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Calculate %Z autotransformers in open delta?
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Author:  haze10 [ Tue May 05, 2015 7:44 am ]
Post subject:  Calculate %Z autotransformers in open delta?

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

Author:  haze10 [ Tue May 05, 2015 9:41 am ]
Post subject:  Re: Calculate %Z autotransformers in open delta?

Correction:
Equivalent KVA = (75+75) x2 x.86 = 258KVA

Author:  engrick [ Mon May 11, 2015 10:02 am ]
Post subject:  Re: Calculate %Z autotransformers in open delta?

check out:
http://forums.mikeholt.com/showthread.php?t=126891

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