Pros and cons of copper conductors in power cables. Life cycle cost, failure resistance, repairability, application suitability, compactness, environmental performance, recyclability, life cycle assessment

1. Pros and Cons of copper conductors in power
cables
March 2018

2. Summary of pros and cons
| Cu vs Al in power cables2
Life cycle cost
Failure
resistance
Repairability
Environmental
performance
Application
suitability
Compactness
• High performance
• Stranded cable
• Submarine
• Corrosion
• Water & aluminium
• Thermal expansión
• Creep
• Electrical conductivity • Recyclability
• Life cycle
assessment

3. Life cycle cost
| Cu vs Al in power cables3
For electrical-equivalent sections, copper conductors are more expensive than their aluminium
counterparts.
However, this difference is significantly reduced when taking into consideration the cost of other
materials used in the cable, such as the insulation (this is notably true in high voltage cables).
When adding installation, operation & maintenance and disposal costs the difference fades out.
Finally, if the higher residual value of copper is taken into consideration, there are good qualitative
reasons to opt for copper cables, as the cost difference is lower than 2%.
400 kV
Cu 1.000 mm2 €1.556.000
Al 1.600 mm2 €1.559.000
400 kV
Cu 1.200 mm2 €1.663.000
Al 2.000 mm2 €1.627.000
110 kV
Al 630 mm2 €849.000
Cu 400 mm2 €867.000
Failure data analyzed
For this study, failure data of a European DSO has been
analysed in order to see the impact of conductor material on
failures. This data, which has been collected over the last
years, comprises the conductor material of the cable and the
cause of failure. This provides the opportunity to understand
the impact of conductor material on failures.
Reference
Jicable 2015 - Copper or Aluminium cable conductors, broadly compared in
a life cycle perspective. Wim BOONE, Remco BAL; DNV GL,The
Netherlands
Lifetime costs comparison between copper and aluminium

4. Failure resistance
Corrosion 1
| Cu vs Al in power cables4
Corrosion – typically defined as the deterioration of metals through the combined actions of oxygen,
water, other metals and salts – is a well-known degradation phenomenon which under some
circumstances can be ”life threatening”.
Corrosion through exposure to oxygen
Aluminium oxidizes readily when exposed to air. A strongly attached, hard outer layer of electrically insulating oxide
quickly forms around the metal. Copper also oxidizes when exposed to air, but to a much lesser extent. The oxide which
forms is relatively soft and – contrary to aluminium – is conductive, although not as conductive as the base metal.
Galvanic corrosion
Galvanic corrosion can occur when dissimilar metals are in contact with each other and an electrolyte. For aluminium, a
reactive metal in the galvanic series, this is the most common cause of corrosion. When aluminium comes into contact
with a more cathodic material it acts as a sacrificial anode and becomes susceptible to corrosion. Copper, which is a
relatively noble metal, does not usually exhibit a great deal of galvanic corrosion.
Consequences of corrosion
Corrosion can become threatening for two basic reasons:
• Loss of material, and consequently loss of vital functions of the aluminium conductor and aluminium laminated
covering, inevitably resulting in failure.
• Introduction of an additional resistance, resulting in heat development and ultimately in failure. This is particularly
important when considering the installation of a connector.

5. Failure resistance
Corrosion 2
| Cu vs Al in power cables5
Corrosion: aluminium vs. copper
The corrosion of aluminium is generally recognized to be a major problem, although work is still being done to fully
understand the mechanism, its impact on reliability [3] and the development of related protection methods. However,
particularly when preparing joints on aluminium conductors, attention must be paid to the connector in regard to the
phenomenon of oxidation. The oxide layer should be removed, and often an oxide-inhibiting compound can be applied to
reduce oxidation. If not properly removed before applying a connector an extra resistance will be created resulting in
overheating. Aluminium connectors require greater care.
For copper, corrosion is not an issue. Copper is resistant to most organic chemicals and can operate indefinitely in most
industrial environments. A green patina may be formed after long exposure to the atmosphere, but this is a function of
the protective surface film and does not indicate a harmful attack. The protection of copper is in fact unnecessary, even
when used in offshore installations when it is exposed to a salty atmosphere.
References
1. R. Frank, C. Morton: Comparative corrosion and current burst testing of copper and aluminum electrical power connectors, IEEE Industry
Applications Conference 2005.
2. A. Mak: Corrosion of steel, aluminum and copper in electrical applications, General Cable publication.
3. S. Pelissou, J. Cote, R. Savage, S. St-Antoine: Influence of corroded conductors on the performance of MV extruded cables, Jicable 03.

