The field-magnets whose windings may be in series are often excited by a
separate direct current generation. Some are self-exciting, one or more
of the armature coils being separated from the rest, and connected to a
special commutator, which rectifies its current.
By properly spacing the coils with respect to the poles of the field,
and connecting each set of coils by itself to separate connecting rings,
several currents can be taken from the same machine, which currents
shall have a constant difference in phase. It would seem at first sight
that the same result could be attained by using as many separate
alternators as there were currents to be produced. But it would be
almost impossible to preserve the exact relation of currents and current
phase where each was produced by its own machine. The currents would
overrun each other or would lag behind. In a single machine with
separate sets of coils the relation is fixed and invariable.
Fig. I35. DIAGRAM OF ARRANGEMENT OF ARMATURE COILS AND
COLLECTING RINGS IN AN ALTERNATING CURRENT DYNAMO.
Dynamo, Alternating Current, Regulation of.
Transformers, converters, or induction coils are used to regulate
alternating current dynamos, somewhat as compound winding is applied in
the case of direct-current dynamos. The arrangement consists in
connecting the primary of an induction coil or transformer into the
external circuit with its secondary connected to the field circuit. Thus
the transformer conveys current to the field picked up from the main
circuit, and represents to some extent the shunt of a direct-current
machine.
Dynamo, Commercial Efficiency of.
The coefficient, q. v., obtained by dividing the mechanically useful or
available work of a dynamo by the mechanical energy absorbed by it. This
only includes the energy available in the outer circuit, for doing
useful work.