Check out this subsea inverter-duty induction motor:
It's rated 42kW (56HP), 60Hz, 3,000V, 11A.
It is 15" X 10" and weighs 191lbs.
It is designed for 3,000V because it's at the end of a 3km cable.
Now compare that to a similar industrial AC induction motor:
It's rated 60HP, 60Hz, 460V, 70A.
It is 33"" X 20" and weighs 869lbs.
The industrial motor weighs 4.5X as much as the subsea motor, and takes up 8X the volume of the subsea motor.
Why is the subsea motor so much smaller? I know you can decrease the size by increasing the frequency, but they're both rated 60Hz. I've never heard that you can decrease motor size by increasing voltage, and actually it seems there would be no gain from that. Sure, the winding wire woul be smaller, but it seems that would be counteracted by the need for thicker insulation (especially being inverter duty rated). And that theory seems to be supported by others:
It's rated 42kW (56HP), 60Hz, 3,000V, 11A.
It is 15" X 10" and weighs 191lbs.
It is designed for 3,000V because it's at the end of a 3km cable.
Now compare that to a similar industrial AC induction motor:
It's rated 60HP, 60Hz, 460V, 70A.
It is 33"" X 20" and weighs 869lbs.
The industrial motor weighs 4.5X as much as the subsea motor, and takes up 8X the volume of the subsea motor.
Why is the subsea motor so much smaller? I know you can decrease the size by increasing the frequency, but they're both rated 60Hz. I've never heard that you can decrease motor size by increasing voltage, and actually it seems there would be no gain from that. Sure, the winding wire woul be smaller, but it seems that would be counteracted by the need for thicker insulation (especially being inverter duty rated). And that theory seems to be supported by others:
So what's the deal? The only other thing I can think of is the amount of iron in the frame. An industrial induction motor requires a frame with more mass, and cooling fins, to dissipate the heat. The subsea motor is submerged in cooling water so less frame mass is needed. But can that one difference account for such a huge disparity in size? I mean, even the rotor is half the length.John Malinowski, Baldor product manager for ac and dc motors, points out that MV motors also are somewhat larger than similar LV ratings due to more active materials needed in the motor, and thicker insulation required to contain those higher voltages.