Speed control by armature voltage
method of speed control, armature is supplied from a separate variable Ac
voltage source, while the field is separately excited with fixed rate dc voltage
as shown in figure. Here the armature resistance and field current are not
varied. Since the no load speed the speed versus Ia characteristic will shift parallel as shown in figure for
different values of Va.
remains constant, this method is suitable for constant torque loads. In a way
armature voltage control method dissimilar to that of armature resistance
control method except that the former
one is much superior as next repower loss takes place in the armature
circuit. Armature voltage control method is adopted for controlling speed from
base speed down to very small speed, as one should not apply across the
armature a voltage, which is higher than the rated voltage.