$(20$ Points$)$ Assuem that the field current of the generator in Problem $1$ is adjusted to achieve rated voltage $(13\mathrm{.}8$ kV $)$ at full$-$load conditions in each of the following questions.

$($a$)$ What is the efficiency of the generator at rated load?

$($b$)$ What is the voltage regulation of the generator if it is loaded to rated kilovoltamperes with $0\mathrm{.}9$ PF$-$lagging loads?

$($c$)$ What is the voltage regulation of the generator if it is loaded to rated kilovoltamperes with $0\mathrm{.}9$ PF$-$leading loads?

$($d$)$ What is the voltage regulation of the generator if it is loaded to rated kilovoltamperes with unit loads?