$4\mathrm{.}8$

Fig. Pd

Figure P$4\mathrm{.}5$ shows a step$-$down transformer connecting a $69$ kV and a $13\mathrm{.}8$ kV bus. The transformer has $\backslash (12\backslash \%\backslash )$ reactance and $\backslash (1\backslash \%\backslash )$ resistance on a $30$ MVA base. Its effective capacitance on the L$.$V$.$ side is $\backslash (11,000\backslash$mathrm$\{$pF$\}\backslash ).$ The impedance of the supply is negligible.

A fault on the L$.$V$.$ bus is interrupted by opening the circuit breaker $($CB$).$ What will be the peak TRV of the circuit breaker? How soon after current interruption will it occur? Assume a symmetrical fault current. Do not waste time solving this problem formally. Use somic engincering judgment.