EP2422580B1 - Heating device with a power inductor, power inductor and oven with such an equipment - Google Patents

Description

• une alimentation électrique à haute fréquence.
• un inducteur de puissance pour chauffer un élément,
• et un montage capacitif dans le circuit de l'inducteur.

The invention relates to an induction heating device of the kind comprising:

• a high frequency power supply.
• a power inductor for heating an element,
• and a capacitive circuit in the inductor circuit.

By the term "high frequency" is meant a frequency equal to or greater than 5 kilohertz (kHz) and which can reach 1 megahertz (1 MHz) or more. By the expression "power inductor" is meant an inductor crossed by a current whose intensity is at least 100 amperes.

• séchage de produits de revêtement divers (peinture, revêtement organique notamment antifinger, etc.) ;
• traitement thermique
• chauffage avant traitement: (recuit,...)
• amélioration de la productivité de four conventionnel.

The invention relates in particular, but not exclusively, to the induction heating of any electrically conductive product on the run for various applications such as:

• drying of various coating products (paint, organic coating including antifinger, etc.);
• heat treatment
• heating before treatment: (annealing, ...)
• Improvement of conventional oven productivity.

High frequency induction heating is efficient, but the overall energy efficiency is affected by the energy efficiency of the inductor because an electric power is dissipated as heat in the inductor. The inductor, in the following description, is of the longitudinal flow type, but it can also be of the transverse flow type, in particular for heating non-magnetic parts or of particular geometry.

EP 0 577 468 proposes an electromagnetic induction heating coil comprising a particular cooling device for the conductors of the coil. This solution is interesting for frequencies below 10 kHz, but the efficiency decreases significantly at higher frequencies.

WO 2007/141 422 discloses an induction heating device having a high frequency power supply which makes it possible to transfer high power through the inductor while reducing the construction difficulties created by the electrical voltages, in particular at the inductor connections and the inductors. capacitors. For such a heating device, it is also desirable to improve the energy efficiency.

JP 10-50217 A relates to a field different from that of the invention since it is a method of manufacturing a deflector armature to deflect an electron beam in a cathode ray tube. Litz wires are provided in two rows to facilitate welding. There is no question of induction heating.

The object of the invention is, above all, to provide a high-frequency induction heating device in which the heating losses of the inductor are reduced.

EP 1 604 551 proposes a setting in series and parallel of monospires which could be advantageously be used for the connection of the turns (mono or multispires) made from cables of Litz.

The invention aims in particular to limit the energy losses, including losses due to the current path in the inductor, as well as the connection losses at the capacitors and those due to the current path in the capacitors.

• une alimentation électrique à haute fréquence,
• un inducteur de puissance pour chauffer un élément induit,
• et un montage capacitif dans le circuit de l'inducteur,

est caractérisé en ce que l'inducteur comprend au moins un câble à brins multiples isolés entre eux, appelé communément câble de Litz, et les brins du câble, à leur extrémité de raccordement sont déployés en éventail pour être raccordés en parallèle à une barre métallique formant borne d'alimentation électrique,
le diamètre d'un brin de câble étant choisi de telle sorte qu'il permet de s'affranchir des pertes par courants de Foucault haute fréquence générés par les conducteurs voisins, le nombre de brins ou fils en parallèle dans un câble étant suffisamment élevé pour permettre le passage de l'intensité correspondant à la puissance élevée de chauffage.According to the invention, an induction heating device comprising:

• a high frequency power supply,
• a power inductor for heating an induced element,
• and a capacitive circuit in the circuit of the inductor,

characterized in that the inductor comprises at least one multi-strand cable insulated from each other, commonly referred to as a Litz cable, and the strands of the cable at their connecting end are fan-shaped to be connected in parallel to a metal bar. forming a power supply terminal,
the diameter of a cable strand being chosen such that it makes it possible to overcome the high frequency eddy current losses generated by the adjacent conductors, the number of strands or wires in parallel in a cable being sufficiently high to allow the passage of the intensity corresponding to the high heating power.

The intensity of the current, for the heating power, can reach several hundred to several thousands of amperes. To give an order of magnitude, non-limiting, the diameter of a strand of the cable may be 0.1 mm for a frequency of 50 kHz.

Advantageously, the development of the drivers back and forth is provided vis-à-vis.

