Question

The p.u. parameters for a 500 MVA machine on its own base are:
Inertia, M=20 p.u.; Reactance, X=2 p.u.
The p.u values of inertia and reactance on 100 MVA
common base, respectively, are

• A. 4, 0, 4
• B. 100, 10
• C. 4, 10
• D. 100, 0.4

Answer 1

The correct option is D 100, 0.4

$(M_{pu}{)}_{new}=(M_{pu}{)}_{old}\times \frac{(MVA{)}_{old}}{(MVA{)}_{new}}$
$=20\times \frac{500}{100}=100p.u$
$(X_{pu}{)}_{new}=(X_{pu}{)}_{old}\times \frac{(MVA{)}_{old}}{(MVA{)}_{new}}\times \frac{(kV{)}_{old}^2}{(kv{)}_{new}^2}$
$=2\times \frac{100}{500}=0.4$ $\left[\right(kV{)}_{old}=\left(kV{)}_{new}\right]$