How to Calculate Heat Dissipation for Busbar

http://cr4.globalspec.com/search/sitesearch?do=show&order=asc&sort=textmatchrank&srch=Busbar%20sizing

Duplicate post.

Why the protocol for doing that is not already in the facility's Design Manual is abstruse.

even after you crunch the numbers you'll have to prove your numbers with a lab test to verify them. I'd suggest setting up your test before cruising forums looking for others to calculate your numbers, but that's just me

What color are your bus bars?

Is there a picture of them in your text book?

The calculations will be the same regardless of your country of origin.

R = ρL/A

W = I*I*R
wat i found difficult is, the Power dissipation varies if i consider the whole busbar used i.e 2 runs of 80*10 mm for each phase.my calculation is

Lenght of copper = 10 meters(horizontal running busbar) * 3(no of phase) = 30 meters

so watts= ((2500)*(2500)*17.2*E-9*30) / 2*80*10*E-6) = 2015.6 W

but if i consider 2 runs of busbar as my whole length then the calculation will be

Lenght of copper = 10 meters(horizontal running busbar) * 2(runs)* 3(no of phase) = 60 meters

so watts= ((2500)*(2500)*17.2*E-9*60) / 2*80*10*E-6 = 4031 W

my query is, do i have to consider both runs of busbar as my total length?

Now we're getting somewhere.

I see that you used the resistivity of annealed copper. I am a little surprised that you didn't compensate for your 30° warmer temperature. If you include this change you'll find that annealed copper at 50°C will have a resistivity of 19.2E-9 (Ω*m). I also see that part of your problem here is that the question is slightly ambiguous. It is not clear if your current value is the current per phase (1/2 current per bus bar) or per bus bar. I would answer the question by stating the assumption of assuming this to be per bus bar on the grounds that this will be a worst case scenario. Next calculate the resistance of a bus bar and note in the answer the possible problem of contact resistance. Now you have to be careful with unit sizes here. All dimensions must be in the correct dimension for proper calculation. Your cross sectional area should be in square meters.

I see that you correctly calculated the wattage using a bad resistance value for the bus bar (Thermal variance). When I calculate full current through each one meter long bus bar I get 150 watts for each bus bar. Now if the current is evenly shared across two bus bars then it is only about 37.5 watts per bus bar.

The number of phases in this exercise should only affect the number of bus bars needed for a final total power calculation. I also do not understand what the number of cubicles has to do with this. Presumably it will also change the number of buss bars in this exercise but this needs to be clarified better.

Something is wrong, then. Maybe it has something to do with not splitting the current between the bars in the 2 runs scenario versus the first.

Have another go.

This might help....

http://www.copperinfo.co.uk/busbars/pub22-copper-for-busbars/sec3.htm

Never mind. I re-read the OP so I know the color.

See #1.

SolarEagle recommendation is very good. Still you have to know more a little about busbar geometry: the distance between parallel bar of the same phase and the distance between phases. In this case you may state the skin effect[more or less 1.15] and proximity effect [more or less 1.05].Then you may calculate one bar resistance R[20dgr.C]=1/58*1/(80*10)*1.15*1.04 and I recommend 105 dgr.C as final busbar temperature then you have to multiply by (234.5+105)/(234.5+20)=1.33 .

Then R[105dgr.C]=1/58*1/(80*10)*1.15*1.04*1.33= 3.428E-05 ohm.

Let's say the phase current will split equally in the two bars then I=2500/2=1250 A/per one bar. Losses=1250^2* 3.428E-05 ohm=53.56 w/one bar. For 2*3=6 bars the losses=6*53.56= 321.36 w. However, there are other losses-as contact losses, outgoing busbar or cables and other. The compartment [situated] beneath could introduce other losses.

If the busbar is closed in a non-ventilated compartment another temperature drop of 5-10 it has to be added to the ambient.

The ABB Switchgear Manual [ed.11] Table 13-4 "Current-carrying capacity of copper conductors [DIN 43671]" could asist you to evaluate the ampacity.