The strands of the cable may be surrounded, or not, by an electrically insulating envelope.

The ends of the cable ends can be connected by welding on the bar, or other mode of connection such as crimping, or superimposed ends.

Advantageously, the length of the metal bar is at least five times the diameter of the cable, preferably greater than ten times the diameter of the cable.

Depending on the number of strands of the cable, the fan may concern subgroups of strands. In addition, several parallel fan plies can be provided. The plies of fan blades are connected flat against the bar. Advantageously, the thickness of the plies or subgroups of strands is less than the penetration depth of the high frequency current in the power supply terminal bar.

Each fan ply of cable strands for the connection preferably has a mean plane passing through or near the geometric axis of the end of the cable. The fan is deployed on either side of the extension of the axis of the end of the cable.

The angle formed between the strands constituting the extreme edges of the fan and the geometric axis of the end of the cable can reach, or even exceed, 60 °.

Preferably, the power supply terminal of a range of strands is connected, on the side opposite the fan, to at least one capacitor frame.

In the case of a scroll heating with longitudinal flow, the average plane of the connection fan may be orthogonal to the direction of travel of the element to be heated; alternatively, this plane can be inclined in this direction.

The average plane of the fan would be vertical for a band to be heated moving horizontally.

In the case of an inductor whose cable is helically wound in several turns (multispire inductor), the connection range can be placed in a plane passing through the axis of the flow.

More generally, when the heating device comprises an inductor whose cable is helically wound in several turns (multispire inductor), the number of turns free from any orientation constraints of the fan.

For longitudinal flow heating, the inductor comprises one or more turns. The turns can be electrically connected in series or in parallel. The winding (s) surround the element to be heated, thus taking the form of a profile of the element to be heated, in particular the shape of a frame when the element to be heated is of flat shape or the shape of a circle when the element to be heated is cylindrical, or any shape adapted to the profile of the element to be heated.

The inductor may be formed of a single cable, or may comprise at least two cables or groups of multiplet strand cables insulated from each other, connected to capacitor plates at their ends, forming a parallel oscillating circuit. The power supply for maintaining the oscillation of the circuit will be placed in parallel with the capacitor or capacitors, or one of the capacitors Alternatively, the power supply can be connected in series, being interposed between the inductor and the capacitor. one of the capacitors directly or through a transformer, the inductor then being mounted in a series oscillating circuit. The accompanying drawings only describe the case of the parallel oscillating circuit but the duality of the series circuit can be envisaged.

It will sometimes be necessary to realize the capacitor by putting in series of elementary capacitors. It will then be advantageous to distribute the capacitors all along the turn, as shown by WO 2007/141 422 .

According to one variant, the inductor may comprise four groups of cables forming a quadrilateral surrounding the element to be heated and connected at their ends, forming the vertices of the quadrilateral, to four armatures or groups of capacitor plates.

The inductor may comprise several turns orthogonal to the geometric axis of the inductor, and juxtaposed according to a stack. Advantageously, means for compensating the inductance of the end turns are provided to prevent overheating of these turns.

These compensation means may comprise additional turns adjacent to the end turn, of increasing diameter, located in a plane orthogonal to the axis of the inductor, or whose centers of the sections are arranged in a curve away from the axis of the inductor.

According to another possibility, the compensation means comprise at least one current transformer, or mediating or compensating inductor or current balancing, connected between the end turn and at least one other internal turn, in particular the penultimate adjacent turn or any other internal turn, to balance the intensity of the currents between the end turn and the other internal turn, the intensity through the end turn being reduced while that of the other internal turn is increased . It is possible to add a larger number of transformers in order to balance the current in several turns near the ends of the inductor. The number of current transformers can reach the number of turns.

A multi-strand cable insulated from one another may comprise at least one cooling device, in particular constituted by a flexible conduit, made of a non-electrically conductive material, in particular a plastic material, for the passage of a cooling fluid, the strands being wrapped or braided around the flexible conduit

The cooling device may further comprise a sheath surrounding the cable, in which a cooling fluid passes, in particular air or water or any coolant.

The heating device may comprise a capacitor, or a capacitor bank, connected between the terminals of the power supply, and N distinct elementary inductive parts, connected together in series by N-1 capacitors or capacitor banks of connection.

The range of strands or subgroups of strands can be curved. The power supply terminal can be curved

The heating device may comprise monospires or multispires which are connected singly or in groups in series, or in parallel.

