Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – With housing or support means
Reexamination Certificate
2002-07-22
2004-10-12
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
With housing or support means
C335S132000, C335S174000
Reexamination Certificate
active
06803844
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to a switching pole for low-voltage switching units having a linearly movable contact support for a movable switching contact. Preferably, it relates to one which interacts with a fixed-position switching contact which is mounted on a connecting rail, and includes a drive apparatus for the movable contact support.
BACKGROUND OF THE INVENTION
Switching units having a switching pole are described, by way of example, in DE 12 50 532 B or DE 18 14 550 C1. These are contactors. Specific features of contactors, which appear to be advantageous, cannot, however, be used without problems in circuit breakers, as will be described in more detail in the following text.
Low-voltage circuit breakers include a number of assemblies which are matched to the different task elements and are connected to one another during production of the circuit breakers. The largest assemblies, or units, in this case form the switching poles, that is to say the contact systems (which are composed of stationary and removable switching contacts) with their supporting insulation and the drive apparatus, which is shared by a number of such contact systems). In this case, the movement sequences which are provided by the drive apparatus are transmitted to the contact systems via a switching shaft which is mounted in a fixed position. For this purpose, the switching shaft, which is mounted such that it can rotate and can be pivoted through a specific angle via a spring store or some other switch drive, is provided with levers which originate from this switching shaft and continue further, via which the individual switching poles, or movable contacts which are arranged on contact supports, are operated. Contact supports such as these have until now generally been mounted in low-voltage circuit breakers such that they can pivot. This results in a relatively high physical shape, with effects on the physical height of the switch enclosure, and in a relatively complicated design.
Such conventional configurations of lever arrangements for transmission of the drive force for low-voltage circuit breakers are described, by way of example, in DE-C 44 16 088 and in EP Patent Application 0 225 207. In the case of contact supports which have a number of parallel contact levers, assembled structures, which can be pivoted by means of a shaft, have always been used until now, in which a body is used only to hold the contact levers, and side walls or levers, generally in the form of metal parts, have been attached to this body at the side, by means of screw connections or in some other way, with these then representing the mounting of the contact support.
A movable contact support of this type has been disclosed in DE 35 39 786 A1. Here, the bearing arms are a component of a bearing bracket, whose dimensions are matched to a holding body for the contact levers. This is a structure comprising a number of metal parts. Movable contact supports are also known which are assembled from a combination of plastic moldings and metal parts. For example, DE-296 15 556 U describes a movable switching contact arrangement for a low-voltage circuit breaker with contact levers and with a contact lever support which holds the contact levers and is mounted by bearing arms at the side such that it can pivot for connection and disconnection. This contact lever support has a center part, which comprises a base body and at least one additional body which can be attached to this base body, with the bearing arms being mounted on the center part, on both sides. Both the movable contact supports which have been mentioned are assembled in a conventional manner from a number of individual components. Furthermore, parasitic voltages can occur in the case of supporting arms composed of metal.
The contactors which were mentioned initially have contact supports which move in straight lines. These are connected to an armature of a drive magnet and contain bridge contacts with associated contact force springs. However, this is completely unusual for circuit breakers. Contact links which have become known for circuit breakers have considerable problems (quite apart from other difficulties that are still to be mentioned) with regard to the dissipation of the switching gases. Although two disconnection points can allow a higher switching rating, two switching chambers are required, by way of example, from which it is necessary to provide dissipation of the switching gases. Particularly in the case of high switching ratings, the primary problem is the dissipation of the switching gases for the second disconnection point. If the contact link is arranged vertically, there are difficulties with the course of the arc, since the switch components are located above the disconnection point. The lower arcing chamber therefore cannot be used.
If the contact link is arranged horizontally, there is a problem in dissipating the switching gases on one side, since this would have to be done to the side on which, in the case of the circuit breakers, their peripheral devices, such as auxiliary and signaling devices, are located. This is extremely disadvantageous. If the switching gases are dissipated to the side, the distances to the side walls of the inset frame are also too small. Furthermore, the guidance of the busbars with respect to the contacts when the contact link is arranged horizontally results in considerable problems. Thus, a vertical arrangement of the contacts might represent the best solution. But, as has already been stated above, this cannot be achieved using a contact link.
Another problem is that the arrangement with a contact link is mechanically unstable. There is no certainty as to which contacts of the link will open first, that is to say where the greater erosion will occur. Considerable technical complexity is involved in designing such contact links reliably, with regard to the contact forces or the simultaneous opening of both contacts. The arrangement of two arcing chambers also represents not inconsiderable additional complexity.
In the case of low-voltage circuit breakers, particularly in the case of devices with a high switching rating, the geometry of the switching pole must be maintained as precisely as possible in order to avoid over designing in widely different ways, and in order to ensure correct operation. This includes exactly ensuring the penetration to achieve the necessary contact force, the contact opening and other parameters. However, this is not feasible with contact links, as has been described above.
Leading and main contacts are required in order to cope with the switching rating, as is disclosed by way of example in FIGS. 9 to 12 in U.S. Pat. No. 3,585,329, which illustrate the profile of the contact movement during disconnection of a switch. In this case, it can be seen that the main contact opens first followed by the auxiliary contact, which indicates that the disconnection arc is transferred from the auxiliary contact to a dissipation lug. This avoids arc formation on the main contact and prevents the main contact from being worn by contact erosion.
This sequence of a switching process can also be found in EP-PS 0325 767 B1, in particular in FIGS. 3 to 5 there. Although this describes a connection process, it is nonetheless clear that the procedure for disconnection takes place in the opposite sequence. Here, too, it can be seen that the erosion of the main contact is avoided by later opening of the contact.
From the problems which have been described, it can be seen that a linearly movable contact support with contact links, as is normal for contactors, cannot be used for low-voltage circuit breakers. In addition to the risk of contact opening as a result of clectrodynamic forces, the disadvantage is that only one contact link per pole and, possibly one three-pole contact link support for three contact links per operating rod are feasible, while circuit breakers have individual poles, three or four poles of which can be joined together, depending on the size of the device.
SUM
Bach Michael
Schmidt Detlev
Sebekow Michael
Seidler-Stahl Guenter
Thiede Ingo
Donovan Lincoln
Harness & Dickey & Pierce P.L.C.
Siemens Aktiengesellschaft
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