short circuit
short circuit
(OP)
I've got myself confused. I've got a utility with 3phase Isc=68.1MVA X/R=3.80218 going to a 3000kVA, 13.8kv/480V, 3phase, z=5.69%. Am I to calculate asymmetrical or symmetrical for sc?
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RE: short circuit
RE: short circuit
The ANSI Standards has established Multiplying Factors for the calculated symmetrical fault currents. For MF applied to HV circuit breakers you may refer to ANSI/IEEE C37.010-1979 and for LV circuit breakers ANSI/IEEE C37.13-1990.
Bear in mind that PCBs are tested with X/R ratios specified by industry standard with a given symmetrical fault current and breaker contact parting time...then this establishes the allowed asymmetrical S.C. current the breaker is allowed to interrupt. The actual calculated X/R ratio is too high, then the asymmetrical fault current may exceed the PCB interrupting capability.
You may also want to check out IEEE Std. 141-1993 pages 129 up to 138 (Red Book).
You may also want ot check out the latest revision of the ANSI Std C37.04 and ANSI Std C37.09 (for HV PCBs)using the %Idc in establishing the PCB interrupting current at a specified contact parting time.
RE: short circuit
RE: short circuit
Mike
RE: short circuit
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