How to calculate the breaking capacity(like 15ka,20ka) of
Circuit breaker (MCB,MCCB,ACB)
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Answer Posted / t s gupta
Breaking Capacity of MCCB is pre-calculated permissible amount of fault current (value of current can flow from contacts before opening/tripping the MCCB without damaging) which may facilitate the safe operation of MCCB and distribution transformer both.
It shall be calculated/derived from the distribution Transformer MVA rating and %impedance = kVA*100/ system voltage of load side * % Impedance rating
e.g. 20 kVA transformer with 5% Impedance, secondary voltage 440V i.e. 0.440 kV
Fault current Isc = 20*100/.440*5 = 10kA approx.
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