Switch device having an insulating screen inserted between the contacts during breaking

A switch in which a screen inserted between the contacts shears the opening arc. The screen is associated with a sheath that surrounds a contact support and slides on the latter when the gas pressure it is subjected to causes it to move at a velocity which is a function of the energy of the arc. The switch is applicable in particular to protective apparatus designed to limit fault current or breaking devices in which steady-state current is fairly high.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an electric switch wherein a housing contains an 
insulating screen which is inserted at high speed between the two contacts 
to de-stabilize the arc that strikes when the contacts part by shearing 
the arc against a neighbouring insulating wall. 
Switches of this type, which result in extremely fast current breaking, can 
be used to advantage either in apparatus or combinations of apparatus 
designed specifically to protect lines against short-circuit currents, or 
else in breaking devices designed to open on high steady-state currents. 
2. Description of the Prior Art 
Screened switches such as those described above are already known, wherein 
the screen is propelled either by electro-magnetic devices assembled in 
series, or by elastic means. 
In any case, it is not easy to establish a synchronism and/or relation 
between the screen motion speed and the increase rate or level of the 
current to be opened; the purpose of the invention is therefore to provide 
suitable means so that a screened switch is able to open current in such a 
way that breaking speed increases as current increases, and to take 
advantage of the energy of the arc that strikes when the contacts part. 
SUMMARY OF THE INVENTION 
With the invention, the purpose is attained owing to the fact that the two 
contacts of the switch are borne by a fixed insulating support, surrounded 
by the sliding skirt of a mobile insulating case, the internal volume of 
which, enclosed between a bottom of this sheath acting as a driving 
component when exposed to the gas pressure and the contact support 
mentioned, houses the two contacts, whilst the screen is displaced by the 
movement of the sheath at least at the moment when the arc is sheared. 
Various embodiments of the switch, designed in particular and without any 
restriction to enable the incorporation of the switch in generally 
cylindrical housings similar to those used for fuses or small distribution 
circuit-breakers, must not be considered in any way as an intention to 
restrict the scope of use of the invention to such technical areas.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As illustrated in FIG. 1, the switch features two contacts 1, 2 which in 
this case are both mobile. These contacts are for instance borne by two 
symmetrical and parallel levers 3, 4 which pivot around 5, 6 in a chamber 
8 inside a fixed insulating support part 7 and contact pressure is ensured 
by springs indicated schematically by 9, 10 acting on the said levers. 
Contact-opening devices may differ according to the purpose of the circuit 
breaking; if the switch is designed to act as a protection against heavy 
overcurrents in its circuit, each one of the levers described above may be 
driven by a transmission shaft coupled to a magnetizable frame or core, 
which in turn is pulled by a coil provided in series with the contacts; if 
the value of the current to be opened are as high as limit values 
associated with full short-circuits, the levers may be operated by the 
electro-dynamic forces developed in the levers, on one hand owing to the 
loop effect and on the other hand thanks to the known use of U-shaped 
magnetizable attraction parts. 
An insulating support part 7 includes a base 15 which is e.g. joined to a 
housing 16 of the apparatus, and a transversal bottom 17 held by the sides 
18, 19; a first opening 20 through the base is aligned with a second 
opening 21 through the bottom in a plane PP' which is basically a symmetry 
plane. The outer surface 33 of the insulating part is e.g. cylindrical, 
see FIG. 1, and is fitted with a sliding clearance in an insulating sheath 
22, preferably cylindrical, one end of which 23 is located at rest near 
the bottom 17 and which has a skirt 24 that carries near its end 24a a 
transversal pin 25 designed to move in an oblong slot 26 in the insulating 
part parallel to plane RR'; this slot extends up to the first opening 20 
through which a thin insulating screen 27 slides, coupled at one end 28 
outside chamber 8, to the pin 25 which in turn is connected to the skirt 
24. In the idle position of the switch as illustrated, the opposite end 29 
of the same screen is near the switch contacts. 
It can be seen that in this layout the screen moves at the same time as the 
sheath and that in a particular sheath position the tip 29 is inserted 
between the contacts when they are open and then, with no detectable 
clearance, goes into opening 21, hence dividing chamber 8 into two 
half-chambers 8a, 8b which are insulated from each other by baffled 
overlaps (30, 31) between the longitudinal edges of the screen 27 and 
insulating part 7, see FIG. 2. The contacts are within the inner volume 
40a of the sheath. 
For this particular position of the sheath and of the screen or during 
motion towards this position, one set of vents 32, 37 in the skirt leave 
the cylindrical surface 33 of the insulating part where they were 
positioned, whilst a second set of vents 34, 35 in the same skirt comes in 
front of openings such as 36a, 36b, leading to chambers 8a, 8b 
respectively. 
In the embodiment illustrated here, the magnitude of the forces that 
separate the contact levers by electro-dynamic repulsion when an 
overcurrent flows through, arriving for instance through conductors 38a, 
38b connected to the line, is enhanced by providing U-shaped magnetizable 
structures 39a, 39b surrounding the levers. Shock-absorbing devices are 
provided between the housing and the sheath to prevent the latter from 
bouncing at the end of its stroke, and also resetting devices to return 
the sheath to the position shown in the opposite direction to F. 
In this case the switch operates when an overcurrent flows in the circuit, 
since the overcurrent first causes the contacts to part; as soon as this 
occurs, the arc arising between them causes a pressure in chamber 8, which 
is transferred through the second opening 21 to the volume 40 located 
between bottoms 17, 23 and impels the sheath in the direction indicated by 
the arrow F. As a result of this extremely fast motion the edge 41 of the 
screen shears the arc against the partition 17 and simultaneously 
establishes total electric insulation between the half-chambers 8a and 8b. 
