Task $2$

$(20$ points$)$

The newly purchased transformer is a one$-$phase transformer rated at $15$kVA,$\frac{400}{200}V,50$ Hz $.$ The transformer is expected to be used as a step$-$down transformer delivering a rated full load current at unity power factor. The load voltage at the low voltage side is expected to be equal to the rated secondary voltage $($i$.$e$.200$V$).$ The following results were obtained from conventional open$-$circuit and short$-$circuit tests in a students' experiment.

$\backslash$table$[[,$Measured Voltage,$\backslash$table$[[$Measured$],[$Current$]],\backslash$table$[[$Measured$],[$Power$]],$Testing Condition$],[\backslash$table$[[$Open$-$circuit$],[$test$]],V_{oc}=200V,I_{oc}=0\mathrm{.}6A,P_{oc}=60W,\backslash$table$[[$Done on the low$],[$voltage side$]]],[\backslash$table$[[$Short$-$circuit$],[$test$]],V_{sc}=15V,I_{sc}=9A,P_{sc}=80W,\backslash$table$[[$Done on the high$],[$voltage side$]]]]$

Answer the following questions:

$($a$)$ State the purposes of the above$-$mentioned open$-$circuit and short$-$circuit tests.

$(2$ pts$)$

$($b$)$ Obtain the equivalent circuit referred to the high voltage side of the transformer.

$(6$ pts$)$

$($c$)$ Calculate the copper losses on full load at unity power factor. $($Hint: Copper losses refer to the losses at the windings.$)$

$(3$ pts$)$

$($d$)$ Calculate the full load efficiency at unity power factor.

$(3$ pts$)$

$($e$)$ Calculate the terminal voltage at the high voltage side.

$(4$ pts$)$

$($f$)$ How can we decrease the core losses?

$(2$ pts$)$