Patent GB-416866-A (GB)
Title: Improvements relating to repeating stations for telephone and like systems
IPC: H03F1/54
Filed: 1933-03-23
Abstract: 416,866. Converting. STANDARD TELEPHONES & CABLES, Ltd., Connaught House, Aldwych, London.-(Western Electric Co., Inc.; 195, Broadway, New York, U.S.A.) March 23, 1933, No. 8778. [Class 38 (ii).] Plate voltage is supplied to the repeaters of a telephone system over the lines from a terminal station, and means are provided whereby alternating current for cathode heating, which is normally obtained from a local source, may be automatically derived from the direct-current plate supply should the local source fail. Cathode heating-current for the repeaters is normally supplied from A.C. mains 34, but should these fail direct current is taken from bus bars 17, 20 and converted into A.C. of suitable voltage in the inverters 27, 41. The rectifier 11 at the terminal station comprises two diodes 35, 36 giving full-wave rectification from A.C. mains 38 to D.C. output 14, 14<1>. which are connected over the telephone line to busbars 17, 20 at the repeater station. A battery 39 in series with a copper oxide rectifier 40 is floated across the D.C. output leads, and suitable smoothing means is provided. The mains supply 42 at the repeater station is normally connected through back contacts of unenergized relay 43 to the leads 34, which supply the cathode-heating transformer 33 for the amplifiers and the heater circuit 49 for the inverter 27. Should the supply fail or the voltage rise or fall beyond suitable limits, one or other of the relays 45, 46 closes its contact thus energizing relay 47 by connecting it across the busbars 17, 20. The inverter 27 is thus connected to the busbars 17, 20, and the inverter delivers alternating current of suitable voltage at its output terminals 50 and so operates a relay 51. Other contacts on the relay 47 energize the relay 43, so that current is supplied from the inverter output 50 to the heater leads 34, which are now disconnected from the local supply mains 42. The extra current taken by the inverter 27 causes relays 53, 54 at the rectifier 11 to be energized so giving a greater step-up ratio to the transformer 37. In this way the supply voltage for the plates of the amplifiers is kept up to a suitable value. When the voltage on the supply line 42 is again normal all relays return to normal position. A set of several inverters is provided at each repeater station the number in the set being dependent on the number of amplifiers to be supplied, and each set includes a spare inverter 41 which is brought into service in case any one of the inverters fails. If the relay 51 of any inverter fails to operate, its lower back contact completes a circuit from the busbars 17, 20 through a relay 55, thereby bringing into action the spare inverter 41. At the same time the relay 55 by its uppermost contact closes a holding circuit for each of the relays 51 that is operative, so preventing the spare inverter from being overloaded should a second inverter fail. Before the spare inverter 41 is brought into action, its heaters are energized over back contacts of a relay 58 from the heater leads 34, but when it comes into action relay 58 is operated and transfers the heater circuits to its own output. The output of the spare inverter is conveyed through leads 52 and back contacts of the inoperative inverter to front contacts of corresponding relay 43 and thence to the heater leads 34.