JP2023135383A - Twisted wire, insulated wire, coil and transformer - Google Patents

Abstract

To provide a twisted wire that minimizes transmission loss in a twisted wire while achieving reduction in production cost, an insulated wire including the twisted wire, a coil including the insulated wire, and a transformer including the coil.SOLUTION: In an insulated wire 1A for transformers and coils, a twisted wire 2A is formed by twisting a plurality of strands 10 together, each of the strands having a conductor 11 and an enamel layer 12 surrounding the conductor. The conductor has a circular cross section. The ratio of the thickness of the enamel layer to the diameter of the circle is 0.08-0.5.SELECTED DRAWING: Figure 1

Description

The present invention relates to stranded wires, insulated wires, coils, and transformers.

BACKGROUND ART In electrical and electronic equipment, switching power supplies that include an inverter and a transformer are usually used. For example, the commercial power source in Japan is a low frequency power source of 50 Hz or 60 Hz. When transforming such a low frequency power source without changing its frequency, a large power source is required to obtain the required output. Therefore, before transforming the voltage in the transformer, we used a switching element to increase the frequency of the commercial power supply to several tens of kHz or more, increasing the amount of power transmitted per second and reducing the size to a practical size. Switching power supplies are commonly used.
When a transformer installed in a switching power supply transforms a high-frequency AC voltage, resistance increases due to the skin effect, and transmission loss (conductor loss) due to the coil increases. In order to suppress this transmission loss, transformers used at high frequencies are generally equipped with a coil in which a wire with a conductor radius smaller than the skin depth determined by the frequency is wound around the core.
In order to increase the output of such a transformer, it is necessary to increase the conductor cross-sectional area of the wire wound around the core. When using an electric wire with a small conductor radius, the conductor cross-sectional area of the electric wire can be increased by increasing the number of wires wound. For example, it is known to use a twisted wire (Litz wire) in which a plurality of wires are twisted together in a spiral shape to increase the conductor cross-sectional area (for example, Patent Document 1).

JP2009-283397A

A transformer usually includes an input side (primary side) coil and an output side (secondary side) coil, and the voltage and current value of the current applied to each coil are set. In a transformer, usually one of the primary coil and the secondary coil is a low-voltage, high-current coil, and the other is a high-voltage, low-current coil.
Conventionally, the low-voltage, high-current side coil of a high-frequency transformer has a small-diameter conductor (strand conductor) designed to take into account the influence of the skin effect mentioned above, and a thin enamel layer (strand wire conductor) that covers this conductor. An insulated wire has been used in which a stranded wire is prepared by twisting together wires consisting of an insulating layer), and a thin insulating layer (stranded wire insulating layer) is further formed on the outer periphery of the stranded wire. Even if the wire insulating layer or the stranded wire insulating layer is formed into a thin film, sufficient insulation can be ensured as a low-voltage, high-current coil through which a low-voltage current flows. Furthermore, by forming these insulating layers into thin films, the number of strands constituting the stranded wire can be increased, which has the advantage of increasing the total conductor cross-sectional area.

As mentioned above, the insulated wires constituting the coil of a transformer have traditionally been made of stranded wires made by twisting strands of wire with a thin-film strand insulating layer, especially as a low-voltage, high-current coil. Attempts have been made to increase the total conductor cross-sectional area by using insulated wires coated with an insulating layer. On the other hand, there is a problem in that increasing the number of strands constituting a stranded wire increases the manufacturing cost of the stranded wire. An increase in the manufacturing cost of the stranded wire also leads to an increase in the manufacturing cost of an insulated wire using the stranded wire, a coil using the insulated wire, a transformer having the coil, and the like.
Therefore, the present invention provides a stranded wire that can reduce the transmission loss of the stranded wire and reduce manufacturing costs, an insulated wire using the stranded wire, a coil using the insulated wire, and a transformer including the coil. The challenge is to provide the following.

The above-mentioned problem of the present inventors is solved by the following means.
[1]
A stranded wire in which a plurality of wires each having a conductor and an enamel layer surrounding the conductor are twisted together, the conductor having a circular cross section, and the ratio of the thickness of the enamel layer to the diameter of the circle. A stranded wire in which (thickness of enamel layer/diameter of conductor cross section) is 0.08 to 0.5.
[2]
An insulated wire having an insulating layer surrounding the stranded wire.
[3]
The insulated wire according to [2], wherein the insulating layer is composed of three or more layers.
[4]
A coil using the insulated wire according to [2] or [3].
[5]
A transformer having the coil according to [4].

