ELECTRIC ARC-CONTROL DEVICE
Background of the invention
The invention relates to the field of electric arc
5 breaker devices.
When breaking a circuit, an electric arc is struck
between electrical contacts. The arc creates a back
electromotive force (emf) in the network that tends to
oppose the source of the network. In an alternating
10 current (AC) network, the magnitude of the current
passing through the terminals of the breaker equipment
passes periodically through zero. For example, these
passages of the current through zero take place every
10 milliseconds (ms) in a 50 hertz (Hz) network. When
15 the current passes through zero, the conductive arc cools
down suddenly and the ions of the plasma of the arc then
recombine. This recombination takes place more or less
quickly depending on the extinction technique (splitting
or lengthening), on the degree of pollution, and on the
20 type of plasma. This recombination enables the break to
withstand the network voltage that is still present at
its terminals. If that is not so, then a electrical
breakdown restarts the arc in the break, until the next
time current passes through zero.
25 An arc voltage greater than the network voltage
30
enables this dielectric recombination phenomenon to be
started sooner than the natural passage of the current
through zero, thereby increasing the chances of breaking
the current.
Nevertheless, a problem arises for existing breaker
devices resulting from the possible erosion of electrical
contacts by the electric arcs that are generated. This
erosion can affect the lifetime of such breaker devices.
There therefore exists a need to have novel breaker
35 devices available with improved lifetime, in which the
erosion of contacts due to the electric arc is limited.
2
Object and summary of the invention
To this end, in a first aspect, the invention
proposes an electric arc breaker device comprising:
· a contact zone in which there are present at least
5 one stationary contact and at least one movable contact
that is movable relative to the stationary contact, the
contacts being capable of being put into contact with
each other and of being separated from each other; and
· an arcing horn present facing the stationary
10 contact, the heigh~ of the arcing horn being greater than
or equal to the height of the stationary contact, and the
arcing horn presenting a folded-back arc switching
portion extending in a direction away from the stationary
contact.
15 Because of the presence of a folded-back switching
portion, the arcing horn serves to push the arc back to
the back of the breaker device, to improve splitting of
the arc, and to move the arc away from the stationary
contact. The movement of the arc from the stationary
20 contact towards the arcing horn also serves to reduce
erosion of the stationary contact because of limited
contact between the electric arc and the stationary
contact, thereby enabling the lifetime of the breaker
device to be improved. The arc switching portion
25 constitutes a sacrificial element that is consumed by the
arc instead of consuming the stationary contact, thereby
enabling the lifetime of the stationary contact to be
improved and thus increasing the lifetime of the breaker
device.
30 In an embodiment, the material forming the arc
switching portion may have a change-of-state temperature
that is higher than the change-of-state temperature of
the material forming the stationary contact. This
applies for example when the arcing horn is made of steel
35 and the stationary contact is made of copper.
Thus, the material forming the arc switching portion
may have a melting temperature or a vaporization
3
temperature that is higher than the melting temperature,
or respectively the vaporization temperature, of the
material forming the stationary contact.
Using such an arcing horn is advantageous for
5 reducing arc erosion both of the stationary contact and
of the arcing horn since the arcing horn is made of a
material that withstands arc erosion. Consequently, such
a configuration makes it possible to further lengthen the
lifetime of the breaker device.
10 In an embodiment, t.he breaker device may be present
15
20
25
30
35
in a box, with the .arcing horn having a width L equal to
the inside width of said box.
Using such an arcing horn makes it possible to
reduce, or even to avoid, the gas of the plasma passing
laterally arotutd.it. As a result, this enables.thecpath
followed by the gas to be lengthened and thus enables the
gas to be cooled better before being discharged to the
outside of the breaker device. Such a configuration
advantageously serves to minimize potential arcing
outside the breaker device.
In an embodiment, the breaker device may also
further include an extinction chamber containing a stack
of electric arc splitting plates present facing the
arcing horn.
Such a device serves to further improve the breaking
capacity of the device and thus further limit erosion of
the electrical contacts due to the arc.
In a variant, the breaker device need not have a
stack of electric arc splitting plates.
Such a device advantageously makes it possible to
have a solution for extinguishing an electric arc that is
simple and inexpensive.
