Answer Posted / nilesh kumar singh

Selection of Circuit breaker
CURRENT RATING:
Transformer Rating (X)kVA
%age impedance of transformer - Z%
I Full load = X*1000/Sq. root 3*VL
Where X = Transformer rating in kVA
VL = Line Voltage
BREAKING CAPACITY:
Breaking Capacity of the breaker> I Fault Current

Fault Current (Level) = 1.1*VL/Sq. root 3*Z
Where Z = Impedance of Transformer
VL = Line Voltage

Z= %Z*10*(kV)*(kV)/KVA
MAKING CAPACITY:
Making Capacity depends upon the following:
a) Power Factor
b) Instant of switching ratio 'n' between required rate s/c
making capacity and rated s/c breaking capacity.

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