GB2376134A

GB2376134A - Busbar casing

Info

Publication number: GB2376134A
Application number: GB0109530A
Authority: GB
Inventors: Colin Schroder
Original assignee: Voestalpine Metsec PLC
Current assignee: Voestalpine Metsec PLC
Priority date: 2001-04-18
Filing date: 2001-04-18
Publication date: 2002-12-04
Also published as: GB0109530D0

Abstract

A casing for a busbar comprising first and second elongate, inter-engageable components each of which is formed by cold roll-forming from metallic strip material and each of which incorporates opposite first and second shaped regions co-operating in use with respective first and second shaped regions of the other component to secure the components together to define the casing, said shaped regions being such that during inter-engagement of the components neither component engages an edge of the material of the other component.

Description

BUSBAR CASING This invention relates to a casing for a busbar assembly.

A busbar assembly conventionally comprises a plurality of elongate copper conductors, often in the form of copper bar, supported spaced from one another, but extending generally parallel to one another, in a matrix or carrier of electrically insulating material. It is known to provide such a busbar assembly with an external metal casing formed from galvanised mild steel strip by a cold roll-forming operation. A conventional busbar casing includes two elongate components which are snap-fitted together. Both components are cold roll-formings and although both are generally channelshaped having a base wall and opposite upstanding side walls, it is perhaps convenient to refer to one of the components as the body, and the other of the components as the lid. Figures 1 and 2 of the accompanying drawings illustrate a prior art arrangement in which the body 11 has a base wall 12 and parallel upstanding side walls 13 at opposite sides respectively of the base wall 12. The upper, free edges of the side walls 13 are turned inwardly to define longitudinally extending inwardly directed flanges 14 the free, innermost edges of which are the original cut edges of the galvanised mild steel strip from which the body 11 is rolled. The elongate lid 15 is, relative to the body 11, an inverted channel having a base wall 16 and downwardly extending opposite, parallel side walls 17. The spacing between the side walls 17 is such that the side walls 17 can pass between the inner edges of the flanges 14 of the body 11. At their free ends the side walls 17 of the lid 15 are turned outwardly to provide longitudinally extending inclined flanges 18

the free ends of which are the cut edges of the galvanised mild steel strip from which the lid 15 is formed.

In order to assemble the busbar construction the busbar assembly comprising the busbars and the electrically insulating carrier is inserted into the body 11 through the open top face and the lid 15 is then offered to the body 11 and moved towards the base 12 so that the flanges 18 engage the free edges of the flanges 14 and slide on the free edges of the flanges 14 as the lid 15 is pressed towards the body 11. This movement of the lid 15 relative to the body 11 flexes the side walls 13 outwardly and the side walls 17 inwardly so that the free edges of the flanges 18 ultimately ride around the free edges of the flanges 14 and then spring out to seat underneath the flanges 14 thus locking the lid 15 in place on the body 11. The base wall 16 of the lid 15 may well be pierced at a number of points along its length to facilitate making of electrical connections to the busbars contained within the casing.

A difficulty which arises in relation to the prior art construction illustrated in Figures 1 and 2 is the presence of slivers and/or flakes of the zinc alloy galvanising coating or the mild steel strip which can become detached from the lid 15 and body 11 and which can enter the cavity of the casing and give rise to short circuits and earth leakage paths within the busbar construction.

The slitting operation which cuts the galvanised strip material to size prior to cold roll-forming to produce the body and lid can give rise to the formation of such metallic slivers and flakes. Furthermore, such slivers and flakes can be dislodged by the engagement of the lid 15 with the body 11, particularly as a result of sliding motion involving cut edges of the strip material. Thus as the flanges 18 slide across the cut edges of the flanges 14 metallic flakes

and slivers can be dislodged into the interior of the casing. Furthermore, as the free edges of the flanges 18 spring back to engage beneath the flanges 14 further slivers and flakes can be dislodged into the interior of the casing. It is found that the presence of such metallic slivers and flakes can give a failure rate, during testing of assembled busbar constructions, of around 10%. It is an object of the present invention to provide a busbar casing by cold rolling from metal strip, conveniently galvanised mild steel strip, in which the aforementioned disadvantage is minimised.

In accordance with the present invention there is provided a casing for a busbar comprising first and second elongate, inter-engageable components each of which is formed by cold roll-forming from metallic strip material and each of which incorporates opposite first and second shaped regions cooperating in use with respective first and second shaped regions of the other component to secure the components together to define the casing, said shaped regions being such that during inter-engagement of the components neither component engages an edge of the material of the other component.

Preferably said shaped regions are such that when the components are interengaged, the longitudinal edges of the material from which the components are formed are disposed outside of the enclosure defined by the inter-engaged components.

Preferably both of said first and second components are elongate channels having a base wall and opposite side walls, said first and second shaped regions being regions of the side walls of the respective channel.

