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
>
>
> The Erie Lackawanna Mailing List
> Sponsored by the ELH&TS
> http://www.elhts.org
> To Unsubscribe: http://lists.elhts.org/erielackunsub.html
This is the best explanation of transition that I have heard.
Bill Herkner
The Erie Lackawanna Mailing List
Sponsored by the ELH&TS
http://www.elhts.org
To Unsubscribe: http://lists.elhts.org/erielackunsub.html
------------------------------
End of EL Mail List Digest V3 #2338
***********************************
This HTML page is © 2000-2009 Blue Moon Online System and The Railfan Network
This page and the data contained therein may not be reproduced
for any form of commercial use without the explicit permission
of J. Henry Priebe Jr. or his duly authorized agent.