the higher the induced current.

These high currents circulate exclusively in the magnetic core without leaving it and generate heating by the Joule effect. However, the more the temperature of a core increases, the more the magnetic permeability of the material of the core decreases, which leads to a drop in the value of the inductance and consequently an increase in the current flowing in the conductor, in particular for its high-voltage components. frequency. This increase in current generates a stronger induced current and therefore greater heating. The applicant has even observed in certain cases a thermal runaway which can lead to the destruction of the magnetic core.

To limit the heating of the magnetic circuits, it would be possible to implement magnetic cores made from materials having a higher electrical resistivity. However, their magnetic characteristics are much worse than those of conventional magnetic cores.

The evacuation of the heat produced in the magnetic core can be done by increasing the volume of the magnetic core in order to increase its contact surface with the ambient air. It is also possible to provide a heat sink fixed to the core. Whatever the solution chosen to evacuate the heat, cala leads to an increase in mass and volume of the inductance.

A first object of the invention is to reduce the mass and the volume of an inductor implementing a magnetic core. This object is achieved by limiting the appearance of high frequency current in the magnetic core around which the conductor of the inductor is surrounded.

To limit the appearance of high frequency current in the magnetic core, a conductive screen is arranged between the conductor of the inductance and the magnetic core. This screen has the function of moving the generation of looped induced currents from the magnetic core to the screen. The induced currents are opposite to those flowing in the conductor. Thus the magnetic core is subjected to two opposing currents, which tends to reduce the magnetic flux and therefore the induced currents that can circulate in the magnetic core. In other words, the presence of the screen makes it possible to very clearly reduce the appearance of induced currents in the magnetic core and therefore its heating.

• un noyau magnétique
• au moins un câble électrique enroulé autour du noyau magnétique en formant au moins une spire, le câble électrique étant destiné à véhiculer un signal électrique possédant au moins une composante alternative indésirable se superposant à une fréquence fondamentale du signal électrique et
• un écran électriquement conducteur, isolé électriquement de son environnement, l'écran étant disposé entre le noyau magnétique et le câble électrique de façon à permettre la génération dans l'écran, par induction électromagnétique, d'un courant dont la fréquence est supérieure à la fréquence fondamentale,
  l'écran étant configuré de façon à ne pas permettre le circulation d'un courant dans une direction parallèle à celle de la ou des spires formées par l'enroulement du câble électrique autour du noyau magnétique.

More specifically, the subject of the invention is an inductive filtering device comprising:

• a magnetic core
• at least one electric cable wound around the magnetic core forming at least one turn, the electric cable being intended to convey an electric signal having at least one undesirable alternating component superimposed on a fundamental frequency of the electric signal and
• an electrically conductive screen, electrically isolated from its environment, the screen being arranged between the magnetic core and the electric cable so as to allow the generation in the screen, by electromagnetic induction, of a current whose frequency is higher than the fundamental frequency,
  the screen being configured so as not to allow the flow of a current in a direction parallel to that of the turn or turns formed by the winding of the electric cable around the magnetic core.

When the device is intended to filter a given frequency, the screen advantageously has a thickness at least equal to δ = (p/π.f.µ) ^1/2 with ρ: the resistivity, and µ: the absolute magnetic permeability of the material chosen to make the screen.

In a first embodiment of an inductive filtering device according to the invention, the electric cable extends along an axis and the screen is arranged around the electric cable in a coaxial manner.

In this first mode, the magnetic core can be of cylindrical shape extending around an axis, the screen advantageously protrudes from the magnetic core beyond the turn or turns formed around the magnetic core. The protrusion is advantageously at least equal to a characteristic external dimension of the magnetic core.

The cable can be wound several times around the magnetic core by forming several turns around the magnetic core.

In a second embodiment of an inductive filtering device according to the invention, the screen is arranged on at least one face of the magnetic core.

In the second mode, the screen can comprise several parts, each part being arranged so as to cover one of the faces of the magnetic core.

In the second mode, the screen can comprise two shells fitting one inside the other.

The magnetic core may have a central recess and the electrical cable may be wound around the magnetic core passing through the central recess.

