Motor Housing

[czping]

Hi all,

I was told that the motor housing plays a part in containing the magnetic flux generated when the 3 phase volatge is applied to the stator. Is this true?

If there is a hole in the housing (happened actually, I ahve this motor which is exposed to acid and the acid actually burnt a hole in the housing, luckily the stator was not affected), and the hole is not covered properly, will it affect the performance of the motor?

Thanks in advance!

 

[ERaySir]

czping

It may effect the cooling and leave the motor more susceptible to contamination. The magnetic circuit is within the stator. If the stator, which is iron holding the windings, is not dissolved it shouldn't effect the operation unless the cooling is somehow compromised.

Best Regards

Ray Micallef, P. Eng.
Power Generation/Utility Industry

 

[jclough]

I don't think in this case that motor performance will be changed much. However the motor housing contributes to and acts as parts of the stators "back iron".Some years ago we looked at changing to aluminum housings but couldn't live with the changes to the speed torque curves.

 

[czping]

ERaySir

Thanks! So, if the stator is not damaged, and there is a hole in the housing (presume that nothing is falling into the housing), it should perform as good as ever?

Then we do some people have the idea that the flux cannot be contained? Do you think it is applicable to some other cases?

 

[jbartos]

Suggestion: It depends how big that hole is. If it is small, and away from bolts or screws, then it will have a small effect on the motor performance. It would be more practical to cover the hole since there may be a very little protection left to the stator windings.

 

[czping]

Hi Jclough,

I do not understand your statement: "changing to aluminum housings but couldn't live with the changes to the speed torque curves". Is there a change in the characteristic to the motor?

For your information,I actually cover the hole in my motor housing using a steel plate, so far it is running ok. The size of the hole is about 5cm in diameter.

 

[UKpete]

DC motors nearly always use the frame as part of the magnetic circuit, regardless of size. This is because the stator field is virtually static.

However AC motors ideally do not use the frame as the field is alternating and requires the iron to be laminated to reduce iron losses. Inevitably though there will be some leakage of flux into the frame if it is iron or steel, and this could have a marginal effect on performance (particularly if the designer was cutting corners a little to save on lamination material). But if the 5cm hole is small relative to the overall size, or if the frame is aluminum anyway, then don't worry about it.