Data from a Swedish rail switch may reduce train delays in cold climates

The prevalent use of heated switches is on the right track, so to speak. But according to researcher William Liu with the Railway Group at KTH Royal Institute of Technology, heating a single switch in the Stockholm region costs about 12,000 Swedish kronor annually (about €1,136). 

Even then, heating problems lead to more than 1,000 disruptions annually, affecting hundreds of thousands of passengers.

Those cost estimates are based on data the KTH researchers collected over the course of a year from an operational rail switch outside of Stockholm. Their analysis revealed ways in which energy costs could be cut by two-thirds, to keep the trains running on time – for less.

Liu says timing, energy source and temperature make all the difference, especially as climate change causes more extreme swings in weather like high winds, heavy snowstorms and freeze-thaw cycles. The research suggests the need for automated control so switch heat can be adapted to multiple weather conditions – not outside just temperature.

The heaters on Sweden’s railways are kept at a temperature of 8C to 8.6C, but the new research shows that actual heat loss depends on other factors than external temperatures – namely wind speed, moisture and the presence of snow,” Liu says.

Liu says these factors dramatically change heat transfer rates, yet the existing system lacks this data – especially wind, which the study calls critical.

“This leads to unpredictable rail temperatures and failures at low temperatures or during gusts,” he says. “Wind is a big problem.”

A computer model was developed to predict how a switch warms up under different weather conditions, including factors like air temperatures, wind and precipitation. The predictions successfully compared with field data gathered from the switch they studied.

The collected data revealed that switches warm up in less than 10 minutes when power is increased, which indicates heaters do not need to run at full power all the time. The study also found that wind speed affects heat loss, which indicates wind must be measured to improve heater control.

The model also predicts rail temperatures under different air temperatures and wind speeds, which would enable control strategies, such as running at lower power most of the time and using short boost periods before snowfall or during wind gusts.

The study also found that more affordable and sustainable underground heat can be tapped to heat many switches, which now get their power from the grid. “Ground heat works best in certain types of rock, like granite, which is common in Sweden,” Liu says. “There are about 12,000 switches in Sweden and heating a single one near Stockholm costs as much as 12,000 Swedish kronor per year."

The cost amounted to about 90,000 kronor over a 12-month period a few years ago on Sweden's nearly 400-kilometer "iron ore line", the Malmbanan, which transects the Arctic Circle.

Using ground heat at least two-thirds of electricity costs could be saved, he says. With the use of heat pumps an energy efficiency (COP) rating of 3 could be reached, theoretically leading to more savings.

Other sustainable solutions for power could be installed too, such as solar panels and wind turbines. And in a twist of irony, Liu suggests heating power could even come from the same wind that keeps freezing the switches.

While the study results are promising, Lius says more study is needed to address uncertainties that are not included in the numerical model.

https://doi.org/10.1007/978-3-032-04774-8_41