Correct Answer - Option 2 : actual impedance / base impedance
Per unit value of a quantity is defined as the ratio of its actual value to its base value.
Per unit impedance = actual impedance / base impedance
Important Point:
The relation between new per-unit value & old per unit value impedance
\({({Z_{pu}})_{new}}\; = {({Z_{pu}})_{old}} \times {\left( {\frac{{k{V_{base}}}}{{k{V_{new}}}}} \right)^2} \times \;\left( {\frac{{MV{A_{new}}}}{{MV{A_{old}}}}} \right)\)
Also \({Z_{pu}} = \frac{{{Z_{Actual}}}}{{{Z_{base}}}}\)
\({Z_{base}} = \frac{{kV_{base}^2}}{{MV{A_{base}}}}\)
Where,
(Zpu)new = New per unit value of impedance
(Zpu)old = Old per unit value of impedance
kVbase = Old base value of voltage
kVnew = New base value of voltage
MVAnew = New base value of power
MVAold = Old base value of power