Question

current in dc generator can be increased by increasing the

Answer 1

There are 2 ways. Turn the armature faster and or increase the field current. But there is a limit on each of these methods. Increasing the speed of rotation is limited to a maximum safe design speed

Increasing the field current is also limited by the winding size and the core saturation limit.

Yes it can be done but you are stepping outside the design limitations with the possible effect of decreasing the life of the machine or increasing the possibility of failure.