Re: MD-80 Electrical

Date:         06 Jun 98 15:39:18 
From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
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James Matthew Weber <> wrote:
> >Yes, 3-P motors easily reverse. They have lots of advantages, &
> >disadvantages to boot. One is, they need 3 phases to start.

> Take a good look a switching locamotive some
> time. If you look carefully you will find this big piece of metal that
> almost looks like chian link fence. Its the external rotor resistor that is
> switched in when the engineer starts up the train.

Uh, are you still talking about three-phase motors?  If so, then this is
wrong.  With the exception of some recent road locomotives, and perhaps
some ancient electrics, locomotives use DC traction motors, not AC.  At
least those built or operated in North America.  No Diesel-electric
switchers have been built with AC motors to my knowledge.

Perhaps you are thinking of the dynamic brake grid.  To restrain a train
on a long downgrade, without burning up a lot of brake shoes, the traction
motors are used as generators with large resistor grids used to load them.
(In a pure electric, the generated power can be fed back into the power
feed, helping trains coming *up* the hill.  This is called regenerative
braking.)  Dynamic brakes are used on road locomotives; switchers very
rarely have them.

[Obviously this tangent is way off the original thread and topic.
Please followup if you like in e-mail, not by posting to the group.]

Karl Swartz	|Home
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