Electricity + Control June 2017

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STANDBY + BACK-UP PLANT MAINTENANCE, TEST + MEASUREMENT
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shortage of copper, which was in huge demand
for the arms industry. By the 1960s, when copper
prices rocketed due to high demand, aluminium
again became popular in windings; previous
technological problems were overcome, and
these transformers became more reliable.
Since 1970, aluminium was used intensively
in the United States and the technology of alumini-
um-wound transformers was further enhanced; it has
now gained widespread acceptance in European countries
and other parts of the world.
Just a myth
One of the myths that has been disproved is the belief that alumini-
um-wound transformers have bigger losses of electricity. While the
aluminium conductors are larger than copper conductors, they are
lighter; the result is that the mass of the core in an aluminium trans-
former is 5 to 20% more, but the total transformer mass is almost
the same – for the same level of electrical loss.
Temperatures
With regard to the respective thermal properties, aluminium has
a lower melting point than copper but it is still well above the real
working temperatures of the windings. In normal circumstances, the
‘hot-spot’ temperature in the windings is between 105°C and 120°C,
while aluminium only melts at 665°C. More importantly, the lower
thermal conductivity of aluminium does not affect the performance;
the temperature differences in the conductor are negligible in rela-
tion to the temperature difference between the ambient air and the
windings. Also, as a result of the difference in the material properties
of the two metals, Eddy loss in aluminium winding is 38 % less than
in copper with the same volume of conductor.
Conclusion
While there was historically some concern about joining and terminat-
ing aluminium – either to itself or to copper – when it was to be used
outdoors, these joints and terminations are today made without any
problems. Techniques such as bolting, crimping and arc welding un-
der inert gas (with or without refractory electrodes) have undergone
severe testing over many years and have been proven.
Enquiries: Tel. +27 (0) 11 723 6000 or email
Visit
Aluminium bus bar.
Aluminium coil. Winding underway at WTA's Wadeville
manufacturing facility.
Aluminium connectors.
• Aluminium windings and copper windings give
transformers the same quality of operation and per-
formance.
• Aluminium-wound transformers do not have bigger
losses of electricity.
• Global specialist, WEG Transformers, successfully
manufactures transformers with aluminiumwindings.
41 June ‘17 Electricity+Control