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The Skovde and Herrljunga Interlocking Plants. By Captain T. H.son Almqoist, signal engineer district II of the Swedish Gov't Ry. service. hen planning the interlocking plants for Herr- signal cabin (fig. 3) on the north side of the station W ljunga and Skovde in District No. II of the building. The interlocking machine is provided with Swedish Gov't Railways, the fundamental idea was nine point and skotch block levers, five point locking to have an interlocking machine which need be levers, two levers for manoeuvering the crossing gates, manoeuvered only for the movements of trains and only and thirteen signal levers. A switchboard for power by the train dispatcher himself. distribution, an illuminated track plan and the necessary Both of these interlocking plants have been de­ relays are also mounted in the signal cabin. livered and erected by Signalbolaget, Stockholm, sales The track plan is placed at eye-level on the company for railway signal and safety devices manu­ wall in back of the interlocking machine, and factured by L. M. Ericsson and by the Avos company is a true reproduction of the entire track system. The of Orebro. The greater part of the electric devices various track sections (track circuits) are shown on in these plants are of Ericsson manufacture. this plan. A small electric lamp — one for each section — denotes The Skovde plant. whether a section is The Skovde sta­ clear or not, a tion serves its pur­ glowing lamp indi­ pose mainly as a cating a clear sec­ through station, as tion. By observ­ all the trains on the ing this track plan, main line Stockholm the train dispatcher —Gothenburg pass can follow the through it. The various train move­ trains from Karls- ments and switch­ borg, however, do ing operations out in not run further than the station yard. Skovde. The relays are The area covered mounted in a spe­ by this plant is cial cabinet with glass doors, under shown on the track R 776 Fig. 2. The Interlocking Machine at Skovde plan in fig. 1. Spe­ the track plan. cial mention should be made of the fact that the start­ Cabinets with signal indicators, whose lamps are on ing signals for the side tracks can be used for all the the same circuits as the regular signal lamps, are also sidings in the station yard, so that — when the traffic placed under the track plan. These signal indicators is heavy — a certain train (freight train) may leave show the positions of the signals. the station on a given signal no matter whether it is All the signals are electric day signals. Since the standing on a locked track or not. main line through Skovde is electrified, the light sig­ As already mentioned, the interlocking machine is nals have — as far as possible — been mounted on not manned except during the passage of a train. For the posts and gantries which support the wires for the shunting purposes, the points provided with central traction current (see figs. 4 & 5). Where this was control are set locally: consequently, there is no not feasible, concrete posts have been erected for necessity to manoeuver the interlocking machine on such this purpose. occasions. The signals are controlled by means of signal relays The plant is provided with an electric interlocking (D. C. relays) mounted in the signal cabin, these machine of standard type (see fig. 2), placed in the relays, in turn, being actuated by the aid of the signal 87 Fig.1 In addition to the normal, front lamp, all red signals are provided with an extra rear lamp, the current for this lamp passing through a resistance to reduce its levers in the interlocking machine. The signal relays voltage. If the front lamp should not burn, the rear are also influenced by one or more of the above- lamp will show a weak but still quite discernible red mentioned track circuits, so that a signal cannot be ight. set to "clear" as long as a track section forming a part The light signals receive their current (110 volts, of the track in question is occupied by any form of Fig. 9. 50 cycles) over a feed line from the interlocking rolling stock. machine. Transformers, mounted in cabinets in the The lights of the signals conform to the formation vicinity of the respective signals, reduce the tension of of the night signal of a semaphore, i. e. a red light thus giving the train a false signal. This is prevented this current to about 12 volts. A good luminosity means "stop", and one, two or three steady green by placing a balancing resistance or balancing impe- is obtained with this low voltage, since the glowing lights means a clear incoming main or side track dans in circuit before the lamp transformers. As soon substance, which is relatively small, can be concentrated respectively. as one lamp ceases to glow, these resistances prevent in the theoretical focus of the lens system. When a signal consists of two or three green lights, the current from reaching the other lamps and all the The advance signals used by the Swedish Gov't it is possible that one of the lights does not burn, green lights are extinguished. Railways have both green and white intermittent 88 — 89 — flash-lights. Green is set to stop. If indicates that the co­ this starting signal operating main sig­ should be set to nal is set to "stop"; clear, this is indicat­ the white one, that ed by means of a it is set to clear. white flash-light in­ Since certain trains stead of the green. pass through Skov­ Should the incoming de over the main or home signal be track without stop­ set to stop, or — by ping, it was found means of one or two desirable to provide green lights — in­ the main starting dicate that the in­ signals with ad­ R 777 Fig. 3. The Skovde Signal Cabin. coming train is vance signals, so as being directed to a to advise the loco­ side-track, the posi­ motive engineer as tion of the starting soon as possible of signal is not indi­ the position of the cated on the home starting signal. This signal. has been arranged The current for by using one of the the advance signal green lights of the of the starting sig­ home signal — the nal is obtained over third one — for a the signal relays of green flash-light, the starting signals and by placing a and home signals in white flash-light in question. the unoccupied All the local space between the point setting ar­ second and third rangements are con­ green lights (the R 778 Fig. 4. Home Signals at Skovde for Trains from Stockholm (Ulvaker"! and Karlsborg (Igelstorp). structed according right hand signal in to the principle fig. 4). These two adopted by the flash-lights serve as Swedish Gov't advance signals for Railways, compris­ the starting signals ing an electric of the main tracks switch located near so that at the same the point and which time as a steady energizes a relay green light at the mounted in the sig­ head of the signal nal cabin. When mast indicates a the relay energizes, clear incoming the control circuit track, a green flash­ for the correspond­ light at the foot of ing point lever in the mast indicates the interlocking ma­ that the correspond­ chine is broken, a ing starting signal circuit which fur­ in the direction of nishes current to the the incoming train R 779 Fig. 5. Starting Signals at Skovde for Trains to Stockholm (Ulvaker) and Karlsborg (Igelstorp). switch motor being - 90 - simultaneously closed. If the control magnet contacts do sulated track sections. The track relay for each section not break the circuit when the point is set locally, a is placed in a wooden cabinet beside its respective special relay is provided which then energizes and section. The positions of the track relays are repeated closes an alarm circuit, simultaneously cutting the by special d. c. relays mounted in the signal cabin, supply of control current for the entire interlocking which close circuits to the different lamps mounted machine and causing all the signals to be set to stop. behind the track plan. Further, the circuits providing Those points and skotch blocks which are not con­ current for the various signals are closed over these trolled by the interlocking machine but nevertheless relays in various contact combinations, and the relays must be included in the installation, are provided with a locking device (see fig. 6). Contacts actuated by the point itself close a current over a locking magnet on the locking lever, naturally on condition that the point is in a position permitting of its being locked. If this is not the case, the locking lever cannot be set. The crossing gates at both ends of the station yard are also power driven and controlled by means of levers in the interlocking machine. The signal relay R 780 Fig. 6. Locking device. R 781 Fig. 7. Crossing Gates at the North Grade Crossing, Skovde. current is influenced by the position of these gates. are used for various other purposes, such as track When a train for which the gates have been lowered releasing, point locking etcetera. enters a certain track section, the crossing gate lever The track circuits are fed by a 220-volt 50-cycle in the interlocking machine can be restored to normal, alternating current with the exception of the one but the gates will not be raised until the train has farthest to the South, which is fed by battery current.

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