The invention also relates to a power inductor, for heating an induced element, having the characteristics listed above.

The invention also relates to a heating furnace for electrically conductive element characterized in that it comprises an induction heating device as defined above.

• Fig. 1 est une coupe verticale, transversale, schématique d'un dispositif de chauffage selon l'invention.
• Fig. 2 est un schéma électrique du dispositif de Fig. 1.
• Fig. 3 est une vue partielle en élévation verticale, à plus grande échelle, de l'extrémité droite de raccordement du dispositif de Fig. 1.
• Fig. 4 est une vue de dessus, à plus grande échelle, de l'extrémité droite du dispositif de Fig. 1.
• Fig. 5 est un schéma en perspective d'un inducteur multispire avec éventail des brins dans un plan passant par l'axe du flux magnétique.
• Fig. 6 montre, semblablement à Fig.5, un inducteur multispire avec éventail des brins dans un plan perpendiculaire à l'axe du flux magnétique.
• Fig. 7 est une vue partielle à plus grande échelle selon la flèche VII de Fig.6 des barres de raccordement des brins des éventails.
• Fig. 8 est un schéma en coupe verticale d'un dispositif de refroidissement extérieur de conducteurs de l'inducteur
• Fig. 9 est une coupe verticale transversale illustrant, à plus grande échelle que sur Fig. 8, le dispositif de refroidissement avec regroupement de quatre câbles dans une gaine.
• Fig 10 est une coupe schématique verticale axiale de l'extrémité d'un inducteur avec spires supplémentaires déviatrices.
• Fig. 11 montre, semblablement à Fig. 10, une variante de réalisation des spires supplémentaires déviatrices.
• Fig. 12 est un schéma électrique d'un moyen de compensation de l'inductance plus faible des spires d'extrémité, avec un transformateur de courant.
• Fig. 13 est un schéma électrique, en élévation verticale, d'un inducteur à spires concentriques.
• Fig. 14 est une coupe schématique suivant la ligne XIV-XIV de Fig. 13.
• Fig. 15 est une vue schématique en élévation verticale d'un conducteur avec spires permutées par quatre.
• Fig. 16 est une vue schématique suivant la ligne XVI-XVI de Fig. 15.
• Fig. 17 est une vue schématique en élévation verticale d'un inducteur constitué de quatre parties inductives élémentaires, formant un quadrilatère, reliées entre elles à leurs sommets par des batteries de condensateurs, et
• Fig. 18 est un schéma électrique équivalent de l'inducteur de Fig. 17.

The invention consists, apart from the arrangements set out above, in a certain number of other arrangements which will be more explicitly discussed below with reference to exemplary embodiments described with reference to the appended drawings, but which are not in no way limiting. On these drawings:

• Fig. 1 is a vertical cross section, schematic of a heating device according to the invention.
• Fig. 2 is a circuit diagram of the device Fig. 1 .
• Fig. 3 is a partial view in vertical elevation, on a larger scale, of the straight end of the connection of the Fig. 1 .
• Fig. 4 is a view from above, on a larger scale, of the right end of the Fig. 1 .
• Fig. 5 is a perspective diagram of a multispire inductor with a range of strands in a plane passing through the axis of the magnetic flux.
• Fig. 6 shows, similarly to Fig.5 , a multispire inductor with a range of strands in a plane perpendicular to the axis of the magnetic flux.
• Fig. 7 is a partial view on a larger scale according to arrow VII of Fig.6 connecting rods of the fans strands.
• Fig. 8 is a vertical sectional diagram of an external cooling device of inductor conductors
• Fig. 9 is a transverse vertical section illustrating, on a larger scale than on Fig. 8 , the cooling device with grouping of four cables in a sheath.
• Fig 10 is an axial vertical schematic section of the end of an inductor with additional deviating turns.
• Fig. 11 shows, similarly to Fig. 10 , an alternative embodiment of the deviating additional turns.
• Fig. 12 is a circuit diagram of a means of compensation of the lower inductance of the end turns, with a current transformer.
• Fig. 13 is an electrical diagram, in vertical elevation, of an inductor with concentric turns.
• Fig. 14 is a schematic section along line XIV-XIV of Fig. 13 .
• Fig. 15 is a schematic view in vertical elevation of a conductor with turns permuted by four.
• Fig. 16 is a schematic view along line XVI-XVI of Fig. 15 .
• Fig. 17 is a diagrammatic view in vertical elevation of an inductor consisting of four elementary inductive elements, forming a quadrilateral, interconnected at their vertices by capacitor banks, and
• Fig. 18 is an equivalent electrical diagram of the inductor of Fig. 17 .

