Tolerance for rated short time withstand current in MV switchgears

[Jpascp]

I was checking IEC 62271-200 and I did not find anything about short circuit tolerances.

For example SIEMENS MV Switchgear 8DA10 (40,5 kV/2500 A) model has 40 kA (3 sec).

For some project we get IK3"= 40,66 kA.

What is your experience about it?

 

[dpc]

I don't know about IEC, but for the ANSI standards, there's no tolerance. The maximum is the maximum. From a practical viewpoint, you have to take into account the accuracy of your short circuit calculation. There are generally impedances that are neglected in most calculations, such as impedance in breakers, terminations, etc that can tend to reduce the actual fault current slightly. You might be able to sharpen your pencil and come up with a slightly lower worst-case calculation.

But if you are the responsible engineer, then you probably can't just say that it's so close, I'm sure it is fine.

 

[waross]

I have been there a couple of times with low voltage installation, 208 V to 600 V.
When the ASCC of a transformer was a little too high for the switchgear, I then factored in the impedance of the conductors from the transformer to the switchgear.
That gave me a documented, acceptable, value.