Later EMD AC Traction.

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Later EMD AC Traction.

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Feb 8, 2014, 4:06pm

I finished reading EMD Locomotives a while ago and have a question. In the later descriptions he describes the prime mover attached to an alternator, which pushes the AC power(1 phase, 3 phase, ?) into a rectifier or whatever to create DC and then into another device to convert it back to 3 phase. The frequency of the phases can then be varied to control speed and pulling capacity.

First off, I wonder if I'm reading this correctly. If I am then why? He mentions something in the article about being easier to control. As you can tell, my grasp of this subject is rather poor.

Any references or books that could explain it to me in terms that a guy with a bit of wiring background and generator knowledge from home use and telephone system backups in both AC and DC power might understand?

Modificato: Feb 8, 2014, 4:23pm

Simple answer: induction motors are lighter, cheaper, more reliable than DC motors (no need for two sets of windings, no brushes), but when you use them in traction you ideally need to be able to control the frequency of the supply current to be able to regulate their speed. With power semiconductors you can do that quite efficiently, but in the old days it wasn't possible, so railways used DC or low frequency AC motors.

I've got a book called Electric traction systems by Douglas Hinde, but it's a bit out of date. You could try here:

Feb 10, 2014, 5:18am

You might also find the Wikipedia page on induction motors helpful:

Feb 11, 2014, 3:08pm

Once I finish museum, flower show, newsletter and taxes I plan to get back to this and back to my reading. Thank you for the information on this and on the 4 rail layouts on the underground. ceu