Question

230/ 115 V single phase transformer takes a current of 2 A at 0.2 lagging with the l.v. winding open circuited. On load, the l.v. winding delivers a current of 15 A at 0.8 p.f. lagging. The primary current is

• A. 9.5 A
• B. 13 A.
• C. 9.1 A
• D. 6.5 A

Answer 1

The correct option is C 9.1 A


$I_0=2A$

$I_2=15A\Rightarrow I_2^1=\frac{15}{2}=7.5A$

$\varphi =co{s}^{-1}\left(0.2\right)-co{s}^{-1}\left(0.8\right)={41.59}^o$

$\therefore I_1=\sqrt{I_2^{1^2}+I_0^2+2I_0{I}_2^{1}cos\varphi }=9.09A$