Multi-layered insulated wire for high frequency transformer winding

Abstract: A bundled conductor manufactured by bundling a plurality of small diameter conductors 1, or a bundled conductor 2 manufactured by giving an extremely rough twisting pitch, which is 20 times or more larger than an outer diameter of said bundled conductor, to the bundled conductor is formed. Then, an insulating layer 3 comprising 3 layers 3a, 3b and 3c, each comprising a heat-resistant plastic film, is arranged around the bundled conductor above. A required voltage resistance characteristics is provided and maintained by any 2 of the aforesaid 3 insulating layers, and each of the 3 insulating layers described above is independent respectively and can be separated from other ones. The multi-layered insulated wire constructed as described above is available as an insulated electric wire for a winding to be used in a transformer which satisfies various requirements for safety such as IEC and UL, and with this multi-layered insulated wire it is possible to suppress heat emission in a high frequency switching transformer.

Description: This device relates to an insulated wire for a winding suited to be used in a high frequency transformer, a high frequency reactor, or a high frequency coil used in such devices such as a switching power source. Generally a magnet wire manufactured by forming an insulating layer made of such a material as polyurethane resin or polyester resin on a single wire conductor has been used as an insulated wire for a winding for a switching power source. A safety transformer for such a device as a switching power source must follow the following restrictions based on IEC (International Electrotechnical Commission) or UL (Standards of Underwriter's Laboratories, Inc.,) as well as on other various types of safety standard; (1) An insulation resistance must be provided between layers of an electric wire or between the primary and secondary winding with the help of a specified insulating film. (2) To secure a creepage distance between a winding and a core, a space insulation must be provided with an insulating barrier between the winding and the core. (3) It is necessary to carry out a processing for insulation by using such a material as an insulating tube when connecting a lead wire to a pin terminal. Because of the restrictions required by the safety standards as described above, when using a magnet wire, sometimes the user may face many troubles such as difficulty in minimising a transformer, requirement for parts and processes to carry out various types of processing for insulation, or difficulty in obtaining a compact and high performance transformer. To solve these problems it has been proposed to use a three-layered insulated wire for a winding to be used in a transformer, as described in Japanese Utility Model Application No: 49802/1990, Japanese Patent Application No: 150174/1990, and Japanese Utility Model Application No: 49801/1990, and now it is possible to satisfy the safety standards such as IEC or UL. GB-A-2230208 discloses a further conductor for use in a transformer winding, according to the preamble of claim 1. In a switching power source, a high frequency in a range from several tens kHz to several hundred kHz is now used for a switching frequency to improve the switching efficiency. However, in such a high frequency band area as described above, an eddy current loss in a conductor of a transformer winding and a loss due to the skin effect become very large, which causes heat emission from a transformer and may degrade characteristics of not only an insulated electric wire for a winding, but also a transformer itself. This invention was made to solve the problems as described above, and the object is to provide an insulated electric wire for a winding to be used in a transformer, which satisfies the various types of requirements for safety as described above and can contribute to reduction of heat emission from a transformer even if the switching frequency is in a high frequency band area. To achieve the object as described above, this invention provides a multi-layered insulated electric wire for a winding to be used in a high frequency transformer comprising: at least three insulating layers, around a conductor, any two of said at least three insulating layers providing an insulating resistance of 3.75 KV for one minute; characterised by: each layer of said at least three insulating layers comprising an extruded layer formed by extruding heat-resistant material; the conductor being a bundled conductor manufactured by bundling a plurality of conductors; and each of the aforesaid at least three insulating layers being mutually independent and separable from the other layers. In a first multi-layered insulated wire for a first