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I certainly know that it is the switch gear that controls transitioning and not the traction motor themselves. I used to teach classes on electrical machines. On Tuesday, January 16, 2018 7:22 AM, "thommack@yahoo.com [CBQ]" <CBQ@yahoogroups.com> wrote: A slight correction in John's comment about DC traction motors. It is not the traction motors themselves that allow for transition. It is the switch gear in the electrical cabinet. Thus the locomotive can transition to various combinations of series and parallel TMs. The TM's themselves are series wound. There are two cables for the field coils, and two for the armature (four in total). The four wires are always wired in series - power goes through the field coils then series through the armature (or vice versa). The reason for four cables is so that you can reverse the TM. Since the reverser contactors (magnetic or motorized) are in the main electric cabinet, the cabling for the field coils (whose polarity is reversed to reverse the TM) must also go back to the main cabinet. That is why you don't have just two cables going to the TM (a positive a negative). If you did, then when you tried to reverse the TM you would reverse polarity to both the armature and the field and the motor would continue to spin the same direction regardless of the polarity to the TM. So while there are four cables to a DC TM, it does not have to do with transition, just reversing the TM's. In essence there is still just a single positive and single negative connection to the DC TM. The transition is all done by a separate set of contactors in the electrical cabinet. On early EMD switchers the transition was from all TM's in series (same amperage through all TMs with a voltage drop across all TM's). Thus whatever maximum amperage could come out of the main generator would be seen across all the TM's. Amperage equals torque equals tractive effort. At a certain speed your generator voltage output would max out, and since the voltage across the four TMs would be only one-fourth the voltage of the main generator, you would hit a maximum speed, which might be around 20-25 MPH or even less. At that point the switcher would go through transition where the TM's were put into a series-parallel configuration where each pair of TMs was in series and the two series pairs of TMs were in parallel. Hence your amperage dropped in half across the two sets of TMs (less tractive effort) but the voltage from the main generator only dropped one-half (vs. one-fourth in series), so the voltage to the TM's now doubled, which provides higher speed. At higher speeds you don't need as much tractive effort, so the drop in amperage across the two TM pairs is not critical. I won't get into field shunting (where the TM field is weakened), but this is also used to add speed to the TM. Different locomotives are set up for different modes of transition. One of the problems with the GP35's was that they went through so many stages of transition that it was hard to keep all the contactors maintained and working properly at the right time.. That all went away with the development of the AR10 AC main alternator (AC vs a DC main generator) which could provide a huge amount of amperage compared to DC main generators. So on C&S SD40's, for example, the locomotive started out in series-parallel (three parallel sets of two TM's each in series for maximum amperage and tractive effort) and then went to straight parallel where all TM's saw the full voltage of the main alternator for speed. One thing that John brings up is a very valid and interesting point. If the E5's had manual transition (the engineer decided when to change from one transition mode to another) then Q mechanical staff could actually observe and play with the point when the best time for transition would be on the commuter locomotives. Automatic transition is programmed in at basically a set speed point, although it can be based on more than just a speedometer point. Once the circuitry is in place the engineer has no control over this. So imagine you have a car with an automatic transmission and you want to modify the shift points for when you are doing highway driving vs. when you are doing street driving. you would experiment in manual transmission mode, then take your findings and reprogram the automatic transmission controller. If you can't manually shift the transmission, you could never experiment with different shift points - its locked into the transmission. I think John is right. Since you can't put an E8 or E9 into manual transition mode, use the E5 with manual transition, then take that data and use it to set the transition circuits on the E8s and E9s. BTW, since transition is controlled electrically (and now electronically in a computer), you can set a locomotive up with two different transition settings, and control those with a switch on a control stand. Thus you would sometimes see a switch marked Yard and Road on the control stand so that you could kick cars better when a road switcher was used in the yard, vs. when you were on the road and needed a faster transition for speed. Tom Mack Cincinnati, OH
---In CBQ@yahoogroups.com, <icrr1680@...> wrote : Here are just some thoughts on this question. By 1950,
Burlington management was considering replacing the old, worn out, steam
engines in commuter service with diesels. There was a concern as to how the
diesels would perform, in the start-stop service. So why not use a surplus (for the Q) engine in
a test? There is a well known characteristic of reciprocating steam
engines, stationary or mobile, that they have maximum torque (read acceleration)
at zero speed. Series wound DC motors (like traction motors) share this
characteristic. However, locomotive traction motors are not purely series wound
motor. If they were, only low speeds would be possible. To overcome this,
locomotives have “transitioning”. The E-5’s had manual transitioning, which made
them perfect for the experiment. Later Q E-8’s and E-9’s had their
transitioning modified for the stop-start operation. Anyone who ever rode an E
unit powered dinky knew the engineer could really “pin her ears back”. So it
wasn’t as easy as just taking an off the shelf E unit and putting it in
combination service (my dad used to say “Nothing in this world is ever SIMPLE”).
__._,_.___ Posted by: John Mitchell <icrr1680@yahoo.com> __,_._,___ |