Metal working – Method of mechanical manufacture – Electrical device making
Patent
1993-01-06
1994-11-15
Picard, Leo P.
Metal working
Method of mechanical manufacture
Electrical device making
2281101, 296021, 336220, 336232, H01F 2728
Patent
active
053635485
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
Transformers are often provided with sheet-wound 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.times.1000 mm and bar width of 80 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
REFERENCES:
patent: 3195088 (1965-07-01), Sandoz
patent: 3668588 (1972-06-01), Walsh, Jr.
Forsberg Erik
Lundstrom Lennart
Zetterlund Uno
Asea Brown Boveri AB
Picard Leo P.
Thomas L.
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