winding according to the invention, a small diameter conductor such as copper wire, copper alloy wire, or a tin-or solder-plated copper wire is generally used a conductor for the element wire. A diameter of a conductor is selected case by case according to a specification of a transformer, but generally a conductor having a cross-sectional area in a range from approximately 0.032 mm2 (AWG 32) to 0.52 mm2 (AWG 20) is used, taking into account the high frequency characteristics of a bundled conductor. The reason why a plurality of these small diameter conductors are bundled almost in parallel to each other into a bundled conductor having a round cross section or an extremely long twisting pitch, which is twenty times or more larger than an outer diameter of a bundled conductor, is given to said conductor is that an eddy current loss in a bundled conductor or a loss due to the skin effect under a high frequency is reduced by raising a contact resistance by means of reducing contact between element wires contacting each other in a bundled conductor. As an insulating layer for the multi-layered insulated wire, an extruded layer manufactured by extruding a heat-resistant resin such as various types of fluorine resin or various types of engineering plastics several times over a conductor is available. If necessary, each layer may be colored differently by, for instance, using a resin having a different color for each insulating layer respectively, to clearly identify each insulating layer. The requirement that each layer of three insulating layers is independent and can be separated from other layers means that each layer can be separated from other layers and exists as one independent layer. As a means for separating an insulating layer, such a method as using a stripper, removing an insulating layer by giving a slit flaw to the insulating layer, or removing an insulating layer by removing an insulating layer by burning and cutting the insulating layer with a heated knife, is available. In contrast to it, a coating for magnet wire is formed by applying insulating paints several times around a conductor and fusing the paints, and each layer cannot be separated from other layers, so that sometimes a magnetic wire is not recognised as a multi-layered insulating wire. A bundled conductor according to this invention is manufactured by bundling a plurality of small diameter conductors almost in parallel into a conductor having a round cross section , or by giving an extremely long twisting pitch, which is twenty times or more larger than an outer diameter of the bundled conductor, so that element wires contacting each other in the bundled conductor form a point contact continuity in the cross section thereof. For this reason, electric resistance of eddy current circuits in the bundled conductor is high and generation of eddy current is suppressed, so that increase of high frequency resistance accompanying an eddy current loss can be prevented. Also, as a surface area of a bundled conductor is far larger than that of a single wire conductor, increase of a loss due to the skin effect can largely be reduced. Furthermore, by giving a twisting pitch, which is twenty times or more larger than an outer diameter of a bundled conductor, to the bundled conductor, a length of used conductor can be shortened by the difference of twisting lengths of the bundled conductor as compared to an ordinary twist line, so that also DC current in the coil can be reduced proportionately. Also, in the multi-layered insulated wire, at least three independent insulating layers, each comprising a heat-resistant extruded layer, are arranged, and insulating resistance (3.75 kV in case of IEC 950) required by the safety standards are provided and maintained by any two of the three layers, so that it is accepted as an insulated wire for a winding having appropriate insulating characteristics required by the safety standards and is free from many of the aforesaid regulations required by conventional types of transformer. As the conductor of a second multi-layered insulated wire according to the invention, a wire manufactured by forming an insulating layer made of such a material as polyurethane resin or polyester resin on a single wire conductor such as a copper wire, a copper-alloy wire, and tin-or solder-plated copper wire is used. Construction of the conductor is selected flexibly according to a specification of a transformer, but generally a conductor generally a conductor comprising a plurality of magnet wires and having a cross-sectional area of 0.032 mm 2 (AWG 32) to 0.52 mm 2 (AWG 20) is used. The bundled conductor according to this invention may be manufactured by bundling a plurality of the aforesaid magnet wires almost parallel to each other into a conductor having a round