Bus 1sec fault rating vs IEC 60909-0

[bdfig]

Hi,

I have a bus which has a 25kA/1sec fault rating. Is this normally compared to IEC 60909-0 sub-transient, transient or steady state fault level? Any help is appreciated.

 

[7anoter4]

IEC 60909 it is a method how to calculate the short-circuit currents, indeed, but you have to calculate these currents according to your actual network configuration-involved impedances and source voltages. The bus bar rating you can appreciate according IEC 60865 "Short-circuit currents - Calculation of effects".

 

[bdfig]

My question is for the generators in my network, which impedance (sub-transient, transient or synchronous) is used when trying to establish if the 25kA/1sec fault rated bus is adequately rated.

 

[Kiribanda]

bdfig,
It should always be sutransient to get the maximum symmetrical short circuit current at the location to compare with bus rating.

 

[bdfig]

Hi Kiribanda,

Is there a standard (preferably IEC or AS) which specifies this? I certainly support this approach(especially since the switchboard does not have a shorter time rating). However I have been getting some pushback saying this is overly conservative, and would like something concrete to point to.

 

[ScottyUK]

I think IEC 61439 is likely the place to start. I'm not at work right now so I can't check the exact wording in the standard, however there is some discussion in section 8 of

http://www05.abb.com/global/scot/sc...17e48257a700024a13b/$file/1SDC007110G0201.pdf

which does make note of special conditions close to generators.