The gases released by the arc generation then escape through the vents, and 
the volume and the two half-chambers return to atmospheric pressure. 
After opening this way, the contacts can either return to the idle position 
and thus bear on the opposite faces of the screen, or else be held open by 
locks not shown or by devices driven by a mechanism coupled to a 
magnetizable frame or core associated to a series mounted coil 42. 
In the switch just described, the two contacts, housed in a volume enclosed 
by the sheath, open before the screen starts moving. 
In an embodiment sketched in FIG. 3, the screen 44 or the sheath 45 if 
there is no play between them, are moved suddenly either by an elastic 
mechanism 46' previously set and released by the core or frame of a 
magnetic coil 43', or else directly by devices 43", 46"; in this case, the 
end 47 of the screen has a bevelled leading edge to separate the two 
contacts 48, 49, and the arc which is then generated causes as previously 
a movement of the sheath which is compounded with the mechanism or core 
effect, but only after the contacts have parted. 
As in the example in FIG. 1, where contacts open before the screen starts 
moving, the screen 44 and the sheath 45 can be associated with a measure 
of axial clearance XX' so that when the screen is moved by the device 46 
it first causes an initial opening of the contacts, and the rapid arc 
shearing movement is then produced when the screen is impelled by the 
sheath. 
In FIG. 4, the sheath 110 and the screen 111 are coupled axially and mobile 
contact levers 112, 113 are moved before them, either simultaneously by an 
energy accumulation mechanism such as 115 which is triggered as above by 
the action of a coil 114, or else simultaneously by mechanical 
transmissions means 117 associated with this coil. It is also possible to 
provide for a combination of these means. 
In the embodiments described above, both contacts are mobile; comparable 
results can also be obtained if one of the contacts is fixed, e.g. contact 
50 shown in FIG. 5; in this case the latter does not lie in the path 
followed by the screen 51. 
Lastly, it is possible for the two mobile contacts 53, 52, used as before, 
to be brought to bear in the idle position on a common intermediate 
contact 55, see FIG. 6, which is borne by screen 54 and which penetrates 
right into a slot 57 to ensure arc shearing, preferably against a heel 56 
of the screen. 
An intermediate contact of this type has the advantage that it cascades two 
arc voltages. 
In the provisions described above, the screen receives a thrust from the 
right hand side of the figures; in the layout shown in FIG. 7, the screen 
85 is pulled from the left of the figure, because the end 86 of this 
screen is joined to the bottom 87 of sheath 88. Here also the part 89 
supporting contacts 90, 91 has a bottom 92, but the latter has two 
openings 93, 94 which on one hand enable the pressure prevailing in each 
chamber 95a, 95b to be transmitted to the volumes 96a, 96b placed between 
the first bottom and the bottom 87 of sheath 88 and hence to move the 
latter, and on the other hand, enables the gas contained in the chambers 
to be vented through outlets 97, 98 of the sheath. In order to shear the 
arc, the screen has an slot 100 through which the mobile contact(s) pass, 
and passes with a functional clearance through an opening 101 in the 
bottom 92 with the same section; thanks to lateral guides and baffles 
comparable to those used in FIG. 2, the screen establishes efficient 
electrical insulation between chambers 95a, 95b, 96a, 96b when slot 100 is 
blocked in opening 101. 
A variation of the apparatus described above, illustrated in FIG. 8, uses a 
bond between the screen and the sheath comparable to the one illustrated 
previously. 
The insulating part 62 which here receives two contact levers 63, 64 has no 
bottom, but in the plane PP' it has a central rib 65 with an opening 66 
into which the two contacts 67, 68 enter. A sheath 69 with a bottom 70 
also has a cylindrical skirt 71 which slides on surface 62s of the 
insulating part; this sheath which includes at least one flat screen 
parallel to the longitudinal plane PP' such as 72 which bears on rib 65 
and has an opening 65g, can also have another screen 73. This screen, or 
these two screens, extend laterally up to the skirt, defining two 
half-chambers 74a, 74b which only communicate in the idle position of the 
sheath, see FIG. 8; as previously vents 75a, 75b provide an outlet to the 
atmosphere in a particular operating position of the sheath; an outlet 77 
may be provided between the end 78 of the rib and the bottom of the sheath 
to enable or control air intake into the volume 80 when the sheath is 
pushed by the gas in the direction of the arrow F. 
All the provisions mentioned hereabove to operate the contacts and as 
applicable to arrange for an intermediate contact are also applicable 
here, provided the latter is located in the opening 66. 
Although neither position limitation devices nor shock-absorbers for screen 
and sheath movement, nor resetting means designed to return them to the 
idle position after operating have been explicitly described, their 
presence and operation should be mentioned in all the variations. 
In all the different embodiments and implementations of the switch 
according to the invention, the bottom of the sheath, which can if 
required have calibrated openings connected or not to the atmosphere to 
reduce the pressure, acts as a driving component for the sheath and the 
screen coupled to it with or without any axial play. The section of this 
sheath, which for technical convenience has been illustrated as circular, 
can also have any other shape inasmuch as this sheath and the contact 
support part can be made by molding suitable plastics; 
Although for the sake of drawing simplification contact pressure springs 
and flexible conductors to supply power to contact levers have not always 
been shown, it must be inferred that these items, which are well known as 
such, are provided for in the switch or in association therewith, as well 
as the means to reduce external nuisance (noise, smoke) caused by the 
arcing. 
If the switch is applied to a breaking device with a fairly high rated 
steady-state current, manual or electro-magnetic mechanical means shall 
naturally be implemented to take care of the circuit opening and closing 
operations the switch is designed for; in this case also, resetting means 
designed to return the sheath to its idle position shall be associated 
with these different controlling devices.