Referring to the drawings, particularly Fig. 1, 3 and 4 , there can be seen an induction heating device 1 having a high frequency power supply with frequency converter 2. The frequency is greater than 5 kHz and can exceed 400 kHz.

The device 1 comprises a power inductor 3 adapted to heat an induced element 4. In the example shown, the inductor 3 comprises turns surrounding the induced element 4 which scrolls horizontally inside the coils of the inductor 3 , in a direction orthogonal to the plane of Fig.1 . The inductor 3 can be formed by a juxtaposition or stack of monospires each located in a vertical plane orthogonal to the direction of movement of the element 4. The turns are connected in parallel. The inductor 3 provides longitudinal flow heating. The induced element 4 is constituted in particular by a metal strip, in particular a steel strip.

This example is not limiting. The heating device could be of the transverse flux type, in which case the mean plane of the turns of the inductor would be substantially parallel to the plane of the induced element so that the electromagnetic field created is substantially orthogonal to the plane of the induced element.

The turns of the power inductor are traversed by a current whose intensity is generally at least 100 A. The power of the inductor 3 normally leads to consider its realization with at least one conductor of large cross section.

On the contrary, according to the invention, despite such power involved, the inductor 3 is made with cables Litz 5a, 5b strands 6 multiple insulated between them, usually by a varnish. The individual diameter of the strands 6 is sufficiently small so that it makes it possible to overcome the skin effect due to the high frequency of the current. The diameter of a conducting strand is in particular of the order 0.1 mm (1/10 ^th of a millimeter) for a frequency of 50 kHz.

The number of strands 6 is a function of the total current flowing through the turns of the inductor 3. The strands or wires 6 are fed in parallel. They are grouped generally in the form of a twisted or braided cable. The strands may be surrounded by an envelope sheath 7 of insulating material, but such an envelope is not essential. Due to the high intensity required by a power inductor, the number of wires or strands 6 of a cable can be many thousands or tens of thousands.

According to the example of Fig. 1 where the element to be heated is flat to rectangular section, the cables 5a, 5b form a substantially rectangular frame surrounding the armature element 4. Alternatively, this frame could be formed with a single cable bent to the desired contour. Each cable has a substantially horizontal central portion held by supports 8 of insulating material. The ends of the conductors 5a, 5b are curved towards the horizontal plane containing the band 4 and their end is curved substantially in the plane of this band. The ends of the cable 5a have been designated 5a1 and 5a2. The cable 5b is preferably offset in a direction orthogonal to the plane of the strip.

At the ends of the cables, the conductive wires 6 are disengaged from the possible sheath 7 over a length sufficient to allow the multitude of wires 6 to expand into a fan for connection to a metal bar elongate.

For the cable 5a, the fans 9.1, 9.2 at each of its ends constitute plies whose average plane is vertical, orthogonal to the direction of movement of the strip 4. Depending on the number of bundled cables, several parallel fan plies can be formed. .

The opening of the fan 9.1, 9.2 is such that sufficient space exists between the wires released from their envelope 7 to reduce the effects of parasitic inductance. The fan 9.1, 9.2 is preferably spread on either side of the geometric axis XX ( Fig. 3 ) of the cable end concerned. The opening of the fan is advantageously such that the strands or son 6 at the limit of the fan form with the axis XX an angle α that can wait or exceed 60 °. The ends of the strands 6 are released from their insulating varnish and are connected in parallel to the metal bar 10.1 or 10.2 by welding, in particular tin welding. It is essential to ensure the development of the conductors back and forth in order to ensure a minimum inductance and a good current distribution in the strands, it is possible to maintain a section of passage of the current to about constant, a constant current density.

The bars 10.1, 10.2 form with a metal bar 11 a single piece or possibly two associated parts. The assembly is held by bars 12 of insulating material, which are not represented on Fig. 4 .

