estimating rotor weight 5

[electricpete]

Does anyone have any convenient thumbrules for estimating rotor weight for a squirrel cage induction motor?

I am particularly interested in estimating rotor weight for a 3600rpm 100hp frame 405TS TEFC 480 volt motor.

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[electricpete]

My motor is Siemens. I found the almost identical motor (Reliance) here:

http://www.reliance.com/pdf/pdf/acds/611740-1.pdf

They give total weight of 1,150 pounds for the motor. Would rotor weight be about half that?

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[Skogsgurra]

I have a Siemens Motor Catalogue available. Inertia is listed. Is that what you are after? Or just weight?

Gunnar Englund

http://www.gke.org

 

[CJCPE]

My guess is that the total motor weight for a cast iron TEFC motor would be more like 1/3 rotor, 1/3 stator, 1/3 frame.

 

[electricpete]

Just interested in weight. At the moment I'm considering changing grease on a set of problem-motors ... F.A.G's grease chart requires knowledge of both both D*N and C/P to determine types of grease required for various categories high-speed, high-load etc. I'm trying to estimate P based on 1/2 rotor weight.

Also rotor weight arises on various charts to determine greasing intervals and quantities so I'd like a thumbule for my back pocket. 1/3 of motor weight sounds more reasonable.


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[jraef]

I happen to have specs on an MV motor here in front of me with the rotor and total weight listed. Rotor is 31% of the total.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[ozmosis]

electricpete
There is a link here:

http://www.sea.siemens.com/motors/product/mtnemaapmanual.html

click on "Mechanical Data" and this shows the weight (and inertia) of all rotors for all NEMA Siemens motors. It depends on whether it is Epact efficiency or Premium Efficiency (216lbs or 232lbs resp.)

 

[electricpete]

Aha - that is exactly what I needed.

It is type RGZPSD which is EPACT. 216 pounds rotor weight.

Looking in section 4 I see the same motor weighs 1250 pounds total. So in this case rotor weight is around 17% of total weight! That'll teach me not to guess.

Thx.

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[ozmosis]

you're welcome.
The irony is that had you asked for this on the European IEC motors I would never had found it (I looked on both internet and intranet!)other than asking one of the development people.

 

[aolalde]

Electricpete. Trying to find a formula, I have noticed that the ratio of the motors rotor weight does not keep constant. The number of poles affects the ratio of the Stator lamination outside diameter (OD) and inside diameter or bore (ID). The stator back iron length is much larger on 2 poles than for say 20 poles. Different manufactures or designers have variations on criteria.
Approximated ratios OD/ID are:
2Poles OD/ID~ 2,
4Poles OD/ID ~ 1.5,
6&8 Poles OD/ID~ 1.3
10Poles< OD/ID ~ 1.25

Rotor weight ~= (stator & rotor weight)*(ID/OD)^2

Stator & rotor weight could be approached to 2/3 of total motor weight as CJCPE suggested, note that the rotor has the shaft but the stator winding is normally heavier than the rotor winding.

 

[Mendit]

Pete, I see you are looking at changing greases. Shell have just introduced a new bearing grease for motors called Stamina. Check the details here.

http://www.shell-ubricants.com/products/pdf/StaminaRLS.pdf

Point to note most motor bearings run at less than mimimum load as per the SKF bearing book

 

[electricpete]

Thanks for the link. Reminds me of Christmas.

Noel, noel...

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