Patent GB-190705506-A (GB)
Title: Improvements in or relating to Alternating Current Dynamo-electric Machines of the Commutator Type
Inventor: LAMME BENJAMIN GARVER
Filed: 1907-03-07
Granted: 1908-02-20
Abstract: 5506. Lamme, B. G. March 15, 1906, [date applied for under Patents Act, 1901]. Dynamos, alternating-current ; motors, alternating- current; motors, controlling.-Alternating-current series commutator motors for propelling railway and other vehicles are prevented from acting as generators of direct current, when the connexions of the armature and field-magnet windings 1, 6, Figs. 3 and 4, are reversed with reference to each other, by shunting the field-magnet winding 6 by an impedance device 12 having a high inductive resistance and a low ohmic resistance compared with the field-magnet winding. The impedance device then acts as a by-pass for direct current. The motor is connected to line through an autotransformer 2 and regulating-switch 3. A smaller device 12 may be used by shunting it across both the field-magnet winding and a resistance connected in series therewith. To enable a motor to operate as an alternating-current generator, for example in braking, the field strength is maintained substantially constant by constructing the impedance device so that its core is just magnetically saturated, i.e. at the bend of its magnetization curve, when the field of the motor is at normal strength. To vary the field strength, the magnetization of the core 12 may be varied, for example by altering the number of turns, Fig. 3, or by arranging a movable section 21 in the air-gap, Fig. 4. By arranging a solenoid 22 in the armature circuit, the field strength may be varied in accordance with variations in the armature current. The Specification in the original form as published under the Act of 1901 comprises also the following subject-matter. (1) A series motor is prevented from acting as a generator of direct current by supplying its field - magnet winding from the secondary of a transformer, the primary of which is arranged in the armature circuit, or by connecting an impedance device across the armatute brushes. (2) Alternating-current series commutator motors are operated as braking generators to return energy to line by separately exciting their field - magnet windings during the braking period from a phase - changing device, so that the armature electromotive force of the motors may coincide in phase with the line electromotive force. This method of braking is applicable to motors of the Winter-Eichberg type. (3) A series motor may also be operated as a braking generator by separately exciting its field-magnet winding from the circuit supplying the armature and by connecting a high ohmic resistance in the field circuit. In braking a Winter-Eichberg motor, the stator and rotor windings are excited separately from the same circuit, and a resistance is inserted in the rotor circuit. (4) A direct-current series motor may be converted into a braking generator by separately exciting its field - magnet winding from the supply circuit, either directly or through a motor-generator ; or its field-magnet and armature windings may be permanently connected in series and the motor-generator connected in shunt to the field-magnet winding. This subject-matter does not appear in the Complete Specification as accepted.