• [Fig. 1] la figure 1 représente une première variante d'enroulement d'un câble d'un premier mode de réalisation de l'invention ;
• [Fig. 2] la figure 2 représente une seconde variante d'enroulement du câble du premier mode de réalisation de l'invention ;
• [Fig. 3] la figure 3 représente un second mode de réalisation de l'invention ;
• [Fig. 4] la figure 4 représente un noyau magnétique et un écran mis en œuvre dans une variante du second mode de réalisation de l'invention ;
• [Fig. 5] la figure 5 représente le premier mode de réalisation adapté à une variante de noyau magnétique ;
• [Fig. 6] la figure 6 représente le second mode de réalisation adapté à la variante de noyau magnétique de la figure 5.

The invention will be better understood and other advantages will appear on reading the detailed description of several embodiments given by way of example, description illustrated by the attached drawing in which:

• [ Fig. 1 ] the figure 1 shows a first winding variant of a cable of a first embodiment of the invention;
• [ Fig. 2 ] the figure 2 represents a second variant of winding of the cable of the first embodiment of the invention;
• [ Fig. 3 ] the picture 3 represents a second embodiment of the invention;
• [ Fig. 4 ] the figure 4 represents a magnetic core and a screen implemented in a variant of the second embodiment of the invention;
• [ Fig. 5 ] the figure 5 represents the first embodiment adapted to a variant of a magnetic core;
• [ Fig. 6 ] the figure 6 represents the second embodiment adapted to the magnetic core variant of the figure 5 .

For the sake of clarity, the same elements will bear the same references in the various figures.

The figure 1 shows an inductive filtering device 10 comprising a magnetic core 12 and an electric cable 14. In other words, the inductive filtering device 10 forms an inductance. The magnetic core 12 is formed around a central recess 16. The magnetic core 12 is tubular in shape extending around an axis 18. The central recess 16 develops around the axis 18. The magnetic core 12 is closed and for example without air gap. On the figure 1 , the magnetic core 12 has a circular cross-section perpendicular to the axis 18. Other cross-sections are possible within the scope of the invention, for example a rectangular, triangular cross-section, etc. The circular cross-section is well suited to the passage of an electric cable 14 also of circular cross-section passing through the central recess only once. The cable 14 extends along an axis 19. In the case of a single passage, the axes, 18 of the magnetic core 12 and 19 of the cable 14, are substantially coincident except for functional play between the cable 14 and the central recess 16. As will be seen below, the electric cable 14 can pass through the central recess 16 several times. It may then be advantageous to arrange the various passages in the central recess 16 to occupy a section different from a circular section. The shape of magnetic core 12 may also be guided by the environment of device 10. It may be easier to store a device 10 whose magnetic core 12 is rectangular in section.

This type of closed magnetic core without an air gap is usually called "toroidal" by many manufacturers. This qualifier goes far beyond the shape of a torus as defined mathematically. There are in particular so-called toroidal magnetic cores with a circular or rectangular section, etc. The absence of an air gap makes it possible to keep the magnetic field developing in the magnetic core 12 only in the material of the magnetic core without being disturbed by an air gap.

According to the invention, the device 10 comprises an electrically conductive screen 20, arranged between the magnetic core 12 and the electric cable 14. The screen 20 is electrically insulated from the electric cable 14 and from the magnetic core 12. In the embodiment represented on the figure 1 , the screen 20 is arranged around the electrical cable 14. The screen 20 is coaxial with the cable 14. An electrical insulator 22 is arranged between the cable 14 and the screen 20. The insulator 22 may be an outer sheath of cable 14. Another electrical insulator 24 is disposed between screen 20 and magnetic core 12. In the embodiment shown in figure 1 , the insulator 24 covers the screen 20. Alternatively, the insulator 24 can cover the magnetic core 12 and in particular the internal face of the central recess 16.

The arrangement of the screen 20 between the cable 14 and the magnetic core 12 allows the circulation of currents in the screen 20. These currents are generated by electromagnetic induction formed by the current circulating in the cable 14.

