JP2001143943A - Transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the converting efficiency of a transformer by increasing the temperature of an iron core for reducing an iron loss. SOLUTION: A transformer content 1 is provided with an iron core 2, a thermal insulating plate 5 covering the whole face of the iron core 2, and a coil 7. When a fixed power is supplied to a primary coil 7a, heat is generated inside the iron core 2 due to an iron loss, and heat radiation is suppressed by the heat insulating plate 5 as a thermal insulting means so that the temperature of the iron core 2 can be increased. Thus, the iron loss can be reduced according to the increase of the temperature of the iron core 2, and the converting efficiency of the transformer can be increased. Also, the temperature of the iron core 2 can be controlled in a fixed high temperature by operating negative feedback such as the decrease of the generated heat due to the decrease of the iron loss to the iron core 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer having a small loss caused by an iron core.

[0002]

In recent years, demands for energy-saving electrical equipment have been increasing in response to increasing power demand. There is also a demand for a high-efficiency transformer with low loss. A typical three-phase power transformer is
A primary winding and a secondary winding are wound around the outer periphery of a three-phase three-legged or three-phase five-legged iron core to constitute a transformer. There are mainly closed type transformers and dry type transformers, and the closed type transformers are filled with the contents of the transformer in a tank and cooled by injecting insulating oil or SF6 gas into the tank. The dry-type transformer is configured such that the windings and the like of the transformer are formed so as to be covered with a molding resin to enhance safety and are exposed to the outside air.

[0003] Generally, a copper wire is used for the winding,
A ferromagnetic metal core material such as silicon steel or permalloy is used for the iron core. Ideally, the conversion efficiency is 100%. However, in actuality, these are copper loss caused by electric resistance of the windings, leakage magnetic flux, etc., and iron loss caused by hysteresis loss, eddy current loss, etc. of the iron core. The power loss occurs due to the loss, and the conversion efficiency decreases. Conventionally, in order to increase the conversion efficiency, the core, which is one of the factors of power loss, is configured as a vortex by using a laminated core formed by laminating plate-shaped steel plates or a wound core formed by winding sheet-shaped steel plates. Methods have been used to reduce current loss. This method is generally used because iron loss can be reduced at low cost. However, there is a high demand for a high-efficiency (energy-saving) transformer with even less loss, and various improvements have been made to reduce iron loss loss.

[0004] For example, there is a method of reducing iron loss by increasing the cross-sectional area of an iron core. When a certain amount of electric power is supplied to the primary winding, the larger the cross-sectional area of the iron core, the smaller the magnetic flux density, so that the iron loss can be reduced. However, in this method, it is necessary to increase the size of the iron core, which causes problems such as an increase in size and weight of the transformer and an increase in cost. As another method, there is a method of reducing iron loss by using a high-grade material having a high orientation for the iron core. This is to increase the electrical resistance in the iron core and reduce the iron loss by artificially performing a high degree of crystal orientation of the ferromagnetic metal core material and subdividing the magnetic domains. Although the iron loss can be reduced by this method, the reduction is limited because the iron loss is an intrinsic value depending on the material.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a transformer which is relatively inexpensive and has high conversion efficiency.

[0006]

According to a first aspect of the present invention, there is provided a transformer including a core having a core, windings attached to the core, and heat insulating means for suppressing heat radiation of the core. It is characterized by the following. According to such a configuration, when power is supplied to the winding, the heat generated in the core is suppressed by the heat insulating material, and the core is maintained at a high temperature. As a result, the electric resistance inside the iron core increases, and the eddy current loss decreases. Therefore, since the iron loss is reduced, the conversion efficiency of the transformer can be increased, and the cost can be relatively low because only the heat insulating means is provided.

A transformer according to a second aspect is characterized in that the heat insulating means is made of a heat insulating material covering the entire surface of the iron core. According to such a configuration, since the heat generated in the core is hardly dissipated, the core can be heated to a high temperature in a short time after the power supply to the primary winding is started, and the conversion efficiency is further improved. Can be better.

According to a third aspect of the present invention, the transformer is characterized in that the heat insulating means has at least a heat insulating material interposed between the iron core and the winding. With such a configuration, the same effect as that of the first aspect can be obtained.

