Re: (erielack) Re: EL Mail List Digest V3 #2336

[Bill Herkner <gwherk_@_earthlink.net>]

On 3/31/07 10:21 PM, "Janet & Randy Brown" <jananran_@_mymailstation.com>
wrote:

> The reason for transition is that as traction motors gain speed, their
> armature and field windings begin to act as generators and produce drag --
> back electromotive force, or EMF.  To counter the EMF, transition changes the
> relationships of the motors to each other, and the relationships of the
> individual motor fields to their armatures.  The steps are Full Series (all
> fields receiving full excitation and motors wired in series); Series Shunt
> (motor field current is shunted around the fields to lower excitation; Full
> Parallel (fields on full current again, but the motors wired in parallel,
> usually in pairs); and Parallel Shunt (reduced excitation to the motors, which
> are connectd in parallel.
> 
> This is why an accelerating diesel locomotive will sound like it is "shifting
> gears" -- because, electrically speaking, it is.  Most switchers didn't have
> transition; they were meant to drag.  Road locomotives had it, to enable them
> to go faster.  In early road locomotives, it was manual, at the discretion of
> and executed by the engineer.  Frequent misuse led designers to make it
> automatic after the FT.
> 
> Randy Brown
> --------------------------------------------------------------
>> PS, What is transition?
> 
> 
> "Transition" - at a high level - is when a diesel-electric's electrical system
> is changed from a parallel to series (and backwards) system. I can't remember
> what the initial state is, but the traction motor can be wired in parallel
> (output from generator is fanned out to each traction motor) or in series
> (output of generator goes to one traction motor, which then outputs the next
> traction motor, and so on)
> 
>    - Paul
> 
> 
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This is the best explanation of transition that I have heard.
    Bill Herkner


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End of EL Mail List Digest V3 #2338
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