Ques. In the operation of a shunt dynamo what is its characteristic feature?
Ans. The voltage at the dynamo remains practically unchanged, and the current varies according to the load.
Ques. Does the voltage remain constant for all loads?
Ans. There is a certain maximum load current that the shunt dynamo is capable of supplying at constant voltage; beyond this, the voltage will decrease, the machine finally demagnetizing itself, and ceasing to generate current.
Ques. Why does the voltage not remain constant for all loads?
Ans. Because there is a drop in the voltage in forcing the current through the armature windings which increases with the load.
Ques. What is the usual method of regulation for shunt dynamos?
Ans. The method of varying the current through the field coils by means of a rheostat inserted in series with the field winding as shown in fig. 194.
Moving the lever L of the rheostat to the right increases the resistance in series with the field winding, and this reduces the amount of current in that winding, thus reducing the strength of the magnet and consequently the voltage at the brushes. The contrary movement of the lever, by cutting out the resistance, produces the opposite effect.
The Compound Dynamo.—This class of generator is designed to automatically give a better regulation of voltage on constant pressure circuits than is possible with a shunt machine. It possesses the characteristics of both the series and shunt machines, of which it is in fact a combination.