Collective Bus AIC rating

[dannyrzk]

Good morning, I'm designing for a decision making switch gear where two transformers rated for 55KAIC each will tie up together in the bus. How do you calculated the combine AIC rate of each transformer in the switch-gear bus?
Is it still only 55AIC or does it add up?
Thank you

 

[charlie b]

If you put two transformers in parallel, their secondary impedances will be essentially a pair of identical resistors in parallel. The net resistance is half of the individual transformer resistance. The fault current will therefore double.

 

[dannyrzk]

If you put two transformers in parallel, their secondary impedances will be essentially a pair of identical resistors in parallel. The net resistance is half of the individual transformer resistance. The fault current will therefore double.

charlie, brilliant and easy to understand. I know the gears will be more costly, but that's what I will have to do.

Thank you

 

[ron]

If you put two transformers in parallel, their secondary impedances will be essentially a pair of identical resistors in parallel. The net resistance is half of the individual transformer resistance. The fault current will therefore double.

Agreed, if both sources can contribute in parallel, add the short circuit current.

If the main - tie- main transition with be a break before make (open transition), then you can consider the higher of the two fault currents of the sources, and that's it.

 

[dannyrzk]

Agreed, if both sources can contribute in parallel, add the short circuit current.

If the main - tie- main transition with be a break before make (open transition), then you can consider the higher of the two fault currents of the sources, and that's it.

my biggest problem here, is that I also have Cogen added to that bus, and I can't divide their contribution. otherwise the open transition sound like a tremendous idea.

Thanks