A transformer according to a fourth aspect of the present invention is characterized in that at least a part of the support for supporting the iron core is made of an insulating material having a heat insulating effect and high mechanical strength.
According to such a configuration, it is also possible to perform heat insulation without interposing a heat insulating material between the iron core and the support.

According to a fifth aspect of the present invention, at least a surface of the winding corresponding to the iron core is made of an insulating material having a heat insulating effect and high mechanical strength. According to such a configuration, by providing the winding with the heat insulating means, the heat insulating material between the iron core and the winding can be omitted.

According to a sixth aspect of the present invention, in the transformer, the heat insulating means is constituted by a closed container for storing the iron core, and the inside of the closed container is evacuated. According to such a configuration, the heat insulation effect can be enhanced by the vacuum heat insulation, and the oxidation of the iron core due to the reaction between the high-temperature iron core and the air can be prevented.

A transformer according to a seventh aspect of the present invention is characterized in that the heat insulating means is constituted by a closed container for accommodating an iron core, and the closed container is filled with a gas having excellent thermal decomposition resistance. With such a configuration, the same effect as that of the sixth aspect can be obtained.

According to an eighth aspect of the present invention, the transformer according to any one of the first to fifth aspects is accommodated in a tank, and a gas excellent in heat decomposition resistance is sealed in the tank. It is characterized by having. According to such a configuration, oxidation of the iron core due to the reaction between the high-temperature iron core and the air can be avoided. In addition, when the insulating oil is injected into the tank, the insulating oil is exposed to the high-temperature iron core, causing thermal deterioration of the insulating oil. When the tank is filled with SF6 gas, the silicon and SF6 gas in the silicon steel plate iron core are deteriorated. And the generation of harmful gas due to the reaction with

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. First, FIG.
Shows the configuration of the three-phase transformer contents 1. FIGS. 1A and 1B are cross-sectional views taken along lines AA and BB in FIG. The iron core 2 is shown in FIG.
As shown in (b), a silicon steel plate cut into a predetermined shape and thickness is laminated, and is formed by a bad joint system in which the iron core legs 3 and the iron core yokes 4a and 4b are alternately stacked. It is a laminated three-phase tripod core. The silicon steel sheet is a directional silicon steel sheet which is rolled into a belt shape by a rolling mill to reduce iron loss in a rolling direction, and has an insulating coating on both surfaces.

A ceramic heat insulating plate 5 serving as a heat insulating means, which is cut into a plate for each surface according to its surface area, is adhered to the entire surface of the iron core 2 with an adhesive 6 made of silicone resin. Is attached. The heat insulating plate 5 is a class H insulating material and has a maximum heat resistance temperature of 180 ° C. The winding 7 is a copper strip winding, and is provided on the outer circumference of the three iron core legs 3.
Each of the primary windings 7a is wound in a rectangular cylindrical shape, and the secondary winding 7b is wound around the outer periphery of the primary winding 7a in a rectangular cylindrical shape.

Next, as shown in FIG. 2, a plurality of bolts 10 for fixing lower clamps 9, 9 serving as supports are provided on the upper surface of a nonmagnetic steel pedestal 8 for fixing the iron core 2. It is vertically projected and fixed. Lower core yoke 4a
The lower clamps 9, 9 are made of non-magnetic steel and have a T-shaped (or L-shaped) having the same length as the length of the lower core yoke 4a in the rolling direction.
And a horizontal surface portion thereof is arranged in parallel with the upper surface of the base 8 so as to be in contact therewith, and the iron core 2 surrounded by the heat insulating plate 5 is sandwiched and fixed between the vertical surface portions. A through hole is provided in a horizontal plane portion of the lower clamps 9, 9, and a bolt 10 vertically fixed to the upper surface of the pedestal 8 is passed through the through hole and fixed with a nut 11.

Upper clamp 1 of upper core yoke 4b
Reference numerals 2 and 12 are made of non-magnetic steel, and have a plate shape having the same length as the length of the upper core yoke portion 4b in the rolling direction. The iron core 2 surrounded by the heat insulating plate 5 is sandwiched and fixed. still,
The transformer contents 1 are housed in a tank (not shown), and the tank is filled with insulating oil or SF6 gas to form a sealed transformer. The wire 7 is formed as a dry transformer by being resin-molded. In the closed type transformer, the base plate of the tank may be used in place of the pedestal 8.

