Short circuit KVA calculation.

**Tarique Latif Jarwar** · 07-30-2012, 08:28 PM

Hello everyone,
Iam new here and this is my first post. I need help from u guyz.
Correct me if iam wrong,
"If a short circuit occurs on the Bus bar/Feeder the reactors limit the S.C KVA which flows back to the source(alternator).
My question is that the S.C KVA will equally distribute to all the alterantors which are in synchronism to each other or
it will de synchronise the nearest alternator. And what will be the impact on other alternators that are in synchronism".

AWAITING ANY RESPONSE.......

**surgeArrester** · 07-31-2012, 04:08 PM

So, you are implying that there are some alternators/generators that are connected in parallel. And, when short circuit/fault occurs at the bus (to where the alternators are connected) the short circuit KVA is distributed among the alternators that are connected. Is that right?

My opinion: It is true that short circuit current is distributed among the alternators that are connected in the system. Whenever or not they are connected on the same bus or not, still the fault will be distributed. I cannot really say that the source connected nearest to the fault will be isolated first. Few things are needed to be considered: relay settings, time discrimination, alternator sizes, and fault contribution among the sources. You can equally distributed if only the alternators are of same impedances and also connected at the same bus.

I think that you should verify it using short circuit calculations and see the difference prior to making conclusions. And for synchronizing, you can use transient analysis softwares to simulate these.

Hope this helps. You can use simple reactance diagrams to show it.

**Tarique Latif Jarwar** · 08-06-2012, 07:54 AM

Thank you

**etapexpert** · 12-25-2012, 10:43 PM

I agree with surge arrestor. It will contributed back to the source in equal value if the fault accure in immediate board next to the source..
But,
Only the 10% (approx) of the total fault value would be flowing back to the source (as per etap) remaining fault value would be flow to earth through nearby protective conductor.