In the present invention and this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as lower and upper limits. For example, when "A to B" is written, the numerical range is "A to B".

The stranded wire of the present invention can reduce manufacturing costs while suppressing transmission loss.

1 is a schematic cross-sectional view showing a preferable example of an insulated wire of the present invention. 1 is a schematic cross-sectional view showing a preferable example of an insulated wire of the present invention. FIG. 1 is a schematic cross-sectional view showing a preferable example of the stranded wire of the present invention. FIG. 1 is a schematic cross-sectional view showing a preferable example of the strand of the present invention.

The stranded wire of the present invention is a stranded wire in which a plurality of wires each having a conductor (strand conductor) and an enamel layer (strand insulation layer) covering the conductor are twisted together. By satisfying the configuration (A) below, each of the strands constituting the stranded wire of the present invention can reduce manufacturing costs while suppressing transmission loss.
(A) The cross section of the conductor is circular, and the ratio of the thickness of the enamel layer to the diameter of the circle (thickness of the enamel layer/diameter of the cross section of the conductor) is 0.08 to 0.5.
In the above (A), the units of the thickness of the enamel layer and the diameter of the cross section of the conductor are the same (for example, both are μm).

Below, with reference to the drawings, the insulated wire of the present invention, the stranded wire constituting the insulated wire of the present invention, the strands (elemental conductor and strand insulating layer) constituting the stranded wire, and the stranded wire. Although preferred embodiments of the surrounding insulating layer (stranded wire insulating layer) will be described, the present invention is not limited to these embodiments except as specified in the present invention. Note that in the drawings, the outline shape of the stranded wire insulating layer constituting the insulated wire is shown as a ring, but in the insulated wire of the present invention, the stranded wire insulating layer may fill the gap between the stranded wires. . Further, the contour shape is not limited to a perfect circle. For example, the circularity of the contour shape can be 0.7000 to 1.0000, preferably 0.8000 to 1.0000, preferably 0.9000 to 1.0000, and 0.9500 to 1.0000. It is also preferable to set it to 1.0000 to 1.0000, and it is also preferable to set it to 0.9800 to 1.0000. Circularity is calculated by the following formula (1).

Circularity = 4π x (area) ÷ (perimeter) ² (1)

In addition, in the drawings, a form in which the cross section of the strand conductor or strand is circular is shown as having a perfect circular cross section, but a form in which the strand conductor or strand is circular in cross section is is not limited to a perfectly circular shape. For example, the circularity of the cross section of the wire conductor or wire can be 0.7000 to 1.0000, preferably 0.8000 to 1.0000, and also 0.9000 to 1.0000. It is preferably from 0.9500 to 1.0000, and more preferably from 0.9800 to 1.0000.
That is, in the present invention, all those having a cross-sectional circularity of 0.7000 to 1.0000 are included in the concept of a "circular" cross-section.

[Insulated wire]
As shown in FIG. 1, a preferable insulated wire 1A of the present invention includes a stranded wire 2A formed by twisting seven strands 10, and a stranded wire insulating layer 3A covering the outer periphery of the stranded wire 2A.

A preferable insulated wire 1B of the present invention is the same as the insulated wire 1A except that the insulating layer 3B has a three-layer structure, as shown in FIG. In the insulated wire 1B, each layer forming the three-layer structure is set to have the same thickness, but in the present invention, the relationship between the thicknesses of each layer is not particularly limited.

<Twisted wire>
The stranded wire of the present invention is not particularly limited as long as it is formed by twisting together a plurality of wires that satisfy the above (A).
The number of wires to be twisted together can be, for example, two or more. Considering the alignment of the strands, a structure in which a plurality of strands (side wires) are twisted around one central strand (core wire) is preferable. The number of strands to be twisted is preferably 7 or more, and preferably 100 or less in consideration of AC resistance and practical workability. The number of strands to be twisted is more preferably 7 to 61, still more preferably 7 to 37, particularly preferably 7 to 19.
When twisting the wires together, the arrangement of the wires, the twisting direction, the twisting pitch, etc. can be set as appropriate depending on the purpose, use, etc. Typically, it is preferable that the wires constituting the stranded wire are arranged in a close-packed manner so as to be in contact with each other. Here, "closest packing" means that all wires are arranged so that the distance between the wire conductors of adjacent wires is twice the thickness of the wire insulating layer, as shown in Figures 1 to 3. This means arranging them so that In other words, it means that the distance between the strand conductors of adjacent strands is determined by the thickness of the strand insulating layer.

