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# How to Calculate Heat Dissipation for Busbar

06/26/2013 6:35 AM

hi,

I want to calculate heat dissipation for busbars which is to be used in a electrical enclosure. The details are below.

Busbar size : 2 runs of 80*10 mm copper busbar per phase

Length of busbar : 1000 mm per cubicle of enclosure

no of cubicles : 10

current rating : 2500A

deg : 50 deg C

Can any one help me with calculation? I am from UAE

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#1

### Re: how to calculate Heat Dissipation for Busbar

06/26/2013 6:46 AM
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#2

### Re: how to calculate Heat Dissipation for Busbar

06/26/2013 7:27 AM

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

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#3

### Re: how to calculate Heat Dissipation for Busbar

06/26/2013 7:51 AM

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

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#4

### Re: how to calculate Heat Dissipation for Busbar

06/26/2013 9:02 AM

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.

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#7
In reply to #4

### Re: how to calculate Heat Dissipation for Busbar

06/26/2013 11:58 AM

the calculation will change according to the region. Here in UAE(gulf) the nominal temperature considered is greater than 40 deg it will be much lesser in europe countries. anyway thanks genius!!!

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#5

### Re: how to calculate Heat Dissipation for Busbar

06/26/2013 9:31 AM

I'm so glad to hear that you want to learn how to calculate anything. I think I see that your problem is reading comprehension. You see, when you meticulously entered all of the details of your problem for us to read you failed to read and comprehend the FAQ that is included with every new thread entry. I repeat that FAQ for you again.

Do your own homework. CR4 is not a homework cheat site. While some here might relish the opportunity to sharpen up old rusty skills by working the homework problem, consider the following and consider it well. If you cheat on your homework by using someone else's answers, you are only cheating yourself, because the purpose of any homework or other academic assignments is to help you learn - by practice, repetition, and self-discovery.

Now if you show us some initiative by solving part of any homework problem and explain to us why your baffled by the rest, then I will do my very best to help you. I will not rob you of your education.

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#6
In reply to #5

### Re: how to calculate Heat Dissipation for Busbar

06/26/2013 9:46 AM

Well, that tears it.

Now, I'll never know what color his bus bars were, if they existed at all.

Maybe Carnac the Magnificient can tell me.

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#8
In reply to #5

### Re: how to calculate Heat Dissipation for Busbar

06/26/2013 12:47 PM

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?

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#11
In reply to #8

### Re: how to calculate Heat Dissipation for Busbar

06/26/2013 4:13 PM

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.

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#13
In reply to #8

### Re: how to calculate Heat Dissipation for Busbar

06/27/2013 3:36 AM

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.

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#9

### Re: How to Calculate Heat Dissipation for Busbar

06/26/2013 1:14 PM
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#10

### Re: How to Calculate Heat Dissipation for Busbar

06/26/2013 3:51 PM

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

See #1.

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#12

### Re: How to Calculate Heat Dissipation for Busbar

06/27/2013 3:00 AM

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.

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### Users who posted comments:

7anoter4 (1); Anonymous Poster (1); Fredski (1); lukman2121986 (2); lyn (3); PWSlack (2); redfred (2); SolarEagle (1)

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