Question

Tests are performed on a 1- phase, 10 kVA, 2200/220 V, 60 Hz transformer and the following results are obtained.
$\begin{array}{ccc}& \text{Open circuit -test}& \text{short circuit -test}\\ & \text{(HV side open)}& \text{(LV side shorted)}\\ \text{Voltmeter}& 220V& 150V\\ \text{Ammeter}& 2.5A& 4.55A\\ \text{Wattmeter}& 100W& 215W\end{array}$

The approximate equivalent circuit is :

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

Lets take circuit referred to low voltage side,

$\text{Watt meter reading =}VI\cos \varphi$

$\cos \varphi =\frac{100}{220\times 2.5}=0.1818$

$\sin \varphi =\sin \left({\cos }^{-1}\right(0.1818\left)\right)=0.9833$

$I_c=I_0\cos \varphi =2.5\times 0.1818=0.4545A$

$I_m=I_0\sin \varphi =2.5\times 0.9833=2.46A$

$\therefore R_c=\frac{V}{I_c}=\frac{220}{0.4545}=484\Omega$

$\therefore X_m=\frac{V}{I_m}=\frac{220}{2.46}=89.43\Omega$

$\therefore$ option c is the only equivalent circuit matching.