The conductor cross-sectional area ratio of the stranded wire of the present invention is preferably 20% or more, more preferably 25% or more, and 30% The above is more preferable. The above-mentioned conductor cross-sectional area ratio refers to the cross-sectional area of each conductor relative to the area (S1) of a circumscribed circle circumscribing the stranded wire (for example, circumscribed circle C, see Figure 3) in the cross-sectional shape of the stranded wire (planar view). It is the percentage ((S2/S1)×100) of the total value (S2).

(Elementary wire)
The strand of the present invention has a conductor (strand conductor) and an enamel layer (strand insulating layer) surrounding the conductor, and other configurations are acceptable as long as the above (A) is satisfied. Not particularly limited.

As the wire conductor, it is possible to use a wide variety of wires conventionally used in winding wires for coils and the like. Examples include metal conductors such as copper wire and aluminum wire.
The diameter (wire diameter, diameter of the stranded conductor) of the circular cross section of the stranded conductor is not particularly limited as long as the above (A) is satisfied. For example, the diameter can be 0.05 to 0.50 mm, more preferably 0.08 to 0.45 mm, even more preferably 0.10 to 0.40 mm, and even more preferably 0.10 to 0.45 mm. More preferably, it is 0.35 mm. In the present invention, when the cross-sectional circular shape of the wire conductor is not a perfect circle, the above-mentioned diameter means a circle equivalent diameter (diameter of a perfect circle having the same area).

The enamel layer covering the periphery of the wire conductor is a wire insulating layer formed by applying and baking resin varnish around the wire conductor. This enamel layer may be a thermoplastic resin layer or a thermosetting resin layer, and is preferably a thermosetting resin layer. The resin used to form the enamel layer is not particularly limited. For example, thermosetting resins having imide bonds such as polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), and polyesterimide (PEsI), polyurethane (PU), thermosetting polyester (PEst), Examples include H-type polyester (HPE), polyimidohydantoin-modified polyester, polyhydantoin, polybenzimidazole, melamine resin, and epoxy resin, and one or more of these can be used.

The enamel layer may contain various additives commonly used in electric wires. In this case, the content of the additive is not particularly limited, but is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, based on 100 parts by mass of the resin component.

The thickness of the enamel layer is not particularly limited as long as the above (A) is satisfied, and is appropriately adjusted in relation to the diameter of the wire conductor. The thickness of the enamel layer is determined by measuring the thickness of the enamel layer at 20 random locations in the cross section of the wire (the shortest distance between the surface of the wire conductor and the surface of the enamel layer on the opposite side of the wire conductor). , is the arithmetic mean of 20 measured values. Note that the thickness of the stranded wire insulating layer can also be determined in the same manner.

The enamel layer can be formed by a known method. For example, it is preferable to apply a varnish made of a resin component such as a thermosetting resin to the outer periphery of the conductor and then bake it. This varnish contains a resin component, a solvent, and, if necessary, a curing agent for the resin component or various additives. The solvent is preferably an organic solvent, and one that can dissolve or disperse the resin component is appropriately selected.
As the method for applying the varnish, a conventional method can be selected, such as a method using a varnish application die having an opening similar or substantially similar to the cross-sectional shape of the conductor. Baking of varnish is usually performed in a baking oven. Although the conditions at this time cannot be uniquely determined depending on the type of resin component or solvent, for example, the conditions include a furnace temperature of 400 to 650° C. and a passing time of 10 to 90 seconds.

<Twisted wire insulation layer>
The stranded wire insulating layer may be any layer that covers a stranded wire obtained by twisting a plurality of wires together, and preferably a layer containing a thermoplastic resin, which will be described later, as a resin component. The thickness of the stranded wire insulating layer is not particularly limited, and is preferably, for example, 50 to 300 μm, more preferably 50 to 150 μm.
The stranded wire insulating layer is not particularly limited in the manner in which the stranded wire is covered, as long as it can cover the stranded wire. This insulating layer can be, for example, a layer (extrusion coating layer) formed by extrusion molding (extrusion coating).

The stranded wire insulating layer may be a single layer or may have a laminated structure of two or more layers. The stranded wire insulating layer preferably has a laminated structure of three or more layers, more preferably three to five layers. With a laminated structure of three or more layers, sufficient creepage distance can be secured for the insulated wire when used as a winding wire constituting a coil or transformer, so the insulating tape normally used to ensure insulation can be used. Can be omitted. This is also effective in reducing the size of the coil or transformer.
When the stranded wire insulating layer has a laminated structure, the thickness of each layer is not particularly limited. For example, the thickness of each layer is preferably 10 to 100 μm, more preferably 15 to 50 μm. The thickness of each layer may be the same or different.

