Generator connected to Isolated load:-
When the prime mover I/p is increased while the excitation remains constant; it results in an increase in frequency. The increase in frequency increases the terminal voltage for the same excitation. The increase in terminal voltage causes the static load to increase their respective demands as their power consumption is proportional to square of the voltage. The rotating load have their respective speed increases because of the increase in frequency that increases their synchronous speed.
The increase in voltage results to increase in their developed torque and consequently the power demand may increase particularly when they are driving constant torque load. The twin factors results in as increased power demand by the rotating power load as well.
The final conclusion is that an increase in prime mover I/P alone results in increase in frequency as well as increase in Unit loading.
If the excitation increases while the prime over I/P remains constant the terminal voltage increases. This results in increased power consumption by the connected loads as explained above. Since the increased power demand is not met by prime over, it is fed from the stored Kinetic energy of the rotating mass resulting in reduction of frequency to restore the frequency to the previous value; the prime mover i/p must be increased.