Answer / wareagle

You have not given the required information to answer your
question. Voltage? power Factor? Type Load? Fault current?

Answer / karthik ccel

If i consider your 644kW load as a motor then,

I Assumed some parameters are:
644kW Motor, Power Factor - 0.9, Efficiency - 0.9, Load
Connected Voltage - 415V Then,


I = (644*1000) / (1.732*415*0.9*0.9) = 1106Amps
Considering 20% Margin = 1106 * 1.20 = 1327Amps

Conclusion:
So, We can choose Breaker rating is higher than that
1327Amps. Generally no one use the MCCB breaker above
800Amps. So, we can prefer the 1600Amps VCB Breaker for that
644kW Load.

Answer / antaratara ghosh

assuming the load as motor,operating voltage as 415 V,pf
as .85, efficiency as .95,

rated current, Ir= (644)/(1.732*0.415*0.85*0.95)
= 1110 A (approx)
now considering VFD starting for the motor,
starting current, Ist= 2*Ir
= 2220 A
considering margin of 20%, maximum current flowing =
2220*1.2 = 2664 A

Since MCCB are not used above 630 A in India, you have to
go for 3150 A (which is just greater than 2664 A and
available in market) ACB...

Answer / lokeshraj

Use 1600 Amp ACB.

Answer / ahmed raza

Formulla for calculation of breaker is...
Total load in Watts/380(voltage)*0.8(pf)*1.732(delta to Y
conversion)
So
= 644/380*0.8*1.732
= 1223.10
we can say
= 1250AMPs breaker should be use....

Answer / sami

Calculate 644kw load Amp
Breaker Selection Formula ( Amp*125% )
for Example : 1000A*125%=1250
Instal 1250Amp Breaker

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