The insulating layer preferably contains a thermoplastic resin as a resin component. As the thermoplastic resin, any thermoplastic resin commonly used as an insulating layer of an insulated wire can be used without particular limitation. The thermoplastic resin may be crystalline or amorphous.
Examples of the thermoplastic resin include polyamide (PA, nylon), polyetherimide (PEI), polyacetal (POM), polycarbonate (PC), polyphenylene ether (PPE, including modified polyphenylene ether), and polybutylene terephthalate (PBT). ), general-purpose engineering plastics such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or ultra-high molecular weight polyethylene;
Polysulfone (PSF), polyethersulfone (PES), polyphenylene sulfide (PPS), polyarylate (PAR), polyetherketone (PEK), polyaryletherketone (PAEK), tetrafluoroethylene-ethylene copolymer (ETFE) , polyetheretherketone (PEEK, including modified PEEK), polyetherketoneketone (PEKK), tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), thermoplastic polyimide resin ( Super engineering plastics such as TPI), thermoplastic polyamideimide (TPAI), or liquid crystal polyester;
Polymer alloys based on polyethylene terephthalate or polyethylene naphthalate, ABS/polycarbonate, nylon 6,6, aromatic polyamide resins, polyphenylene ether/nylon 6,6, polyphenylene ether/polystyrene, or polybutylene terephthalate/polycarbonate, etc. Examples include polymer alloys including engineering plastics.
One type or two or more types of thermoplastic resins may be contained.

When the stranded wire insulating layer has a laminated structure, the resin components contained in each layer may be the same or different from each other.

The stranded wire insulation layer may contain various additives commonly used in electric wires. In this case, the content of the additive is not particularly limited, but is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, based on 100 parts by mass of the resin component.

The stranded wire insulating layer is preferably formed by extrusion molding a resin composition containing a thermoplastic resin as a base around the outer periphery of the stranded wire. The resin composition contains the above-mentioned resin component and, if necessary, various additives. The extrusion method cannot be determined uniquely depending on the type of resin component, etc., but for example, an extrusion die having an opening similar or approximately similar to the cross-sectional shape of the stranded wire may be used to extrude at a temperature higher than the melting temperature of the resin component. An example is a method of extruding at temperature.
The stranded wire insulating layer is not limited to extrusion molding, but can be formed by coating and baking in the same manner as the enamel layer, using a varnish containing the above-mentioned thermoplastic resin, a solvent, etc., and various additives if necessary. You can also do that.

The diameter of the wire conductor and the thickness of the enamel layer are as described above. In the present invention, the ratio (h2/h1) of the thickness (h2) of the enamel layer to the diameter (h1) of the wire conductor is 0.08 to 0.5 (see FIG. 4), and 0.10 to 0. 45 is preferred, 0.12 to 0.40 is more preferred, 0.14 to 0.40 is even more preferred, 0.18 to 0.40 is even more preferred, and 0.20 to 0.40 is particularly preferred.
In the present invention, the lower limit of the ratio is controlled to a higher value than that of conventional wires forming the stranded wire. As described above, in order to increase the total conductor cross-sectional area, a stranded wire in which strands of wire having a thin strand insulating layer are twisted together has been conventionally used. However, after repeated studies, the present inventors found that when the value of the above-mentioned ratio was increased to 0.08 or more in the strands constituting the stranded wire, the resistance could be suppressed more than expected. Considering the suppression of this resistance, it is better to make the wire insulating layer thicker so that it satisfies the value of the above ratio, to ensure the same performance as before when used as a coil or transformer winding wire. It has been found that manufacturing costs can be reduced by reducing the number of strands. Therefore, in the present invention, as described above, the value of the ratio is controlled to be between 0.08 and 0.5.
The reason why the upper limit of the above ratio value is 0.5 is because if the above ratio value exceeds 0.5, the thickness of the enamel layer becomes relatively thick, and we tried to secure the necessary conductor cross-sectional area. This is because, in some cases, the finished diameter of the stranded wire must be increased. That is, in the present invention, the upper limit of the above ratio is set to 0.5, which is a realistic thick film.