cross section, or by twisting a plurality of the aforesaid magnet wires by means of bundle-twisting, coaxial twisting, or litz twisting into a conductor having a round cross section. As an insulating layer for the multi-layered insulated wire, an extruded layer manufactured by extruding a heat-resistant resin such as various types of fluorine resin or various types of engineering plastics several times over a conductor is available. If necessary, each layer may be colored differently by, for instance, using a resin having a different color for each insulating layer respectively, to clearly identify each insulating layer. The requirement that each layer of three insulating layers is independent can be separated from other layers means that each layer can be separated from other layers and exists as one independent layer. As a means for separating an insulating layer, such a method as using a stripper, removing an insulating layer by giving a slit flaw to the insulating layer, or removing an insulating layer by removing an insulating layer by burning and cutting the insulating layer with a heated knife, is available. A coating of a magnet wire is formed by applying insulating varnishes several times around a conductor and baking the varnishes, but a single insulating layer is formed, so that each layer can not be separated from other layers and the insulating wire is not recognised as a multi-layered insulated wire. Also in this invention, a magnet wire is used, but it is not used in a state of single wire as a multi-layered wire, but as an insulated element wire constituting a bundle conductor. The bundled conductor according to this invention is manufactured by bundling a plurality of magnet wires almost in parallel to each other into one conductor having a round cross section or by twisting a plurality of magnet wire into a conductor having a round section, and generation of an eddy current can be suppressed to a low level because each element conductor of the magnet wire is insulated respectively, so that increase of high frequency resistance accompanying an eddy current loss can be prevented. Also in a bundled conductor, a surface area of conductor is larger than that of a single wire conductor, increase of a loss due to the skin effect can largely be suppressed. Also, when a plurality of the aforesaid magnet wires are bundled into a conductor having a round cross section, or when a plurality of the aforesaid magnet wires are twisted into a conductor having a round cross section, a length of twisted conductors can be shortened, and also DC current in a coil can be reduced in proportion to the shortened length of the twisted conductors. Also, in the multi-layered wire according to this invention, at least three independent insulating layers, each made of heat-resistant resin, are arranged, and insulation resistance (3.75 kV in case of IEC 950) is provided and maintained by any two of the three layers above, so that the multi-layered insulated wire is accepted as an insulated wire for a winding having appropriate insulation characteristics required by the safety standards and is free from many of the restrictions to conventional types of transformer as described above. Preferred embodiments of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a drawing showing a cross section of a first multi-layered insulated wire for a winding to be used in a transformer according to the invention; Fig. 2 is a drawing showing a cross section of a second multi-layered insulated wire for a winding to be used in a transformer according to the invention; Embodiment 1-1 Fig. 1 is a drawing showing a cross section of a multi-layered insulated wire according to the first embodiment of this invention. A copper wire having a diameter of 0.12 mm was used as an element wire conductor 1, and nineteen lines of this copper wire were bundled almost in parallel to each other into a bundled conductor 2 having a diameter of 0.60 mm. Then, a multi-layered insulated wire 24 was manufactured by arranging an extruded layer formed by extruding red fluorinated ethylene propylene resin (FEP) (Teflon 100 J, product name of Mitsui Dupont FluoroChemical Corp.) with a thickness of about 0.06 mm around this bundled conductor 2 as a primary insulating layer 23a, arranging an extruded layer formed by extruding natural color FEP with a thickness of about 0.06 mm around the primary insulating layer 23a as a secondary insulating layer 23b, and furthermore arranging an extruded layer formed by extruding a blue FEP with a thickness of about 0.06 mm around the secondary insulating layer 23b as a tertiary insulating layer 23c. Each layer of the insulating layer 23 of this multi-layered insulated wire 24 could be separated from other ones by either giving a slit flaw on a surface of the