Patent GB-190313547-A (GB)
Title: Improvements in Exciting and Regulating Alternating Current Motors and Alternators having Collectors.
Inventor: BLONDEL ANDRE
Filed: 1903-06-17
Granted: 1904-01-14
Abstract: 13,547. Blondel, A. June 17, A.D. 1902, [date applied for under Patents Act, A.D. 1901]. Dynamos, regulating; motors, controlling. - Relates t o methods of exciting and regulating sychronous motors for traction purposes &c. which have the usual collectors or fixed collectors and rotating brushes, and h a v e their stators and motors fed independently by mono- or poly-phase currents, the methods being also applicable in some cases to generators. The feed-currents of the stator and rotor may be taken from the same source at the same or different tensions. The principle of the regulation consists in increasing the feed tension of the rotor at starting and at small speeds and in regulating its value and phase so that it nearly counterbalances the electromotive force generated in the rotor by the inductive effect of the slip, so that energy is driven back from the rotor into the stator or into the main ; or, by exciting the rotor, energy is driven back from the stator into the rotor or the main. Diagrams are shown by means of which it is stated that the value and phase of the starting feed tension can be calculated. When the setting of the brushes may be varied, the excitation is varied partly by altering their position and partly by altering the feed tension by means of transformers ; the phase of the exciting- current supplied to the rotor may otherwise be varied by the use of a commutator which alters the connections of the brushes with the transformers. Preferably, however, the changes in the phase of the feed-current of the rotor are produced by means of transformers or autotransformers which regulate both the phase and tension of the current. These transformers &c. may be the same as those which feed the stator. In a simple case, self-induction bobbins having movable cores are placed in the leads which connect the mains to the rotor. The feed tension is increased as desired by withdrawing the cores when starting. Fig. 3 shows a case in which the rotor R of a two-phase motor is supplied from transformers T<1>, T<2>, connected to the mains L<1>, L<2>, L<3>, L<4> to which the stator X is directly connected. Each transformer has two secondary coils which are connected to the rotor through switches F', F', m<1>, m<2> in such a manner that any desired number of windings of the coils S<1>, S<2>, s<1>, s<2> can be put in the circuits. The connections may also be reversed by the use of pole-changers. Three transformers are employed in the case of a three-phase motor as shown in Fig. 4. In this case a fixed and a variable electromotive force, differing by a quarter period of phase as in the case shown in Fig. 3, are supplied to each brush B<1> &c. of the rotor by the fixed or constant secondary s<1> &c. of the transformer p<1> &c. and by the alterable secondary S' &c. of the transformer P' &c., so that a current of high tension may be supplied to the rotor at starting. The transformers of each pair may be united in one, if desired. The position of the brushes in any of the above cases is stated to be calculated from the diagram, as the lag of the brushes and of the feed tension are additive as regards their effect on the phase of the current in the rotor. The brushes, being set, do not require to be moved, as they are fed with a fixed electromotive force sufficient to cause the formation of a field equal to the normal field with no load, and also with a variable electromotive force which can be adjusted to produce the torque required. It is also shown by means of a diagram how a three-phase motor may be regulated by the use of two or three-phase excitations. In addition to the above and similar methods of altering the phases of the feed tensions, the current inlets to the stator or the setting of the brushes may be altered to produce similar results. The stator X in the case shown in Fig. 3 is provided with regularly-spaced terminals a, b, c, &c. for this purpose. The alteration of the connections may be made by means of controllers which connect the supply leads to the proper wires of a number leading to the points a, b, c, &c. The tension and phases of the currents supplied to the stator may be altered by means of transformers which supply the current, the magnetic flux and the torque being then adjustable. In slowing down the motor, the direction of rotation of the field both in the stator and rotor is reversed, but may also be maintained in its original direction while the rotor is still moving. For this purpose, the applied electromotive force is set slightly in advance of that induced in the stator, and is regulated at a value a little greater than that of the electromotive force in the rotor, so that it increases as the slip increases. The slowing down may finally be hastened by reversing the fields. It is stated that the motor speed may, when necessary, be increased beyond synchronism by giving the applied electromotive force a lag of about half a period. The phase and tension regulator may be placed in the stator circuit instead of as described above, or the stator may be used as an auto-transformer to supply currents of the desired phase and tension. The regulator applied to the rotor may also be some of the windings of the transformer which supplies both the stator and rotor. A similar arrangement is shown by the dotted lines in Fig. 3, the stator being then fed from the secondaries S<1>, s<1> of the transformers T', T<2>; these secondaries may feed both stator and rotor. All the arrangements described may be used in combination with means for the employment of starting-resistances and for reducing sparking, the resistances being cut in temporarily, if desired, between successive positions of the switch contacts. The phase or tension of the current from a generator is stated to be regulated by regulating the generator in accordance with the general principles of the systems described above.