Bus Bar Bracing in 480V Switchboard

[CeliaNeil]

Does anyone have a legit chart, spec, anything to go by for bracing bus bars for 150k?

I've looked at UL 891, ABS, IEEE, NEC, nothing except UL 891 calls out specifics on the bus bar bracing, and that is only up to 100k.

I am designing a 480V switchboard to be rated for a fault current of 150k. I've seen UL 891 Supp B in the past for designing boards for requirements of 85k and even 100k, but can't find any spec/documentation that specifies bus bar bracing for over 100k.

 

[ScottyUK]

There's a fairly good theoretical analysis in

http://www.cda.org.uk/megab2/elecapps/pub22/index.htm.

Might be a starting point to determine mechanical forces involved.


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If we learn from our mistakes I'm getting a great education!

 

[CeliaNeil]

This is a great resource, as I have referenced it many times concerning copper bus bars, the joining of, the bolt hole patterns etc. However, once again, the topic of "where to brace" is very vauge. For instance, Ul 891 states for a system to be rated at 100k, the bus should be supported no less than every 21". I just need that statement...to say "to be rated at 150k, the bus should be supported no less than every _____"
Going thru an actual short circuit test to prove the bracing is adequate is not an option at this point as that would be too costly and time consuming.

What I found on the copper bus website:

Maximum stresses

When a busbar system is running normally the interphase forces are normally very small with the static weight of the busbars being the dominant component. Under short-circuit conditions this is very often not the case as the current rises to a peak of some thirty times its normal value, falling after a few cycles to ten times its initial value. These high transitory currents create large mechanical forces not only in the busbars themselves but also in their supporting system. This means that the support insulators and their associated steelwork must be designed to withstand these high loads as well as their normal structural requirements such as wind, ice, seismic and static loads.

 

[desertfox]

Hi CeliaNeil

From the "copper for busbars book" you should be able to get an idea of where to support your busbars from calculation.

http://www.cda.org.uk/frontend/download.htm#d11

Haven't used this link myself so I don't know how good it is.

However my approach to your problem would be :-

1/ Find proof stress of copper at the appropriate
temperature.

2/ Calculate stress and deflection for the short circuit
forces based on beam theory.

3/ Once you know the deflection for a given stress (the
stress being the proof stress divide by a safty factor)
and a given span you can increase or decrease the number
of supports to suit your design.

best regards

desertfox

 

[desertfox]

Hi CeliaNeil

Sorry ignore my link its not relevent to your question however ScottyUK,s link is.

regards

desertfox