Arc flash Calcs - two open delta transformers, different ratings and impedences

[wsbeih]

I need perform arc flash study using SKM. I need to model utility two single phase Delta-Delta transformers; one transformer has 75kVA, Z=1.3%, and the other has 50kVA, Z=1.2%.
These two single phase transformers are configured as open delta configuration to take 3 phase 13.2kV LL and step it down into delta secondary 240/120V
as shown in the

I'm working with SKM to calculate Arc flash IE's on the buses fed off these utility transformers. I need to model everything as 3 phase.

I plan to have two cases;
1- MAX SC - Model a 3-phase (Delta-Delta) 75kVA transformer with its open delta rating of 43.3kva (75x57.7%) and Z=1.3%, with 10% tolerance.
2- MIN SC - Model a 3-phase (Delta-Delta) 50kVA transformer with its open delta rating of 28.9.3kva (50x57.7%) and Z=1.2%, with 10% tolerance.

Am I on the right track to end up with conservative Arc flash results? Any other suggestion? Thanks in advance for your help.

 

[dionysius]

You need to post the calcs so we can review them.

 

[wsbeih]

You need to post the calcs so we can review them.

I haven't ran the study yet. I am looking for guidance on modeling the utility transformers before running the study.

 

[jim dungar]

I haven't ran the study yet. I am looking for guidance on modeling the utility transformers before running the study.

Go with your original post.

There not much reason not to try your assumptions by running the AF module in SKM. You likely don't need the entire model just to test ideas.