Rare Earth Magnets and Other Options: Bookmarks


Trying to find more information on the timeline and development of rare-earth magnets, and then their use in motors, I found this paper – bookmarking it here.  It’s a discussion of the advantages and disadvantages of rare earth magnets, along with some detailed discussion of alternatives.  Along the way, you get a nice, concise description of all the various types and flavors of motor designs in use.

Part One:

1-s2.0-S2214993715000032-gr2The sintered Neodymium Iron Boron (NdFeB) hard magnetic material was patented by Sumitomo Special Metals in 1983 and brought about a step change in terms of electric motor performance. Neodymium is a member of the family of materials known as Light Rare Earth Elements (LREE), along with others including for example Lanthanum (used in optics) and Samarium (also used in magnetic materials).

Part Two:

In an electric traction motor, NdFeB magnets allow a very strong magnetic field to be generated in a very small volume. The alternative would be to use electromagnets, where a magnetic field is generated by passing current through a conducting coil. It can be shown that a 3 mm thick piece of NdFeB magnet produces the equivalent magnetic field to passing 13 A (being the rating of a UK home electrical socket) through a coil with 220 turns of copper wire.

In terms of space, if a current density of 10 A/mm2 is assumed in the conductor (which is typical for normal operation of a traction motor), then an equivalent electromagnetic coil might have five times the cross sectional area of the NdFeB magnet. At the same time the coil would produce losses in the windings of 50 W or more per metre length of the coil, arising due to the electrical resistance of the conductor. To put this in perspective, in a representative 80 kW traction motor the optimum use of NdFeB magnets would theoretically be equivalent to saving perhaps 20% in total motor volume and, conservatively, in the order of 300 W of winding loss.1-s2.0-S2214993715000032-gr4

The paper then goes on to discuss the options and alternatives.  A great read, but for my purposes, probably not too important.  The questions will be on the test, however – better read up!



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