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Date: 10/29/24 13:38
how does a transition work?
Author: dragoon

First gen EMD units (and possibly the other guys - GE, Alco, Baldwin, etc ) had/have.a distinct drop in RPMs when 'transitioning' the traction motors from series to parallel connections to the generator.

I hope that is a reasonable description of it?

Was that operation initiated automatically or manually?



Date: 10/29/24 13:48
Re: how does a transition work?
Author: HotWater

dragoon Wrote:
-------------------------------------------------------
> First gen EMD units (and possibly the other guys -
> GE, Alco, Baldwin, etc ) had/have.a distinct drop
> in RPMs when 'transitioning' the traction motors
> from series to parallel connections to the
> generator.
>
> I hope that is a reasonable description of it?

Pretty much, yes.


> Was that operation initiated automatically or
> manually?

Very early units, like EMC/EMD FT models were manual transition, as done by the Engineer. Later forward transition was automatic, with backward transition requiring the Engineer to throttle down to say, #3. As time and development progressed, all transition was automatic.



Date: 10/29/24 14:52
Re: how does a transition work?
Author: Greatdome

To avoid overheating traction motors from a standing start, current is directed thru all traction in series ("daisy chain"). Once the train is moving, they switch to each motor getting current/voltage independently.



Date: 10/29/24 14:55
Re: how does a transition work?
Author: dan

when amtrak started running UP e's over donner what was the problem again?  you or someone said different set ups? controls/procedures?



Date: 10/29/24 15:45
Re: how does a transition work?
Author: HotWater

Greatdome Wrote:
-------------------------------------------------------
> To avoid overheating traction motors from a
> standing start, current is directed thru all
> traction in series ("daisy chain"). Once the train
> is moving, they switch to each motor getting
> current/voltage independently.

Not quite, i.e. "To avoid overheating the traction motors". The purpose of "transition" is to protect the MAIN GENERATOR, and still allow it to supply DC voltage and current to the traction motors.



Date: 10/29/24 15:47
Re: how does a transition work?
Author: HotWater

dan Wrote:
-------------------------------------------------------
> when amtrak started running UP e's over donner
> what was the problem again?  you or someone said
> different set ups? controls/procedures?

Another cryptic post!



Date: 10/29/24 16:50
Re: how does transition work?
Author: timz

If you're going to disconnect motors and reconnect them,
you naturally don't want llarge currents flowing thru them
while you're doing it. So the control system cuts
engine power (to zero? Dunno.)

Road diesels never connected all their motors
in one series string. On the other hand, many
diesels never got into full parallel.



Date: 10/29/24 17:07
Re: how does transition work?
Author: HotWater

timz Wrote:
-------------------------------------------------------
> If you're going to disconnect motors and reconnect
> them,
> you naturally don't want llarge currents flowing
> thru them
> while you're doing it. So the control system cuts
> engine power (to zero? Dunno.)

During forward transition, the load on the main Generator/engine is only "interrupted" for a few seconds, which the load regulator and engine governor handle easily.

> Road diesels never connected all their motors
> in one series string.

How did you come up with THAT?

On the other hand, many
> diesels never got into full parallel. 

Again, how did you come up with THAT?



Date: 10/29/24 17:16
Re: how does transition work?
Author: timz

You've looked at that few manuals?

There's a question: what was the first C-C
to use full parallel? Maybe the Train Master?
No Baldwin C-C did, nor the SD7-SD9 (and
SD18 I assume). Did any FM diesel before
the Train Master use full parallel?

(Oops -- I see the RSD5 did.

https://www.rr-fallenflags.org/manual/rsd5-op.pdf

Looks like Baldwin C-Cs always had three motors
in series

https://www.rr-fallenflags.org/manual/as616-om.pdf

As for full series: try to name a road diesel
that used it.



Edited 2 time(s). Last edit at 10/29/24 17:28 by timz.



Date: 10/29/24 18:38
Re: how does transition work?
Author: santafe199

This thread just kicked ‘ground relay’

🤪

Posted from iPhone



Date: 10/29/24 19:19
Re: how does a transition work?
Author: dragoon

HotWater Wrote:

> Very early units, like EMC/EMD FT models were
> manual transition, as done by the Engineer. Later
> forward transition was automatic, with backward
> transition requiring the Engineer to throttle down
> to say, #3. As time and development progressed,
> all transition was automatic.

thanks for clarifying, but one more question:
 
was forward/reverse manual transmission accomplished by just getting throttle position 3 or was there another condition, maybe a certain speed?



Date: 10/29/24 20:42
Re: how does transition work?
Author: SP4360

In the spirit of the upcoming season, "Bells will be ringing".

santafe199 Wrote:
-------------------------------------------------------
> This thread just kicked ‘ground relay’
>
> 🤪
>
> Posted from iPhone



Date: 10/29/24 20:51
Re: how does transition work?
Author: santafe199

SP4360 Wrote: > ... "Bells will be ringing" ...

I love it!

:^)

 



Date: 10/30/24 05:27
Re: how does a transition work?
Author: dan

HotWater Wrote:
-------------------------------------------------------
> dan Wrote:
> --------------------------------------------------
> -----
> > when amtrak started running UP e's over donner
> > what was the problem again?  you or someone
> said
> > different set ups? controls/procedures?
>
> Another cryptic post!