Device 10 allows inductive filtering of a current flowing in cable 14. This current can be noisy. More precisely, the current circulating in the cable 14 comprises a fundamental frequency and higher frequencies whose amplitude it is sought to reduce by means of the device 10. In the case of a direct current circulating in the cable 14, the fundamental frequency is zero. The higher frequencies are formed of any alternating components superimposed on the direct current component or on the alternating fundamental component in the case of an alternating current flowing in the cable 14. These alternating frequency components higher than the fundamental frequency can be due to the production of direct current by means of a rectifier. Indeed, we find, superimposed on the direct current, traces of frequencies present upstream of the rectifier. The undesirable alternating components can also be due to current rejections emitted by the loads supplied by the cable 14 or to electromagnetic disturbances which the cable 14 can undergo. In the screen 20, one is mainly interested in the generation of currents induced by the undesirable alternating components of the current flowing in the cable 14.

It is possible to adapt the thickness of the screen 20 to the frequencies which it is desired to filter. These frequencies can be well beyond the fundamental frequency. In general, in a solid conductor, the high frequency currents essentially circulate in the skin of the conductor. Therefore, to effectively filter a given frequency and the higher frequencies, the thickness δ of the screen 20 must have at least the thickness of the skin in which the current flows at the given frequency. Below this thickness, the filtering of the given frequency remains, but with less efficiency. He is possible to take a safety margin in determining the thickness δ of the screen 20 by choosing a thickness at least equal to two or three times the thickness of the skin in which the current flows at the given frequency. The skin thickness is given by the following formula: $$\mathrm{\delta }={\left(\mathrm{\rho }/\mathrm{\pi }\mathrm{.}\mathrm{f}\mathrm{.}\mathrm{\mu }\right)}^{\mathrm{1}/\mathrm{2}}$$

with ρ: the resistivity, and µ the absolute magnetic permeability of the material chosen to produce the screen 20.

Along the axis 19 of the cable 14, the screen 20 has a finite length L along the axis 19 of the cable 14, advantageously greater than the length I of the magnetic core 12 along its axis 18. The fact that the length L of the screen 20 is finished makes it possible to avoid the circulation in the screen 20 of current in a direction parallel to the axis 19 of the cable 14. Such currents are not desirable because they would oppose the passage of the fundamental frequency in the cable 14 forming a transformer. In practice, the passage of the cable 14 through the central recess 16 is assimilated to a turn surrounding the magnetic core 2. More precisely, when a current flows in the cable 14, the latter forms a closed circuit with at least a generator and a load. This closed circuit forms a turn around a section of the magnetic core 12, a section formed in a plane containing the axis 18. Furthermore, the circulation of a current in the screen 20 parallel to the axis 19 of the cable 14 would form in the same way another turn around a section of the magnetic core 12. The turn of the cable 12 and that of the screen would then form the transformer mentioned above, a transformer which it is desirable to avoid.

It is possible to fix the potential of the screen 20 by electrically connecting it, for example, to an electrical ground of the equipment in which the device 10 is installed. This connection must be made at a single point of the screen 20 in order to avoid creation by the screen 20 of a turn around the magnetic core. Alternatively, to simplify the production of device 10, screen 20 can be electrically insulated from its environment, ie screen 20 has no electrical connection. The potential of screen 20 is left floating. Internal tests have shown that this complete electrical isolation allows the screen to fulfill its main function of limiting the heating of the magnetic core 12. In other words, when the device is in operation, the screen 20 is electrically connected neither to the magnetic core 12, nor to the cable 14, nor to any source of potential of the equipment to which the device belongs.

The screen 20 surrounding the cable 14, currents rotating around the axis of the cable can develop there. Such currents are in particular induced by the undesirable alternating components of the current flowing in the cable 14.

The material forming the magnetic core 12 having electrical conduction properties, in the absence of screen 20, the undesirable alternating components induce, in the magnetic core 12, currents rotating around the central recess 16. The presence of the screen 20 in which rotating currents induced by the undesirable AC components flowing in the cable 14 develop makes it possible to attenuate the rotating currents in the magnetic core 12. Indeed, the magnetic core is subjected by induction to rotating currents in the cable 14 and to opposite currents rotating in the screen 20. This opposition of the currents rotating in the cable 14 and in the screen 20 makes it possible to limit the generation of currents induced in the magnetic core 12, which makes it possible to limit its heating by Joule effect.

