View source for Talk:Selection of a circuit-breaker/Archive 1

Should include a discussion of the considerations of power factor (or X / R equivalent) of the fault current. Because the short circuit tests are performed with a power factor set by the rule should be noted that if the power factor of the fault is less than the power factor of the test, then you must derate the breaking capacity protection (or edit the value of symmetrical fault current expected) due to the presence of an asymmetric dc component fault current higher than that for the protection assay. 

The current to be compared to the breaking capacity of the IEC is the current protection interrupt Ib (IEC 60909) and this is a current rms compared with symmetrical interrupting capacity of protection. In this way, is not included in the fault current under increasing dc component due to short-circuit power factor less than that specified by the test in IEC 60947-2. 

In the standards of American origin, there are tables that indicate the correction factor symmetrical fault current (ANSI / IEEE Std 242) to be comparable with interrupting ratings BT protections, but the power factor test established by the ANSI C37.13 is different from those established by IEC 60947-2. I do not know if there is equivalent to tables manufactured protections under IEC standards. 

Yours sincerely,
 
Rodrigo Del Canto.
Ingeniero Eléctrico
Valparaíso, Chile.
rodrigo.delcanto@gmail.com