Patent GB-453241-A (GB)
Title: Improvements in braking arrangements for compound wound electric traction motors
IPC: B60L7/12
Filed: 1935-06-24
Abstract: 453,241. Master control of D.C.motors. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and CROFT, E. H., c/o General Electric Co., Ltd., Witton, Birmingham. June 24, 1935, No. 18062. [Class 38 (iii)] Regenerative and non-regenerative braking.- A braking arrangement for a compound wound traction motor, the armature and series field winding of which are adapted to be connected in a braking circuit for the purpose of braking the vehicle in the event of running back thereof, comprises a master controller arranged to control a normally closed contactor for completing the braking circuit and a relay adapted to be influenced by the armature voltage and to prevent closure of the contactor while the voltage is above a predetermined value. In the arrangement shown, as applied to a trolley bus, the circuit for the armature 13 and series field 12 between the trolleys 1, 2 includes circuit breakers 3, 4, overload relay coils 5<1>, 6<1>, the current coil 7 of a reverse current relay, line switches 8, 9, series resistance 10 and contacts of a hand operated reverser 11. Control is effected by a pedal-operated master controller 50 which in successive positions closes contacts 24 ... 28 to short-circuit sections of the resistance 10 and then opens contactors 17 ... 22 to insert sections of a resistance 16 in series with the shunt field winding 14. Should the contacts 5 or 6 of an overload relay operate, the coils 81, 9<1> of the line switches 8, 9 are de-energized and the line switches open. Before operation can be resumed, the controller must be returned to the off position and a reset button 55 operated to energize the re-set coils 5<2>, 6<2> of the overload relays. Backward movement of the controller energizes a contactor 23 through a segment 44 and strengthens the shunt field. Further backward movement closes the contactors 17 ... 22 and regenerative braking is initiated. Excess voltage during regeneration operates a relay 56<1> to energize the closing coil 57<1> of a contactor 57 which inserts a resistance 58 across the armature 13 and series field 12. Rheostatic braking during forward running is automatically initiated under the control of the reverse current relay, which in addition to the current coil 7 includes a voltage coil 67 and contacts 62 and 66, of which the former are closed and the latter are open, except when regenerative current is flowing. Contacts 66, when closed, maintain closed the energizing circuit of the contactor 28, so that during regeneration the series resistance 10 is short-circuited, irrespective of the position of the master controller. When the contacts 62 close, the coil 63 of a brake relay 52 is energized, and in responding the relay de-energizes the operating windings 8<1>, 9<1> of the line switches 8, 9 and energizes the winding 65<1> of a contactor 65 which connects the sections 59, 60 of the resistance 58 in series with the armature and series field. The circuit of the coil 65<1> includes auxiliary contacts 53 of the runback contactor 68, so that the brake contactor 65 cannot be closed if the run-back contactor is closed. The coil 68<1> of the runback contactor is energized from the segment 29 through the wire 68<2> as long as the controller is in an operative position. It is also connected to the trolley 1 independently of the controller through the normally open contacts 69 of a run-back relay having an operating coil 69<1>. This relay is such that the contacts 69 are closed unless the voltage across the armature and series field is sufficiently low to avoid undesirably strong braking current on closure of the run-back contactor 68. When the latter closes it places a section 60 of the resistance 58 in series with the armature and series field. Failure of the power supply also de-energizes the winding 68<1> and allows the contactor 68 to close. Rheostatic braking when the vehicle is running in the forward direction may be obtained, during coasting, by moving the reverser 11 to a coasting braking position 79 in which the segments effect reversal of the armature relatively to the series field and connect the armature and field in series with the resistance sections 59, 60. In a modified arrangement, the coil 68<1> of the run-back contactor is connected in parallel with the circuit of the shuntfield 14, in series with normally open contacts of the line switch 9, which contacts are bridged by the contacts of the run-back relay. The coils 81, 9<1> of the line switches are connected in parallel, and only the coil 8<1> is in series with auxiliary contacts of the run-back contactor corresponding to the contacts 53. With this arrangement, the run-back contactor automatically becomes effective, not only if the controller is returned to the off position, if the power supply fails or if a trolley leaves the overhead conductor, but also if either of the circuit-breakers 3 or 4 opens, e.g. on account of overload whilst climbing a hill.