What are the dimensions of the bar? If "200*10*3" refers to the physical size, what is your unit of measurement? When that is known, the resistance of the bar can be calculated using resistivity * length/(height * width).
Assuming your dimensions are in centimeters and current is in the direction of the longest dimension, then (at 50°C (323 K), the resistivity is about 20 nΩ-m), the resistance is 2*10-8 Ω-m* 2 m/(0.10 m * 0.03 m) = 13 µΩ. Note: there is a chart of copper resistivity vs. temperature at http://hypertextbook.com/facts/2004/BridgetRitter.shtml
The power dissipated at 5000 A is then I2R = 333 Watts.
Do you need to know the thermal resistance from the bar to the ambient environment? That's more difficult - it depends on how the bar is mounted, whether it has convective or forced airflow over it or is in an unvented enclosure, etc. You can find a tutorial, Introduction to Thermal Management, at http://www.wakefield.com/pdf/thermal_tutorial.pdf. It's written for semiconductor users, but some of the basic considerations for removing waste heat may apply to your case.
The <...thermal resistance from the bar to the ambient environment...> only influences the temperature of the <...bar...>, and not the actual <...Heat dissipation...>.
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Heat dessipation calculation of copper busbar
Re: Heat dessipation calculation of copper busbar
