Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design Busbar Design

1. Busbar Design Basics

2.  High electrical conductivity
• only silver is better than copper
 Good thermal conductor
• heat reaches surface quickly
 Strong (at working temperature)
•
•
to withstand short circuit stresses
low creep
 Easy to joint
• resistant to corrosion
Materials for Busbar Systems

3. Busbar System Current Ratings
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
Busbar ratings are determined only by the
maximum desired working temperature
At working temperature:
heat generated = heat lost

4. Busbar System Current Ratings
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
Busbar ratings depend on:
• Working and ambient temperatures
• Heat lost from the busbar
– by convection
– by radiation
• Heat generated in the busbar

5. v0.25
7.661.25
Pcv 
Power dissipated by convection is given by:
where
 is the temperature rise above ambient
v is the vertical height of the surface
Busbar System Current Ratings
Pcv1Pcv2
v
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org

6. Power dissipation per metre length v Vertical height
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
0
40
80
120
160
0 50 150 200100
Vertical height (mm)
Powerdissipationpermetrelength(W)Convection (for 80 C temperature rise)
Busbar System Current Ratings

7. Power dissipatedby radiation is given by:
1
4 4
2
8
TP  5.7r  T 10
where
Pr is the power dissipated per square metre
T2 is the working temperature, K
T1 is the ambient temperature, K
 is the emissivity
Busbar System Current Ratings
Pr
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
Pr

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
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
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!
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
Busbar System Current Ratings

10. Busbar System Current Ratings
Pr
Pr
Pr
Pr
Pr Pr
No radiation heat loss
from internal surfaces
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org

11. Radiation power dissipation v Working temperature
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
0
20
40
60
80
100
273 373323
Absolute Working Temperature (K)
Powerdissipation(Wpersqm)
Radiation (for 30 C ambient)
Busbar System Current Ratings

12. 600
500
400
300
200
100
0
700
800
900
for 100 mm vertical height, 30 C ambient
Total power dissipation v Working temperature
1000
40 60 120 14080 100
Working temperature (C)
Powerdissipation(Wpersqm
Convection
Radiation
Total
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
Busbar System Current Ratings

13. P  I 2
R
a
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
P  I 2 l
The power generated by current in the busbar is:
where
 is the resistivity of the material
a is the cross sectional area
l is the length
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.
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
Pi  Pc Pr
Busbar System Current Ratings

15. Calculation method:
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
1
2
3
4
5
6
Select working and ambient temperatures
Assume initial current density of 8 amps/mm2
Find appropriate size in standard range
Calculate heat generated due to current
Calculate heat loss at working temperature
If 4>5, increase size and return to 4
When 4=<5, this is smallest possible size
Minimum size calculation

16. The most economic size gives the lowest
lifetime cost. It is the minimum total cost of
•material
•installation and
•energy costs
over the circuit lifetime.
Higher purchase cost - lower running costs
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
Best economic sizing

17. Best economic sizing
Cost of bar
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
0
5
10
15
0 100 200 300 400 500 600
Cross sectional area (sqmm)
Costofbarpermetre($)

18. Best economic sizing
Cost of losses - 5 years
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
0
10
20
30
0 100 200 300 400 500 600
Cross sectional area (sqmm)
Costoflossesover5years($)

19. Economic Sizing of Busbars
Total cost - 5 years
0
10
20
30
0 100 200 400 500 600300
Cross sectional area (sqmm)
Lifetimecostpermetre($)
Cost of bar
Cost ofloss
Total
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org

20. Busbar calculation software
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org

21. Busbar calculation software
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org

22. Busbar calculation software
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org

23. Further considerations
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
Having calculated the size of the bar, there are
three further considerations:
•
•
voltage drop
skin effect
– increases apparent resistance by reducing
effective area - important for:
 thick busbars
 high frequencies
 harmonics generated by non-linear loads
• short circuit current

24. Summary of Busbar Material Characteristics
Copper Development Association
www.cda .org .ukwww.le ona rdo-e ne rg
y.org
High Conductivity
• low loss, low voltage drop
• >101.5 % IACS
Easy Formability
• due to small grain size and advanced production
technology
• easy to bend without surface deformation
Good Flatness
• simple reliable jointing
Good Straightness
• easy installation, lower joint stress