High-voltage switches with arc preventing or extinguishing devic – Arc preventing or extinguishing devices – Arc chute assembly
Reexamination Certificate
1999-12-02
2001-07-24
Scott, J. R. (Department: 2832)
High-voltage switches with arc preventing or extinguishing devic
Arc preventing or extinguishing devices
Arc chute assembly
C200S015000, C218S030000
Reexamination Certificate
active
06265685
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electrical switch gear apparatus, in particular a switch, equipped with at least one pair of separable contact means comprising a first long, slender contact means defining a longitudinal axis and a first and a second ends and having a contact zone on the same side as its first end and an electrical connection zone on the same side as its second end, and a second contact means having a contact zone, the pair of contact means being able to take a closed position in which the two contact means are in contact with one another via their respective contact zones, and an open position in which the two contact means are separated from one another, the opening movement being such that when separation of the two contact means takes place, the speed of the contact zone of the second contact means with respect to the first contact means has a predominant component following an axis perpendicular to the longitudinal axis of the first contact means.
A conventional apparatus of this type is represented for example purposes in
FIG. 1. A
pole
10
of this apparatus comprises a movable contact means
12
, a stationary contact means
14
and an arc extinguishing chamber
16
with separators
18
. The stationary contact means
14
comprise a contact zone
20
and a connection zone
22
.
Likewise, the movable contact means
12
comprise a contact zone
24
and a connection zone
26
. The two means
12
,
14
are long and slender and placed in the extension of one another so that in the closed position the current lines
28
flowing between the two connection zones are appreciably loop-free. The movement of the movable contact means when opening takes place follows a direction
30
appreciably perpendicular to the direction of the current lines before opening, so that the electrical arc
32
which arises between the contact zones
20
,
24
at the level of the last contact points A, B tends to flee towards the ends of the two contact means, at A′ and B′ , according to the directions
34
,
36
. In particular, the foot of the arc is directed towards A′ in the direction
34
opposite to the arc extinguishing chamber
16
. This movement is not favorable to entry of the arc into the chamber. In conventional switch gear, the ionization generated by the arc at the beginning of opening is sufficient for a new arc breakdown to take place according to a line of smaller distance between the two contacts. The geometry of the pole is such that this line is situated close to the chamber and passes via the free end B′ of the movable contact means
12
, so that the new arc extends in the latter, whereas the first arc is extinguished.
This operating mode is satisfactory when the required performances are low, with overload currents lower for example than 6 I
n
, I
n
being the nominal current. It is no is longer suitable when higher performances are sought for, for example with overload currents reaching 8 I
n
, or when closing and opening cycles on overload are required. The breaking time with such a device is in fact long, and the stagnation of the arc at the end of the contact means causes excessive erosion of the contact zones when the overload currents are high.
It is moreover known that it is possible to direct the arc to the chamber by adopting a stationary contact means having a U shape. However, such a configuration, commonly used for circuit breakers, results in large dimensions.
SUMMARY OF THE INVENTION
The object of the invention is therefore firstly to overcome the shortcomings of the state of the technique without notably increasing the dimensions, and at low cost. In particular its object is to adapt a switch gear apparatus, in particular a switch, so as to limit the movement of the foot of the electrical arc towards the end of one of the contact means.
According to the invention, these objects are achieved by means of an electrical switch gear apparatus, in particular an electrical switch, equipped with at least one pair of separable contact means comprising a first long, slender contact means defining a longitudinal axis and a first and second ends, and having a contact zone on the same side as its first end and an electrical connection zone on the same side as its second end, and a second contact means having a contact zone, the pair of contact means being able to take a closed position in which the two contact means are in contact with one another via their respective contact zones, and an open position in which the two contact means are separated from one another, the opening movement being such that when separation of the two contact means takes place, the speed of the contact zone of the second contact means with respect to the first contact means has a predominant component according to an axis perpendicular to the longitudinal axis of the first contact means, characterized in that the first contact means comprises a slot arranged between its contact zone and its connection zone, close to its contact zone, and opening out on the same side as the first contact means facing the contact zone of the second contact means in the open position.
When the contact means are in the closed position, the current lines are propagated in the material of the first contact means approximately according to the longitudinal direction thereof. When opening takes place, the effective contact surfaces between the two contact means tend to move in the opening direction, and the current lines are forced to run round the slot and to follow a direction approximately parallel to the flank of the slot situated on the side where the contact zone is located. At the moment when separation of the contact means takes place, the curved current lines in the first contact means are relatively stable so that the foot of the arc does not tend to flee towards the free end of the contact means. Due to the movement of the head of the arc towards the end of the second contact means, which takes place in the same way as in the previously described state of the technique, the arc moves globally away from the free end of the first contact means.
The slot opens out on the same side as the first contact means where the contact zone of the second contact means is situated in the open position. The depth of the slot must be sufficiently large for the curving of the field lines to be significant. Furthermore, it must not be too large as the residual material thickness must be sufficient not to cause destructive overheating when short-circuit currents flow in the contact means. The depth of the slot is preferably comprised between {fraction (
1
/
3
)} and {fraction (
2
/
3
)} of the total thickness of the first contact means, measured along said axis perpendicular to the longitudinal axis and in which the opening movement has a predominant component. In practice, good results have been obtained with a depth of about a half of the total thickness of the first contact means.
The flanks of the slot may be parallel or tapered, and the mid-line bisecting the slot may be more or less recumbent with respect to the longitudinal axis of the first contact means. In particular, the slot can extend in the depth of the contact means in a direction forming a small angle, comprised between −45° and +45° , with the axis perpendicular to the longitudinal axis of the first contact means.
The width of the slot, i.e. the distance separating the edges of the slot, must be sufficient to prevent a drop of molten metal from partially obstructing the slot and forming a bridge. It is therefore advantageous to arrange for the slot to have a width larger than 1 mm.
According to one embodiment, the slot has a width such that an electrical arc extending between the contact zones when the contact means are in the open position is able to pass from one edge of the slot to the other. This implies a maximum width to be determined according to the performances of the apparatus.
According to one embodiment, the slot is extended, inside the first contact means, by a cavity extending a
Faure Michel
Sirolli François
Terpend Serge
Parkhurst & Wendel LLP
Schneider Electric Industries SA
Scott J. R.
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