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Inertia of inductrial motors

Inertia of inductrial motors

Inertia of inductrial motors

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

RE: Inertia of inductrial motors

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"


RE: Inertia of inductrial motors

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

RE: Inertia of inductrial motors

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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RE: Inertia of inductrial motors

(OP)
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

RE: Inertia of inductrial motors

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

RE: Inertia of inductrial motors

Some more options:

Search for motor speed and horsepower at:
http://www.reliance.com/cgi-bin/mtrquery.pl#modelc...

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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RE: Inertia of inductrial motors

(OP)
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.

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