coating or using a stripper. Embodiment 1-2 A tin-plated copper wire having a conductor diameter of 0.12 mm was used as an element wire conductor 1, and nineteen lines of this tin-plated copper wire were formed into a bundled conductor 2 having an outer diameter of 0.60 mm and also having a round cross section by giving a twisting pitch of 24 mm to the bundled conductor. Then, a multi-layered insulated wire 24 was manufactured by arranging an insulating layer 23 comprising three extruded layers 23a, 23b and 23c around this bundled conductor 2 according to the same procedure as that in embodiment 1-1. Voltage resistance characteristics Results of withstand voltage tests for the multi-layered insulated wires in embodiment 1.1 and embodiment 1.2 carried out to identify a relation between an outer diameter of a wire and the voltage resistance characteristics using samples having layers as described above are shown in Table 1, and any difference between embodiment 1-1 and embodiment 1-2 was not observed. As clearly shown in Table 1, the insulated wire having the construction as described above could satisfy the voltage resistance characteristics required by IEC 950, namely 3.75 kV for 1 minute. Sample Outer diameter (mm) Breaking test (AC,KV) Sample with up to primary insulating layer 0.720 2.1 Sample with up to secondary insulating layer 0.840 6.1 Sample with up to tertiary insulating layer 0.960 9.1 Temperature up test in a transformer A switching transformer in which a three-layered insulated wire according to the embodiment 1.1 of this invention was used as a secondary winding and a switching transformer in which 0.038 mm polyurethane coated copper wire with a diameter of 0.60 mm was used as a secondary winding were manufactured, using the completely same parts and components in other sections. To test a switching transformer with an oscillation frequency of 50 kHz using in a switching power source with an output of 136 W, these switching transformers were run under the conditions of output voltage of 161 V and output current of 0.5 A, and surface temperature of the winding in each transformer was measured using a thermistor thermometer. The results are as shown in Table 2. Secondary winding material Surface of transformer winding (°C) Room (°C) Temp. difference ΔT (°C) Wire in embodiment 1-1 68.7 26.3 42.4 Polyurethane copper wire 75.2 26.3 48.9 As clearly shown in Table 2, in the switching transformer in which the multi-layered insulating according to this invention was used, temperature was lower by 6.5 °C than that in the transformer in which a conventional type of single copper wire was used. In the multi-layered insulated wire, a bundled conductor manufactured by bundling a plurality of small diameter conductors almost in parallel to each other into a conductor having a round cross section, or by giving a twisting pitch, which is twenty times or more larger than an outer diameter of said bundled conductor is used, so that heat emission due to an eddy current loss or the outer skin effect in the conductor can largely by suppressed, and because of this effect it is possible to suppress heat emission from a switching transformer even when the switching frequency is high, which contributes to improvement of efficiency of a switching power source. Embodiment 2-1 Fig. 2 is a drawing showing a cross section of a multi-layered wire according to a second embodiment of this invention. A class 2 polyurethane copper wire having a diameter of 0.10 mm and a finished diameter of 0.120 mm as a magnet wire 51 was used, and a bundled conductor 52 having a diameter of 0.60 mm was formed by bundling 19 lines of this polyurethane copper wire almost in parallel to each other. Then, a multi-layered insulated wire 54 was manufactured by arranging an extruded layer formed by extruding red fluorinated ethylene propylene resin (FEP) (Teflon 100 J, product name of Mitsui Dupont FluoroChemical Corp.) with a thickness of about 0.06 mm around this bundled conductor 52 as a primary insulating layer 23a, arranging an extruded layer formed by extruding natural color FEP with as thickness of about 0.06 mm around the primary insulating layer as a secondary insulating layer 23b, and furthermore arranging an extruded layer formed by extruding a blue FEP with a thickness of about 0.06 mm around the secondary insulating layer 23b as a tertiary insulating layer 23c. Each layer of the insulating layer 23 of this multi-layered insulated wire 54 could be separated from other ones by either giving a slit flaw on a surface of the coating or using a stripper. Embodiment 2-2 A class 2 polyester copper wire having a diameter of 0.10 mm and a finished outer diameter of 0.120 mm was used as a magnet wire 51, and a bundled conductor with a bundled outer diameter of 0.60 mm was manufactured