As is the cable 5a. the cable 5b comprises at each end at least one fan ply 9.1b formed of strands connected in parallel, by welding, to a metal bar 10.1b ( Fig.4 ) for fan 9.1b, while the bar and fan on the other end are not visible in the drawings.

On the opposite side to the cables 5a. 5b, the bars 10.1, 10.1b (see Fig. 4 ) are electrically connected to the armatures 13.1, 13.1b of capacitor C1, these armatures being separated by a dielectric insulation layer 14, in particular a layer of air.

According to the example of Fig. 4 four turns are juxtaposed and connected to four capacitors or capacitor banks C1, C1.1, C1.2, C1.3.

Each cable 5a, 5b comprises a cooling device comprising at least one duct 15a, 15b of insulating material, in particular of plastic, traversed by a cooling fluid, in particular water or air. Preferably, the strands 6 are wound helically or braided around the conduit 15a or 15b which extends along the geometric axis of the cable considered.

At the level of the range of wires released from their possible envelope 7, as visible on Fig. 3 , the flexible cooling duct 15a is disengaged from the fan and connected by a connector 16 to a fluid circuit that can be provided in the bar 11. Another end of the bar is provided with a connection 17 for feeding or the evacuation of the cooling fluid.

As visible on Fig. 3 several plate-shaped capacitor plates may be connected in parallel to the corresponding metal bar 10.1. Four armatures 13.11, 13.12, 13.13 and 13.14 are provided according to the variant of Fig. 3 , to which correspond four other frames vis-à-vis, connected to the cable 5b.

Sure Fig. 4 it appears that the cooling device comprises a pipe 15c, 15d, brazed on a bar 10.1, 10.1b or on the bar 11. Alternatively, instead of the pipes 15c, 15d, the cooling device comprises at least one drilled conduit in the metal of the bar 11. The cooling pipes 15a, 15b of the cable are of flexible material insulating electricity. The pipes 15c, 15d of the bars 10.1, 10.1b are made of copper or brass or any other good heat conducting metal. The fixing of the capacitor plates 13.1, 13.1b on the bars 10.1, 10.1b can be carried out using horizontal screws 18.1, 18.1b passing through the plates 13.1, 13.1b to the bars 10.1, 10.1b where they are screwed . Other conventional fasteners may be used.

Fig.5 shows an inductor formed by an insulated multi-strand cable 5 wound helically along a plurality of turns to form a multispire having a certain extent along the YY axis of the magnetic flux. It is then possible to place the fan 6 in a plane passing through the axis YY, or parallel to this axis. without creating a congestion problem. Indeed, the range 6 is included, or substantially included, between the two end planes of the multispire orthogonal to the axis YY.

However, as shown on Fig.6 , it is also possible to place the fan 6 of a multispire in a plane perpendicular to the axis YY, or inclined on this axis.

The length H ( Fig.7 ) of the metal rod 10.1, 10.1b, forming a connection terminal, is equal to at least five times the diameter of the cable 5, 5a, 5b and preferably greater than ten times the diameter of the cable. By way of non-limiting example, the height H may be of the order of 400 mm, while the diameter of the cable is of the order of 30 mm. Depending on the number of strands of the cable, several parallel fan plies can be provided. The strands of strands or subgroups of fan-shaped strands are soldered flat against bar 10.1, 10.1b. Advantageously, the thickness Ep of the superposed layers is less than, or of the same order as, the penetration depth P of the high frequency current in the power supply terminal bar. By way of non-limiting example, the penetration depth P may be of the order of 0.1 mm to 0.5 mm, depending on the frequency and the metal used.

The solution of the invention makes it possible to obtain a low current density up to the capacitors by the arrangement of the fan-shaped strands, and this independently of the type of cooling of the cable.

The fan-shaped connection of the wires 6 to the bars or terminals 10.1, 10.1b makes it possible to greatly limit the connection losses at the capacitors C1 ... C1.3, and in the current path in the capacitors.

As visible on Fig. 1 the cable 5a at its left end 5a2 is connected in the same manner as on the right end by a fan 9.2 of wires to a bar 10.2. It is the same for the cable 5b with another bar not visible. On the opposite side to the fan 9.2, capacitor plates 13.31, 13.32, 13.33 are connected to the bar 10.2. The flexible cooling ducts 15a, 15b are connected to the circuit located in the bar 11, itself connected to collectors G of cooling fluid.

