JP2014175398A - High frequency transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high frequency transformer of low manufacturing cost capable of saving the labor of maintenance and inspection, by cooling heat generating primary coil and secondary coil by air-cooling.SOLUTION: A transformer body is constituted by sequentially winding a first insulating layer, a primary coil formed of a Litz wire, a second insulating layer formed of an insulating sheet having high thermal conductivity, and a secondary coil formed of a flat conductor around one core leg of a core. The transformer body is housed in a fully closed shielding container formed of a non-magnetic plate and shielded. Furthermore, outside air is fed, as cooling air, into the shielding container by means of a ventilation cooling system, and discharged from the other vent hole of the container, so that the cooling air is recirculated forcibly in the shielding container thus ventilation cooling the transformer body.

Description

  The present invention relates to a high-frequency transformer used for induction heating or the like.

  In general, in a high-frequency transformer for high-frequency induction heating, the higher the frequency, the greater the heat generated by the coil conductor due to the skin effect or the like. In order to cool the heat generated by such a coil, as shown in Patent Documents 1 and 2, at least one of the primary coil and the secondary coil is formed of a conductor having a water passage inside a conductor such as a copper pipe. A water-cooled high-frequency transformer is known in which a coil is cooled by passing cooling water through the water passage.

Japanese Patent No. 4094032 Japanese Patent No. 5057534

  However, in such a water-cooled high-frequency transformer, the cooling water is cooled through the coil conductor of the primary coil or the secondary coil. Therefore, if the quality of the cooling water is poor, the water passage of the coil is blocked or the cooling water is cooled. There is a problem that the coil is burned out or a ground fault is caused due to a decrease in water insulation performance. Also, even if high-quality water is used for the cooling water, the copper material of the coil conductor is ionized by energization and melts in the cooling water during use. Cooling water may cause deterioration of water quality and cause coil burnout. For this reason, it is important to maintain and manage the quality of the cooling water. For this reason, not only does the configuration of the cooling device of the high-frequency transformer become complicated and large, but also there is a problem that requires maintenance and inspection of the cooling device.

  Furthermore, when a pipe-shaped conductor is used as the coil conductor, if the iron core composed of the ferrite core is small and the curvature when winding is small, the hollow path serving as the cooling water flow path of the pipe conductor is prevented from being constricted. Therefore, a special manufacturing technique is required, and there is a problem that the manufacturing cost increases.

  In order to solve such a problem, the present invention provides a high-frequency transformer that can cool the heat generation of the primary coil and the secondary coil by air cooling, is low in manufacturing cost, and does not require maintenance and inspection. It is an object to do.

  In order to solve the above-described problems, the present invention provides an iron core, a first insulating layer formed by winding an insulating sheet around the core leg of the iron core, and a litz wire wound around the outer side of the first insulating layer. A primary coil formed by winding several times, a second insulating layer formed by winding an insulating sheet having a high thermal conductivity around the outer periphery of the primary coil, and a flat conductor on the outer side of the second insulating layer The transformer body is constituted by a secondary coil formed by winding so as to approach and surround the primary coil, and this transformer body is housed and shielded in a fully closed shielding container formed of a nonmagnetic flat plate. In addition, a separate vent is provided below and above the shielding container, and outside air is sucked into the shielding container as cooling air from one vent of the shielding container and discharged from the other vent of the shielding container. In this shielding container. In which characterized in that a ventilation cooling system for ventilating cooling the transformer body to compulsorily flow air.

  In the present invention, a part of the flat conductor forming the secondary coil can be brought into contact with the second insulating layer so that the primary coil can be brought closer to the secondary coil.

  The primary coil may be integrally formed by fusing the litz wire forming the primary coil to each other with an insulating fusion resin adhered to the litz wire.

  If the litz wire forming the primary coil is made by twisting a plurality of strands having a strand diameter of 0.3 mm or less, heat generation due to the skin effect can be further suppressed.

  Further, the transformer main body accommodated in the shielding container is supported between the transformer main body and the inner wall of the shielding container by supporting the four corners of the iron core with an insulating support block made of a heat-resistant insulating material. When the ventilation path is formed, the cooling effect can be further enhanced.

