As far as current used by the motors, I would guess 500 to 700A_rms. The cables have to be inverter grade as the switching waveforms require attention to insulator loss and skin effect loss.
Straight DC goes to 1000 Amps, maybe more.
Motor phase current in AC traction motors would be limited by the size of wiring interconnecting the motor to inverter. If I recall 3 aught was common.
I looked up the ampacity of 3/0 insulated wire and was seeing numbers between 400 and 500 amps. This would imply 500 amps max for a traction motor. The higher terminal voltage possible when not having to deal with a commutator translates into lower current for a given horsepower.
Another neat thing with an induction motor with a variable voltage variable frequency drive is that the motors can provide braking force down to zero speed.
R.J.Russell, who ended his career as a Metroliner engineer, ran BP-20s on the Long Branch. These were A-1-A with Westinghouse hexapole motors. He said it was normal when starting to see the 2000A ammeter .peg’, and then stay on the peg for about 30sec. of acceleration, when it would start sagging down. I found that extraordinary.
The hexapole motors were inherently lower voltage and higher current than quadrupole motors. The larger number of poles meant 1.5X as many brushes (more current carrying capacity), but also meant fewer commutator bars between brushes. A rule of thumb is no more than 20V between commutator, which translates to hexapole motors having a lower maximum terminal voltage than quadrupole motors.
Also keep in mind that the motors on the GG1 were rated for ~235V max. AC series motors were a compromise, with rectifiers and DC traction motors being cheaper and more efficient.
Another comment with respect to the 2,000+ amp current draw of the hexapole motors. The updated version of the GE-750 motor was rated for 900HP continuously at 480 amps. The kicker was that the motor was rated for 1,500V across the terminals. The 750’s used in the Joe’s were rated for 375 amps, but a lot of progress had been made (think Kapton) between 1949 and 1969. Maximum short term current rating was 750 amps for both the 1949 and 1969 version of the 750’s - the 8 motor Joe’s would be producing on the order of 10,000 dbhp under those conditions, drawing 3,000 amps.
As a follow on to the 3,000VDC electrifications. A number of year ago I came across some flyers (pdf’s) from a Polish company making power electronic systems for railroad use. One was an inverter for railcars that ran off of 3,000VDC and another was a DC/DC converter to reduce 3,000VDC to various DC low voltages. More recently, Powerex has some IGBT half-bridge modules with 6,500V rated IGBT’s - recommended max DC link potential is 3,600VDC (50% derating is due to cosmic ray induced neutrons). These would be suitable for supplying a 300HP traction motor. Powerex has some SiCFET modules with 10KV breakdown.
The DL&W commuter electrification was originally 3,000VDC and was changed over to 25KV/60Hz about 40 years ago, in part to provide commonality with other NJ commuter lines. An advantage of staying with the DC electrification is that the cars could have been several tons lighter due to not needing a transformer.