WO1992017890A1

WO1992017890A1 - Transformer core assembly and method of manufacture thereof

Info

Publication number: WO1992017890A1
Application number: PCT/GB1992/000545
Authority: WO
Inventors: Roy Kerry
Original assignee: Geo L. Scott & Co. Ltd.
Priority date: 1991-03-26
Filing date: 1992-03-25
Publication date: 1992-10-15
Also published as: GB2254964A; GB9106425D0

Abstract

A transformer core assembly (1) comprises a stack (2) of first laminations (4) and a stack (3) of second laminations (5). The first laminations (4) each have a base portion (6) and at least two parallel limb portions (7, 8, 9:23, 24) extending from the base portion (6:22) so as to define at least one channel (10, 11). The second laminations (5) include a longitudinally extending edge (15, 27) which are located in abutment with the free end faces (12) of at least two of the limbs (7, 8, 9:23, 24). Interengagement devices (13, 18, 19) are provided for interlocking the two stacks (2, 3), each interengagement device including two portions, one on each stack (2, 3). The interengagement portions each have abutment surfaces (13a, 13b, 19a, 19b) which interlock the two stacks (2, 3) when a force is applied in a direction (20, 21, 29, 30) normal to the abutment edge (15:27). A method of producing such an assembly by locating the stacks (2, 3) so that the free end faces (12) of at least two of the limbs (7, 8, 9:23, 24) are in abutment with the edge (15, 27) and then applying a force in a direction (20, 21, 29, 30) normal to the edge (15) is also disclosed.

Description

TRANSFORMER CORE ASSEMBLY AND METHOD OF MANUFACTURE THEREOF

The present invention relates to a transformer core assembly and to a method of producing a transformer core using such an assembly. More particularly, the present invention relates to a transformer core assembly which can be readily interengaged so as to produce a transformer core defining at least one internal aperture.

Transformer cores are of course well known. Such cores are often formed from stacks of two differently shaped sets of laminations. The most commonly used laminations are, respectively E-shaped and i-shaped. Although referred to in the art as I- shaped these laminations are effectively simple bars. In other words, they do not have end flanges. A manufacturer will, in general, produce appropriate sets of laminations. A customer or manufacturer then provides each stack with appropriate electrical windings and connects the two stacks to form a transformer core or connects the two stacks and then applies one or more windings thereto.

The connections can be effected in a number of different ways. Thus, the simplest way of achieving this, in theory, is to interleave the laminations in the two stacks so that, in the finished core, the laminations are in a continuing alternating sequence of EIEIEI. The major advantages of such a method of connection are that the laminations do not need to be modified in any way and the core is formed in a manner which is unlikely to cause physical damage to the laminations. However, such a method gives rise to certain disadvantages. Firstly, there is no physical connection between the laminations. Secondly, the interleaving process, even if mechanised, is complex and time consuming.

A further known method of producing a transformer core is to align stacks . of E-shaped laminations and of I-shaped laminations with one another such that the I-shaped laminations lie along the end faces of the arms of the E-shaped laminations. The two stacks are then interconnected by welding. It will be appreciated that the thus-formed core has a substantially rectangular outline defining two internal bores which are also substantially rectangular in cross-section. This produces a more securely connected core than that produced by the interleaving method but the welding is liable to cause eddy currents to be set up when the core is used. Moreover, such welding can adversely affect the electro-magnetic properties of the assembly.

A more recently devised method necessitates a slight modification of the shape of both the E-shaped and the I-shaped laminations. In such an arrangement, the outer arms of each E-shaped lamination are each provided, on their external surfaces, with inwardly extending blind bores, each bore extending towards the central arm of the E. In other words, these bores extend parallel to the upright portion of the E. The I-shaped laminations are also modified in that a unilaterally extending flange portion is provided at each end of the I. The two sets of laminations are then aligned with one another in a manner similar to that described hereinbefore with respect to the method in which welding is employed. However, in this instance, the end portions of the flanges provided on the I-shaped laminations are aligned with the blind bores formed in the external arms of the E-shaped laminations. The two stacks are then retained in position whilst pressure is applied simultaneously at the two opposed ends of the stacks of I-shaped laminations in directions which force the end portions of the flanges of the I-shaped laminations into the corresponding blind bores in the E-shaped laminations.

It will therefore be appreciated that such application of pressure is, effectively, a pincer operation. Such operation produces a fixed connection between the two sets of laminations but has the disadvantage that the laminations are subjected to physical deformation. This is almost certain to affect the operation of the transformer core thus produced in an adverse manner. Moreover, the deformation of the material exceeds its elastic limit and the resilience thereof is lost. Accordingly, such treatment is not entirely satisfactory.

