Briefly explain the classification of DC machine.
Depending upon the method of excitation of field winding ,DC machine are classified into two classes:-
1) Separately excited machines.
2) Self excited machines.
SEPARATELY EXCITED MACHINES
In separately excited machines the field winding is provided with a separate DC source to supply the field current as shown in figure.
SELF EXCITED MACHINES
In case of self excited machines no, separate source is provided to drive the field current, but the field current is driven by its own emf generated across the armature terminals when the machine works as a generator self excited machine are further classified into the three types, depending upon the method in which the field winding is connected to the armature:
a) SHUNT WOUND MACHINES
b) SERIES WOUND MACHINES
c) COMPOUND WOUND MACHINES