Monday, April 4, 2016
As per IEC 62271.1, the rated short circuit current has a time constant of 45ms (approximately X/R=14.1 at 50 Hz). If your application requires a higher time constants, you may purchase a breaker designed to operate on short circuit currents with a time constant of 120ms. Thus if you assume that the relay takes 10mS to detect the fault and actuate circuit breaker shunt trip, it will be interrupting more DC current if the time constant is 120mS, while the AC component remains same.
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