Desirably the shaped regions of at least one of said first and second components are formed with inclined surfaces which slidingly engage surfaces of the shaped regions of the other component during interengagement of the components.

In accordance with a further aspect of the present invention there is provided a casing for a busbar assembly comprising, first and second elongate interengageable components which, when inter-engaged, define an elongate receptacle in use receiving a busbar assembly, each of said first and second components being formed by cold roll-forming from metallic strip material and said first component being generally channel-shaped having a base wall and opposite side walls, each side wall of said first component being bent to define an inwardly protruding portion and each inwardly protruding portion including a longitudinally extending inwardly directed region extending towards the opposite side wall of the first component, each longitudinally extending inwardly directed region being bent at its inner extremity to provide a longitudinally extending outwardly directed region, and, said second component including opposite longitudinally extending edge portions engageable in use beneath respective inwardly protruding portions of said first component, each of said portions including a longitudinally extending region bent from the remainder of the component to extend inwardly towards the equivalent region of the opposite edge portion of the second component, the inwardly protruding portions of the first component and/or the edge portions of the second component being bent to include inclined ramp surfaces which co-operate with surfaces of said portions of the other component to facilitate flexure of one or both components during interengagement of the components to engage said inwardly extending regions of

said second component beneath said inwardly extending regions of said first component.

Conveniently the material from which said first and second component is formed is galvanised mild steel strip.

Preferably both the inwardly protruding portions of the first component and the edge portions of the second component include inclined ramp surfaces which slide on one another during assembly of the components to facilitate flexure of one or both components during the inter-engagement thereof.

In the accompanying drawings Figures 1 and 2 are transverse cross-sectional views of a known busbar casing; Figure 3 is an enlarged diagrammatic cross-sectional view of part of a busbar casing in accordance with a first example of the present invention, Figures 4 and 5 are transverse cross-sectional views of first and second alternative busbar casings assembled, Figures 6 to 9 inclusive are views similar to Figure 3 of a first class of alternative profiles, and Figures 10 to 14 inclusive are views similar to Figure 3 of a second class of alternative profiles.

The prior art busbar casing depicted in Figures 1 and 2 has been described above, and like components in Figures 3,4 and 5 carry the same reference numerals. Referring now to Figures 3 and 4 of the accompanying drawings it can be seen that the body 11 of the casing is cold roll-formed from metal strip to define an elongate channel-section having a base wall 12. Integral with the base wall 12 the strip material is bent upwardly to define parallel upwardly extending side walls 13 each of which is turned inwardly at its upper longitudinally extending boundary to define a respective inwardly extending flange 14 overlying the base wall 12 parallel thereto. The strip material is bent through approximately 1350 at the innermost boundary of each flange 14 to terminate in an outwardly extending inclined flange 21 which extends throughout the full length of the side walls 13. The opposite cut edges of the strip material from which the body 11 is formed are the free edges of the flanges 21.

The lid 15 is also formed by cold roll-forming of a strip of galvanised mild steel to produce a shallow, inverted channel section having a base wall 16, downwardly extending side walls 17 and, integral with the side walls 17 outwardly extending flanges 18 subtending an angle of approximately 45 with their respective side walls 17. Furthermore, the outer margins of the flanges 18 are turned inwardly to define inwardly directed flanges 22 terminating adjacent the outer surfaces of the side walls 17. The opposite cut edges of the strip material from which the lid 15 is formed are the free edges of the inwardly directed flanges 22, adjacent the outer surfaces of the side walls 17. It will be recognised that as is conventional in cold roll-forming of galvanised mild steel each bend in the strip material will be a radiused bend, the radius being determined by the gauge of the material and the minimum

radius through which the strip material can conveniently be bent without damaging the galvanised coating on the strip material.

The spacing between the inward protrusions of the side walls 13 defined by the flanges 14 and 21 is such that the side walls 17 of the lid 15 can fit therebetween, with the outward protrusions of the lid defined by the flanges 18 and 22, disposed beneath the protrusions of the side walls 13. In practice, when the lid 15 is assembled to the body 11 to define the busbar casing the outer surface of the flanges 22 seat beneath the under surfaces of the flanges 14.

During assembly of the lid 15 to the body 11 the busbar assembly is first introduced into the body 11, and thereafter the lid 15 is offered to the body 11 with the inclined flanges 18 presented to the substantially parallel inclined flanges 21. Depression of the lid 15 towards the body 11 causes the surface of the flanges 18 to ride on the surface of the flanges 21 thereby flexing the side walls 13 outwardly and the side walls 17 inwardly to permit the outward protrusions of the side walls 17 to ride past the inward protrusions of the side walls 13. As the rounded comers defined between the flanges 18 and 22 ride over the rounded comers defined between the flanges 14 and 21, the side walls 13 and 17 can flex back to their rest configurations engaging the flanges 22 beneath the flanges 14. It will be recognised that in this position of the lid 15 relative to the body 11 the busbar assembly, conveniently appropriately parts of the insulator of the busbar assembly, are trapped between the inner face of the lid base wall 16 and the inner face of the body base wall 12.

