Monocyclic Alternators.—This type of alternator was designed prior to the introduction of the polyphase systems, to overcome the difficulties encountered in the operation of single phase alternators as motors. A single phase alternator will not start from rest as a motor, but must first be started and brought up to the proper speed before being connected with single phase mains. This condition constituted a serious difficulty in all cases where the motor had to be stopped and started at comparatively frequent intervals.
Fig. 1,407.—Monocyclic system diagram showing transformer connections.
Fig. 1,408.—Diagram showing section of monocyclic alternator armature illustrating the armature winding. The main coils are wound on every other tooth, and the teazer coils are placed in quadrature with them, as shown.
The monocyclic alternator is a single phase machine provided with an additional coil, called a teaser coil, wound in two phase relationship with, and connected to the center of the main single phase coil. It is provided with three collector rings; two for the single phase coil, and one for the free end of the teaser coil.
Fig. 1,409.—Diagram showing connections of General Electric Monocyclic alternator. For 2,300 volt machine, connect as shown by solid lines. For 1,150 volt machine, omit connections A to B, C to D, E to F, and G to H, and connect as shown by dotted lines. The armature of a standard monocyclic alternator rotates in a counter clockwise direction facing the commutator. When the alternator is loaded, the voltage between the teazer coil and the two terminals of the main coil may be different; therefore, it is necessary to have the commutator connected in corresponding ends of the main coil. If the machine has not been arranged for clockwise rotation, the following change in the connections on the commutator-collector must be made if the machine is to be run in parallel with another. Fig. 1,410 shows the connections of monocyclic alternators. In fig. 1,409, the studs on the commutator-collector marked 1 and 6 are the terminals of the main coil. These should be reversed. The numbers are stamped on the ends of the stud and may be seen with the assistance of a mirror. By reference to this diagram it is a simple matter to trace out the connections with a magneto, after the armature leads are disconnected and the brushes raised.