Patent GB-190602367-A (GB)
Title: Improvements in or relating to Single Phase Alternate Current Motors and Generators.
Inventor: FYNN VALERE ALFRED
Filed: 1906-01-30
Granted: 1907-01-30
Abstract: 2367. Fynn, V. A. Jan. 30. Motors, controlling; field magnets. -Relates to means for operating single - phase motors having a shunt characteristic at any desired speed independently of the periodicity of the supply and the number of poles of the motor. In the simple form of motor shown in Fig. 1, the field due to the stator or transformer winding S generates by static induction an electromotive force which may be designated ET across the brushes C, corresponding to the electromotive force impressed upon the armature of a direct-current motor, and, by the rotation of the armature, an electromotive force across the brushes D giving rise to the motor field and differing in phase by ninety degrees from that of the mains. By rotation of the armature conductors in the motor field, a second electromotive force EB is produced between the brushes C corresponding to the back electromotive force of a directcurrent motor. According to this invention, the speed of a shunt motor, in which the self-induction of the rotor in the armature axis C-C is practically neutralized, is varied by varying electro-magnetically the relations between the working electromotive force ET and the back electromotive force EB, or any of the factors that influence their magnitudes. The motor shown in Fig. 1 combines the features of a transformer for conveying the outside current into the rotor along the armature axis C-C and of a phase converter for producing an electromotive force having a ninety-degree phase difference from that of the mains in the motor field axis D-D. The motor field may be partly or wholly excited by a phase converter independent of the motor, in which case the transformer winding may be dispensed with, and either the rotor winding itself or a winding on the stator may be used as the field winding. Four classes of motors are described : (1) motors in which the phase converter is separated from the motor proper and the transformer winding S dispensed with, the armature current being conveyed into the rotor by conduction, Fig. 2 ; (2) motors having transformer windings and separate phase converters, Fig. 6 ; (3) motors with transformer windings in which the motor field is generated wholly in the motor itself, or partly in the motor and partly by a separate phase converter, Figs. 5, 7, 9, and 10 ; and (4) motors of Class 3 but without transformer windings, the armature current being conveyed into the rotor by conduction, Figs. 11<a> and 13. In a motor of Class 1, Fig. 2, the field winding F is excited by a phase converter MP, of the induction-motor or other type, and the self induction of the rotor in the armature axis C-C is neutralized by means of a winding K, which may be short-circuited on itself, the speed being varied by varying the electromotive force impressed upon the brushes C, by varying the electromotive force E<2>, or by a combination of these methods. The speed of motors of Class 2 with transformer winding S, Fig. 6, may be varied by varying the transformer field, by varying the electromotive force E<2>, by including between the brushes C an electromotive force cophasal with that of the supply, e.g. derived from the mains through a transformer, or by combinations of these methods. Both the induction and conduction motors may be compounded by providing them with auxiliary stator windings S', Fig. 6, situated in the motor field axis. One converter could be used to supply a group of motors, or one of the latter could be used for the purpose. In a motor of Class 3, Fig. 5, the motor field is generated wholly in the motor itself by arranging a sectional winding F provided with a contact-arm LF in the motor field axis between the brushes D. The rotor winding in the axis D-D and the winding F both act as field windings, which may be made to coincide or to oppose each other. In the arrangement shown in Fig. 7, the electromotive force responsible for the motor field is generated partly in the motor and partly by a separate phase-converter feeding the variable transformer T, or the voltage supplied by the converter may be varied. In Fig. 9, an auxiliary electromotive force E<3>, derived, e.g., from the mains through a shunt transformer T, may be supplied to the brushes C to vary the electromotive force ET independently of the transformer field. To avoid self-induction in the armature axis, a non- inductive resistance or a capacity W may be permanently connected across the brushes C. The transformer may be embodied in the motor itself by connecting the brushes C through an auxiliary winding on the stator co-axial with the winding S. Another method, Fig. 10, consists in making use of a greater or smaller part of the motor field for producing the back electromotive force. Two stators A, B are placed side by side embracing a double rotor R', R<2>. The stator A carries the winding S, the stator B being unwound. The rotors carry two windings, one, the field winding, embracing both rotors and short-circuited by brushes D at rightangles to the axis of the winding S, while the other, the armature winding, embraces one rotor only and is short-circuited by brushes C co-axial with the winding S. The armature conductors cut only part of the motor field, and, by varying the reluctance of the stator B, the field threading the armature and therefore the back electromotive force may be varied. Another method consists in making the inductive relation between that winding in which the electromotive forces EB and ET are generated and the transformer field different from the inductive relation between the winding responsible for the motor field and the motor field, e.g. by the employment of two windings having separate commutators on the rotor R, Fig. 1, and the adoption of different brush arrangements in the armature and field axes, or one winding may be well distributed and the other concentrated in a few slots, or the two windings may have different numbers of turns. The speed of motors of Class 3 may also be varied by varying the transformer field, keeping constant the electromotive force ET by including between the brushes C an electromotive force cophasal with that of the mains, or keeping the motor field constant by introducing electromotive force between the brushes D, or by combinations of the methods described. In an application of the invention to motors of Class 4, Fig. 11<a>, the impressed electromotive force is varied by means of a transformer switch LA, the armature self-induction is neutralized by means of the winding K, and the stator winding S, which may form part of the winding K, gives rise to the motor field across the brushes D. In the arrangement shown in Fig. 13, one transformer T is used for both armature and field cir. cuits, the brushes are short-circuited in pairs, and an auxiliary stator winding ST is provided for starting the motor as a series induction machine, the connexions of Fig. 11<a> being afterwards established. Two separate rotor windings may be used in any of the above cases. The speed of motors of Class 4 may also be varied by supplying the brushes D with an auxiliary electromotive force derived from a phase converter, by disposing the field winding partly on the rotor and partly on the stator and varying the resultant field, or by combinations of these methods. The power-factor of all the forms of motor may be improved by including in their field or armature circuits electromotive forces of suitable phase preferably through transformers, as described in Specifications No. 22,712, A.D. 1902, and Nos. 26,897 and 27,260, A.D. 1905. For example, in the case of the motor shown in Fig. 7, two electromotive forces may be impressed upon the brushes D, Fig. 1, through variable transformers having their secondaries connected in series, the first in quadrature with that of the mains helping to build up the motor field, while the second cophasal with that of the mains improves the power-factor. In compensating the motor shown in Fig. 9, a non-inductive resistance or a capacity is preferably connected across the brushes. All these motors may act as generators, and for traction purposes as brakes to return energy to the mains. To avoid sparking, the motor and transformer fields should be so varied that the electromotive force induced in a coil undergoing commutation by the transformer action of the motor field should be equal and opposed to that generated by its rotation in the transformer field.