A unit substation has a $4\mathrm{.}16kV-208\frac{Y}{120}V,$ three$-$phase, $1000$ kVA transformer. The available fault current at the main secondary bus is $50,800$A symmetrical. The unit substation services $10$ feeders. The continuous load for each feeder is $400-$A with $45,000$ A symmetrical fault current.

$($a$)$ Select the frame size for the main secondary circuit breaker.

$($b$)$ Select the frame size of the feeder circuit breakers.

$($c$)$ Design the unit substation including the dimensions for all the sections.

$($d$)$ Determine the size of the electrical room that should house the unit substation.