A $20$ MVA transformer, which may be called upon to operate at $25\%$ overload, feeds $11-$kV busbars through a circuit breaker. The busbar is connected to a single outgoing feeder. The transformer circuit breaker is equipped with $1000/5$ A CTs and the feeder circuit breakers with $500/5$ A CTs$.$ Both transformer and feeder are protected by IDMT relay type. The relay at the feeder circuit breaker has a $125\%$ plug setting and a $0\mathrm{.}4$ time dial setting. If a three$-$phase fault current of $7500$ A flows from the transformer to the feeder, find the: i$.$ Operating time of the feeder relay. ii$.$ The minimum plug setting of the transformer relay. The plug setting of the relay ranging from $50\%$ to $200\%,$ in steps of $25\%.$ iii. The transformer relay time dial setting by assuming a discriminative time margin of $0\mathrm{.}5$ second.