The scheme of Fig. 2 shows the electric circuit realized with the inductor 3 of Fig 1 . The same references have been used to designate symbolic representations of inductances and capacitances. It appears that the generator 2 is connected to the terminals of the capacitor C1 and that from one terminal of this capacitor to the other are connected in series the inductance formed by the conductor 5a, the capacitor C2 situated at the opposite end of the conductors 5a and 5b and the inductance formed by the conductor 5b.

This montage conforms to the teaching of WO 2007/141422 allows to increase the operating voltage of the inductor.

Fig. 8 illustrates another cooling device cables 5a, 5b which are surrounded by an electrically insulating sheath 19a, 19b, for example silicone tube, defining an annular passage around the cables 5a, 5b. An inlet 20a, 20b for the cooling fluid is provided, substantially mid-length of the ducts, which open towards the bent end of the driver, before reaching the fan 9.1 or 9.2. Cooling gas, in particular air is blown through the inlets 20a, 20b and is distributed on both sides to cool the outside cables 5a, 5b.

Fig. 9 shows in cross-section two electrically insulating tube sheaths 19a1, 19b1 in which four cables are grouped together 5a, 5b. Each sheath has its inlet 20a1, 20b1 for the cooling fluid.

The cooling fluid could be constituted by a liquid, in particular by water, in which case a collector would be provided to collect the cooling water in the vicinity of each end near the fan 9.1, 9.2.

The provision of Fig. 9 , grouping several cables in the same sheath makes it possible to reduce the number of forced ventilation ducts. It is possible to group the cables by four especially if you work with a double pitch at the capacitors.

Several individual or monospiral turns ( Fig.10 ), each formed by cables 5a and 5b, may be provided coaxial, orthogonal to the axis of the inductor, juxtaposed parallel to the direction of movement of the element to be heated. A turn such as 21 ( Fig. 10 ) located in the stack thus formed is between two other turns which contribute to increase the inductance, or self, of the turn 21. An end turn such as 22, located at the right end according to Fig. 10 , has a turn adjacent to one side, so that the inductance of the coil 22 will be lower than that of the inner turns. This end turn 22 will then be traversed by a current of greater intensity, generating overheating, when the turns are connected in parallel.

To prevent this overheating, as shown on Fig. 10 a compensating means formed, in the mean plane of the turn 22, by at least one turn 23, of greater diameter, surrounding the turn 22. The turn 23 has a stronger inductance, and its proximity effect increases. the inductance of the turn 22. It is possible to add a new turn 24 of greater diameter than the turn 23, and so on, until the inductance or self of the end turn 22 is equal to or substantially equal to that of an internal turn such as 21.

Fig. 11 shows an alternative embodiment of the compensation means to prevent overheating of the end turn 22. Additional turns 25, 26, 27, 28 of larger diameter, following the end turn 22, are arranged such that so that the centers of their sections are on an arc of curve 29 convex outwardly connecting to the straight line 30 of alignment of the centers of the sections of the inner turns. The diameter of the turns 25-28 increases gradually

Fig. 12 illustrates another embodiment of the compensation means to prevent overheating of the end turn 22.

The inductor turns, schematically represented on Fig. 12 , are monospires connected in parallel between two supply lines E1, E2 under the voltage U. The inner turns such as 21 have a self L. To prevent overheating of the end turn 22, there is at least one transformer of intensity 31 between a strand of the turn 22 and at least one internal turn, in particular the turn 32 close to 22. The compensating inductor can be connected to any of the poles of the turn, the important is that the ampere-turns generated by one of the turns neutralizes those of the other turn. The two windings of the transformer 31 are subjected to opposite voltages + U and -U.

The intensity transformer 31 ensures a decrease in the intensity in the end turn 22 and an increase in the intensity in the inner turn 32, so as to balance the currents in the two turns 22 and 32, and to bring back the intensity passing through these turns to a value close to the intensity passing through the internal turns such as 21.

