Busbar design involves selecting materials with high electrical conductivity like copper or aluminum. The current rating of busbars depends on factors like working temperature, ambient temperature, heat dissipation via convection and radiation. Busbar size is calculated iteratively to ensure the heat generated by current equals the heat lost to the environment. The most economic size minimizes total material, installation and energy costs over the busbar's lifetime.

1. Busbar Design Basics

3. Busbar System Current Ratings Busbar ratings are determined only by the maximum desired working temperature At working temperature: heat generated = heat lost

6. Convection (for 80 C temperature rise) Busbar System Current Ratings

8. The emissivity,  , describes how effectively the surface radiates heat For a perfectly polished surface, the value is close to zero - a very poor radiator For a matt black surface, the value is close to 1 - a very good radiator Busbar System Current Ratings

9. Bright copper has an emissivity of about 0.1 During use, the emissivity of the copper surface increases - and the current rating increases - as the copper darkens to reach an emissivity value of about 0.7 Tin plated copper has an emissivity of about 0.3 to 0.5 But painting bars reduces the current rating! Busbar System Current Ratings

10. Busbar System Current Ratings No radiation heat loss from internal surfaces P r P r P r P r P r P r

11. Radiation (for 30 C ambient) Busbar System Current Ratings

12. for 100 mm vertical height, 30 C ambient Busbar System Current Ratings

14. At some temperature, the heat generated in the busbar is equal to the total heat lost by convection and radiation. Busbar System Current Ratings

15. Calculation method: 1 Select working and ambient temperatures 2 Assume initial current density of 8 amps/mm 2 3 Find appropriate size in standard range 4 Calculate heat generated due to current 5 Calculate heat loss at working temperature 6 If 4>5, increase size and return to 4 When 4=<5, this is smallest possible size Minimum size calculation

17. Best economic sizing

18. Best economic sizing

19. Economic Sizing of Busbars

20. Busbar calculation software

21. Busbar calculation software

22. Busbar calculation software