Fig. 136. COMPOUND WOUND DYNAMO.
Dynamo. Compound.
A compound wound dynamo; one which has two coils on its field magnet;
one winding is in series with the external circuit and armature; the
other winding is in parallel with the armature winding, or else with the
armature winding and field winding, both in series. (See Winding, Long
Shunt--Winding, Short Shunt.)
Such a dynamo is, to a certain extent, self-regulating, the two coils
counteracting each other, and bringing about a more regular action for
varying currents than that of the ordinary shunt or series dynamo.
The extent of the regulation of such a machine depends on the
proportions given its different parts. However good the self-regulating
may be in a compound wound machine, it can only be perfect at one
particular speed.
To illustrate the principle on which the approximate regulation is
obtained the characteristic curve diagram may be consulted.
Fig. 137. CURVES OF SERIES AND SHUNT WINDINGS SUPERIMPOSED.
One curve is the curve of a series winding, the other that of a shunt
winding, and shows the variation of voltage in each with resistance in
the external or working circuit. The variation is opposite in each case.
It is evident that the two windings could be so proportioned on a
compound machine that the resultant of the two curves would be a
straight line. This regulation would then be perfect and automatic, but
only for the one speed.