  According to the present invention, the skin effect of the primary coil is obtained by configuring the coil conductor forming the primary coil of the transformer main body constituted by the iron core and the primary coil wound around the iron core with the litz wire. The heat generated by the transformer can be suppressed, so that the heat generated by the transformer body can be suppressed. The transformer body with reduced heat generation is shielded by a shielding container with a vent hole and forced into the shielding container by the ventilation cooling device. Since ventilation is performed, the transformer body can be sufficiently cooled by air cooling without using water cooling. For this reason, it can be set as the high frequency transformer which is easy to handle and does not require maintenance and inspection.

BRIEF DESCRIPTION OF THE DRAWINGS It is an external appearance block diagram which shows the Example of the high frequency transformer of this invention, (a) is a perspective view, (b) is a side view. It is side surface sectional drawing which shows the Example of the high frequency transformer of this invention. It is front sectional drawing in alignment with the AA of FIG. FIG. 3 is a plan sectional view taken along line BB in FIG. 2. It is a circuit block diagram of the induction heating apparatus using a high frequency transformer. It is a figure which shows the electric circuit constant of the induction heating apparatus when not using with the high frequency transformer of this invention. It is a figure which shows the saturation temperature and temperature rise value of each part when the temperature evaluation test of the high frequency transformer of this invention is carried out. It is front sectional drawing which shows the other Example of the high frequency transformer of this invention.

  Embodiments of the present invention will be described based on examples shown in the drawings.

  1 to 4 show an embodiment of the present invention.

  The high frequency transformer 10 of the present invention has an appearance as shown in FIG.

  The shielding container 20 is composed of a rectangular parallelepiped fully closed box formed of a nonmagnetic flat plate such as an aluminum plate. The connection terminals 14c and 14d of the secondary coil 14 of the transformer are drawn out from the front wall of the shielding container 20 via the insulating bush 25 (see FIG. 4), and the connection terminals of the primary coil 13 from the back wall facing the front wall. 13c and 13d are drawn out through an insulating bush 24 (see FIG. 2). A ventilation cooling fan 30 as a ventilation cooling device is provided below the rear wall of the shielding container 20 as a ventilation cooling device that cools the inside of the container by sending outside air as cooling air from a vent (not shown) into the shielding container 20. . A grill-like air vent 22 is provided on the top wall of the shielding container 20 so as to flow through the container and discharge cooling air. At the lower end of the shielding container 20, a mounting leg 23 for mounting and fixing is provided.

  The shielding container 20 configured in this way accommodates and shields the main body 11 of the high-frequency transformer therein. The air is sent as cooling air sent by the ventilation cooling fan 30 at the lower part of the shielding container 20 accommodated in the transformer main body 11, and the inside of the transformer main body 11 is made to flow from the lower side to the upper side. Can be cooled.

  Next, the detail of the structure of the main body 11 of the high frequency transformer accommodated in the shielding container 20 is demonstrated with reference to FIGS.

  The transformer main body 11 includes an iron core 12 having three iron core legs configured by, for example, a ferrite core. The iron core 12 forms three iron core legs 12a, 12b, and 12c by joining two rectangular annular iron cores. An insulating sheet is wound around the iron core leg 12 b at the center of the iron core 12 to form the first insulating layer 15. A cylindrical primary coil 13 is formed by winding the coil conductor 13a on the outside of the insulating layer 15 and winding the coil conductor 13a a required number of times, here six times.

  The litz wire used as the coil conductor 13a of the primary coil 13 is an insulated thin wire formed by coating the surface of a thin conducting wire with an insulating enamel, and a plurality of the strands are twisted to obtain a required current capacity. It is what I did. Since the litz wire is formed by twisting thin strands, the skin effect is suppressed, so that heat generation can be suppressed even when a high-frequency current is passed. Litz wire has a higher effect of suppressing the skin effect when the wire diameter of the wire is 0.3 mm or less. Therefore, when a litz wire composed of a wire having a wire diameter of 0.3 mm or less is used, the primary coil generates heat. The suppression effect is increased.

