Electricity: electrical systems and devices – Safety and protection of systems and devices – Load shunting by fault responsive means
Patent
1991-04-04
1992-08-25
Stephan, Steven L.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Load shunting by fault responsive means
379345, 379412, H02H 900
Patent
active
051424290
ABSTRACT:
An overvoltage and overcurrent protection for an exchange terminal circuit which has two input terminals (a, b) and a number of output terminals (T1-T). The input terminals are connected to a two-wire line and the output terminals are connected to equipment for the transmission of analog as well as digital signals over the line via the exchange terminal circuit. The exchange terminal circuit comprises an impedance matching network having a transformer at the primary as well as secondary sides of which there are networks that are symmetric in respect to earth. The network at the primary side comprises two primary winding halves (L1, L2) between which a capacitor (C) is series connected. The novel features of the invention is a varistor (V1) that is connected in parallel with the capacitor (C). When a surge pulse has charged the capacitor to the rated voltage of the varistor the varistor goes conductive thereby increasing the current through the primary winding until the core of the transformer is saturated. At the secondary side of the transformer there is a varistor (V2) and Zener diodes (Z5-Z8) which act to stepwise reduce the surge pulse as transformed to the secondary to a voltage which is safe for the connected equipment.
REFERENCES:
patent: 4032718 (1977-06-01), O'Neill
patent: 4398066 (1983-08-01), Sinberg
patent: 4539443 (1985-09-01), Jaki
patent: 4590334 (1986-05-01), Jaki
Stephan Steven L.
Telefonaktiebolaget L M Ericsson
To E. H.
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