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Start by
Musonda Kawele
11-08-2013 08:26 PM

What is the most severe transient symmetrical fault

What is the most severe transient symmetrical fault that can occur; L-L-L, L-L-L-N-G or  L-L-L-N?
11-08-2013 11:03 PM
Top #2
Leonardo Lima
11-08-2013 11:03 PM
a) calculate them all;
b) compare the results;
c) convince yourself that they are all the same.

11-09-2013 01:17 AM
Top #3
Bill Swingle, P.E.
11-09-2013 01:17 AM
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.
11-09-2013 03:33 AM
Top #4
ishan mehrotra
11-09-2013 03:33 AM
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..
11-09-2013 06:24 AM
Top #5
Bill Swingle, P.E.
11-09-2013 06:24 AM
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.
11-09-2013 08:33 AM
Top #6
Rizky Rahmani
11-09-2013 08:33 AM
I think it's same, because the equivalent circuit is same
11-09-2013 10:54 AM
Top #7
Bill Swingle, P.E.
11-09-2013 10:54 AM
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.
11-09-2013 01:35 PM
Top #8
William Chaparro
11-09-2013 01:35 PM
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.
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