The present invention therefore seeks to provide laminations suitable for use in producing a transformer core and a method of producing a transformer core from such laminations wherein the connection of the laminations is effected positively without causing undue deformation of the laminations themselves, without the need for welding and without the need for specialised equipment, such as jigs, to effect such deformation and connection.

Furthermore, the present invention seeks to provide a method of producing a transformer core from laminations whereby the laminations themselves can be produced in a so-called "scrapless" manner. "Scrapless" in this context, is a term well-known in the art. According to the present invention, there is provided a transformer core assembly comprising a stack of aligned and connected first lamination members, each member comprising a base portion and at least two limb portions extending substantially parallel to one another in a direction away from said base member, said limb portions and said base portion jointly defining at least one open channel and a stack of aligned and connected second lamination members, each said member having a longitudinally extending edge, the edges of such members, when stacked, forming a longitudinally extending face, said face being located in abutment with the free end face of at least the outer limbs of the stack of first lamination members to close said channel and form at least one window, said two stacks jointly defining at least two interengagement devices for maintaining said faces in abutment with one another whereby interengagement is caused by applying a force characterised in that each said interengagement device comprises an interengagement portion formed on said stack of first lamination members and an interengagement portion formed on said stack of second lamination members, said interengagement portions having abutment surfaces which form an interlock between said stacks when a force is applied to said stacks in a direction to the abutment face of said stack of second lamination members.

The force may be produced by holding one of the stacks and applying a force in the desired direction to the other stack or by applying a plurality of forces to one or both stacks such that the resultant of such forces is substantially normal to the abutment face. Thus, for example, two opposed forces each acting in a direction which is normal to the abutment face may be applied, one to each stack. Preferably, the first lamination members each have a substantially E-shaped cross-section. In such a case, it is desirable if the second lamination members each have a substantially I-shaped cross-section.

Alternatively, the first lamination members may each have a substantially U-shaped cross-section. In this embodiment, it is advantageous if the second lamination members each have a substantially T-shaped cross-section. Further preferably in such an arrangement, the abutment face of the stack of second lamination members is formed by the underside of the cross bar of each T-shaped member.

In both embodiments, it is desirable if the interengagement devices comprise recesses formed in one of the stacks of lamination members and corresponding protrusions formed on the other stack of laminations whereby the protrusions fit into the recesses.

Advantageously, the recesses formed in the first stack of laminations are disposed in the free end faces of the limbs at the edges thereof. Further advantageously, the protrusions formed in the longitudinally extending face of the second stack of laminations are disposed adjacent to the end regions thereof.

The interengaging portions of the component stacks may not be exactly correspondingly shaped. Instead, the abutment portions of the interengagement devices may subtend a slight angle with one another so as to improve the engagement between such portions.

Also according to the present invention, there is provided a method of producing a transformer core assembly from a stack of aligned and connected first lamination members and a stack of aligned and connected second lamination members, the first lamination members each comprising a base portion and at least two limb portions extending substantially parallel to one another in a direction away from the base portion, said base portion and said limb portions jointly defining at least one open channel and the second lamination members each having a longitudinally extending edge such that, when stacked, the edges form a longitudinally extending face, the two stacks being provided with co-operating interengagement devices, comprising locating the two stacks in abutment with one another such that the longitudinally extending face is in abutment with the free end faces of at least the outer limbs and applying a force to one of the stacks in a direction at right angles to the abutment face of the stack of second lamination members, so as to cause closure of said at least one channel thereby forming at least one window and the interengagement of said interengagement devices. The manner in which the force is produced is as described hereinbefore.

The present invention will be further described, by way of example, with reference to the accompanying drawings, in which: -

Fig. 1 shows a plan view of a first embodiment of a transformer core assembly in accordance with the present invention;

Fig. 2 shows a plan view of a second embodiment of a transformer core assembly in accordance with the present invention; and Fig. 3 shows, on an enlarged scale, a detail of interengagement members forming part of the core assemblies shown in Figs. 1 and 2 and being ringed at A in both Figs. 1 and 2.