Next, the operation of this embodiment will be described with reference to FIG. Now, when an AC voltage is applied from the power supply to the primary winding 7a of the winding 7, an alternating current flows through the primary winding 7a, and a magnetic flux is generated in the iron core 2. At this time, an induced voltage is generated in the secondary winding 7b by an electromagnetic induction action. Since the magnitude of the induced voltage is proportional to the turn ratio between the primary winding 7a and the secondary winding 7b, the power supply voltage is transformed and output.

At this time, heat is generated in the iron core 2 due to iron loss such as hysteresis loss and eddy current loss. Since the laminated core has better thermal conductivity in the direction of the rolled steel sheet than in the direction of lamination of the rolled steel sheet, the generated heat is easily conducted in the direction of the steel sheet. 2 surfaces (front and rear surfaces of the iron core 2 in FIG. 2) and surfaces orthogonal to the two surfaces (upper and lower surfaces of the iron core 2 in FIG. 2,
The left and right sides become hot. Since the entire surface of the core 2 is covered with the heat insulating plate 5, heat radiation is suppressed, and the temperature of the core 2 rises. Since the electrical resistivity of iron increases with an increase in temperature, an increase in the temperature of the iron core 2 increases the electrical resistance.

On the other hand, since the eddy current loss generated in the iron core 2 decreases as the electric resistance of the iron core 2 increases, the iron loss decreases as the temperature of the iron core 2 increases. This relationship is shown in FIG. 3 as the relationship between the iron loss (power loss of the iron core per weight) with respect to the temperature of the iron core 2 and the magnetic flux density. FIG. 3 shows characteristics in the case of a silicon steel sheet. For example, when the magnetic flux density is 1.7 T, the iron loss is 1.1 W / k at room temperature.
g, 1.0 W / kg at 100 ° C., 0.92 W / kg at 200 ° C., 0.86 W / kg at 300 ° C., about 9% at 100 ° C. and about 16 %, And about 22% of iron loss at 300 ° C. can be reduced. As described above, as the temperature of the iron core 2 increases, the iron loss can be reduced, and the conversion efficiency of the transformer can be increased. When the temperature of the iron core 2 exceeds about 150 ° C., the effect of reducing the iron loss gradually increases the conversion efficiency of the transformer, so that it is practically effective to make the iron core 2 exceed 150 ° C. .

Further, since the iron loss of the iron core 2 decreases as the temperature increases due to the generated heat, the amount of generated heat also decreases. Due to this property, a certain constant power is supplied to the primary winding 7a.
When the iron core 2 is supplied, the core 2 generates heat and becomes high in temperature. However, negative feedback of the calorific value is applied to reduce the iron loss, and the core 2 is maintained at a certain high temperature state. Therefore, the temperature of the iron core 2 can be controlled by adjusting the supply voltage to the primary winding 7a. Also, it is possible to prevent the iron core 2 from rising to the Curie temperature and decreasing the magnetic permeability.

Since the temperature of the iron core 2 becomes high, it is preferable to use a heat insulating material having an allowable temperature exceeding 150 ° C., for example. Preferably, the core 2 can be raised to 180 ° C. by using a class H insulating material having a maximum allowable temperature of 180 ° C. Further, the use of the C-type insulating material allows the temperature of the iron core 2 to be further increased. Therefore, when an H-class insulating material such as the ceramic insulating plate 5 of the present embodiment is used as the heat insulating material, the temperature of the iron core 2 is controlled so as to be maintained at more than 150 ° C. and at most 180 ° C. When a seed insulating material is used, the temperature of the core 2 is controlled so that the temperature of the insulating material is preferably 180 ° C. or more and the maximum allowable temperature or less.

As described above, according to the present embodiment, the heat insulating plate 5 made of an H-class insulating material is mounted on the entire surface of the iron core 2 so that a constant amount of power is supplied from the power supply to the primary winding 7a.
The temperature of the iron core 2 was maintained at more than 150 ° C. and 180 ° C. or less. Thereby, the temperature of the iron core 2 is maintained at a high temperature and iron loss is reduced, so that the conversion efficiency of the transformer can be increased. Therefore, the conversion efficiency of the transformer can be increased without increasing the sectional area of the iron core 2 or using an expensive high-grade material as the material of the iron core 2.

