Transformers and substations
T
he pros and cons of copper versus aluminium conductors have
been debated for many years. Many of the concerns are based
on old information andmisinformation. The concerns centre on
the very different properties of the two materials and their suitability
for application within the electrical equipment industry. Reliable
performance from the conductors, the joints and terminations of the
conductors, are essential to the operation of the electrical system.
Customers are seeing the recent increases in the price of copper
passed onto them by the equipment manufacturer.
In 2003 a study was conducted for the Canadian Copper and Brass
Development Association (CCBDA) in Toronto by Powertech Labs of
Surrey, BC. The objective of the study was to compare the connector
performance under equivalent, severe environmental conditions for
the following three configurations:
• Copper connectors on copper conductor
• Aluminium connectors on copper conductor
• Aluminium connectors on aluminium conductor
The power connectors, conductor and oxide inhibitor used to make
the samples were standard commercial varieties, obtained from
several different manufacturers. The sizes were 2/0 AWG copper and
4/0 AWG aluminium.
Background
Copper connectors are available for use with copper conductors,
and aluminium connectors are available for use with copper and alu-
minium conductors. There are significant differences in the material
and electrical properties of aluminium and copper and their oxides,
which may affect their long-term performance.
Aluminium oxidises readily when exposed to air and a strongly
attached hard outer layer of electrically insulating oxide quickly forms
around the metal. For this reason, aluminium connectors are often
manufactured with an outer tin coating, which is intended to prevent
surface oxidation of the connector from occurring. Aluminium crimp
connectors are also pre-filled with oxide, inhibiting the compound
to reduce oxidation between the conductor and connector when
in service. Aluminium conductors must always be wire-brushed to
remove the oxide layer, and oxide inhibiting oxidation.
Copper also oxidises when exposed to air, but the oxide which
forms is relatively soft and conductive, although not as conductive
as the base metal. Copper connectors can therefore often be installed
without the oxide inhibitor. Wire brushing of the conductor, although
recommended, is not as critical as with aluminium. Copper connectors
are oftenmanufactured with a tine coating to reduce surface oxidation
and discoloration, but they are also available without a tin coating.
When copper and aluminium are brought into direct contact in
the presence of moisture, a strong galvanic reaction takes place due
to the dissimilar properties of the metals. Therefore aluminium con-
nectors cannot be used with copper conductors unless an interface
material, which is more compatible with both copper and aluminium,
is present, such as tin. However, tin is also susceptible to oxidation
and if the tin layer is compromised, then galvanic corrosion between
the base metals can still occur.
The differences in properties of copper and aluminiummay result
in a significant performance difference in the various types of electri-
cal connectors in long term service.
For this study, copper-to-copper, aluminium-to-copper and
aluminium-to-aluminium connections were subjected to accelerated
ageing which consisted of 2 000 hours of environmental exposure and
high current, short time testing. The copper-to-copper connections
had very little change in resistance during testing and performed the
best in this study.
Test samples
The test samples used in this study were combinations of copper and
aluminium conductors and connectors, with all components being
The great debate:
Copper versus aluminium
By E Swanepoel, Copper Development Association Africa (CDAA)
The variance in cost between equipment with copper versus aluminium conductors is now affecting the customers’ buying decision. But should it?
Electricity+Control
December ‘13
28
