I should add that the Sacramento Northern used real dynamotors, not things commonly confused for dynamotors that are really M-G sets and the like.


600/750V motors are fairly commonplace. 1500V motors are expensive and exotic. The issue is the commutators. Look at the number of bars and distance between brushes in a 600V motor. That's good enough for 600V, but 1500 will flash over that. 1500V motors have larger diameter commutators with more bars to have enough insulation to avoid 1500 volts flashing over. A more complex and expensive motor by a wide margin.

There's no such thing as a 3000V traction motor. To avoid flashover, the commutator would have to be enormous, and it wouldn't fit where traction motors go. If there was such a thing, you would have seen 6000V DC electrifications. Remember doubling voltage cuts transmission losses by 75%, so they pushed trolley voltage as high as they affordably could.

Insulating for a higher voltage to ground is not a big deal.

With DC motors your equipment must have one transition to have a decent speed range. With 4 motors, a car goes series-parallel to full parallel... or it goes full series to series/parallel. In the latter case, top motor voltage is half trolley voltage, but the motors must be insulated for trolley voltage to ground obviously.

Now, how would you optimize for cost, given what I just said? :)

That's what I suspected, that there are no 3000V motors. Paired-up 1500V motors would have been key to the South Shore rewiring their Little Joe-like GE units to 1500 V catenary voltage.

Steve

Updating just for a record:

I blundered upon this online list seemingly accounting for all the MU's:

http://www.21pw.com/dictionary/Erie-Lac ... Cars_68253