GB2131626A - Variable set core for choke or transformer - Google Patents

Abstract

A laminated core comprises an E-shaped member (3) bridged by a generally I-shaped member (11) so as to form an air-gap (4) adjacent the end face of the centre leg of the former. The I-shaped member is weakened at its centre by a slot (10) and is seam-welded (12) at its outer edges to the end faces of the outer legs of the E-shaped member. The said end faces and the corresponding facing surfaces of the I-shaped member define small acute angles at the respective seam welds, enabling the air gap to be set by inelastically deforming the I-shaped member. <IMAGE>

Description

SPECIFICATION Variable set choke This invention relates to chokes and other electromagnetic devices incorporating ferromagnetic cores having pre-set air gaps and to cores for such devices.

More especially, it relates to cores of the type comprising a first member consisting of a stack of E-shaped laminations bridged by a second member consisting of a stackofl-shaped laminations. Hitherto such cores have either been constructed with a fixed air gap between the endface of the centre leg ofthe E-shaped member and the adjacent face of the I-shaped bridging member by seam-welding the ends of the I-shaped bridging memberto the outer edges of the outside legs of the E-shaped member, or have been constructed with a settable air gap by providing adjustable clamping means to hold the bridging member closely adjacentthe E-shaped member.

Settable chokes have also been made by bridging an E-shaped member having a shortened centre leg with a deformable I-shaped member and clamping the members together by encasing the assembly in mild steel. The air gap between the l-shaped member and the centre leg of the E-shaped member is then set by compressingthe appropriate opposite faces of the enclosed assembly. Owing to the low elasticity of mild steel, the I-shaped member does notspring back to an appreciable extent from the centre leg of the E-shaped member when the compressing force is removed, enabling the air gap to be set quite easily. An object of the present invention is to provide an alternative core construction which has advantages over these previous proposals as will be apparent from the following description.

However, before describing the present invention, reference will be made to Figures 1 to 3 ofthe accompanying drawings, in which Figure 1 shows a conventional choke core with a fixed air gap Figure 2 shows a conventional choke with an air gap set by an adjustable clamp Figure 3 shows a conventional deformable choke core assembly designed to beclampedwithin a mild steel casing.

Referring to the drawings, Figure 1 shows a welded joint 1 holding an I-shaped bridging member2 across an E-shaped member3 having a shortened central leg, therebyforming a fixed air gap 4. This arrangement has the obvious disadvantage that close tolerances in the dimensions of all the components are necessary in orderto achieve a reproducable inductance.

Figure 2 shows an I-shaped member 5 clamped to an E-shaped member3 by insulating clamps 6 which sandwich the core assembly. Two of the bolts 7 pass through elongated holes 8 in the clamps, enabling the distance betweenthetwo core members 3 and 5 to be adjusted. This clamping arrangement is liable to become loosened by vibration and mechanical shock, and results in increased manufacturing costs.

Figure3 shows an I-shaped core member 9 located against an E-shaped core member 3. The assembly is held together by a steel casing (not shown) and the air gap 4 adjusted by compressing the encased assembly in the directions shown bythearrows,thereby bending the core member in the region ofthe slot 10.

This arrangement is also liable to become loosened and misaligned to a certain extent.

According to the present invention a core for an electromagnetic device includes a firstferromagnetic member which makes line contact with a second ferromagnetic member at two spaced places only, the lines of contact being parallel, at which places it is welded to the second member; and the shapes of the said members are such that the first said member is deformabletovaryagap between part of the first member and part of the second member whilst maintaining said line contact.

The use of welded joints together with the use of conventional inelastic core materials such as silicon steels ensure thatthe gap remains at a setvaluewhen the deforming force is removed, thereby dispensing with the need for a steel casing.

Preferably at least the first said member consists of astackoflaminationslying perpendiculartothe said lines of contact. Preferably a slot is formed in the first member between and parallel to the lines of contact on the side ofthe first member opposite to the said gap. Preferablythe first member comprises a stack of I-shaped laminations which are stamped out in a slotted form, so that the slot in thefirst member is formed by registering the slots in the laminations.

The scope and advantages of the invention will become clearer on consideration of Figures 4 and 5 of the accompanying drawings.

Figure 4 shows an elevation of one example of choke core according to the present invention. An I-shaped member 11 makes contactwith an E-shaped member 3 at points 12 where it is seam-welded. The angles 13 are acute, enabling the width of the air-gap 4 to be set by applying a force to the member 11 as shown by the arrow. The member 11 bends mainly in the region weakened by the slot 10, as shown in an exaggerated manner by the dotted lines. Modern conventional core materials such as silicon steels are sufficiently inelasticforthe member 11 to remain in the position indicated by the dotted lines when the force is removed.

The invention therefore provides a simple and permanent method of setting an air gap. Preferably the depth of the slot is at least 40% ofthethickness of the I-shaped member. Use of an E-shaped member having legs of equal length enables cores without air-gaps (e.g. for transformers) to be made simply by welding Eandlshaped memberstogetherwiththe position of the latter reversed, so that the surface 14 abuts the legs, or by welding togetherthe respective legs of two oppositely facing E-shaped members.

Figure 5 again shows byway of example another core construction in accordance with the invention. In this construction an I-shaped member 15 incorporating a slot 10 seam-welded at 16 to an E-shaped member 17. Theair-gap 4 is adjusted by deforming the I-shaped member 15 in the direction shown by the arrow. In this case the I-shaped member has a generally rectangular cross-section, and the angles 18 are acute. It is clearthatthe invention includes within its scope adaptations and combinations of the examples shown in Figures 4and 5, aswell as chokes and transformers incorporating cores so constructed.

Claims (7)

1. A core for an electromagnetic device, comprising an inelastically deformable first ferromagnetic member which makes line contactwith a second ferromagnetic member attwo spaced places only, the lines of contact being parallel, at which places it is welded to the said second member, the shapes of the said members being such thatthe said first member is deformable to vary a gap between parts of the said members whilst maintaining said line contact.

2. Acore according to Claim 1 in which a slot is formed in the first member between and parallel to the lines of contact on the side of the first member opposite the said gap.

3. Acore accordingto Claim 1 orClaim2inwhich the said first memberconsists of a stack of laminations lying perpendicularto the said lines of contact.

4. Acore according to any preceding Claim whereinthefirst member is generally Shaped, the second member is generally E-shaped and is secured to the first member by seam welds at the ends of the respective outer legs of the E-shaped second member, the said welds constituting the said line contact.

5. A core according to Claim 4wherein the end faces of the legs ofthe second member are coplanar.

6. A core substantially as described hereinabove with reference to Figure 4 of the accompanying drawings.

7. A core substantially as described hereinabove with reference to Figure 5 ofthe accompanying drawings.