Help answer part D$)$ the correct result is: $)11\mathrm{.}5$ ohm at an angle of $31\mathrm{.}8$ ; $3\mathrm{.}8$ ohm at an angle of $31\mathrm{.}8.$

Question $4$

Describe how a variable speed drive $($VSD$)$ is used to control the speed of an induction motor.

$[4$ marks$]$

A star$-$connected $3-$phase supply, in which the e$.$m$.$f$.$ generated in each phase is $450$ V $,$ supplies a delta connected $100$ hp induction motor which has a full load efficiency of $\backslash (96\backslash \%\backslash )$ and a power factor of $0\mathrm{.}85$ lagging.

Calculate

$($a$)$ the line current for the supply

$($b$)$ the terminal voltages on the motor

$($c$)$ the phase current for the induction motor

$($d$)$ the impedance per phase and the equivalent star$-$connected impedance per phase of the induction motor.

$[5$ marks$]$