Referring now to the drawings, there is shown, in Fig. 1, a transformer core assembly 1. The assembly 1 is formed from two stacks of aligned laminations 2 and 3. Since Fig. 1 is a plan view, only the uppermost lamination in each stack is visible. Each individual lamination 4 in the stack 2 has a substantially E-shaped section comprising a base portion 6 having a plurality of limb portions 7, 8, 9 formed thereon. The limb portions 7, 8, 9 all extend parallel to one another in the same direction away from the base portion 6. it can therefore be seen that two open channels 10 and 11 are defined by the stack 2 of laminations 4. As shown, the outer limb portions 7 and 9 are longer than the central limb portion 8. If desired, however, all of the limb portions 7, 8 and 9 could be of identical lengths. Each limb portion 7, 8, 9 terminates in an end face 12. At the outer end of the end face of each of the two outer limb portions 7 and 9, a recess 13 is formed. The reason for the provision of such a recess will become apparent hereinafter.

Each individual lamination 5 in the stack 3 has a substantially bar or I-shaped section. Although referred to in the art as an I-section, it should be noted that such laminations do not normally have end flanges 18 and 19 which project laterally outwardly of the main body portion 14 of the I. The main body portion 14 includes two parallel opposed longitudinally extending edges 15 and 15^. The flanges 18 and 19 each project beyond the edges 15 by an amount which is substantially identical to the depth of the recesses 13. Similarly, -the width of the flanges 18 and 19 are each substantially identical to the width of the recesses 13.

To form a transformer core, the two aligned and connected stacks 2 and 3 are brought into contact with one another so that one of the faces formed by the aligned edges 15 is in abutment with at least the end faces 12 of the outer limb members 7 and 9. A force is then applied in a direction shown by arrow 20 at right angles to the base portion 6 of the laminations 2, in a direction shown by arrow 21 at right angles to the non- abutment face 15 or by applying opposing forces in the direction of arrows 20 and 21 simultaneously.

This closes the channels 10 and 11 and forms windows. Moreover, the two stacks are interengaged by means of the recesses 13 and the flanges 18 and 19. Similarly, the sections 18 and 19 are caused to enter the recesses 13. The laminations are generally made of materials which are, to some extent, resilient and this resilience helps to prevent the interengagement from becoming detached when the force is removed. Moreover, the elastic limit of the material from which the laminations are formed is not exceeded.

Moreover, as shown in Fig. 3, the abutment surfaces of the interengagement devices are disposed at a slight angle, for example 5° to one another. This further assists the interengagement of the relevant surfaces. As can be seen in Fig. 3, the flange 19 is provided with two interconnected radiused portions 19a_ and 19b and the recess 13 in the end face 12 of the arm 7 is also defined by two interconnected radiused portions 13a. and 13b_. A slightly modified embodiment of the invention is shown in Fig. 2. In this embodiment, the stack of lamination 2 is U-shaped and the stack of laminations 3 is T-shaped. Again, although referred to in the art as U-shaped laminations, the base 22 of the U is flat and not arcuate. The U includes two limb portions 23 and 24 which extend parallel to one another in a direction away from the base 22. The free end faces of the limbs 23 and 24 each have a recess 13 formed in their outer end edges. The T-shaped laminations have a cross-piece portion 25 and an upright portion 26. The underside 27 of the cross- piece portion 25, that is to say, the face from which the upright portion 26 extends, corresponds to the edge 15 of the I-shaped laminations 5 shown in Fig. 1. The underside 27 is provided with projections 18 and 19 extending parallel to the upright portion and corresponding to the flanges 18 and 19 shown in Fig. 1. The recesses and the projections 18 and 19 are, again, shaped as shown in Fig. 3 and as described hereinbefore.

The interengagement of the two stacks of laminations is effected in a manner which is similar to that described with reference to the embodiment shown in Fig. 1. In other words, the stacks of laminations 2 and 3 are aligned and brought into abutment with one another and a force is then applied either to the base portion 22 or the non-abutment face 28 in a direction at right angles to such portions in the direction of arrow 29 or 30 respectively. Alternatively, two opposing forces may be applied in the direction of the arrows 29 and 30 simultaneously. In each of the two embodiments described, the external surfaces of the core assembly produced are substantially flat. Various minor modifications may be made to the present invention without departing from the scope thereof. Thus, for example, the embodiment shown in Fig. 1 could be modified by the provision of a second stack of E-shaped laminations which are interengaged with the same stack of I-shaped laminations to provide a transformer core having an E-I-reversed E configuration. Moreover, a transformer core assembly could be formed from U-shaped and I-shaped laminations. Still further, an assembly having an E-reversed E configuration could be produced, although the two stacks of laminations would be different from one another in that the outer limbs 7 and 9 of one stack would have recesses 13 formed in their end faces 12 whilst the other stack would have projections instead of recesses.

