RISE has been using a climate chamber in Borås to test one possible future solution to improving punctuality on Sweden’s railways. In an effort to minimise icing, the team has developed the basics for a smart system using current in overhead power lines.
“The aim was to identify methods for keeping overhead power lines free from ice in a cost-effective manner without disrupting timetables,” says Urban Lundgren, a research scientist at RISE.
When moisture, precipitation, wind and below-zero temperatures attack overhead railway cables, the result may be a build-up of ice on the lines, with subsequent delays to train services due to worn lines and damaged rolling stock. Reliability is key if we are to encourage more people to travel on public transport. The Europe-wide social cost of delayed trains is estimated at € 120 million every day.
The EU-funded project IceControl has studied a method whereby heat generated by current in overhead power lines is used to prevent icing when cold weather strikes.
“One of the smartest elements of this is that we are looking at methods of solving the problem without major installations; that the existing cables can be used,” explains Urban Lundgren.
Utilising the electrical resistance of cables
The method is based on the electrical resistance of overhead cables. When large currents pass through a cable, heat is generated in the same way as an electric radiator in the home. By controlling the current through overhead lines, it is possible to heat cables in a controlled manner to prevent icing.
The scenario in question applied to a railway in Spain. The RISE research team constructed a 1:10 scale model for the project, which was then exposed to severe weather conditions in a climate chamber.
“Our aim was to identify ways to resolve the problem without expending too much energy, with builtin weather surveillance so that preventative methods can be implemented in a timely manner. We were able to demonstrate that heating cables before temperatures sink below freezing is more efficient than heating them afterwards in order to melt ice,” says Urban Lundgren.
Accounting for tough conditions
The tests used a material with one hundred times the electrical resistance of copper, the material usually used for overhead power lines on railways. This allowed testing at a current of 100 amperes with the same results as the 1,000 amperes of current that passes through cables on Spanish railways.
As well as testing cooling effects, the climate chamber was used to simulate high winds and other climate effects that may need to be accounted for. This provided a good overall picture of the strengths of the solution. This provides a good foundation for reducing delays due to frozen overhead power lines.
“Previous studies have looked at what could be done to deal with Swedish conditions; however, it would certainly be interesting to look more closely at this,” says Urban Lundgren.