2 transformers Z

[chris kennedy]

I have 2 100kVa transformers I’m doing available fault current calc for.
240V delta system
I know I add the kVa’a together and I also need to add the Z’s together also correct?

Thanks

 

[chris kennedy]

Apparently the Z’ are not added together.

 

[jim dungar]

I have 2 100kVa transformers I’m doing available fault current calc for.
240V delta system
I know I add the kVa’a together and I also need to add the Z’s together also correct?

Thanks

You do not simply add the kVA of the two single phase transformers when they are connected in a three phase open delta configuration.
When the individual transformers are the same size, you take 86.6% of the sum of the two which is equal to taking 57.7% of the total of a closed delta.

I believe the impedance are simply added together (I am too lazy to look it up).

 

[LarryFine]

Are you talking about two 1ph units in open delta a la Jim's response, or two separate 3ph units?

And, if two 3ph units, are they each separately fed in parallel, or in a step-up/step-down setup?

 

[chris kennedy]

I’m sorry
2 single phase units wired 240V open delta.

 

[LarryFine]

I’m sorry
2 single phase units wired 240V open delta.

Then I would think you'd treat each one individually, as independent loads.

Or are you asking about the impedance of the secondaries as a 3ph source?

If so, then my instincts say that the higher impedance is the limiting factor.