Open Delta Fault Current

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xguard

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There are a few threads concerning fault current of an open-delta transformer. A couple people suggested adding the currents, or a portion of, from each transformer.

Below is the only source I've been able to find. It seems to suggest ignoring the smaller transformer of the two and looking at it as a single phase situation. Does anyone have any other links, references, books, etc they could suggest to backup either approach? Thanks.

http://light.dakotaelectric.com/Handbook/Pages1/Transformer Max Fault Current Values.aspx

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.
 
If the fault is on the secondary output, I see no reason to ignore fault current from a smaller transformer in parallel.
If you have (not realistic) five transformers in parallel, would the fault current be only one fifth of what you would get from a single transformer five times as large?
Now, if you say to use only the larger of the two transformers that make up the open delta (no paralleling), I agree with that. Unlike the case for a closed delta, the other transformer(s) cannot contribute to a single phase fault.
(An earlier thread dealt with an open delta of three transformers, two in parallel on one leg.)
 
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Quote "Now, if you say to use only the larger of the two transformers that make up the open delta (no paralleling)"

That was the OP's question.
 
GoldDigger said:
If the fault is on the secondary output, I see no reason to ignore fault current from a smaller transformer in parallel.
If you have (not realistic) five transformers in parallel, would the fault current be only one fifth of what you would get from a single transformer five times as large?
Now, if you say to use only the larger of the two transformers that make up the open delta (no paralleling), I agree with that. Unlike the case for a closed delta, the other transformer(s) cannot contribute to a single phase fault.
(An earlier thread dealt with an open delta of three transformers, two in parallel on one leg.)
Click to expand...

I agree with the parallel transformers contributing to the fault current. With this thread I was trying to get information on calculating fault current for a typical open delta situation without paralleled transformers. Thanks for the feedback!
 
Short-Crcuit Amps for 3-Phase Open-Delta Connected Transformers

Short-Crcuit Amps for 3-Phase Open-Delta Connected Transformers

XGuard...

The 3-ph, SC-Ampere level on the secondary of an open-delta connection is very dependent on its parameters. For instance using only the %Z you listed yields about 74kA.

Using GE data* transformers with 4.16kV primary windings yield a value of about about 45kA, while those with 13.8kV primaries yield 37.3kA!

* D. Beeman, Industrial Power Systems Handbook!

Regards, Phil Corso (Cepsicon@aol.com)
 
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