Patent GB-191112579-A (GB)
Title: Improvements in and relating to Electric Signal Systems for Railways and the like.
IPC: B61L23/16
Filed: 1911-05-24
Granted: 1912-03-28
Abstract: 12,579. British Thomson-Houston Co., [General Electric Co.]. May 24. Electrical systems, automiatic. - The system described in Specification 18,868/10 is extended to obtain an overlap (that is, to place three signals in the rear of a train under control of that train) by providing means under control of the train for shifting the phase of the track current to three different positions and combinations of track relays responsive to the three different phases. Five modifications are described, in the first two of which three track relays per section, and in the others two track relays per section, are used, the track coils being connected in series in each case. In the first system, Fig. 1, the train is protected by two signals at danger and one at caution; in the second system, one signal is set to danger and two at caution. In these two cases, each track relay for a section has one coil permanently supplied with current of a particular phase from a three-phase two-phase supply. In a third system, two relays per section are used, one having back contacts in addition to front contacts, and the overlap is one section; the current in the fixed coil of the double-function relay is reversed by a switch on the semaphore spindle. In a fourth system, two track relays are used, and sections are divided into two parts giving an overlap of a cut section or half a block. In the fifth system, cut sections are used with two relays per section, the overlap being a complete block. The sources of energy in adjacent sections are reversely connected, so that, if any leakage occurs between sections, the relays exert an opening torque and put the signals to danger. In the system shown in Fig. 1, current is supplied to each track section from transformers E ... E<4>, the primaries of which are energized from transformers C ... C<9> through the well-known three-phase two-phase connexions; impedances c prevent short circuits when a train is near the track transformers, and when the signal switches f are in a mid position. A train in the block A<5> de-energizes the relays D<12>, D<13>, D<14> and the signal F<3> is set at danger. The phase of the voltage impressed on, and the current in the coils d<2> of, the track relays are shown by Figs. 2 to 6, ov<1>, oi<1> referring to the relays D<12>, D' and others in similar position, ov<2>, oi<2> to the relay D<13> &c., and ov<3>, oi<3> to relay D<14> &c. Fig. 2 refers to block A<5>, Fig. 3 to block A<4>, and so on. The current supplied to the block A<4> from transformer E<4> is shown by oi on Fig. 3. This is derived from the transformer C<9> through the back contacts of relay D<14> and switch f. The phase of this track current is so adjusted as to lead the current oi<3> in relay D" by 45 degrees and lag behind the currents oi<1> in relay D<9> by 45 degrees and oi<2> in relay D<10> by 135 degrees. The track relays are arranged to close their front contacts when the track current leads that in the coils d<2> only. The relays D', D<10> remain open, and the relay D" closes and changes the connexion of transformer E<3> from the transformer C' to transformer C‹ through the switch f and the front contacts of the relay D" without interrupting the circuit, since the front contacts close before the back contacts open. The current in the track rails A<3> is thus advanced 90 degrees and leads the current in the relays D<6>, D', which both close. The signal F<1> moves to ' caution,' and the switch f connects the transformer E<2> to the left half of the transformer C<5>, advancing the track current a further 90 degrees, as indicated in Fig. 5. Sections A<2>, A' represent a cut block, and relays are arranged in the section A<2> to supply current to the section A' of the same phase as to section A<2>, as shown in Fig. 6. The track current leads the current in coils d<2> of the track relays D, D', which are thus energized, and the signal F moves from ' caution ' to ' clear,' but does not alter the connexions of the switch f.