Patent GB-190705652-A (GB)
Title: Improvements in or relating to Alternate Current Motors also capable of use as Generators.
Inventor: FYNN VALERE ALFRED
Filed: 1907-03-08
Granted: 1908-03-07
Abstract: 5652. Fynn, V. A. March 8. Armatures commutators ; field magnets ; motors, controlling ; sparking, preventing.-To improve the power-factor, commutation, and torque of a neutralized singlephase series conduction motor or generator having its normal motor field produced by a winding at least partly disposed on the rotor, an auxiliary field is produced in the motor in a direction not coinciding with that of the motor field by means of an auxiliary winding disposed on the stator, on the rotor, or on both. In one arrangement, Fig. 3, the rotor winding produces the motor field by the use of auxiliary commutator brushes f, f<1> excited by a series transformer T, the armature field is neutralized by means of a winding N, and the auxiliary field is produced by a winding C connected across the mains through a transformer T<1>. The two sets of brushes need not be exactly displaced by ninety degrees. The transformer T may be dispensed with by providing two independent windings on the rotor and connecting the brushes a<1> f<1>. The phase of the auxiliary field may be changed as the speed increases, for example by impressing electromotive forces of different phase upon the winding C, and by changing their relative magnitudes, or directions, or both. Such electromotive forces may be obtained in the motor itself, either directly or through transformers, for example at the terminals of the armature A, or the windings A, N, at the brushes f, f<1> at the primary or secondary terminals of the transformer T, and the pressure of the mains, or an external source such as a polyphase supply, phase-converter, or phase-splitter may be used. In addition, special commutating poles or teeth excited by means of shunt or series transformers &c. may be placed in the commutating zones. In a modification, the auxiliary winding C is connected directly across the terminals of the armature A. In the form shown in Fig. 5, part of the neutralizing-winding N is utilized as the auxiliary winding and is excited from the mains through the transformer T<1>, while the rotor carries two windings acting respectively as armature and field windings. The rotor winding may be made to serve both as armature and field winding, either by displacing the brushes a, a<1> from the neutral position, Fig. 6, or by using the rotor winding shown in Fig. 6<b>, in which each coil consists of two or more turns 1, 2, 3, 4 and 5, 6, 7, 8 disposed in planes preferably displaced with respect to each other by ninety degrees in a two-pole machine. To vary the motor field, a stator winding having a variable number of turns may be arranged in the motor field axis so as to assist or oppose the field due to the rotor winding. To reverse the motor, two sets of brushes positioned on either side of the axis of the winding N may be used, one being used for rotation in one direction and the other set in the other direction ; or two sets of windings may be disposed on either side of the brush axis a, a<1>, and similarly used. In the latter case, if the angle a equals forty-five degrees, and the two sets of windings are at ninety degrees to each other, one set of windings can do duty as field winding. Another modification consists in separating each winding N, C into two units N', N" and C', C<11>, Fig. 8, the motor being reversed by reversing the current through at least one unit of each set ; or both the windings N, C may be distributed windings, and the direction of rotation may be changed or the field turns varied by changing the diameter of entry of the current. The winding C may be fed by two transformers respectively in shunt and in series with the motor, or by a single transformer in series with the motor, or directly with the motor current ; it may be shunted by an impedance for regulating purposes. The winding C can be disposed on the rotor, either by the use of an additional rotor winding and an additional set of brushes, or by supplying the auxiliary electromotive force to the brushes a, a<1> ; an additional winding may be used in conjunction with the last modification, preferably in series relation with the rotor winding along the armature axis. In Fig. 15, that part of the rotor winding acting as armature winding is shown in heavy lines, and is excited by series transformers T', T<2> so that no current tends to flow from a to ao or from a<1> to a1o, the remaining part of the rotor winding acting as field winding. The field current is introduced at the central point 1 of the secondary of the transformer T<1> and is taken out at the central point 2 of the secondary of the transformer T<2>, so that these secondaries are non-inductive as far as the field current is concerned. Alternatively, the field current may be introduced by series transformers, and the armature current non-inductively; or, as shown in Fig. 17, pairs of brushes a, f and a', f may be connected to the secondaries t<1>, t<2> of a transformer T. By short-circuiting the "field" brushes f, f<1>, the motor may be converted into a machine of the type described in Specifications No. 27,260, A.D. 1905, and No. 2367, A.D. 1906. These motors may be operated as braking generators, for example in traction work, and their speed may be varied by altering the magnitude or phase of the auxiliary field. They may be operated by continuous current, for example in passing from an alternating-current to a continuous-current supply.