4 ms·

I'm not sure, but I think modern trains usually use electrical braking instead of friction.

deleted 6y ago
[deleted]
rootusrootus 6y ago
Perhaps an all-electric train could, do they just feed it back into the grid? Freight trains mostly use air brakes, which are friction.
- liability 6y ago
  A diesel-electric freight train locomotive can use dynamic braking by dumping the electrical energy into a bank of resistors (known as rheostatic braking, opposed to regenerative braking, but collectively called dynamic braking.) However apparently this form of braking is only a small portion of braking that freight trains do since only driven axels can participate in it and most freight cars are unpowered. I didn't consider that.
detaro 6y ago
As far as I know only rarely, and even those trains do have mechanical brakes too. Modern electric locomotives can do engine braking, but brake power needs to be applied everywhere on the train, so most of the train brakes mechanically. (And if you want to engine brake, the energy still needs to go somewhere - so you have additional complexity of feeding it back into the grid or you are limited by how much energy you can dump to heat) Only (mostly high-speed) passenger trains with driven wheels everywhere can brake well only electrically for non-emergencies. Some also have additional eddy-current brakes that interact with the rails. For the German high-speed trains they try to design the speed profiles so that they have to waste as little energy as possible by using the motors as generators and feeding it back to the grid. But they still have and use eddy-current and mechanical brakes too. (You can tell the difference if they are delayed: they brake later and more aggressively to make up time. And a full-on emergency stop is loud and smelly.)
- ehnto 6y ago
  This was part of the design behind the N700 bullet trains of Japan. They have motors in all trains in order to distribute weight and thus braking and acceleration ability evenly across the whole train. It reduces wear on all wheels and components but as you mentioned adds complexity in the overall aparatus. They brake at stations using mechanical brakes though if I am not mistaken, the sound is pretty hard to ignore!

deleted 6y ago

[deleted]

Perhaps an all-electric train could, do they just feed it back into the grid? Freight trains mostly use air brakes, which are friction.

liability 6y ago
A diesel-electric freight train locomotive can use dynamic braking by dumping the electrical energy into a bank of resistors (known as rheostatic braking, opposed to regenerative braking, but collectively called dynamic braking.) However apparently this form of braking is only a small portion of braking that freight trains do since only driven axels can participate in it and most freight cars are unpowered. I didn't consider that.

detaro 6y ago

As far as I know only rarely, and even those trains do have mechanical brakes too. Modern electric locomotives can do engine braking, but brake power needs to be applied everywhere on the train, so most of the train brakes mechanically. (And if you want to engine brake, the energy still needs to go somewhere - so you have additional complexity of feeding it back into the grid or you are limited by how much energy you can dump to heat) Only (mostly high-speed) passenger trains with driven wheels everywhere can brake well only electrically for non-emergencies. Some also have additional eddy-current brakes that interact with the rails. For the German high-speed trains they try to design the speed profiles so that they have to waste as little energy as possible by using the motors as generators and feeding it back to the grid. But they still have and use eddy-current and mechanical brakes too. (You can tell the difference if they are delayed: they brake later and more aggressively to make up time. And a full-on emergency stop is loud and smelly.)

ehnto 6y ago
This was part of the design behind the N700 bullet trains of Japan. They have motors in all trains in order to distribute weight and thus braking and acceleration ability evenly across the whole train. It reduces wear on all wheels and components but as you mentioned adds complexity in the overall aparatus. They brake at stations using mechanical brakes though if I am not mistaken, the sound is pretty hard to ignore!