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NSW Annual Seminar and Exhibition
Metals for Busbars
Alex GouchTechnical 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 BusbarsWhy copper ?
– Aluminium is much cheaper– Overhead conductors are now mostly aluminium– Copper has
• 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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CopperC11000
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.
Electrical Properties & Price
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CopperC11000
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
Mechanical Properties
Copper much easier to handle in the workshop
Copper more robust
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Material Testing Temp. °C
Min. Creep Rate % per 1000 h
Stress MPa
Aluminium (1080) annealed 20 0.022 26
HC Cu annealed 150 0.022 26
Creep
Material Fatigue strength N/mm²
No. of cycles x 106
HC Aluminium annealed 20 50
half-hard (H8) 45 50
HC Copper annealed 62 300
half-hard 115 300
Fatigue
Copper is much less likely to fail at bolted connections by creep or stress relaxation.
Copper more tolerant of higher operating/fault temperatures.
Copper better able to withstand repeated mechanical stresses.
Mechanical Properties
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CopperC11000
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
Thermal Properties
Copper less liable to hot spots.
Copper needs less support.
Copper less prone to thermal fatigue failure.
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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
Thermal Properties
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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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28%
12% 9%9%
42%
Electrical/ElectronicConstructionTransportConsumer/GeneralIndustrial Machinery
Copper & Aluminium Use
Copper
17,974,300 tonnes (2007)
22%
26%
14% 8%
22%8%
Electrical/ElectronicConstructionTransportConsumer/GeneralIndustrial MachineryPackaging
Aluminium
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
Hard drawn busbar only loses about 2 – 3% IACS.
C11000
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Grades of Copper
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Oxygen
Other
100% IACS>99.95%Oxygen freeC10200
100% IACS>99.90%ETPHC
C11000
ConductivityMinimum
(Annealed)CopperNameAlloy
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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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5
10
15
20
25
97.0
97.5
98.0
98.5
99.0
99.5
100.
0
100.
5
101.
0
101.
5
102.
0
102.
5
103.
0
103.
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Standard Busbar OC-ETP Busbar
Conductivity, %IACS
Frequency
Oriental Copper maintain this standard –only use best quality cathodes
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Softening in service
Metals soften when they recrystallise.
There is a recrystallisation temperature, which varies a little depending on the prior cold work.
TensileStrength,MPa
Elongation,%
Conductivity,% IACS
C11000
Annealing temperature, oC
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Making BusbarsRaw material -cathode
Reheat Colddraw
Melt
Cast
Extrude
Underwater runout
Busbar
[Tin Plate]
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Extrusion Process
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Bending• Effect of Copper Structure
Copper Grain Size
Bending of OC-ETP® : Smooth surface Bending of other copper 1 : Orange peel
Microstructure of OC-ETP®
(Grain size = 25 microns)Microstructure of other copper 1
(Grain size = 75 microns)
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Where to use tin plated 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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Thank you for your attention
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