Consider the internal phase-neutral voltage of a synchronous generator to be at 25558 V. The generator is connected to an infinite bus with phase-neutral voltage 19320.5 V. If armature resistance is negligible and synchronous reactance of the machine is 11 ohms, find the power angle and the power factor of the machine when it delivers 45 MW in the following cases:
a) When excitation voltage is decreased to 72.2% of its original value.
b) When excitation voltage is decreased to 59.3% of its original value.
c) If the maximum delivered active power of the generator is 45 MW, find
the minimum excitation below which the generator loses synchronism.