Inertia of inductrial motors 1

[c2sco]

Can anyone point me to data on the inertia of motors in the 1kW to 100kW range?
Thanks
Stuart

 

[jraef]

It is something you must obtain from the motor manufacturer. Different designs and materials used will change the WK^2 from one mfgr to another.

"Venditori de oleum-vipera non vigere excordis populi"

 

[mc5w]

The inertia of the driven machine also needs to be taken into account. For a direct drive fan most of the inertia will likely be in the motor. For most other loads, the machine inertia outweighs the motor inertia.

Mike Cole, mc5w@earthlink.net

 

[electricpete]

NEMA MG-1 has a formula for estimating motor rotor inertia for the purposes of dynamic braking calculations.
WK^2 =0.02*2^(poles/2)*hp^(1.35-0.05*poles/2)

WK^2 in ft^2-pounds
HP in HP
poles is unitless

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[c2sco]

Many thanks for your replies. I'd hoped there might be a handy list of some common ones or even a manufacturer's range somewhere. I do go to manufacturer when the chips are down!
I'm mainly interested in centrifugal pumps so generally the motor is the dominant factor (mag couplings excepted) but yes I take your point on driven loads.
The equation is interesting - I'll try it out on the few that I know and see if it seems reliable enough.
Regards,
Stuart

 

[c2sco]

PS I last did Latin 35 years ago! but that looks like a vitriolic quotation!!

 

[electricpete]

Some more options:

Search for motor speed and horsepower at:

http://www.reliance.com/cgi-bin/mtrquery.pl#modelchar

Find a motor and look at the performance sheet, like this one I found:

http://www.reliance.com/pdf/pdf/aced/L1821A-V.pdf

wk^2 is listed in a box near the top.

Also if you can estimate equivalent steel cyclinder, it's an easier matter to estimate wk^2 from i.d., o.d., length.

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[c2sco]

Thanks for the link electricpete - splendid database. Lots of data. Judging by the variability, it's no wonder the algorithm is only approximate (often misses by a factor of 3 I've found). However when all else fails it's a good start. The formulae for inertia are simple I know, but given that the rotors are a variety of materials I'd thought that would be an unreliable method. Still data from this database gives me the overview I was looking for - thanks again.