Help in understanding single line diagram!

Hi Guys, really need some help here due to my lack of knowledge in the electrical field. basically i dont understand the circuit in the following link
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From the left side, 3 phase grid voltage 240v, current ~4A is coming in (4 wires, 3Live 1 neutral). after the first MCB on the left, i noticed there is a MCT which im assuming is some current transformer. below them is earth leakage relay and a shunt trip, below going back into the MCCB.

can anyone explain to me what is the purpose of having the current transformer??? and also if i can actually 'simplify' this circuit by replacing the center protection to just a MCCB with ELCB functions?

THANKS!!!