I saw a 1MW synchronous AC motor be started up the other day. They had 
to spin it up with a DC motor to get it up to speed before they could 
switch on the main line. I guess I don't understand the difference 
between this gigantic motor and a normal AC induction motor other than 
the size. Surely someone here knows?

The place I was touring was the Alstom motor shop simulation facility. 
They test entire subway truck assemblies. The huge AC motor I mentioned 
spins two equally [physically] large DC motors. One is the source, one 
is the load for the device under test [actually several smaller DC 
motors feed the larger DC motor which acts as a generator to recycle 
some power]. They control field current in the DC motors to keep 
voltages where they need to be. Sorry I don't have any pictures, I'm not 
certain they would have let me take pictures if I had brought my camera.
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Martin Klingensmith
http://infoarchive.net/
http://nnytech.net/
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