Dynamo, Alternating Current

A dynamo-electric machine for producing an alternating current; an alternator. They are cla ified by S. P. Thompson into three cla es--I. Those with stationary field-magnet and rotating armature. II. Those with rotating field magnet and stationary armature. III. Those with both field magnet part and armature part stationary, the amount of magnetic induction from the latter through the former being caused to vary or alternate in direction by the revolution of appropriate pieces of iron, called inductors. Another division rests on whether they give one simple alternating current, a two phase current, or whether they give multi phase currents. (See Current, Alternating--Currents, Multiphase.) A great many kinds of alternators have been constructed. Only an outline of the general theory can be given here. They are generally multipolar, with north and south poles alternating around the field. The armature coils, equal in number in simple current machines, to the poles, are wound in opposite senses, so that the current shall be in one direction, though in opposite senses, in all of them at anyone time. As the armature rotates the coils are all approaching their poles at one time and a current in one sense is induced in every second coil, and one in the other sense in the other coils. They are all in continuous circuit with two open terminals, each connected to its own insulated connecting ring on the shaft. As the coils pa the poles and begin to recede from them the direction changes, and the current goes in the other direction until the next poles are reached and pa ed. Thus there are as many changes of direction of current per rotation as there are coils in the armature or poles in the field. IMG:8956969607833025625_194F134.jpg: Fig. 134. ALTERNATING CURRENT DYNAMO WITH