AC motors, especially synchronous motors, are different then DC motors. A synchronous motor will always try to spin at a certain RPM dependent on the input frequency. It takes a certain amount of kw/kva to accomplish this task. This motor has to use more or less a constant wattage/volt amps to stay in sync regardless of load, in other words if it takes 50 horsepower to hold speed over the various frictions, then they put in a motor rated at 50 horse continuous, and it will always need 50 horsepower to work. (horsepower and wattage are the same thing) As you drop the input voltage the current draw will increase, in an attempt to keep the power draw the same. A * V = W, W * Pf = va.

Once the amperage draw exceeds the rating on the windings, excessive heating will occur. You might also find the 'weak spot' if the amperage exceeds the ability of any part without fusing (meltdown).

http://ecmweb.com/design/highs-and-lows-motor-voltage

The converter is essentially a high speed switch. The speed of the rotor has to remain constant and in time with the input frequency. I'd have to study the design closer but my belief is that if the rotor is even a few degrees of sync, it might suffer a spectacular failure.

With that being said, I would also consider that it may be an enormous risk to run the unit off of a generator, especially more risky as the size of the generator decreases in relationship to any applied loads. (this being a 2 megawatt converter, typically the biggest 'unit' generators are 2 megawatts as well...beyond that size is pretty much firmly into 'power plant' territory). Also older generators have more droop in frequency under loads, and are slower to recover as well. What that means is if the inertia of the converter rotor causes the converter to go out of sync due to a sudden change in generator frequency, you may be back into arcs and smoke territory again. As this is a museum, you might have an older generator, many older sets would be expected to start at 62hz output and then droop to 58hz at full load.

Back in 1947, the 1500 kW rotary converter in Pacific Electric's Toluca substation "ran away and "self destructed", with part of the unit going through the reinforced-concrete roof. (from pages 386-387 of Pacific Electric Sub-Stations, Vol 2, published by the Electric Railway Historical Association of Southern Calif., 2014). Many years ago I was told what happened, so the details are hazy; as I recall, the AC feed was lost, and the DC from the feeder system back-fed into the generator side, and with no synchronization from the AC, it started "motoring". The unit had an overspeed trip, but apparently it didn't work and the machine ran wild until it finally "blew up". PE had to run a portable sub into Toluca Yard to power the subway and nearby lines until the machine could be rebuilt or replaced.

The converter has been successfully moved to the Youngstown Steel Heritage Museum, and is now housed in its own "temporary" enclosure. Full set of photos here: https://www.flickr.com/photos/33523379@ ... 667854548/

As an FYI, I just got the bill for moving the converter. Total came to roughly $4,900 and that was for the 60,000 lb. lift for a day, three semis for a day, boom truck and permits. About $680 of that was for trucking permits.