Answer Posted / dipak

Here I want to add to Pratik answer. During fault, say on EHV line, line protection sense the fault and gives trip command to CB. The time involved from detection of fault to opening of CB(including response time of trip relay and CB opening mechanism) is about 30 to 40 msec. By this time, Sub transient and DC component of fault current get damped and CB actually get open in transient component of fault current.
However, during closing of CB, if fault is there on line(say dead fault), CB has to sustain Sub transient fault current during closing on dead fault. Hence, making capacity is always more than breaking capacity.
Also, CB is designed for considering its application as Generator CB because fault level is highest at generator terminal and therefore higher making and Breaking capacity is required for Generator CB.

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