MCCB,ACB,VCB all the three are protective devices only. 
They are used to isolate the system which is connected 
below them at fault conditions. Eg, Overload, Short 
circuit,Earth fault.

Depending upon the operating voltages and level of 
protection(Fault Level) needed for the system ,these three 
protection device are selected.

For Eg: If the operating voltage are below 1100V, depend 
upon the fault level we can use MCCB or ACB.

Simillarly if operating voltage are more than 1100V,VCB are 
used.