Busbar Design Basics David Chapman Copper Development Association
[email protected]
Copper Development Association
Materials for Busbar Systems
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 Copper Development Association
Busbar System Current Ratings
Busbar ratings are determined only by the maximum desired working temperature
At working temperature: heat generated = heat lost
Copper Development Association
Busbar System Current Ratings Busbar ratings depend on: • Working and ambient temperatures temperatu res • Heat lost from the busbar – by convection – by radiation • Heat generated in the busbar
Copper Development Association
Busbar System Current Ratings Power dissipated by convection is given by: 1.25
P cv
7.66 θ =
v
0.25
Pcv2
Pcv1
v
where θ is the temperature rise above ambient v is the vertical height of the surface
Copper Development Association
Busbar System Current Ratings Convection (for 80 C temperature rise) Power dissipation per metre length v Vertical height 160 ) W ( h t g n e 120 l e r t e m r e p 80 n o i t a p i s s i d 40 r e w o P 0 0
50
100
150
200
Vertical height (mm)
Copper Development Association
Busbar System Current Ratings Power dissipated by radiation is given by: Pr
P r
=
5.7ε
4 4 T 2 − T 1
× 10
−8
Pr
where Pr is the power dissipated per square metre T2 is the working temperature, K T1 is the ambient temperature, K ε is the emissivity Copper Development Association
Busbar System Current Ratings
The emissivity, ε, 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
Busbar System Current Ratings 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
Busbar System Current Ratings Pr
Pr
Pr
Pr
Pr
Pr
No radiation heat loss from internal surfaces
Copper Development Association
Busbar System Current Ratings Radiation (for 30 C ambient) Radiation power dissipation v Working temperature 100
) 80 m q s r e p 60 W ( n o i t a p i s 40 s i d r e w o P 20
0 273
323
3 73
Absolute Working Temperature (K)
Copper Development Association
Busbar System Current Ratings for 100 mm vertical height, 30 C ambient Total power dissipation dissipation v Working temperature
1000
q s r e p W ( n o i t a p i s s i d r e w o P
900
Convection
800
Radiation
700
Total
600 500 400 300 200 100 0 40
60
80
100
120
140
Working temperature (C)
Copper Development Association
Busbar System Current Ratings The power generated by current in the busbar is: 2
P = I R
P = I
2
ρ l a
where ρ is the resistivity of the material a is the cross sectional area l
is the length Copper Development Association
Busbar System Current Ratings
At some temperature, the heat generated in the busbar is equal to the total heat lost by convection and radiation.
P i
=
[ P c ] + [ P r ]
Copper Development Association
Minimum size calculation Calculation method: 1
Select working and ambient temperatures
2
Assume initial current density of 8 amps/mm2
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=101.5 % IACS
Easy Formability • due to to small small grain grain siz size e and and advanc advanced ed produ productio ction n technology • easy easy to bend bend withou withoutt surface surface deform deformatio ation n
Good Flatness • simple reliable jointing
Good Straightness • easy installation, lower joint stress Copper Development Association
David Chapman Copper Development Association
[email protected]
Copper Development Association