Fig. 13 and 14 schematically illustrate a double-layer inductor with concentric turns. The patterns of Fig. 13 and 14 show internal turns formed by cables 3.11 ... 3.n1 and 3.12 ... 3.n2 located in the same vertical plane orthogonal to the direction of movement of the element 4 to be heated. The conductors of each turn are connected, at their ends, respectively to the plates of the capacitors C1, C2 in a manner similar to the diagrams of FIG. Fig.1 and 2 Generator 2 is connected across capacitor C1. Concentric outer turns are made with conductors 103.11 ... 103.n1 on one side of the plane of the element 4 and 103.12 ... 103.n2 on the other side of the plane of the element 4, these turns being connected in parallel with the plates of the capacitors C1 and C2 as illustrated on Fig. 13 .

The inner turns, formed by the conductors such as 3.11-3.12, have an inductance L1 lower than the inductance L2 of the outer turns formed by conductors such as 103.11-103.12. The intensity I1 of the current flowing through the inner turns is therefore greater than that of the current flowing through the outer turns.

The doubling of the conductor layers illustrated on Fig. 14 allows to increase the ampere-turns, so the magnetic field.

Fig. 15 and 16 show a variant according to which the turns are exchanged in pairs or multiples, here advantageously four to balance the inductance values of the different turns as well as the currents. Strands of four cables are formed ( Fig. 16 ) and twisted, for example 180 °, from a capacitor C1 to capacitor C2 so that the two cables 3.11-3.21 which are in the inner layer at the connection to the capacitor C1 are in the outer layer at the connection to the capacitor C2, and vice versa for the cables 103.11 and 103.12 of the group of four cables. The inductances of each turn formed of four cables are then equal, as are the currents.

The cables grouped by four also make it possible to obtain a lateral permutation in the end turns and to promote the balancing of the currents in these end turns.

Fig. 17 shows an embodiment according to which the inductor comprises four cables or groups of cables 5a, 5b, 5c, 5d forming a quadrilateral, substantially in the shape of a rectangle, surrounding the element to be heated 4. The wires released at each end of the conductors are deployed and fan-connected to a metal bar connected on the other side to one or more capacitor plates C1-C4.

For example, the ends of the cable 5a are connected by bundles of fan wires 9.a1, 9.a2 to bars 10ad and 10ac. The latter is connected to a power supply terminal of source 2. Another bar (not visible on Fig. 17 ) is located behind the bar 10ac and is connected to the range of wires 9c1 of the driver 5c. In contrast to the fans, the bars are connected to the plates of the capacitor C1. It is the same for the other summits of the quadrilateral.

The connecting bars 10ac, 10ad, 10bd, 10cb are inclined with respect to the mean plane of the element to be heated 4, and are substantially orthogonal to the bisector of the angles at the vertices of the quadrilateral, which makes it possible to minimize the radii of curvature of the cables. However, the inclination of the connecting bars may be different, the bars may even be vertical or horizontal.

The ends of the cables 5a-5d are curved concavely outwards. The outer curvature of the cables, designated 33 for the left end of the cable 5a, is provided to reduce the number of bends, as well as the space to be magnetized.

The montage illustrated on Fig. 17 is schematized on Fig. 18 . This is a montage "quadruple". Such an arrangement makes it possible to mount at high voltages, at high frequencies.

Whatever the embodiment adopted, the high-frequency power inductors, according to the invention, in multi-strand cables insulated from each other, make it possible to obtain a high efficiency. The connection of the wires at their ends is designed to limit as much as possible the connection losses at level of the capacitors, as well as the current path in the capacitors.

Claims (22)