The picture 2 represents a variant of the embodiment of the device 10 represented in the figure 1 . The picture 2 represents an inductive filtering device 30, also forming an inductor and in which we find the magnetic core 12, the cable 14 and the screen 20. Unlike the device 10, the cable 14 of the device 30 passes through the recess twice central 16 by forming a second turn 32 around the magnetic core 12. In the context of the invention, it is of course possible to make as many turns 32 as necessary to ensure the desired filtering. The axis 19 of the cable 14 follows the shape of the turn 32 and the screen 20 here remains coaxial with the cable 14. In other words, the screen 20 follows the axis 19 of the cable 14. The axes 18 and 19 are not confused. As in the variant of figure 1 , the screen 20 of the device 30 does not form a turn around the magnetic core 12. The electrical insulator 24 is of interest here to avoid short circuits between the turns formed by the screen 20 around the magnetic core. Indeed, such short-circuits would cause rotating currents parallel to the current circulating in the cable 14.

The screen 20 has a length L defined along the axis 19 of the cable 14. The screen 20 protrudes from the magnetic core 12 on either side of the passage of the cable 14 through the central recess 16. internal tests have shown that to obtain optimal filtering efficiency, it is advantageous for the screen 20 to protrude on each side of the magnetic core 12 along the axis 18. An optimal protrusion is at least equal to a characteristic external dimension of the magnetic core 12 perpendicular to its axis 18. For example for a cylindrical magnetic core 12, the overhang is at least equal to the outer diameter φ of the magnetic core 12, as shown in the figure 1 . With such an overrun, there is virtually no induction between the cable 14 and the magnetic core 12. With a magnetic core of tubular shape and with a square or rectangular section, the characteristic dimension is for example the diagonal of the section square or rectangular. More generally, an optimum overshoot is at least equal to a characteristic largest outer dimension of the magnetic core.

As before, in the variant of the figure 2 , the potential of the screen 20 can be fixed by connecting it electrically, for example to an electrical ground of the equipment in which the device 30 is installed. This connection is made at a single point of the screen 20 in order to avoid creation by the screen 20 of a coil around the magnetic core 12.

The screen 20 can be made by means of a strip or a metal braid, for example of copper or aluminum alloy surrounding the cable 14. Any other electrically conductive material can of course be implemented. It is possible to implement a metallized plastic film. The actual plastic film fulfills the function of the insulator 24 and the metallization that of the screen 20.

The picture 3 represents a second embodiment of an inductive filtering device 40 in accordance with the invention. In this embodiment, we find the magnetic core 12 as well as the cable 14 and its insulator 22. On the picture 3 , the cable 14 forms a turn 32 around the magnetic core 12. The second embodiment can be implemented with as many turns 32 as necessary or even without coil 32 as in the variant of the figure 1 . The device 40 comprises a screen 42 arranged between the magnetic core 12 and the cable 14. Unlike the devices 10 and 30, the screen 42 is not arranged around the electric cable 14 in a coaxial manner. The screen 42 is arranged on at least one face of the magnetic core 12. An electrical insulator 43 is interposed between the screen 42 and the magnetic core 12. The electrical insulator 43 fulfills the function of the electrical insulator 24 present in the first embodiment. The screen 42 and the insulator 43 can be made using a metallized plastic film.

In the embodiment of the picture 3 , the screen 42 comprises two parts 42a and 42b. Part 42a is placed on an internal face 44a of magnetic core 12 and part 42b is placed on an external face 44b of magnetic core 12. Likewise, insulator 43 comprises two parts 43a and 43b. Part 43a is placed on the inner face 44a of the magnetic core 12 and part 43b is placed on the outer face 44b of the magnetic core 12. More precisely, the faces 44a and 44b are concentric with the central recess 16. The faces 44a and 44b have cylindrical sections about axis 18. Face 44a forms an inner wall of the tubular shape of magnetic core 12 and face 44b forms an outer wall of the tubular shape of magnetic core 12. When cable 14 does not crosses the central recess 16 only once, as in the variant of the figure 1 , the part 42a arranged on the internal face 42a is sufficient and it is not necessary to produce a part 42b on the external face 44b to arrange the screen between the cable 14 and the magnetic core 12. On the other hand, when the cable 14 crosses several times the central recess 16 to form one or more turns 32, the part 42b is advantageous to complete the arrangement of the screen 42 between the cable 14 and the magnetic core 12.

