Rotational inertia of 75 hp motor 1

[iainuts]

I'm looking for a quick and dirty number for the rotational inertia of a 75 hp, 460 V, 3 phase TEFC motor. Nothing super accurate, just a ballpark.

Thanks in advance for the help.

 

[7anoter4]

From ABB catalog:
NEMA 460 V [60 Hz] 8 poles 75 hp 59 lb-ft^2: 6 poles 75 hp 39 lb-ft^2; 4 poles 100 hp 23 lb-ft^2 ; 2 poles 100 hp 14.5 lb-ft^2

 

[iainuts]

Thanks. Is that catalog online anywhere? I couldn't find it.

 

[electricpete]

Another quick easy estimate: NEMA MG-1 has a formula for estimating motor rotor inertia for the purposes of dynamic braking calculations.
WK2 = 0.02*2^(poles/2)*hp^(1.35-0.05*poles/2)
where
HP is output power rating in HP.
WK^2 in ft^2-pounds

They don't distinguish ODP vs TEFC, so that tells you it's not tremendously exact.

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[iainuts]

That's perfect! Thanks electricpete - just what I needed. <star>