6. Failure resistance
Water and aluminium
| Cu vs Al in power cables6
What happens when water meets aluminium?
Water can gain entrance into a cable during shipping, handling, outside storage, accidental damage or cable joint or
termination failures. Aluminium reacts with water to produce hydrogen gas.
What affects the build-up of hydrogen?
Total volume of air space available within the conductor, volume of water contained within the conductor, conductor
temperature and available pure aluminium which could contact the water. The aluminium oxide layer must be penetrated,
either chemically or mechanically to expose pure aluminium for the reaction to occur.
Is it a problem?
The formation of hydrogen can often lead to high pressures inside the cable, with the potential for a damaging expansion
of the cable insulation structure. Joints and connectors can be affected. Also, partial discharges can happen,
subsequently leading to cable failures. These negative effects may not always be recognized as being caused by
hydrogen due to the lack of effective failure investigation procedures
What’s the solution?
Applying radial and longitudinal water blocking protection methods. However, these protection methods are not always
present.
A second and just as effective solution is to use copper instead of aluminium, as copper does not react with water.
Reference
G.J.Luzzi, Gas pressure build-up in aluminium conductor cable, IEEE Transactions on Power Apparatus and Systems, Vol, PAS-101, No. 6, June
1982.
Aluminium power cables can potentially fail due to the following reasons: corrosion, thermal expansion
and the reaction of water with aluminium. This article looks at the latter.

7. Failure resistance
Thermal expansion
| Cu vs Al in power cables7
Thermal cycling
This is a regular phenomenon in the electricity supply system, and involves the cable conductor expanding and
contracting according to the temperature variation. In general, a system can be installed in such a way that the
expansion and contraction are under control. However, if the system contains discontinuities such as joints, mechanical
forces will occur at the joints. If these forces are high enough they may become destructive and result eventually in joint
failure.
Which material to choose?
The tendency to expand and contract due to temperature variation will inevitably result in some sort of problem for
conductors. The most significant consequences of the higher coefficient of thermal expansion of aluminium are
destructive forces in the joint. With regard to these problems, copper is certainly a better choice than aluminium, on
account of its significantly lower coefficient of thermal linear expansion.
References
The effect of high current loads on joints in MV cable systems: 21st International Conference on Electricity Distribution Frankfurt, 6-9 June 2011
The thermo-mechanical behavior of joints in MV cable systems exposed to high current loads: 8th International Conference on Insulated Power
Cables, 2011
Measurement of the force induced by thermal expansion of conductor of MV cables and impact on MV joints: 22nd International Conference on
Electricity Distribution, 2013
Towards In-Field Current Rating Verification of Underground Power Cable Systems: Bernd C. van Maanen, Eindhoven University of Technology,
Department of Electrical Engineering
Thermal expansion is the tendency of matter to change in volume in response to a change in
temperature. The coefficient of thermal expansion for aluminium is 35% greater than that of copper.
This characteristic is of concern when we study the expansion and contraction of conductors in
electrical connections during thermal cycling.

8. Failure resistance
Creep
| Cu vs Al in power cables8
Creep (sometimes called cold flow) is the tendency of a solid material to move slowly or deform
permanently at elevated temperature under the influence of mechanical stresses.
When does it happen?
Creep can occur as a result of long-term exposure of stress still below the yield strength of the material. The temperature
at which the creep begins depends on the alloy composition. It is more severe in materials that are subjected to heat. As
a result of creep the material undergoes a time dependent increase in length which could be dangerous under service
conditions
Which material to choose?
Aluminium has a more pronounced creep behaviour than copper. Copper also has a 25% lower coefficient of expansion.
For instance in case of jointing the use of aluminum connectors may cause problems. It tends to flow out of a
compression termination causing a loose connector that can result in overheating.
What are the solutions?
The problem of creep in aluminium conductors or connectors seems to be solved when using harder type of aluminium in
certain suitable alloys, with almost the same tensile strength as that of copper, however this improvement has to be paid
by a lower conductivity value and a higher price.
References
1. White paper issued by David Meulenbroek, Siemens AG, October 2014
2. White paper issued by Larry Prior, Rick Schlobohm, Bill Brownell, GE August 2015
3. Electric Cables handbook, BICC Cables,3rd edition

