Question

Rotating speed of armature has beend adjusted so that the output of alternator which has been fixed

Answer 1

Voltage is determined by speed and field current. An increase in either of the two, will increase alternator voltage.

Current delivered by the alternator is determined by load. Both the magnitude and phase angle of the load impedance is important. Behaviour of the alternator will be quite different if the load is highly inductive or capacitive.