Patent GB-273201-A (GB)
Title: Improvements relating to railway signalling
IPC: B61L23/16
Filed: 1926-07-12
Abstract: 273,201. Larry, E. C. July 12, 1926. Electrical systems, automatic; lamp signats.-- In a railway signalling system employing insulated track sections and three-position track relays controlling three-indication signals at the entrance ends of the sections, a slow-acting relay is used in each section for changing the polarity of the current supplied to the next section in the rear. The sluggish action of the relay prevents a wrong indication being given corresponding with a de-energized condition of the track relay as the polarity of current supplied is reversed, as in passing from "caution" to "clear" conditions. The invention is described as applied to colour light signals but is applicable also to position light signals. The track rails are divided into insulated sections H, I, J. Each section has a threeposition track relay T, T' bridging the rails at the entrance end, slow-acting relays SR, SR<1>, CR, CR<1> and signals S with "danger," "caution," and "clear" lamps R, Y, G. The local windings of the three relays T, SR, CR are energized in parallel from the secondary of a transformer 6, the primary of which is supplied from a transformer 4 connected to the supply mains 3. The other winding of transformer T is energized from the secondary of transformer 7<1> of the section J ahead over front contacts 10<1>, 15<1>, of the relay CR'. The primary of transformer 7<1> is supplied from the secondary transformer 4<1> over polechanging contacts (back or front) 20<1>, 24<1> of relay SR<1> so that the instantaneous polarity of current supplied to the winding of relay T depends upon whether relay SR<1> is energized or de-energized. Contacts 30, 51 of relay T occupy one or other of the extreme positions indicated according to the polarity of the track current so that, when the relay T is energized either way a circuit is closed from the secondary of transformer 6 over contact 30, wire 32 and winding of relay SR, which is thus energized when relay T is energized. With the track clear, the conditions are as shown, a circuit being closed to light "clear" lamp G from transformer 6 over wire 46, contact 53 of relay SR, contact 51 of relay T, lamp G and wires 48, 38. A pick-up circuit is also closed from transformer 6 over wires 38, 39, relay winding CR, resistance 42 and contact 44 of relay SR, so that current of normal polarity is supplied over contacts 10. 15 to the track section H owing to front contacts 20, 24 being closed. When section I becomes occupied, relay T is de-energized with consequent de-energization of relay SR. Lamp G is thus extinguished at contact 51, and a stick circuit is closed from transformer 6 over wire 46, back contact 53, contact 59 of relay CR, "danger" lamp R, winding of relay CR and wires 39, 38. Lamp R and relay CR being thus in series, failure of lamp R would de-energize relay CR, and owing to inclusion of the contact 59, a momentary failure would be sufficient to effect this. Contacts 10, 15 would thus be opened, cutting off current supply to the rails of section H, so that a "danger" signal would be given at the entrance to that section. With lamp R intact contacts 10, 15 remain closed and a current of reversed polarity is supplied to section H owing to back contacts 20, 24 of de-energized relay SR being closed. Relay CR is sluggish to ensure that its contacts 59 shall not open in the short period between breaking the pick-up circuit and closing the stick circuit at contacts 44, 53. Contacts 44, 53 may be adjusted so that one or other is always closed in which case relay CR need not be sluggish. When the train passes on to section J, a similar operation to that described above occurs, a "danger" signal being given at that section, and current of reversed polarity supplied to the rails of section 1. Relay T is thus energized with its contacts 30, 51 thrown to dotted line position. Relay SR is thus re-energized restoring the pick-up circuit of relay CR and closing front contacts 20. 24 to supply normal current to section H. At the same time a circuit is closed from transformer 6 over wire 46, front contact 53, contact 51, wire 61, "caution" lamp Y, and wires 48, 38. When the train leaves section J, a "caution" signal is given in that section and normal current is supplied to section I so that the "clear" conditions shown are restored. Relay SR is made sluggish so that its contacts 53, 54 do not open when its circuit is momentarily broken as the contacts of relay T move from right to left in changing from "caution" to "clear" so that no false indications are given. Specification 270,917 is referred to.