Overmod:
An eight axle P-motor would have been good for 4/3rds the power of the P1. The 6 axle design looks to be the better choice as it allows a 1/2/3 progression of running speeds versus the 1/2/4 progression with 8 axles. The three field strength options gave a total of 9 running speeds, which is pretty flexible for a non-chopper equipped DC locomotive.
The motors were designed for 1500V, and probably would run well at 1750V which would increase the speed for a given T.E by 10%. The 1969 era GE-750 motors that would have been used on the C-C's proposed to the Milwaukee were good for a continuous output of 900HP per motor, with short term ratings of maybe 1200HP per motor.
An aside about motor ratings. The voltage limit is imposed in part by the insulation of the wiring, although this has more of an effect when running two 1500V motors in series for operation on 3000V. The more important limitation is the commutator, where more than 20V between segments is almost guaranteed to cause problems (flooding the commutator with SF6 might help). Long term power ratings are set by thermal limits, particularly so in the days before silicone and polyimide (Kapton) insulation - these ratings are related to current, varying little with voltage. Short term power rating are often limited by commutation (even for interpole motors), excessive current on the armature can cause magnetic field distortions at the pole faces leading to excessive sparking at the commutator and potential for ringfire. This problem is often made worse with field shunting.
The P-1's were somewhat less powerful than the Westinghouse "Quills" on the Milwaukee, though more flexible and presumably less of a maintenance headache. The Quills also had regenerative braking, which was not strictly needed for the P's.
About Kapton insulation. Some time in the 1970 - 1980s (?) the FAA came out with an airworthiness directive that all replacement wiring on aircraft would be kapton. You could still splice onto the older ( May have changed ) but you can imagine the problems especially cable mining when feasible.. Replacement wiring all has to have a unique identifier stamped on the wiring that original had or did not have.. As well sometiimes color coding for the various guages. Interesting machine to stamp the identifier.
I've heard conflicting stories about Kapton for aircraft wiring, it's flexible but also more prone to wear than other insulators. One advantage for aircraft is that Kapton maintains its flexibility to (or almost to) liquid helium temperatures.
For motors, Kapton has the highest operating temperature of any common polymer and has a very high dielectric strength (i.e. hih breakdown voltage for a gien thickness). The high temperature allows for more current in a given winding and the high dielectric strength means that the insulation could be made thinner, which allows for more copper and also promotes better heat transfer. Both mean more currnt and thus more power out of a motor.
The NYC P motors were designed for short trips with fast acceleration, so GE may have tweaked the motors for ability to handle large overloads.
Erik_MagI've heard conflicting stories about Kapton for aircraft wiring, it's flexible but also more prone to wear than other insulators.
In my opinion, the difficulty is less 'wear' per se than that the insulation is relatively soft and pressure tends to distort it. So pressure at an 'edge' can cause cold flow ultimately resulting in exposure of point contact if the edge is conductive or grounded to some reference.
Some of the usual methods for mechanically or chemically hardening the material surface to 'preclude' this sometimes founder because the underlying plasticity, at required thickness for "cost-effectiveness", makes the applied coating fail in strain as the substrate yields. This is not dissimilar to what is seen in some hard-coating failure in bearings where deforming of the underlying surface is often the 'proximate cause' .
In my opinion, the difficulty is less 'wear' per se than that the insulation is relatively soft and pressure tends to distort it. So pressure at an 'edge' can cause cold flow ultimately resulting in exposure of point contact if the edge is conductive or coupled to some ground reference.
Not too surprising about the tenders. There was a former PRR coast-to-coast tender at 18th Street in Chicago into the 1980's.
Naturally the motors were different, and I believe so were the drives (the GG1 twin 'universal' motors were capable of operating on DC, but of course PRR did not operate them that way). GG1 had fairly good quill drive; I think the P-motors were nose-suspended (original motor 278C, rebuilt motor 755A for those who want to look up motor data).
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Were the GG1 electric motors capable of running on DC?
Yes, the were DC-style commutated series-ound motors, but doesn't the inductance of their windings limit current when fed (even 25 Hz) AC? If you fed them DC, could they not overload?
Now don't tell me to post this at the Classic Toy Trains forum, but can you run a Lionel or American Flyer motor on DC? They are, series-wound commutated motors, by the way.
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul MilenkovicI think the P-motors were nose-suspended
To my knowledge they were NOT quill-drive.
There should be enough construction pictures and diagrams here and on the MR forum (courtesy of Ed, 'gmpullman') to determine precisely how the motors were provided, and what changed when they were swapped out in the 750V conversion.
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