Western Railroad Discussion > Traction motor transition

I was reading a 1950's article about problems with traction motor transition from series to parallel. Do modern locomotives still do this? Passenger and freight?
Does it ever cause problems?
TIA.

Locomotives still transition, and yes it can still cause problems. Older locomotives often have problems when relays fail to pickup.

Ted Curphey
Ontario, OR

The technology has evolved a bit in the past 60 years...

The other day had a UP SD70M on Point with an older UP C40-8 behind. The SD70M had that transition problem... I noticed it the most between 16-24mph. That old dash8 never missed a beat! lots of life still left in her.

SD70Ms don't have traction motor transition, they have alternator transition; the TMs are wired in permanent parallel.

EMD went to alternator transition starting with the 50-series, GE with the Dash-8s. All ACs are in permanent parallel also.



Edited 1 time(s). Last edit at 08/03/14 15:36 by Labiche.

Transition was never in the traction motor but in the way traction motors are connected.

As motors rotate under power they also generate electricity called back emf. Eventually the emf (voltage) applied equals the back emf (voltage)generated and the motor is in balance and will not pull harder nor go faster.

So the locomotive is set up so the traction motors are connected in series, series parallel and parallel.

In series each traction motor receives 1/4 or 1/6 of the voltage and all of the amperage. This is good for starting out. This works well until the back emf balances the emf and the locomotive will not go any faster. So transition occurs and the traction motors stay in series but the trucks connect in parallel. The motors get 1/2 the voltage and a lesser share of the amperage. Eventually that nasty back emf rears it's ugly head and locomotive acceleration peaks again. The final transition occurs and each traction motor is in parallel to get maximum voltage from the alternator. It will not balance until back emf reaches this high voltage level which may be higher than track speed. Motor amperage is at the individual lowest level but the locomotive speed is high enough the traction motors are not digging and scratching to get the loads moving.

There are also traction motor shunts and gear ratios involved to make this all work better.

Posted from Windows Phone OS 7



Edited 1 time(s). Last edit at 08/03/14 18:09 by fbe.

FBE has just provided the best most concise definition of why locomotive transition I've seen.--and my instructor at choo-choo U when I was an engineer trainee took a whole day to try to explain it!

Agreed!

DrLoco Wrote:
-------------------------------------------------------
> FBE has just provided the best most concise
> definition of why locomotive transition I've
> seen.--and my instructor at choo-choo U when I was
> an engineer trainee took a whole day to try to
> explain it!

Thank you, gentlemen for the kind words. This was rehearsed for nearly 30 years and who knows how many trainees.

Posted from Windows Phone OS 7

This hits the nail right square on the head: "Transition was never in the traction motor but in the way traction motors are connected."

>SD70Ms don't have traction motor transition, they have alternator transition;
>EMD went to alternator transition starting with the 50-series, GE with the Dash-8s.

No such thing.

Early AC electrics, like the VGN and N&W, used cocantenation, but all they got out of the deal was two running speeds.

>So the locomotive is set up so the traction motors are connected in series, series parallel and parallel.

Diesels used only series-parallel and parallel, which to keep things crystal clear, were called "series" and "parallel".

"Transition" means "change" (from series to parallel and vice versa) not a particular combination of traction motor connections, including field shunting.

DrLoco Wrote:
-------------------------------------------------------
> FBE has just provided the best most concise
> definition of why locomotive transition I've
> seen.--and my instructor at choo-choo U when I was
> an engineer trainee took a whole day to try to
> explain it!

I 2nd the motion!!!

Now, to make things really interesting--and perhaps FBE can provide the answer--"Why did Amtrak order all of the EMD SDP40Fs to start and go through the entire sequence in Parallel? Unlike their sister freight units the SD40-2s?" Unlike the ATSF (and MILW RD) FP45s they were based upon (aside from the SDP40Fs going from the 3600 V-20 to the by-then-standard 3000 HP V-16?). And granted, even the AMTK EMD SDP40Fs had a "Series Start Switch" in front of the hoghead for "starting out on tough grades." The best explanations that I've heard was that with two of these big bruisers (SDP40Fs) up front, most trains could start in pure parallel, and that is was "smoother." To just start out in parallel all the way from 9-to 90 or whatever.

