Patent GB-276109-A (GB)
Title: Improvements in and relating to railway signal-operating machines
IPC: B61L5/18
Filed: 1926-06-11
Abstract: 276,109. British Power Railway Signal Co., Ltd., Glenn, S. L., And Pierce, E. E. June 11, 1926. Alternating-current motors; armatures and field magnets; casings; driving-arrangements; electromagnets.-A railway signal is operated by an electric motor of the singlephase induction type having a stator with two windings, one of which has a high reactance and the other has a high resistance; a variable reactance is connected in series with the reactance winding of the motor. The signal spectacle is moved from its " normal " position to " reverse " by the motor, is held there by an electromagnetic retaining device and is eventually returned to its " normal " position by gravity. The coils 3 of the reactive winding of the stator have a large number of turns of large section, and the overhang is situated so that it is cut by the maximum flux, while the coils 2 of the resistance winding have few turns of small section. The stator core is built up of laminations insulated on one side and the plates 11 are of heavier section than the other laminations. The core is held in an annular casing 12 and is secured in position by an end ring 13. The rotor is built up of insulated laminations 17 mounted on an aluminium spider 18 secured by means of a skewed key and by four small clamp plates 19, which are equally spaced around the periphery of the spider. The slots are of the semi-closed type and the winding is held in place by impregnated wooden wedges. The coils consist of enamel covered and each coil is short-circuited upon itself and is independent of the other windings. A modified form of core may be used where it is desired to employ a rotor of the squirrel-cage type. The rotor is keyed to the spindle 20 and locked by a clamping nut 21. The pinion 23 on the spindle for driving the spectacle gear is of the usual friction type and has a spring 24 which can be set to slip at any desired loading. The spindle also carries a toothed disc 25 used in connection with the retaining device. The motor casing is provided with a detachable cover 31 held in placed by a clamp screw 32 operated by a handle 33, and this renders the parts easily accessible. The reactance 5, permanentlv connected in series with the reactance winding 3 of the motor, is variable through tappings of the winding or other means. The magnet for retaining the spectacle in position has fixed and movable cores 64, 58, Fig. 8, and coils 69 wound on tubes 70 held by the supporting bracket 62. The moving core 58 has shading ring polepieces and carries a bolt 59 connected) by a spring 61 to a crosshead 57 secured to one end of the connecting rod 49, Fig. 2. The other end of the rod is attached to a double link 40 which carries a pivoted dog 39 to engage the teeth of the wheel 25 on the rotor shaft. The dog is held against a pin 45 by a spring 44 and its action on the wheel 25 may be reversed by moving the pin 45 to a hole on the opposite side of the dog and moving the spring 44. A spring 74 is connected between the centre of the rod 49 and the framework. The spectacle is operated from " normal " by the motor, and before it reaches the "reverss" position the supply to the motor is cut off by a circuit-breaker, and the coils 69 of the electromagnet are excited. The momentum of the rotor is sufficient to complete the signal movement and the dog 39 engages the wheel 25 owing to the parts 58. 49. 40 being raised by the electromagnet. This retains the signal in its operated position. When the electromagnet is de-energized the spectacle returns to " normal " under the action of gravity.