Transformer

Abstract: A transformer (1) includes a stator core (2), primary coils (3a, 3c), secondary coils (3b, 3d), and heat radiating plates (4, 4a, 4b, 4c, 4d) each of which projects outward from between interior layers of the primary coil (3a, 3c) and/or secondary coil (3b, 3d). An A.C. arc welder includes the transformer (30) therein, with a movable core (34) which can move to and fro between the primary coils (32) and secondary coils (33) and which has different widthes in the movable direction. An A.C. arc welder also includes openings (23, 24, 25) for taking in air in a front portion of a case cover (21) and a fan (26) for exhausting air in a rear portion of the case cover (21).

Description: The present invention relates to a transformer which is used in an A.C. arc welder and the like, and which requires a large current. Generally in a transformer which deals with a large current, Joule heating of I 2 R is generated by a current I flowing in the transformer and a conductor resistance R. The temperature of the transformer rises following the generation of Joule heating so that insulating elements of the transformer become harmfully high temperatures. Therefore, a measure such as forced air cooling, cooling by circulation oil and the like is taken to meet the situation. In an A.C. arc welder which employs a transformer, it is demanded that the A.C. arc welder is made small-sized for lowering the cost of material, obtaining disposition space, improving carryability and the like. When the transformer is made small-sized to meet the demand, a diameter of a winding of a coil is made small, or a width or thickness of the transformer is made small. When the diameter of the winding is made small and a predetermined current flows in the winding, heat generation becomes great due to the increase of winding resistance. Therefore, the cooling ability must be improved and therefore small-sizing of the A.C. arc welder is difficult to realize. US-A-3,243,744 - which forms the basis of the preamble of claim 1 - discloses a transformer in which coils are wound around a core, the transformer comprising heat radiating plates which are provided between layers of the coils and which project outside of the coils. It is the object of the present invention to minimize a transformer in size while heat generation thereof is taken care of. This object is solved by a transformer according to claim 1. Preferred developments of the invention are given in the subclaims. When the transformer is employed, though the heat radiating plate is projected from the inner space between layers of coils, the heat of the coils is efficiently radiated by providing the heat radiating plate between the layers which become the most high in temperature and by employing forced cooling. Therefore, rising temperature is suppressed using a comparatively small fan even when the thickness and the width of the windings of the coils are made small. When the transformer of claim 3 is employed, the heat radiating plate is securely fixed between the layers of the coils so that positional shifting and coming out of the heat radiating plate due to outer force such as vibration, impact and the like are prevented from occurring. Also, the heat of the coils is efficiently conducted to the heat radiating plate especially through the welded sections so that heat radiating ability is improved. Brief Description of The Drawings Figure 1 is a front view of a transformer; Figure 2 is a perspective view of a heat radiating plate which is to be incorporated in the transformer; Figure 3 is a cross sectional view illustrating an incorporated condition of the heat radiating plate; Figure 4 is a plan view of a main portion of the transformer; and Figure 5 is a side view of a main portion of the transformer. Detailed Description of The Preferred Embodiments Fig. 1 is a front view of a transformer which is used for an A.C. arc welder according to the present invention. The transformer 1 includes a core 2 which has a rectangular outer shape and a rectangular opening, and four coils 3a, 3b, 3c and 3d which are wound to the core 2. The transformer 1 also includes heat radiating and cooling fins (heat radiating plates) 4a, 4b, 4c and 4d. Each fin is provided at a position which corresponds to about a half of the entire winding layers of each coil, that is, at an intermediate position between the winding starting layer and the winding ending layer. Each fin is provided in a projecting manner from each coil. In this embodiment, though the coils 3a and 3b, the coils 3c and 3d are provided adjacent to one another, respectively, the heat radiating plates 4a and 4c are projected leftward in Fig. 1, while the heat radiating plates 4b and 4d are projected rightward in Fig. 1. When the coils 3a and 3b, the coils 3c and 3d are not adjacent to one another, respectively, the heat radiating plates 4a and 4b, the heat radiating plates 4c and 4d may be projected in directions which direct their projecting portions toward one another. However, there still should be sufficient insulating spaces between the leading edges of the heat radiating plates 4a and 4b, and the heat radiating plates 4c and 4d. The reason for determining the clipping position of each heat radiating plate between layers of each coil to be the intermediate position (central layer position) between the winding starting layer and the winding ending layer is that the outer face portion of each coil easily radiates its heat by air cooling, and the portion near to the core 2 easily radiates its heat through the core 2, but the intermediate portion of each coil has difficultly radiating its heat. With the invention, then, the heat of the intermediate portion of each coil is radiated through the heat radiating plate. Fig. 2 illustrates a specific shape of the heat radiating plate 4 (4a, 4b, 4c, 4d). The heat radiating plate 4 includes a first flat section 5 which is clipped between winding layers, a second flat section 6 which is formed at one edge portion in a direction which is vertical to a winding direction of each coil 3, and plural V-shaped grooves 7 which have increasing depthes from the second flat section 6 to the other edge portion. The heat radiating plate 4 is formed by applying pressing processing to an aluminium plate or the like. The reason for forming V-shaped grooves 7 in the heat radiating plate 4 is that the heat radiating area should be increased to twice or three times comparative to that of a flat plate. Also, the reason for providing the second flat section 6 instead of forming the entire heat radiating face with V-shaped grooves is to provide strength for the heat radiating plate 4 in a direction which is vertical to the winding direction of the coil. When the heat radiating plate 4 is clipped between the winding layers of the coil 3, an insulating sheet (paper tape) 8 is wound to the core 2, then the winding 9 is wound. After that, the insulating sheet 8 is wound to the wound winding layer, then the winding 9 is wound. Thereafter, winding of the insulating sheet 8 and the winding of the winding 9 are alternately repeated, as is illustrated in Fig. 3. When the thickness of the wound insulating sheet 8 and the wound winding 9 becomes half of the total thickness of the coil 3, the first flat section 5 of the heat radiating plate 4 is put on the uppermost insulating sheet 8, then the winding 9 is wound so that the first flat section 5 is clipped therebetween. Thereafter, winding of the insulating sheet 8 and the winding of the winding 9 are alternately repeated, as is illustrated in Fig. 3. Flat rectangular wire made of aluminium, copper or the like may be used as the winding 9. Fig. 4 illustrates a plan view of only one coil section of the transformer which has been made in the above manner and has the heat radiating plate, while Fig. 5 illustrates a side view thereof. In the transformer, wind is blown by a fan (not illustrated) in a direction illustrated by an arrow so that the transformer is forcibly air cooled. Therefore, sufficient cooling is realized using a comparatively small fan so that the apparatus in its entirety is minimized in size and so that cost for material is reduced. In the above embodiment, description was made of a case where four coils are wound to the core, but the number of coils may be varied depending upon the necessity. Further, the heat radiating plate is provided at the central layer position of the coil in the above embodiment. However,the heat radiating plate may be clipped at a layer position which is the most raised in temperature. Furthermore, U-shaped grooves, rectangular grooves and the like may be employed instead of the V-shaped grooves. Further, V-shaped grooves may be omitted. The transformer according to the present invention is effective in application to an A.C. arc welder, but the transformer is applicable to various apparatus which cause temperature rising in the transformer. It is preferable that the heat radiating plate is made of copper or aluminium.