[Coil and transformer]
<Coil>
The coil of the present invention uses the above-mentioned insulated wire of the present invention. Specifically, the insulated wire of the present invention is wound around an iron core made of a ferromagnetic or ferrimagnetic material, or an air core.
In the present invention, the size of the core, such as an iron core, is appropriately selected depending on the purpose and the like. Further, the method of winding the insulated wire, the number of turns (two or more turns), pitch, etc. are also appropriately selected depending on the purpose, use, etc.
The coil of the present invention can be used as a primary side (input side) coil or a secondary side (output side) coil that constitutes a transformer. More specifically, it can be used as a low-voltage, large-current side coil that constitutes a transformer, and can also be used as a high-voltage, small-current side coil. In the present invention, the low-voltage, large-current side coil means a coil through which a relatively low-voltage, large-current current flows between the two coils; , means a coil through which a current of high voltage and small current flows. The coil itself is publicly known, and for example, the description in Japanese Patent Application Laid-Open No. 2018-190980 can be referred to.

<Trans>
The structure or size of the transformer of the present invention is not particularly limited as long as it has the coil of the present invention. For example, it includes a plurality of coils including an input side coil (primary coil) and an output side coil (secondary coil). A transformer can convert alternating current voltage depending on the turn ratio of the primary coil and the secondary coil.
The transformer of the present invention includes two or more, preferably two, coils, at least one of which includes the coil of the present invention as a low voltage, high current side coil. More preferably, the low voltage, high current side coil is a coil of the present invention, and the high voltage, low current side coil is also a coil of the present invention.
The transformer of the present invention may have a primary coil and a secondary coil in which insulated wires are wound around different cores, and the insulated wires of the primary coil are wrapped around the same core either directly or through an insulating tape or the like. Alternatively, the secondary coil may be wound with an insulated wire. The transformer itself is publicly known, and for example, the description in Japanese Patent Application Laid-Open No. 2018-190980 can be referred to.

The coil and transformer of the present invention are preferably used for power supplies, particularly for switching power supplies. A power supply is a device that supplies a specific voltage and current.
The coil and transformer of the present invention are preferably used for switching power supplies, and in particular, alternating current (AC)/direct current (AC)/direct current (AC) that transforms and rectifies AC commercial power and converts it into DC with a voltage suitable for electrical and electronic equipment. It is preferably used for DC) converters.

EXAMPLES Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited thereto.

[Coil production]
<Example 1-1>
A polyamide-imide resin varnish is applied to the surface of the wire conductor, which has a circular cross section (perfect circle) and a diameter of 0.3 mm, and is baked to form an enamel layer with a thickness of 0.025 mm. I got it. The ratio (h2/h1) of the thickness (h2) of the enamel layer to the diameter (h1) of the cross section of the strand conductor in this strand (h2/h1) is 0.08.
Next, with the same six strands arranged in a close-packed manner around the one strand obtained above, these strands are twisted together to determine the number of strands (twisting). A stranded wire with a number) of 7 was obtained. The finished diameter (diameter of circumscribed circle), total cross-sectional area of each conductor, and conductor cross-sectional area ratio of the stranded wire were 1.05 mm, 0.495 mm ² , and 57%, respectively.
Next, the prepared stranded wire was wound around the outer peripheral surface of the bobbin for 10 turns so that the strands were in contact with each other (forming two rows (parallel number 2) of 5 turns without any gaps), A coil of Example 1-1 was produced. This bobbin had an outer diameter of 11.1 mm around which the strands were wound, and an axial length of 10.45 mm.

<Example 1-2>
A coil of Example 1-2 was produced in the same manner as Example 1-1 except that the thickness of the enamel layer was 0.07 mm. The composition of the strands and strands in the coil is shown in Table 1 below.

<Conventional example 1-3>
A coil of Conventional Example 1-3 was produced in the same manner as Example 1-1 except that the thickness of the enamel layer was 0.01 mm. The composition of the strands and strands in the coil is shown in Table 1 below.

<Example 2-1>
The procedure was the same as in Example 1-1, except that the diameter of the cross section of the wire conductor was 0.18 mm, the thickness of the enamel layer was 0.025 mm, and the number of twists of the wire was 19, and the wires were twisted in a close-packed manner. Thus, a coil of Example 2-1 was produced. The composition of the strands and strands in the coil is shown in Table 1 below.

<Example 2-2>
A coil of Example 2-2 was produced in the same manner as Example 2-1 except that the thickness of the enamel layer was 0.075 mm. The composition of the strands and strands in the coil is shown in Table 1 below.

