A 10 kVA, 500/100 V transformer has the following circuit parameters referred to primary:
Equivalent resistance, R_{eq}=0.3\: ohm; Equivalent reactance, X_{eq}=5.2\: ohm. When supplying power to a lagging load, the current, power and voltage measured on primary side were 20 A, 8 kW and 500 V, respectively. Calculate the voltage on the secondary terminals under these conditions. Draw the relevant phasor diagram.
Question : A 10 kVA, 500/100 V transformer has the following circuit pa...
Rating of transformer =10\: KVA=10*10^{3}\: VA
Power factor on primary side,
cos\: \phi _{1}=\frac{P}{V_{1}I_{1}}=\frac{8*10^{3}}{500*20}=0.8\: kg
\therefore sin\: \phi _{1}=sin\: cos^{-1}\: 0.8=0.6
Primary induced emf, E_{1}=V_{1}-I_{1}R_{ep}\: cos\: \phi _{1}-I_{1}\: X_{ep}\: sin\: \phi _{1}
=sin\: 500-20*0.3*0.8-20*5.2*0.6=432.8\: V
Transformation ratio, K=\frac{100}{500}=0.2
Secondary induced emf, E_{2}=E_{1}*K=432.8*0.2=86.56\: V
Secondary terminal voltage on load,
V_{2}=E_{2}=86.56\: V (since all the parameters are referred to primary side)
The equivalent circuit and phasor diagram is shown in Fig. 2.42(b).