Claims: A transformer having coils (3a, 3b, 3c, 3d) wound around a core (2), the transformer comprising; a heat radiating plate (4, 4a, 4b, 4c, 4d) which is provided between layers of said coils (3a, 3b, 3c, 3d), which projects outside of said coils (3a, 3b, 3c, 3d), and which comprises a plurality of grooves (7), characterized in that each of said plurality of grooves (7) elongates from a first flat edge portion (6) towards a second edge portion opposite said first edge portion (6) of said heat radiating plate (4, 4a, 4b, 4c, 4d) in parallel to a winding direction of said coils (3a-3d), and each of which has a depth which increases following departure from said first edge portion (6). A transformer as set forth in claim 1, wherein said heat radiating plate (4, 4a, 4b, 4c, 4d) is provided between intermediate layers between a winding starting layer and a winding ending layer of said coils (3a, 3b, 3c, 3d). A transformer as set forth in claim 1 or 2, wherein an edge (5a) of said heat radiating plate (4, 4a, 4b, 4c, 4d) opposite to the direction of projecting is fillet welded (4f) to said coils (3a, 3b, 3c, 3d). A transformer as set forth in claim 3, wherein said coils (3a, 3b, 3c, 3d) and said heat radiating plate (4, 4a, 4b, 4c, 4d) are made of copper or aluminium, and said fillet welding (4f) is carried out using tungsten inert gas welding.

Inventors: OKAUCHI TERUO, TAGUCHI TOSHIO, TERASHIMA TSUNEAKI, OKAUCHI, TERUO, TAGUCHI, TOSHIO, TERASHIMA, TSUNEAKI, OKAUCHI, TERUO, C/O YASHIMA ELEC. CO., LTD., TAGUCHI, TOSHIO, C/O YASHIMA ELEC. CO., LTD., TERASHIMA, TSUNEAKI, C/O YASHIMA ELEC. CO., LTD.
Applicants: YASHIMA DENKI KK, YASHIMA ELECTRIC CO., LTD.
Application year: 1995
Main classification: H01F27
IPC codes: H01F27, H01F29, H01F38