<Conventional example 2-3>
A coil of Conventional Example 2-3 was produced in the same manner as Example 2-1 except that the thickness of the enamel layer was 0.005 mm. The composition of the strands and strands in the coil is shown in Table 1 below.

<Example 3-1>
The procedure was the same as in Example 1-1, except that the diameter of the cross section of the wire conductor was 0.13 mm, the thickness of the enamel layer was 0.02 mm, and the number of twists of the wire was 37, and the wires were twisted in a close-packed manner. Thus, a coil of Example 3-1 was produced. The composition of the strands and strands in the coil is shown in Table 1 below.

<Example 3-2>
A coil of Example 3-2 was produced in the same manner as Example 3-1 except that the thickness of the enamel layer was 0.05 mm. The composition of the strands and strands in the coil is shown in Table 1 below.

<Conventional example 3-3>
A coil of Conventional Example 3-3 was produced in the same manner as Example 3-1 except that the thickness of the enamel layer was 0.004 mm. The composition of the strands and strands in the coil is shown in Table 1 below.

<Example 4-1>
The procedure was the same as in Example 1-1, except that the diameter of the cross section of the wire conductor was 0.1 mm, the thickness of the enamel layer was 0.019 mm, and the number of twists of the wire was 61, and the wires were twisted in a close-packed manner. Thus, a coil of Example 4-1 was produced. The composition of the strands and strands in the coil is shown in Table 1 below.

<Example 4-2>
A coil of Example 4-2 was produced in the same manner as Example 4-1 except that the thickness of the enamel layer was 0.03 mm. The composition of the strands and strands in the coil is shown in Table 1 below.

<Conventional example 4-3>
A coil of Conventional Example 4-3 was produced in the same manner as Example 4-1 except that the thickness of the enamel layer was 0.004 mm. The composition of the strands and strands in the coil is shown in Table 1 below.

<Example 5-1>
PET (polyethylene terephthalate) resin was extruded around the outer periphery of a stranded wire produced in the same manner as in Example 1-1 to a thickness of 100 μm to obtain an insulated wire having an additional insulating layer around the stranded wire. . Next, the obtained insulated wire was wound around a bobbin to produce a coil of Example 5-1. The composition of the strands and strands in the coil is shown in Table 1 below.

<Example 5-2>
A coil of Example 5-2 was produced in the same manner as Example 5-1 except that the thickness of the enamel layer was 0.07 mm. The composition of the strands and strands in the coil is shown in Table 1 below.

<Conventional example 5-3>
A coil of Conventional Example 5-3 was produced in the same manner as Example 5-1 except that the thickness of the enamel layer was 0.01 mm. The composition of the strands and strands in the coil is shown in Table 1 below.

[Coil performance evaluation]
The AC resistances of the coils according to the above embodiments and conventional examples were evaluated using the following R/Rdc as an index.
Using an LCR meter (trade name: E4980A, manufactured by Agilent), the resistance value (R) was measured when an alternating current with a frequency of 1 MHz was applied. R/Rdc was calculated by dividing the resistance value by DC resistance (Rdc), and this value was used as an index of AC resistance.
Table 1 below shows the R/Rdc of each coil, and also shows the resistance reduction rate with respect to the conventional example, which is calculated by the following formula (2).

(1-[R/Rdc of Example]/[R/Rdc of Conventional Example]) x 100 (2)

As shown in Table 1, when comparing coils with the same wire conductor diameter, the coils of each example have a lower resistance than the conventional example in which h2/h1 is smaller than specified by the present invention. It was found that it was possible to reduce the Therefore, by setting h2/h1 within the specification of the present invention, it is possible to maintain the conventional performance while reducing the number of strands constituting the stranded wire, that is, to maintain the conventional performance while maintaining the conventional performance. It can be seen that manufacturing costs can be reduced.

1A, 1B... Insulated wire, 2A... Stranded wire, 3A, 3B... Insulating layer, 10... Element wire, 11... Conductor, 12... Enamel layer.

Claims (5)

A stranded wire in which a plurality of wires each having a conductor and an enamel layer surrounding the conductor are twisted together,
A stranded wire in which the cross section of the conductor is circular and the value of the ratio of the thickness of the enamel layer to the diameter of the circle is from 0.08 to 0.5. An insulated wire having an insulating layer surrounding the stranded wire. The insulated wire according to claim 2, wherein the insulating layer is composed of three or more layers. A coil using the insulated wire according to claim 2 or 3. A transformer comprising the coil according to claim 4.

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