Question

Three single phase transformers of rating 50 kVA, 2000 V/1000 V are connected in $\Delta /\Delta$. The current in the primary windings of the transformer when supplying a balanced three phase load of 40 kW at 1000 V and 0.8 power factor lagging is

• A. 32.32 A
• B. 28.86 A
• C. 16.66 A
• D. 8.33 A

Answer 1

The correct option is D 8.33 A

$\sqrt{3}{V}_L{I}_{L}cos\left(\varphi \right)=40000W$

$\sqrt{3}\times 1000\times I_L\times 0.8=40000W$

$I_L=\frac{40000}{\sqrt{3}\times 1000\times 0.8}=28.86A$

The current in the winding of the transformer secondary,
$I_{ph2}=\frac{28.86}{\sqrt{3}}=16.66A$

Current in the primary winding of the transformer,
$I_{ph1}=16.66\times \frac{1000}{2000}=8.33A$