Mccb is moulded case circuit breaker.
ACB is air circuit breaker.
VCB is vacuum circuit breaker.

MCCB,VCB,ACB all are of different type with same 
functioning.
all of them are used to isolate the power or to trip the 
power at the time of fault in line and thus save the 
circuit from further damage and isolate unheathy part from 
healthy one.
if the circuit if of low rating we can go ahead with MCCB 
but for high rating circuit we go for costlier CB that is 
ACB/VCB because they are more reliable and have long life.

MCCB - Thermomagnetic operaton-For large surges in ct- In
distribution boards-bimetallic strip responding to less
extreme but longer_term over_current conditions-applicable
for    
low voltages.
ACB - low volt power cb-trip characteristics r
adjustable-air s the arc quenching medium-applicable upto 440V.
VCB - medium volt power cb-trip char. adjustable-mechanical
sys. used for trip & open-Vaccuum s the arc quenching
medium-applicable upto 36kV.

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.

Mccb is moulded case circuit breaker.
ACB is air circuit breaker.
VCB is vacuum circuit breaker.
But Basic Differnce Is

Mccb use for Low value of current(16A,10A..)
Mccb depend upon Number of Pole
ACB USE FOR PROTECTION IN TRANSMISSON OF POWER IN POWER PLANT
VCB USE FOR PROTECTION IN DISTRIBUTION OF POWER IN POWER PLANT

MCB is stand for miniture circuit breaker.It is for low 
voltages.         
MCCB is stand for moulded case circuit breaker. It is for 
medium voltages. 
ACB is stand for Air circuit breaker.It is for high 
voltages.

MCCB: means moulded case circuit breaker which use ark 
quenching device as AIR which is used upto 500 Amps only
ACB:air circuit breaker which use quenching device as air 
and used upto 3000 Amps at 415 volts 
VCB:vaccum circuit breaker which use ark quenching device 
as a vaccum and used for 415 volts.6.6 KV,11 KV,33 KV,132 
KV,220 KV also.

Mccb is moulded case circuit breaker.
ACB is air circuit breaker.
VCB is vacuum circuit breaker.
MCB is stand for miniture circuit breaker.It is for low 
voltages.         
MCCB is stand for moulded case circuit breaker. It is for 
medium voltages. 
ACB is stand for Air circuit breaker.It is for high 
voltages.

MCCB which is nothing but moulded case circuit breaker.
ACB is nothing but Air circuit breaker and Vcb is Vaccum 
circuit breaker..The main difference between last two thing 
is the arc quenching medium.ACB is air and VCB is 
vaccum.these two things are used for power tr and 
distribution and MCB,MCCBs are used in small rating 
machines also...