9. Compactness
Conductivity and cross-section 1
| Cu vs Al in power cables9
More joints means more failures
A larger conductor cross-sectional area means that less cable can be stored on a drum. This results in shorter cable
lengths and thus more joints per unit circuit length. Unfortunately, the more joints, the greater the potential for failures
due to the following reasons:
• Joints are man-made and therefore sensitive to jointing errors.
• Joints are not always effectively tested when they have been installed, so jointing errors and other defects are not
always identified during post-installation testing.
• Joints are a discontinuity in the cable system, which are therefore liable to thermal-mechanical forces due to
temperature cycling.
Reduced flexibility
The bending force is proportional to the square of the conductor’s cross-sectional area and thus on the fourth power of
the diameter! So the larger the conductor’s cross-sectional area, the less flexible the cable.
Difficult duct installation
For installation in ducts a cable with a larger cross-sectional area and less flexibility will aggravate the installation
process.
One of the major differences between copper and aluminium is that copper has a significantly higher
specific electrical conductivity than aluminium. This difference is particularly relevant when designing
and installing electrical networks and related components. Aluminum conductor will have a cross-
sectional area 56% larger than copper for the same current-carrying capability. This leads to a number
of serious drawbacks.

10. Compactness
Conductivity and cross-section 2
| Cu vs Al in power cables10
Copper or aluminium?
Replacing aluminium conductors with copper conductors reduces the number of joints necessary and thus reduces
system failures. This leads to benefits in both CAPEX (installation cost) and OPEX (failure costs). Due to its smaller
cross-sectional area, the copper cable will be more flexible and easier to install, which is a particular benefit when
installing cables in ducts.
References
BICC Electric Cables handbook, third edition
A Comparison of Aluminum vs. Copper as used in Electrical Equipment – Larry Pryor et al, GE Consumer & Industrial.

11. Application suitability
Flexible stranded conductor
| Cu vs Al in power cables11
Copper or aluminium?
Both copper and aluminium can be stranded. However, a key difference is that stranded aluminium is only available at
nominal cross-sectional areas of 10 mm2 and above. Copper, on the other hand, is available in very low conductor
cross-sections, for example 0.5 to 10 mm2. The reason lies with the difference in tensile strength and fatigue endurance
limit of the two materials.
So-called ‘finely stranded’ and ‘extra finely stranded’ conductors (0.5 to 6 mm2) are only available in copper, and the
finest aluminium conductors available are significantly stiffer than the finest copper conductors.
Stranded aluminium does offer better control of skin effect than stranded copper, however, this advantage only plays a
significant role for conductor cross-sections above 800 mm2.
Conclusion
Copper is more widely available as a stranded conductor than aluminium, and the strands can be of a much smaller
diameter, resulting in a more flexible cable.
References
Conductor stranding http://www.calmont.com/?pgid=46
Electric cables BICC Handbook 3rd edition
A stranded conductor is composed of a number of thinner conductors twisted together into a cohesive
cable. It is widely used in applications which require considerable movement or where the wire needs to
be bent into complex shapes. A stranded conductor can be manufactured in a variety of configurations,
(concentric, bunched and rope).

12. Application suitability
Submarine cable 1
| Cu vs Al in power cables12
Burying underneath the seabed
A traditional way of burying cables is to use high-pressure water jets from nozzles. The water causes the seabed to
become fluidized and the cable sinks down in the slurry. Empirical evidence from a cable manufacturer indicates that
lighter cables do not sink sufficiently fast and therefore the cable does not reach the required laying depth, resulting in
the necessity to repeat the laying procedure.
Laying on the seabed
This is a faster and less expensive method, but leaves the submarine cable subject to movement across the seabed due
to tidal currents. This raises the likelihood of premature cable failure due to abrasion damage, or due to damage caused
by fishing gear as the cable is no longer protected.
The ongoing energy transition makes offshore networks develop fast. Increasingly long connections to
shore with subsea MV and HV cables are required. The hostile deep sea environment leads to a
multitude of challenges for submarine cables. The selection of the correct material can have a
significant effect on how these challenges are overcome.
There are two main methods of installing a submarine cable: burying it underneath the seabed, or
laying it on top of the seabed.

