Patent GB-612951-A (GB)
Title: Improvements in or relating to speed control systems for electric motors
IPC: B65H23/195
Filed: 1946-06-11
Abstract: 612,951. Automatic electric motor control systems. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. June 11, 1946, No. 17423. Convention date, June 16, 1945. [Class 38 (iv)] [Also in Group XXXVII] Current ; power.-In a variable speed drive, two rotary direct-current machines have their respective armatures mechanically coupled, each of said machines having separately excited field windings, supply means for said armatures, and controllable circuit means connected to said field windings so as to vary automatically the field excitation in said machines in opposite directions relative to each other, said circuit means including a regulating generator having an armature connected to said field windings and a field winding to control the voltage supplied by said regulating generator, whereby said machines both function as drive motors when said circuit means are in condition for low speed operation, while one machine functions as a booster and is driven by the other machine when said circuit means are in condition for high speed operation. As shown, a rolling mill or the like and a winder are driven by a motor MM, and mechanically-  coupled dynamo-electric machines M1 and M2, respectively. The armatures of the three machines are supplied in common from a generator MG which is driven, together with an exciter EG, by a constant-speed motor 11. The machine M1 is provided with differentiallywound field windings 19 and 20, the machine M2 having cumulative field windings 21 and 22. The machine M2 always acts as a motor, whilst the machine M1 functions either as a motor or as a booster for the machine M2. The windings 20 and 22 are supplied in common from the exciter EG through a calibrating resistance. The windings 19 and 21 are energized from a regulating generator RG which is driven by the motor 11 and is provided with a pattern field winding 25 and a field winding 27 which is connected across a resistor 18 and is thereby energized in accordance with the armature current of the machines M1 and M2. The regulating generator has also a series field winding 28, which is provided with a rheostat 29 which may be adjusted so that the resistanceline of the field winding is approximately coincident with the no-load saturation characteristic of the regulating generator. A rectifier 30 is connected in series with the field windings 19 and 21 to ensure correct excitation thereof. At starting, the field windings 25 and 27 are balanced, the field windings 19 and 21 being thereby unexcited. The machine M2 functions as a motor and drives the machine M1 which acts as a booster generator. As the reel builds up, the armature current of the machines M1 and M2 increases and the generator RG excites the windings 19 and 21 to reduce the boosting voltage of the machine M1 and to strengthen the field excitation of the motor M2. The increase of armature current is thereby counteracted, the total power output of the two machines being kept substantially constant over the whole speed-range. The resultant field excitation of the machine M1 will be reversed and, over the latter part of the range, both machines will operate as motors.