Next, a second embodiment of the present invention will be described with reference to FIGS. 4 (a) and 4 (b). FIG. 4 (a),
(B) has shown the transformer content 13 which replaces the transformer content 1 of 1st Example. The same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described below.

The winding 7 is a copper strip winding. A primary winding 7a is wound around a cylindrical winding core 14, and a secondary winding 7b is wound around the outer periphery of the primary winding 7a. It is configured. The core 14 is formed of a ceramic heat-insulating material (H-class insulating material) which is a heat-insulating means. The winding 7 is fixedly mounted on the outer periphery of the three iron core legs 3 with a support member (not shown), and a rubber-like material having cushioning properties is provided between the core 14 and the iron core 2. The adhesive 15 made of silicone resin is injected. That is, in the second embodiment,
Thermal insulation plate 5 mounted on iron core leg 3 in the first embodiment
Are omitted, and the winding core 14 performs instead.

According to the second embodiment, the same effects as those of the first embodiment can be obtained. In particular, since the core 14 inherent in the core-shaped winding 7 is provided with a heat insulating function, the material is accordingly reduced. Can be reduced, and since the adhesive 15 made of silicone resin also has heat insulating properties, the heat insulating effect is improved. Further, the adhesive 15 reduces the area where the iron core 2 comes into contact with the outside air, so that oxidation of the iron core 2 can be prevented. Further, the thermal expansion of the iron core 2 is absorbed by the rubber-like adhesive 15 and is canceled.

Next, a third embodiment of the present invention will be described with reference to FIGS. 5 (a) and 5 (b). FIG. 5 (a),
(B) shows a transformer content 16 instead of the transformer content 13 of the second embodiment. Note that the same parts as those in FIG. 4 are denoted by the same reference numerals and description thereof is omitted, and only different parts will be described below. The lower clamp 17 and the upper clamp 18 which are a part of the support for supporting the iron core 2 have the same configuration as the lower clamp 9 and the upper clamp 12 described in the second embodiment, but are made of ceramic which is a heat insulating means. It is formed of a heat insulating material (H-class insulating material) made of stainless steel. The heat insulating plates 5 on the front and rear surfaces of the core yoke portions 4a and 4b and the heat insulating plate 5 on the lower surface of the lower core yoke portion 4a are omitted, and a lower clamp portion 17 and an upper clamp portion 18 are used instead of these.

As described above, according to the third embodiment, the same effects as those of the second embodiment can be obtained. In particular, a heat insulating material is interposed between the iron core 2 and the windings 7 and the clamps 17 and 18. Since there is no need, the manufacturing process of the transformer contents 16 is simplified, and further less material is required.

Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 6 shows a sealed transformer 19 using the transformer contents 1 of the first embodiment. The same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described below. The contents 1 of the transformer are housed in a tank 20, and the tank 20 is filled with a nitrogen gas 21 which is a gas having excellent thermal decomposition resistance. Tank 20
Bushings 22 and 23 are mounted on the upper surface, and a primary terminal (not shown) and a secondary terminal (not shown) of the winding 7 are connected to the bushings 22 and 23, respectively.

As described above, according to the fourth embodiment, by oxidizing the contents 1 of the transformer, the nitrogen gas 21 is sealed in the tank 20. Moreover, the nitrogen gas 21
Is cheap. In addition, when the insulating oil is injected into the tank 20, the insulating oil exposed to the high-temperature iron core is thermally decomposed into a tar-like state, thereby preventing a decrease in insulating power. Alternatively, the silicon on the surface of the iron core 2 made of a silicon steel plate that has become hot when SF6 gas is sealed in the tank 20 is S
It is possible to avoid generation of a harmful gas by reacting with the F6 gas. The same effect can be obtained even if the transformer contents 13, 16 are stored in the tank 20.

