GB2037089A - Ferromagnetic core having a gap - Google Patents

Abstract

A device, particularly a transformer, comprises a ferromagnetic core 1 having a gap 7 which is divided into a plurality of partial gaps 71-74, filled with a solid, non-ferromagnetic material consisting of a glue and glass particles, the gaps being magnetically arranged in series by means of plates 13, 15, 17 of a ferromagnetic material. The dimensions of the glass particles determine the gap widths. Division of the air gap helps to limit the stray field 9 that penetrates the aluminium foil primary winding 3 wound on the ferrite core 1. The secondary coil 5 is of copper wire. <IMAGE>

Description

SPECIFICATION Ferromagnetic core having an air gap The invention relates to a device having a ferromagnetic core which forms a magnetic circuit interrupted by at least one air gap, which air gap is divided into at least two partial air gaps, which are magnetically arranged in series by means of one or more plates of ferromagnetic material.

An example of such a device is described in the German Patent Specification 526,1 75.

Dividing the air gap has for its object to limit the lateral extension of the magnetic stray field in situ of the air gap to a considerable extent. This lateral extension is undesirable when there are components near the device whose operation can be disturbed by such a stray field and also when the core is enveloped in situ of the air gap by a coil consisting of foil. In the latter case the stray field produces eddy-current losses in the foil.

It is an object of the invention to provide a device of the type defined in the opening paragraph, wherein the lengths of the partial air gaps can be accurately determined without the necessity of measuring these lengths during manufacture. According to the invention the device is therefore characterized in that the partial air gaps are filled with a nonferromagnetic solid material consisting of a mixture of a glue with glass particles. The plate or plates of ferromagnetic material can be simply cemented together with the glue, the dimensions of the glass particles determining the length of the partial air gaps.

The invention will now be further explained with reference to the accompanying drawing in which: Figure 1 shows an elevational view of a transformer according to the invention, and Fi 2 is a detailed cross-sectional representation of the portion of the core where the air gap is located.

Fig. 1 shows a transformer having a ferromagnetic core 1, for example consisting of ferrite, a p3 imary coil 3, wound from aluminium foil and a secondary coil 5, wound of copper wire. In situ of the primary coil 3 the core 1 is interrupted by an air gap 7 (depicted by means of a dotted line).

Fig. 2 shows in detail the air gap 7 and its immediate surroundings. The air gap 7 is divided into four partial air gaps 71, 72, 73, 74, which are magnetically arranged in series by plates 13, 15, 1 7 of ferromagnetic material, preferably of the same material as that used for the core 1. Each of these partial air gaps is of such length that the magnetic stray field has only a very small lateral extension. For this reason the lines of force 9 of this stray field hardly reach the first layers 11 of the foil coil 3, so that substantially no eddy current losses are produced. If the coil 3 in a different embodiment is kept at a small distance from the core 1 by use of a coil former (not shown), the eddy current losses can even be completely prevented from occurring.

The partial air gaps 71, 72, 73, 74 are filled with a mixture of glue (for example a synthetic resin) containing glass particles. The dimensions of the glass particles help to determine the length of the partial air gaps.

The number of partial air gaps depends of course on the length of the original air gap 7 and on the permissible lateral extension of the stray fields. A significant reduction in this extension is already achieved when the original air gap is divided into at least two partial air gaps.

1. A device having a ferromagnetic core which forms a magnetic circuit interrupted by at least one air gap, which air gap is divided into at least two partial air gaps which are magnetically arranged in series by means of one or more plates of a ferromagnetic material, characterised in that the partial air gaps are filled with a non-ferromagnetic solid material which consists of a mixture of a glue with glass particles.

2. A device as claimed in Claim 1, in which the core carries primary and secondary transformer windings.

3. A device having a ferromagnetic core which forms a magnetic circuit interrupted by at least one air gap, substantially as hereinbefore described with reference to the accompa nying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Ferromagnetic core having an air gap The invention relates to a device having a ferromagnetic core which forms a magnetic circuit interrupted by at least one air gap, which air gap is divided into at least two partial air gaps, which are magnetically arranged in series by means of one or more plates of ferromagnetic material. An example of such a device is described in the German Patent Specification 526,1 75. Dividing the air gap has for its object to limit the lateral extension of the magnetic stray field in situ of the air gap to a considerable extent. This lateral extension is undesirable when there are components near the device whose operation can be disturbed by such a stray field and also when the core is enveloped in situ of the air gap by a coil consisting of foil. In the latter case the stray field produces eddy-current losses in the foil. It is an object of the invention to provide a device of the type defined in the opening paragraph, wherein the lengths of the partial air gaps can be accurately determined without the necessity of measuring these lengths during manufacture. According to the invention the device is therefore characterized in that the partial air gaps are filled with a nonferromagnetic solid material consisting of a mixture of a glue with glass particles. The plate or plates of ferromagnetic material can be simply cemented together with the glue, the dimensions of the glass particles determining the length of the partial air gaps. The invention will now be further explained with reference to the accompanying drawing in which: Figure 1 shows an elevational view of a transformer according to the invention, and Fi 2 is a detailed cross-sectional representation of the portion of the core where the air gap is located. Fig. 1 shows a transformer having a ferromagnetic core 1, for example consisting of ferrite, a p3 imary coil 3, wound from aluminium foil and a secondary coil 5, wound of copper wire. In situ of the primary coil 3 the core 1 is interrupted by an air gap 7 (depicted by means of a dotted line). Fig. 2 shows in detail the air gap 7 and its immediate surroundings. The air gap 7 is divided into four partial air gaps 71, 72, 73, 74, which are magnetically arranged in series by plates 13, 15, 1 7 of ferromagnetic material, preferably of the same material as that used for the core 1. Each of these partial air gaps is of such length that the magnetic stray field has only a very small lateral extension. For this reason the lines of force 9 of this stray field hardly reach the first layers 11 of the foil coil 3, so that substantially no eddy current losses are produced. If the coil 3 in a different embodiment is kept at a small distance from the core 1 by use of a coil former (not shown), the eddy current losses can even be completely prevented from occurring. The partial air gaps 71, 72, 73, 74 are filled with a mixture of glue (for example a synthetic resin) containing glass particles. The dimensions of the glass particles help to determine the length of the partial air gaps. The number of partial air gaps depends of course on the length of the original air gap 7 and on the permissible lateral extension of the stray fields. A significant reduction in this extension is already achieved when the original air gap is divided into at least two partial air gaps. CLAIMS

1. A device having a ferromagnetic core which forms a magnetic circuit interrupted by at least one air gap, which air gap is divided into at least two partial air gaps which are magnetically arranged in series by means of one or more plates of a ferromagnetic material, characterised in that the partial air gaps are filled with a non-ferromagnetic solid material which consists of a mixture of a glue with glass particles.

2. A device as claimed in Claim 1, in which the core carries primary and secondary transformer windings.

3. A device having a ferromagnetic core which forms a magnetic circuit interrupted by at least one air gap, substantially as hereinbefore described with reference to the accompa nying drawing.