Fault Current Calculation for Open Delta

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Mark M

New member
Location
Seattle, WA, USA
I am hoping somebody can share the equations for how to calculate fault current through the (2) transformers in an open delta. I have 26,000 AIC at the primary of the transformers which are 25kVA and 75kVA. I have an open delta with B phase Hi-Leg.

As a follow up is there a way to calc this with something similar to the infinite bus method?
 
P

Phil Corso

Senior Member
Location
Boca Raton, Fl, USA
Mark M said:
I am hoping somebody can share the equations for how to calculate fault current through the (2) transformers in an open-delta. I have 26,000 AIC at the primary of the transformers which are 25kVA and 75kVA. I have an open delta with B phase Hi-Leg.

As a follow up is there a way to calc this with something similar to the infinite bus method?
Click to expand...

Mark...

Contact me if you would like a one-page Excel calc covering 2 and 3-transformer configurations. All that is needed is Xfmr kVA and %Imp of each Xfmr. If greater accuracy is required then include X/R ratio!

Regards, Phil Corso
 
T

topgone

Senior Member
"For situations such as mixed banks and open delta banks, use the 3-phase transformer size
equal to 3 of the largest single phase transformers present for the maximum available short
circuit."
LINK
 
Julius Right

Julius Right

Senior Member
Occupation
Electrical Engineer Power Station Physical Design Retired
topgone said:
"For situations such as mixed banks and open delta banks, use the 3-phase transformer size
equal to 3 of the largest single phase transformers present for the maximum available short
circuit."
LINK
Click to expand...

In my opinion instead of 3 times has to be only sqrt(3) times the largest single phase transformer.
 
T

topgone

Senior Member
Julius Right said:
In my opinion instead of 3 times has to be only sqrt(3) times the largest single phase transformer.
Click to expand...

The internet is full of info that needs to be digested to be useful to us. Take this webpage for example which says:
Notes and Additional Information:
V-Phase (Open Wye-Open Delta) services have maximum fault currents equal to or less than single-phase services with the same transformer size and voltage. Use the single-phase table and the larger of the two transformers to identify the maximum secondary fault current.
Click to expand...
It's even lower than your suggestion of 1.732 times the largest phase transformer!
 
W

wsbeih

Member
Location
USA
Phil Corso said:
Mark...

Contact me if you would like a one-page Excel calc covering 2 and 3-transformer configurations. All that is needed is Xfmr kVA and %Imp of each Xfmr. If greater accuracy is required then include X/R ratio!

Regards, Phil Corso
Click to expand...

May I have a copy please?
 
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