CHAPTER IX.
Chanok From Double Current to Sinole Current Motor.
A description is given elsewhere of a method of operating al-ternating current motors by first rotating their magnetic polesuntil they have attained synchronous speed, and then alternatingthe poles. The motor is thus transformed, by a simple changeof circuit connections from one operated by the action of two ormore independent energizing currents to one operated either bya single current or by several currents acting as one. Anotherway of doing this will now be described.
At the start the magnetic poles of one element or field of themotor are progressively shifted by alternating currents differingin phase and passed through independent energizing circuits, andshort circuit the coils of the other element. When the motorthus started reaches or passes the limit of speed synchronous withthe generator, Mr. Tesla connects up the coils previously short-cir-cuited with a source of direct current and by a change of the cir-cuit connections produces a simple alternation of the poles. Themotor then continues to run in synchronism with the generator.The motor here shown in Fig. 41 is one of the ordinary forms, withfield-cores either laminated or solid and with a cylindrical lamin-ated armature wound, for example, with the coils a b at right angles.The shaft of the armature carries three collecting or contact ringso D e. (Shown, for better illustration, as of different diameters.)
< )ne end of coil a connects to one ring, as c, and one end ofcoil u connects with ring d. The remaining ends are connectedto ring e. Collecting springs or brushes e g h bear upon therings and lead to the contacts of a switch, to be presently de-scribed. The field-coils have their terminals in binding-posts kk, and may be either closed upon themselves or connected witha source of direct current l, by means of a switch m. The mainor controlling switch has five contacts abode and two levers/'g , pivoted and connected by an insulating cross-bar h, so as tomove in parallelism. These levers are connected to the line