GB2089764A

GB2089764A - Coil former for transformer

Info

Publication number: GB2089764A
Application number: GB8135389A
Authority: GB
Original assignee: Legrand SA
Current assignee: Legrand SA
Priority date: 1980-11-25
Filing date: 1981-11-24
Publication date: 1982-06-30
Also published as: FR2494889A1; IT8168497A0; FR2494889B1; LU83773A1; IT1145743B; GB2089764B; DE8133597U1; BE890882A

Abstract

A former (10) for a transformer (22) comprises a tubular body on which an electrical coil (12) is wound and which receives internally a component (13) of a magnetic circuit (14). Two rigid parallel beads (17) project inwardly from each of two opposed walls of the tubular body and the wall of the tubular body has at least one aperture (20) between the beads (17), so that, when the transformer (22) is in use, a ventilation shaft (23) is formed between the beads (17) and the component (13) of the magnetic circuit (14) to ventilate the electrical coil (12). <IMAGE>

Description

SPECIFICATION Carcass for a transformer and a transformer including such a carcass The invention relates to transformers.

Transformers basically comprise an electric circuit, usually of copper wire, and a magnetic circuit, usually made of suitably stacked steel plates, the electric circuit being wound around at least a portion of the magnetic circuit.

The invention is particularly concerned with transformers where, for convenience of manufacture, a mandrel or former, commonly described as the carcass, is interposed between the electric circuit and the magnetic circuit. The carcass comprises a tubular body, in practice with a four-cornered crosssection on which the electric circuit is wound and which internaily receives said portion of the magnetic circuit.

In some constructions, such as described in French Patent number 1 325 184, the tubular body of such a carcass is provided on one internal surface with two flexible beads, projecting inwardly and extending obliquely to the wall which carries them.

The purpose of the beads is to provide a good hold for said portion of the magnetic circuit, and replaces blocks normally provided for that purpose. On insertion of the portion of the magnetic circuit in the tubular body, the beads are resiliently crushed. An opposed surface of the tubular body is provided with two rigid beads of relatively limited amplitude, forming an air shaft between them.

One of the problems which has to be solved as a general principle in the manufacture of transformers, whether or not they include a carcass, is to improve the efficiency, that is to say to reduce the losses during operation, particularly those losses occurring in the electric circuit.

The invention has among its objections to provide a construction which makes it possible to take advantage of a carcass which has rigid beads projecting inwardly therefrom so as to reduce losses.

According to the invention there is provided a carcass for a transformer comprising a tubular body on which an electric circuit is or is to be wound and receiving and locating orto receive and locate therein a component of a magnetic circuit, the tubular body having at least two spaced apart rigid parallel beads, extending longitudinally, projecting inwardly and forming or to form, with said component of the magnetic circuit when inserted into the tubular body, a longitudinally extending air passage, wherein the wall of the tubular body between the spaced apart beads has an aperture therein so that, when the transformer is in use, said air passage forms a ventilation shaft to ventilate heat from the electric circuit.

Provision of such a ventilating shaft can appreciably lower the temperature of the electric circuit in operation.

If conditions are otherwise equal, an effective drop in temperature of at least 1 SOC can be obtained.

The electrical resistance of copper is known to increase with temperature and thus, by reducing the temperature, losses during operation will thus be reduced.

In the above-mentioned French Patent number 1 325184 the flexible beads of the carcass are crushed in operation, as mentioned above.

Consequently they do not then form a ventilating shaft between them, and any space left between them is in any case insufficient to provide for satisfactory air circulation.

Then again, the rigid beads also provided in French Patent number 1 325 184 are too limited in amplitude for the shaft formed between them to provide a ventilation shaft.

Moreover in French Patent number 1 325 184 no aperture is provided in the walls of the carcass, so that in any case the electric circuit cannot be ventilated from any space that may be left between the beads projecting inwardly from the wall.

In the carcass of the invention the beads used are rigid and thus non-deformable and can have an amplitude such that, cooperating with the aperture in the wall which carries them they can provide for effective air circulation.

The invention also concerns a transformer including a carcass with rigid beads and an aperture as described above.

The invention is diagrammatically illustrated by way of example in the accompanying drawing, in which Figure 1 is a perspective view of a carcass for a transformer according to the invention, and Figure 2 is a fragmentary view on a larger scale, with the righthand half in elevation and the lefthand half in cross-section, of a transformer including a carcass according to the invention.

