High-voltage switches with arc preventing or extinguishing devic – Arc preventing or extinguishing devices – Arc chute assembly
Reexamination Certificate
2003-04-07
2004-09-21
Donovan, Lincoln (Department: 2832)
High-voltage switches with arc preventing or extinguishing devic
Arc preventing or extinguishing devices
Arc chute assembly
C218S156000
Reexamination Certificate
active
06794595
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electrical switchgear apparatus, in particular a current limiting apparatus such as a current limiting circuit breaker, the external manifestations whereof when breaking is performed are reduced or even non-existent.
STATE OF THE ART
In the document FR 2,589,624 a conventional arc extinguishing chamber for a low-voltage power circuit breaker is described. The chamber is situated facing the separable contacts of the circuit breaker and is provided with gas outlet orifices on a rear wall opposite from the contacts. Flat metal fins are arranged inside the chamber, between the contacts and the gas outlet orifice, perpendicularly to the side walls. In the event of a short-circuit occurring, separation of the contacts gives rise to an electric arc which is projected into the chamber by an electromagnetic loop effect. As it progresses in the chamber, the arc encounters the fins which absorb a part of its energy. The arc also exchanges heat with the side walls of the chamber which are made of synthetic gas-generating material. The arc cools progressively and its voltage increases so that, when the current crosses zero, the arc is definitively extinguished. The thermal and kinetic effects of the arc plasma during breaking cause a sharp increase of the pressure in the arc extinguishing chamber. The outlet orifices enable the emitted gases to be removed and the pressure to be contained at an acceptable level inside the case of the switchgear apparatus. This removal of the partially ionized breaking gases does however impose minimum safety distances between apparatuses on any one electrical panel in order to prevent any risk of arcing between live adjacent units. It also requires arrangements to be made for overpressures so as not to damage the panel itself. Moreover, the gases outlet from the unit can be considered to be polluting and therefore have to be filtered.
Electrical switchgear apparatuses are moreover known whose case is air-tight so as to eliminate any external manifestation when breaking takes place, as described for example in the document GB 2,119,575. The case then has to be provided with high-performance sealing devices and its mechanical pressure resistance has to be increased. Air-tightness is obtained at the cost of lower breaking performances with respect to a conventional apparatus of the same volume. Furthermore, the cost of such apparatuses as compared to conventional apparatuses is very high, which results in their only being implemented under extreme conditions, for example in explosive environments.
A tightly-sealed low-voltage power circuit breaker is described in the document WO95/08832. This circuit breaker comprises an arc extinguishing chamber arranged facing the contacts and equipped with cooling fins which are arranged between the contacts and an orifice for outlet from the chamber. A recirculation channel directs the gases from the outlet of the chamber to the contact drive mechanism, passing via a de-ionizing filter. The gases emitted when breaking takes place at the level of the arc extinguishing chamber thus flow in a closed circuit in the case and are finally redirected to the contacts and to the inlet to the chamber after they have been cooled and de-ionized. This strong convection enhances high-speed displacement of the arc inside the chamber, which is considered in this document as being particularly advantageous for speeding-up breaking. The arc, as it moves in the chamber, in fact constantly encounters new cold surfaces which perform cooling of the arc. However, the size of the chamber necessary to achieve high breaking performances is thereby increased as the energy absorption capacity of the fins is not fully used due to the rapid progression of the arc. Furthermore, the recirculation channel makes the case more bulky and more complex. Finally, the arc may leave the chamber totally via the outlet opening due to the strong convection. In this case, the arc is no longer in contact with the fins and is no longer cooled.
To better use the heat exchange surface provided by the cooling fins and to prevent the arc from leaving the arc extinguishing chamber, it has been proposed, in the document DE 2,410,049, to house the fins in an enclosure made of gas-generating material, one wall whereof opposite the contacts is provided with gas outlet slits, and to fit a mask comprising holes of small diameter outside the enclosure, the mask being pressed against the wall comprising the slits. The fins are cut into a V-shape so as to form an attack slit. When the circuit breaker opens on a short-circuit current, the arc enters the chamber in centered manner. On reaching the back of the chamber, the arc is deflected onto one or the other of the sides and returns to the contacts diving up between the fins, and is then re-established between the contacts before being projected into the chamber again. The foot of the arc therefore follows a path in the form of a loop until the arcing energy has been dissipated in the fins. The fins are thus used in homogeneous manner. However, the flow of the arc gives rise to periodic restrikings of the arc on the contacts, which damage the contacts.
In the document DE 2,624,957 arc extinguishing plates are described designed for an arc extinguishing chamber of an electrical switchgear apparatus. The plates have a cut forming a tapered U or V-shaped neck extended by a slit opening out onto a circular broadened part. This shape is supposed to ensure a good localization of the arc and fast extinguishing thereof. It is scheduled to cover the extinguishing plates with a plastic or ceramic insulating material, notably polytetrafluorethylene, so as to stabilize the positioning of the arc in the circular broadened part. The plates can be made of soft iron and covered, at the level of the broadened circular part at least, with a soft and electrically insulating magnetic material to prevent the arc from forming a foot on the periphery of the broadened part. According to this teaching, the arc can be localized in the circular broadened part, but nothing is provided to perform extinguishing of the arc. In particular, the arrangements made to stabilize the arc and prevent an arc foot from forming have the consequence of the energy exchange between the arc and its environment being greatly reduced. Apparently the arc can only effectively exchange with the ridges of the plates, at the level of the circular broadened part. The lateral part of the plates is therefore not used efficiently for cooling the arc. Finally, the treatment of the plates in several layers of different materials increases the cost of the device considerably.
SUMMARY OF THE INVENTION
The object of the invention is therefore to remedy the shortcomings of the state of the art so as to be able to propose a switchgear apparatus with good performances and greatly reduced external manifestations, in a small volume.
According to the invention, this problem is solved by means of an electrical switchgear apparatus, comprising:
a case defining a longitudinal geometric reference plane and containing:
an opening volume and
an arc extinguishing chamber opening out onto the opening volume and bounded by two opposite side walls parallel to the geometric reference plane, a rear wall located away from the opening volume, a bottom wall and a top wall;
a pair of separable contacts arranged in the opening volume and comprising a first movable contact movable along a flat path in the geometric reference plane between a contact position and a separated position and a second contact;
cooling fins arranged inside the arc extinguishing chamber, perpendicularly to the geometric reference plane, each fin having a free attack edge exposed to the arc;
a bottom longitudinal electrode in electrical connection with the second contact, the bottom electrode at least partially covering the bottom wall of the chamber;
wherein:
the free edges laterally bound a gulley extending in the heightwise direction from the bottom electrode to the top wall, the gulle
Charles Richard
Dye Stéphane
Moreau Luc
Fishman M.
Parkhurst & Wendel L.L.P.
Schneider Electric Industries SAS
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