The magnetic core 12 comprises two faces 46 and 48 perpendicular to the axis 18. It is possible to complete the screen 42 and the insulator 43 by covering one of the faces 46 and 48 or even both. By covering one of the faces 46 or 48 the screen 42 can ensure electrical continuity between the parts 42a and 42b. If the two faces 46 and 48 are covered by the screen 42, it is important to break the electrical continuity of the screen 42 so as to avoid any possibility of current rotating in the screen 42 parallel to the turn(s) made by the cable 14 passing through the central recess 16.

The screen 42 can be made in the form of a metal braid arranged on the relevant faces of the magnetic core 12.

Fixing the potential of the screen 42 is not useful. It is therefore possible to keep the screen 42, whether it is made in a single part or in several parts 42a and 42b, to keep the screen 42 or even its various parts completely electrically isolated from their environment.

The figure 4 represents a variant of a screen adapted to the second embodiment. In order not to overload the figure 4 , only the magnetic core 12 and the screen are shown. The screen is formed of two shells 50 and 52 fitting one inside the other. The shell 50 includes a flat face 50a in contact with the face 46 of the magnetic core 12. The shell 50 also includes two cylindrical faces 50b and 50c extending along the axis 18 of the magnetic core 12. The cylindrical face 50b is in contact with the internal face 44a of the magnetic core 12 and the cylindrical face 50c is in contact with the external face 44b of the magnetic core 12. Similarly, the shell 52 comprises a planar face 52a in contact with the face 48 of the magnetic core 12. The shell 52 also comprises two cylindrical faces 52b and 52c extending along axis 18 of magnetic core 12. Cylindrical face 52b is in contact with cylindrical face 50b of shell 50 and cylindrical face 52c is in contact with cylindrical 50c of the shell 50. The shells are for example made of machined or molded metal. For each shell 50 and 52, its flat face and its cylindrical faces are electrically continuous. The shells 50 and 52 are covered with an electrical insulator at least between their faces in contact with the magnetic core 12 itself. The electrical insulator also provides insulation between the two shells 50 and 52 in order to avoid the formation of a turn around the magnetic core 12 as mentioned above. The electrical insulation can be formed from a plastic film completely or partially covering each of the shells 50 and 52.

As before, the two half-shells can be completely electrically isolated from their environment.

The figures 5 and 6 show the invention adapted to another form of magnetic core. More specifically, on the figures 5 and 6 , the magnetic core 60 has an elongated shape surrounded by the cable 14. In the example shown, the magnetic core 60 has no recess passing through it. Alternatively, it is possible to implement a magnetic core having one or more recesses, and to wind the cable 14 around this magnetic core without crossing the recess or recesses. The magnetic core 60 has a cylindrical shape with a solid and circular section extending along an axis 62. Any other cylindrical shape of magnetic core is possible, for example having a section perpendicular to the axis 62 of square or rectangular shape. The magnetic core 60 can be pierced right through along the axis 62.

On the figure 5 , we find the cable 14 of the figures 1 and 2 surrounded by the first insulator 22, the screen 20 and the second insulator 24. The cable 14 is wound around the magnetic core 60. The axis 62 forms the winding axis of the cable 14. On the figure 5 , the cable 14 is wound on two turns. It is of course possible to implement the invention regardless of the number of turns of the cable 14 around the magnetic core 60. In this configuration, the screen 20 reduces the appearance of high frequency currents in the magnetic core 60 induced by high frequency components present in the signal conveyed by the cable 14. In the example represented on the figure 5 , the screen 20 is arranged around the cable 14 coaxially all along the part of the cable 14 wound around the magnetic core 60. As before, it is advantageous for the screen 20 to be extended beyond the winding of the cable 14 around the magnetic core 60. In this embodiment, the excess of the screen beyond the winding is advantageously at least equal to the diameter φ of the magnetic core 60. The minimum excess is shown on the figure 5 .

