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Percent Impedance

Percent Impedance

Percent Impedance

(OP)
Question on determining maximum short circuit current. Three single phase 100KVA transformers, 2.9% impedance,2.7% impedance and 2.1% impedance, connected 13.2kV to 4.16kV Y-Y. How do you determine the percent impedance for the bank in order to determine the maximum available fault current?

Thanks.

RE: Percent Impedance

For the SCC calcs, I would use the lowest impedance as the impedance of the 3 phase bank. Always consider the likelihood of one or more of the transformers being replaced with a unit of lower impedance.

For exact figures, you would do a short circuit test, like it is done a unit at the factory to determine it %Z.

Rafiq Bulsara
http://www.srengineersct.com

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