Calculate the nominal currents and three$-$phase short$-$circuit levels at each breaker.

Select the transformation ratios of the CTs:

The transformation ratio of the CTs is determined by the larger of the following two values:

$I_{\text{n}\text{o}\text{m}}$

maximum short$-$circuit current without saturation being present. To fulfil this condition and assuming that a C$100$ core is used and that the total burden is $1,I_{sc}(\frac{5}{x})100A,$ where $I_{sc}$ is the short$-$circuit current.

Determine the values of the pick$-$up setting, time dial and instantaneous settings of all phase relays to ensure a co$-$ordinated protection arrangement.

Find the percentage of the line BC protected by the instantaneous unit of the overcurrent relay associated with breaker $2.$

Draw the time$/$current characteristics of the relays on the system.