Patent GB-190501951-A (GB)
Title: A New or Improved System of Automatic Block Signalling for Electric Railways.
Inventor: TOWNSEND FITZHUGH
Filed: 1905-01-31
Granted: 1906-02-28
Abstract: 1951. Townsend, F. Jan 31. Electric railways.-Automatic alternating-current signalling-systems are described, employing the bonded traffic rails which are insulated into blocks as return paths for both signalling and power currents, either direct or alternating power current being employed. Fig. 1 shows a form in which an alternating power-generator A is employed with a power conductor or third rail 6, the insulated traffic rails 8, 9 being bonded through devices E, F. Return power current flows from the rails 8, 9 through the coil 11 of the bond E meeting in the centre of the coil, thus not magnetizing the core 10, and by the lead 17 to the centre of the coil 13 of the bond transformer F and out each way to the rails 8, 9, again not magnetizing the core 12. The primary 14 of the transformer F is connected at one end through the lead 15 to the signalling-current generator B and at the other end to the centre of the coil 13, through which the signalling- current passes both ways to the rails 8, 9 and back to the generator B. The coil 13 also acts as the secondary of the transformer F and thereby excites a signalling difference of potential across the rails 8, 9, producing a current in the moving coil K of the relay H to be short-circuited by a vehicle entering a block, so placing the semaphore 30 controlled by the relay H at " danger." This signalling difference of potential exciting the coil K will be maintained despite the connexion of the rails by the coils 11, since this coil upon its unmagnetized core has a reactive effect on the signalling potential difference. The field core 20 of the relay H is traversed by current from the secondary 21 of a transformer I, an adjustable inductive resistance J being included in the circuit. The primary 22 of the transformer I is connected across the source of signalling-current. The moving coil K of the relay H is weighted to lie normally with its arms 25 against a stop out of contact with a contact 28 of a local circuit containing the battery 26 and the solenoid 27 of the semaphore 30. When the coil K is energized (no train being in the corresponding block), it turns into contact with the contact 28, lowering the semaphore to "safety." The connexions of the primaries 14 of the transformers F in adjacent sections are reversed to avoid interference with the relays by leakage currents from adjacent-sections, the connexions of the relay coils K being correspondingly reversed. To lessen the resistance of the return paths for the currents, a conductor 23, which may be the structure of an elevated railway for instance, is connected to the generators and to the rails through wires 32 and bond devices L similar to the bonds E. In a modified form, Fig. 2, a two-phase generator A supplies both power and signalling currents, one phase current being led through the primary 5 of a transformer C, the secondary 16 of which supplies the signalling-current. In this case also, the transformers I, Fig. 1, are dispensed with, the field coils 20, Fig. 2, of the relays H being connected directly across the source of signalling-current, that is, between the signalling supply-lead 15 and the rails through the devices F. In a further modification, Fig. 3, a single generator A is employed, and only one supply-lead 6 for both power and signalling currents, the signalling-current being segregated from the power current and passing from the lead 6 through the fixed coil 20 of the relay H and back through the rails, and also from the lead 6 through the primary 14 of the transformer F and back through the rails. In a further modification, a direct power-current generator is employed together with an alternating signalling-current generator. The bonds E, F, Fig. 1, are replaced by two bonds E, and an additional transformer is used in each block to excite the signalling difference of potential across the rails, the primary of this transformer being connected across the signalling-current lead and the rails while the secondary is connected across the two rails.