Patent GB-766785-A (GB)
Title: Control circuit for electric motors
IPC: B61L5/06
Filed: 1951-07-27
Abstract: 766,785. Operating railway points. STANDARD TELEPHONES & CABLES, Ltd. July 27, 1951 [Aug. 3, 1950], No. 17855/51. Class 104 (1). [Also in Group XXXVII] In an electric circuit controlling an electric motor capable of movement in either of two directions between stops the circuit includes relay means, determining in which one of the two directions the motor shall move, including inter alia two mechanically interlocked latching relays one of which must be operated before the other can be released, the condition of the latching relays corresponding to the direction in which the motors shall move, and means under the control of the relay means indicating at which of the stops the motor is resting and providing the required indication only after the motor has completed its movement in one of the two directions and all the relays are in a condition both mechanically and electrically (having been actuated through operation and release) to be operated to move the motor in the other of the two directions. A positive potential applied to a conductor 5 moves rail points from the normal to the reverse position and when applied to a conductor 6 moves the points in the reverse direction. With the points in the normal position and without a potential applied to conductors 5, 6, a control relay C/2 is energized from + through a fuse F 1, a winding 1 of a differential relay p/2, contact d3, conductor 1, points contact r1, motor contact m1, conductor 2, contacts g3, d2, f3, and e3, winding of relay C/2, contact p1, winding 2 of relay P/2, and fuse F2 to earth. Since windings 1 and 2 of relay P/2 are in opposition the relay P/2 is not energized. A lamp L1 is lit to indicate that the rail points are in their normal position by the control relay C/2 being thus energized to close a contact c2. If an earth fault develops the relay P/2 will operate and this operation can actuate an alarm. When a positive potential is applied to conductor 5 to initiate movement of the points to reverse setting, a current flows through winding 3 of the differential relay P/2 through the contact g1, thereby to cut out the relay C/2 at p1 and so to extinguish lamp L1 by the opening of contact c2. Release of relay C/2 causes a slow release relay D/5 to be energized through winding 2 from the conductor 5 and contacts gl, p2, c1. An operating circuit is now closed through contact d4 to a relay E/3 and a latching relay G/3 is energized over a contact e1. Relays G/3 and H/0 are interlocked and when relay G/3 is energized to move contact g1 current ceases to flow through winding 3 of relay P/2, thereby to release relay P/2 and also the current through winding 2 of relay D/5 is interrupted but since this relay is slow to release it will hold until current flows from + potential through winding 1 to earth after passing through the motor M, winding Wl, contact m2 and contact e2. The motor M will now rotate to open contacts r1, m1 and close contact nl and when it has travelled its full course it will open contact m2 to interrupt the current through winding 1 of relay D/5 which will release, and close contact n2, r2 and release relay E/3, the relay G/3 remaining in its latched position. Contacts d2, d3 are again closed to establish a circuit through windings 1 and 2 of relay P/2 via contacts r2, n2, g3, d2, f3, e3 and relay C/2 contact c2 of which now lights lamp L2 over contact g2 in its latched setting. When the points are in reverse position the circuit contacts m2, d1 are open and motor M cannot be operated by stray currents and an earth fault on conductor 1 will cause an unbalance in the current flowing in windings 1 and 2 of relay P/2 to actuate relay P/2 and hence release relay C/2 to extinguish lamp L1. When a positive potential is applied to conductor 6, to return the points to their normal position, with the relay G/3 in the latched operated position the relay P/2 is energized through contact g1 and winding 3 to effect through the actuation of relays D and F rotation of motor M in the reverse direction through winding W2. If the motor stops before completing its travel from normal to reverse positions or vice versa neither of the lamps L1, L2 is lit. The positive potential is in such event transferred from the operative conductor 5 or 6 to the other conductor 6 or 5 to return the motor to its initial position and the operation is recommenced. The circuit may be applied to the control of two sets of points operated in tandem.