Linear Induction Motors

I've done a little reading up about linear induction motors (LIM's) in connection to various maglev projects as well as Vancouver's SkyTrain and the new AirTrain at JFK Airport.

My question: Might there be a place for LIM technology in conventional (i.e., non-maglev) high-speed trains? It seems like the technology has quite a few advantages over normal rotary motors in terms of speed, braking, and ease of maintanence. (Biggest advantage: No moving parts to wear out.)

The big problem with maglev trains is that they require an entirely new infrastructure. But what if standard high-speed tracks were outfitted with a continuous LIM reactor plate between the rails, with the motor units of high-speed trains designed to work with this system?

Presumably, overhead catenary would still be required to supply motive and HEP power to the train, but it seems like this might be a way to combine some of the best features of maglev with conventional TGV-style trains. In areas where high-speed trains share tracks with conventional trains (near terminals, etc.), the reactor plate wouldn't prevent regular trains from using the same tracks.

Has anybody else studied this possibility? What are your thoughts and comments? I'll admit I don't know much about LIM technology, but it seems promising.

You are still talking about wheels. They are moving parts and might start to "hydroplane" or whatever the word should be for air.

You still have to install a wide steel stator plate down the center of the tracks with a very close clearance to the over part of the motor. That is what makes a linear motor.

All of this was taken care of by Mag-Lev. The whole train floats.

Yes, but maglev is still developing technology. It requires an entirely new infrastructure with a massive capital investment, and IMO, will only be practical for certain limited applications.

You are still talking about wheels. They are moving parts and might start to "hydroplane" or whatever the word should be for air.

At what speed would this become a problem? What I have in mind is trains operating in the neighborhood of 250-300 MPH, which I don't think is fast enough to cause any "hydroplaning" action.

You still have to install a wide steel stator plate down the center of the tracks with a very close clearance to the over part of the motor. That is what makes a linear motor.

Yes, that's what I described in my opening post. And the problem with this is....?

Compared to upgrading the track and installing catenary wires, I suspect that the stator plate wouldn't be all that expensive.

And would a LIM-driven train even need catenary, or is there some way to pick up electricity from the stator plate without making physical contact with it?

maglev is still developing technology. It requires an entirely new infrastructure with a massive capital investment

Apart from end-point stations, so does conventional HSR.

As for JFK's Airtrain, I saw a conventional third-rail in place there.

Given that France already tested a TGV at about 321 mph, and that Spain's Talgo 350 is supposed to operate at about 220 mph in revenue service, I'd say that the bounds of steel-wheel-on-steel-rail haven't been fully strained just yet...

LIM has to do with power transmission and nothing else, AFAIK—using inducers within the ground to power motors above the ground, and it's actually been considered to power electric buses with it as an alternative to using trolley wire. Nothing about it would be a replacement for Maglev, or a cheaper alternative for it.

BTW, I've never heard of trains "hydroplaning", though I could be wrong—you need a flat surface upon which water can build up for that to occur, and the phenomenon refers to pneumatic tires riding on a film of water.

There is magnetic attraction between the plates and the train , so any sort of planing would be less of a problem than with convential technology .
I have read that the trains have to slow down at the crest of a hill on one tgv line , as there is a danger of them becoming airborne at that point !
but the gradients are alot steeper on the tgv line than a normal rail line .

I have read that the trains have to slow down at the crest of a hill on one tgv line , as there is a danger of them becoming airborne at that point

That would have to do with the aerodynamics, or lack thereof, of the trainset. Modern aerodynamics of land-based vehicles have as their intent the effect of defeating lift and replacing it with the effect of pushing the vehicle towards the ground in order to promote better traction.

I have a hunch that the reason Airtrain, Skytrain, etc use LIM is actually quite simple. They're all fully automated systems with no onboard driver. Well, a LIM can allow regenerative barking to near 0mph, and predicatable braking/motoring. This greatly simplifies the control software, because we now know how the car's gonna react and wheel slip isn't an issue.

As a bonus, since there's no tread braking at any real speed, wheel wear becomes nill.

I noticed Airtrain has a nasty rough transition from regen to air brake, and it's around 5mph or less. I'm willing to bet that the motors do *all* the non emergency braking above that speed.

The other bonus is no gearboxes to maintain.

Of course, this is offset by tighter track requirements plus the need to have that darn reaction plate in the center. $$$$$ there.

Well, a LIM can allow regenerative barking to near 0mph...

Nice typo there.

Of course, this is offset by tighter track requirements plus the need to have that darn reaction plate in the center. $$$$$ there.

What's the reactor plate actually made of? For a brand-new high-speed ROW, I imagine the cost would be a drop in the bucket compared to that of the overall project. But then, I could be wrong.

Depending on what it's made of, I could see a problem in some areas where it would be swiped by vandals and sold for scrap in order to feed a meth habit. This was such a big problem in rural Oregon that the state DOT had to switch from aluminum to steel guardrails on mountain roads because so many of the aluminum ones were getting stolen. Go figure.

I have to raise the question again as to why discuss LIM in a HSR forum, since LIM has naught to do with any such system.

Irish Chieftain wrote:I have to raise the question again as to why discuss LIM in a HSR forum, since LIM has naught to do with any such system.

If you had bothered to read my opening post on this thread, you'd have noticed that I was exploring the theoretical possibility of adapting LIM technology for high-speed rail. It even says so right in the title.

And last time I checked, your name isn't listed as a Moderator for this forum.

Hmm? WADR, what's my not moderating this forum have to do with my asking a question that I feel to be valid? I read your opening post and didn't see a premise that was terribly concrete. You're inviting criticism, so be happy that it's constructive in my case.

LIM is a power source and nothing else. Conventional HSR already uses high-voltage catenary wire as a power source and there is no reason to use the more expensive and unproven-at-high-speeds LIM system. LIM would not "magnetize" your train to the rails to act as a factor in traction, braking, adhesion or any such thing—it is not that manner of system.

LIM's not a power source, it's a propulsion system. Hence, linear induction <i>motor</i>

It in essence describes both, after a fashion, correct? The inducers are the power source for the motors.

the inducers are part of the motor . they effectively become one magnetic field , whose influence on the other magnetic field produced by the train , propel the train .
i would say braking could be alot better than with rail wheel , there is no loss of friction , as the force is magnetic .

The easiest way to describe LIM is this: Take a regular 3 phase AC motor. "unroll" the stator (windings). Now, "unroll" the rotor. the rotor is the 'reaction plate' on the tracks.

This shouldn't be confused with inductive pickup, which is in fact used out west somewhere on a really short 'trolley' line. In that system, the power is transmitted via the indfuction system, and conventional motors move the train.

In LIM, the reaction plate doesn't supply electricity to the train, but rather is just an 'unrolled' rotor for the windings to slide along. You could have a LIM train powered by anything - even a diesel-generator set, if you wanted.