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Your typical Foucault's current brakes operate on a disk, which is placed in an electromagnetic field in order to transform kinetic energy into heat without friction. The problem is that the disk still overheats, just like an usual disk brake. In the case of railways this also needs that the wheels have adherence to rail.

Theoretically, it would be as simple as to place two huge magnets around both rails in order to brake the train. A simple mechanical design could move the magnets up and down whether we want braking or not. The magnetic field would turn kinetic energy into heat, but this would not overheat as the heat would advance along the train itself. Also this would not require any friction, and as thus, no mechanical parts have to be changed due to use. (Friction braking is still required for stopping the train once a low speed would has been attained with Foucault's current braking).

This would have the following advantages :

  • Braking doesn't rely on rail adherence
  • Since permanent magnets can be used, no electricity needed to operate the braking device (work on non-electrified railways, or in emergency when there's damage to the overhead lines)
  • No risk of overheating in the long run since the dissipated heat moves along the rail.
  • Don't damage brake pads, and don't damage rails as does the usual emergency brake which applies friction to the rails.

The only major problem I'd see with such a system is that the magnets would also attract the rail itself (made from steel) - but if magnets on both rails are in reverse directions each force will cancel the other, so the magnets just have to be very solidly attached.

Is such a system possible or have I missed something ? If it's possible, why isn't it more widely used ? Or would the magnets needs to be too strong for this idea to be any effective, and this would have effects on passengers or their belonging ?

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  • $\begingroup$ What is the mass of a train? How hot will the rails get if the train has to stop in the shortest possible distance? Will that cause distortion of the rails? $\endgroup$
    – Solar Mike
    Apr 23, 2019 at 14:41
  • $\begingroup$ @SolarMike Trains of hugely different mass exists and it's definitely unacceptable if the rails are damaged. Breaking on the shortest possible distance is only required for emergency braking, but this could be used for regular breaking as well (although regenerative breaking is preferable - but unavailable on non-electrified lines). $\endgroup$
    – Bregalad
    Apr 23, 2019 at 18:59
  • $\begingroup$ This equipment is rarely used, as it isn't at all energy-efficient (you want to use regeneration to recover some of the braking energy, not consume extra energy to power the electromagnets) and consider the consequences if the power suddenly fails and you have no braking; there would be a (somewhat scary) delay before the conventional braking system can take over. The sole advantage is that the braking energy is dissipated in the rail, not on the train, which could be important in some applications (e.g. very prolonged down-gradient).. $\endgroup$
    – jayben
    Jan 22, 2022 at 10:25

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Yes they can and they are in use. Details on Wiki

enter image description here

By Sebastian Terfloth User:Sese_Ingolstadt - Own work, CC BY-SA 3.0

A linear eddy current brake in a German ICE 3 high-speed train in action.

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  • $\begingroup$ Usually so much heat is generated in the rail in an emergency stop that traffic is halted until the rail is check for distortion and reduction of strength. $\endgroup$
    – Michael Harvey
    Dec 6, 2020 at 14:06
  • $\begingroup$ That's a lot of energy conversion. I would have expected the high inertial forces translated to lateral force on weight transfer more than a thermal problem. $\endgroup$
    – Tony Stewart EE75
    Dec 8, 2020 at 3:19
  • $\begingroup$ But then thermal stress on continuous 1/4 mile tracks can cause lateral shift from high temp expansion. Michael which trains did you have in mind? ICE3 or Metrolink or ? $\endgroup$
    – Tony Stewart EE75
    Dec 8, 2020 at 3:33

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