Guest writer: Paul Walker
There is a drive on the rail infrastructure to reduce the overall cost of signalling power and other installations and increase electrical efficiency. One of the main tenants of this philosophy is the use of aluminium due to its low cost. As such there is also a drive to use transformers with aluminium windings to reduce costs further.
FT Power Transformers have taken on the challenge of producing aluminium transformers for trackside infrastructure in the 500VA to 100kVA range.
But is aluminium (Al) really so much better than the traditional copper (Cu)? Below is a base table of the pro and cons of both aluminium and copper transformers, based on both experience and research.
These studies have led FT Transformers to believe that large aluminium power transformers have advantages over similarly sized copper units when it comes to cost and weight. The efficiency of the units is about the same.
However, small trackside units that are rarely maintained will, over the life of the installation, suffer from increasing levels of resistance due to aluminium oxide. This will be a future issue for current trackside transformers, particularly for signalling power units, and will show up as an insulation fault at the permanent insulation monitors (Bender units located with the Principle Power Supply buildings) for the signalling power class II IT feeders.
Regular inspection and maintenance will be required. However, once a signalling power feeder is commissioned, it is often not maintained until there is an issue.
Therefore, it is FT Transformers’ opinion that the life of signalling power feeders will be greatly reduced using aluminium, increasing the whole life cost.
Paul Walker is a mechanical design engineer with FT Power Transformers.
Edvard Csanyi – Aluminium vs. Copper: Conductors in Low Voltage Dry Type Transformers (Electrical Engineering Portal, October 2010)
Hans De Keulenaer – Reliability of Terminations: Copper vs Aluminium (Leonardo Energy, August 2018)
Ronaldo Bertoldi – Aluminium vs. copper conductors in transformer manufacture (EE Publishers, March 2017)
Tahir Ayub – Eliminating Copper, the next step (Rail Engineer, July 2017)
Powersmiths International Corp – Transformer Inrush Currents and Protection (Critical Power Group, June 2013)
This article first appeared in Issue 177 of Rail Engineer, Aug/Sep 2019.