Brief description of the drawings
Other characteristics and advantages of the
invention appear from the following description of
particular embodiments of the invention, given as non4
limiting examples and with reference to the accompanying
drawings, in which:
Figures 1 to 3 show a first example of a breaker
device of the invention;
5 Figure 4 shows a detail of the breaker device
shown in Figures 1 to 3;
· Figures 5 to 8 show how an electric arc behaves in
the breaker device of Figures 1 to 3; and
· Figure 9 shows a variant of the breaker device of
10 the invention.
Detailed description of embodiments
Figure 1 shows an example of an electric arc .breaker
device 1 of the invention. The device shown serves to
15 extinguish an•electric arc in air. The breaker. device 1
has a contact zone 2 in which there are present at least
one stationary contact 3 and at least one movable contact
4 that is movable relative to the stationary contact 3.
The contacts 3 and 4 can be put into contact with each
20 other and they can be separated from each other, the
movable contact 4 in the example shown being configured
to perform a movement in rotation about a pivot axis when
the contacts are separated. The contact head 3 and the
stationary support 15 form a stationary subassembly
25 enabling the breaker device 1 to be connected in an
electrical installation. The contact head 3 may be made
of metal material, e.g. of copper. When the movable
contact 4 is in contact with the contact head 3,
electricity can flow between these elements. When the
30 movable contact 4 is separated from the contact head 3,
electricity can no longer flow between these elements.
The breaker device shown is a double-break rotary
breaker device having two blades and extinguishing two
arcs (see Figure 2). It would not go beyond the ambit of
35 the invention for the breaker device to be of some other
type, e.g. of the bladed single-break rotary type or of
the double-break type with blades moving in translation.
5
In addition, the breaker device 1 includes an arcing
horn 10 present facing the contact head 3 on the
stationary support 15. The arcing horn 10 is fastened to
the stationary support 15 by a mechanical connection.
5 The arcing horn 10 has a tab 14 and an arc switching
portion 12. The arcing horn is made of an electrically
conductive material, for example the arcing horn 10 may
be made out of a metal material, e.g. steel. In the
example shown, the tab 14 is in contact with the
10 stationary support 15, but it .would .not. go beyond the
ambit of the invention for the arcing horn 10 not to be
in contact with the stationary support 15 but to be
fastened to the box constituting the outer casing of the
breaker device. Under such circumstances, the distance
15
20
FJet.\veen the arcing .horn 10 and the .stationary.,_support. 1 c; .
may be less than or equal to 1 millimeter (mm) for
example. An electric arc generated from the movable
contact 4 is to be made to move over the arc switching
portion 12, as described in detail below.
As shown, the height he of the arcing horn 10
corresponding to the height at which the end 13 of the
arc switching portion 12 is present, is greater than the
height ht of the contact head 3. The arc switching
portion 12 is folded back and extends in a direction
25 opposite from the stationary contact 3 (i.e. it extends
away from the stationary contact 3). As shown, the
switching portion 12 forms a bend l2a. The height he of
the arcing horn 10 and the height h'c at which the bend
12a is present are both greater than the height ht of the
30 contact head 3 in the example shown. The heights he, h'e,
and ht are measured from the surface S of the stationary
support 15 facing the arcing horn 10, and perpendicularly
to the surface S.
The breaker device 1 is present in a box 35. In the
35 example shown, the box comprises the combination of two
half-boxes (see Figures 2 and 3). Together with the
other half-box (not shown), the half-box forms the outer
6
casing of the breaker device. This casing enables the
breaker device to be installed in an electrical
installation. The arcing horn 10 is of a width equal to
the inside width of the box 35 in order to reduce, or
5 even prevent, the gas of the plasma passing laterally
around said arcing horn 10. Figure 4 shows the arcing
horn and illustrates the fact that it is of sufficient
width to limit the extent to which the gas can pass
laterally around it. The width L of the arcing horn 10
10 corresponds to its greatest dimension measured
perpendicularly to its height.
15
20
In addition, the breaker device 1 in the example
shmm in Figure 1 includes an extinction chamber 20
having a stack of splitting plates 21. The electric arc
spli·tt.ing plates 21 i'lre mounted on ·:a··.platec support ::22.- ·
(see Figure 3}. Mounting the splitting plates 21 on the
plate support 22 makes it possible to form an extinction
chamber 20 that is rigid. The splitting plates 21 are
made of mild steel, for example. By way of example, the
plate support 22 may be made of vulcanized card. In a
variant, the splitting plates may be mounted directly on
the box constituting the outer casing of the breaker
device. The extinction chamber 20 shown has a plurality
of stacked splitting plates 21, e.g. at least three
25 stacked splitting plates 21, e.g. at least five stacked
splitting plates 21. By way of example, the splitting
plates may be V-shaped or U-shaped when observed in a
direction perpendicular to the plane in which they
extend.
