QUESTION $3$

A $\backslash (10\backslash$mathrm$\{$kVA$\},120/480\backslash$mathrm$\{$~V$\}\backslash )$ single$-$phase transformer is to be used as an autotransformer to supply a $480$ V circuit from a $600$ V source. When it is tested as a two$-$winding transformer at a rated load, the unity power factor its efficiency is $0\mathrm{.}979.$

$($a$)$ Determine its kVA rating as an autotransformer.

$($b$)$ Find its efficiency as an autotransformer at full load with $0\mathrm{.}85$ power factor lagging.

QUESTION $4$

a$.$ In Figure $4$ a is shown an autotransformer used to supply a load of $2$ kW at $230$ V from a $400$ V a$.$c$.$ supply. Find the currents in parts AC and BC $,$ neglecting losses and no$-$load current. Also, find the copper saving percent due to the use of an autotransformer instead of using a winding transformer: Assume purely resistive load.

b$.$ A $\backslash (10\backslash$mathrm$\{$kVA$\},230/110\backslash$mathrm$\{$~V$\}\backslash )$ transformer is to be used as an autotransformer. What will be the voltage ratio and output rating of an autotransformer?