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 windings with a 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 a 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 minimizing a transformer, requirement for parts and processes to carry out various types of processing for insulation, or difficulty in obtaining acompact and high performance transformer. To solve these problems, this invention proposed use of a 3-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 laid-open No.4042515/1992, Japanese Utility Model Application No. 49801/1990, and EP-A-0 258 036 which describes a multi-layered insulated wire according to the preamble of claim 1, and now it is possible to satisfy the safety standards such as IEC or UL. In a switching power source, a high frequency in a range from several tens KHz to several hundreds 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 wire for a winding to be used in a high frequency transformer comprising: (i) at least two first insulating layers around a conductor, which is a bundled conductor manufactured by bundling a plurality of conductors; (ii) each of said at least two first insulating layers comprising: a) a wound layer formed by winding heat-resistant plastics film; b) an extruded layer formed by extruding heat-resistant material; or c) a coated layer formed by applying heat-resistant paints; and characterized in that: (i) each of said plurality of conductors has a second insulating layer comprising: a) a wound layer formed by winding heat-resistant plastics film; b) an extruded layer formed by extruding heat-resistant material; or c) a coated layer formed by applying heat-resistant paints; (ii) any two of said at least two first insulating layers and said second insulating layer provide an insulating resistance of 3.75kV for one minute; and (iv) each of said at least two first insulating layers and said second insulating layer is mutually independent and separable from the other layers. The aforesaid bundled insulated conductor according to this invention may be manufactured by bundling a plurality of the aforesaid insulated element wires almost in parallel to each other into a conductor having a round cross section, or by bundling a plurality of the aforesaid insulated element wires by twisting said element wires by means of bundle-twisting, co-axial twisting, or litz twisting. In a multi-layered insulated wire for a winding to be used in a high frequency transformer, generally a small diameter wire such as a copper wire, a copper-alloy wire, or a tin- or solder-plated copper wire is used as a conductor for the element wire. Generally, a size of this small diameter conductor is in a range from 0. 08 mm (AWG 40) to 0.20 mm (AEG 32). As an insulating layer for a multi-layered insulating wire, a layer manufactured by winding a heat-resistant plastic film such as, for instance,a polyimide film, an aromatic polyamide film, a polyether ether ketone film, a polyphenylene sulfide (PPS) film, or a polyester film in an overlapped relation is used. Also, a heat-sensing adhesive layer may be arranged on the aforesaid heat-resistant plastic film, and after said film is wound around a conductor, heat may be applied to integrate the heat-sensing adhesive layer with the heat-resistant film. Furthermore, if it is necessary, films having different colors may be used for each layer respectively, or each layer may be colored differently by employing such a method as adding a specific dyestuff to a heat-sensing adhesive layer for a film with a heat-sensing adhesive layer to color each layer differently, to clearly identify each insulating layer. As an extruded layer made of a heat-resistant resin, 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. A paints-coated layer coated with heat-resistant paints is formed by applying fluorine paints-based dispersion paints, silicon acryl resin, or acryl fluoride-based resin several time. Also in this step, each layer may be colored differently as described above. The requirement that each insulating layer 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, removing an insulating layer by burning and cutting the insulating layer with a heated knife, or winding back a wound film, is available. In contrast to it, a coating for magnet wire is formed by applying insulating varnishes several times around a conductor and baking the varnishes, and each layer can not be separated from other layers, so that sometimes a magnet wire is not recognized as a multi-layered insulating wire. The bundled insulated conductor according to this invention is manufactured by bundling a plurality of insulated element wires almost in parallel to each other into one conductor having a round cross section or by twisting a plurality of insulated element wires 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 insulated element wire is insulated respectively, so that increase of high frequency resistance accompanying an eddy current loss can be prevented. Also in bundled insulated conductor, a surface are 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 insulated element wires are bundled into a conductor having a round cross section, or when a plurality of the aforesaid insulated element 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 twist conductors. Also, the multi-layered insulated wire is constructed so that insulation resistance (3.75 kV in case of IEC 950) required by the safety standards is provided and maintained by any 2 insulating layers of the at least 3 insulating layers comprising an insulating layer for the insulated element wire and insulating layers on the bundled insulated conductor, 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 aforesaid restrictions to conventional types of transformer. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a drawing showing a cross section of a 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 another embodiment of the multi-layered insulated wire for a winding to be used in a transformer according to the invention. Description is made for preferred embodiments of this invention with accompanying drawings. Embodiment 1 FIG 1 is a drawing showing a multi-layered insulated wire according to the invention. A copper wire 31 having a diameter of 0.12 mm was used as an element wire conductor 31, and an insulated element wire was manufactured by arranging a primary insulating layer 33a with a coating thickness of 0. 04 mm formed by means of applying polytetra fluoroethylene (PTFE) dispersion paints around this copper wire 31. 19 lines of this insulated element wire were bundled into a bundled insulated conductor 32 having an outer diameter of 1.00 mm and also having a round cross section by giving a twisting pitch of 30 mm to the bundled conductor. Then, a 3-layered insulated wire 34 was manufactured by arranging an extruded layer formed by natural color fluorinated ethylene propylene resin (FEP) (Teflon 100 J, product name of Mitsui Dupont Fluoro-Chemical Corp.) with a thickness of about 0.06 mm around this bundled insulated wire 32 as a secondary insulating 23b, and furthermore by arranging an extruded layer formed by extruding blue FEP with a thickness of about 0.06 mm around this secondary insulating layer 23b as a tertiary 23c. Each layer of the insulating layer 33 of this 3-layered insulated wire 34 could be separated from other ones by a giving a slit flaw on a surface of the coating or by using a stripper. Embodiment 2 FIG. 2 is a drawing showing a cross section of a multi-layered insulated wire which is a modified one according to the this invention. A copper wire having a conductor diameter of 0.12 mm was used as an element wire conductor 31, and an insulating element wire was manufactured by arranging a primary insulating layer 43a by means of extruding natural color FEP with a thickness of 0.04 mm. Then, 19 lines of this element insulated wire were bundled almost in parallel to each other into a bundled insulated conductor 32 having a round cross section and also having an outer diameter of 1.00 mm. Then, a 3-layered insulated wire 44 was manufactured by arranging a secondary insulating layer 43b by means of winding a white PPS film (3.5 mm width × 0. 03 mm thickness ) with 1/2 laps around this bundled insulated conductor 42, and furthermore by arranging a tertiary insulating layer 43c by means of winding a white PPS film (3.5 mm width × 0.03 thickness) with 1/2 laps around the secondary insulating layer 42. The primary insulating layer 43a could be separated by a stripper, while the secondary insulating layer 43b and the tertiary insulating layer 43c of the insulating layer 43 in this 3-layered insulated wire 44 could be separated by winding back each film respectively. Voltage resistance characteristics Results of withstand voltage tests for the multi-layered insulated wires in embodiment 1 and embodiment 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 and embodiment 2 was not observed. Sample Outer diameter (mm) Breaking test (AC,KV) (1) Sample with up to primary insulating layer 1.00 2.0 Sample with up to secondary insulating layer 1.12 5.9 Sample with up to tertiary insulating layer 1.24 9.0 Note (1) indicates a result of breakdown voltage measured by winding each wire around a mandrel with a diameter of 10 mm (with 15 turns). 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. Temperature up test in a transformer A switching transformer in which a 3-layered insulated wire according to the embodiment 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 shown in Table 2. 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 6.3 °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 3-1 68. 9 26.3 42.6 Polyurethane copper wire 75.2 26.3 48.9 In the multi-layered insulated wire, a bundled insulated conductor manufactured by bundling a plurality of insulated conductors almost in parallel to each other into a conductor having a round cross section, or by twisting a plurality of the aforesaid insulated element wires into a conductor having a round cross section is used, so that heat emission due to an eddy current loss or the skin effect in the conductor can largely be 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.

Claims: A multi-layered insulated wire (34,44) for a winding to be used in a high frequency transformer comprising: (i) at least two first insulating layers (23b, 23c; 43b, 43c) around a conductor, which is a bundled conductor manufactured by bundling a plurality of conductors (31) ; (ii) each of said at least two first insulating layers (23b, 23c; 43b, 43c) comprising: a) a wound layer formed by winding heat-resistant plastics film; or b) an extruded layer formed by extruding heat-resistant material; or c) a coated layer formed by applying heat-resistant paints; and characterized in that: (i) each of said plurality of conductors (31) has a second insulating layer (33a; 43a) comprising: a) a wound layer formed by winding heat-resistant plastics film; or b) an extruded layer formed by extruding heat-resistant material; or c) a coated layer formed by applying heat-resistant paints; (ii) any two of said at least two first insulating layers (23b, 23c; 43b, 43c) and said second insulating layer (33a; 43a) provide an insulating resistance of 3.75kV for one minute; and (iv) each of said at least two first insulating layers and said second insulating layer is 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 (31) 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 bundled conductor is manufactured by twisting and bundling said plurality of the conductors (31) into a conductor having a round cross section. A multi-layered insulated electric wire according to claim 1, claim 2 or claim 3 in which the plurality of ccnductors (31) are copper wires.

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: H01F27, H01B7