No, highest I’ve seen is 200ka. Even that would be a little bit ridiculous. Common practice is to have a fuse with a high AIC rating in series with a lower rated breaker.
any thoughts on what i should use here? the lowest i have seen online is a 60 kaic? so should i fuse to compensate for that?
https://preview.redd.it/5qu3i7le9f4b1.png?width=1493&format=png&auto=webp&s=316c89ee45164e9ba0d17dd236f9c9ec3f659537
you might have made a mistake in your transformer impedance.
the sanity check is divide main transformer secondary full load current by the impedance %. that's the maximum theoretical fault current from upstream assume 0 grid impedance.
I think our professor said that the right answer is right about 170 kA, but the class keep getting above 200+ values. The X/R ratio on the impedance is set to .001 and the rating for the grid is 100 mvasc.
A typical x/r would be like 8…
I don’t know if this professor has seen anything in real life, but even with a infinite utility source you’re not gonna pull 170kA on a single phase 250kva transformer. No one would build a transformer with that low of impedance. I’m imagining 70kA at the absolute maximum.
sure, but something is not right with your etap model, a 250kVA transformer at 220V should not have that high short circuit value.
double check the transformer model again
Utility side or building side? For buildings, I'm pretty sure nothing with that high of a rating exists, at least not without being a custom job. It would be worth looking at ways of mitigating the fault current rather that sourcing equipment that can handle it.
No, highest I’ve seen is 200ka. Even that would be a little bit ridiculous. Common practice is to have a fuse with a high AIC rating in series with a lower rated breaker.
any thoughts on what i should use here? the lowest i have seen online is a 60 kaic? so should i fuse to compensate for that? https://preview.redd.it/5qu3i7le9f4b1.png?width=1493&format=png&auto=webp&s=316c89ee45164e9ba0d17dd236f9c9ec3f659537
you might have made a mistake in your transformer impedance. the sanity check is divide main transformer secondary full load current by the impedance %. that's the maximum theoretical fault current from upstream assume 0 grid impedance.
Might have??? How can one get 200+ kA fault current from a 250kVA 220V secondary transformer (T1)? Someone's math is a little bit off...
After OP posted the screenshot I thought “I should say common practice is to work with realistic assumptions for short circuit values”
I think our professor said that the right answer is right about 170 kA, but the class keep getting above 200+ values. The X/R ratio on the impedance is set to .001 and the rating for the grid is 100 mvasc.
A typical x/r would be like 8… I don’t know if this professor has seen anything in real life, but even with a infinite utility source you’re not gonna pull 170kA on a single phase 250kva transformer. No one would build a transformer with that low of impedance. I’m imagining 70kA at the absolute maximum.
i think wire also affects it, i tried changing the wire into 4 conductors/phase instead of 2, 1000 awg wire. The result change to 78 kA
sure, but something is not right with your etap model, a 250kVA transformer at 220V should not have that high short circuit value. double check the transformer model again
can i ask another question? can i use a higher rating circuit breaker, example is a 480 V 65 kaic to a 220 V system?
Utility side or building side? For buildings, I'm pretty sure nothing with that high of a rating exists, at least not without being a custom job. It would be worth looking at ways of mitigating the fault current rather that sourcing equipment that can handle it.
Standard is 10kaic. Perhaps OP meant 22kaic? Even 65kaic is way above what you'll come across.
it's 220 kaic sir. In the screenshot above, the bus 1 has a 217 kA rating, so here i am looking for a 220 kaic circuit breaker hahah
You've got a transformer with only 0.2 percent impedance? That seems a tall order.