Water cooling mod for AC Motor?

[JCG]

Hi all, I wanted to get some opinions on something that's been on my mind for a long time.

One of the best things about working with the EV1 was the awesome high-power and torque (103 kW/149 Nm!) yet compact induction motor. The key to its power to weight ratio was the fact that it was water-cooled.

Induction motors are cheap but really heavy because the ones you buy off the shelf are all air-cooled. So, what I'd like to start discussing is the possibility of modifying a cheap, let's say 3-5 hp TENV/TEFC/XP to be water-cooled and overloaded. Any initial thoughts?

 

[rhitee05]

Mostly induction motors are heavy because they're close to a solid chunk of metal, most of which is the rotor cage, windings, laminations, etc and not the casing. I have the rotor from an industrial AC induction motor at home, I think it came from something like a 5-10 hp motor. It probably weighs 15 lbs - I use it as a doorstop!

You would definitely get much higher power density from a water-cooled motor, but I think it would still be big and heavy compared to a PMDC.

 

[JCG]

Ok, let's assume that you don't change anything about the rotor and focus on the stator. Let's say we had a 3 phase, 1 hp TENV motor and paired it with a 3 hp drive (same voltage rating but higher current capability), and used it to spin a 3 hp load at the rated speed. More phase current means more heat developed than the motor was designed to dissipate, but want happens to efficiency? I guess that goes down because the windings aren't made for those high currents, is that right? So to keep high efficiency you'd have to rewind the stator? Just trying to get a feel for what goes wrong when you overload an AC motor and how much changing cooling could help.

 

[rhitee05]

Resistive losses in the motor vary with current squared, so if you feed 3x the current you'll see 9x the loss all other things being equal. You could re-wind for lower loss. Eventually the iron will saturate and that's the most you can wring out of the motor. I have no idea how far above the rated spec that would be. But re-winding wouldn't help increase the peak torque capability. Operating the motor at higher than rated frequency would also increase power output for the same current. At some point losses would increase here, too.

Don't get me wrong, I know that industrial induction motors are very conservatively rated. The rating is usually for 24/7 duty at elevated ambient (40C, I think). I'm sure significant gains could be made with water cooling to pull heat away.

 

[bigmoose]

JCG what you want to investigate is the "Power Dense" electric motor developed by BGSU, Bowling Green State University under contract with Lincoln Electric for a supercapacitor augmented electric bus.

http://www.bgsu.edu/downloads/tech/file55536.pdf

http://www.bgsu.edu/colleges/technology/EVI/page55493.html

I have the paper here somewhere. They upgraded the power output of a Lincoln Electric 3 phase AC motor by a factor of 10. The key was internal oil cooling of the motor with a mist. Injection around the shaft. The oil flowed across the ends of the rotor and took heat out there. The oil then was misted into the end turns of the windings and removed heat. Gravity brought the oil back down and it was pumped and cooled.

Great design! The electric propulsion department of BGSU has been disbanded, their lab was sold off and closed. I talked to the remaining prof about 8 months ago. It was a sad story. He was headed to one of the TTXGP's as a consultant/mechanic. They were ahead of their time, and unappreciated.

A loss to the community.

 

[JCG]

Great find there Dave. As you might have guessed I'm a big fan of what the BGSU group accomplished over the years. The University didn't know what a gem it had.

I kind of figured that liquid cooling would be a way to somewhat mitigate the positive feedback problem or high current --> heat --> higher resistance --> more heat --> higher resistance... I would like to try something like this with a cheap AC motor.

At any rate, here's that whitepaper:

Link

I suppose with a less fancy setup you could get decent results. Worth a good read tonight!

 

[bigmoose]

I have been looking... they used to have the good paper on the web that had a drawing of the motor internals. I can't find a web link...

but I did save a copy locally and found it! PM me your email and I will send you what I have if you are interested.

 

[JCG]

PM sent - thanks!

Jason