Patent GB-396042-A (GB)
Title: Improvements in or relating to the control of alternating electric currents particularly applicable to railway block signalling
IPC: B61L1/18
Filed: 1932-01-21
Abstract: 396,042. Control systems for consuming-devices. BRITISH THOMSONHOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Suits, C. G.; 514, Union Street, Schenectady, New York, U.S.A.) Jan. 21, 1932, No. 1905. Convention date, Jan. 21, 1931. [Classes 38 (ii) and 38 (iv).] Switching systems. - When the current through inductance 2 of non-linear characteristic is varied, resonance with a condenser 3 occurs at a given current. The rise of p.d. across this condenser is employed to saturate an inductance 6 in a second a.c. circuit and vary, the current in a load 8 substantially as shown by the curve 13 in Fig. 4. The characteristics of the curve 13 may be varied by resistance 4 in series with the devices 2, 3, and the load current may be caused to change at different points depending on whether the primary variable is rising or falling. The voltage of the a.c. source 1 may be varied or a resistance 12 in parallel with the condenser 3 may be changed, to produce the effect desired. The resistance may be varied by any means such as pressure temperature, light intensity or the like. A rectifier 5 is in series with the saturating winding of the inductance 6, and in one form the condenser is connected between the grid and cathode of an electrode discharge device in circuit with the saturating winding. The rectifier preferably has a resistance decreasing with increase of current, as in the copper copper-oxide type, to cause a constant current after the sudden rise. A saturable choke 18 in series with the devices 2, 3 may be employed with a variable impedance 17 in series with a saturating winding effecting control as shown in Fig. 6. In this case the rise in current at resonance changes the impedance of the choke 18 and pulsation may be set up at a frequency depending on the voltage of the source 1 and the value of the resistance 17 which pulsation may be applied in the control of flashing signals for aerodromes and road crossings. To prevent pulsation a stabilizing inductance or resistance 19 having a linear characteristic is connected as shown to carry say, 80 per cent of the current. An auto-transformer may step-up the condenser voltage. In a modification the saturable choke 18 is in parallel with the stabilizing inductance. The control may be exercised through circuits in tandem the load 8 being placed in the intermediate circuits by the saturating winding of an inductance in the succeeding circuit and a rectifier. The condenser 3 may be connected to the terminals of an electromagnetic switch 30, Fig. 13, which responds at the resonance condition to control a load circuit. To increase the average value of the current in the saturating winding of the inductance 6 an inductance having a linear characteristic may be included in series with the devices 2, 3 or the core of the inductance 2 may have a portion which saturates at a small magnetizing force and may consist of an alloy of nickel and iron. Fig. 9 shows the invention applied to railway signalling, the decreased current in the inductance 2 when a train enters the block causing a fall of potential on the condenser 3 and a decrease in current through the rectifier 5 and saturating windings of reactors 6 included in the circuits of signal lamps 24. The rectifier also acts to compensate the change in resistance between the rails 21 with weather. The source 1 only may be connected at one end of the block and the remaining apparatus at the other, an inductance being connected, optionally, across the rails to compensate for changes induced by weather. In another arrangement the modification described with reference to Fig. 6 is used and the train shunts the saturating winding of the inductance 18.