Patent GB-190821596-A (GB)
Title: Improvements in Signal Systems for Railways and the like.
Filed: 1908-10-12
Granted: 1909-09-23
Abstract: 21,596. British Thomson-Houston Co., [General Electric Co.]. Oct. 12. Automatic systems. - In an automatic electric signalling- system in which the track rails are continuous and serve as conductors for both power and signalling - current, the signalling-current is alternating and the relays controlling the signals are connected to two points of one rail at a short distance apart, the impedance of the track rails being sufficient to cause a drop in voltage over a distance of twenty-five to fifty feet large enough to energize a suitable relay. Several modifications are described. In the system shown in Fig. 1, the signal current is single-phase alternating and the power current is continuous. Signalling- current is supplied to the rails through the transformers E, E', the secondaries of which include impedances e, e<1> to keep down the current when a train is over the points of connexion to the rails. The transformer E supplies two closed parallel circuits through the track rails on each side of it and the impedances G, G<1> which may be inductive or non-inductive. The relays shown are of the two - phase induction type having one coil supplied through a phase-changing device f and the other supplied from the track rails. The latter is composed of two separate coils each of which is connected to two points in one of the track rails at a suitable distance apart, as a shunt to a short length of rail. Normally, with the block clear, the relay coils are energized to keep the signal-operating circuit closed. This circuit is controlled by two relays of each block supplied from one transformer. A train approaching the impedance G in the direction of the arrow short - circuits the impedance and so causes a slight rise in the current in the relay coils f<1>. As the wheels pass the impedance G they gradually shortcircuit the relay coils f<1>, and before the distance spanned by the coils is traversed the relay coils are de-energized, the relay F opens its contacts and the signal goes to danger behind the train. The relay F remains de-energized until the train has passed the transformer E. Before passing the transformer, however, the relay F<1> is de-energized on account of short-circuiting the transformer E. The coils f of the relay F<1> will not be energized until the train has passed clear of the impedance G<1> so that the signal-operating circuit will not be restored until the train has passed clear of the block. The current from the transformer of an adjacent block can only exert a torque opposed to the closing torque of the relay, and tends to open the relay contacts. This counter-torque may be increased by introducing a primary winding connected to the signal linewires so as to induce an electromotive force in the impedance G, G', &c. which produces a countertorque in the windings f<1> when the transformer E is short-circuited. It is preferable to use a double winding for the coils f <1> as by this means a larger torque may be obtained with a short length of rail shunted by the windings, and saturation by the power current is avoided as this current produces opposite magnetomotive forces in the two coils. The relay track coils may, if desired, be supplied through a transformer, With the arrangements as in Fig. 1 a car with a short wheel base as compared with the length of rail shunted by the relays might stand over the impedance G, G<1>, &c. without de-energizing either relay. Fig. 4 shows an arrangement by which this is avoided while only using one track winding for the relays F, F<1>, &c. The impedances G, G', G<2>, are connected to the rails at points not directly opposite one another and the relays are shunted to the overlapping rail-lengths. A train always de-energizes one or mora of the relay windings f<1> which may shunt a greater length of rail than the wheel base of a car. The longer rail-length enables less current in the rail circuit to be used to give the same relay torque. In the modified arrangement shown in Fig. 5 current from different phases of a two-phase generator is supplied to the rails, the circuit from each transformer being completed through the adjacent transformer so that the resultant current in the relay windings connected to the rails differs in phase from either supply current by forty-five degrees. The current component supplied to the coils f<1> of the relay F' from the transformer E is in phase with that in the coil f<2> so that this does not exert a torque to close the relay F<1>; such a torque is exerted by the current from the transformer E<1> except when a train is between the relay and that transformer. A train approaching the transformer E in the direction of the arrow gradually short-circuits it, but does not affect the relay until it is over the length of rail shunted by the relay coils. The point at which the signal goes to danger is limited to this length of rail. The relay is not de-energized so as to clear the signal until the train has passed the transformer E'. The relay winding is adjusted so as to exert no torque tending to close the contacts when supplied only with current from the adjacent transformer. The proportions of resistance to reactance in the impedances in series with the transformers are adjusted to be the same as those of the rails, in order that the phase of the current in the relay may not be altered by the presence of the train in the section. In further modifications, two two-phase currents of different frequency are used, thus obviating the necessity of careful adjustment of relays which are then arranged to respond to one frequency only. The system of Fig. 5 has the relays close to the transformers to which they must not respond and removed from those coils that energize them. This objection is overcome by the arrangements of Fig. 7 in which each section signal is controlled by two relays which are placed one at each end of the section and are energized by one transformer mid-way between them, adjacent sections being fed with current of different phase from a two-phase generator D. The relay coils are supplied through a phase-changing device j<3> from that phase of the generator which does not supply the transformer energizing the track coils, f<1>. With this arrangement so soon as a train clears the length spanned by coils f<1> at the exit of a section the relay is energized and the signal clears when the train is at a very definite point, since the circuit from the transformer E' is along the rails A, past the shunted lengths of rail at relay F<1>, along the train axles and back along the rails, thereby giving a larger current in the rails than the normal circuit which extends as far as the next transformer. The relay thus has a greater torque when it is required to pick up its armature again. An arrangement by which the relay at the exit of a section is not re-energized until the adjacent relay at the entrance to the next section is de-energized, while enabling the track coils of the relay to be connected to both track rails and be of considerable length is shown in Fig. 8. The relay F<1> has two track coils f<1>, which are connected to lengths of rails near the impedance G<1> and are supplied with current from the transformer E. The signal H is controlled by the relays F, F<1>. The circuit of the coil f<2> of the relay F<1> is controlled by contacts h on the signal H<1> and by contacts on the armature of the relay F<1> so that once the relay F<1> is de-energized to put the signal H to 'danger' it cannot be again energized until the. signal H<1> is put to danger,' energizing the coil f<2>, and this cannot take place until the train has passed sufficiently into the section. Since with this arrangement the positive point of short-circuiting of the relay is of minor importance, the impedances G, G', may be replaced by bonds of low impedance and low resistance and a single coil may shunt a length of both rails and the bond. A similar arrangement may be adopted at points or switches to ensure that a signal for a section may be cleared when a train runs off that section over a switch. The points on being re-set for a through road are made to close the circuit of the relay coil f<2>. A further modification is described in which the contacts h on the signal are replaced by back contacts on the relay armatures ; in this case it is necessary that, when power is first switched on the signal wires, the relay F<1> should close its contacts betore the relay F' opens its back contacts. [Reference has been directed under Section 7 of Patents &c. Act, 1907, to Specifications Nos. 12,795 and 18,500, A.D. 1908.]