Compound-wound motors aim to
get the best features of the series and shunt-wound motors, namely a
high starting torque and good speed regulation. The separately excited
motor (Figure 1.56(d)) has separate control of the armature and field
currents. The direction of rotation of the motor can be obtained by
reversing either the armature or the field current. Figure 1.57 indicates
the general form of the torque-speed characteristics of the above motors.
The separately excited motor has a torque-speed characteristic similar to
the shunt wound motor. The speed of such d.c. motors can be changed by
either changing the armature current or the field current. Generally it is
the armature current that is varied