standalone_fault calculation

[samundra24]

Hi,
This might be a simple problem but I am having some difficulty. I am trying to design a switchyard for a standalone system, 0.4/11kV. There are three synchronous generators of 16,31.3 & 31.3kVA and a transformer of 85kVA. For the fault calculation, I saw an example which is also for a standalone system where SC MVA is mentioned around 50MVA. My doubt this(SC MVA)is normally found by some upstream transformer or grid..so how did they assumed this value for a "standalone system"? However, With this SC MVA my symmetrical fault current comes to around 2.6kA when faulted at 400V bus, without it comes only around 482A.Which one should I choose. Can you pls clarify?
Thanks in advance

Sam

 

[7anoter4]

The data provided by you is not clear. The 3 generators are on the 0.4 kV side of the transformer and the Switchyard is for 11 kV side, I guess. The generators and the transformer reactance are missing.
However, if the calculation of the short-circuit current followed IEC-60909-0 way then
it is not important how many generators work in this System.
If your system is not located on board ship or aeroplane the calculation has to be correct.
One has to consider near-to-generator short circuit condition.