Short circuits elctromenchanical force on paralle busbars, 2

[Yaling]

Hello, everyone
I am trying to calculate the fiber stress on the paralle busbars,can anyone tell me if I need to calculate the force caused by each individual bus, or I can treat either positive bus or negative bus as one whole thing, thanks indeed.

 

[desertfox]

Hi Yaling

Have a look here:-

http://www.copperinfo.co.uk/busbars/pub22-copper-for-busbars/sec6.htm#Electromagnetic

Stresses

http://www.copperinfo.co.uk/busbars/pub22-copper-for-busbars/homepage.shtml

this should help

desertfox

 

[jghrist]

Interesting question, but I don't have an answer. I guess you'd also have to consider that the current won't be equally distributed among the bus bars. But if this is dc, maybe the current is equally distributed.

 

[Yaling]

Thanks, Desertfox.
I have read througn the articles per above links, and also checked IEEE 608-1998 before posting this. They all talked about two buses.

 

[desertfox]

Hi Yaling

I assume your talking about AC short circit currents and from my understanding when calculating the strength of busbars under short circuit you look for the worst case scenario on the system ie a single phase short circuit.
Now bear in mind also that during a short circuit the currents are out of phase and therefore reach there peak values at different points in time, so you isolate the point in time between a pair of conductors that gives the worst stress case, which will be repeated 50 or 100 times a second throughout the duration of the short circuit depending on frequency.
I copied these statements from the link I gave you:-


In a three-phase system a short-circuit between two phases is almost identical to the single-phase case and although the phase currents are normally displaced by 120°, under short-circuit conditions the phase currents of the two phases are almost 180° out of phase. The effect of the third phase can be neglected


In a balanced three-phase short-circuit, the resultant forces on any one of the three phases is less than in the single-phase case and is dependent on the relative physical positions of the three phases.

In the case of a single-phase short-circuit, the forces produced are unidirectional and are therefore more severe than those due to a three-phase short-circuit, which alternate in direction.

So to answer your question direct I would say can consider each set of busbars as a whole thing
look at the link I gave earlier and scroll down till you come to this figure below it shows several bars as representing one phase:-


Figure 14 - Proximity factor for rectangular copper conductor

desertfox