Your answer was " Yes. Three-phase fault calculation for each source " ; to what Mr. PKJENNY 22 May 20 18:17 question asked was " ... what I mean is phase to phase short circuit of the 2 different sources at the ..."
I am of the opinion that there is an "over look "? . The key words are " [phase to phase short circuit of the 2 different sources]* ".
We look forward to your learned advice based on the above key words *.
Che Kuan Yau (Singapore)
I actually didn't overlook anything. Equipment ratings for three-phase equipment is generally based on three-phase faults. I understand also that there are two different sources - that is the purpose of an automatic transfer switch.
A. "I actually didn't overlook anything...."
Q. Please tell us your learned advice with the situation when the ATS failed. With a dead-short between the same phase, but at worst condition when they are out of phase.
Take the following into consideration:
1. An ATS CAN fail even equipped with [mechanical and electrical inter-locks].
2. It can be assumed that the two separate independent sources [phase-sequence] must had been phased out, during the initial commissioning.
3. However, the two [separate independent] sources can be or are running at slightly different frequencies, voltages, though at same phase-sequence but may NOT be in synchronism.
Che Kuan Yau (Singapore)
That's why i'm not sure how a fault scenario analysis can be done for this kind of fault, and wonder how normal it's being done, and want some advice here from any expert.
The calculation will depend on the purpose of the analysis. You haven't told us that. The ATS has a fault withstand rating based on current through the ATS. This assumes the current is coming from one source or the other. So just take the worst case if you are interested in determining if the ATS has an adequate short circuit rating. Even if both sources are energized, the fault current through the ATS will be coming from one source or the other, not both.
If the fault is INTERNAL to the ATS, AND both sources are energized, then the fault current will be the sum of the two sources, assuming they are in sync. But what is the purpose of this calculation? Perhaps an arc-flash calculation for the ATS if you assume both sources will contribute to the fault. If the two sources are not in synch, then the calculation is much more difficult and depends on your assumption about relative phase angles.
