GB2179797A

GB2179797A - Electrical switch

Info

Publication number: GB2179797A
Application number: GB08620476A
Authority: GB
Inventors: Terence Victor Mcghie; Douglas Eaves
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1985-08-23
Filing date: 1986-08-22
Publication date: 1987-03-11
Also published as: ES2001561A6; EP0212983A3; EP0212983A2; GB8521140D0; GB8620476D0; AU6111386A; JPS6255815A; ZA866251B; FI863412A0; FI863412A

Abstract

A switch includes first and second contacts (1), (9), each having a substantially rectangular contact area, at least one of the contacts (9) being movable between an open and closed position. The contact area of each of the contacts is provided with contact regions (7, 10, 11, 12) separated by arc rooting zones (4, 5, 13, 14) of high electric field intensity. The contacts are disposed such that on separation thereof each of the contact regions (7), of the first contact (1) are separated from those (10, 11, 12) of the second contact (9) substantially simultaneously. In the event of arcing occurring on separation of the contacts, the arc rooting zones (4, 5, 13, 14) are such that the arcing is encouraged to follow a number of paths between the contacts. The contacts may consist of finger portions with slots therebetween. Alternatively the arc rooting zones may consist of projections or holes. <IMAGE>

Description

1 GB2179797A 1

SPECIFICATION

Elecrical switch A This invention relates to electrical switches, which term is herein defined to include electric circuit breakers and the like. The invention is especially directed to switches which interrupt relatively large electric currents, such that on operation of the switch, arcing occurs across the contacts thereof.

Known switches attempt to contain arcing between the contacts by means of. a conical arc chamber into which the arc is encouraged to pass. However it is known that the path which the arc will take may be influenced by the proximity of ferromagnetic material, such as the metallic casing of the switch. In such cases the arc will occasionally travel to the side of the contacts, causing uneven erosion thereof. In addition the arcing in these cases is of a relatively long duration as compared with that obtained in arcing travelling directly between the contacts. This may allow a current still to be flowing some time after operation of the switch.

It is further known that the arcs which flow in adjacent conducting paths of multi-pole, or multi-phase switches, will attract or repel one another according to the polarity or the phase displacement of the magnetic fields produced by the currents which flow in the adjacent arcs. This attraction or repulsion also leads to uneven erosion of the contacts.

In order to combat uneven erosion of the contacts, it is known to provide one of the contacts in the form of a plurality of discrete fingers. Thus, even though one or more of the fingers may be severely eroded, a good elec trical contact may still be obtained by the flush engagement of the other fingers. How ever, the problem of the arc occasionally be ing deflected towards the casing of the switch still affects the performance thereof.

It is an object of the present invention to 110 provide an electrical switch which overcomes, at least in part, the above described disadvan tages.

Accordingly there is provided a switch in- cluding first and second contacts, each of the first-and second contacts having a substantially rectangular contact area, at least one of the contacts being movable with respect to the other between a closed position in which it is in electrical contact therewith, and an open position in which it is spaced therefrom such that an electric current will not flow therebetween; the contact area of each of the first and second contacts being provided with a plurality of contact regions separated by a multiplicity of arc rooting zones adapted to produce a high electric field intensity, the contacts being disposed such that on separation thereof each of the contact regions of the first contact are separated from those of the sec- ond contact substantially simultaneously, and the arc rooting zones are such that, in the event of arcing occuring across the contacts, the arcing is encouraged to follow a multipli- city of paths between the contacts.

By producing a multiplicity of arcs, there is set up a mutually attractive force therebetween. As the arcs are attracted one to another they are less likely to be influenced by external forces such as those from ferromagnetic materials surrounding the contacts.

The arc rooting zones preferably extend parallel one to another longitudinally along the contact area. Conveniently the contact area of at least one of the contacts comprises contact regions in the form of a plurality of discrete elemental portions and the sub-divisions therebetween constitute the arc rooting zones of high electric field intensity. in a convenient ar- rangement the contact area of at least one contact comprises finger portions.with slots therebetween, the finger portions being substantially parallel one to another.

Alternatively one or more of the arc rooting zones may be provided by projections extending from the surface of the contact. Pins, studs or rivets may all be incorporated to produce sharp edges projecting from the contact.

In another arrangement one or more of the arc rooting zones are provided by holes or recesses in the surface of the contact. Conceivably one of the contacts is provided with one or more projections, and the other contact is provided with one or more holes or recesses, the arrangement being such that the one or more projections are received in the one or more holes when the contacts are in their closed position.

According to a further aspect of the inven- tion there is provided a switch including first and second contacts, at least one of the contacts being movable with respect to the other between a closed position in which it is in electrical contact therewith, and an open position in which it is spaced therefrom such that an electrical current will not flow therebetween; the first and second contacts being each provided with a plurality of contact regions separated by a multiplicity of arc rooting zones adapted to produce a high electric field intensity, the arc rooting zones extending parallel one to another longitudinally of the contacts, the contacts being disposed such that on separation thereof each of the contact re- gions of the first contact are separated from those of the second contact substantially simultaneously, and the arc rooting zones are such that, in the event of arcing occuring across the contacts, the arcing is encouraged to follow a multiplicity of paths between the contacts.

The invention further resides in a pair of contacts for a switch, the contacts being each provided with a plurality of contact regions separated by a multiplicity of arc rooting 2 GB2179797A 2 zones adapted to produce a high electric field intensity such that in the event of arcing oc curing across the contacts on separation thereof, the arcing is encouraged to follow a multiplicity of paths between the contacts.

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

Figure 1 is a schematic elevational view of the contacts of an electrical switch according to the invention, the contacts being in a closed position; Figure 2 is an elevational view of the con tacts of Figure 1, shown in an open position; and Figure 3 is a schematic view of a pair of contacts according to an alternative embodi ment of the invention.