OK JACKHERE YOU GO STRAIGHT OUT OF THE HORSES MOUTH
13:17
Re: Amtrak: When UP E units had to step back
Author: HotWater WAF Wrote:
-------------------------------------------------------
> spnudge Wrote:
> --------------------------------------------------
> -----
> > I think he meant "transitions". We didn't get
> the
> > dope on the manual transition until they had
> been
> > out there for months. I guess we must have
> burned
> > up the electrical on a bunch of them.
>
> Thanks Nudge. Yes a bunch of Es were burned up
> until they were corrected

OK, now THAT makes sense. The "issue" with earlier "E Units", was; they had automatic FORWARD transition, but upon slowing down under load, the throttle MUST be reduced to something like 3 or 2, for BACKWARD transition to take place. Thus, having any older "E Units" on a heavy grade, without making BACKWARDS transition, promptly burned up the main generators.

of course e8 and e9's were later e's

 

 



Edited 1 time(s). Last edit at 10/30/24 05:29 by dan.



Date: 10/30/24 06:58
Re: how does a transition work?
Author: funnelfan

This discussion seems to be missing some important aspects, namely Back EMF (BEMF) and Field Shunting. But first let's go over another major point. At very low speeds where the DC traction motors are slowly rotating, amperage, or the flow of electrons can get very high. And that high flow can cause the motor windings to get very hot to the point of melting down. So by connecting the traction motors in series, you increase the resistance and that lowers the flow (amperage) and results in more actual effort from the flow being applied to the rails.
Now the issue is that as speed increases the DC traction motors start acting like generators, creating a backflow of voltage known as BEMF. This cancels out the voltage being supplied by the generator. And since the traction motors are connected in series, it doubles the voltage much like how two batteries in series doubles the voltage. So at around 20~25mph you want to transition to having all the traction motors in parallel so the generator is only trying to overcome the BEMF voltage of each traction motor individually. But again as speed increases the BEMF is still going up trying to cancel out the generator voltage. This is where field shunting comes into play. The idea is you want those Traction Motors to become less effective generators. So you start shunting the field so it cannot produce as much BEMF and the generator can more easily overcome the BEMF voltage. There is some trade off as the Generator voltage is also getting less field strength to apply traction, but at speed it doesn't need all that field strength as it can only supply just so much power.

Ted Curphey
Ontario, OR



Edited 1 time(s). Last edit at 10/30/24 06:59 by funnelfan.



Date: 10/30/24 07:42
Re: how does a transition work?
Author: callum_out

Ted, excelllent summation.

Out 



Date: 10/30/24 09:15
Re: how does transition work?
Author: HotWater

timz Wrote:
-------------------------------------------------------
> You've looked at that few manuals?
>
> There's a question: what was the first C-C
> to use full parallel? Maybe the Train Master?
> No Baldwin C-C did, nor the SD7-SD9 (and
> SD18 I assume). Did any FM diesel before
> the Train Master use full parallel?
>
> (Oops -- I see the RSD5 did.
>
> https://www.rr-fallenflags.org/manual/rsd5-op.pdf
>
> Looks like Baldwin C-Cs always had three motors
> in series
>
> https://www.rr-fallenflags.org/manual/as616-om.pdf
>
>
> As for full series: try to name a road diesel
> that used it.

Pretty sure that ALL EMD four axle units from FT models through GP35 and GP40 models started in full series. Must admit that I didn't read all that many manuals, as I learned by working on the various EMD models and used the electrical schematic wiring diagrams. I started my career with EMD on June 1, 1962 in the Field Service Dept. and retired at the end of 1998. Have you ever actually work on any locomotives, steam or diesel electric?



Date: 10/30/24 10:37
Re: how does transition work?
Author: timz

> Have you ever actually work on any locomotives,
> steam or diesel electric?

Never.

Here's the F3 operator manual; it tells about
transition on page 101 of the manual, on page 2
of the PDF

https://rr-fallenflags.org/manual/f3-s010.pdf

Later in the manual it's more specific about
what "series-parallel" means, in Figure 6-1
on p604 in the manual, page 3 of the PDF

https://rr-fallenflags.org/manual/f3-s060.pdf

Here's a puzzle: a 1952 manual for the RSD5

https://rr-fallenflags.org/manual/rsd5-op.pdf

says (page 8 of the manual, page 6 of the PDF)
it starts with two motors in series, and
transitions to full parallel. But a 1954 Alco
maintenance manual says the "1600 hp
6 motor locomotive" starts with three motors
in series and transitions to two motors in series,
with no mention of any full parallel. (Pinkepank
mentions some Alcos having a larger GT-566
generator -- maybe it's something to do with that.)



Date: 10/30/24 12:59
Re: how does a transition work?
Author: dragoon

funnelfan Wrote:
-------------------------------------------------------
...But again as speed increases the
> BEMF is still going up trying to cancel out the
> generator voltage. This is where field shunting
> comes into play. The idea is you want those
> Traction Motors to become less effective
> generators. So you start shunting the field so it
> cannot produce as much BEMF and the generator can
> more easily overcome the BEMF voltage.

were the field shunting resistors on the motors? where - and they got pretty hot, were engine fires caused by these?



Date: 10/30/24 13:07
Re: how does a transition work?
Author: HotWater

dragoon Wrote:
-------------------------------------------------------
> funnelfan Wrote:
> --------------------------------------------------
> -----
> ...But again as speed increases the
> > BEMF is still going up trying to cancel out the
> > generator voltage. This is where field shunting
> > comes into play. The idea is you want those
> > Traction Motors to become less effective
> > generators. So you start shunting the field so
> it
> > cannot produce as much BEMF and the generator
> can
> > more easily overcome the BEMF voltage.
>
> were the field shunting resistors on the motors?

No.

> where -

Generally, in the top rear of the electrical cabinet.

and they got pretty hot,

Yes.

were engine fires
> caused by these?

No.



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