Fig. 1,447.—Diagram of connections of self-exciting image current alternator.
When the armature is rotated, a pressure will be generated between the brushes 2 and 4, and a current will flow from C through the coils XX to B, producing a flux through the armature at right angles to the residual magnetism and establishing a resultant magnetic field between D, B, and D, C. This field will generate a pressure between the brushes 1 and 3, and a current will flow D through XX to E in such a direction that it will at first be opposed to the residual magnetism, and afterward reverse the direction of the latter. At the moment the residual magnetism becomes zero, the only magnetism left in the machine will be due to the currents from the brushes 2 and 4, and their field combining with the vertical reversed field will produce a resultant polar line between B and E. As these operations are cyclic, they will recur at periodic intervals, and the phenomena will become continuous. The negative field thus set up in the air gap of the machine will cut the conductors of the stator and will be cut by the conductors of the rotor in such a manner that the electromotive forces generated between the brushes of the armature will be equal and opposite to those between the terminals of the stator.
CHAPTER L
CONSTRUCTION OF ALTERNATORS
The construction of alternators follows much the same lines as dynamos, especially in the case of machines of the revolving armature type. Usually, however, more poles are provided than on direct current machines, in order to obtain the required frequency without being driven at excessive speed.
The essential parts of an alternator are:
- 1. Field magnets;
- 2. Armature;
- 3. Collector rings;
and in actual construction, in order that these necessary parts may be retained in proper co-relation, and the machine operate properly there must also be included:
- 4. Frame;
- 5. Bed plate;
- 6. Pulley.