Patent GB-190526897-A (GB)
Title: Improvements in Single-phase Commutator Motors.
Inventor: FYNN VALERE ALFRED
Filed: 1905-12-23
Granted: 1906-06-14
Abstract: 26,897. Fynn, V. A. March 25, [date applied for under Patents Act, 1901]. Field magnets; motors, controlling; sparking, preventing.-Relates to single - phase commutator motors which start as repulsion motors and run in normal operation as induction motors, as described in Specification No. 22,712, A.D. 1902, and the power factor and torque of which are improved b y impressing upon the rotors auxiliary electromotive forces of suitable phase. To allow of the motors being reversed without the use of brush-shifting devices or the employment of duplicate sets of phase-compensating apparatus, they are provided with divided field windings which may be coupled up in various ways to shift the resultant magnetic axis. Fig. 4 shows the rotor A of a commutator motor shortcircuited by means of two sets of brushes H, R, displaced from one another by #/n degrees, where n is the number of poles. The motor is started as a repulsion motor with the brushes R situated at an angle of between ten and thirty degrees with respect to the stator field axis F. The motor may be converted into an induction motor by shortcircuiting the brushes H by means of the switch shown in Fig. 4, or by short-circuiting a number of points on the rotor winding by means of slip-rings or the like. Two fields differing in phase are then set up in the motor, their axes coinciding with the brush axes h, r. To improve the power-factor, an electromotive force E<1> of the same phase as the field in the axis h is impressed on the brushes H, this electromotive force being derived from an auxiliary machine, such as a squirrel-cage induction motor, by means of a transformer T. The auxiliary motor M is provided with two field windings, one D<1> of which is the working winding while the other D<11> is displaced with regard to the first by an angle a equal to the angle between the axes F, r. The auxiliary electromotive force may be varied by making the transformer T adjustable or by the use of variable resistances. The winding D" may feed the brushes H direct. If the brushes re shifted so that the axis r coincides with the stator field axis F, the phase of the auxiliary electromotive force coincides with that of the supply electromotive force, and the brushes H may be fed from the mains through the transformer T. The motor may be started with both sets of brushes H, R closed. In Fig. 5, the compensating electromotive force is shown derived from an auxiliary winding N disposed on the stator along the axis r. In the arrangement shown in Fig. 6, the compensating electromotive force is introduced into the rotor by way of the starting-brushes R, the auxiliary winding N being situated along the axis h. At a sufficiently high speed, the brushes Hare short-circuited either directly or through resistance, inductance, or capacity. The application of the invention to motors provided both with commutators and slip-rings or other short-circuiting devices in connexion with single or separate rotor windings, as described in the above-mentioned Specification, is also illustrated. The stator winding consists of two parts S', S", Fig. 8<a>, connected in series and situated #/n degrees apart along the brush axes r, h, producing a resultant field F. When the ampere-turns of the two parts of the stator winding differ, as in Fig. 8<a>, the axis r is preferably co-axial with the axis of the greater part S'. By reversal of the direction of the current in one of the sections S<1>, S<11>, the resultant F is displaced from one side to the other of the brush axis r and the motor is reversed, as shown in Fig. 8<b>, the connexions of the auxiliary stator winding N being also reversed. To prevent sparking, a number of points on the rotor winding may be shortcircuited by means of slip-rings &c. after the normal speed has been reached.