Referring to Figure 1, a fixed contact, shown generally at 1 comprises a base por tion 2 and a contact portion 3, separated by a curved portion 24. The contact portion 3 has slots 4, 5 cut therein at its free end so as to form three fingers 7. The slots 4, 5 extend only partly along the length of the contact portion 3 to leave a solid area 8 adjacent the curved portion 24.

Resting on the fixed contact 1 at the con tact area 8 is a movable contact 9, the con tact 9 being movable by biasing means shown 95 schematically at 50. The movable contact comprises three finger elements 10, 11, 12, the finger elements lying closely alongside one another with small spaces 13, 14 there between. With the switch in its closed posi- 100 tion, as depicted in Figure 1, an electric cur rent flows across the contacts 1 and 9.

When the switch is moved to its open posi tion the movable contact 9 is raised away from the contact area 8 as shown in Figure 2. 105 In the event of a relatively large electric cur rent being interrupted, arcing will occur be tween the contacts 1 and 9. The arcing will be in the form of arcs 15 between the edges of the finger elements at the spaces 13 and 110 14, and the edges of the fingers 7 at the end of the slots 4 and 5. Thus at least two sub stantially parallel arcs will be formed, the arcs being prevented from straying towards the sides of the contacts by the mutual attraction 115 therebetween.

Referring to Figure 3, the fixed contacts 1 and movable contact 9 are shown as before, the slots and finger elements being absent as the contacts of Figure 3 are substantially solid in character. Fixed contact 1 is provided with holes 51 arranged in two lines such as to divide the contact into three contact regions 52, 53 and 54. Movable contact 9 is provided with projections 55, again in two lines to divide the contact into three contact regions 56, 57 and 58. The projections 55 and holes 51 are arranged such that the projections are received in the holes when the switch is in its closed position with the movable and fixed contacts in engagement one with the other.

On opening of the contacts arcing is likely to occur, the arcs 15 being formed between the projections 55 and the corresponding holes 51. As before a plurality of substantially parallel arcs are formed rooted to the sharp edges constituting zones of high electric field intensity, The arcs are prevented from straying towards the sides of the contacts by the mutual attraction therebetween.

Claims

1. A switch including first and second contacts, each of the first and second contacts having a substantially rectangular contact area, at least one of the contacts being movable with respect to the other between a closed position in which it is in electrical contact therewith, and an open position in which it is spaced therefrom such that an electrical current will not flow therebetween; the contact area of each of the first and second contacts being provided with a plurality of contact regions separated by a multiplicity of arc rooting zones adapted to produce a high electric field intensity, the contacts being disposed such that on separation thereof, each of the contact regions of the first contact are separated from those of the second contact substantially simultaneously, and the arc rooting zones are such that in the event of arcing occuring across the contacts, the arcing is encouraged to follow a multiplicity of paths between the contacts.

2. A switch according to Claim 1 wherein the arc rooting zones extend parallel one to another longitudinally along the contact area.

3. A switch according to Claim 1 or Claim 2 wherein the contact area of at least one of the contacts comprises contact regions in the form of a plurality of discrete elemental portions and sub-divisions therebetween constitute the arc rooting zones of high electric field intensity.

4. A switch according to Claim 3 wherein the contact area of at least one contact comprises finger portions with slots therebetween, the finger portions being substantially parallel one to another.

5. A switch according to any of Claims 1 to 4 wherein one or more of the are rooting zones of at least one of the contacts comprise projections extending from the surface of the contan.

6. A switch according to any of Claims 1 to 5 wherein one or more of the arc rooting zones of at least one of the contacts comprise holes or recesses in the surface of the contacts.

7. A switch according to Claims 5 and 6 wherein one of the contacts is provided with one or more projections, and the other contact is provided with one or more holes or recesses, the arrangement being such that the one or more projections are received in the 3 GB2179797A 3 1 10 one or more holes or recesses when the contacts are in their closed position.

8. A switch including first and second contacts, at least one of the contacts being mov- able with respect to the other between a closed position in which it is in electrical contact therewith, and an open position in which it is spaced therefrom such that an electrical current will not flow therebetween; the first and second contacts being each provided with a plurality of contact regions separated by a multiplicity of arc rooting zones adapted to produce a high electric field intensity, the arc rooting zones extending parallel one to another longitudinally of the contacts, the contacts being disposed such that on separation thereof each of the contact regions of the first contact are separated from those of the second contact substantially simultaneously, and the arc rooting zones are such that, in the event of arcing occuring across the contacts, the arcing is encouraged to follow a multiplicity of paths between the contacts.

9. A switch substantially as hereinbefore de- scribed with reference to the accompanying drawings.

10. A pair of contacts for a switch according to Claim 8 the contacts being each provided with a plurality of contact regions sepa- rated by a multiplicity of arc rooting zones adapted to produce a high electric field intensity, the contacts being shaped such that, on separation thereof, each of the contact regions of one contact are separated from those of the other contact substantially simultaneously, the arc rooting zones extending parallel one to another longitudinally of the contacts such that in the event of arcing occuring across the contacts on separation thereof, the arcing is encouraged to follow a multiplicity of paths between the contacts.

11. A pair of contacts for a switch according to any Claims 1 to 7 the contacts being each provided with a substantially rectangular contact area the contact area of each of the contacts being provided with a plurality of contact regions separated by a multiplicity of arc rooting zones adapted to produce a high electric field intensity, the contacts being shaped such that, on separation thereof, each of the contact regions of one contact are separated from those of the other contact substantially simultaneously, the arc rooting zones being such that in the event of arcing occuring across the contacts on separation thereof, the arcing is encouraged to follow a multiplicity of paths between the contacts.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8817356, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A l AY, from which copies may be obtained.