Patent GB-783835-A (GB)
Title: Improvements in electric control circuits
IPC: H04B3/44
Filed: 1956-01-03
Abstract: 783,835. Protective arrangements; supply systems; automatic current control systems. WESTERN ELECTRIC CO., Inc. Jan. 3, 1956 [Jan. 5, 1955], No. 159/56. Class 38 (4). [Also in Group XXXIX] Relates to the control of current supplied to a submarine telephone cable having spaced repeaters embedded therein, and having, at each end of the cable, two D.C. sources in parallel so that, in the event of failure of one source, the cable may be supplied from the remaining sources. As shown, one supply source comprises rectifier 10 for passing current through space discharge device 30 to the cable, and an A.C. source 18 coupled to the input of the rectifier. A resistor 31 is placed in the grid circuit of the tube 30, and when the cable-current passing through the resistor increases, for example, the voltage - drop across the tube increases whereby the current - in - crease is minimized. The variations of voltage-drop across the tube 30 are not always of sufficient magnitude to compensate for variations due to earth potentials introduced in the load circuit, and, for this reason, the saturating winding 62 of a saturable reactor is connected across the space discharge path. When the voltage-drop deviates from a predetermined value, the inductance of reactor winding 61 is altered and the field winding 65 of a motor 25 is energized. This causes a brush 24 to be driven and so reduce the output of auto transformer 19 in response to increase of voltage across the tube 30, for example. In addition, means responsive to an abnormally high load voltage or current are provided for energizing a relay 66 and connecting field winding 65 across tappings 22, 23, in the auto transformer. As a result, the motor drives the brush 24 in a direction to reduce the output of the transformer 19 until the load voltage or current have been reduced sufficiently to allow the relay to release. Thus, three saturable reactors 75, 77, 79 have saturating windings 88, 89, 90, subjected to the voltage applied to the cable, the windings 87, 86, 85, of the reactors being connected in series with rectifiers 76, 78, 80, through which relays 104, 105, 106, are energized. An excessive cable voltage energizes these relays which control, in turn, relays 113, 114, 115, the arrangement being such that at least two of the three relays 113, 114,115 must operate to effect energization of the relay 66. The failure of one of the A.C. sources 18, 18a will not prevent the energization of two of the relays 113, 114, 115, in response to excessive cable load voltage since magnetic amplifier 75 and one of the magnetic amplifiers 77, 79, will be energized from that source which is still effective. A similar arrangement for preventing excessive current comprises two relays which are energized by magnetic amplifiers responsive to the load current whilst a third relay is energized directly by the load current, Fig. 2 (not shown). As before, simultaneous operation of two or more of the relays is necessary before the load current is reduced sufficiently to allow the operated relays to release. A manual switch is provided for reducing the cable current in an emergency. The control apparatus referred to above is associated with the two A.C. sources at one end of the cable. Similar control apparatus is provided for use with the two sources at the other cable-terminal.