Correct Answer - Option 1 : 60, 0.67

Given that, pu parameters for a 300 MVA machine on its own base

Inertia: M_{old} = 10 pu

Reactance: X_{old} = 4 pu

New base = 50 MVA

New pu value of inertia,

\({M_{Pu\;new}} = {M_{Pu\;old}} \times \frac{{{{\left( {MVA} \right)}_{old}}}}{{{{\left( {MVA} \right)}_{new}}}}\)

\(\Rightarrow \;{M_{Pu\;new}} = 10 \times \frac{{300}}{{50}} = 60\;Pu\)

New pu value of reactance,

\({X_{Pu\;new}} = {X_{Pu\;old}} \times \frac{{{z_{Base\;old}}}}{{{Z_{Base\;new}}}}\)

\(\Rightarrow {Z_{Base}} = \frac{{{{\left( {kV} \right)}^2}}}{{MVA}}\)

\(\Rightarrow {X_{Pu\;new}} = {X_{Pu\;old}} \times \frac{{{{\left( {MVA} \right)}_{new}}}}{{{{\left( {MVA} \right)}_{old}}}} \times \frac{{\left( {kV} \right)_{old}^2}}{{\left( {kV} \right)_{new}^2}}\)

Now (kV)_{old} = (kV)_{new} [not given]

\(\Rightarrow {X_{Pu\;new}} = 4 \times \frac{{50}}{{300}} = 0.67\;Pu\)

**Note:**

We know that Pu value depends on the base value of that quantity hence the actual value of that quantity is always equal-

pu value old = actual/old base

Now, new pu value = actual/new base

⇒ Pu_{old} × Base old = Pu_{new} × Base_{new}

⇒ pu new = (pu old × old base)/(new base)