Patent GB-571057-A (GB)
Title: Electric motor control systems
IPC: H02P5/46
Filed: 1943-08-31
Abstract: 571,057. Control of several motors. ENGLISH ELECTRIC CO., Ltd., and CARNEGIE, H. S. Aug 31, 1943, No. 14189. [Class 38 (iii)] Varying electromotive force. In boiler house or other plant including two or more separately electrically driven devices, such as forced and induced draught fans and a mechanical stoker, of which the speeds are required to be varied both simultaneously and relatively to each other, at least one device is driven by an induction motor the speed of which is varied both simultaneously with and independently of the motors driving the other devices by variation of its applied E.M.F. As shown in Fig. 1, auxiliary plant for one boiler comprises induction motors 1, 2 driving induced and forced draught fans, respectively, and a D.C. motor 3 driving means for feeding fuel to the boiler, this motor being supplied by a Ward-Leonard generator 9 driven by an A.C. motor 10 connected to constant voltage A.C. mains 17. Motors 1, 2 are supplied from busbars 6 through induction regulators, tapped transformers, or D.C. controlled saturable reactors or transformers 4, 5 which permit individual control of the motors, whilst individual control of motor 3 is provided by field regulators 11, 12. Group control of the three motors is effected by means which varies the voltage of the busbars 6 and which is linked with the slider of a potentiometer 13 connected across D.C. mains 14 and through which the generator field is supplied. The voltage varying means 7 is supplied from A.C. busbars 8 common to a number of boilers-as also are the D.C. mains 14 which are tapped across a potentiometer 16 connected to a constant voltage D.C. source. A voltage varying means 15 connected between busbars 17, 8, and linked to the slider of potentiometer 16 permits combined control of a number of boilers. In a modified arrangement a variable speed commutator motor may replace the Ward- Leonard set 3, 9 10; alternatively the generator 9 may be omitted and the armature of motor 3 fed through rectifiers from the variable voltage busbars 6, or, if the generator is retained, its field may be supplied by these rectifiers. Fig. 2 shows an arrangement in which unit control of induction motors driving fans 1, 2 is provided by saturable reactors 4, 5 fed with D. C. through regulators 17, 18 from busbars 19, which also feed the field of the generator 9 through regulator 11, the voltage across these bus bars being variable to permit group control of the motors 1, 2 and the motor 3 driven by generator 9, control being effected by a potentiometer 20 connecting busbars 19 to busbars 21 which are energized by a generator 22 having its excitation derived from a potentiometer 25 across constant voltage busbars 23 supplied by a generator 27. Busbars 21 feed the plant for a number of boilers which may be controlled simultaneously by adjustment of potentiometer 25. The regulators 11, 17, 18 may be fed from the constant voltage busbars 23 and actuated automatically by electromagnetically adjustable governors driven by the associated motors to maintain a predetermined speed, the adjusting devices having individual manual control as well as common control from the busbars 19. Alternatively, the automatic regulating devices may actuate voltage varying devices, such as 4 and 5, which are connected across a constant voltage source, instead of the regulators 17, 18. Some devices may be driven by constant speed A.C. motors through electromagnetic slip couplings as described in Specification 568,730, [Group XXXV].