Generation of heat and cooling of an AC motor ??

[cymeryss]

I have a 200 hp. 12000 rpm AC induction motor, and would like to raise its power output. It is currently being air cooled from the outside by a fan blowing air through fins attached to the outside of the motor casing, the stator. My main question is where most of the heat is generated? Is it in the stator or the rotor? At this time the only heat that is being rejected is through the stator. My second question is regarding cooling. If in fact stator and its windings do produce most heat, a liquid cooled sleeve around the housing might improve heat extraction. If rotor is the crucial component, are there any good methods for rotor, shaft cooling?? I would appreciate any info on heat generation and cooling. A recommendation for a good source for AC motor design would also be great. Thanks.

Cymeryss

 

[jbartos]

Suggestions marked ///\\I have a 200 hp. 12000 rpm AC induction motor, and would like to raise its power output. It is currently being air cooled from the outside by a fan blowing air through fins attached to the outside of the motor casing, the stator. My main question is where most of the heat is generated?
///Visit

http://super-em.snu.ac.kr/paper/087_00_12.pdf

etc. for more info
It may depend on the motor design and operation.\\Is it in the stator or the rotor?
///See above.\\ At this time the only heat that is being rejected is through the stator. My second question is regarding cooling. If in fact stator and its windings do produce most heat, a liquid cooled sleeve around the housing might improve heat extraction. If rotor is the crucial component, are there any good methods for rotor, shaft cooling??
///Shaft cooling\\ I would appreciate any info on heat generation and cooling. A recommendation for a good source for AC motor design would also be great.
///M.G. Say, Alternating Current Machines
etc.

http://www.geocities.com/thomas_b_34654/

etc.\\\

 

[GusD]

Hi cimeryss

Did you really mean 12,000 rpm ,or is it a typo ?

Some years ago EPRI (Eectric Power Research Institute)did a study On the "Squirrel Cage Rotor".The principal
objective of the study was the development of a Squirrel cage rotor analyses to determine the design life of the rotor under service conditions.These papers may have some info that may help you to understand electric motors thermal responses to varying service requirements.

If you like to get a copy, just send me an E-mail.
gdalmeida@shaw.ca

good luck

GusD

 

[cymeryss]

Thanks guys for the info. When it comes to the rpm, the motor is controlled by a, you can say a VFD, so its operating range is between 0 and 12000 rpm. This motor is used for an automobile, thus it's operating speed depends on the driving cycle. Any more info would still be appreciated. thanks

 

[jraef]

Since you have typed it twice, it appears as though you really have a 12000 RPM motor. That being the case, I think you will have significant difficulty in altering the power output capacity without overheating it.
You are right that a water jacket on the stator can keep it cool, but that will likely have little effect on the rotor heat. If you had a 1200 RPM motor, I might sugest a hollow shaft design with coolant flowing through the shaft as this is done somewhat regularly. The 10x speed issue presents a significant challange however in that seals needed on the coolant system would have difficulty operating on a shaft at that speed.

Quando Omni Flunkus Moritati

 

[UKpete]

It is difficult to say what the proportionate losses are, for example the thickness of the stator laminations is very influential. However, you can be sure that there will be significant rotor losses, although the rotor of an induction motor can run at higher temperatures than the stator (there is no insulation to degrade). These losses will be largely due to rotor current and also windage (it being a relatively high speed machine).

A water (or oil) cooled jacket will be more effective than air cooling at moving the stator losses. Although oil is slighly less effective than water, if you have oil bearings rather than grease you will be able to use the same supply.

Rotor losses can be moved by internal airflow through the airgap - in particular the windage loss will be removed, using a separate blower, or even a vacuum pump (the lower pressure may reduce the windage loss). Unfortunately it is difficult to use a single blower to cool both stator and rotor as the required pressure head for each is probably incompatible.

Another method I have seen for rotor cooling in a high speed machine is oil spray cooling. Again, if the machine has oil bearings the oil spray can be from the same feed, sprayed onto the ends of the rotor from spray-nozzles mounted adjacent to the bearings and using a common oil drain.

UKPete