Patent GB-832510-A (GB)
Title: Improvements in or relating to railway track-circuit signalling systems
IPC: B61L23/10
Filed: 1956-04-17
Abstract: 832,510. Railway track circuits signalling systems. SIEMENS & GENERAL ELECTRIC RAILWAY SIGNAL CO. Ltd., and CANDLER, J. E. April 17, 1967 [April 17, 1956], No. 11704/56. Class 105. [Also in Group XXXV] In a railway track circuit signalling system of the kind in which traction power return currents flow through impedance bonded rails a track circuit comprises at the feed end an impedance bond having a centre-tapped current coil connected between the running rails and an auxiliary coil connected in series with capacity for supplying A.C. current signals across said rails and at the detector end, an impedance bond having a centre-tapped current coil connected between the running rails and an auxiliary coil connected in series with capacity in a signal responsive circuit that is connected across the running rails, the weights of the current coil and of the ferromagnetic core of the feed end impedance bond are both less than the corresponding weights of the detector end impedance bond, e.g. 15 or 25% and 50% less respectively, whether of the same or different materials. The D.C. resistance of the feed end impedance is not greater than the D.C. resistance of the detector end bond. In an embodiment of the invention the impedance  bond comprises a core 24 of non-ageing silicon iron alloy such as " Stalloy " (Registered Trade Mark) made up of E-shaped laminations stacked side by side the' cross-sectional area of the central limb at the feed end and receiver end bonds respectively being 9 and 25 square inches with a core weight of 45 lbs. and 135 1bs. respectively and a plurality of rectangular laminations, also stacked side by side to form a yoke 25 across the free ends of the limbs 26, 27, 28 of the E-laminations, the laminations being held together by bolts 29. The current coil 31 has a small number, viz. 8 turns for both bonds formed by two strips of copper 32, 33 of cross-sectional area 0.4 square inches spaced by vulcanized fibre 34, 35. Centre-tapping of the coil 31 is effected by a copper connecting strip 36 connected to the outer end of strip 32 and by a short copper strip 37 passing beneath the coil to the inner end of strip 33. The other connections to the coil 31 are effected by a copper strip 38 connected to the inner end of strip 32 and by a copper strip 39 connected to the outer end of strip 33. The total weights of the current coil 31 and connecting strips 36, 38, 39 are 21 lbs. and 33 lbs. respectively for the feed end and detector end bonds. The strips 36, 38, 39 are continued through an oiltight gland (not shown) in the oil filled casing of the impedance bond. The coil 31 occupies the lower part of the " window " 40 between the limbs, substantially filling the available space and insulated from the core by fibrous material 41. The auxiliary coil 42 is wound on the centre limb between the coil 31 and the yoke 25 filling the remaining part of the " window." For both the feed end and detector end bonds these coils have 328 turns. The gap between the core 24 and yoke 25 is filled with fibrous material 41. In a modified construction the current coil is wound in two identical halves on the centre limb one above the other and consists of turns of copper strip insulated from one another by e.g. vulcanized fibre. The inner ends of the coils are connected together to form the centre tap, the coils being wound outwards in opposite senses. To reduce further the weight of the core and yoke of the bond at the feed end, an anisotropic steel strip having its highest permeability in a direction parallel to the longitudinal axis of the strip, may be employed for the core and yoke construction by winding the strip into a rectangular coil which is then cut into two unequal parts by a plane that is parallel to two opposite sides of the coil and into the other opposite sides at right angles, resulting in two 0-shaped cores, one having long limbs to be used as the core and the other short limbs to be used as the yoke, the E-shaped core and yoke being formed by placing two such coils together with two corresponding sides adjacent.