Power bridge
Current bridge is a term used in electrical engineering for a device in the series connection of incandescent lamps, for a component in vehicle electrics or for a component in rail vehicles.
Device for connecting incandescent lamps in series
If several incandescent lamps are connected in series, e.g. B. with fairy lights , if one lamp fails, all other lamps also fail. In addition, the defective light bulb is difficult to find. There are therefore versions with voltage-dependent resistors ( varistor , VDR) installed parallel to the filament . (Larger VDRs are often built into the lamp holder and therefore, in contrast to the picture, are not visible.) They only become conductive when a defined voltage is exceeded. If all lamps are intact, only the partial voltage of the associated incandescent lamp is applied to the VDR. This is below the breakdown voltage of the varistor. If the lamp is defective, the entire operating voltage of the light chain is applied to the varistor. The breakdown voltage is exceeded and the varistor becomes electrically conductive. With suitable dimensioning, a voltage is established that deviates only slightly from the partial voltage when the lamp is intact. This allows the other lamps to continue to shine; the defective lamp is easy to find because it is the only one that does not light up.
Current bridges can also be implemented using an oxidized aluminum wire. Such a design is mentioned in patent specification DE 847 782 and in the book by E. Rhein. For this purpose, the internal holding and supply wires to the filament are wrapped with an anodized aluminum wire. If, due to a lamp failure, the voltage and thus the electric field strength between the thin, insulating oxide layer and the connecting wires is high enough, the dielectric strength is exceeded and the oxide layer breaks down. The metals, which were previously only electrically isolated from one another by the non-conductive oxide layer, weld and become electrically conductive. The typical dielectric strength of pure aluminum oxide is around 20–30 kV / mm or V / µm. Thus, with a breakdown voltage of 100 volts, for example, an oxide layer a few micrometers thick is sufficient to implement this function. The lack of voltage drop after triggering is disadvantageous. Therefore, the voltage on the remaining lamps in the chain increases. This can lead to an avalanche effect in which all lamps are destroyed. Because the microfuse is often missing , the current increases so much that exploding lights can cause a fire.
The use of thermistors as current bridges is also conceivable .
Component in vehicle electrics
The currently used in motor vehicles blade fuses have a socket. These are connected to the on-board voltage with one of the contacts. This contact is designed as an integrated contact for several fuses in the fuse box into which the fuse is inserted and is called a current bridge . (mentioned in the patent application DE 102004053577)
Component in rail vehicles
In electrically powered rail vehicles, one pole of the supply voltage is an overhead line or a power rail , the other pole is the track. If rubber-sprung wheels are used in rail vehicles, the problem arises that the chassis of the car, which must be conductively connected to the track, is electrically isolated from the track. The required electrical connection is made with a sliding contact . This is called a current bridge (mentioned in utility model DE 297 02 851).
Footnotes
- ↑ E. Rhein: You and the electricity. Berlin, Ullstein 1940. p. 314 ff, a candle goes out