Not a very well-informed brain re locomotives. But I have been wondering:
I know the advantage of diesel-electric locomotives over a straight coupling (via a transmission say in a caterpillar earth mover) of a diesel engine to driving wheels is the full torque even at low speeds. But what is the actual physical mechanism of that? As the traction motor receives “juice” from the ramping up diesel via the generator, what factor is at full play at all speeds…is it amperage, voltage or what? You can tell I am not conversant, but curious.
What was the limitation to the DC traction motors? I heard that the actual physical wiring, coil size etc. has limitations in DC, such that the higher power required means unmanageable sizes of physcial wiring etc. Is it that the AC current is only energizing the coils half the time that give the edge to AC over DC in efficiency so that they can be of useful size even carrying huge currents?
In loco information where is sometimes is said that various types of trucks are swapped for another, say in a rebuild do the traction motors always mate in some universal way? So if the old AAR trucks say, are swapped out for Blombergs or HT-C trucks, are the traction motors kept or do they have to be matched to the type of truck coming in, or do they come in a set of trucks with traction motors?
Locomotives use electric transmission because nobody can build a clutch that will withstand even 1300 HP, let alone 4 or 5 thousand hp. You have to have a clutch to use a straight mechanical gearbox. The other bennie of electric drive is you get full torque at stall (zero rpm). The diesel prime mover runs at it’s best speed, turning a generator which flows juice to the traction motors. The magnetic fields inside the motor pull as hard as they can even if the motor is not turning at all.
The other thing, when the traction motors are not turning, they generate NO back emf, so very modest voltages will cause enormous currents to flow. They used to switch all the traction motors into series with each other so the enormous current would flow thru the first motor, make it try to turn, then the same current would enargize the next motor and the next. Since non of the motors is turning, the voltage needed to drive them all in series is very little more than the voltage to turn one. Once speed built up, the traction motors were switched into parallel.
[quote user=“Gerome”]
What was the limitation to the DC traction motors? I heard that the actual physical wiring, coil size etc. has limitations in DC, such that the higher power required means un
Good info Dave. I’m not sure of compatibility of switching out traction motors from various makes and especially where the gearing is concerned. There where issues w/ 1st generation high speed gearing (EMD, not sure of GE or Alco)) as the axle gear needed to be so small that it was machined into the axle. Changing out pass to freight required switching out the truck or a complete teardown of the entire assy. Traction motors and there mounting may be somewhat universal to make, but not sure as to mounting to various gearcases.
Have no idea if this was solved in the new 2nd gen locos.