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Western Railroad Discussion > how does a transition work?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. |