GB551978A - Improvements in or relating to remote control systems - Google Patents

Abstract

551,978. Signalling over power circuits. NEWTON, E. P. (Telefonaktiebolaget L. M. Ericsson). May 28, 1941, No. 6865. [A Specification was laid open to inspection under Sect 91 of the Acts, Oct. 20, 1941.] [Class 40 (iv)] Signalling over power mains is effected with the aid of voltageresponsive receivers and transmitters which raise the peak voltage of the supply without correspondingly raising its R.M.S. value. For example, the transmitter may insert a D.C. source in the neutral wire of a 3-phase supply system or an A.C. source in the neutral wire of a 3-wire D.C. supply system. In other arrangements, the rise in peak voltage is produced by increasing the amplitude of the third harmonic in the supply current. This may be done, Fig. 4 (not shown), by connecting the secondary of a transformer of which the primary is in the neutral wire to the respective phases through saturable chokes. In a modification of this arrangement Fig. 5, the signalling contact r1 alternatively causes the saturation of the chokes and the saturation of the transformer to reduce the impedance of the neutral wire. In another arrangement, dry rectifiers are used instead of chokes for distorting the wave form and in another, a three-phase grid-controlled mercury rectifier is used. Transmission may be in part over a high-voltage section of the network, signals being received and repeated over a low voltage section at a transformer station. The Specification as open to inspection under Sect. 91 comprises also an arrangement in which an auto-transformer TS, Fig. 6 (Cancelled), charges a condenser C at each half cycle in a particular direction until the difference between the secondary voltage and the supply voltage exceeds the flash voltage of a discharge tube Gs, whereupon the condenser discharges and causes a surge in the supply system. This subject-matter does not appear in the Specification as accepted.