Patent GB-190715151-A (GB)
Title: Improvements in or connected with Dynamo Electric Machines of the Neutralised Conduction Type.
Inventor: FYNN VALERE ALFRED
Filed: 1907-07-01
Granted: 1908-06-18
Abstract: 15,151. Fynn, V. A. July 1. Motors, alternating-current; fieldmagnets.-A static transformer, adapted to transmit from the mains to the machine the power required by it, is embodied in the structure of alternating-current machines of the neutralized conduction type and particularly of the self - excited conduction machines described in Specifications No. 2367, A.D. 1906, and No. 5652, A.D. 1907, the axis of the magnetic field of said transformer or the axis of the transformer windings either coinciding with the axis of the armature and neutralizing-winding or being displaced therefrom by an angle less than ninety electrical degrees. As applied to motors, the transformer field serves also to improve the power factor, commutation, and torque. In one modification, Fig. 1, the armature A, neutralizing-winding -N, and field winding F are connected in series with the secondary winding S<2> of a transformer S', S' disposed on the stator ; the number of turns of the windings may be varied by the use of the movable contacts K<1>, K<2>, K<3>. The transformer may be of the auto type, the windings S<o>, Fig. 2, acting both as primary and secondary, and the field winding may be disposed on the rotor by the use of extra brushes f, f<1> connected in series with the armature through the transformer T<2>. The rotor may carry two windings, one doing duty as armature winding and the other as field winding. The brushes f, f<1> may be supplied with current from the secondary winding of a separate transformer, the primary winding of which is in series with the stator winding S‹ ; or the brushes f, f<1> may be connected directly in series with the winding S‹ or with the winding S<1>, if the arrangement of Fig. 1 is adopted. Part of the field winding may be disposed on the stator, and the motor field may be varied by reversing or regulating the part disposed on the stator. The neutralizing-winding N may be combined with the primary winding S' of the transformer, Fig. 5, and the rotor winding may serve both as field and armature winding by displacing the brushes a, a', Fig. 6, the belts shown in heavy lines serving as armature winding and the remaining belts as field winding. The speed may be regulated by shifting the brushes. In the example shown in Fig. 7, four brushes are used, the "field" electromotive force being impressed upon the brushes a, ao and a<1>, a<1>0 by means of transformers T<1>1, T<1>2, the primary windings of which are connected in series with the auto-transformer winding S‹. The armature part of the rotor winding, indicated in heavy lines, and the neutralizing-winding N are fed from the secondary part of the winding S<o>, connexions being made at the middle points 1, 2 of the transformer secondaries, as shown. This last arrangement may be reversed, the armature current being derived from the transformers T<1>1 and T<1>2, and the field current from the secondary of the auto-transformer S<o> ; in this case the neutralizing-winding may be divided into four parts, two being included in the circuit of one of the secondaries, and the others in the circuit of the other secondary. The modification shown in Fig. 2 may be applied to a shunt conduction motor in which the brushes f,f<1> are short-circuited either directly or through resistances or impedances. To improve the power factor of a motor of this type, a compensating electromotive force derived, for example, from the transformer winding S', Fig. 9, may be impressed upon the brushes f, f<1> ; a part F of the field winding may be disposed on the stator for regulating purposes. The brushes may be slightly displaced from the positions shown. Several methods of starting shunt conduction motors are described. In one method, a disposition of brushes similar to that shown in Fig. 7 is used, and the motor is started in either direction by connecting a pair of diametrically opposite brushes to the supply in the manner shown in Fig. 6, the other pair being open-circuited. Another method is shown in Fig. 11. A part of the primary winding S' of the transformer does duty as neutralizing. winding, its secondary winding S<2> may be connected to the "armature" brushes a, a<1>, and a winding S<3> inserted m the field circuit compensates the motor. Two three-way switches M<1>, M<2> are provided. To start the motor in one or the other direction, the switches are placed on the contacts 1, 4 or 3, 6 ; when up to speed, the switches are moved over to the contacts 2, 5. The motor may also be started as a neutralized series conduction machine by feeding the brushes f, f<1> by means of a series transformer; or it may start as a shunt conduction motor, or as a repulsion motor. Fig. 13 shows the construction of a two-pole machine connected as indicated in Fig. 6 but with indepen. dent primary and secondary transformer windings S', S'. The stator is furnished with well-defined projections D and detachable projections B, the latter carrying the transformer Windings. The turns of the rotor winding acting as armature winding are neutralized by means of a winding which is disposed in slots m on the periphery of the projections D. To prevent the transformer and field fluxes from closing round the projections D and B respectively, a short-circuited coil shaped like the number eight may be disposed on one or both of the projections close to the armature. The conductors crossing at the waist of the eight are not in electric contact, and are disposed parallel to the shaft and approximately in the centre of the projections so that each loop embraces about one-half of the cross-saction of the projection. In a modification, the projections B, D are connected together at their inner peripheries by thin iron bridges so that a part of the transformer flux closes round the transformer windings without threading the rotor, and the magnet frame has two removable yokes to allow the transformer windings to be readily placed in position. All these motors may operats as generators or as brakes, and may be operated from a continuous - current or a polyphase supply.