Patent GB-671591-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: B21B37/54
Filed: 1950-03-27
Abstract: 671,591. Control of two D.C. motors. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. March 27, 1950. [April 26, 1949] No. 7590/50. Class 38 (iii). [Also in Group XXXV] In a rolling mill a dynamo-electric machine 12 drives the reel 13 and acts either as a reel motor or a drag generator in winding or unwinding a strip of material 15 which is being worked upon by the rollers 16. The rollers are driven by a motor 20 provided with a field winding 20b energized from a suitable source via resistor 24a and conductors 22, 23, the motor being supplied with electrical energy from a generator 25, provided with a series field 25b, and a main field 25c connected between the conductors 22, 23, through "forward" and "reverse" switches 29 and 30 and rheostat 24b. A field winding 12b for the motor 12 is energized from the conductors 22, 23, through a rheostat 32 provided with an operating motor 33 whose field winding is connected to the conductors 22, 23, the motor 33 being controlled by a generator 35 having a shunt field winding 35b, series winding 35c, an IR drop compensating winding 35d, a voltage field winding 35e, and a pattern field winding 35f. The winding 35f is energized from a pilot generator 38 coupled to the motor 20 and the windings 35e and 35d are connected across the armature of motor 12, and across a resistor 40 in the armature circuit of motor 12 respectively, so that when the speed of the motor 12 falls due to the strip being wound on the reel 13 and the back e.m.f. of the motor 12 falls accordingly, the winding 35f of the generator 35 predominates and causes the rheostat 32 to operate in a direction to increase the excitation of the field winding 12b to restore the back e.m.f. to its original value. When the mill is reversed by operating press-button switch 30 the rheostat motor 33 operates in response to the continuously increasing speed of the reel 13 as the strip unwinds to progressively weaken the field of the dynamo-electric machine 12 which now operates as a drag generator. A generator 42 having a separately excited field winding 42b, and a regulating field winding 42c supplies energy to the machine 12. Operation of the master rheostat 24, controlling the mill speed, is effected by a motor 44, through the "raise" push-button 46 or "lower" push-button 47. To energize the field winding 42c, a generator 50 is provided, having an anti-hunt field winding 50b, series winding 50c, current responsive field winding 50d, connected across resistor 40 in the armature circuit of machine 12, a pattern field winding 50e, which is energized from conductors 22, 23, through a potentiometer 52 . adjustable to maintain different values of armature current in the motor 12, and is connected differentially with respect to winding 50d, and an inertia compensating winding 50f, which is differential or cumulative with respect to 50e according to the position of switches 46, 47, to maintain the tension more constant during changes in the speed of the mill. The generator 50 regulates the energization of the field winding 42c to maintain a substantially constant armature current during normal operation. To start the mill the switches 29 and 27 are closed and operation of the dynamo-electric machine as a reel motor is initiated by operating the pushbutton 68 and switch 69. This operates the start relay 65 to energize the field winding 42c from conductors 22, 23, and interrupts the circuit of a time delay relay 63 which interrupts the energizing circuit of a transfer control relay 60 for a predetermined time after the machine 12 is initially energized to prevent operation of the relay 60 in response to the starting surge of armature current. When the strip 15 is wrapped on the reel 13 the armature current increases and after the time delay the relay 60 operates to energize the transfer relay 56 which disconnects the field winding 42c from the conductors 22, 23, and connects it to the regulating generator 50. When a push-button 46 or 47 is operated to raise or lower the speed of the mill, a time delay 70 is operated which energizes an auxiliary control relay 72 for a predetermined time, and this completes holding circuits for the windings of relay 56 to prevent it from operating if the armature current of the motor 12 should be momentarily reduced.