30 As shown in Figure 1 in particular, an electric arc
30 is formed after the contacts 3 and 4 have separated.
The arc 30 is struck at the location of the last
electrical contact. The arc 30 is subjected to the
Laplace (or Lorentz} force induced by the flow of
35 electric current, with this flow being represented by
curves 31. The arc 30 is in a current loop and the
Laplace forces acting on the loop tend to open it. This
-' -· :-: _:_ __ ::C:_,_~--
7
effect is commonly referred to as the loop effect. The
Laplace force acting on the arc 30 tends to push the arc
30 towards the back of the breaker device 1.
There follows a description of the behavior of the
5 arc 30 generated between the contacts 3 and 4.
The contacts continue their separation movement.
The arc 30 then moves to the end 3a of the contact head 3
and to the end 4a of the movable contact 4 (see
Figure 5). The plasma coming from the cooled arc can
10 follow a predetermined path represented by arrows 32.
Because an arcing horn 10 of sufficient width is used,
the gas follows a longer path and is thus better cooled
prior to being discharged to the outside of the breaker
device. This may advantageously serve to minimize
15 potential arcing outside the breaker.device•. ·The
majority of the volume of this plasma gas is deflected
towards an exhaust orifice 40 and flows in the volume
defined by the switching portion 12 and the splitting
plates closest thereto. This gas enables the medium
20 close to the arcing horn to be in better electric
breakdown conditions (dielectric strength decreases with
increasing temperature).
The contacts continue their separation movement.
The arc at the end of the contact head (configuration P1
25 shown diagrammatically in Figure 6) then switches onto
the switching portion 12 of the arcing horn 10
(configuration P2) since its length becomes shorter after
switching. Such switching can be explained by the fact
that it is preferable for the electric arc to extend
30 along a path having as little "impedance" as possible,
corresponding in this example to a path having the
shortest possible length. This switching results from an
electric breakdown phenomenon. Furthermore, the arc in
the configuration P1 is also subjected to the loop effect
35 resulting from the flow of current, which tends to deform
it and to give it a curved shape (see dashed-line
configuration P' in Figure 6). This deformation serves
8
to further facilitate switching the arc onto the arcing
horn. In the example shown, in which the movable contact
4 rotates during separation of the contacts, the arc
moves radially when switching onto the arcing horn, i.e.
5 perpendicularly to the axis of rotation of the movable
contact.
After switching, the root of the arc beside the
arcing horn is subjected to a Laplace force (arrow shown
in Figure 6) due to the loop effect (current flow 31),
10 which pushes i·t tovJards the back .of the breaker device.
1.5
20
25
30
35
In so doing, because of its very high temperature, the
root of the arc erodes the switching portion 12. Thus,
the switching portion 12 constitutes a sacrificial
portion of the breaker device that is consumed instead of
the stationary· contact. 3. This makes it ·•possibl.e t·o ·'
lengthen the time during which the contacts of the
breaker device can be used, thereby improving the
lifetime of the breaker device.
The contacts still continue their separation
movement. The arc penetrates into the extinction chamber
and is split. As a result, it maintains a certain fixed
voltage level (cathode voltage drops and anode voltage
drops at the various arc roots) and it cools (exchanges
between the arc and the splitting plates serving to
increase impedance). After the contacts are completely
separated, the arc is totally split in the extinction
chamber (see Figures 7 and 8).
This extinction principle can also apply without
splitting plates, thus making it possible to provide a
simplified breaker device 50, as shown in Figure 9. The
switching of the arc from the contact head 3 onto the
arcing horn 10 takes place as with the extinction
chamber. After switching, the arc no longer stabilizes
in the extinction chamber, but lengthens to the back of
the breaker device 50. This lengthening results from the
Laplace forces that are the consequence of the loop
effect. The lengthening enables the arc to increase its
i
i
i ,I
il
I i;
9
impedance. The arc lengthens along the inside wall of
the box, thereby tending to cool the arc and also to
increase its impedance. The arc root becomes stabilized
at the end of the switching portion 12, with this zone
5 being a sacrificial zone, as described above.
The breaker device of the invention can be used for
breaking direct current (DC), or alternating current
(AC). Breaker devices of the invention can be used in
the low voltage range (U AC