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 Post subject: Calculate %Z autotransformers in open delta?Posted: Tue May 05, 2015 7:44 am
 Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 510
Location: New England
I have two single phase 480V-120V 75KVA 5.0% Impedance transformers, 625A secondary.
They are connected as boosting autotransformers in open delta, 480V primary, 600V secondary.

I need to calculate fault current on the secondary.
The equivalent transformer capacity would be 625A x 600V x1.73 = 469KVA

But I'm not sure how to calculate the equivalent impedance.

Any direction to reference material or a mathematical method is appreciated. I am not in a position to physically measure impedance by shorting the secondaries and varying input voltage.

gary

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 Post subject: Re: Calculate %Z autotransformers in open delta?Posted: Tue May 05, 2015 9:41 am
 Arc Level

Joined: Thu Jan 10, 2008 8:49 pm
Posts: 510
Location: New England
Correction:
Equivalent KVA = (75+75) x2 x.86 = 258KVA

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 Post subject: Re: Calculate %Z autotransformers in open delta?Posted: Mon May 11, 2015 10:02 am
 Sparks Level

Joined: Fri Apr 15, 2011 7:43 am
Posts: 178