Also, FBE, perhaps a bit of explanation about the difference between 6-axle and 4-axle loocomotives? As I've heard varying and confusing explanations on this, and, such things as that such units as SD24s had a very confusing, or more multi-staged transition, and also that the GP30-Series did as well, and were more cantakerous that later EMD 4-axle locos? And nobody ever sufficiently explained to me the difference between 4-axle and 6-axle locos. And, I never got the same transition steps on GP40s or GP50s that I did on SD40-2s!

Also, at the risk of adding to too much into this, along with the "transition at the alternator" part of this discussion, true that EMD began this with the 50-Series. But GE began this with the Dash 7s, not with the Dash 8s!



Edited 1 time(s). Last edit at 08/04/14 11:44 by Red.

I wouldn't want to ride a passenger train and get a transition kick. Transition can be a rough event on some engines.

fbe Wrote:
-------------------------------------------------------
> Transition was never in the traction motor but in
> the way traction motors are connected.


Thanks fbe for posting this great lesson!

Chuck



Edited 1 time(s). Last edit at 08/04/14 06:54 by RailDawg.

The GE Dash-8s and up don't make any type of transition. The SD70 does, not sure about the SD70M-2.

Passenger units are generally always full parallel and never make transition. Metra's F40Cs were originally built with the series start button like the SDP40F, but that feature was later removed.

Posted from Android



Edited 1 time(s). Last edit at 08/04/14 08:29 by MetraUPWest.

> Passenger units are generally always full
> parallel and never make transition.

Units built since the 1960s, he meant.

In the 1950s many freight units never got into
parallel, but no road units connected all their
motors in one series string. The SW1 did--
was it the only one?

Dunno why he says "no such thing" as alternator
transition-- must be a semantic quibble. SD50s
(and SD60s? and SD70s?) had two sets of stator
windings in their alternator/generators and
reconnected them instead of reconnecting
the motors.

Thanks for the correction. I should've specified modern passenger. The SD60s and SD70s- with the possible exception of the SD70M-2- make alternator transition just like the SD50s, so there defintely is "such a thing".

Posted from Android



Edited 1 time(s). Last edit at 08/04/14 10:42 by MetraUPWest.

MetraUPWest Wrote:
-------------------------------------------------------
>- with the
> possible exception of the SD70M-2-

They make transition too, and just as violently as the rest of them.

Lol! Thanks for the info. Never had one in the lead so I wasn't sure.

Posted from Android

>Also, FBE, perhaps a bit of explanation about the difference between 6-axle and 4-axle loocomotives? As I've heard varying and confusing explanations on this, and, such things as that such units as SD24s had a very confusing, or more multi-staged transition, and also that the GP30-Series did as well, and were more cantakerous that later EMD 4-axle locos? And nobody ever sufficiently explained to me the difference between 4-axle and 6-axle locos.

As far as I know, both the older six motor EMDs and GEs (pre-c1970 era) had only series(-parallel) and parallel because two motors were connected in series and then reconnected in parallel. In four motor locomotives there were two sets of these two-motor connections, in six motor units, there were three sets. It was different with electric railways: two motors were permanently connected in parallel, and these pairs were connected either in series or parallel with other identical permanently paired motors.

Early EMDs (up to 1950s) had manual transition, meaning the engineer had to perform the transition using that lever on the left of side of the round control stand. Mixed in with the steps on this lever were field shunting positions, and this is what gave rise to the erroneous terms "series transition", "field-shunting transition", and so forth.

>I wouldn't want to ride a passenger train and get a transition kick. Transition can be a rough event on some engines.

SP's 3200s had [traction motor] transition (series-parallel to parallel), which was pretty smooth. Traction motors usually used shunt transition, which could be accomplished pretty smoothly. Main gen/ main alternator transition must be a different thing, possibly more difficult to control unloading/loading rates for the change-over, more like the results with open transition and traction motors.

>Dunno why he says "no such thing" as alternator transition-- must be a semantic quibble. SD50s (and SD60s? and SD70s?) had two sets of stator windings in their alternator/generators and reconnected them instead of reconnecting the motors.

I said it because I've never heard of it being applied to the main generator and alternator connections before.

I grew up riding behind ALCO RS-2s and RS-3s on the New York Central River Division. The kick wasn't there, but the sound was memorable (and unfortunately not duplicated in sound decoders for HO-scale ALCOs. The sounds associated with the transition were very similar to what you would here when a truck shifted gears. The engineer would close the throttle, make the transition, and then open up the throttle again.

John