Linear Motors

[flypie]

I noticed a while ago that the German ICE 3 train has linear eddy current braking that uses the track, as the stator. I wondered with the track could be used as the stator for a linear motor. There are several systems which do use linear motors but all seem to use a separate stator, in the middle of the track. They are all the primary means of propulsion on these systems. The braking system serves as high speed braking like the Hydro Kinetic did on the APT. Would a linear motor be useful for improving the acceleration of say HST above 75mph? If it the same coils could also be used for braking it would be very useful. Also less prone to leaves on the track.

https://en.wikipedia.org/wiki/Eddy_current_brake
https://en.wikipedia.org/wiki/Linear_motor#Train_propulsion

 

[najaB]

Would a linear motor be useful for improving the acceleration of say HST above 75mph?

I could be wrong, but I think linear induction motors produce maximum power at low speeds. That's why they are used for roller coasters: fast acceleration from zero.

 

[flypie]

You a probably right. Rotary motors produce max torq at 0 revs. However, a little extra never did any harm.
Though they could still be of use if they aided the acceleration at low speed it would allow the gearing on the standard motors to be changed to perform better at higher speeds. Having the different force generators tuned to different parts of usage might still be useful.

 

[edwin_m]

A quick look at Wikipedia suggests that linear motors are less efficient because of two reasons: typically a larger air gap than a rotary motor, and "end effects". The latter are worst if the reaction rail is very long as would be the case with a railway running rail.

The few trains that use linear motors have a reaction plate between the rails, which I think is actually a series of plates with gaps to provide electrical isolation between them and thus avoid end effects.

 

[flypie]

The eddy current braking on the ICE 3, do not seem to have much of an air gap at all. Though the end effects bit would be problematic.

 

[asylumxl]

Many moons ago, I asked a question regarding eddy current brakes in the UK. The gist of the answer I got was that they are avoided because of potential issues with signalling equipment due to interference.

 

[jopsuk]

Flypie: is that the permanent position or do they lower to there when needed?

 

[flypie]

Flypie: is that the permanent position or do they lower to there when needed?

That is down, this is up.

http://www.sciencedirect.com/science/article/pii/S2095756415302956

 

[flypie]

Many moons ago, I asked a question regarding eddy current brakes in the UK. The gist of the answer I got was that they are avoided because of potential issues with signalling equipment due to interference.

When was this? I can see it being a problem with say 30ma current loops but not modern digital.

 

[asylumxl]

When was this? I can see it being a problem with say 30ma current loops but not modern digital.

Few years back. It wasn't on here I asked mind you, it was somebody from NR giving a guest lecture at my work.

 

[flypie]

Few years back. It wasn't on here I asked mind you, it was somebody from NR giving a guest lecture at my work.

So like a typical kind of Managment answer we haven't tested it or thought about it so doing it might cause the end of the world.

Well now the ICE system is up, proper tests can be done, I doubt it will only effect UK based comms.

 

[asylumxl]

So like a typical kind of Managment answer we haven't tested it or thought about it so doing it might cause the end of the world.

Well now the ICE system is up, proper tests can be done, I doubt it will only effect UK based comms.

Essentially, yes.

It's hardly any different with other new railway technology in the UK mind you. Procrastinate and run trial after trial to prove technology which is already proven...

 

[najaB]

It's hardly any different with other new railway technology in the UK mind you. Procrastinate and run trial after trial to prove technology which is already proven...

The issue is that the railway, much like the aerospace, industry has to prove something like six nines reliability in all environments. Just because something works in another country, with another country's S&T doesn't mean it will work in ours.

Does Germany have AWS and TPWS, for example?

 

[flypie]

The issue is that the railway, much like the aerospace, industry has to prove something like six nines reliability in all environments. Just because something works in another country, with another country's S&T doesn't mean it will work in ours.

Does Germany have AWS and TPWS, for example?

The have https://en.wikipedia.org/wiki/Balise which are very very similar.

 

[najaB]

The have https://en.wikipedia.org/wiki/Balise which are very very similar.

With respect, they are not. Completely different physical design to both TPWS grids and AWS ramps and totally different methods of operation.

I don't *think* that linear induction motors/brakes would affect either but NR would have to prove it.

 

[flypie]

With respect, they are not. Completely different physical design to both TPWS grids and AWS ramps and totally different methods of operation.

I don't *think* that linear induction motors/brakes would affect either but NR would have to prove it.

Sorry Acronym Blindness cutting in https://en.wikipedia.org/wiki/Automatic_warning_system_(railways) https://en.wikipedia.org/wiki/Train_Protection_&_Warning_System

Provided the eddy brakes are not on the same carriage as the sensor for those devices. Then I cannot see a problem. If there were then the magnetic devices you could have close to the line in adjacent buildings would be very limited.

Any ETCS roll out would make definitely get rid of any problem. That problem happen before NR could do enough testing.

 

[najaB]

If there were then the magnetic devices you could have close to the line in adjacent buildings would be very limited.

Magnetic field power falls off as the square of distance - which means a very powerful field such as would be created by an induction motor/brake will fall off to almost nothing a metre or two away. The issue being that equipment in the four foot isn't tens of centimetres away (by definition it can't be more than 72cm from the rail).

 

[flypie]

Magnetic field power falls off as the square of distance - which means a very powerful field such as would be created by an induction motor/brake will fall off to almost nothing a metre or two away. The issue being that equipment in the four foot isn't tens of centimetres away (by definition it can't be more than 72cm from the rail).

I was thinking of the field interfering with the signal not the equipment.

Which means that unless the passing brake causes permanent damage or switches it off the system between the rails it is unlikely to be a problem, and given that at least on some trains the electric motor is in the bogie, complete with it magnetic fields

, some degree of tolerance must be built in.

 

[edwin_m]

The issue is probably to do with track circuits. These typically pass a current of around one amp through the rail, and I imagine the eddy currents induced by a brake or a linear motor would be far more than this. It would be necessary to prove to an ultra-high degree of confidence that this current couldn't find its way into the track circuit and generate a wrong-side failure (effectively making the train invisible to the signalling). This would have to be proved in unusual situations such as a train stopped over a track circuit joint or in numerous possible failure modes.

I believe the Germans have historically used signalling equipment which is far less prone to this sort of interference, because their trains used AC motors before the advent of modern power electronics, which were far more "noisy" electrically (and of course eddy current brakes too). Modern signalling equipment used in the UK has better electromagnetic immunity, and axle counters eliminate any electrical connection between the rails and the signalling equipment. But there is still much older kit out there including track circuits that could be failed wrong side by a either AC at a single frequency or by DC flowing for a second or so.

 

[najaB]

I was thinking of the field interfering with the signal not the equipment.

As was I.

 

[flypie]

As was I.

My comment earlier should have read
"Provided the eddy brakes are NOT on the same carriage as the sensor for those devices".

 

[najaB]

My comment earlier should have read
"Provided the eddy brakes are NOT on the same carriage as the sensor for those devices".

As edwin_m said, the question that needs to be answered is will any induced currents (and fields) have an impact on any other signals - e.g. track circuits, ATP loops, axle counters, etc. I don't expect that they will, but the railway needs to prove (as far as practicable) that they won't.