REALLY big motors

Don't have any pics of the rolling mill motors. It was about five or six years ago when I was there. The motors are horizontal, with the shafts about knee high from the main floor. The rotors extend down into the basement. Shafts are about 2 feet in diameter, with 4 or 5 foot diameter by 4 to 6 inch thick flanges on the ends for coupling. (Flanges are bolted to each other by 30 or so 3" diameter bolts.) Rotors are about 8-10 feet in diameter, and stators about 20 feet. Each motor is about 30 feet long, and three are coupled together to drive one shaft.

The overall setup is actually three stages. First there are four large synchronous AC motors, running on 33KV if I recall correctly. They are about 13,500HP each, and run at constant speed. Each AC motor drives a set of three 700 volt DC generators (4,500HP each). The 12 generators are connected to the 18 DC motors (three 3000HP motors on each of 6 shafts, driving the 6 roll stands). They are connected in such a way that even with 2 of the 4 AC motors (and

6 of the 12 generators) out of service, they can still run the mill (at reduced capacity).

The electronics controls the generator field current, which controls the generator armature voltage, which is connected to the motor armatures and determines the motor speed. The motors are precisely controlled to roll the steel, maintaining the proper tension between each stage. As the steel is rolled, it gets thinner and longer, so the final stages need to run faster than the earlier stages. The motors vary accordingly - the first few stages are shorter and fatter to develop more torque. The very first stage goes thru a gear reduction before driving the rolls. A back of the envelope calculation says the torque at the first stage rolls is about two million foot-pounds. (9,000HP at 20-something RPM.)

The whole arrangement was just mind boggling - not only are the individual motors huge, but the football field sized room is just full of them - between the AC motors, the generators, and the DC motors there are 36 huge machines on 10 shafts, totalling over

150,000HP.

I _really_ wish I had pictures of it!

Here are some less impressive photos that I found on the web. Some of these motors are even bigger, but the photos don't do them justice.

(look closely at the right hand pic - there's a guy on a ladder inside the stator)

Regards,

John Kasunich

Another couple pics. The one on the back of the brochure (where it says DC testing) is similar to a rolling mill motor, very high torque at rather low speed.

Regards,

John Kasunich

Thanks, John, for taking the time. Very interesting, indeed.

Garrett