Design a $25$kVA core type, oil$-$cooled, $3-$phase Y $-$Y transformer with a voltage

rating of $11000/400$V$.$ The recommended flux density $1\mathrm{.}6$T$.$ It is advised that

per turn voltage should be $42$ Volt. Calculate:

$($a$)$ The cross$-$section area of the core.

$($b$)$ Number of turns in each winding.

$($c$)$ The full load current of both LV and HV windings.

$($d$)$ Cross$-$sectional area of the copper conductor $($use max current density of

$1\mathrm{.}8$mm$2/$A$)$