Electricity: electrothermally or thermally actuated switches – With diverse art-type actuator for single switch
Patent
1997-06-20
1999-05-25
Picard, Leo P.
Electricity: electrothermally or thermally actuated switches
With diverse art-type actuator for single switch
337 17, 337 19, 337 31, 337 34, 337 4, 337 5, 338 67, 200 6108, 218154, 218158, H01H 3100, H01H 8500, H01H 3302, H01C 1300
Patent
active
059072709
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns a current-limiting switch with current connections and contacts, at least one of which is movable, having an associated drive for opening the movable contact when a predefined electric current intensity is exceeded, the drive being a thermoelectric drive, where, in a closed housing made of insulating material, at least one disk-shaped resistor body is present between the contacts for high-intensity discharges.
BACKGROUND INFORMATION
In the international patent application WO-A-95/03619, a switch of the aforementioned type is proposed for us as a limiter. A large-surface resistor body, with an electrical resistivity that is considerably higher than that of a metal, is used to prevent localized fusing of the electrodes n the case of a short-circuit shutoff due to the plane propagation of the current flow; uniform heating of a gas volume present in the closed housing made of insulated material is also favored by the high-intensity discharges on the resistor material.
Switching with thermoelectric drive, which is the principle of the above-described switch, is therefore based on heating suitable resistor elements, such as disks made of carbon black-filled polyethylene, instantaneously at the contacting boundary surfaces and producing a high-pressure gas blanket through material decomposition that releases mechanical energy through a piston in the case of a short circuit. The thermal and electrical properties of the best resistor materials currently available require that the nominal current be limited to a current density of approximately 1 A/cm.sup.2 at a contact pressure of approximately 100 N/cm.sup.2 for AC3 operation. Electrodes and resistor disks of approximately 18 cm diameter and contact forces of approximately 25 kN would be needed to extend the above-mentioned switching principle to nominal currents of 250 A, for example.
This means that the mechanical design of a thermoelectric switch suitable for higher nominal currents must be extremely sturdy, with it individual components having a relatively high weight. However, the necessity of moving large electrode weights makes achieving a sufficient speed of the thermoelectric drive difficult.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide a switch with a thermoelectric drive that can be used for low-voltage networks with nominal currents of several hundreds amperes. In particular, higher amounts of mechanical energy and larger drive paths are to be achieved, while a compact design is to be preserved.
This object is achieved according to the present invention by connecting, in a housing made of insulating material, a plurality of resistor bodies and associated electrode disks acting as contacts electrically in parallel and mechanically in series. In particular, the housing made of insulating material forms a cylindrical switching chamber inside and has a stack of a plurality of, for example, six, electrodes acting as movable and fixed contacts and a number diminished by one, for example five resistor bodies between said contacts, both of which are arranged in alternating layers one on top of the other.
The present invention allows, for example, the contact force to be reduced to approximately 5 kN and the diameter to be reduced to 8 cm compared to the above-mentioned values in an embodiment for a nominal current of 250 A, for example. The effective drive path increases approximately 5-fold, so that a stroke of 5 to 10 mm can easily be achieved.
One particular advantage of the present invention is that the electrodes can be designed not for mechanical strength but for electrical conductivity and the required heat removal, which results in considerable weight savings. In particular, a weight reduction in the proportion of 11:1 is achieved in comparison with the aforementioned example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically shows the cross-section of an electrothermal switch.
FIG. 2 schematically shows the top view of said switch sectioned alon
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Branston David Walter
Jaehner Wilfried
Pohl Fritz
Picard Leo P.
Siemens Aktiengesellschaft
Vortman Anatoly
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