  In addition, since the litz wire is a stranded wire, there are places where the forming is somewhat difficult, and if it is simply wound, the winding is returned, and the formed coil may be deformed. If the molded primary coil is likely to be deformed, a fusible litz wire in which an insulating resin having a fusible property is previously applied to the litz wire is used. The primary coil that is formed into a cylindrical shape by winding this fusible litz wire as a coil conductor is heat-treated, so that the coil conductor of the primary coil is fused with an insulating coating having a fusibility, and this is integrated. Can be hardened.

  Further, an insulating sheet having high thermal conductivity is wound around the outer periphery of the primary coil 13 to form the second insulating layer 6. A secondary coil 14 wound once by a flat coil conductor made of a copper flat plate or the like is disposed outside the second insulating layer 16. The secondary coil 14 includes coil conductors 14a and 14b each having a flat conductor divided into a substantially C-shaped cross section, and the two divided coil conductors are opposed to each other so that the C-shaped openings face each other. The one end side is clamped and coupled to each other by a coupling screw 14e for electrical connection, and the other end is opened to form connection terminals 14c and 14d, thereby forming a one-turn coil.

  As shown in FIG. 4, the secondary coil 14 has a second insulating layer 16 on the outer periphery of the primary coil 13 so as to approach the primary coil 3 in order to increase the degree of electromagnetic coupling with the primary coil 13. It arrange | positions so that the part 14x spaced apart so that it may become a ventilation path in order to improve the cooling effect and the part 14x which contacts.

  Thus, the transformer main body 11 is configured by winding the primary coil 13 and the secondary coil 14 on the central core leg 12b of the iron core 12 through the insulating layer. When the thus configured transformer body 11 is housed in the shielding container 10, an insulating support block 19 having an L-shaped cross section is formed between the corners of the four corners of the iron core 12 and the inner wall of the shielding container 20. By fitting, the transformer body 11 is supported away from the inner wall of the shielding container 20. Thereby, a space serving as a cooling air passage is formed between the transformer main body 11 and the inner wall of the shielding container 20.

  Thus, the transformer main body 11 is accommodated in the shielding container 20 provided with the ventilation cooling fan 30, thereby completing the high-frequency transformer 10 in which the transformer main body 11 is shielded by the shielding container 20. The high-frequency transformer according to the present invention configured as described above has an air-cooling type cooling structure, and thus has a simple structure, and uses a litz wire instead of a pipe-like conductor for the coil conductor, facilitating coil molding and manufacturing cost. Can be made inexpensive.

  During operation, the high-frequency transformer 10 of the present invention drives the ventilation cooling fan 30 and sends outside air as cooling air into the shielding container 20 through the vent 21. As shown by arrows in FIGS. 2 to 4, the cooling air fed into the container 20 flows through the container 20 from below to above and is discharged from the exhaust port 24 on the upper wall. During this time, the cooling air is a space between the iron core 12 of the transformer main body 11 and the inner wall of the container, a space 14y between the secondary coil 14 and the primary coil 13, and a space between the iron core 12 and the secondary coil 14. It flows here as a ventilation path, and the iron core 12 and the secondary coil 14 are directly cooled. Further, since the heat of the primary coil 13 is transmitted to the iron core 12 and the secondary coil 14 via the first insulating layer 15 and the second insulating layer 16, the cooling that flows in contact with the iron core 12 and the secondary coil 14. It can be cooled by air. And since cooling air flows also into the space 14y part between the secondary coil 14 and the primary coil 13 in FIG. 4, a part of primary coil 13 was comprised with the insulating sheet with high heat conductivity. The cooling air is cooled through the insulating layer 16. For this reason, the primary coil 13 and the secondary coil 14 which are energized can be cooled satisfactorily.

  Furthermore, when the shielding container 20 that shields the entire transformer main body 11 is made of an aluminum plate that is a non-magnetic material having high thermal conductivity, the container itself becomes a heat radiating body, and the ventilation cooling effect of the transformer main body can be enhanced.