by bundling 19 lines of this polyester copper wires into a conductor having a round cross section with a twisting pitch of 24 mm. Then, a multi-layered insulated wire 54 was manufactured by arranging an insulated layer 23 comprising 3 FEP extruded layers 23a, 23b and 23c around this bundled conductor like in embodiment 2-1. Each insulating layer in this multi-layered insulated wire 54 could be separated according to the same procedure as that in embodiment 2-1. Voltage resistance characteristics Results of withstand voltage tests for the multi-layered insulated wires in embodiment 2-1 and embodiment 2-2 carried out to identify a relation between an outer diameter of a wire and the voltage resistance characteristics using samples having layers as described above are shown in Table 3, and any difference between embodiment 2-1 and embodiment 2-2 was not observed. Sample Outer diameter (mm) Breaking test (AC,kV) Sample with up to primary insulating layer 0.721 2.2 Sample with up to secondary insulating layer 0.841 6.2 Sample with up to tertiary insulating layer 0.961 9.2 As clearly shown in Table 3, the insulated wire having the construction as described above could satisfy the voltage resistance characteristics required by IEC 950, namely 3.75 kV for 1 minute. Temperature up test in a transformer A switching transformer in which a three-layered insulated wire according to the embodiment 2-1 of this invention was used as a secondary winding and switching transformer in which 0.038 mm polyurethane coated copper wire with a diameter of 0.60 mm was used as a secondary winding were manufactured, using the completely same parts and components in other sections. To test a switching transformer with an oscillation frequency of 50 kHz using in a switching power source with an output of 136 W, these switching transformers were run under the conditions of output voltage of 161 V and output current of 0.5 A, an surface temperature of the winding in each transformer was measured using a thermistor thermometer. The results are as shown in Table 4. As clearly shown in Table 4, in the switching transformer in which the multi-layered insulating according to this invention was used, temperature was lower by 7.7 °C than that in the transformer in which a conventional type of single copper wire was used. Secondary winding material Surface of transformer winding (°C) Room (°C) Temp. Difference ΔT (°C) Wire in embodiment 4-1 67.5 26.3 41.2 Polyurethane copper wire 75.2 26.3 48.9 In the multi-layered insulated wire according to this invention, a bundled conductor having a round cross section prepared by bundling a plurality of magnet wires, or by twisting a plurality of magnet wires is used, so that heat emission due to an eddy current loss and the skin effect in the conductor can largely be reduced, and because of this effect also it is possible to suppress heat emission in a high frequency switching transformer, which can contribute to improvement of the switching efficiency.

Claims: A multi-layered insulated electric wire (24,54) for a winding to be used in a high frequency transformer comprising: at least three insulating layers (23), around a conductor, any two of said at least three insulating layers (23) providing an insulating resistance of 3.75 kV for one minute; characterised by: each layer of said at least three insulating layers (23) comprising an extruded layer formed by extruding heat-resistant material; the conductor being a bundled conductor manufactured by bundling a plurality of conductors (1,51); and each of the aforesaid at least three insulating layers (23) being mutually independent and separable from the other layers. The multi-layered insulated electric wire according to claim 1, wherein the aforesaid bundled conductor is manufactured by bundling said plurality of conductors (1,51) almost in parallel to each other into a conductor having a round cross section. A multi-layered insulated electric wire according to claim 1, wherein the aforesaid bundled conductor is manufactured by twisting and bundling said plurality of the conductors (51) into a conductor having a round cross section. A multi-layered insulating electric wire according to claim 1, claim 2 or claim 3, wherein the insulating layers comprises a heat-resistant resin. A multi-layered insulated electric wire according to any preceding claim in which the conductors (51) are magnet wires. A multi-layered insulated electric wire according to any preceding claim in which each conductor (51) is surrounded by an insulating layer.

Inventors: KATAGIRI NAOKI, MURAMATSU MASATAKA, YAMAGUCHI TADASHI, KATAGIRI, NAOKI, MURAMATSU, MASATAKA, YAMAGUCHI, TADASHI
Applicants: TOTOKU ELECTRIC, TOTOKU ELECTRIC CO., LTD.
Application year: 1992
Main classification: H01F27
IPC codes: H01B7, H01F27