With the magnetic core 60, it is possible to make a screen as described in the picture 3 , that is to say, disposed on at least one of the faces of the magnetic core 60. The figure 6 describes a screen 66 surrounding the cylindrical face 64 of the magnetic core 60. In order not to overload the figure, the cable 14 is not shown. It is rolled up as on the figure 5 . To avoid generating induced currents in the screen 66, the latter is interrupted substantially along a generatrix of the cylindrical shape of the magnetic core 60. The interruption can be made according to another shape, for example in a helix around the axis 62 of the magnetic core 60 or even by following a broken line. It is advantageous for the screen 66 to overlap beyond one revolution at the level of its interruption. Such a covering 68 is visible on the figure 6 . To ensure an overlap without electrical contact between the ends of the screen at its interruption, the screen 66 can be made by means of a conductive film covered on both sides with an electrical insulator. On one of the faces, the insulator ensures the insulation of the screen 66 vis-à-vis the magnetic core and on the other face vis-à-vis the screen itself at the level of the recovery and possibly vis-à-vis -cable screw 14. Here again, it is unnecessary to electrically connect the screen 66 and the electrical insulation covering it can be made in the form of a continuous film.

In the different embodiments, the cable 14 is shown with a single electrical conductor passing through the magnetic core 12. It is entirely possible to implement the invention with a cable 14 comprising several electrical conductors insulated from one another. The conductors are then intended to carry different electrical voltages, for example the positive voltage and the negative voltage of the output of a DC power supply or the phase and the neutral of a single-phase AC power supply. It is also possible to provide more than two electrical conductors grouped together in the same cable, for example to filter the different output phases of a polyphase AC power supply.

Claims (9)

Inductive filtering device comprising: - a magnetic core (12; 60) - at least one electrical cable (14) wound around the magnetic core (12; 60) forming at least one turn (32), the electrical cable (14) being intended to convey an electrical signal having at least one undesirable alternating component superimposing on a fundamental frequency of the electrical signal and - an electrically conductive screen (20; 42; 50, 52; 66), electrically isolated from its environment,
the screen (20; 42; 50, 52; 66) being arranged between the magnetic core (12; 60) and the electric cable (14) so as to allow generation in the screen (20; 42; 50, 52 ; 66), by electromagnetic induction, of a current whose frequency is higher than the fundamental frequency,
the screen (20; 42; 50, 52; 66) being configured so as not to allow the flow of a current in a direction parallel to that of the turn or turns (32) formed by the winding of the electric cable (14) around the magnetic core. Inductive filtering device according to Claim 1, the device being intended to filter a given frequency, in which the screen (20; 42; 50, 52; 66) has a thickness at least equal to δ = (p/π.f .µ) ^1/2 with ρ: the resistivity, and µ: the absolute magnetic permeability of the material chosen to produce the screen (20; 42; 50, 52; 66). Inductive filtering device according to Claim 1, in which the electric cable (14) extends along an axis (19) and in which the screen (20) is arranged around the electric cable (14) in a coaxial manner. Inductive filter device according to claim 3, in which the magnetic core (12) is of cylindrical form extending around an axis (18), in which the screen (20) protrudes from the magnetic core (12) above beyond the turn or turns formed around the magnetic core (12; 60), the excess being at least equal to a characteristic external dimension of the magnetic core (12). Inductive filter device according to one of the preceding claims, in which the cable (14) is wound several times around the magnetic core (12; 60) forming several turns (32) around the magnetic core (12; 60). Inductive filter device according to one of the preceding claims, in which the screen (42; 66) is arranged on at least one face (44a, 44b, 46, 48; 64) of the magnetic core (12; 60). Inductive filtering device according to Claim 6, in which the screen (42) comprises several parts (42a, 42b), each part being arranged so as to cover one of the faces (44a, 44b, 46, 48) of the magnetic core ( 12). Inductive filtering device according to Claim 6, in which the screen comprises two shells (50, 52) fitting one inside the other. Inductive filter device according to one of the preceding claims, in which the magnetic core (12) has a central recess (16), and in which the electric cable (14) is wound around the magnetic core (12) passing through the central recess (16).

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