In both embodiments shown, only the outer limbs of the first stack of laminations abut against the other stack of laminations. Thus, in Fig. 1, the central limb portion 8 is shorter than the limb portions 7 and 9 such that an air-gap 31 is defined between the end face 12 of the limb portion 8 and the face 15. Similarly, in the embodiment shown in Fig. 2, the upright portion 26 of the T-shaped laminations does not extend to the internal surface of the base of the U-shaped laminations and an air gap 32 is defined.

However, if desired, these portions 8 or 26 could be made longer such that no air-gap is provided. This latter is, of course, conventional in transformer core design.

Claims

1. A transformer core assembly (1) comprising a stack (2) of aligned and connected first lamination members (4), each member comprising a base portion (6:22) and at least two limb portions (7, 8, 9: 23, 24) extending substantially parallel to one another in a direction away from said base member (6:22), said limb portions (7, 8, 9: 23, 24) and said base portion (6:22) jointly defining at least one open channel (10, 11) and a stack (3) of aligned and connected second lamination members (5), each said member having a longitudinally extending edge (15:27), the edges of such members, when stacked, forming a longitudinally extending face, said face (15, 27) being located in abutment with the free end face (12) of at least the outer limbs (7, 9:23,24) of the stack (2) of first lamination members (4) to close said channel and form at least one window, said two stacks (2, 3) jointly defining at least two interengagement devices (13, 18, 19) for maintaining said faces in abutment with one another whereby interengagement is caused by applying a force characterised in that each said interengagement device comprises an interengagement portion (13) formed on said stack (2) of first lamination members (4) and an interengagement portion (18, 19) formed on said stack (3) of second lamination members (5), said interengagement portions having abutment surfaces (13JΪ, 13b_, 19_a, 19b_) which form an interlock between said stacks (2, 3) when a force is applied to said stacks (2, 3) in a direction (20, 21, 29, 30) normal to the abutment face (15) of said stack (3) of second lamination members (5).

2. A transformer core assembly as claimed in claim 1 characterised in that the first lamination members (4) each have a substantially E-shaped cross- section and the second lamination members (5) each have a substantially I-shaped cross-section.

3. A transformer core assembly as claimed in claim 1 characterised in that the first lamination members (4) each have a substantially U-shaped cross- section and the second lamination members (5) each have a substantially T-shaped cross-section.

4. A transformer core assembly as claimed in claim 3 characterised in that the abutment face (27) of the stack of second lamination members is formed by the underside of the cross bar of each T-shaped member (5).

5. A transformer core assembly as claimed in any preceding claim characterised in that the interengagement devices comprise recesses (13) formed in one of the stacks of lamination members and corresponding protrusions (18, 19) formed on the other stack of laminations whereby the protrusions fit into the recesses.

6. A transformer core assembly as claimed in any preceding claim characterised in that the recesses (13) formed in the first stack (2) of laminations (4) are disposed in the free end faces of the limbs (7, 9) at the edges thereof and the protrusions (18, 19) formed in the longitudinally extending face of the second stack (3) of laminations (5) are disposed adjacent to the end regions thereof.

7. A transformer core assembly as claimed in any preceding claim characterised in that the abutment portions (13ja, 13b_, 19^, 19t of the interengagement devices subtend a slight angle with one another so as to improve the engagement between such portions.

8. A method of producing a transformer core assembly (1) from a stack (2) of aligned and connected first lamination members (3) and a stack (4) of aligned and connected second lamination members (5), the first lamination members each comprising a base portion (6: 22) and at least two limb portions (7, 8, 9: 23, 24) extending substantially parallel to one another in a direction away from the base portion (6:22), said base portion and said limb portions (7, 8, 9: 23, 24) jointly defining at least one open channel and the second lamination members (5) each having a longitudinally extending edge (15:27) such that, when stacked, the edges (15:27) form a longitudinally extending face, the two stacks being provided with co¬ operating interengagement devices (13, 18, 19), comprising locating the two stacks (2, 3) in abutment with one another such that the longitudinally extending face (15) is in abutment with the free end faces (12) of at least the outer limbs (7, 9: 23, 24) and applying a force to one of the stacks (2, 3) in a direction at right angles to the abutment face (15:27) of the stack (3) of second lamination members (5), so as to cause closure of said at least one channel thereby forming at least one window and the interengagement of said interengagement devices (13, 18, 19).