rotor inertia of AC 3 phase motor

[sundep]

Hello,

Can anyone provide an estimated rotor inertia for a 25 hp, 1750 rpm, 575 volt, 284T frame, severe duty AC motor?

Thank you

 

[macmckim]

Really depends on brand - checking couple of books, average rotor inertia for a 4P-25HP is 4.0 lb-ft.2

 

[electricpete]

NEMA MG-1 has a formula for estimating rotor inertia
WK2=0.02*2^(poles/2)*hp^(1.35-0.05*poles/2)
where
HP in HP. WK^2 in ft^2-pounds

For this motor (poles-4, HP=25), we calculate
WK2 = 0.02*2^(4/2)*25^(1.35-0.05*4/2)
WK2 = 4.47 FT^2*lb

Same as above

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