[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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 electrical contact may still
be obtained by the flush engagement of the other fingers. However, the problem of
the arc occasionally being deflected towards the casing of the switch still affects
the performance thereof.
[0005] It is an object of the present invention to provide an electrical switch which overcomes,
at least in part, the above described disadvantages.
[0006] Accordingly there is provided 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 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 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.
[0007] 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.
[0008] 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 arrangement the contact area of at least one contact comprises
finger portions with slots therebetween, the finger portions being substantially parallel
one to another.
[0009] 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.
[0010] 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.
[0011] According to a further aspect of the invention 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 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.
[0012] 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 zones adapted to produce a high electric field intensity 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.
[0013] 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 contacts of Figure 1, shown in an open position;
and
Figure 3 is a schematic view of a pair of contacts according to an alternative embodiment
of the invention.
[0014] Referring to Figure 1, a fixed contact, shown generally at 1 comprises a base portion
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.
[0015] Resting on the fixed contact 1 at the contact area 8 is a movable contact 9, the
contact 9 being movable by biasing means shown 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 therebetween. With the switch in its closed position,
as depicted in Figure 1, an electric current flows across the contacts 1 and 9.
[0016] When the switch is moved to its open position the movable contact 9 is raised away
from the contact area 8 as shown in Figure 2. In the event of a relatively large electric
current being interrupted, arcing will occur between 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 14, and the edges of the fingers 7 at the end of the slots 4 and 5. Thus at
least two substantially parallel arcs will be formed, the arcs being prevented from
straying towards the sides of the contacts by the mutual attraction therebetween.
[0017] 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.
[0018] 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.
1. A switch including first and second contacts (1), (9), each of the first and second
contacts having a contact area, at least one of the contacts (9) being movable with
respect to the other (1) 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 (7,10,11,12; 52,53,54,56,57,58)
separated by a multiplicity of arc rooting zones (4,5,13,14; 51,55) adapted to produce
a high electric field intensity, the contacts being disposed such that on separation
thereof, each of the contact regions (7; 52,53,54) of the first contact (1) are separated
from those (10,11,12; 56,57,58) of the second contact a substantially simultaneously,
characterised in that the contact area is substantially rectangular 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 characterised in that the arc rooting zones extend
parallel one to another longitudinally along the contact area.
3. A switch according to Claim 1 or Claim 2 characterised in that the contact area
of at least one of the contacts (1,9) comprises contact regions in the form of a plurality
of discrete elemental portions (7; 10,11,12) and sub-divisions therebetween (4,5;
13,14) constitute the arc rooting zones of high electric field intensity.
4. A switch according to Claim 3 characterised in that the contact area of at least
one contact comprises finger portions (7) with slots (4,5) therebetween, the finger
portions being substantially parallel one to another.
5. A switch according to any of Claims 1 to 4 characterised in that one or more of
the arc rooting zones of at least one of the contacts comprise projections (55) extending
from the surface of the contact.
6. A switch according to any of Claims to 5 characterised in that one or more of the
arc rooting zones of at least one of the contacts comprise holes or recesses (51)
in the surface of the contacts.
7. A switch according to Claims 5 and 6 characterised in that one of the contacts
(9) is provided with one or more projections (55), and the other contact (1) is provided
with one or more holes or recesses (51), the arrangement being such that the one or
more projections (55) are received in the one or more holes or recesses (51) when
the contacts ai,e in their closed position.
8. A switch including first and second contacts, (1),(9) at least one of the contacts
(9) being movable with respect to the other (1) 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 (7,10,11,12;
52,53,54,56,57,58) separated by a multiplicity of arc rooting zones (4,5,13,14; 51,55)
adapted to produce a high electric field intensity, characterised in that the arc
rooting zones extend parallel one to another longitudinally of the contacts, the contacts
being disposed such that on separation thereof each of the contact regions (7; 52,53,54)
of the first contact (1) are separated from those (10,11,12; 56,57,58) of the second
contact (9) 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 pair of contacts for a switch according to Claim 8 the contacts (1),(9) being
each provided with a plurality of contact regions (7,10,11,12; 52,53,54,56,57,58)
separated by a multiplicity of arc rooting zones (4,5,13,14; 51,55) adapted to produce
a high electric field intensity, characterised in that the contacts are shaped such
that, on separation thereof, each of the contact regions (7; 52,53,54) of one contact
(1) are separated from those (10,11,12; 56,57,58) of the other contact (9) substantially
simultaneously, and the arc rooting zones extend 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.
10. A pair of contacts for a switch according to any of Claims 1 to 7 the contacts
(1),(9) being each provided with a contact area, a plurality of contact regions (7,10,11,12;
52,53,54,56,57,58) separated by a multiplicity of arc rooting zones (4,5,13,14; 51,55)
adapted to produce a high electric field intensity, the contacts being shaped such
that, on separation thereof, each of the contact regions (7; 52,53,54) of one contact
(1) are separated from thos (10,11,12; 56,57,58) of the other contact (9) substantially
simultaneously, characterised in that the contact area is substantially rectangular,
and the arc rooting zones are 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.