1. Field of the Invention
The present invention generally relates to current limiting contact systems which are typically used in circuit breakers. In particular, the present invention relates to a contact system, which contact system is composed of several parallel contact fingers for each pole to be switched and each pole to be protected, and, when there is a short circuit, limits the short circuit current by means of electrodynamic opening, until the breaker mechanism is tripped.
2. Background Information
A three-phase circuit breaker with a contact system of the type described above is disclosed in European Patent Application No. 353 948 A2. Three contact systems are arranged next to one another in a molded housing. Each contact system is composed of a stationary contact with a stationary contact piece, and a moveable contact with moveable contact pieces. Each stationary contact leads into a first phase connector. The moveable contact is composed of several contact fingers arranged parallel to one another, each with a moveable contact piece. The contact fingers are mounted on an axle, and each contact finger is connected by means of a V-shaped, flexible connection lead to the connection lead. The connection leads are connected to a second phase connector.
Each contact finger is acted upon by a helical compression spring, which compression spring is braced against a contact carrier. The contact carrier grips longitudinally in a U-shape around the contact fingers, and the axle of the contact fingers is mounted in the contact carrier. The contact fingers are mounted on a transverse selector shaft by means of a swivel pin. Each contact carrier is acted upon by a cam-operated toggle mechanism. In addition, two helical tension springs serve as energy stores or energy storage mechanisms, and engage between the swivel pin and the axles of cam follower rollers, which cam follower rollers are mounted in a linked manner in the switch axle. The central moveable contact is additionally connected to the toggle system of a breaker mechanism via the selector shaft by means of lateral supports. The necessary contact pressure force between the moveable contact pieces and the stationary contact piece is produced by the helical compression springs. During tripping or manual shutting off by means of the breaker mechanism, essentially all moveable contacts are swivelled by their spring-activated coupling with the toggle spring mechanism over the selector shaft, in order to open the contact pieces.
In case of extreme short circuiting, the electrodynamic repulsive forces caused by the short circuit current flowing in the V-shaped connecting leads, as well as the high current density on the contact pieces, exceed the contact compression force which leads to spinning off of the moveable contact concerned. The toggle spring mechanism then falls into its second stable tilted position. This tilted position is maintained until the circuit breaker is opened by the subsequent tripping breaker mechanism in all phases. The arc occurring between the separated contact pieces is extinguished with additional arcing contacts and an arcing chamber. Elastic stops are housed in the molded housing, which on the one hand collect the high kinetic energy of the electrodynamically spun-off contact concerned, and on the other hand tilt this contact back into the first stable position after tripping of the breaker mechanism.
The disadvantages of the contact system described above are, on the one hand, the complex means for the conductive connection between the contact fingers and the second phase connector the complex means; for the production of the necessary contact compression force the complex means; and for the collection of the kinetic energy of the spun-off contact; and, on the other hand, the considerable number of elements which are necessary for transferring movement from the breaker mechanism to the moveable contact. A further, crucial disadvantage is that with increased wear of the contacts, in particular by burning, the contact compression forces diminish, leading to an increasing degradation of the switching properties.
In German Patent Application No. 31 33 285 C2 an automatic circuit breaker is disclosed. This automatic circuit breaker includes a moveable contact carrier mounted in a fixed pivot, which moveable contact carrier can be operated by means of a breaker mechanism and is latched separately from the breaker mechanism by a locking lever. Thus, during rapid opening by means of a striker on the moveable contact carrier, a tension lever is moveable with respect to the contact compression force and thus the latch on the contact carrier is released. As such, the free ends of the locking lever and of the tension lever, which are mounted in the fixed pivot and which guide a compression spring, are joined together in an articulated manner, and support a sliding roller in the region of the articulated joint. The moveable contact carrier is provided with an essentially kidney-shaped slide plate in the direction of the switching operation, which slide plate forms a slip-in guide for the spring-tensioned sliding roller. A projection provided on the sliding plate in the proximity of the lock forms, together with the sliding part, a latching point. The angle of rotation of the tension lever is approximately the same as that of an angle of opening of the moveable contact carrier limited by a stop.
Apart from the fact that, in German Patent Application No. 31 33 285 C2, only a single finger contact system is described, this contact piece has disadvantages in that separate means are required to limit the opening movement caused by the short circuit as well as for collecting the kinetic energy occurring therewith, and that, with increasing wear of the contacts, the contact compression forces diminish.