13. Application suitability
Submarine cable 2
| Cu vs Al in power cables13
The weight advantage of copper conductor cables
To avoid the potential drawbacks inherent in both methods, the solution is to select a material with sufficient weight. In
the first scenario, a heavier cable will sink correctly and more quickly into position in the fluidized seabed. In the second
scenario, a heavier cable will mean that when laid on the seabed it can resist the maximum tidal seabed currents
expected, even under storm conditions.
In both respects, the significantly higher specific weight of copper compared to aluminium (by a factor of three) gives it
an advantage, leading to a more efficient cable-laying process and greater stability of cables, whether buried or not. Next
to the specific weight, other aspects give advantages to copper conductors compared to aluminium conductors in
submarine cables. These are higher current rating, smaller size, and higher resistivity against corrosion.
Specific weights of copper and aluminium:
• Copper: 8900 kg/m3
• Aluminium: 2760 kg/m3
References
Electric Cables Handbook/BICC Cbales; edited by G.F.Moore, 3rd edition, 1997.
Mechanical aspects of submarine cable armour, E. Zacone, Spring 2012, ICC submarine cables meeting in Seattle, USA.
DNV-RP-F109, On-bottom stability design of submarine pipelines, October 2007.
Stability of submarine pipelines on liquefied seabeds, T.C. The a.o. Journal of waterway, port, coastal and ocean engineering, July/August 2006.

14. Application suitability
Matching OHL capacity with one cable per phase
Overhead lines offer very high transport capacities (400 kV, 4000 A per circuit). The equivalent
underground circuits use 2 cables per phase to match the transport capacity of its overhead
counterpart.
What is the problem?
The costs of undergrounding as well as the rights of way increase significantly when using two cables per phase, making
the application of underground cable complicated and therefore less obvious.
What is the solution?
Use only one cable per phase, which requires the following:
 Apply the largest available copper conductor (2500 mm2 – 3000 mm2) and reduce as much as possible limiting
effects like skin- effect and proximity-effect
 Improve the thermal surroundings of the installed cables to the lowest available value by applying suitable
backfill material (0.5Km/W and lower)
 Introduce forced cable cooling, to increase current rating , to narrow the cable trench and to reuse the heat of
the cooling water
Aluminium could only match this performance by using sections of about 3500 mm2 or larger, which is out of the current
manufacturing scope.
References
One cable per phase for EHV Cable systems, DNV GL PP, by W.Boone and C.Sonderen 30-4 2014
| Cu vs Al in power cables14

15. Application suitability
Lack of space
Ducts, tunnels and substations are typical installations lacking space.
What is the problem?
Cables are to be as small as possible to cope with the existing space. Pulling force during installation is an important
constraint.
What is the solution?
Copper conductor cables are to be preferred because of smaller conductor size than the aluminium alternative for the
same rating, resulting in smaller pulling force during installation
References
Cables installed in duct banks ,DNV GL report no 14-3197 2015 by W.Boone en J van Eerde
| Cu vs Al in power cables15

16. Repairability (1)
| Cu vs Al in power cables16
When it comes to repairing, a whole set of properties are highly relevant, affecting both easiness of
repair and the quality of the work performed
Bending force
For the same current rating copper conductors have a smaller cross section and are thus easier to bend and shape
when jointing and terminating cables. The bending force is proportional with the square of the conductor cross-section
and thus with the fourth power of the conductor radius .
Brittleness
Copper is less brittle than aluminium . This is particularly evident when using 3-core cables, where core manipulation is
required for correct phasing.
Protection against corrosion
As aluminium corrodes quickly, compared to copper, consequently every repair action requires attention from the jointer
to remove the oxide layer, which by definition will cause problems due to the insulating properties of the oxide layer.
Galvanic action
Galvanic action is typically a problem for aluminium rather than for copper .