Figure 5 illustrates a modification of the arrangement illustrated in Figure 4 in which the relative spacing of the base wall 16 from the base wall 15 is determined by the inter-engagement of the lid and the body and not by the dimensions of the busbar assembly within the casing. Thus it can be seen that Figure 5 differs from Figure 4 in that the spacing between the side walls 17 of the lid 15 is substantially equal to the spacing between the side walls 13 of the body 11, and intermediate the base wall 11 and the flanges 14 the side walls 13 are shaped to include an outwardly extending wall 23 parallel to the base wall 12 and then an upstanding wall 24 parallel to the respective side wall 13. The flanges 14 are inward continuations of the walls 24, and define with the walls 23,24 inwardly facing grooves 25 extending along the full length of the body 11 and within which the outward protrusions 18,22 of the lid 15 seat when the lid 15 and body 11 are inter-engaged.

It will be recognised that in the construction illustrated in Figures 3,4 and 5 the assembly of the lid 15 to the body 11 does not involve any sliding contact with either free longitudinal edge of either of the components, thereby avoiding the risk of metallic slivers and metallic flakes being dislodged from the cut edges into the casing. Furthermore, in the assembled casing the engagement of the flanges 14 and 22 forms the closure points of the enclosure defined within the components 11,15 and it can be seen that the edges of the strip material from which the components 11,15 are formed are outside of that enclosure and so are not exposed to the interior of the casing thus further minimising the risk of metallic flakes and slivers shed from the cut edges entering the casing.

The alternative profiles for the interconnection of the components 11,15 illustrated in Figure 6 to 9 all exhibit the same avoidance of sliding edge contact and avoidance of exposure of strip edges to the casing interior which are present in the embodiment described above with reference to Figures 3,4 and 5. The profiles illustrated in Figures 10 to 14 are slightly less advantageous than those of Figures 3 to 9 but still have significant advantage over the prior art since they avoid sliding edge contact, and so minimise the risk of dislodging flakes and slivers from the material edges, although they do present material edges within the enclosure.

Claims

CLAIMS :- 1. A casing for a busbar comprising first and second elongate, inter- engageable components each of which is formed by cold roll-forming from metallic strip material and each of which incorporates opposite first and second shaped regions co-operating in use with respective first and second shaped regions of the other component to secure the components together to define the casing, said shaped regions being such that during inter-engagement of the components neither component engages an edge of the material of the other component.
2. A busbar casing as claimed in claim 1 wherein said shaped regions are such that when the components are inter-engaged, the longitudinal edges of the material from which the components are formed are disposed outside of the enclosure defined by the inter-engaged components.
3. A busbar casing as claimed in claim 1 or claim 2 wherein both of said first and second components are elongate channels having a base wall and opposite side walls, said first and second shaped regions being regions of the side walls of the respective channel.
4. A busbar casing as claimed in any one of the preceding claims wherein said shaped regions of at least one of said first and second components are formed with inclined surfaces which slidingly engage surfaces of the shaped regions of the other component during interengagement of the components.

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5. A casing for a busbar assembly comprising, first and second elongate inter-engageable components which, when inter-engaged, define an elongate receptacle in use receiving a busbar assembly, each of said first and second components being formed by cold roll-forming from metallic strip material and said first component being generally channelshaped having a base wall and opposite side walls, each side wall of said first component being bent to define an inwardly protruding portion and each inwardly protruding portion including a longitudinally extending inwardly directed region extending towards the opposite side wall of the first component, each longitudinally extending inwardly directed region being bent at its inner extremity to provide a longitudinally extending outwardly directed region, and, said second component including opposite longitudinally extending edge portions engageable in use beneath respective inwardly protruding portions of said first component, each of said portions including a longitudinally extending region bent from the remainder of the component to extend inwardly towards the equivalent region of the opposite edge portion of the second component, the inwardly protruding portions of the first component and/or the edge portions of the second component being bent to include inclined ramp surfaces which co-operate with surfaces of said portions of the other component to facilitate flexure of one or both components during interengagement of the components to engage said inwardly extending regions of said second component beneath said inwardly extending regions of said first component.
6. A busbar casing as claimed in claim 5 wherein both the inwardly protruding portions of the first component and the edge portions of the

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second component include inclined ramp surfaces which slide on one another during assembly of the components to facilitate flexure of one or both components during the inter-engagement thereof.
7. A busbar casing as claimed in any one of the preceding claims wherein the material from which said first and second components are formed is galvanised mild steel strip.
8. A busbar casing substantially as hereinbefore described with reference to any one of Figures 3 to 14 of the accompanying drawings.