In general and in known manner, a carcass for a transformer 10 has a tubular body 11. The body 11 receives a coil of an electric circuit 12 wound thereonto and internally receives a component 13 of a magnetic circuit 14.

In the example illustrated, the tubular body 11 has a four-cornered cross-section, to receive the magnetic component 13 which is of rectangular section. At its ends the body 11 has two integral parallel end flanges 15, projecting outwardly to contain the coil of the electric circuit 12.

In this example, the shape of the end flanges 15 is basically four-cornered, like that of the cross-section of the tubular body 11.

At two opposed edges, the shorter edges in the embodiment illustrated, each of the end flanges 15 is cutaway to form recesses 16.

The tubular body 11 has at least two integral parallel beads 17 projecting inwardly into its internal space.

The beads 17 are rigid, that is to say nondeformable.

In the example shown, two pairs of beads 17 are provided on the two opposed shorter walls of the tubular body 11.

The beads 17 extend perpendicularly to the walls which carry them and run longitudinally over the whole height of the tubular body 11.

Their amplitude, or the height of the projection which they form relative to the walls carrying them is relatively great.

It is greater than the thickness of the walls and, preferably and as shown, at least twice that thickness.

Preferably and as shown, the beads 17 have a chamfer 18 at least one end and preferably at each end.

In the example shown, each of the two beads 17 projecting from one wall of the tubular body 11 is aligned with a respective one of the beads 17 projecting from the opposed wall of the body 11.

Between the two beads 17 on one and the same wall of the body 11, the wall contains at least one aperture 20.

In practice, in the example illustrated, two such apertures 20 are provided, in a continuation of one another, in one and the same wall of the tubular body 11; each of the apertures 20 is elongate like a buttonhole along the respective wall, and extends laterally for the full width available between the corresponding beads 17.

Thus each wall of the tubular body 11 carrying two beads 17 is largely cut away between the beads 17.

In the usual way, the electric circuit 12 which is wound externally over the tubular body 11 to form a transformer is made of copper wire.

The magnetic circuit 14 to be used in the transformer is made of suitably stacked steel sheets.

in practice the sheets in the corresponding stack extend perpendicularly to the direction in which the beads 17 extend from the wall which mounts them.

It will be appreciated that the chamfers 18 on the beads 17facilitatethe insertion of the component 13 of the magnetic circuit 14 inside the carcass 10.

If necessary, packing blocks can be used between the beads 17 and the magnetic component to provide a good hold for the component.

When the resultant transformer 22 is in use, a ventilation shaft 23 is formed between each pair of beads 17 and the component 13 of the magnetic circuit 14. The ventilation shaft extends over the whole height of the carcass 10, and its cross-section is well defined and non-deformable because of the rigidity ofthe beads 17.

By means of the apertures 20 located between the beads 17, the ventilation shaft 23 can provide significant ventilation for the electric circuit 12, in order to cool it.

Claims

1. A carcass for a transformer comprising a tubular body on which an electric circuit is or is to be wound and receiving and locating orto receive and locate therein a component of a magnetic circuit, the tubular body having at least two spaced apart rigid parallel beads, extending longitudinally, projecting inwardly and forming orto form, with said compo nent of the magnetic circuit when inserted into the tubular body, a longitudinally extending air passage, wherein the wall of the tubular body between the spaced apart beads has an aperture therein so that, when the transformer is in use, said air passage forms a ventilation shaft to ventilate heat from the electric circuit.

2. A carcass according to claim 1, in which the aperture in the wall between the two spaced apart beads extends over the full width of the spacing between the beads.

3. A carcass according to claim 1 or claim 2, in which the aperture between the two beads is elongate.

4. A carcass according to any one of claims 1 to 3, in which a further aperture is provided between the two beads, the aperture and further aperture each forming an extension of the other.

5. A carcass according to any one of claims 1 to 4, in which almost the whole of the wall of the tubular body between the two beads is cut away.

6. A carcass according to any one of claims 1 to 5, in which the height of the beads, that is to say the distance by which they extend away from the wall which carries them, is greater than the thickness of said wall and preferably twice the thickness of the wall.

7. A carcass according to any one of claims 1 to 6, in which each of the beads has a chamfer at least at one of the ends of the tubular body.

8. A transformer comprising an electric circuit wound onto a carcass in the form of a tubular body with a component of a magnetic circuit received in the tubular body, wherein the carcass is in accord ante with any one of claims 1 to 7.

9. A carcass for a transformer substantially as hereinbefore described and illustrated with reference to the accompanying drawing.