Question

The system shown in the figure is supplying 100 MVA at 22 kV, 0.6 lagging power factor into an infinite line

Generator: 200 MVA, 22 kV, X = 0.5 pu
Transformer: 100 MVA, 22/66 kV, X = 0.02 pu
Line Reactance: 10$\Omega$
Choosing the base of 100 MVA, 22 kV, the per unit reactance diagram is

• A.
• B.
• C.
• D. None of the above

Answer 1

The correct option is B

Generator: 200 MVA, 22 kV,$X_d^{\prime }=0.5pu$

$X_{dnew}=X_{old}\times \frac{100}{200}\times {\left(\frac{22}{22}\right)}^2$

$X_{dnew}=0.5\times 0.5=0.25pu$

Transformer: 100 MVA, 22/66 kV, X = 0.02 pu

$X_{new}=0.02pu$

Line Reactance: 10$\Omega$

$X_{pu}=X_{\Omega }\times \frac{MV{A}_{base}}{(kV{)}_{base}^2}$

$=10\times \frac{100}{\left({66}^2\right)}$

$X_{linepu}=0.2295pu$

The per unit reactance diagram will be as shown below: