Question $2$

$($a$)$ An engineer is required to design a protection scheme for the power system as shown in Figure Q$2$a below that meets the following requirement. Assume electrical power flows from left to right.

M $-$ current transrormer

Figure Q$2$a

i$)$ Draw the zone of protection and state the protection principle in your design.

ii$)$ Explain the reason for your choice of main and back$-$up protection.

$($b$)$ A $50$ MVA generator is supplying a $33$ kV single feeder network. The current transformer ratio for relays A and B$,$ and its I.D$.$M$.$T$.$L$.$ relays are shown in the Figure Q$2$b below. The relay B is set at $\backslash (125\backslash \%\backslash )$ plug setting and $0\mathrm{.}1$ time multiplier setting. If the three$-$phase fault level at the outgoing feeder from $\backslash ($ B $\backslash )$ is $300$ MVA $,$ find the suitable plug setting and time multiplier setting of relay A in order to achieve a minimum discriminative time margin of $0\mathrm{.}4$ second.