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# What is the theoretical maximum symmetrical fault current?

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## What is the theoretical maximum symmetrical fault current?

What is the theoretical maximum symmetrical fault current that would be available at the secondary terminals of a 3-phase 12,470-480Y/277V, 1000kva, 6.25% impedance transformer?

2. Fault Current = Full Load Amps (FLA) / % Impedance (Z)
FLA = VA / L-L Voltage x 1.732

Here is a thread that explains the equations step by step -> http://testguy.net/threads/1341-Easy...-fault-current

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## Short-circuit

Here the information:
12,470-480Y/277V
1000kVA, 6.25% impedance

another way:

For a impedance of 6.25%, your necessary voltage will be 6.25% of 480 Volts = 30 Volts
What that means:
With secondary shorted, if you apply 30 Volts, you will have full transformer current, which is:
(remeber to multiply by 1000 (KVA to VA conversion)
I = 1202.85 A
from here you calculate your transformer Impedance
Z = V/I......Z = 30/1202.85.......Z = 0.025 Ohms.
I = V/Z.......I = 480/0.025 = 19200 A

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Thanks for the help.

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Originally Posted by joaogemal
Here the information:
12,470-480Y/277V
1000kVA, 6.25% impedance

another way:

For a impedance of 6.25%, your necessary voltage will be 6.25% of 480 Volts = 30 Volts
What that means:
With secondary shorted, if you apply 30 Volts, you will have full transformer current, which is:
(remeber to multiply by 1000 (KVA to VA conversion)
I = 1202.85 A
from here you calculate your transformer Impedance
Z = V/I......Z = 30/1202.85.......Z = 0.025 Ohms.
I = V/Z.......I = 480/0.025 = 19200 A
The link that Second Gen posted doesn't state anything about the additional steps you took dealing with the impedance.

Can anyone confirm?

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## Motor winding Results

Winding test results on a motor indicate possible degradation when the output waveforms show:
Winding waveform symmetry
Noticeable difference in winding waveforms
Chopped waveforms on grounded windings
Chopped waveforms on phase ungrounded windings

Having trouble getting an answer for this.

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