Next, a fifth embodiment of the present invention will be described with reference to FIGS. 7 (a), 7 (b) and 8. FIG.
(A) and (b) show a transformer content 24 instead of the transformer content 1 of the first embodiment, and FIG. 8 shows a sealed container 25 used in the fifth embodiment. . The same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described below. As shown in FIG. 8, the closed container 25 is formed of non-magnetic steel, and includes a leg storage portion 26 for storing the core leg portion 3 and an upper yoke portion storage portion 27 for storing the upper core yoke portion 4b. , Lower core yoke 4
and a lower yoke storing section 28 for storing the “a”. The leg storage portion 26 has three horn-shaped cylindrical bodies 26b having openings 26a at both ends for passing the iron core leg 3 therein.
Are arranged in a line in accordance with the interval between the iron core legs 3, and two flat plates 26c are welded between the lower ends of the cylindrical bodies 26b. Upper yoke storage 2
7. The lower yoke storage section 28 has a container-like shape with one surface opened. A cylindrical vent 29 is provided on a surface corresponding to the upper surface of the upper yoke housing portion 27 for evacuating the inside of the sealed container 25 or sealing gas. A closing plate 26d is welded between the upper ends of the three cylindrical bodies 26b of the leg housing 26 so as to be opposed to the flat plate 26c as described later.

Thus, the lower core yoke portion 4a is stored in the lower yoke portion storage portion 28, the three core leg portions 3 are stored in the leg portion storage portion 26, and the upper core yoke portion 4b is stored in the upper yoke portion storage portion. 27, and the respective storage units 26,
The joining surface between 27 and 28 is welded, and finally the closing plate 26d
Are welded between the upper ends of the cylindrical portions 26b so as to face the flat plate 26c, thereby forming the closed container 25. As shown in FIGS. 7A and 7B, a spacing member 30 is inserted between the two corners of each of the storage portions 26, 27, and 28 and the iron core 2. It is attached with an adhesive 31. The inside of the closed container 25 is evacuated, and a vacuum insulation function as a heat insulation means is provided.

As described above, according to the fifth embodiment, the core 2 is housed in the sealed container 25, and the inside of the sealed container 25 is vacuum-insulated, so that the heat insulating property is enhanced, and the heat radiation suppressing power of the iron core 2 is increased. As a result, the conversion efficiency of the transformer increases. Further, in the fifth embodiment, the inside of the closed vessel 25 may be configured to have a gas insulation function as a heat insulation means by enclosing a nitrogen gas which is a gas having excellent thermal decomposition resistance. Also in this case, since the heat insulating property is increased, the conversion efficiency of the transformer can be increased. In addition, by evacuating the sealed container 25 or filling nitrogen gas therein, oxidation of the iron core 2 can be prevented, and vibration of the iron core 2 caused by magnetostrictive vibration or magnetic vibration can be reduced. Can also be absorbed.

Next, a sixth embodiment of the present invention will be described with reference to FIGS. 9 (a) and 9 (b). FIG. 9 (a),
(B) shows a transformer content 32 which replaces the transformer content 24 of the fifth embodiment. The same parts as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described below. In the sixth embodiment, the closed container 25
Instead of this, a closed container 34 is formed by covering the entire surface of the core 2 with a polymer film via a number of spacing members 33 between the entire surface and the entire surface thereof. Vacuum insulation as a means is provided.

According to the sixth embodiment, the fifth embodiment
The same effect as that of the embodiment can be obtained. In particular, since the sealed container 33 is made of a polymer film, the weight can be reduced. In addition, since a large number of the spacing members 32 are interposed between the core 2 and the sealed container 33 made of a polymer film, the sealed container 33 is not deformed even if the inside is vacuumed. Further, as the material of the sealed container, an organic insulating material having excellent sealing property and heat resistance is suitable, and glass fiber or the like may be used instead of the polymer film.

The present invention is not limited to the embodiment described above and shown in the drawings.
Extension is possible. In the first embodiment of the present invention, the heat insulating means is constituted by the heat insulating plate 5, but may be constituted by winding a tape-shaped heat insulating material around the iron core 2. Examples of the tape-shaped insulating material include a flexible organic insulating material such as a polymer film.

In the first embodiment (FIG. 1), when the winding 7 is resin-molded to form a dry transformer, at least the surface molding resin corresponding to the iron core 2 of the winding 7 has heat insulation. An insulating material having high mechanical strength may be embedded or provided, and the heat insulating material 5 in the iron core leg 3 may be omitted. By doing so, the same effect as in the second embodiment can be obtained.