  Next, an example in which the electrical characteristics of the high-frequency transformer of the present invention are set to a conversion ratio (turn ratio of primary coil to secondary coil) of 6: 1 will be described.

  FIG. 5 shows a circuit configuration of an induction heating apparatus using the high-frequency transformer 10 of the present invention.

For example, when a high-frequency current I ₁ is supplied from a high-frequency power source 40 configured by a high-frequency inverter to the induction heating device 50 via the high-frequency transformer 10, most of the magnetic flux formed by the primary coil 13 of the high-frequency transformer 10 is in the iron core 12. Magnetic flux induced and leaked by the central core leg 12b is absorbed by the core legs 12a and 12c, and leakage to the outside can be suppressed. The high frequency current I ₂ is supplied to the heating coil 51 of the induction heating device 5 by the electromotive force induced in the secondary coil 14 constituted by a flat conductor by the magnetic flux induced in the central core leg 12 b. Here, since the primary coil 13 is wound six times and the secondary coil 14 is wound once, the high-frequency current I ₂ supplied to the heating coil 51 is a high-frequency current six times I _1. . This is because, as shown in FIG. 4, the iron core 12, the primary coil 13, and the secondary coil 14 are arranged close to each other to reduce the leakage inductance of the high-frequency transformer 10. The object to be heated 53 can be induction-heated by supplying the six-fold high-frequency current I ₂ through the matching capacitor 52 and being supplied to the heating coil 51.

  What is shown here as an example of the induction heating device 50 is a steel pipe in which the heating coil 51 is constituted by a three-turn coil having an inner diameter of 70 mm, and the article 53 to be heated is shown as SGP 40A. It is inserted and heated.

  The results of measuring various electric circuit constants of the induction heating device 50 with the LCR meter with the high-frequency transformer 10 removed from the induction heating device 50 are shown in the column A of FIG. 6, and the resistance value R is as low as 14.1Ω. Value. When the induction heating device 50 is connected to the high frequency power supply 40 and operated under this load condition, the induction heating device 50 has a low resistance value, so a high frequency power supply capable of supplying a large current is required, and the price of the high frequency power supply 40 increases.

When power is fed from the high frequency power supply 40 to the induction heating device 50 via the high frequency transformer 10, the circuit resistance R10 viewed from the input terminal A of the high frequency transformer 10 is configured so that the primary coil of the high frequency transformer 10 has the number of turns N1, the secondary coil. Is the number of turns N2,
R10 = R × (N1 ÷ N2) ² (1)
It becomes. Here, R is the resistance of the induction heating device 50.

  As a result, in the circuit shown in FIG. 5, the circuit resistance R10 viewed from the input terminal A of the high-frequency transformer 10 becomes as large as 502Ω as shown in the column B of FIG. As a result, the current supplied from the high frequency power supply 40 can be greatly reduced to 3% or less when the high frequency transformer 10 is not provided. For this reason, the current capacity of the high-frequency power supply 40 is significantly reduced by using the high-frequency transformer 10, and the price can be reduced.

  In addition, when the pipe | tube comprised from stainless steels, such as SUS304 whose resistance value is smaller than the steel pipe comprised from SGP, is made into the to-be-heated material 53, the circuit resistance R of the induction heating apparatus 50 becomes small. In this case, even if a high-frequency current is supplied via the high-frequency transformer 10, the current capacity of the high-frequency power supply 40 increases, and the price increases. In this case, as shown in FIG. 8, the primary coil 13 of the high-frequency transformer 10 is configured in two layers to increase the number of turns, thereby increasing the circuit resistance viewed from the high-frequency power source 40 and the current from the high-frequency power source Can be reduced. For example, if the number of turns of the primary coil 13 is 12 and the number of turns of the secondary coil is 1, the circuit resistance R10 viewed from the high frequency power supply 40 is 140 times or more the circuit resistance R of the induction heating device. Since it can be increased, the current of the high-frequency power supply 40 can be significantly reduced.

