Bus/Equipment Short Circuit Time Selection

[Power0020]

I am designing a PP MV Auxiliary supply and I wonder how to select the bus short time withstand time? common figures I have seen is 1 s and 3 s.

I don't know what time to chose, noting that the backup relay protective time is much less than 3 seconds and even 1 s is greater than that.

any clue? any reference standard?

 

[7anoter4]

If it is about a switchgear busbar then, I think, IEC 60298 it could be the standard.
See IEC Publication 60298 A.C. metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and Including 52 kV sub-clause 4.7
And
IEC 60694 Common specifications for high-voltage switchgear and controlgear
Sub-clause 4.7
According to this standard “The standard value of rated duration of short circuit is 1 s.”. However, “If it is necessary, a value lower or higher than 1 s may be chosen. The recommended values are 0,5 s, 2 s and 3 s.”