As described in the description of the first embodiment of the present invention, since the laminated iron core has a higher thermal conductivity in the direction of the rolled steel sheet than in the laminating direction of the rolled steel sheet, the generated heat is not applied to this steel sheet. Heat is easily conducted in the plane direction, so that the surface of the iron core 2 is perpendicular to the two surfaces (the front and rear surfaces in FIG. 2) of the rolled steel sheet (the front and rear surfaces in FIG. 2). The left and right sides become hot. Therefore, the contents of the transformer according to the present invention require the core 2
The heat insulating means may be provided only on the surface orthogonal to both surfaces on the lamination direction side of the rolled steel sheet. Accordingly, since the amount of heat radiation from both surfaces of the iron core 2 on the lamination direction side of the rolled steel sheet is small, the temperature of the iron core 2 becomes high and the conversion efficiency of the transformer can be increased. Further, the configuration of the heat insulating means is simplified.

The iron core 2 may be made of a high-grade material with reduced iron loss. In this case, a transformer with high conversion efficiency can be realized by a synergistic effect of increasing the temperature of the iron core 2. In the embodiment of the present invention, the present invention is applied to a three-phase transformer, but may be a single-phase transformer. In the embodiment of the present invention, the configuration of the iron core 2 is a laminated core of a bad joint type, but may be a lap joint type.

[0040]

As is apparent from the above description, the transformer of the present invention suppresses heat radiation generated in the iron core when electric power is supplied to the primary winding by the heat insulating means, so that the iron core is heated to a high temperature. Since the configuration is held, the core loss of the iron core is reduced, and an excellent effect of increasing the conversion efficiency is achieved.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a first embodiment of the present invention, in which FIG. 1A is a cross-sectional view taken along line AA in FIG. 2, and FIG. 1B is a cross-sectional view taken along line BB in FIG.

FIG. 2 is a front view

FIG. 3 is a graph showing temperature characteristics of an iron core.

FIG. 4 is a view corresponding to FIG. 1, showing a second embodiment of the present invention;

FIG. 5 is a view corresponding to FIG. 1, showing a third embodiment of the present invention;

FIG. 6 is a view corresponding to FIG. 1, showing a fourth embodiment of the present invention;

FIG. 7 is a view corresponding to FIG. 1 showing a fifth embodiment of the present invention.

FIG. 8 is an exploded perspective view of a closed container.

FIG. 9 is a view corresponding to FIG. 1, showing a sixth embodiment of the present invention.

[Explanation of symbols]

In the drawing, 1,13,16,24,32 are transformer contents,
Is an iron core, 5 is an insulating plate (insulating means), 6, 15, 31 are adhesives, 7 is a winding, 9, 12 are clamps serving as supports, 14
Denotes a winding core, 17 and 18 denote clamps (insulating means) serving as supports, 20 denotes a tank, 21 denotes nitrogen gas, 25 and 34 denote closed containers, and 30 and 33 denote spacing members.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01F 31/00 AS

Claims (8)

[Claims] 1. A transformer, comprising: a transformer having an iron core, windings mounted on the iron core, and heat insulating means for suppressing heat radiation of the iron core. 2. The transformer according to claim 1, wherein the heat insulating means is made of a heat insulating material covering the entire surface of the iron core. 3. The transformer according to claim 1, wherein the heat insulating means has at least a heat insulating material interposed between the iron core and the winding. 4. The transformer according to claim 1, wherein at least a part of the support for supporting the iron core is made of an insulating material having a high mechanical strength and a heat insulating effect. 5. The transformer according to claim 1, wherein at least a surface of the winding corresponding to the iron core is made of an insulating material having a mechanical strength and a heat insulating effect. 6. The transformer according to claim 1, wherein the heat insulating means is constituted by a closed container that stores an iron core, and the inside of the closed container is evacuated. 7. The transformer according to claim 1, wherein the heat insulating means is constituted by a closed container for accommodating an iron core, and the closed container is filled with a gas having excellent thermal decomposition resistance. 8. The transformer according to any one of claims 1 to 5, wherein the contents of the transformer are housed in a tank, and the tank is filled with a gas having excellent thermal decomposition resistance. Transformer.