3. Busbar System Current Ratings Busbar ratings are determined only by the maximum desired working temperature At working temperature: heat generated = heat lost
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
12. for 100 mm vertical height, 30 C ambient Busbar System Current Ratings
13.
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
Welcome to this LE webcast. It discusses the design of busbar systems, including the choice of material, how to size busbars for a particular current rating and how to optimise the lifetime costs.
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