Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Automatic circuit-interrupting devices
Reexamination Certificate
2003-09-11
2004-11-16
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Automatic circuit-interrupting devices
C335S132000, C218S022000
Reexamination Certificate
active
06819205
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to a current-limiting low-voltage circuit breaker. More preferably, it relates to one having a contact system which can be latched by use of a switching mechanism and having at least one moving contact element and at least one fixed contact element per phase. The moving contact element is preferably raised as a consequence of electrodynamic forces against the influence of a contact force spring when heavy currents occur, for example in the event of short circuits. Further, it preferably has the following features:
a drive apparatus for moving the switching contact to a connected position and to a disconnected position,
a latching device which is arranged in the path of the force transmission from the drive apparatus to the switching contact, which latching device, starting with the switching contact in the connected position, can be released by means of an opening force which originates from the switching contact and acts in the direction of the disconnected position, when the opening force exceeds a predetermined limit value, with the latching device being in the form of a mechanical connecting element between the drive apparatus and the moving switching contact, and having at least two interacting working surfaces, which are arranged at an angle to the direction of the opening force, and a contact-pressure spring which acts on the working surfaces.
BACKGROUND OF THE INVENTION
It is desirable for current-limiting low-voltage circuit breakers to have extremely short tripping times, of a few milliseconds. The normal tripping times for circuit breakers are longer because, in the case of a classical design of a dynamically fixed circuit breaker, that is to say a circuit which operates with tripping that can be staggered selectively, the contact system is intrinsically completely rigid. The contacts remain closed until they are released at another point. The tripping magnet must be caused to respond, which takes a comparatively long time, and a complete switching mechanism must be released for this purpose, in which a relatively large number of parts have to be moved. However, this also means that the switch has to withstand the high load from the current carrying capability and that it is not damaged or destroyed in advance by overheating. This can be overcome by using the electrodynamic current forces themselves to open the contacts. There are a number of different principles for achieving this.
One of these principles is to make it possible for the lifting-off contact forces to come into effect when heavy currents occur before normal mechanical latching in the switch drive is released. This is based on the idea that each of the contacts, which meet one another in the form of a butt connection, experiences a repulsion effect as a result of the high current density forces, and they are disconnected at a specific current intensity, unless the contents are held together by external forces. When the contacts are opened, the switching mechanism must then also be moved to the disconnected position and the contact support must once again be locked with the switching mechanism. In the process, it is desirable for possibly a single pole of a multi-pole circuit breaker to be caused to open under the influence of these forces while the others still remain closed, since it is just this one pole which is carrying the heavy current. When this extremely fast opening takes place, a switching arc occurs, and its resistance in comparison to the resistances of the current paths via the entire fault location and the switch are so large that this produces a current-limiting effect. The short-circuit current therefore cannot reach its full magnitude.
The described process can be achieved in a different way. If the requirements are not stringent and if the switching mechanism is designed particularly well, in particular with the parts that need to be moved having a small mass, it is sufficient to release it on three poles. However, as already mentioned, it is better to produce single-pole interruption of the relevant current path, since this results in a higher current limiting factor.
FR-PS 721 451 describes a DC voltage quick-action switch, in which the current forces are produced by way of an electromechanical transducer which is isolated from the contact system and responds to an increase in current. AT-PS 250 479 discloses a current-limiting switch whose moving switching lever is held in the connected position by a latching mechanism which can be released not only by means of an electromagnetic overcurrent release but also by way of a movement of the moving switching lever caused by electrodynamic forces. The transmission of the tripping movement of the overcurrent release to the latching point in this case makes use of two or more intermediate elements.
DE-PS 1 801 071 discloses a low-voltage circuit breaker having a current path which is in the form of a loop and produces contact-opening forces which drive the contacts apart from one another, and in which the switching lever is moved against the force of a spring in the contact system by way of the electrodynamic forces which occur in the event of particularly heavy overcurrents. A rod is provided on the moving contact lever and is supported by a roller on a blocking element. This blocking element, which can itself be moved against spring force, and a roller are used to move and release a catch lever, by which the switching lever can be moved to the disconnected position.
DE 14 63 312 A1 describes another possible way to use current forces to open contacts quickly. In this case, the contact which is raised by a heavy current occurring and which is mounted at a floating rotation point is fixed in the open position by way of a latching mechanism, and the normal energy store tripping shaft is operated via a lever mechanism, by which the switch is moved to its final disconnected position.
DE 15 13 341 A1 describes a further such circuit breaker, in which, when a heavy short-circuit current occurs, the electrodynamic forces result in a repulsion effect occurring between the two contact elements. In the process, when the contact support pivots with the moving contact in a locking device, the locking of the contact support to the switching mechanism is released, and a supporting lever is rotated. The tripping shaft is rotated via two further levers, which act as a double lever, and causes the switching mechanism to unlatch.
DE 1 463 311 A1 discloses another solution for current-limiting disconnection. In this type of construction, the moving contact piece is mounted in a hinged manner on a lever which pivots. In the event of a short circuit, the movement of the moving contact piece causes a contact piece barrier to be released as a result of electromagnetic forces, so that the contact spring stress is released and the moving contact piece is moved to the off position.
DE 25 11 948 A1 describes a switch in which an electrodynamic opening movement of the moving contact piece results in a lever arrangement being operated, in order to unlatch the switching mechanism directly, immediately after contact opening and as the contact spring force rises. To achieve this, the moving contact piece is mounted on a support such that it can rotate and, when it is in the connected position, is pressed against the fixed contact piece by a contact force spring which is supported on the support. The support is mounted at a rotation point whose position is fixed, and is rigidly locked by the switching mechanism in the connected state. The opening movement of the moving contact piece in order to unlock the support is passed via a lever arrangement to the switching mechanism, and to the lock for the support.
EP 0 398 461 A2 discloses a circuit breaker having a drive apparatus and a latching device for a moving switching contact, in which a mechanically nonlinear element is inserted in the drive apparatus. In terms of its method of operation, this is essentially formed from parts which can be pushed into one another tel
Bach Michael
Schmidt Detlev
Sebekow Michael
Seidler Günter
Thiede Ingo
Donovan Lincoln
Harness Dickey
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