# Moment of Inertia of a motor

• posted

Govind View profile More options Jun 24, 5:06 pm Newsgroups: alt.engineering.electrical From: Govind Date: Sun, 24 Jun 2007 12:06:38 -0000 Local: Sun, Jun 24 2007 5:06 pm Subject: GD Square of a motor Reply | Reply to author | Forward | Print | Individual message | Show original | Remove | Report this message | Find messages by this author I want to know about what is the GD square ( Gyrational Torque) of the motor. I am aware that higher kW motors for e.g 5MW motors load torque curves are checked by overlapping with the load curves i.e, for e.g pumps to check weather the selected motor will able to start the load or not. in this scenario i want to know very particularly about the meaning of GD square of the motor and a Pump and also the Wk^2 (Moment of inertia J ) of the motor / load ----- Finally how i have to cross check the values with motor and with load.

How those values are calculated - can anyone suggest a formula to arrive those values for a motor please.

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So what exactly is 'Gyrational Torque' or GD squared? Sounds like some nonsense you made up just to troll. Or maybe you got it from some other troll. If you'r serious, and since you throw in Wk^2, maybe you're getting the idea of inertia mixed up somehow?

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A good applied physics text will explain the concept. Think of 'moment of inertia' as the rotational equivalent of simple inertia.

For a pair of masses suspended on a cross-arm with the pivot point in the middle, the moment of inertia is the sum of mass times distance from pivot squared. (used to use 'weight times k^2' hence Wk^2). For more complex shapes such as cylinders and disks, there are various formula derived from calculous. A simple uniform cyclinder spinning along its axis is 1/2wd^2.

For large motors with fans, spider-web iron with holes passing through the length of the iron punchings it can be quite a bit more complext a calculation. But basically find the moment of inertia for each individual component relative to the shaft (don't forget the shaft itself) and sum them up. If driving a load through gearing, one must account for the gear ratio as well.

daestrom

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