List of top Power Systems Questions on Directional Relays asked in GATE EE

For the three-bus power system shown in the figure, the trip signals to the circuit breakers $B_{1$ to $B_{9}$ are provided by overcurrent relays $R_{1}$ to $R_{9}$, respectively, some of which have directional properties also. The necessary condition for the system to be protected for short circuit fault at any part of the system between bus 1 and the R--L loads with isolation of minimum portion of the network using minimum number of directional relays is:} \begin{center} \includegraphics[width=0.5\textwidth]{06.jpeg} \end{center}