1. An induction heating device comprising:

   - a high-frequency electric power supply (2),

   - a power inductor for heating an induced element (4),

   - and a capacitive mounting in the inductor circuit,

   characterized in that the inductor (3) comprises at least one cable (5a, 5b) with multiple strands insulated from one another, and the strands (6) of the cable, at their connection end, are fanned out (9.1, 9.2) to be connected in parallel to a metal bar (10.1, 10.1b, 10.2) forming an electric power supply terminal,
   the diameter of a cable strand being chosen such that it makes it possible to overcome the high-frequency eddy current losses generated by the adjacent conductors, the number of strands or wires in parallel in a cable being high enough to allow for the flow of the current intensity corresponding to the high heating power.
2. The device as claimed in claim 1, characterized in that the go and return conducters are spread out facing one another.
3. The device as claimed in claim 1 or 2, characterized in that the ends of the strands (6) are connected by welding to the bar (10.1, 10.2; 10.1b).
4. The device as claimed in any one of the preceding claims, characterized in that the length (H) of the metal bar (10.1, 10.1b, 10.2) is equal to at least five times the diameter of the cable (5, 5a, 5b).
5. The device as claimed in any one of the preceding claims, characterized in that a number of parallel fanned-out sheets (9.1) are provided, connected flat against the bar (10.1).
6. The device as claimed in claim 5, characterized in that the thickness (Ep) of the sheets is less than, or of the same order as, the depth of penetration (P) of the high-frequency current into the bar (10.1) forming a power supply terminal.
7. The device as claimed in any one of the preceding claims, characterized in that each fanned-out sheet (9.1, 9.2; 9.1b) accepts a median plane passing through, or in the vicinity of, the geometrical axis (X-X) of the end of the cable.
8. The device as claimed in any one of the preceding claims, characterized in that the angle (α) formed between the strands (6) constituting the extreme edges of the fan (9.1, 9.2; 9.1b) and the geometrical axis (X-X) of the end of the cable reaches, or exceeds, 60°.
9. The device as claimed in any one of the preceding claims, characterized in that the electric power supply terminal (10.1, 10.1b, 10.2) of a fan of strands (9.1, 9.1b, 9.2) is linked, on the side opposite the fan, to at least one capacitor foil (13.1, 13.1b).
10. The device as claimed in any one of the preceding claims, characterized in that it comprises an inductor, the cable (5) of which is helically wound in a number of turns (multiple-turn inductor), the number of turns obviating any constraint on the orientation of the fan (9.1, 9.1b).
11. The device as claimed in any one of the preceding claims, characterized in that the inductor comprises four groups of cables (5a, 5b, 5c, 5d) forming a quadrilateral surrounding the element to be heated (4) and linked at their ends, forming the vertices of the quadrilateral, to four foils or groups of foils of capacitors (C1, C2, C3, C4).
12. The device as claimed in any one of the preceding claims, in which the inductor comprises a number of turns orthogonal to the geometrical axis of the inductor, and juxtaposed in a stack, characterized in that means (23, 24; 25-28; 31) for compensating the inductance of the end turns (22) are provided to avoid an overheating of these turns.
13. The device as claimed in claim 12, characterized in that the compensation means comprise additional turns (23, 24; 25-28) adjacent to the end turn (22), of increasing diameter, situated in a plane orthogonal to the axis of the inductor, or the centers of the sections of which are arranged in a curve (29) moving away from the axis of the inductor.
14. The device as claimed in claim 12, characterized in that the compensation means comprise a current transformer (31) connected between the end turn (22) and at least one other inner turn (32) to balance the intensity of the currents between the end turn and the other inner turn.
15. The device as claimed in any one of the preceding claims, characterized in that a cable (5a) with multiple strands insulated from one another includes at least one cooling device comprising a flexible duct (15a) made of a material that does not conduct electricity, allowing for the flow of a coolant, the strands being helically wound or braided around the flexible duct (15a).
16. The device as claimed in any one of the preceding claims, characterized in that a cable (5a, 5b) with multiple strands insulated from one another includes at least one cooling device comprising a sheath (19a, 19b) surrounding the cable, in which flows a coolant.
17. The device as claimed in any one of the preceding claims, characterized in that it includes a capacitor (C1), or bank of capacitors, connected between the terminals of the electrical power supply, and N distinct individual inductive parts, linked together in series by N-1 linking capacitors or banks of capacitors.
18. The device as claimed in any one of the preceding claims, characterized in that the fan of the strands or subgroups of strands is curved.
19. The device as claimed in any one of the preceding claims, characterized in that the electric power supply terminal is curved.
20. The device as claimed in any one of the preceding claims, characterized in that it includes single turns or multiple turns which are connected individually or by groups in series, or in parallel.
21. A power inductor, for heating an induced element, characterized in that it comprises at least one cable (5a, 5b), with multiple strands insulated from one another, and the strands, at their connection end, are fanned out (9.1, 9.2; 9.1b) to be connected in parallel to a metal bar (10.1, 10.2; 10.1b) forming an electric power supply terminal,
    the diameter of a cable strand being chosen such that it makes it possible to overcome the high-frequency eddy current losses generated by the adjacent conductors, the number of strands or wires in parallel in a cable being high enough to allow for the flow of the current intensity corresponding to the high heating power.
22. An induction heating oven including a heating device as claimed in any one of claims 1 to 20.

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