Electricity: circuit makers and breakers – Liquid contact – Time delay
Patent
1985-12-31
1987-03-03
Macon, Robert S.
Electricity: circuit makers and breakers
Liquid contact
Time delay
H01H 3306
Patent
active
046477411
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a current threshold switching device comprising, in a case, an input terminal, an output terminal and therebetween an electric circuit comprising at least two separable contacts, as well as a rotary screen having an annular wall interposable between the contacts and movable about an axis along a predetermined circumferential path from a first position to a second position, the annular wall moving opposite a fixed wall of cylindrical shape and concentric with the annular wall, said fixed wall comprising an opening for the passage of one at least of the contacts.
In U.S. Pat. No. 2,714,144, such a switching device is described using a cylindrical rotary screen housed between a fixed cylindrical inner core and a fixed cylindrical outer casing. The increase in pressure caused by a current breaking arc risks however causing an explosion of the device; in addition, during normal operation of the device, the gases are discharged to the atmosphere through a simple vent and cause pollution.
It is known from U.S. Pat. No. 1,833,173 and FR Pat. No. 1 217 162 to use, in a switching device for chopping an electric arc generated by the opening of the contacts, a screen in the form of a cylindrical sector interposable between the contacts.
It should be recalled that chopping of an electric arc is achieved provided that a sufficient arc tension is interposed in the circuit. This arc tension corresponds to a resistance of the plasma of the arc which is essentially dependent on its conductivity J, its length L and it section S in accordance with the relationship R.sub.arc =1/J.L/S; furthermore the conductivity of the arc is reduced when its temperature is lowered. It will moreover be readily understood that the time for the appearance of the arc tension and the increase thereof dv/dt, factors which are preponderant for ensuring a good chopping action, will be dependent on the speed of the screen as is stated in the patent application Ser. No. FR 83 01749 of the Feb. 4, 1983 in the name of the applicant.
Rotary screen switching devices of the prior art do not take sufficient advantage of the rotary character of the screen and are generally limited to confining the arc at the end of travel in a slot into which the front edge of the screen penetrates. Furthermore, the above mentioned patent application Ser. No. FR 83 01749 describes a switching device using an arc shearing means formed by a rotary screen which may be propelled at a speed of at least 5m/s between the contacts and engaging at the end of travel in a sealed abutment slit. The result however is a high overpressure of the ionized gases which in some cases requires appropriate arrangements.
The aim of the present invention is to provide a rotary screen switching device providing in a simple and inexpensive way reliable chopping of the arc and avoiding the risks of pollution and explosion.
A further aim is to arrange the arc chopping system so that it may be housed in a switching device of small volume and more particularly small thickness.
In accordance with the invention, in a device of the type mentioned above, the cylindrical fixed wall defines in the case two volumes situated on each side of the wall, whereas a cylindrical lamellar space of a considerable length and small height is defined between the radially inner face of the wall and the radially outer face of the annular sector for defining, in said space, a lamellar path for laminating and cooling the arc, the lamellar space communicating permanently with one at least of the two volumes for allowing expulsion of the gases with expansion from said space to said volume.
By laminating is meant in the present description that an upper limit is imposed on the section of the arc.
Cooling of the plasma of the arc takes place then along the fixed concave wall, the great length of this latter being able to be housed nevertheless in a relatively reduced space of the switching device because of the rounded shape of said wall. This rounded shape, in combination, with the pivoting axis se
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patent: 663612 (1900-12-01), Oxley
patent: 1833173 (1931-11-01), Murray et al.
patent: 2493419 (1950-01-01), Puffer
patent: 2714144 (1955-07-01), Amundson
patent: 2928910 (1960-03-01), Watterberg
patent: 4426562 (1984-01-01), Kemeny
Belbel Elie
Comtois Patrick
Lauraire Michel
Lemarquand Pierre
Moreau Luc
Drucker William A.
La Telemecanique Electrique
Macon Robert S.
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