17. Repairability (2)
| Cu vs Al in power cables17
When it comes to repairing, a whole set of properties are highly relevant, affecting both easiness of
repair and the quality of the work performed
Soldering
Soldering is an easier process for copper than for aluminium.
Qualification and experience of the operator
The competence and experience of the jointer is of greater importance when dealing with aluminium than with copper.
Proper jointing techniques (connector) are absolutely necessary for aluminium, as in case of copper precautions are to a
lesser extent required; one could say that “copper is more forgiving” .
References
Aluminium wiring: understanding the problems and the solutions. The Hartford Loss Control Dep. 2002

18. Environmental performance
Circularity
| Cu vs Al in power cables18
Circularity involves the consideration of total product life cycle. The reuse of the recycled material in the
original system function is the first step in the circular economy. At the moment both aluminium and
copper from electricity cables are not or hardly reused in the same application, however this will change
in future
Circularity advantages
• Proper management of End-Of-Life
• Securing availability of technical materials
• May save costs over the production of new material
• May reduce CO2 emissions

19. Environmental performance
Circularity (2)
| Cu vs Al in power cables19
Green: elements recovered
Red / Yellow : elements lost
Effective recycling policy
• To reuse materials and to minimize waste
• Material loss during recycling should be minimized and high quality recycling should be applied. For copper contrary to
aluminium, many elements can be recovered by subsequent processing, see metal wheel (copper is “carrier metal”)
• As product change is much faster than the change in processing equipment, processing waste must use flexible
technology, such as the highly adaptive manual sorting, and some physical separation and sorting equipment may be
moved to where scrap is being generated.
• The infrastructure and knowledge for the processing of waste into recycled metal is often the same as that used for
primary metal production. Thus, keep a healthy balance between primary and recycled metal production.

20. Environmental performance
Circularity (3)
| Cu vs Al in power cables20
Future aspects
• Future cables could be designed in such a way that materials are easier to separate
• When decreasing the amount of conductor material per cable, the losses will increase
References
• Environmental impact of metal use in electricity cables, CE Delft report, 16.2H95.09, prepared by Sanne Nusselder
and Geert Bergsma, February 2016
• Metal Recycling, Opportunities, Limits, Infrastructure, WRF Publication 2013
.
http://copperalliance.org/wordpress/wp-
content/uploads/2013/03/ica-copper-
recycling-1405-A4-low-res.pdf

21. Environmental performance
Life Cycle Assessment
| Cu vs Al in power cables21
End-of-life recovery is key
Copper cables have lower life cycle impacts than aluminium
cables.
This is in large part due to the fact that copper cables are
recovered to larger extent at the end of their serviceable lives.
The higher scrap value that copper fetches on the market is a
great driver for the recovery of disused cables. This recovery
translates to larger environmental credits when the recycled
copper re-enters the market.
Aluminium cables are recovered to a lesser extent than copper
cables and hence, while theoretically completely recyclable,
much of this potential is lost if the cables remain under-ground
after use. The market statistics, thus, lead to aluminium being
accorded lower environmental credits at the end of life.
Reference
Jicable 2015 - Copper or Aluminium cable conductors, broadly compared in
a life cycle perspective. Wim BOONE, Remco BAL; DNV GL,The
Netherlands
A Life Cycle Assessment consists on an evaluation of the environmental impacts of a product,
considering the three life phases: manufacturing, use and end-of-life. This exercice has been carried
out for electrically equivalent copper and aluminium variants of cables.
Primary Energy
Demand [net]
Tunnel Urban area
Cu Al Cu Al
Total 108,5 122,5 135,6 240,3
Manufacturing 216,7 357,9 216,7 357,9
EoL -108,1 -235,4 -81,1 -117,7
Balance for 1 meter of Medium Voltage cable
Global Warming
Pot. [kg CO2-eq.]
Tunnel Urban area
Cu Al Cu Al
Total 6,8 8,1 8,6 13,2
Manufacturing 13,9 18,3 13,9 18,3
EoL -7,1 -10,2 -5,3 -5,1
Acidification Pot.
[kg SO2-eq.]
Tunnel Urban area
Cu Al Cu Al
Total 0,016 0,019 0,028 0,053
Manufacturing 0,064 0,088 0,064 0,088
EoL -0,049 -0,070 -0,036 -0,035

22. Thank you
| Cu vs Al in power cables22