What is the most severe transient symmetrical fault that can occur; L-L-L, L-L-L-N-G or  L-L-L-N?

a) calculate them all;
b) compare the results;
c) convince yourself that they are all the same.

Cheers

My favorite answer, "It depends."

Mr. Lima is correct. His answers "A" and "B" are the best way to proceed.

I realize this sounds harsh. But the process itself will be educational. Determine the impedances and calculate it for yourself. Just looking at the answers alone is likely to lead you to misunderstandings.

i think LLL is most severe as in other faults we are providing a path for fault current to flow through neutral to ground,,but in LLL fault current still persist in system and can damage the equipements severely..

Yes, the 3ph. has specific characteristics.
The L-G and L-L do as well.
Each one will sometimes be the largest depending on both the system and WHERE the fault occurrs on it. Which is why I said "It Depends".

Each is an important value worthy of investigation. This is why short circuit studies routinely calculate all three.

In my education there was no mention of several important fault related things. Such as X/R, Momentary, Interrupting, Assymetrical... or how and why they matter. There are many facits to the topic.

I think it's same, because the equivalent circuit is same

Pardon me please, but I must disagree.
Look up sequence diagrams and you'll see they most certainly are not the same.

Each fault condition is modeled differently. Some times the results will be similar.
Sometimes they will not. It depends on other factors.

I just found a sequence diagram via a simple google search. But all textbooks will show them. It's an fundamental concept.

Dear Musonda:
The more several "transient" in Shorted Circuits is L-L-L-G, usually, but our Colleagues have reason, is nessary to calculate.
I remember of one condisciple during one Technical Visit, said "I want to see a Three Phase Short to Ground", sure drinked very much.
Regard
William