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As many of you know, many high-speed trainsets (such as Eurostar, Acela, and TGV, as well as all Maglev trains) use linear-induction AC motors (LIMs). It's my understanding that the TMs on AC diesel freight units (such as AC4400 and SD70MAC) are not of the LIM variety. What is it about LIMs that seems to make them innapropriate for freight units?Jonathan Nikiforovs. Milepost 180, CP Belleville Sub.Repainter for Yonder Locomotive Works.
"A crictic is a man who creates nothing and thereby feels qualified to judge the work of creative men. There is logic in this; he is unbiased - he hates all creative people equally." - Lazarus Long
Whoa whoa whoa....John, you're getting really confused here.The most modern high speed trainsets use ASYNCHRONOUS AC motors, not LIM's. I don't 100% understand the difference between synchronous and asynchronous AC motors, but I think it has to do with the brushes, and their connections.As for why one is better than the other? I would think that the less contact you have, the less maintenance you have to do. But it could also be due to that as asynchronous AC motors are newer technology, they may just cost more.LIM's are not traction motors per se....think of it as what happens when you take the field magnet off of a DC motor, lay it out flat, and run your armature over it. At least that's how I understand it.DanAbsolute power corrupts absolutely.
Hi JonFirst some basics - at the most basic level since I'm writing from memory of reading done years ago and high-school physics classes from somewhere in the dawn of prehistory.An induction motor has no brushes or commutator - it uses induction to get currents flowing in the armature. Such motors are often synchronous - they have to rotate at the correct speed to work efficiently and are usually fixed-speed motors (often using for tooling and especially for clocks).A linear induction motor takes the field coils and laminations, straightens them out, and lays them down along the track or route to be followed. They are not a rotating device at all. Any piece of equipment which is running on conventional rails (two rails only or 3rd/4th rail electrification) will not be able to use an Linear Induction Motor. These require that part of the motor is laid between the tracks (or along side them) or burried inside the structure (such as with a monorail). Without that component, a linear induction motor propelled vehicle won't go. It's a bit like trying to make a locomotive for a rack railway which relies entirely on the rack and pinion for traction work on along a track with no rack laid down.For a better understanding, I think you will need to either do a web search or visit our library which is undergoing renovations.Cheers from a fellow Whitby residentJohn
