NSW Annual Seminar
and Exhibition
Metals for
Busbars
Alex Gouch
Technical Manager
Austral Wright Metals
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Metals for Busbars
• Why copper ?
• Copper conductor metallurgy
• The proof of the pudding
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Copper for Busbars
Why copper ?
– Aluminium is much cheaper
– Overhead conductors are now mostly aluminium
– Copper has
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Better electrical properties
Better mechanical properties
Better thermal properties
Better corrosion resistance
Better ease of fabrication
Uses smaller cabinets
Reliable, long lasting connections
– Copper busbars give a more reliable result
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Electrical Properties & Price
Copper
C11000
Aluminium
AA1350
Units
Electrical conductivity (annealed)
101
61
% IACS
Electrical resistivity (annealed)
1.72
2.83
µΩ cm
Temperature coefficient of resistance (annealed)
0.0039
0.004
/° C
Thermal conductivity at 20° C
397
230
W/mK
Coefficient of expansion
17 x 10-6
23 x 10-6
/° C
Tensile strength (annealed)
200 - 250
50 - 60
N/mm²
Tensile strength (half-hard)
260 - 300
85 - 100
N/mm²
0.2% proof stress (annealed)
50 - 55
20 - 30
N/mm²
0.2% proof stress (half-hard)
170 - 200
60 - 65
N/mm²
Elastic modulus
116 - 130
70
kN/mm²
Specific heat
385
900
J/kg K
Density
8.91
2.70
g/cm³
Melting point
1083
660
°C
1 N/mm2 = 1MPa
At the same DC resistance the weight of an aluminium
conductor is about half that of a copper conductor.
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Mechanical Properties
Copper
C11000
Aluminium
AA1350
Units
Electrical conductivity (annealed)
101
61
% IACS
Electrical resistivity (annealed)
1.72
2.83
µΩ cm
Temperature coefficient of resistance (annealed)
0.0039
0.004
/° C
Thermal conductivity at 20° C
397
230
W/mK
Coefficient of expansion
17 x 10-6
23 x 10-6
/° C
Tensile strength (annealed)
200 - 250
50 - 60
N/mm²
Tensile strength (half-hard)
260 - 300
85 - 100
N/mm²
0.2% proof stress (annealed)
50 - 55
20 - 30
N/mm²
0.2% proof stress (half-hard)
170 - 200
60 - 65
N/mm²
Elastic modulus
116 - 130
70
kN/mm²
Specific heat
385
900
J/kg K
Density
8.91
2.70
g/cm³
Melting point
1083
660
°C
1 N/mm2 = 1MPa
Copper more robust
Copper much easier to handle in the workshop
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Mechanical Properties
Creep
Material
Aluminium
(1080) annealed
HC Cu annealed
Testing
Temp. °C
Min. Creep Rate %
per 1000 h
Stress
MPa
20
0.022
26
150
0.022
26
Copper is much less likely to fail
at bolted connections by creep
or stress relaxation.
Copper more tolerant of higher
operating/fault temperatures.
Fatigue
Fatigue strength
N/mm²
No. of cycles x
106
annealed
20
50
half-hard (H8)
45
50
annealed
62
300
half-hard
115
300
Material
HC Aluminium
HC Copper
Copper better able to withstand
repeated mechanical stresses.
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Thermal Properties
Copper
C11000
Aluminium
AA1350
Units
Electrical conductivity (annealed)
101
61
% IACS
Electrical resistivity (annealed)
1.72
2.83
µΩ cm
Temperature coefficient of resistance (annealed)
0.0039
0.004
/° C
Thermal conductivity at 20° C
397
230
W/mK
Coefficient of expansion
17 x 10-6
23 x 10-6
/° C
Tensile strength (annealed)
200 - 250
50 - 60
N/mm²
Tensile strength (half-hard)
260 - 300
85 - 100
N/mm²
0.2% proof stress (annealed)
50 - 55
20 - 30
N/mm²
0.2% proof stress (half-hard)
170 - 200
60 - 65
N/mm²
Elastic modulus
116 - 130
70
kN/mm²
Specific heat
385
900
J/kg K
Density
8.91
2.70
g/cm³
Melting point
1083
660
°C
1 N/mm2 = 1MPa
Copper less liable to hot spots.
Copper needs less support.
Copper less prone to thermal fatigue failure.
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Thermal Properties
Self-extinguishing arcs in copper and aluminium busbars
Copper
Aluminium
Minimum busbar spacing, mm
50
100
Maximum current per busbar, A
4,500
3,220
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Contact Properties
• Copper has better corrosion resistance.
• Copper corrosion products are more conductive.
• Copper contacts are more forgiving.
Copper contacts are much more reliable in the long run
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Copper & Aluminium Use
Copper
12%
9%
28%
9%
Electrical/Electronic
Construction
Transport
Consumer/General
Industrial Machinery
42%
17,974,300 tonnes (2007)
Aluminium
14%
8%
26%
8%
22%
22%
Electrical/Electronic
Construction
Transport
Consumer/General
Industrial Machinery
Packaging
38,108,700 tonnes (2007)
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Busbar Materials
• Why copper ?
• Copper conductor metallurgy
• The proof of the pudding
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IACS
• International Annealed Copper Standard
– Standardised in 1913
– Volume resistivity = 1.7241 m.Ω.cm
• Materials standards written around 97% IACS
– Allows use of hard-drawn C11000
• Modern HC copper is typically 101.5% IACS
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Copper for Conductors
Conductivity
%IACS
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Effect of cold work
C11000
Hard drawn busbar only loses
about 2 – 3% IACS.
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7
Grades of Copper
Alloy
Name
Copper
Other
Conductivity
Minimum
(Annealed)
C11000
ETP
HC
>99.90%
Oxygen
100% IACS
C10200
Oxygen free
>99.95%
-
100% IACS
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Busbar Purity
• Feed for meltshop can be cathode,
electrowon or electrical scrap
• Purest is cathode
– Purest of all is ISA Cathode
• Riskiest is electrical scrap
– Gloves, nails, tube, coke cans etc
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OC-ETP® Copper vs Others
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Frequency
20
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Oriental Copper
maintain this standard –
only use best quality
cathodes
Standard Busbar
103.5
103.0
102.5
102.0
101.5
101.0
100.5
100.0
99.5
99.0
98.5
98.0
97.5
0
97.0
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OC-ETP Busbar
Conductivity, %IACS
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10
Softening in service
Tensile
Strength,
MPa
C11000
Elongation,
%
Metals soften when they recrystallise.
There is a recrystallisation temperature,
which varies a little depending on the
prior cold work.
Conductivity,
% IACS
Annealing temperature, oC
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Making Busbars
Raw
material cathode
Reheat
Extrude
Cold
draw
Busbar
Melt
Cast
Underwater
runout
[Tin
Plate]
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Extrusion Process
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Bending
•
Effect of Copper Structure
¾
Copper Grain Size
Bending of OC-ETP® : Smooth surface
Microstructure of OC-ETP®
(Grain size = 25 microns)
Bending of other copper 1 : Orange peel
Microstructure of other copper 1
(Grain size = 75 microns)
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Where to use tin plated
¾
¾
¾
¾
Climate (Temperature / Humidity)
Acidic or Alkaline condition
Chloride / Sea water condition
Industrial / Polluted area condition
If subject to bad environment,
the use of Tinplated Copper Busbar is required.
Bare Copper Busbars
Tinplated Copper Busbars
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Busbar Materials
• Why copper ?
• Copper conductor metallurgy
• The proof of the pudding
So what ? – Effect of higher %IACS
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http://www.lifeclever.com
Thank you for your attention
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