SHEET-WOUND COILS

Abstract: A procedure when joining the tail ends of sheet-wound coils (1, 2) stacked one on top of the other around an inductive apparatus core with a certain axial space between them, the joint being effected using a thin leader strip (3) which is connected to adjacent parts of the coils and joined to the coils along almost one coil turn.

Description: Sheet-wound coils TECHNICAL FIELD Transformers are often provided with sheet- wo; - coils. A coil on an inductive apparatus core may then consist of two or more wound part-coils stacked one on top of the other, which must be joined together in some way. The present invention comprises a procedure for achieving this. BACKGROUND ART Sheet-wound coils are often used as low-voltage coils and consequently conduct relatively high currents. The output conductors must therefore be dimensioned accordingly. When two sheet-wound coils are stacked one on top of the other around a common transformer core with a certain axial space between them, the two sheet-wound coils are identical. However, they are stacked and joined in such a way that, from the winding-direction point of view, they are directed towards each other. This means, therefore, that if a current travels for an instant from the inner layer of one coil to its outer coil, the current from the outer layer of the other coil will continue to the inner layer of the second coil. It is thus the outer sheet layers of the coils that are joined, i.e. the exterior of the coils. This requires space when electrically dimensioning the main channel to the outer coil. It is therefore of great importance that a joint requires as little space radially as possible. Coils have previously been joined with the aid of a copper bar in the final turn. If the area of sheet and bar is the same, with a sheet dimension of 0.5 x 1000 mm and bar width of SO mm, for instance, the bar thickness will be 6.25 mm. SUMMARY OF THE INVENTION The invention permits connection of stacked coils without their having to be provided with terminals. Each coil is wound approximately a half turn more than is necessary in conventional bar splicing as described above. The coils shall be stacked with respect to winding direction in accordance with the state of the art and shall also be arranged radially so that their outer tail ends are located on a generatrix substantially common to the coils. The invention comprises winding a thin strip of conducting material around the coils and attaching this in some suitable manner to the outer layer of the coils along almost one coil turn. The equally large portion of the coils' periphery which is not joined by the thin strip is necessary to prevent short-circuiting of the coil layers. The above-mentioned generatrix which coincides with the tail ends of the coils is arranged to lie substantially centrally in the unjoined portion. The thin strip which thus joins the outer layers of the two coils must of course be dimensioned to ensure a sufficiently large contact area between this and the outer coil layers and that the current endurance will be at least the same as for the rest of the sheet-wound coil. The thickness of the thin surrounding strip is 0.1 -0.5 mm and therefore offers a considerable saving in space in comparison with the current state of the art. As mentioned, the stacked coils must be spaced a certain distance from each other in axial direction. The thin strip wound around the coils also covers the channel formed between the coils, like a belt. The belt thus electrically screens and protects the corners of the coils facing this channel. To also protect the part of the corners in the above-mentioned unjoined portion of the thin strip, this strip is extended to overlap. However, insulating the overlapping portion from the layer below, will prevent the belt from forming a closed turn of the coil. If now the coils located closest to a transformer core as above constitute a part of a secondary winding, a corresponding part of the primary winding will be located outside these. Such a primary winding can also be constructed as a sheet-wound coil. In order to take full advantage of an exterior belt, the belt concept should also be utilized as an inner belt for sheet-wound coils outside the belt. An inner belt can be joined to the coils inside it in the same way as described for the outer coil layers. For the same reason as above, an inner belt should also be provided with overlap and an insulation intermediate portion. l ne procedure described offers considerable .savings in space as well as higher performance and efficiency than has been the case in previous procedures for joining sheet-wound coils. DESCRIPTION OF THE PREFERRED EMBODIMENT The accompanying drawing shows a preferred embodiment of the invention and illustrates how two stacked coils 1 and 2 can suitably be joined together with the aid of a belt 3. It is also seen, as previously described, how the tail end of the outermost layer of coil J terminals at . , i.e. that the winding direction is clockwise, and that coil 2 terminates at 5 and the winding direction is counter¬ clockwise. Coil 1 has a bar 6 as its inner terminal and the corresponding inner terminal for coil 2 is a bar 7. As mentioned above, the belt 3 consists of a thin strip, preferably of the same material as the sheet-wound conducting material. The belt and the outer coil layers can be effected in many different ways, such as uitrasonically or using spot or seam welding. The joint is indicated by xxx in the drawing. The welded areas of the belt to the outer coil layer must be sufficient to fulfil the require¬ ment of sufficiently low transition resistance. As is evident, the belt also forms an electrical screen for the edges of the coils facing each other. To obtain full protection around the entire periphery a certain peripheral overlapping of the belt is necessary. To prevent this overlap from causing the belt to form a closed coil turn, the overlapping parts must be electrically isolated. This is suitably achieved by placing an insulating strip 8 between the overlapping parts of the belt. The insulating strip should have such peripheral extension that it more than covers the part of the belt which is not joined to the outer coil layers. The inner belt described earlier is applied in the same way as the exterior belt, the belt being joined with overlap to the inner coil layers of the sheet-wound coil, and with an insulating strip at the overlap. The external terminals of these outer coils may then comprise bars connected to the coil ends terminating out¬ side. There is normally always sufficient space for these outer terminals.

Claims: CLAIMS 1 A procedure when joining the tail ends of sheet-wound coils (1, 2) stacked one on top of the other around an inductive apparatus core with a certain axial space between them, which procedure is characterised in that the joint is effected with the aid of a belt (3) consisting of a thin leader strip which is connected to adjacent parts of the coils and joined to the coils along almost one coil turn. 2. A procedure as claimed in claim 1 for joining the tail ends of sheet- wound coils, which procedure is characterised in that the joint is effected as an external belt around the outer layers of the coils. 3. A procedure as claimed in claim 1 for joining the tail ends of sheet- wound coils, which procedure is characterised in that the joint is effected as an internal belt which is connected to the inner layers of the coils. -. A procedure as claimed in claim 1 for joining the tail ends of sheet- wound coils, which procedure is characterised in that the thin leader strip consists of the same conducting material as the sheet-wound coils. 5. A procedure as claimed in claim 1 for joining the tail ends of sheet- wound coils, which procedure is characterised in that the thin strip consti¬ tuting the belt is of such length that the leading end and tail end of the strip overlap. 6. A procedure as claimed in claim 1 for joining the tail ends of sheet- wound coils, which procedure is characterised in that an insulating strip (8) is inserted between the leading end and the tail end of the thin strip. 7. A procedure as claimed in claim 1 for joining the tail ends of sheet- wound coils, which procedure is characterised in that the coil sheet and belt are joined by means of ultrasonic welding.

Inventors: FORSBERG ERIK, LUNDSTROEM LENNART, ZETTERLUND UNO, FORSBERG, ERIK, LUNDSTROEM, LENNART, ZETTERLUND, UNO
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1991
Main classification: H01F41
IPC codes: H01F27