  Next, FIG. 7 shows the result of a temperature evaluation test performed on the high-frequency transformer 10 of the present invention.

In this test, a high-frequency current I ₁ having a frequency of 25 kHz and a size of 144 A is supplied from the high-frequency power source 40 in the circuit of FIG. 5 to the high-frequency transformer 10 and approximately 15 kW of power is applied to the object 53 to be heated. The temperature of the eight places indicated by A to H in FIGS. 2 to 4 of the high-frequency transformer 10 is measured.

  The temperature measurement points A to C are the front side, back side, and right side surface of the third coil conductor 13a of the primary coil 13, and the measurement points D and E are the upper part of the central core leg 12b of the core 12. It is the surface of the back side of this, and the front side. Further, the measurement points F and G are the front side surface of the center part of the right core leg 12c of the iron core 12 and the front side surface of the center part of the left core leg 12a, and the measurement point H is near the entrance of the cooling fan 30. This is the outside air temperature measurement point.

  The temperature at each of these measurement points shown in FIG. 7 rises as time elapses after the operation of the induction heating apparatus is started, but this temperature rise stops when a predetermined time elapses. .

  As a result of this temperature test, as is clear from FIG. 7, the outside air temperature (the temperature at the point H) is 26.6 ° C., but at the point B on the back side of the primary coil 13 in the high-frequency transformer 10, it is 95. A maximum temperature of 5 ° C was indicated. This is a temperature increase of 68.5 ° C. with respect to the outside air temperature.

  If the Litz wire used for the primary coil conductor 13a is subjected to class H insulation, the allowable maximum temperature of this litz wire is 180 ° C., so that this temperature is well within this temperature range. There is no problem.

  Moreover, the temperature of the measurement points F and G of the iron core 12 is 64.7 ° C. and 59.7 ° C., respectively. Only rises. Since the temperature of the iron core is also lower by 50 ° C. or more than 120 ° C., which is the allowable use temperature of the iron core 12 composed of the ferrite core, it is a temperature at which there is no problem.

  As can be understood from such a temperature evaluation test, the high-frequency transformer of the invention can be sufficiently put into practical use because the temperature of the primary coil and the iron core can be maintained in a usable range by air cooling.

1: High frequency transformer 11: Transformer main body 12: Iron core 13: Primary coil 14: Secondary coil 15: First insulating layer 16: Second insulating layer 19: Insulating support block 20: Shielding container 21, 22: Vent 30: Ventilation cooling device

Claims (5)

  An iron core, a first insulating layer formed by winding an insulating sheet around the iron core leg of the iron core, a primary coil formed by winding a required number of turns of litz wire on the outside of the first insulating layer, and A second insulating layer formed by winding an insulating sheet having a high thermal conductivity around the outer periphery of the primary coil and a flat conductor so as to surround the primary coil from the outside of the second insulating layer. A transformer body is constituted by a secondary coil formed by winding, and the transformer body is housed and shielded in a fully-closed shielding container formed of a nonmagnetic flat plate, and separately below and above the shielding container. A ventilation port is provided, and the outside air is sucked into the shielding container as cooling air from one ventilation hole of the shielding container, and the cooling air is forced to flow into the shielding container by discharging from the other ventilation hole of the shielding container. Let the transformer body High frequency transformer, characterized in that a ventilation cooling system for ventilation cooling.   2. The high-frequency transformer according to claim 1, wherein a part of a flat-plate conductor forming the secondary coil is brought into contact with the second insulating layer so as to approach the primary coil by the secondary coil.   3. The high frequency according to claim 1, wherein the primary coil is integrally formed by fusing the litz wire forming the primary coil to each other with an insulating fusing resin adhered to the litz wire. Trance.   The litz wire forming the primary coil is a high-frequency transformer in which a plurality of strands having a strand diameter of 0.3 mm or less are twisted together.   The transformer main body accommodated in the shielding container is cooled between the transformer main body and the inner wall of the shielding container by supporting the corners of the four corners of the iron core with insulating support blocks made of a heat-resistant insulating material. A high-frequency transformer characterized by forming a ventilation path.

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