Patent GB-393347-A (GB)
Title: Improvements in and relating to methods of controlling the speed of electric motors
IPC: H02P5/74
Filed: 1932-01-06
Abstract: 393,347. Rotary converters etc.; transformers ; alternating- current commutator motors. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Hull, J. I.; 70, Bay View Drive, Swampscott, Massachusetts, U.S.A.) Jan. 6, 1932, No. 424. Convention date, Jan. 7, 1931. [Class 35.] Motors 10 driving the various sections of a printing-press are supplied from a machine 16 with a variable frequency voltage having two components, one constant, and one proportional to the frequency. The machine 16, driven by a synchronous motor 33, has two rotor windings, which may be separate or combined, one of which is supplied from a source 21, and the other connected to a commutator 22. It has in addition stator windings 24, 25, the latter being connected in series between the brushes on the commutator 22, and the motors 10. Upon closure of switches 28, 19, 30, and closure of a two-way switch 37 to the right, the motors 10 are supplied with constant voltage of zero frequency from the commutator 22, and are locked at standstill in their proper phase relation. If the switch 37 is then thrown to the left, resistances 35, 38 may be adjusted so that the machine 16 drives the synchronous motor 33 which acts as a.generator supplying current to the resistance 38. The speed of the machine 16 falls below synchronism and the motors 10 are supplied by a voltage of slip frequency having two components, one which is constant from the commutator 22 and the other proportional to the slip frequency from the winding 25. By adjusting the resistances 35, 38, the slip frequency, and therefore the speed of the motors 10, may be varied. If it is desired to bring the machine 16 to synchronism under its own power, switches 19, 28, 32<1> are closed, and a two-way switch 26 is closed to such a position that the phase sequence in the additional stator winding 24 of the machine 16 is opposite to the phase sequence in the winding 25. As one of the stator windings tends to produce a negative slip to the same extent as the other is tending to produce a positive slip the machine 16 runs at synchronism. Before the resistances 35, 38 are adjusted to vary the speeds of the motors 10, the switches 26, 32<1> are opened. The winding 24 is arranged to give a voltage at a predetermined low speed which is equal to the voltage at the commutator 22, so that if the switch 26 be closed so that the phase sequence in the windings 24,'25 is the same the speed of the machine 16, and therefore that of the motors 10, is maintained constant by generator and motor action between the windings 24 and the commutated winding on the machine 16. If the resistances 35, 38 are set too far from the desired constant low speed position, the switch 37 is opened. If it is desired to bring the motors 10 to rest from full speed the switch 37 is thrown from left to right, and the motors 10 are regeneratively braked through the winding 25 and machine 16. To bring the motors to rest more quickly, a switch 32 is closed and resistance 31 adjusted, the motors being regeneratively braked through the resistance 31 and the machine 16, assisted by a circulating current produced by the winding 25, giving a motor torque to help the synchronous motor 33 back to synchronism. If the motor 33 has a smaller number of poles than the machine 16, the latter machine may operate above and below synchronism so that the motors 10 may operate in both directions. In Fig. 2. an induction motor 40 is used in place of the synchronous motor 33. Upon the closure of a switch 45 to the right to make connection with a direct-current supply 13, and closure of a reversing switch 43 in such a direction that the motor 40 runs in the same direction as the machine 16 started under its own power, the machine 16 may be brought to synchronism and the motors 10 locked at standstill as before. If the switch 45 is moved to the left resistance 46 adjusted to a high value, and the switch 43 thrown over, the speed of the machine 16 is reduced and the motors 10 started. By decreasing the resistance 46 and finally throwing the switch 45 over, the motors 10 may be brought to a speed corresponding to double the frequency of the supply 21. In Fig. 3, not shown, the synchronous motor 33 is replaced by an alternating-current brush shifting motor, by shifting the brushes and moving the reversing switch of which the speed of the motors 10 may be controlled in both directions.