Question

What is the per unit reactance of an alternator if the capacity is doubled and voltage is halved?

• A. increases by 4 times
• B. reduced by 8 times
  
• C. increased by 8 times
• D. decreased by 4 times

Answer 1

The correct option is C increased by 8 times

$X_{pu}=X_{actual}\times \frac{MVA}{(kV{)}^2}$

$\therefore X_{pu}\propto \frac{MVA}{(kV{)}^2}$

$\frac{X_{1pu}}{X_{2pu}}=\frac{1.0}{2}\times \frac{(0.5{)}^2}{1}=\frac{1}{8}$

$X_{2pu}=8\left(X_{1pu}\right)$

$\therefore$ Increases by 8 times.